Transforming growth factor beta 1 is an epithelial-derived signal peptide that influences otic capsule formation.

Interactions between epithelial and mesenchymal tissues in the developing inner ear direct the formation of its cartilaginous capsule. Recent work indicates that many growth factors are distributed in the early embryo in vivo in a temporal-spatial pattern that correlates with sites of ongoing morphogenetic events. We report here that the localization of transforming growth factor beta 1 (TGF-beta 1) in both epithelial and mesenchymal tissues of the mouse inner ear between 10 and 16 days of embryonic development (E10-E16). In addition, utilizing a high-density culture system as an in vitro model of otic capsule chondrogenesis, we show that modulation of chondrogenesis by TGF-beta 1 in cultured mouse periotic mesenchyme mimics the in vitro effects of otic epithelium on the expression of chondrogenic potential. We provide evidence of a causal relationship of this growth factor to otic capsule formation in situ by demonstrating that the actual sequence of chondrogenic events that occur in the developing embryo is reproduced in culture by the addition of exogenous TGF-beta 1 peptide. Furthermore, in cultures of mesenchyme containing otic epithelium, we demonstrate the localization of endogenous TGF-beta 1, first within the epithelial tissue and later within both the epithelium and its surrounding periotic mesenchyme, contrasted to an absence of endogenous TGF-beta 1 in cultures of mesenchyme alone. Our results suggest that TGF-beta 1 is one of the signal molecules that mediate the effects of otic epithelium in influencing the formation of the cartilaginous otic capsule.


The armadillo homologs beta-catenin and plakoglobin are differentially expressed during early development of Xenopus laevis.

Plakoglobin and beta-catenin are cytoplasmic proteins associated with the intracellular plaques of cell adhesive junctions. While plakoglobin is present in both adherens junctions and desmosomes, beta-catenin is associated with the cadherins that accumulate only in adherens junctions. Both beta-catenin and plakoglobin are homologs of armadillo, a Drosophila segment polarity gene that is considered to be in the wingless signaling pathway. We have characterized the expression and distribution of both plakoglobin and beta-catenin in Xenopus embryos. As shown by RNA blot analysis, beta-catenin and plakoglobin transcripts are present in fertilized eggs and in embryos through to tadpole stage. Whole-mount in situ hybridization indicates that both genes are expressed in the dorsal ectoderm and mesoderm of tailbud- and tadpole-stage embryos and that beta-catenin is expressed in the midbrain. Both plakoglobin and beta-catenin polypeptides are present during early Xenopus development; however, differences exist in the timing of maximal expression. Plakoglobin is present in the fertilized egg, increases in abundance by neurula stage, then declines at the tailbud and tadpole stages. beta-Catenin, recognized by an anti-arm antibody, is also present in the fertilized egg and in blastula-stage embryos. However, beta-catenin continues to be detected at the neurula, tailbud, and tadpole stages when levels of plakoglobin decline. The presence of multiple homologs of armadillo in Xenopus embryos and the differences in their patterns of expression suggest distinct roles for these proteins in processes affected by cell adhesion.


Expression of a mouse zinc finger protein gene in both spermatocytes and oocytes during meiosis.

In order to identify genes regulating meiosis, a mouse spermatocyte cDNA library was screened for sequences encoding proteins with C2H2-type zinc finger motifs which are typically expressed by the Drosophila Krüppel gene. Three new cDNAs were isolated, and they were designated CTfin33, CTfin51, and CTfin92. Among them, CTfin51 was selected for further study. The deduced amino acid sequence revealed seven zinc finger motifs in its C-terminal region. Northern blot and in situ hybridization showed CTfin51 mRNA expression in spermatocytes after the pachytene stage and in early stage round spermatids of prepuberal and adult males. Immunocytochemical staining with an antiserum against beta-gal-CTfin51 fusion protein was localized within nuclei of spermatocytes and spermatids. Oocyte nuclei after the pachytene stage also were immunoreactive for CTfin51 protein. Immunoblots revealed a band at M(r) 75,000 in protein extracts from the testis and the ovary. These results suggest that the CTfin51 gene encodes a DNA-binding regulatory protein functionally associated with meiosis in both male and female gametogenesis.


Altered morphology in transgenic tobacco plants that overproduce cytokinins in specific tissues and organs.

