Effect of changes in extracellular potassium on intracellular pH in principal cells of frog skin. Intracellular pH (pHi), apical membrane potential (Va), and fractional apical membrane resistance (FRa) were measured in principal cells of isolated frog skin (Rana pipiens) with double-barreled microelectrodes under short-circuit and open-circuit conditions. Basolateral exposure to high K+ concentration or Ba2+ depolarized V(a), decreased short-circuit current, and increased FRa and pHi. However, an increase in K+ subsequent to Ba2+ application did not induce additional changes in these parameters. High basolateral K+, previously shown to increase apical K+ secretion (N. S. Bricker, T. Biber, and H. H. Ussing. J. Clin. Invest. 41: 88-99, 1963), also increased apical Na+ conductance. The depolarization and intracellular alkalinization induced by high K+ were also observed in absence of Na+, Cl-, and HCO3- and in presence of 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid. Under all these conditions pHi moved toward electrochemical equilibrium. Reduced basolateral K+ hyperpolarized V(a) and decreased pHi. The data suggest that depolarization and hyperpolarization of the apical and/or basolateral membrane are associated with an increase and decrease, respectively, in pHi without involvement of Na(+)-H+, Cl(-)-HCO3-, or K(+)-H+ exchange and are apparently also independent of an active H+ secretion pathway. This indicates the presence of a potential-dependent H+ and/or OH- conductance in the apical and/or basolateral cell membrane that may play an important role in pHi regulation and signal transduction.


Distribution and content of renin and renin mRNA in remnant kidney of adult rat. To determine whether kidney hypertrophy secondary to reduction of renal mass affects the intrarenal distribution and concentration of renin mRNA and its protein, adult male Sprague-Dawley rats were studied 4 wk after sham operation (Sham, n = 10), uninephrectomy (UNX, n = 14), or five-sixths nephrectomy (5/6 NX, n = 12). Left kidney weight-to-body weight ratio (x10(3)) was higher in 5/6 NX (6.6 +/- 0.2) than in UNX (4.5 +/- 0.2) or Sham (3.8 +/- 0.1) groups (P < 0.001). The percentage of juxtaglomerular apparatuses (%JGA) containing renin was lower in 5/6 NX (32 +/- 5) than in UNX (56 +/- 2, P < 0.001) or Sham (50 +/- 1, P < 0.05) groups. Renal renin mRNA concentrations (pg renin mRNA/microgram total RNA) detected by radiodensitometric renin mRNA dot-blot assay were lower in 5/6 NX (1.8 +/- 0.3) than in UNX (13.2 +/- 1) or Sham (14.2 +/- 1.1, P < 0.001). In situ hybridization histochemistry demonstrated that in all groups of rats renin mRNA was confined to the JGA. However, the hybridization signals (grains/JGA) were less intense in 5/6 NX (211 +/- 24) than in UNX (486 +/- 35) or Sham (541 +/- 40) groups (P < 0.001). Renal renin concentration (ng angiotensin I.mg protein-1.h-1) tended to be lower in 5/6 NX (20 +/- 15) than in UNX (44 +/- 7.8) or Sham (60.8 +/- 10) groups. In addition, plasma renin activity (ng.ml-1.h-1) was lower in 5/6 NX (3.8 +/- 0.6) than in UNX (8.8 +/- 1.8, P < 0.05) or Sham (14.3 +/- 2, P < 0.001) groups.(ABSTRACT TRUNCATED AT 250 WORDS)


Adaptation of rabbit cortical collecting duct to in vitro acid incubation. Cortical collecting ducts (CCDs) isolated from acid-loaded rabbits and perfused in vitro absorb HCO3-, whereas CCDs from normal animals secrete HCO3-. We have previously shown that CCDs incubated in vitro for 3 h at pH 6.9 show a reduction in net (baseline and stimulated) HCO3- secretion. In this study we ascertained the minimum duration of an acidic stimulus necessary to induce adaptive changes in stimulated HCO3- secretion (determined in the absence of basolateral Cl-) and the roles of protein synthesis and cytoskeletal function in this process. CCDs incubated in acid (pH 6.8, HCO3- 6 mM) for 1 h followed by incubation at pH 7.4 (HCO3- 25 mM) for 2 h showed a 41% reduction in stimulated HCO3- secretion (P < 0.001), similar to that observed after 3 h of incubation at pH 6.8. However, this incubation protocol failed to enhance stimulated HCO3- absorption (determined in the absence of luminal Cl-). Addition of 10 microM anisomycin, a reversible inhibitor of protein synthesis, throughout the entire period of incubation (1 h at pH 6.8 plus 2 h at pH 7.4) blocked adaptive reduction in HCO3- secretion, as did exposure to anisomycin only during the initial 1 h of acid incubation. In contrast, anisomycin application during the 2-h incubation at pH 7.4 failed to block this adaptation of HCO3- secretion. Application of 4 microM actinomycin D, an inhibitor of DNA transcription, during the acid incubation also prevented the adaptive response, as did application during the total or during the 2-h pH 7.4 incubation period of 0.2 microM cytochalasin D, an inhibitor of actin filament function.(ABSTRACT TRUNCATED AT 250 WORDS)


Calculation of oxygen diffusion across the surface of isolated perfused hearts. Although exact mathematical descriptions of oxygen diffusion into unperfused isolated organs are known, no analytic solution is available for perfused organs. Here, we derive an equation for oxygen diffusion across the epicardial surface of perfused hearts. Our oxygen transport model incorporates oxygen delivery from the capillary perfusate, oxygen consumption, diffusion among adjacent capillary exchange regions, and diffusion across the epicardial surface. The wall of the heart is modeled by a slab of tissue. The derived equation fits experimental data on the diffusive oxygen flux across the surface of isolated saline-perfused guinea pig hearts, obtained by measuring oxygen uptake from the perfusate at various oxygen tensions in the surroundings of the isolated heart. The model predicts that in isolated arrested guinea pig hearts suspended in air, 25% of the oxygen taken up from the saline perfusate (PO2 approximately 680 mmHg) diffuses out of the heart across the surface. In beating isolated guinea pig hearts, 5% of the oxygen taken up from the perfusate diffuses across the surface.


Limited left ventricular inotropic response to exercise in early phase of pressure overload in dogs. To study the mechanisms of myocardial adaptation to increased stress in the early phase of left ventricular (LV) pressure overload, 12 dogs were instrumented with LV micromanometer, LV dimensional ultrasonic crystals, aortic catheter, and aortic occluder cuff. After recovery, animals performed graded exercise with acute aortic stenosis (AS) or sustained (24 h) aortic stenosis (SS). At baseline, LV functional parameters with SS were not different from those obtained with AS. LV peak pressure increased similarly during exercise with AS or SS, but LV peak dP/dt was lower with SS than with AS (peak values, 6,292 +/- 525 vs. 7,570 +/- 432 mmHg/s; P < 0.05). LV end-diastolic pressure increased from 9.7 +/- 1.7 to 21.4 +/- 3.3 mmHg (P < 0.05) during exercise with SS, but was unchanged with AS. The decrease of the time constant of isovolumic pressure fall during exercise was significantly smaller after SS than during AS (P < 0.05). In addition, the percentage of subendocardial wall thickening did not increase during exercise with SS (30.3 +/- 3.6%), while it increased significantly with AS (from 29.3 +/- 3.3 to 39.4 +/- 4.5%; P < 0.01). Plasma catecholamine levels were similar at baseline and increased to similar levels during exercise with AS and SS. In the early phase of pressure overload, we conclude that exercise capacity is maintained but that the LV inotropic response to exercise is modified with an altered relaxation process and a lesser utilization of subendocardial inotropic reserve.


Altered pressure-volume relation of right atrium and venoatrial junction in diabetic rats. Previous studies have indicated a blunted volume reflex in diabetic rats. This alteration of the volume reflex may be due to differences in distensibility of the right atrium and venoatrial junction, which contain a large number of volume receptors. This study was designed to determine whether the distensibility of the right atrium and venoatrial junction is altered in the diabetic rat. The distensibility was assessed by measuring the stiffness constants [slope of pressure-volume (P-V) curve] of the right atrium and venoatrial junction in 2-wk streptozotocin-induced diabetic rats. The P-V data of the right atrium and venoatrial junction were measured in control and diabetic rats over a range of 0-10 mmHg by infusion of isotonic saline in KCl-arrested, in situ hearts. Similar P-V data also were determined in an additional group of diabetic rats under daily insulin treatment, which normalized plasma glucose. The mean slope of the P-V curve of the right atrium and venoatrial junction in the diabetic rats was significantly greater than the mean slope of the control and insulin-treated diabetic rats. The results indicate that diabetic rats have stiffer right atria and venoatrial junctions, which may reduce stimulation of the volume receptors to acute volume loading. In addition, the increased stiffness in the diabetic rats was prevented by chronic insulin treatment. An altered afferent limb of the volume reflex in diabetic rats contributing to blunted diuretic and natriuretic responses to volume loading may be due to these documented changes in the distensibility of the right atrium and venoatrial junction.


Long-term calorie restriction enhances baroreflex responsiveness in Fischer 344 rats. Diet influences many aspects of cardiovascular function. Restriction of caloric intake represents a major nonpharmacological means of reducing blood pressure. The aim of the present work was to determine the effects of long-term calorie restriction on mean arterial pressure (MAP) and baroreflex responsiveness of the conscious, normotensive, nonobese Fischer 344 male rat. From 6 wk of age rats ate either ad libitum or 60% of the amount consumed by those eating ad libitum. Calorie restriction had no effect on MAP of rats 12-14 mo of age; the MAP for the ad libitum fed and calorie-restricted groups were 114.6 +/- 1.6 and 111.6 +/- 0.8 mmHg, respectively. Basal heart rate (HR), however, was reduced from 396 +/- 6 beats/min in the libitum-fed group to 333 +/- 5 beats/min in the calorie-restricted group. Administration of sodium nitroprusside (SNP) (both as bolus and constant infusion) and phenylephrine (PE) (bolus alone) elicited tachycardia and bradycardia in both groups. The calorie-restricted group exhibited greater baroreflex responsiveness to hypotensive stress than did the ad libitum-fed group. For constant infusion of SNP, the baroreflex gain of the calorie-restricted group (-5.43 +/- 0.56 beats.min-1.mmHg-1) was significantly greater than that of the ad libitum-fed group (-2.14 +/- 0.19 beats.min-1.mmHg-1). Bolus injections of SNP elicited similar results. Calorie restriction only minimally altered the baroreflex responsiveness to hypertensive stress elicited by bolus injections of PE, although the relationship between HR and MAP was shifted to the left in the calorie-restricted group.(ABSTRACT TRUNCATED AT 250 WORDS)


Spinal stimulation to locate preganglionic neurons controlling the kidney, spleen, or intestine. The organization of sympathetic preganglionic neurons may be a substrate for selective control of sympathetic outflow to different vascular beds. This study was done to determine the spinal segments containing preganglionic neurons controlling discharge of renal, splenic, and mesenteric postganglionic nerves. In urethan-anesthetized rats, preganglionic neurons were stimulated by microinjecting D,L-homocysteic acid (3 nl, 0.17 M) into the lateral gray matter of the third thoracic (T3) to the fourth lumbar (L4) spinal segments. Responses from all three nerves could be elicited from segments T4-T13. The greatest increases in renal nerve discharge were evoked from segments T8-T12, the largest increase of 59 +/- 9% elicited from T10. Increases in splenic and mesenteric nerve discharge were smaller and were evoked more uniformly from T4-L3. The largest increases in discharge of splenic and mesenteric nerves were 19 +/- 5% (from T5) and 26 +/- 4% (from T10), respectively. The widely overlapping spinal cord segments controlling these three organs suggest that location of the preganglionic neurons in different spinal segments is not part of the mechanism for selective sympathetic control. However, the larger renal nerve responses demonstrate that sympathetic output to these organs can be differentiated at the level of the spinal cord.


Neuropeptide Y and coronary vasoconstriction: role of thromboxane A2. We previously reported that coronary constriction following neuropeptide Y (NPY) was alleviated by cyclooxygenase blockade. To determine the role of thromboxane A2 (TxA2), anesthetized dogs received two paired doses of NPY given 2 h apart. Nine control dogs received NPY alone. Nine test dogs received one of three TxA2 receptor antagonists given between the doses of NPY. Also, five dogs received NPY during which prostaglandins were measured. In controls, NPY decreased coronary blood flow and increased aortic pressure; coronary resistance was increased significantly. Heart rate fell, and myocardial oxygen consumption was unchanged. Thromboxane receptor blockers significantly relieved the coronary constrictor effect of NPY. The reduction in coronary blood flow was blunted, while heart rate, first derivative of left ventricular pressure, and myocardial oxygen consumption were unchanged. Alleviation by TxA2 receptor blockade paralleled that reported for cyclooxygenase inhibitors. Also, significant increases in coronary venous TxA2 were seen at the time of maximal increases in coronary resistance, while prostacyclin was unchanged. In summary, TxA2 appears to mediate part of the coronary constrictor effect of NPY.


Cardiac adaptation of sarcomere dynamics to arterial load: a model of hypertrophy. In the past, the dynamics of the left ventricle were studied by its response to altered venous and arterial load for a given heart. This led researchers to propose the concept of an arterioventricular match or optimal point of function. The model of this paper reverses that idea by fixing preload and afterload while computing cardiac function due to altered left ventricular size or shape, resulting from modification of the number of parallel and series sarcounits. A mathematical model of physiological hypertrophy is introduced. Series and parallel arrangements of sarcounits constitute a cylindrical model of the left ventricle. Filling occurs from a venous reservoir with constant pressure through a valve, while ejection takes place into a three-element model of the systemic arterial system through another valve. It is found that the dynamics of the myofibrils can be matched to those of the left ventricle by choosing a ventricular shape that results in a minimum in myocardial O2 consumption (MVO2) for any constant ventricular load. A unique solution for the size of the ventricle results if the rate of MVO2 is specified. The model is able to predict correctly hypertrophy due to hypoxia and due to pressure (concentric) and volume (eccentric) overloads.


Transvascular albumin and IgG flux in skin after a continuous 3-h bradykinin infusion. Bradykinin (1 microgram/min) was infused into the femoral artery of one hindleg of anesthetized rabbits for 3 h. Measurements of the initial extravascular uptake for labeled albumin and immunoglobulin (Ig) G were compared with measurements of the lymph protein flux for endogenous albumin and IgG. With bradykinin, the initial extravascular uptake for both albumin and IgG, calculated as the 1-h extravascular distribution space at plasma concentration divided by time and expressed as a plasma clearance, was 12 times the control values. For both proteins, the lymph fluxes were not significantly greater than the values for extravascular uptake, indicating that the sustained increase in lymph protein flux was not due to washout of interstitial protein. The extravascular uptake for IgG was approximately 80% of that for albumin in both control and bradykinin animals, suggesting that the sustained response did not change the selectivity between the two proteins. Changes in the extravascular masses of endogenous albumin and IgG suggest that the initial response to bradykinin was a transient formation of endothelial gaps that did not restrict transvascular IgG transport more than albumin.


Endothelium-dependent ANF secretion in vitro. Coculture of endothelial cells with atrial cells (R. A. Lew and A. J. Baertschi. Biochem. Biophys. Res. Commun. 163: 701-709, 1989) increased atrial natriuretic factor (ANF) release to 205 +/- 15% (n = 33 experiments) of basal secretion (2.02 +/- 0.33 ng/ml). Stimulation of ANF release by endothelial cells was significantly reduced (P < 0.05) by addition of the calcium channel antagonist nicardipine (Nic, 100 nM; by 69 +/- 4%), the guanylate cyclase activator sodium nitroprusside (SNP, 1 microM; by 97 +/- 27%), or acetylcholine (ACh, 10 microM; by 55 +/- 13%). Endothelial cell-conditioned medium elicited a 62 +/- 10% (n = 10) increase in ANF release. Rat and porcine endothelin (0.1-100 nM) each elicited a dose-dependent increase in ANF release [up to 84 +/- 14% (n = 18) over baseline]. The activity of conditioned medium was not affected by heat or trypsin treatment, but was significantly reduced by addition of Nic or SNP and was attenuated by ACh. Stimulation of ANF by 1 nM synthetic rat or porcine endothelin was also unaffected by heat or trypsin but was significantly reduced by Nic, SNP, and ACh. Addition of endothelin-specific antiserum abolished the ANF stimulatory activity of endothelial cell-conditioned medium. Neither inhibition of superoxide anion by superoxide dismutase nor inhibition of endothelium-derived nitric oxide production by NG-monomethyl-L-arginine affected the ANF release from coculture. Thus endothelial cells release a heat-stable, diffusible ANF stimulatory factor, which is not endothelium-derived relaxing factor or superoxide anion but is biologically and immunologically similar to endothelin.


Sympathetic modulation of blood flow and O2 uptake in rhythmically contracting human forearm muscles. This study tested the effects of sympathetically mediated changes in blood flow to active muscles on muscle O2 uptake (VO2) in humans. Four minutes of graded (15-80% of maximum voluntary contraction, MVC) rhythmic handgrip exercise were performed. Forearm blood flow (FBF) (plethysmography) and deep vein O2 saturation were measured each minute. Forearm O2 uptake was calculated using the Fick principle. In protocol 1, exercise was performed while supine and again while upright to augment sympathetic outflow to the active muscles. Standing reduced FBF at rest from 3.6 to 2.2 ml.100 ml-1.min-1 (P < 0.05). During light exercise (15-40% MVC) FBF was unaffected by body position. Standing reduced FBF (P < 0.05) from 36.0 to 25.2 ml.100 ml-1.min-1 and forearm VO2 from 38.2 to 28.1 ml.kg-1.min-1 during the final work load. In protocol 2, exercise was performed while supine before and after local anesthetic block of the sympathetic nerves to the forearm. Sympathetic block increased FBF at rest from 3.1 to 8.9 ml.100 ml-1.min-1 (P < 0.05), and FBF was higher during all work loads At 70-80% of MVC sympathetic block increased FBF from 35.4 to 50.7 ml.100 ml-1.min-1 (P < 0.05), and forearm VO2 from 45.5 to 54.2 ml.kg-1.min-1 (P < 0.05). These results suggest that in humans sympathetic nerves modulate blood flow to active muscles during light and heavy rhythmic exercise and that this restraint of flow can limit O2 uptake in muscles performing heavy rhythmic exercise.


Baro- and ventricular reflexes in conscious dogs subjected to chronic tachycardia. It has been well documented that the arterial baroreflex is depressed in chronic congestive heart failure. Furthermore, cardiopulmonary reflexes have also been shown to be depressed in heart failure. Because cardiac reflexes can be mediated by both mechanical and chemical stimuli, we undertook the current study to determine whether chemically activated cardiac reflexes (Bezold-Jarisch) are abnormally depressed in dogs with chronic heart failure at a point in time when arterial baroreflexes were clearly depressed. We studied heart rate and arterial pressure responses in 13 conscious instrumented dogs before and after chronic ventricular pacing at 250 beats/min for 4-5 wk. At the time the study was done each dog showed both hemodynamic and clinical signs of congestive heart failure. The arterial baroreflex was evaluated by analyzing the heart rate response to acute injections of phenylephrine and nitroglycerin. The Bezold-Jarisch reflex was assessed in nine dogs by determining the heart rate and blood pressure responses to intracoronary injections of various doses of veratridine. Arterial baroreflex responses were uniformly depressed following ventricular pacing. The phenylephrine slope was reduced by 55.8 +/- 6.9% (P < 0.001), and the nitroglycerin slope was reduced by 67.9 +/- 5.0% (P < 0.0001) in the heart failure state. Significant bradycardia and hypotension were seen at each dose of veratridine given (0.01, 0.1, and 0.4 microgram/kg). When compared with the prepaced control state, the magnitude of the hypotension was no different in the heart failure state in response to any dose of veratridine.(ABSTRACT TRUNCATED AT 250 WORDS)


Heterogeneous distribution of endothelium-dependent relaxations resistant to NG-nitro-L-arginine in rats. Endothelium-dependent relaxations that are resistant to inhibitors of nitric oxide synthase probably are mediated by endothelium-dependent hyperpolarization of the vascular smooth muscle. Experiments were performed to examine the distribution of this type of relaxation along the arterial tree of the rat by measuring changes in isometric force. Acetylcholine induced concentration- and endothelium-dependent relaxations in aortas and in pulmonary, common iliac, femoral, mesenteric, and renal arteries contracted with phenylephrine. In the presence of NG-nitro-L-arginine, the cumulative administration of acetylcholine induced relaxations only in the femoral, mesenteric, and renal arteries. The calcium ionophore A23187 relaxed mesenteric arteries contracted with phenylephrine in a concentration- and endothelium-dependent manner. The concentration-relaxation curve to A23187 was shifted to the right in the presence of NG-nitro-L-arginine. The maximal relaxations induced by lemakalim, a K+ channel opener, were smaller in those arteries that did not exhibit NG-nitro-L-arginine-resistant relaxations. These results suggest that NG-nitro-L-arginine-resistant relaxations are more frequently observed in smaller arteries. The arteries that exhibit NG-nitro-L-arginine-resistant relaxations may be more sensitive to an endothelium-derived substance that causes hyperpolarization of vascular smooth muscle cells.


Correlation of structure and viscoelastic properties in the pericardia of four mammalian species. Although the pericardium is recognized as having important contributions to ventricular function, the relationship between its functional role and structural composition remains poorly understood. Conflicting evidence from low strain rate experiments has shown that differences exist between the mechanical properties of canine, human, and bovine pericardium but with no structural explanation for these differences. This paper examines the pericardia of calves, dogs, pigs, and sheep using a structural/mechanical approach with techniques novel to the pericardial literature. High strain rate mechanical testing for stress-strain response, stress relaxation, and forced vibration response has shown the pericardium to be much more viscoelastic than previously believed under large deformations, but to be quite elastic in small vibrations. The thinner canine and porcine pericardia were found to be significantly stiffer than the thicker bovine and ovine tissues, but equivalently viscoelastic. Biochemical analysis shows these thinner tissues to have significantly higher levels of type III collagen combined with a higher degree of cross-linking. This is the first structural explanation for differences in mechanical properties between the pericardia of different species.