An auxin-inducible bidirectional promoter from the soybean SAUR gene locus was fused to a reporter gene in one direction and a cytokinin biosynthetic gene in the opposite direction and the expression of these fused genes was examined in transgenic tobacco. The Escherichia coli uidA gene, which encodes the enzyme beta-glucuronidase (GUS), was used as the reporter gene and the Agrobacterium tumefaciens ipt gene, which encodes the enzyme isopentenyl transferase, was used as the cytokinin biosynthetic gene. These constructs allowed the overproduction of cytokinins in tobacco in a tissue- and organ-specific manner. Localized overproduction of cytokinins was monitored using the GUS reporter gene and measured by an ELISA assay. The tissue- and organ-specific overproduction of cytokinins produced a number of morphological and physiological changes, including stunting, loss of apical dominance, reduction in root initiation and growth, either acceleration or prolonged delayed senescence in leaves depending on the growth conditions, adventitious shoot formation from unwounded leaf veins and petioles, altered nutrient distribution, and abnormal tissue development in stems. While some of these morphological changes result directly from the localized overproduction of cytokinins, other changes probably result from the mobilization of plant nutrients to tissues rich in cytokinins.


Histone H2A.F/Z mRNA is stored in the egg cytoplasm and basally regulated in the sea urchin embryo.

The sea urchin H2A.F/Z histone is a member of a subclass of highly conserved H2A variants. Sequence analysis confirms that H2A.F/Z mRNA is polyadenylated. In situ hybridization studies demonstrate that maternal H2A.F/Z message is stored in the egg cytoplasm and present at equal levels in all cells of the mesenchyme blastula-stage embryo, suggesting that H2A.F/Z is not coordinately regulated with DNA synthesis. When blastula-stage embryos were exposed to DNA synthesis inhibitors, no effect on the steady-state level of H2A.F/Z mRNA was observed, while the level of late class H2B mRNA decreased substantially. These results provide evidence that the basal mode of regulation of this unusual histone variant is conserved evolutionarily.


Myb p75 oncoprotein is expressed in developing otic and epibranchial placodes.

The c-myb proto-oncogene encodes a transcriptional regulatory protein which is highly conserved throughout evolution. Myb has been considered to be normally restricted to hematopoietic tissues, but there are indications that this might not always be the case. The present work shows the expression of a p75 Myb oncoprotein in the otic vesicle and epibranchial placodes of the early chick embryo. Expression was sequential and followed the same time course as the formation of placode-derived cranial ganglia. The results suggest a potential role for c-myb in regulation of placode development and neurogenesis.


Membrane-associated neurotransmitter stimulating factor is very similar to ciliary neurotrophic factor.

Membrane-associated neurotransmitter stimulating factor (MANS) can modulate sympathetic neurotransmitter expression and promote ciliary neuron survival in cell culture. Previous studies have shown that its biological effects and biochemical properties are similar to those of ciliary neurotrophic factor (CNTF). In addition, CNTF is present in spinal cord, the source of MANS. These observations raised the possibility that MANS preparations contain CNTF. We find that partially purified MANS fractions contain a 24-kD protein that is recognized in Western blots by an antiserum generated against recombinant rat CNTF (rCNTF). This antiserum immunoprecipitates virtually all the cholinergic-inducing and the ciliary neurotrophic activities present in MANS preparations. When iodinated rCNTF is incubated with spinal cord membranes, a significant proportion of the labeled CNTF segregates with the membrane pellet. The membrane-associated exogenous CNTF can be eluted from the membrane fraction by treatment with high-salt solutions, similar to that used to solubilize MANS from spinal cord membranes. Our data suggest that a substantial portion of the cholinergic differentiation and ciliary neurotrophic activities present in MANS preparations can be attributed to CNTF or a CNTF-like molecule.


Electrophysiology of stimulus-secretion coupling in human beta-cells.

Herein, we review the applicability to human beta-cells of an electrophysiologically based hypothesis of the coupling of glucose metabolism to insulin secretion. According to this hypothesis, glucose metabolism leads to the generation of intracellular intermediates (including ATP), which leads to closure of ATP-sensitive K+ channels. Channel closure results in membrane depolarization, the onset of electrical activity, and voltage-dependent Ca2+ entry. The resultant rise in cytosolic Ca2+ leads to Ca(2+)-dependent exocytosis of insulin granules. We found that most of the published experimental evidence for human beta-cells supports this hypothesis. In addition, we present three other emerging lines of evidence in support of this hypothesis for human islet beta-cells: 1) the effects of pHi-altering maneuvers on insulin secretion and electrical activity; 2) preliminary identification of LVA and HVA single Ca2+ channel currents; and 3) validation of the feasibility of Cm measurements to track insulin granule exocytosis. On the basis of this last new line of evidence, we suggest that combinations of Cm measurements and electrical activity/membrane current measurements may help define the roles of diverse electrical activity patterns, displayed by human beta-cells, in stimulus-induced insulin secretion.