Ischemic preconditioning protects against infarction in rat heart. We examined the anti-infarct effect of ischemic preconditioning in the rat heart. All hearts were subjected to 30 min of regional coronary ischemia and 2 h of reperfusion. Infarct size was determined by tetrazolium. The control group had an average infarct size of 31% of the risk zone. Three 5-min cycles of preconditioning ischemia limited the infarct size to 3.7%. Neither the adenosine receptor blocker PD 115,199 nor the ATP-sensitive potassium channel blocker, glibenclamide, could block this protection. Intracoronary adenosine A1-receptor agonist 2-chloro-N6-cyclopentyladenosine offered a significant anti-infarct protection to the isolated rat heart, however. Although one 5-min cycle of preconditioning did not protect the rat heart from infarction (31% infarction in risk zone), it did attenuate arrhythmias. We conclude that 1) the rat heart can be preconditioned, which argues against mitochondrial adenosinetriphosphatase being the mechanism of preconditioning; 2) the threshold for preconditioning is higher in rat than rabbit or dog; 3) a role for adenosine in preconditioning was only partially supported; and 4) a role for ATP-sensitive potassium channels was not supported.


Role of adenosine for reactive hyperemia in normal and stunned porcine myocardium. The role of adenosine for reactive hyperemia in normal and stunned myocardium was examined in 16 open-chest barbiturate-anesthetized pigs. Interstitial adenosine concentration was reduced or enhanced by intracoronary infusion of adenosine deaminase or the nucleoside transport inhibitor R 75231, respectively. In normal myocardium, adenosine deaminase reduced volume of hyperemia (Doppler flowmetry) after a 30-s left anterior descending coronary artery (LAD) occlusion by 20% (6-34%; P < 0.05), whereas R 75231 increased volume of hyperemia by 15% (2-24%; P < 0.05). Adenosine deaminase reduced volume of hyperemia after a 2-min LAD occlusion by 27% (13-37%; P < 0.001), whereas R 75231 increased volume of hyperemia by 66% (53-159%; P < 0.001). Adenosine deaminase and R 75231 did not affect maximal hyperemia. Volume of hyperemia after a 2-min LAD occlusion was reduced in stunned myocardium (%systolic segment length shortening reduced by approximately 45%, ultrasonic technique) but not further altered by either adenosine deaminase or R 75231. These findings show that adenosine contributes to reactive hyperemia after 30-120 s of ischemia in normal myocardium and indicate that the reduced reactive hyperemia in stunned myocardium is due to reduced accumulation of adenosine during ischemia.


Electroporation and recovery of cardiac cell membrane with rectangular voltage pulses. Electroporation of the cardiac cell membrane may result from intense electric fields applied to cardiac muscle, associated for example with defibrillation and cardioversion. We analyzed the distribution of voltage levels sufficient to cause electroporation in enzymatically isolated frog cardiac cells, using the cell-attached patch-clamp technique with rectangular pulses similar to those used in experimental studies of cardiac defibrillation. Five-millisecond monophasic or ten-millisecond biphasic symmetric (1/1) and asymmetric (1/0.5) rectangular pulses of either polarity were applied to the cell membrane in 100-mV steps from 0.2 to 0.8 V. The membrane conductance was continuously monitored by a low-voltage pulse train. In a total of 77 cells, we observed a step increase in conductance, occurring in 21% of cells at a transmembrane potential of 0.3 V, 52% at 0.4 V, 14% at 0.5 V, and 13% at 0.6-0.8 V. Electroporation occurred with this voltage distribution regardless of pulse shape, polarity, or the presence of all of the following ionic channel blockers: tetrodotoxin, barium, tetraethylammonium, 4-aminopyridine, cadmium, nickel, and gadolinium. The time course of membrane recovery was highly variable. The maintenance of a high membrane conductance after the shock pulse was associated with irreversible cell contracture provided that Ca2+ was included in the patch-pipette solution. However, with biphasic asymmetric pulses, the conductance recovered very quickly (< or = 37 ms).(ABSTRACT TRUNCATED AT 250 WORDS)


Left ventricular hypertrophy due to volume overload versus pressure overload. Left ventricular hemodynamic overload produces an increase in stroke work (SW), which is compensated by the development of left ventricular hypertrophy. However, recent reports question the adequacy of this compensation in mitral regurgitation (MR). Accordingly, we examined the adequacy of compensatory hypertrophy in chronic experimental MR. Six dogs with chronic severe MR were matched according to SW with six dogs that had severe chronic aortic stenosis (ASSW). SW in the two groups was increased identically (40%) compared with normals. However, the hypertrophic response was much greater in the AS group [left ventricular wt (g) to body wt (kg) ratio (LVBW) 4.0 +/- 0.2 normals, 5.0 +/- 0.2 MR, and 7.5 +/- 0.2 ASSW; P < 0.05 MR vs. ASSW]. This differing hypertrophic response increased normalized SW, the area within the stress-volume loop, in MR (90 +/- 5 g) vs. 63 +/- 5 g in ASSW (P < 0.05). Thus in MR, each unit of myocardium had to perform more work than in AS. In a separate comparison, four different dogs with AS (ASHy), which had a similar amount of hypertrophy to the MR dogs (LVBW) (5.0 +/- 0.2 MR, 5.2 +/- 0.2 ASHy) were studied. SW was greater in the MR group, suggesting more SW overload was required to produce similar amounts of hypertrophy in MR vs. AS. Contractile function was depressed in the MR group but not in the AS. These findings indicate that the hypertrophic response to a similar SW demand is less in MR than AS, a response associated with contractile dysfunction in the MR group.


Distribution of coronary collateral blood flow at different levels of collateral growth in conscious ponies. Coronary collateral growth was stimulated in chronically instrumented conscious ponies by a previously validated intermittent coronary occlusion method. Changes in regional myocardial function (sonomicrometry) and reactive hyperemia (Doppler method) were used to monitor collateral growth and to program measurements of regional myocardial blood flow (microsphere method). A serial analysis of the transmural and lateral distributions of collateral blood flow was performed at the native and three superimposed levels of collateral growth. Results in nine animals undergoing an average of 553 +/- 188 brief coronary occlusions over 68 +/- 18 days demonstrated that as collateral conductance increased, the perfusion field within the ischemic region increased from the epicardium to the endocardium but not from the lateral edges to the center of the ischemic region. The findings are consistent with an analog model consisting of interarterial collaterals whose collective resistance is in series with arteriolar resistance of the recipient artery. No special protection of deeper myocardial layers by a subendocardial plexus or intramural collaterals was noted. Instead, the findings suggest that coronary extravascular compressive forces play a more important role than the transmural location of collaterals in determining the volume and spatial distribution of collateral blood flow during collateral growth in the pony.


Sodium modulates inotropic response to hyperosmolarity in isolated working rat heart. The present study was designed to examine the effects of acute changes in perfusate Na+ concentrations and osmolarities on left ventricular (LV) mechanics in the isolated working rat heart model. Specifically, we separated the effect of isosmotic perfusates with different Na+ concentrations on LV mechanics. After a control period during which the hearts were perfused in a working mode with a control solution of Krebs-Henseleit bicarbonate buffer (Na+ of 136 meq/l, Ca2+ of 2.6 mM, and osmolarity of 300 mosM), the hearts were subjected to different perfusates (Na+ of 96-156 meq/l and osmolarity of 240-380 mosM, using different mannitol concentrations) in a semirandom order. Peak LV pressure (PLVP), maximal time derivative of LV pressure (dP/dtmax), and cardiac output (CO) were recorded. Increasing Na+ concentrations from 96 to 156 meq/l, using isosmotic perfusates, decreased PLVP, dP/dtmax, and CO in a dose-dependent manner. The dose-dependent behavior was evident for tonicities of 240, 280, 320, and 360 but not for 380 mosM. Increasing Na+ concentration from 96 to 136 meq/l at constant perfusate tonicity (320 mosM) decreased dP/dtmax from 6,753 +/- 133 to 5,602 +/- 418 mmHg/s (P < 0.001). Rearranging the same results to examine the effect of perfusate tonicity with iso-Na+ concentration demonstrated that increasing perfusate osmolarity had a dose-dependent effect on PLVP, dP/dtmax, and CO. At a constant Na+ concentration of 116 meq/l, increasing perfusate osmolarity from 240 to 320 mosM increased dP/dtmax from 6,116 +/- 132 to 7,274 +/- 594 mmHg/s (P < 0.01). Further increase in perfusate tonicity to 380 mosM decreased dP/dtmax to 2,338 +/- 398 mmHg/s (P < 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)


Sodium-calcium exchange-mediated contractions in feline ventricular myocytes. The hypothesis that Ca entry by the sarcolemmal Na-Ca exchange mechanism induces sarcoplasmic reticulum (SR) Ca release, loads the SR with Ca, and/or directly induces contractions by elevating cytosolic free Ca was tested in voltage-clamped feline ventricular myocytes. Intracellular Na concentration was increased by cellular dialysis to enhance Ca influx via "reverse-mode" Na-Ca exchange at positive membrane potentials, at which the "L-type" Ca current (ICa) should be small. Contractions were induced in the presence of Ca channel antagonists by depolarization to these potentials, suggesting that Ca influx via reverse-mode Na-Ca exchange was involved. These contractions had both phasic (SR related) and tonic components of shortening. They were smaller and began with more delay after depolarization than contractions which involved ICa. The magnitude of shortening was graded by the amount and duration of depolarization, suggesting that Ca influx via reverse-mode Na-Ca exchange has the capacity to induce and grade SR Ca release. Small slow contractions could be evoked in the presence of ryanodine (to impair SR function) and verapamil (to block ICa), supporting the idea that Ca influx via Na-Ca exchange is sufficient to directly activate the contractile proteins. Contractions induced by voltage steps to +10 mV, which were usually small when ICa was blocked, were potentiated if preceded by a voltage step to strongly positive potentials. This potentiation was inhibited by ryanodine, suggesting that Ca entry that occurs by Na-Ca exchange may be important for normal SR Ca loading.(ABSTRACT TRUNCATED AT 250 WORDS)


Tissue uptake of insulin and inulin in red and white skeletal muscle in vivo. By employing a tissue uptake technique, the kinetics of the plasma-interstitial equilibration of radiolabeled insulin, inulin, and albumin were followed in four muscles of differing capillarity in anesthetized rats. The soleus muscle (SOL), and the red portion of the gastrocnemius muscle (RG), as well as the extensor digitorum longus muscle (EDL) and the white portion of the gastrocnemius muscle (WG) were investigated. After constant intravenous tracer infusions and repeated plasma sampling under euglycemic clamp conditions, animals were killed at varying time intervals and the muscles mentioned above were dissected out. The radioactivity of tracer per gram of tissue in each muscle divided by the plasma activity of tracer per milliliter of plasma, i.e., "the plasma equivalent space" of tracer, thus could be followed as a function of time. From this function the permeability-surface area (PS) of inulin as well as the distribution volumes at time 0 (V0) of inulin and insulin and their equilibrium distribution volumes (VE) were assessed. The PS for inulin (in ml.min-1.100 g muscle-1) was 0.52 +/- 0.10 (mean +/- SE) in WG, increasing with more red fibers to 1.37 +/- 0.18 in SOL. Also the inulin interstitial distribution volume (at blood-tissue tracer equilibrium; VE) increased in this order (in ml/100 g) from 7.30 +/- 0.91 in WG to 12.93 +/- 0.89 in SOL. The V0 for insulin was found to be approximately fivefold larger than the plasma volume in each muscle sample, indicating a high degree of binding of insulin to structures within the vascular compartment, conceivably to the vascular endothelium.(ABSTRACT TRUNCATED AT 250 WORDS)


Role of myogenic response in enhancing autoregulation of flow during sympathetic nerve stimulation. The effect of sustained sympathetic nerve stimulation on autoregulation of blood flow was examined in the exteriorized cat sartorius muscle using intravital microscopy. Without sympathetic nerve stimulation (SNS), second-order arterioles showed insignificant dilation (3%) during arterial pressure reduction from 110 to 60 mmHg; volume flow fell coincident with pressure reduction. During SNS, these arterioles constricted significantly (25%), and their dilation during pressure reduction (20%) was significant and was significantly greater than that without SNS. Volume flow increased significantly (20-60%) during pressure reduction, a phenomenon termed superregulation of flow. Elevation of ambient oxygen in the suffusate from 0 to 20% caused arteriolar constriction but did not abolish arteriolar dilation during pressure reduction under sustained SNS. Arteriolar response to venous pressure elevation was also affected significantly by sustained SNS. Without SNS, third-order arterioles showed slight dilation (4%) when femoral venous pressure was elevated by 10 mmHg. During SNS, these arterioles constricted significantly and constricted further (20%) when venous pressure was elevated. Using a local anesthetic (lidocaine), we determined that a local venous-arteriolar reflex was not involved in the arteriolar constriction. Our data suggest that superregulation of flow during sustained sympathetic nerve stimulation is not due to metabolic factors but rather to an enhanced myogenic response.


Dobutamine improves afterload-induced deterioration of mechanical efficiency toward maximal. We studied the effect of increased afterload on the ratios of O2 consumption (VO2) to external work (EW), VO2 to the systolic pressure-volume area (PVA), and PVA to EW at control state and with dobutamine in the left ventricles of open-chest dogs. Left ventricular volume was measured with a volumetric conductance catheter and coronary flow with an electromagnetic flowmeter. Hexamethonium bromide and atropine sulfate were administered before changes in end-systolic pressure (Pes) with an infusion of nitroprusside or angiotensin II. Dobutamine enhanced ventricular end-systolic elastance by 100%. In the control, with increases in Pes, EW/VO2 remained unchanged, PVA/VO2 increased by 48%, and EW/PVA decreased by 26%. Dobutamine increased both EW/VO2 and EW/PVA at any given Pes but decreased PVA/VO2. During dobutamine, EW/VO2 increased significantly with increases in Pes. The ratio of measured EW/VO2 to the theoretically predicted maximal EW/VO2 value for a given end-diastolic volume and contractility was 0.83 at a Pes of 70 mmHg, and this ratio decreased by 33% with increases in Pes in the control. During dobutamine, measured EW/VO2 values were almost equal to each corresponding theoretical maximal value, and the average decrease in the ratio with increases in Pes was 7%. Thus the enhanced inotropic state by dobutamine can restore the afterload-induced deterioration of EW/VO2 toward the normal maximal level.


Muscarinic cholinergic receptors in canine adrenal gland. Muscarinic cholinergic receptor stimulation has been reported to modulate adrenal catecholamine and steroid secretion and influence medullary vascular tone. The present study was undertaken to localize and characterize muscarinic cholinergic receptor binding sites in canine adrenal medulla and cortex. Binding studies using semipurified membranes demonstrated specific, saturable binding of L-[benzilic-4,4'-3H(N)]-quinuclidinyl benzilate ([3H]QNB) in medulla, with a dissociation constant (KD) equal to 152 pM and estimated maximal binding sites (Bmax) equal to 179 fmol/mg protein. Displacement of [3H]QNB by cholinergic agents in order of decreasing potency was atropine, pirenzepine, oxotremorine, pilocarpine, and carbamylcholine, suggesting the receptor was M1 subtype, similar to sympathetic ganglion muscarinic receptors. Autoradiographic imaging studies demonstrated highly specific, homogeneous binding throughout the medulla. No specific binding was found in adrenal cortex. These results suggest that muscarinic effects on blood flow may be neurally mediated, rather than the result of stimulation of vascular muscarinic receptors. In medulla, muscarinic receptors are evenly distributed and modulate catecholamine secretion in all cells rather than subpopulations of cells as in other species. Absence of [3H]QNB binding in cortex argues against muscarinic receptor modulation of cortical steroid secretion.


Endotoxin enhances arachidonic acid metabolism by cultured rabbit microvascular endothelial cells. This study demonstrates that bacterial lipopolysaccharide and lipid A exert a significant effect on eicosanoid formation by primary cultures of microvascular endothelial cells (MECs). Qualitative studies using [14C]-arachidonic acid demonstrated that prostaglandin E2 was the primary eicosanoid formed by MECs after 20 h of treatment with either vehicle or lipopolysaccharide. Significant, dose-dependent productions of PGE2 and prostacyclin, beginning at an endotoxin dose of 0.01 ng/ml, were quantified by radioimmunoassay in supernatants of cells treated for 20 h with lipopolysaccharide or lipid A. This eicosanoid production was inhibited by meclofenamate and cycloheximide and occurred without cellular injury. The time course and kinetics of eicosanoid production in response to endotoxin demonstrate a significant, time-related enhancement. Endotoxin-treated MECs responded to exogenous substrate with augmented PGE2 production, suggesting enhanced prostaglandin endoperoxide synthase activity. These results demonstrate a significant interaction of endotoxin with endothelial cells of microvascular origin that results in an enhanced potential for eicosanoid metabolism. This effect may be mediated in part through induction of prostaglandin endoperoxide synthase.


Interstitial exclusion of albumin in rat tissues measured by a continuous infusion method. Steady-state 125I-labeled rat serum albumin (125I-labeled RSA) concentration in plasma was maintained by intravenous infusion of tracer for 72-168 h with an implanted osmotic pump. At the end of the infusion period, the rat was anesthetized and nephrectomized, and extracellular fluid was equilibrated with intravenous 51Cr-labeled EDTA for 4 h. Five minutes before final plasma and tissue sampling, 131I-labeled bovine serum albumin (131I-labeled BSA) was injected intravenously as a plasma volume marker. Samples of skin, muscle, tendon, and intestine were assayed for all three tracers. Apparent distribution volumes were calculated as tissue tracer content/plasma tracer concentration. Interstitial fluid volume (Vi) was calculated as V51Cr-EDTA-V131I-BSA. Steady-state extravascular distribution of 125I-labeled RSA as plasma equivalent volume (Va,p) was calculated as V125I-RSA-V131I-BSA. Steady-state interstitial fluid concentrations of 125I-labeled RSA in skin, muscles, and tendon were measured with nylon wicks implanted postmortem, and steady-state interstitial albumin distribution volumes were recalculated as wick-fluid equivalent volumes (Va,w). Relative albumin exclusion fraction (Ve/Vi) was calculated as 1-Va,w/Vi. For skin and muscle, steady-state 125I-labeled RSA tissue concentrations were reached at 72 h. Ve/Vi for albumin averaged 26% in hindlimb muscle, 41% in hindlimb skin, 30% in back skin, 39% in tail skin, and 54% in tail tendon. For muscle, Ve/Vi corresponds to expectation if all tissue collagen and hyaluronan is dispersed in the interstitium. However, for skin and tendon, albumin exclusion is considerably lower than expected on this basis, suggesting that much of their collagen is organized into dense bundles of fibers containing no fluid accessible to 51Cr-labeled EDTA or 125I-labeled RSA.


PEG-SOD improves postischemic functional recovery and antioxidant status in blood-perfused rabbit hearts. The isolated blood-perfused rabbit heart, subjected to 60 min of cardioplegic arrest and 60 min of reperfusion, was used to assess the effects of polyethylene glycol-conjugated superoxide dismutase (PEG-SOD) on postischemic recovery of left ventricular developed pressure (LVDP), the tissue activity of SOD, and tissue redox state. The five groups studied were the following: PEG-SOD-free control (group A), PEG-SOD as a pretreatment and as an additive during cardioplegia and reperfusion (group B), PEG-SOD as a pretreatment and a cardioplegic additive (group C), PEG-SOD in cardioplegia alone (group D), and PEG-SOD in reperfusion alone (group E). The results show that pretreatment with PEG-SOD improves postischemic recovery of LVDP (72 +/- 2% and 66 +/- 7 vs. 47 +/- 4% in groups B, C, and A, respectively). This protection was associated with an improved tissue redox state. Thus the ischemia-induced rise in oxidized glutathione was reduced from 313 +/- 26% (group A) to 162 +/- 15 and 138 +/- 14% (groups B and C, respectively), and the fall in reduced glutathione was attenuated from 51 +/- 5% to 35 +/- 6 and 13 +/- 5%, respectively. Tissue Mn-SOD activity was also conserved from 36 +/- 4% (group A) to 71 +/- 6 and 94 +/- 4% (groups B and C, respectively). No significant effect was seen when PEG-SOD was applied in cardioplegia or during reperfusion alone.


Different responses of extent and velocity of contraction to dobutamine in conscious sheep. The shortening- and shortening rate-preload-afterload relations, based on the concept of the myocardial end-systolic stress-strain relation (ESSSR), are a newly developed load- and size-independent assessment of myocardial contractility. The purpose of this study was to apply this assessment to compare extent and velocity of myocardial contraction during graded infusions of dobutamine. Seven chronically instrumented unsedated sheep were studied at rest and during graded infusions of dobutamine (2.5-20 micrograms.kg-1.min-1). The ESSSR were linear over a wide range of load alterations, whereas the end-systolic pressure-diameter relations (ESPDR) were generally nonlinear. Midwall shortening rate (SRm) at common preload and afterload representing contraction extent increased with each dose of dobutamine through 20 micrograms.kg-1.min-1. In contrast, midwall shortening (Sm) increased through dobutamine 5 micrograms.kg-1.min-1 but not at higher dobutamine infusion rates. Conventional endocardial shortening and the slope of the ESPDR, fitted to a linear model, exhibited responses similar to Sm. The velocity of circumferential endocardial fiber shortening (Vcf,c), Vcf,c-afterload relation, and maximum first derivative of left ventricular pressure exhibited responses similar to SRm. Thus both the extent and velocity of contraction increased at low doses of dobutamine, whereas only the velocity increased at high doses. Potential mechanisms for the saturated response of the extent of contraction include 1) shorter systolic time for contraction due to earlier onset of relaxation and 2) the utilization of myocardial contractile energy for left ventricular wall deformation at small cavity volumes at high doses of dobutamine.


Biphasic blood volume changes with lower body suction in humans. We recorded blood and plasma mass density and hematocrit of antecubital venous blood in 12 subjects in the supine position before, during, and after 20-40 min of lower body subatmospheric pressure (LBNP) of -35 mmHg. Mass density values decreased during the first minutes of LBNP, indicating a transient 2.8% blood volume gain before they rose as expected. After LBNP, a pronounced further density increase, indicating a further 1.5% hemoconcentration, preceded the return toward control. This pattern suggests reflex-driven transient filtration effects. Computed mass density of fluid exchanged between blood and extravascular space was 1,007.2 +/- 4.4 milligrams (37.0 degrees C); mass density of erythrocytes remained unaltered. We conclude that sudden unloading of central pressure receptors with LBNP causes microvascular fluid gain preceding fluid loss (hemoconcentration) during LBNP, and receptor loading after LBNP additionally causes fluid loss preceding inward filtration (hemodilution) during recovery. These effects can be quantified with high-precision blood and plasma mass densitometry performed by the mechanical oscillator technique.