Insulin is required for the liver to respond to intraportal glucose delivery in the conscious dog.

To determine whether insulin is essential for the augmented hepatic glucose uptake observed in the presence of intraportal glucose delivery, SRIF was used to induce acute insulin deficiency in 5 conscious dogs, and glucose was infused into the portal vein or a peripheral vein in two sequential, randomized periods. Insulin and C-peptide levels were below the limits of detection after SRIF infusion, and the load of glucose presented to the liver was approximately doubled and equivalent during the portal and peripheral periods. Net hepatic glucose output was 2.9 +/- 0.9 and 2.1 +/- 1.1 mumol.kg-1.min-1 during portal and peripheral glucose delivery, respectively. In an additional set of protocols, pancreatectomized dogs were used to investigate the effects of prolonged insulin deficiency (n = 5) and acute insulin replacement (n = 4) on the hepatic response to intraportal glucose delivery. In the prolonged insulin deficiency protocol, SRIF was used to lower glucagon and thereby reduce circulating glucose levels, and glucose was infused into the portal or peripheral circulations in two sequential, randomized periods. As with acute insulin deficiency, net hepatic glucose output was still evident and similar (3.6 +/- 1.1 and 4.2 +/- 1.3 mumol.kg-1.min-1) during portal and peripheral glucose delivery, respectively. When the pancreatectomized dogs were restudied using a similar protocol, but one in which insulin was replaced (4X-basal), and the glucose load to the liver was matched to that which occurred in the prolonged insulin deficiency protocol, net hepatic glucose uptake was 23.6 +/- 6.1 mumol.kg-1.min-1 during portal glucose delivery but only 10.3 +/- 3.5 mumol.kg-1.min-1 during peripheral glucose delivery. These results suggest that the induction of net hepatic glucose uptake and the augmented hepatic response to intraportal glucose delivery require the presence of insulin.


Evidence for distinctive and intrinsic defects in insulin action in polycystic ovary syndrome.

Women with PCO have a unique but poorly characterized disorder of insulin action. Obese (n = 16) and nonobese (n = 14) PCO women and age- and weight-matched normal, nondiabetic ovulatory women (obese, n = 15; nonobese, n = 17) had insulin action determined in vivo with sequential multiple insulin dose euglycemic clamps and in isolated abdominal adipocytes to clarify the mechanisms of insulin resistance. PCO resulted in significant increases in the ED50 insulin for glucose utilization in vivo (P less than 0.001) and in adipocytes (P less than 0.01), without significant changes in adipocyte insulin-binding sites. PCO also resulted in significant decreases in maximal insulin-stimulated rates of glucose utilization in vivo (P less than 0.01) and in adipocytes (P less than 0.01). Obesity resulted in smaller decreases in insulin sensitivity than PCO (ED50 insulin, P less than 0.001 in vivo and P less than 0.05 in adipocytes), but greater decreases in insulin responsiveness (Vmax, P less than 0.001 in vivo and in adipocytes). The ED50 insulin for suppression of HGP was increased only in obese PCO women (P less than 0.001), and the interactions between PCO and obesity on this parameter were statistically significant. No significant correlations between androgen or estrogen levels and adipocyte insulin binding or action were found. Because insulin binding was not changed, we conclude that the major lesion causing insulin resistance in PCO is a striking decrease in insulin sensitivity secondary to a defect in the insulin receptor and/or postreceptor signal transduction. PCO also is associated with modest but significant decreases in glucose transport. These defects in insulin action appear to represent intrinsic abnormalities that are independent of obesity, metabolic derangements, body fat topography, and sex hormone levels. Conversely, changes in hepatic insulin sensitivity appear to be acquired with obesity.


Lp(a) concentrations in NIDDM.