Regional cerebrovascular responses to progressive hypotension after traumatic brain injury in cats. We investigated the effects of hypotension on cerebral blood flow (CBF) after traumatic brain injury (TBI) in cats. Isoflurane-anesthetized cats were prepared for TBI and for microsphere measurements of total (T) and regional (r) CBF. Four groups were studied: sham injury (group I, n = 6); TBI (group II, n = 6); isoflurane anesthesia, no TBI or hypotension (group III, n = 4); and isoflurane and TBI, no hypotension (group IV, n = 8). After TBI or sham trauma, mean arterial pressure (MAP) was reduced to 80, 60, and 40 mmHg by hemorrhage. Group I TCBF did not change significantly from baseline until MAP reached 40 mmHg, but rCBF was more dependent on MAP in anterior hemispheric than in brain stem regions. Group II TCBF was significantly lower than baseline, and group I TCBF at all levels of hypotension and autoregulation was impaired at higher MAP levels in anterior than in posterior brain regions. Groups III and IV indicated that decreases in TCBF were not due to duration of the preparation or to TBI in the absence of hemorrhagic hypotension. We conclude that global and regional autoregulation are absent in response to hemorrhagic hypotension after TBI.


Effect of anesthetic on sympathetic responses evoked from cerebellar uvula in decerebrate cats. The sympathetic mechanisms involved in the conversion of the tachycardia-pressor response evoked by electrical stimulation of the uvula (lobule IX of the posterior cerebellar cortex) in the unanesthetized decerebrate cat to a bradycardia-depressor response in the same, but anesthetized preparation, were investigated. Sympathoexcitation was produced in the inferior cardiac and renal sympathetic nerves in response to short train stimulation (2-5 pulses, 100-500 Hz) of the uvula in the unanesthetized decerebrate cat, and when paired stimuli (conditioning and test) were applied, the test-evoked potential in both nerves was similar to the response elicited by the conditioning stimulus. Anesthetic administered to these same animals caused the test response in both sympathetic nerves to be greatly decreased, yet the conditioning response was unchanged. The attenuation of the test response by the conditioning stimulus diminished during recovery from anesthesia. The recovery of the test response paralleled the time course of the return of the tachycardia-pressor effect evoked by long train stimulation of the uvula. It appears that anesthesia does not block the sympathoexcitatory response but acts to augment sympathoinhibitory processes associated with uvula stimulation; some possible mechanisms are discussed.


Beneficial influence of vasoactive intestinal peptide on ventriculovascular coupling in closed-chest dogs. The effect of vasoactive intestinal peptide (VIP) on ventriculovascular coupling in the intact cardiovascular system has not been defined. We studied seven dogs chronically instrumented with left ventricular (LV) pressure manometers and three sets of diameter gauges before and after infusions of 0.02, 0.05, and 0.10 microgram.kg-1.min-1 VIP. The dogs were studied after autonomic blockade, anesthesia, and intubation, with a fixed heart rate of 160 beats/min. Contractility was assessed using LV elastance at end systole (Ees) and the slope of the stroke work-end-diastolic volume relation. The vascular influence of VIP was quantified by determining effective arterial elastance (Ea) under steady-state conditions. The overall effect on ventriculovascular coupling was assessed using the transfer of mechanical energy from LV to the arterial system (TransPVA) quantified as the percentage of pressure-volume area (PVA) expressed as stroke work. LV relaxation was measured using the time constant of LV pressure decay. The results showed that VIP increased contractility (Ees increased to 129, 156, and 181% of control; P < 0.01 for all vs. control) and decreased effective arterial elastance (Ea fell to 84, 68, and 64% of control; P < 0.0155 vs. control for the two higher doses). VIP had no consistent effects on LV relaxation. Thus, in addition to its positive ventricular effects (increased contractility), VIP has beneficial vascular effects (reduced Ea). These properties combine to improve ventriculovascular coupling, such that VIP enhances delivery of mechanical energy from the LV to the circulatory bed.


Effect of acute ventricular dilatation on fibrillation thresholds in the isolated rabbit heart. We examined the effects of ventricular dilatation on epicardial refractoriness and ventricular fibrillation threshold (VFT) in the isolated, retrograde-perfused rabbit heart. Ventricular size was modified by acutely changing the volume of a fluid-filled balloon secured within either the left or right ventricle. Left ventricular dilatation (to an end-diastolic pressure of 30-38 mmHg) significantly decreased left ventricular effective refractory period (ERP) and myocardial wavelength (calculated as ERP x conduction velocity). Left VFT (determined by scanning the vulnerable period with a train of pulses) decreased from 6.4 +/- 0.9 to 4.4 +/- 0.5 mA; P < 0.01) with left but not right ventricular dilatation. Right ventricular dilatation was associated with a decrease in the right ventricular ERP and myocardial wavelength, and right VFT decreased from 13.6 +/- 1.8 to 4.1 +/- 0.3 mA (P < 0.01). Changes in VFT correlated with the decrease in local refractoriness and shortening of local excitation wavelength.


A new approach to analysis of synchronized sympathetic nerve activity. Renal sympathetic nerve activity (RSNA) recorded from the multifiber preparation is a continuously fluctuating variable in terms of period and amplitude, reflecting a coordinated tonic level of output from the vasomotor center. Yet current methods of analysis cannot simultaneously measure both of these parameters. A new accurate technique for assessing changes in global sympathetic activity is required. We made a novel application of a computerized peak detection algorithm (Cluster program) to recordings of synchronized sympathetic nerve discharges. The procedure was applied to this new area to retrieve information about the characteristics of synchronized RSNA. Peaks in synchronized RSNA activity were detected from short-term (20 ms) integrated recordings in which voltage changes had been digitized at 200 Hz and stored on computer. The program scanned the data series for significant increases followed by significant decreases in a small cluster of voltage values. The program permits the input of the cluster sample sizes for the test peaks and pre- and postpeak nadirs and also the minimum height to be defined as a peak. Once each synchronized RSNA peak had been detected, its corresponding amplitude, width, and peak-to-peak interval were calculated. The program successfully characterized RSNA in a group of eight cats and yielded results comparable to other analysis techniques. The peak-to-peak interval period showed two modes of synchronized discharge, one related to the cardiac cycle and a faster 8- to 14-Hz frequency. The synchronized peak amplitude and width showed unimodal frequency distributions. The relationship between each of the three variables was examined; only the peak height and width were significantly related to each other.(ABSTRACT TRUNCATED AT 250 WORDS)


Effect of adenosine deaminase on cardiac interstitial adenosine. Adenosine deaminase was infused into isolated perfused guinea pig hearts to determine its effect on myocardial adenosine levels. The enzyme was administered during constant coronary flow perfusion at 6.11 +/- 0.36 ml.min-1.g-1. Venous adenosine was measured in samples of pulmonary artery effluent; epicardial and endocardial adenosine were measured with the porous nylon disk technique. Infusion of adenosine deaminase at 2.4 and 4.8 U/ml produced adenosine deaminase activity of 0.92 +/- 0.09 and 2.33 +/- 0.15 U/ml, respectively, in epicardial fluid and 1.93 +/- 0.28 and 4.84 +/- 0.47 U/ml, respectively, in endocardial fluid. Aortic pressure was unchanged by infusion of adenosine deaminase at both infusion rates. Adenosine deaminase (data from both infusion rates pooled) reduced epicardial adenosine from 0.327 +/- 0.028 to 0.139 +/- 0.022 microM, endocardial adenosine from 4.61 +/- 0.42 to 1.64 +/- 0.20 microM, and venous adenosine from 0.017 +/- 0.02 to 0.003 +/- 0.001 microM. The data indicate that infused adenosine deaminase reaches the epicardial and endocardial interstitial fluid (ISF) compartments. The absence of any effect on coronary pressure suggests that adenosine may not be involved in resting basal coronary tone. The presence of significant residual adenosine despite adenosine deaminase infusion indicates that adenosine production in the unstressed isolated guinea pig heart exceeds the degradative capacity of infused adenosine deaminase. Previous studies in which it was assumed that almost all of the endogenous adenosine is inactivated by the infusion of adenosine deaminase should be reevaluated in light of these observations.


Maximal myocardial blood flow is enhanced by chronic hypoxemia in late gestation fetal sheep. The measurement of maximal myocardial blood flow gives information about the total cross-sectional area of the coronary resistance vessels. During a continuous left atrial infusion of adenosine (60 micrograms.kg-1.min-1), maximal myocardial blood flow was measured in 4 fetuses hypoxemic for a minimum of 5-8 days (pH = 7.33 +/- 0.01, arterial PCO2 = 49.8 +/- 4.2 Torr, arterial PO2 = 16.1 +/- 1.3 Torr, and arterial concentration of O2 = 5.3 +/- 1.2 ml/dl). These data were compared with an identically instrumented group of normoxemic fetuses (n = 7) following the same study protocol (pH = 7.38 +/- 0.02, arterial PCO2 = 43.1 +/- 3.8 Torr, arterial PO2 = 19.8 +/- 2.0 Torr, and arterial concentration of O2 = 7.9 +/- 1.0 ml/dl) (P < 0.05). At comparable arterial pressures, the maximal myocardial flow (ml.min-1.100 g tissue-1) for hypoxemic vs. normoxemic fetuses was 974 +/- 273 and 630 +/- 181 for the total myocardium, 986 +/- 367 and 602 +/- 192 for the left ventricular free wall, 1,025 +/- 346 and 614 +/- 178 for the septum, and 1,231 +/- 274 and 757 +/- 269 for the right ventricular free wall, respectively (P < 0.01). These data suggest that hypoxemia in the fetus can significantly alter the coronary vascular bed, which, if confirmed, would represent an important adaptation in the developing fetus.


The endocardial endothelium.

The endocardial endothelium. The heart wall with its complex trabecular structures is covered with a very thin layer of endocardial endothelial (EE) cells. EE cells appear early during cardiac development; they are involved in myocardial trabeculation and the formation of primitive nutrient vessels. This process precedes the development of coronary vessels, Purkinje fibers, and nerve fibers. EE has a different cell shape and cytoskeletal organization than vascular endothelium. The differences in permeability between EE and the coronary vascular endothelium in the subendocardial myocardium might assign characteristic electrochemical properties to the endocardium. Modulation of EE function by substances in the blood constitutes an important intracavitary autoregulation of muscle-pump performance of the heart, i.e., by altering the duration of contraction without significantly altering early contraction dynamics. Such an autoregulation resets the timing of ventricular relaxation and rapid filling with little effect on early systolic contraction and ejection. Both the release by the EE of various substances with inotropic properties and a trans-EE physicochemical control are postulated as possible underlying mechanisms.


Digital image analysis of shark gills: modeling of oxygen transfer in the domain of time. Digital radiographic imaging of blood circulation through leopard shark gills establishes a secondary lamellar transit time of 6.5 s. This duration, combined with estimates of cardiac output and hemoglobin-oxygen affinity, permits novel modeling of gill oxygen transfer in the time domain. The temporal model allows assessment of factors contributing to previously noted discrepancies between physiological and morphometric branchial oxygen conductance estimates. Lamellar transit time for shark blood is 20 times greater than human alveolar transit time, and thus correlates with a slower rate of hemoglobin-oxygen binding and a greater diffusion distance.