NIDDM patients have a two- to fourfold increased risk of CHD relative to nondiabetic subjects. This excess risk is explained only partially by increased levels of standard risk factors. We compared the plasma concentrations of Lp(a) in NIDDM patients (n = 260) and nondiabetic subjects (n = 336) who participated in a population-based study (San Antonio Heart Study). Lp(a) was measured using a monoclonal anti-Lp(a) antibody. NIDDM patients and nondiabetic subjects had similar Lp(a) concentrations for both men (13.6 +/- 1.5 vs. 16.1 +/- 1.4 mg/dl) and women (12.6 +/- 0.8 vs. 15.9 +/- 1.3 mg/dl) (P = 0.361). Duration of diabetes and level of fasting glycemia were not significantly related to Lp(a) concentrations. Lp(a) levels were significantly higher in patients who had higher total and LDL cholesterol levels. We conclude that in a large population-based study, Lp(a) levels are not increased in NIDDM patients.


Prevention of adoptive transfer in BB rats by prophylactic insulin treatment.

Prophylactic insulin can prevent diabetes in the BB rat. We evaluated its use to prevent adoptive transfer of diabetes by activated splenocytes. ConA-activated spleen cells from acutely diabetic BB rats were divided into two equal aliquots and injected intravenously in paired diabetes-prone BB rat littermates. At the time of cell injection, subcutaneous insulin injections (15 U.kg-1.day-1) were started in one of each pair (n = 21) of littermates, and the control littermates (n = 21) were injected with saline. The incidence of diabetes, observed 35 days after cell injection, was 95% in control rats compared with 29% in insulin-treated rats (P less than 0.05). To confirm the absence of diabetes, insulin was stopped in all nondiabetic insulin-treated rats at 63 days of age. An OGTT was performed at 65 days of age: 4 rats were glucose intolerant. All rats received comparable numbers of ConA-activated splenocytes. At the time the rats were killed, 3 insulin-treated rats had a completely normal morphology and a normal glucose tolerance. All control rats had insulitis whether they were diabetic or not. No significant difference in any mononuclear subset was observed in relation to insulin treatment. We conclude that prophylactic insulin can prevent adoptive transfer of diabetes in the BB rat without inducing changes in the mononuclear cell subsets.


Comparison of effects of high and low carbohydrate diets on plasma lipoproteins and insulin sensitivity in patients with mild NIDDM.

Previous studies indicate that diets rich in digestible carbohydrates improve glucose tolerance in nondiabetic individuals, but may worsen glycemic control in NIDDM patients with moderately severe hyperglycemia. The effects of such high-carbohydrate diets on glucose metabolism in patients with mild NIDDM have not been studied adequately. This study compares responses to an isocaloric high-carbohydrate diet (60% of total energy from carbohydrates) and a low-carbohydrate diet (35% of total energy from carbohydrates) in 8 men with mild NIDDM. Both diets were low in saturated fatty acids, whereas the low-carbohydrate diet was rich in monounsaturated fatty acids. The two diets were matched for dietary fiber content (25 g/day). All patients were randomly assigned to receive first one and then the other diet, each for a period of 21 days, in a metabolic ward. Compared with the low-carbohydrate diet, the high-carbohydrate diet caused a 27.5% increase in plasma triglycerides and a similar increase in VLDL-cholesterol levels; it also reduced levels of HDL cholesterol by 11%. Plasma glucose and insulin responses to identical standard breakfast meals were studied on days 4 and 21 of each period, and these did not differ significantly between the two diets. At the end of each period, a euglycemic hyperinsulinemic glucose clamp study with simultaneous infusion of [3-3H]glucose revealed no significant changes in hepatic insulin sensitivity; and peripheral insulin-mediated glucose disposal remained unchanged (14.7 +/- 1.4 vs. 16.5 +/- 2.3 microM.kg-1.min-1 on the high-carbohydrate and low-carbohydrate diets, respectively).(ABSTRACT TRUNCATED AT 250 WORDS)


Pentosidine formation in skin correlates with severity of complications in individuals with long-standing IDDM.

Pentosidine is an advanced glycosylation end product and protein cross-link that results from the reaction of pentoses with proteins. Recent data indicate that long-term glycation of proteins with glucose also leads to pentosidine formation through sugar fragmentation. In this study, the relationship between the severity of diabetic complications and pentosidine formation was investigated in collagen from skin-punch biopsies from 25 nondiabetic control subjects and 41 IDDM patients with diabetes duration greater than 17 yr. Pentosidine was significantly elevated in all IDDM patients versus control subjects (P less than 0.0001). It correlated strongly with age (P less than 0.0001) and weakly with duration (P less than 0.082). Age-adjusted pentosidine levels were highest in grade 2 (severe) versus grade 1 and 0 complication in all four parameters tested (retinopathy, proteinuria, arterial stiffness, and joint stiffness). Significant differences were found for retinopathy (P less than 0.014) and joint stiffness (P less than 0.041). The highest degree of association was with the cumulative grade of individual complication (P less than 0.005), determined by summing indexes of all four parameters. Pentosidine also was significantly elevated in the serum of IDDM patients compared with control subjects (P less than 0.0001), but levels were not significantly correlated with age, diabetes duration, complication, or skin collagen pentosidine (P greater than 0.05). A high correlation between pentosidine levels and long-wave collagen-linked fluorescence also was observed, suggesting that pentosidine is a generalized marker of accelerated tissue modification by the advanced glycosylation/Maillard reaction, which is enhanced in IDDM patients with severe complications.


Heterogeneity of messenger RNA that encodes the rat insulin receptor is limited to the domain of exon 11. Analysis by RNA heteroduplex mapping, amplification of cDNA, and in vitro translation.

Structural isoforms of the insulin receptor that occur in various tissues have been postulated to be involved in certain actions of insulin in target cells. To determine whether these insulin-receptor subtypes are caused by alterations in the receptor primary structure, we used RNA heteroduplex mapping and amplification of cDNA to detect variation in the coding region of insulin-receptor mRNA from 5 rat tissues. A complete series of overlapping antisense [32P]RNA probes was prepared from plasmids containing segments of a full-length rat insulin-receptor cDNA, and probes were hybridized individually in solution with polyadenylated RNA from rat brain, kidney, liver, skeletal muscle, and spleen. After ribonuclease digestion, probe fragments were analyzed by denaturing gel electrophoresis. Tissue-specific cleavage of the mRNA:RNA probe heteroduplex, attributable to sequence mismatch, was detected only for a single probe covering the distal alpha-subunit, as expected for the known alternative splicing of rat insulin-receptor mRNA in this region. No evidence for additional heterogeneity of the receptor mRNA coding region was observed in the 5 tissues studied either by RNA heteroduplex mapping or, in some areas, by regional amplification of insulin-receptor cDNA. Cell-free translation of size-fractionated polyadenylated RNA was used to further demonstrate that each of the major insulin-receptor mRNA size classes in rat liver contained both forms of the alternatively spliced mRNA transcripts and produced two insulin-proreceptor polypeptides. These results suggest that heterogeneity of the insulin-receptor mRNA coding region affecting the receptor primary structure is limited to the distal alpha-subunit near the subunit cleavage site.(ABSTRACT TRUNCATED AT 250 WORDS)


Influence of glycemic control on interaction of very-low- and low-density lipoproteins isolated from type I diabetic patients with human monocyte-derived macrophages.

The VLDL and LDL fractions were isolated from 29 patients with type 1 diabetes at the time of admission to the hospital to restore glycemic control and again at discharge. These lipoprotein fractions were incubated with human monocyte-derived macrophages, and the rates of macrophage CE synthesis were determined. The rates of CE synthesis in human macrophages were significantly greater (P less than 0.005) when incubated with VLDL isolated from type I diabetic patients before compared with after glycemic control was attained and averaged 1.84 +/- 0.52 and 1.09 +/- 0.27 nmol (1.20 +/- 0.34 and 0.71 +/- 0.18 micrograms) [14C]cholesteryl oleate synthesized.mg cell protein-1 x 20 h-1, respectively. In contrast, when LDL isolated from the same patient during the same period was incubated with human macrophages, the rates of cellular cholesteryl ester synthesis did not differ significantly and averaged 4.23 +/- 1.26 and 3.91 +/- 0.96 nmol (2.75 +/- 0.82 and 2.55 +/- 0.63 micrograms) [14C]cholesteryl oleate synthesized.mg-1 cell protein.20 h-1, respectively. There was a significant increase in the total cholesterol content of VLDL isolated before glycemic control compared with that isolated after glycemic control was attained (P less than 0.05) resulting from a significant increase in the FC and CE (P less than 0.05) contents of these VLDL particles. There was a significant decrease in the ratio of FC to PL in VLDL, but not LDL, isolated after glycemic control (P less than 0.05). The percentage of apoE in VLDL was significantly decreased (P less than 0.05) after glycemic control was attained.(ABSTRACT TRUNCATED AT 250 WORDS)


Relationship between decrements in glucose level and metabolic response to hypoglycemia in absence of counterregulatory hormones in the conscious dog.