Atrial natriuretic factor binding sites in rat area postrema: autoradiographic study. The area postrema (AP) is a brain stem circumventricular organ implicated, among other functions, in central cardiovascular (CV) regulation. Competition binding analysis performed by quantitative in vitro autoradiography demonstrated specific, high-affinity (Kd, 0.32 +/- 0.11 nM), low-capacity (Bmax, 57.5 +/- 10.9 fmol/mg protein) atrial natriuretic factor (ANF) binding sites in the AP. C-ANF [des-(Gln116-Gly120)ANF-(Arg102-Cys121)-NH2] and ANF-(Phe106-Ile113)-NH2 (two ligands endowed with selectivity for the ANF-C receptor), as well as C-type natriuretic peptide (CNP), did not compete noticeably at pathophysiological concentrations for 125I-ANF binding. 125I-[Tyr0]CNP bound to the AP to a much lower extent than 125I-ANF. Electron microscopic autoradiography in vivo disclosed that 125I-ANF was preferentially bound to axon, dendrite, and astrocyte plasmalemma. These studies demonstrate that the AP contains natriuretic peptide binding sites with pharmacological characteristics of the ANF-A and ANF-B but not of the ANF-C receptor subtype. In the AP, ANF interacts with those sites resembling ANF-A receptors. Cellular localization of these binding sites may relate to their possible involvement in the centrally mediated salt and water regulation and/or CV effects of circulating ANF.


Vasopressin and angiotensin II in reflex regulation of heart rate: effect of water deprivation. This study tested the hypothesis that endogenous angiotensin II (ANG II) and vasopressin enhance baroreflex-mediated increases in heart rate in water-replete dogs and in dogs water deprived to chronically elevate plasma ANG II and vasopressin concentrations. The baroreflex was assessed by examining the heart rate response to infusion of increasing doses of nitroprusside (0.3, 0.6, 1.5, and 3.0 micrograms.kg-1.min-1). The effect on the baroreflex of pretreating the dogs with the competitive ANG II antagonist saralasin, a V1-vasopressin antagonist, or a combined V1/V2-vasopressin antagonist, alone or in combination, was determined. Nitroprusside infusion produced dose-dependent increases in heart rate, and the heart rate response was greater in water-deprived dogs in association with higher plasma levels of ANG II and vasopressin than in water-replete dogs. ANG II blockade alone depressed reflex increases in heart rate in water-deprived but not water-replete dogs. In both water-replete and water-deprived dogs, blockade of V1-vasopressin receptors reduced the heart rate response to hypotension, but this effect could be produced only when ANG II receptors were also blocked. In addition, administration of saralasin and the V1/V2-vasopressin antagonist led to a further reduction of the reflex tachycardia. These data suggest that endogenous vasopressin, acting at both V1- and V2-receptors, can amplify the increase in heart rate produced by hypotension. In addition, the results further support a physiological role for chronic elevations in endogenous ANG II in the maintenance of normal baroreflex function.


Roles of catecholamines and corticosterone during anoxia and recovery at 5 degrees C in turtles. The roles of the catecholamines and corticosterone in glucose regulation during 28 days of submergence anoxia and air-breathing recovery at 5 degrees C in the turtle Chrysemys picta were examined. Anoxia resulted in an increase in mean plasma epinephrine and norepinephrine levels (from 42 and 49 to 966 and 3,826 pg/ml, respectively) and a decrease in hepatic glycogen levels. Despite the increase in plasma catecholamine levels, plasma glucose levels did not change, and the percent of the alpha form of hepatic glycogen phosphorylase was decreased compared with normoxic controls. Plasma levels of lactate increased from 1.5 to 95 mM, and corticosterone decreased during anoxia. During recovery in air, corticosterone returned to control levels within 1 day, and plasma lactate levels slowly decreased. In contrast to a previous study on anoxic turtles at 22 degrees C, at 5 degrees C the catecholamines do not stimulate hepatic glycogenolysis by increasing the level of glycogen phosphorylase alpha. The results do not support the hypothesis that corticosterone enhances lactate clearance from turtle plasma during recovery from anoxia.


Stress in birds due to routine handling and a technique to avoid it. The stress that might result in animals from the routine handling that most experimental studies involve, e.g., weighing, injecting, and blood sampling, is usually assumed to be minimal when the animals look quiet. However, the intensity of this stress remains largely ignored. We have developed a system that allows blood samples to be taken from freely behaving geese without entering the animal room. In these entirely undisturbed geese, the humoral indexes of stress, i.e., blood levels of catecholamines, corticosterone, and lactate, were as low or even lower than the lowest values previously reported for birds. Remarkably, the mean basal values for epinephrine and norepinephrine were 90-fold and 5-fold, respectively, below the lowest values in the literature. Stress-induced variations in pH that would have concealed detection of nutrition-induced changes in pH were eliminated. In contrast, even though the birds looked quiet during a short 5-min routine handling procedure, to which they had been accustomed for weeks, there was a dramatic increase in the level of humoral indexes of stress. These increased severalfold within only 2 min, and the return to initial values could take up to 1 h. Acid-base balance was also disrupted. Thus, in studies on animals, the absence of stress cannot be deduced from only behavioral observations. Only a system for taking blood without human interference may enable stress-free investigations.


Early insulin response after food intake in geese. Plasma glucose and insulin levels were measured in chronically catheterized, freely moving, undisturbed geese, which were offered a free standard meal after an overnight fast. The insulin level markedly rose within the first minute after the start of food ingestion, whereas plasma glucose did not increase. This early insulin response was not correlated with the size of the meal. In contrast, both postabsorptive insulin response and plasma glucose changes were dependent on meal size. When a small amount of food (2-6 g) was eaten, insulin returned to basal level within 30 min, whereas plasma glucose remained unchanged. Larger meals (15-20 g) maintained plasma insulin at a higher level and induced a sustained rise of plasma glucose. These results indicate that there is a cephalic phase of insulin secretion at the beginning of the meal in birds as previously described in mammals.


Whole body insulin sensitivity in Osborne-Mendel and S 5B/Pl rats eating a low- or high-fat diet. To determine whether whole body insulin sensitivity differs between a rat strain that does not (S 5B/Pl) and a strain that does [Osborne-Mendel (OM)] become obese when eating a high-fat diet, we performed euglycemic clamp studies in animals from each strain during low- and high-fat feeding. Clamps were performed after 2 days ("initial clamp") and 9 days ("final clamp") on each diet. Plasma glucose and insulin levels during the final 60 min of initial and final clamps were similar in S 5B/Pl and OM rats regardless of diet. Insulin sensitivity, measured as the glucose clearance rate during the final 60 min of the clamp, averaged 35 +/- 3 ml.kg-1.min-1 in S 5B/Pl rats after 2 days on a low-fat diet. This did not change significantly during an additional 7 days on the low-fat diet. The high-fat diet was associated with a 13% reduction in insulin sensitivity after 2 days and a 30% reduction after 9 days in S 5B/Pl rats. OM rats exhibited similar patterns of insulin sensitivity during low- and high-fat diets, albeit at lower insulin sensitivity overall (P < 0.0005 vs. S 5B/Pl). Mean glucose clearance after 2 days on the low-fat diet was 27 +/- 2 mg.kg-1.min-1 and did not change significantly during seven more days of low-fat feeding. The high-fat diet was associated with a 19% reduction in glucose clearance after 2 days and a 38% reduction after 9 days in OM rats. The magnitude of reduction in insulin sensitivity during high-fat diets did not differ significantly between strains.(ABSTRACT TRUNCATED AT 250 WORDS)


Reversal of high-fat diet-induced obesity in female rats. The purpose of the present study was to test whether the degree of obesity or the duration of the obese state affects the reversibility of diet-induced obesity. This was accomplished by initially feeding adult female Wistar rats either a low-fat diet (Chow) or one of two high-fat diets (HFDs; 30 and 60% of total calories as dietary fat; 30% HFD and 60% HFD, respectively). Fifty-four days, reversal 1 (R1), or ninety-seven days, reversal 2 (R2), later the HFDs were substituted with the low-fat control diet in subgroups of rats. Animals from all groups were sampled at three intervals: the start of R1 (R1 start), and the completion of R1 (R1 end) and R2 (R2 end). At the end of each interval the 60% HFD-fed group had increased body weight, carcass lipid content, and retroperitoneal and parametrial white adipose tissue (RWAT and PWAT) pad weight, fat cell diameter, and fat cell volume, but not fat cell number (FCN), compared with the other groups. The 60% HFD-fed rats also exhibited a marked and persistent hyperphagia that continued even as most of the indexes of obesity approached their maximal values (R1 end). The 60% HFD group had a transient increase in RWAT and PWAT lipoprotein lipase activity that followed the development of most obesity indicators. A clear intermediate level of obesity did not develop in the 30% HFD-fed group. Instead, these animals had nonsignificant increases in these measures of adiposity, making it impossible to test whether the severity of the obesity affected its reversibility in age-matched groups.(ABSTRACT TRUNCATED AT 250 WORDS)


Metabolic state of the in situ perfused trout heart during severe hypoxia. An in situ perfused heart preparation was used to study the effects of severe hypoxia in the rainbow trout, Oncorhynchus mykiss. Hypoxic trout hearts were capable of generating similar power outputs and ATP turnovers to normoxic counterparts at subphysiological work regimes. However, lactate efflux was 35-fold higher and glycolytic rate was calculated to be > 10-fold higher in hypoxic than in normoxic hearts. The surprising ability of trout hearts to withstand severe hypoxia appears to be related to the rapid removal of lactate and associated protons from the heart. An increase in power demand to normal in vivo levels caused rapid failure in hypoxic hearts. Failure was caused by a decline in stroke volume (contractility) and was not a consequence of heart rate deterioration. Hypoxia caused marked declines in the concentration of creatine phosphate but not ATP, and we suggest that an increase in intracellular phosphate was the primary cause of failure.


Injection of cobalt protoporphyrin into the medial nuclei of the hypothalamus elicits weight loss. Intracerebroventricular administration of small amounts (0.1 mumol/kg body wt) of cobalt protoporphyrin (CoPP), a synthetic analogue of heme, results in transient hypophagia and prolonged reduction in body weight of rats. Statistically significant hypophagia is detectable within 3 h of CoPP infusion. These changes are accompanied by prompt and sustained reductions in running wheel revolutions, a measure of spontaneous locomotor activity. Bilateral intrahypothalamic injections of CoPP at far lower doses (4 nmol/rat) resulted in similar findings following infusion into the paraventricular, dorsomedial, and ventromedial nuclei, but the compound had no such effect when injected into the thalamus or the lateral hypothalamic area. These effects were also observed following microinjection of the natural metalloporphyrin, heme, into the medial hypothalamic nuclei. Inorganic cobalt, iron, protoporphyrin, and magnesium protoporphyrin injected similarly were without such effect. These findings provide further evidence that the site of the previously described actions of CoPP in reducing food intake and body weight in rats resides, at least in part, in the medial hypothalamus. Furthermore, this study expands the spectrum of metalloporphyrins that act in the central nervous system to elicit these changes from synthetic compounds such as CoPP to heme, the natural, physiological metalloporphyrin.


Dynamics of gastric emptying during and after stomach fill. Gastric contents were sampled at various points during and after intragastric infusions of glucose solution (6.25, 12.5, 25%) delivered at rates typical of normal ingestion in the rat. The postinfusion results were consistent with those reported in the literature in that glucose solute emptied at a relatively stable rate over time and across stimulus concentrations. During fill (1.0 ml/min; experiment 1), by contrast, solute (caloric) emptying rate increased about threefold as stimulus concentration was raised. For each concentration, emptying rate was uniformly higher during than after fill (approximately 4 times higher at the lowest concentration). In experiment 2, gastric emptying rate during 12-min intragastric infusions of 12.5% glucose varied directly with the volumetric rate (0.5, 1.0, 2.0 ml/min) at which they were delivered. These results show that different rules govern gastric emptying during and after stomach fill. The results also suggest that a large proportion of a liquid meal may empty before feeding is terminated and that variations in the rate of ingestion could affect the gastric/postgastric distribution of ingesta and, in turn, the satiation process.


Effect of reproductive function on cold tolerance in deer mice. Thermoregulatory responses were evaluated in male deer mice (Peromyscus maniculatus nebrascensis) after exposure to short photoperiod and either warm or cold ambient temperature (T(a)). Deer mice were chosen for this study because males exhibit differential reproductive responses to short day length (SD); this difference has a genetic basis, and both phenotypes are found within natural breeding populations. Deer mice undergoing SD-induced gonadal regression significantly improved their cold limit to -32.9 degrees C after exposure to SD/warm T(a) and to -47.4 degrees C after SD/cold T(a) exposure, relative to long day length/warm T(a) controls (-17.4 degrees C). In contrast, deer mice maintaining reproductive function despite SD exposure significantly improved cold limit to -27.2 degrees C only after exposure to SD/cold T(a), relative to controls (-16.3 degrees C). Maximum norepinephrine-induced nonshivering thermogenesis (NST) did not vary with reproductive state, indicating differences in cold tolerance were not due to capacity to produce heat by NST. Comparison between phenotypes of heat production during cold tolerance tests indicated that greater cold tolerance among mice exhibiting SD-induced gonadal regression can be accounted for by 1) lower rates of heat loss and 2) greater improvement of heat production. These findings suggest a functional relationship between reproductive function and seasonal thermoregulatory adjustments and indicate a significant cost to breeding during the winter months.


Calcium channel blockers inhibit amiloride-stimulated short-circuit current in frog tadpole skin. The larval frog skin has a very high electrical resistance and a corresponding low rate of transepithelial ion transport. Amiloride, a blocker of sodium transport in adult skin, transiently stimulates rather than inhibits short-circuit current (Isc) across larval skin. The time course and concentration response to amiloride and the effects of calcium channel blockers on Isc were studied with larval frog skin mounted in modified Ussing chambers. The amiloride (1 mM) transient was markedly blunted if the skin was previously exposed to low amiloride (0.01-0.1 mM) concentrations. The calcium channel blockers verapamil, nitrendipine, diltiazem, W-7, and lanthanum all blocked the amiloride transient. Diltiazem itself caused a rapid transient in Isc, indicating that it may be a partial agonist. These data suggest that the amiloride-stimulated cation channels rapidly desensitize in a manner similar to the acetylcholine receptor. The decline in Isc after amiloride stimulation could be caused by amiloride block of the open channel. Blockade of amiloride stimulation by well-known calcium channel blockers suggests that these larval cation channels may have some characteristics in common with calcium channels.


Cerebrovascular and coronary effects of endothelin-1 in the goat. In vivo and in vitro effects of endothelin-1 (ET-1) on cerebral and coronary vasculature of goats were examined and compared. In six anesthetized goats intravenous injections of ET-1 (0.1-0.8 nmol) increased arterial pressure, did not change the middle cerebral (MCA) and left anterior descending or left circumflex coronary (LCC) arterial blood flows (electromagnetically measured), and increased cerebral and coronary vascular resistances. In four other anesthetized goats intra-arterial injections of ET-1 (0.01-0.3 nmol) decreased the MCA flow less than the LCC flow (maximal reduction was 20 and 80%, respectively) and only the highest dose increased arterial pressure. In isolated segments from large arteries ET-1 (10(-11) to 10(-7) M) caused concentration-dependent isometric contractions, the concentration causing 50% of the maximal effect and the maximal contraction being lower in cerebral arteries than in coronary arteries. The in vitro reactivity of both arteries was unaffected by endothelium removal or by indomethacin (10(-5) M). Therefore ET-1 produces cerebral and coronary vasoconstriction in vivo and in vitro, probably by acting directly on vascular musculature. Although the sensitivity is higher in isolated cerebral arteries than in coronary arteries, the reactivity in vivo could be lower in the cerebral circulation than in the coronary circulation to this endothelium-derived peptide.


Hemodynamic effects of central angiotensin I, II, and III in conscious rabbits. We have examined the hemodynamic effects of intraventricular angiotensins in conscious rabbits. Fourth ventricular injections of angiotensin II (ANG II, 8 fmol to 25 pmol) produced dose-dependent pressor responses at doses 400 times less than equipressor intravenous doses. Lateral ventricle administration of doses up to 1,000 pmol had little effect on mean arterial pressure (maximum +7 +/- 3 mmHg, P < 0.05, n = 9). Comparison of dose-response curves to ANG I, II, and III showed that all three had similar maximum pressor effects (27 +/- 3 mmHg), with ANG I being four times less potent than ANG II, and ANG III as potent as ANG II. Central pretreatment with the ANG-converting enzyme inhibitor enalapril abolished the pressor response to ANG I, suggesting that it was mediated entirely through ANG II. Examination of the hemodynamic changes after ANG I, II, and III in rabbits instrumented with aortic, mesenteric, or hindquarter flow probes showed that the rise in blood pressure to all three agents was due entirely to a decrease in total peripheral conductance, since cardiac output and heart rate fell. Peripheral conductance changes were not uniform, with the mesenteric bed showing an average 20 +/- 3% fall in conductance, while the hindquarter conductance increased (+12 +/- 3%). In sinoaortic-denervated rabbits, however, central angiotensins reduced conductance equally in the hindlimb and mesenteric beds, suggesting that the hindlimb dilatation in the baroreceptor intact rabbit was due to baroreflex buffering of the pressor effect. In conclusion, these studies suggest that the main sites for ANG effects on the cardiovascular system are located in the brain stem.(ABSTRACT TRUNCATED AT 250 WORDS)


Does reducing the rate or efficiency of digestion reduce food intake? Two strains of rats (Charles River CD and Lewis) were fed high-moisture (71% water) diets containing 50-300 mg acarbose/kg dry diet for 1-3 wk. Acarbose impaired carbohydrate digestion in both strains, as evidenced by increased fecal excretion and increased intestinal contents. For both strains the highest dose of acarbose tended to stimulate food intake, whereas an intermediate dose (100 mg/kg) inhibited food intake. The lowest dose (50 mg/kg) had no significant effect. In general the food intake-promoting effect of acarbose was more pronounced in CD rats, whereas the food intake-inhibiting effect of acarbose was more pronounced in Lewis rats. To determine whether increased intestinal bulk, due to undigested food, was responsible for the reduced food intake, another experiment was conducted in which Lewis rats were fed diets containing 5-25% cellulose. Although this level of cellulose should have increased fecal bulk to the same degree as acarbose, cellulose increased rather than decreased food intake. It is proposed that the presence of incompletely digested food in the digestive tract can inhibit food intake for several days. Because manipulating diet moisture altered energy intake without altering percentage of food excreted as feces, it is proposed that acarbose and diet moisture alter food intake by different mechanisms.


Intraventricular CCK-8 reduces single meal size in the baboon by interaction with type-A CCK receptors. Intraventricular cholecystokinin COOH-terminal octapeptide (CCK-8) decreases meal size in the meal-trained baboon. In the present study, we tested whether this action is mediated by CCK-A receptors, CCK-B receptors, or both. Intraventricular administration of the selective CCK-A receptor agonist A71623 at 1 and 10 nmol/kg suppressed 30-min meal size 69 +/- 22% and 75 +/- 7%, respectively. Additionally, intraventricular A71623 was equipotent to CCK-8 at 1 nmol/kg (% suppression of meal by CCK = 59 +/- 17). However, intraventricular administration of the CCK-B receptor agonist A63387 at 10 nmol/kg had no effect on 30-min meal size (% suppression = 18 +/- 29). Intravenous administration of 10 nmol/kg A71623 did not result in an alteration of meal size, but prandial plasma insulin and glucose responses were delayed and blunted. Basal plasma insulin levels doubled after intravenous administration of A71623. Both behavioral and metabolic responses to A71623 in the baboon are virtually identical to those we have previously observed after CCK-8 treatment. Thus we conclude that the predominant receptor population with which intraventricular CCK-8 interacts are type-A CCK receptors that are accessible to the ventricular system of the baboon.


Effects of CGRP on baroreflex control of heart rate and renal sympathetic nerve activity in rabbits. We examined the effects of intravenous infusion of calcitonin gene-related peptide (CGRP) and sodium nitroprusside (SNP) on baroreceptor afferent nerve activity, renal sympathetic efferent nerve activity (RSNA), and heart rate in alpha-chloralose-anesthetized rabbits. Baroreceptor afferent nerve activity was measured from aortic nerves during CGRP- and SNP-induced hypotension. Decreases in aortic nerve activity in response to decreases in mean arterial pressure were not different during CGRP and SNP infusion. Progressive infusion of CGRP (12-120 pmol.kg-1.min-1) increased RNSA by 83 +/- 14 (mean +/- SE), 175 +/- 26, 246 +/- 36, and 343 +/- 41%, and heart rate by 8 +/- 2, 24 +/- 3, 37 +/- 4, and 47 +/- 6 beats/min during falls of blood pressure of 5, 10, 15, and 20 mmHg, respectively. These increases in RSNA and heart rate produced by CGRP were significantly greater than those produced by SNP. The alterations in heart rate and RSNA with CGRP were reversed by restoring blood pressure with phenylephrine HCl. In rabbits with sinoaortic and vagal deafferentation, the responses of heart rate and RSNA to a fall of blood pressure were abolished during both CGRP and SNP infusion. Therefore, it is suggested that the facilitated responses of heart rate and RSNA during CGRP infusion occurred by way of the arterial baroreflex arc.


Effect of age and blood pressure on the heart rate, vasopressin, and renin response to hypoxia in fetal sheep. The purpose of these studies was to determine whether attenuating the increase in arterial and central venous pressure (CVP) during acute hypoxia can augment the renin and arginine vasopressin (AVP) responses to isocapnic hypoxia in chronically instrumented sheep fetuses. Young (122 +/- 2 days; n = 7) and old (133 +/- 1 days, n = 7) fetuses were exposed to hypoxemia (arterial PO2 = approximately 12-13 Torr) without and with attenuation of the increase in mean arterial pressure (MAP) and CVP with the simultaneous infusion of sodium nitroprusside (NP). NP did not attenuate the bradycardia induced by hypoxia. Plasma renin activity did not increase with hypoxia even when the potentially inhibitory effect of increased MAP and CVP was attenuated with NP. The AVP response to hypoxia was greater in the old fetuses. Furthermore, NP did augment the AVP response to hypoxia in the young but not old fetuses. We conclude that increases in MAP and CVP (i.e., baroreceptor input) do not influence the decrease in heart rate and lack of renin responses to acute hypoxia in the sheep fetus and that increased MAP and CVP seems to restrain the AVP response to hypoxia in younger sheep fetuses.


Clonidine in the prepyriform cortex blocked anorectic response to amino acid imbalance. Ingestion of imbalanced amino acid diets (IMB) has been associated with a decrease in norepinephrine (NE) concentration in the prepyriform cortex (PPC), an area essential for the anorectic response to IMB. Decreased NE could result from activity-induced release (and subsequent metabolism) of the transmitter. If activity of the NE system is important in the rat's anorectic response to IMB, reduced NE activity should result in increased IMB intake. Therefore, the feeding response to IMB was measured after injecting clonidine (Clon) into the PPC to inhibit NE release. At 3 and 6 h after Clon (1.0 and 1.5 micrograms/rat) injections, IMB intake was increased from 69 (the usual response to IMB in untreated animals) to > 100% of control intake. Effective injection sites did not include the gustatory neocortex, an area important for conditioned taste aversions. Thus activation of the NE system in the PPC may be associated with the initial reduced intake of IMB, suggesting that NE activity in the PPC has a role in the neural mechanisms that subserve recognition of amino acid deficiency.


Elevated muscle acidity and energy production during exhaustive exercise in humans. This study examined the effect of previous intense exercise on energy production during exhaustive exercise. Subjects (n = 6) performed dynamic knee extensor exercise to exhaustion twice (Ex1 and Ex2) separated by 16 min of recovery consisting of 10 min of rest, 3.5 min of very high-intensity intermittent exercise, and a further 2.5 min of rest. This resulted in an elevated muscle lactate concentration of 13.1 mmol/kg wet wt before Ex2. Muscle lactate concentration was the same at end of Ex1 and Ex2, but the accumulation of lactate and net lactate release during Ex2 was reduced (P < 0.05) by 67 and 38%, respectively. The time to exhaustion was 3.73 and 2.98 min, respectively, and the mean rate of net lactate production for Ex2 was lower (P < 0.05) than for Ex1 (4.6 +/- 1.2 and 9.6 +/- 1.7 mmol.min-1.kg wet wt-1, respectively). Leg O2 uptake was the same for Ex1 and Ex2. Muscle pH (6.85) was lowered (P < 0.05) before Ex2, but at the end of Ex2 (6.77) it tended (P < 0.1) to be higher compared with that at the end of Ex1 (6.73). In summary, the net lactate production rate is reduced but the aerobic energy production is not significantly altered when intense exercise is repeated. Fatigue and the lowered glycolysis do not appear to be caused by the elevated acidity per se before exercise.


Developmental changes in hindlimb muscles and diaphragm of sheep. In this study, plasma thyroxine, contractile and histochemical (adenosinetriphosphatase and NADH) characteristics of soleus (SOL), medial gastrocnemius (MG), and extensor digitorum longus (EDL) were examined in 140-day-gestation fetal sheep and in 2-, 5-, and 30-day-old lambs and adult ewes. Electrophoretic separation of myosin heavy chains was also done on all muscles and the diaphragm. There were no differences in the twitch contraction and relaxation times of MG and EDL at the different ages; in contrast SOL contraction times were significantly shorter in the fetus and newborn than in the adult. Fast glycolytic fibers first appeared in EDL, MG, and diaphragm at 5, 30, and 5 days after birth, respectively. The proportion of slow oxidative fibers decreased after birth and with postnatal development in EDL, whereas they increased in MG and diaphragm. Plasma thyroxine concentrations were higher in the fetus and day-old lambs than in 2-, 5-, and 30-day-old lambs or adult sheep. It is suggested that contractile specialization of the fast-twitch diaphragm, MG, and EDL is largely achieved in utero and is probably mediated by thyroid hormone. In contrast, SOL changed postnatally, probably influenced by the altered neural drive.


Platelet-activating factor antagonists limit glycine changes and behavioral deficits after brain trauma. Tissue damage after traumatic brain injury (TBI) results in part from delayed biochemical changes initiated by the insult. Platelet-activating factor (PAF) is an alkylphospholipid that has been implicated in tissue damage after cerebral ischemia. PAF is toxic to certain neuronal cell lines in culture, reduces cerebral blood flow, alters the blood-brain barrier, and can enhance phospholipid hydrolysis. The recent development of receptor antagonists to PAF permits examination of its possible role in delayed tissue injury after neurotrauma. Treatment with the PAF receptor antagonists BN 52021 and WEB 2170 before injury significantly enhanced neurological recovery after fluid percussion-induced TBI in rats. Pretreatment with WEB 2170 also significantly limited alterations in tissue water content and tissue glycine levels after trauma, and reduced posttraumatic levels of extracellular glycine in ipsilateral hippocampus. These findings implicate PAF in the pathophysiology of TBI, through actions at PAF receptors. A possible role for glycine in this process is suggested.


Iron uptake in relation to transferrin degradation in brain and other tissues of rats. The possibility that iron uptake by the brain involves transcytosis of the iron-transferrin complex across the brain capillaries, followed by degradation of the transferrin (Tf) within the brain, was investigated using diferric 125I-[59Fe]Tf and [59Fe]Tf coupled to 125I-tyramine cellobiose (TC). The radiolabeled catabolic products of proteins labeled with 125I-TC remain in the cells where degradation occurs. The TCTf complex behaved normally with respect to its ability to donate iron to rat reticulocytes in vitro or to the brain, liver, kidneys, and femurs in vivo. In the brain there was little difference in the uptake of 125I derived from Tf and TCTf, and the amounts were equivalent to only a small fraction of the 59Fe uptake. Hence, the rate of Tf catabolism in the brain was insufficient to account for the rate of accumulation of iron from plasma Tf. It was concluded that Tf recycles to the plasma after delivering its iron to the brain. The uptake of 125I from TCTf by the liver and kidneys accounted for 40-50% of the total rate of Tf catabolism. This indicated that they were important but not the only sites of degradation of this protein.


Gestational changes in Ca2+ transport across rat placenta and mRNA for calbindin9K and Ca(2+)-ATPase. The unidirectional maternofetal clearance (Kmf) of 45Ca was measured across the rat placenta over the last one-third of gestation. Kmf for 45Ca normalized to its diffusion coefficient in water (Kmf/Dw) increased 72-fold between days 15 and 22 of gestation from 3.5 +/- 0.3 to 253.1 +/- 22.0 cm/g placenta, respectively. At 15 and 18 days of gestation, Kmf/Dw for 45Ca was similar to Kmf/Dw for the paracellular marker [14C]mannitol, but at 21 and 22 days of gestation, Kmf/Dw for 45Ca was significantly higher than Kmf/Dw for [14C]mannitol, indicating that an additional route of transfer, other than diffusion, becomes available to calcium during this period. Northern hybridization analysis demonstrated that rat placental calbindin9K-to-beta-actin mRNA ratio increased 135-fold between 15 and 22 days of gestation and was temporally associated with the gestational increase in Kmf/Dw for 45Ca. In contrast, rat placental Ca(2+)-ATPase-to-beta-actin mRNA ratio increased only two- to threefold over the same gestational period and did not mirror the gestational changes in calcium clearance. These trends suggest that the expression of placental calbindin9K, but not Ca(2+)-ATPase, may be rate limiting to placental calcium transport in the rat.


Tissue-specific effects of physiological ANP infusion on blood-tissue albumin transport. Blood-tissue transport of 131I-labeled bovine serum albumin (BSA) during intravenous infusion of synthetic atrial natriuretic peptide (ANP) was examined in anesthetized male Wistar rats. Plasma volumes were maintained at pre-ANP levels by infusion of 2% BSA in lactated Ringer solution (LR) to minimize compensatory responses to ANP-induced hypovolemia. 131I-BSA clearance was measured over 30 min, and 125I-BSA was injected terminally to correct for intravascular volume. Thirty-minute infusion of 20 ng.kg-1.min-1 ANP resulted in a tissue-selective increase in 131I-BSA clearance in jejunum and colon compared with controls given LR only. Smaller but significant increases in tracer clearance also were observed in fat, kidney, left ventricle, and skeletal muscle exposed to 400 ng.kg-1.min-1 ANP. The observed elevation in tracer albumin extravasation was not associated with any measurable increase in tissue extravascular water content. Furthermore, it was shown that coupling of 131I-BSA transport to filtration induced by hindlimb venous congestion was similar in control and ANP-treated rats. In a second series of experiments, plasma ANP levels were determined after 30-min ANP infusions from 0 to 180 ng.kg-1.min-1. Significant linear associations between physiological ANP levels (62-578 pg/ml) and 131I-BSA clearance were demonstrable for small intestine, colon, fat, kidney, and skeletal muscle but not for skin, heart, diaphragm, and lung. We conclude that raising plasma ANP by infusion of the synthetic peptide results in a filtration-independent, tissue-selective increase in albumin transport. Tissue uptake of albumin is a potential mechanism for extrarenal fluid shift during circulatory volume overload.


Indomethacin attenuates exercise-induced proteinuria in hypertensive miniature swine. Exercise-induced proteinuria may be increased in hypertensives. The mechanisms underlying the increased proteinuria are not known, and it has not been determined whether animal models of hypertension exhibit a similar response. We investigated whether indomethacin (Indo) altered exercise-induced proteinuria in normal and hypertensive deoxycorticosterone acetate (DOCA) Yucatan miniature swine (YMS). Five normal and four DOCA YMS underwent 30 min of treadmill exercise at 80% of maximal heart rate. Cumulative (exercise + recovery) albumin excretion in the DOCA YMS was 25-fold (P < 0.01) greater than observed in the normal YMS. Indo had no effect on resting or exercise-induced proteinuria in the normal YMS. However, Indo decreased the slightly elevated proteinuria at rest, and normalized the exaggerated exercise-induced proteinuria in the DOCA YMS. The antiproteinuric effect of Indo in the DOCA YMS was not associated with altered exercise, recovery blood pressure, or glomerular filtration rate. Thus hypertensive DOCA YMS exhibit an exaggerated exercise-induced proteinuria. It is suggested that eicosanoids are involved in this abnormal renal proteinuric response to exercise.


A network model of respiratory rhythmogenesis. A mathematical model of the three-phase respiratory network proposed by Richter et al. (News Physiol. Sci. 1: 109-112, 1986) is developed and its properties are examined. The model reproduces the experimentally determined trajectories of membrane potential for the five physiologically distinct types of neurons included. Stepwise parameter changes can produce a respiratory rhythm with only two separate electrophysiological phases, result in apnea, or produce more complex patterns of firing. The phase-resetting behavior of the model was obtained with perturbing stimuli and is comparable to experimentally determined phase-resetting data. There is reasonable agreement between model predictions and experimental results. In the model, the properties of the phase singularity make termination of the respiratory rhythm by an appropriately timed perturbation virtually impossible, which is in agreement with experimental observations. The rhythm can be stopped by alterations that simulate the effect of input from the superior laryngeal nerve; the rhythm is locked in the postinspiratory phase. We conclude that our results are consistent with the concept of a network oscillator as the source of the respiratory rhythm.