To determine the relationship between decreases in glucose and metabolic regulation in the absence of counterregulatory hormones, we infused overnight-fasted, conscious, adrenalectomized dogs (lacking cortisol and EPI) with somatostatin (to eliminate glucagon and growth hormone) and intraportal insulin (30 pmol.kg-1.min-1), creating arterial insulin levels of approximately 2000 pM. Glucose was infused during one 120-min period, two 90-min periods, and one 45-min period to establish levels of 5.9 +/- 0.1, 3.4 +/- 0.1, 2.5 +/- 0.1, and 1.7 +/- 0.1 mM, respectively. NE levels were 1.24 +/- 0.23, 1.85 +/- 0.27, 2.04 +/- 0.26, and 2.50 +/- 0.20 nM, respectively. During the euglycemic control period, the liver took up glucose (7.5 +/- 1.9 mumol.kg-1.min-1), but hypoglycemia triggered successively greater rates of net hepatic glucose output (3.0 +/- 0.7, 4.6 +/- 0.9, and 6.9 +/- 1.4 mumol.kg-1.min-1). Total gluconeogenic precursor uptake by the liver increased with hypoglycemia. Intrahepatic gluconeogenic efficiency rose progressively (by 106 +/- 42, 199 +/- 56, and 268 +/- 55%). Both glycerol and NEFA levels rose, indicating lipolysis was enhanced. Net hepatic NEFA uptake and ketone production increased proportionally, but the ketone level rose only with severe hypoglycemia. In conclusion, despite marked hyperinsulinemia and the absence of glucagon, EPI, and cortisol, we observed that lipolysis and glucose and ketone production increase in response to decreases in glucose. This suggests that neural and/or autoregulatory mechanisms can play a role in combating hypoglycemia.


Recovery of glucose-induced insulin secretion in a rat model of NIDDM is not accompanied by return of the B-cell GLUT2 glucose transporter.

The NSTZ rat model combines loss of glucose-induced insulin secretion with a reduced amount of the high Km B-cell glucose transporter, GLUT2. The purpose of this study was to determine whether the restoration of glucose-induced insulin secretion was paralleled by an increase of GLUT2. Rats injected at 2 days of age with 90 mg/kg STZ were studied at 8-13 wk of age. Insulin secretion was assessed in the isolated perfused pancreas with 16.7 mM glucose preceded by 40 min of 0 or 5.5 mM glucose. In control rats, 16.7 mM glucose caused the same large biphasic insulin response whether preceded by 0 or 5.5 mM glucose. In NSTZ rats, after 5.5 mM glucose, 16.7 mM glucose elicited virtually no rise in insulin release. In contrast, after 0 mM glucose, a large insulin response to the glucose challenge occurred that was equal to that of the control groups when the differences in B-cell mass were taken into account. However, the dose-response curve for glucose-induced insulin secretion was shifted to the left, and no second phase of insulin secretion was observed. GLUT2 was assessed after the perfusions by indirect immunofluorescence with anti-GLUT2 antisera. Both control groups showed homogenous staining in all B-cells. NSTZ rats perfused with 5.5 mM glucose had a marked diminution in GLUT2 staining. We observed no increase in GLUT2 staining in the NSTZ rats perfused with 0 mM glucose.(ABSTRACT TRUNCATED AT 250 WORDS)


Forebrain ischemia in diabetic and nondiabetic BB rats studied with 31P magnetic resonance spectroscopy.

In spontaneously diabetic BB rats, the effect of chronically maintained blood glucose levels on the degree of energy failure and brain pH change during an ischemic insult, and on subsequent recovery after reperfusion, was studied with in vivo 31P magnetic resonance spectroscopy. Short duration forebrain ischemia (10-min carotid occlusion plus hypotension of 50 mmHg) was induced in diabetic and nondiabetic male BB rats whose blood glucose levels were maintained with insulin. Spectra were obtained in 1-min blocks before, during, and for 1 h after ischemia. Before ischemia, hypoglycemic (blood glucose less than 3 mM) diabetic rats had an increased Pi peak intensity, with no significant pH change, compared with other groups. During ischemia, the rate and extent of hydrolysis of high-energy phosphate metabolites (as measured by an increase in Pi) decreased, and the severity of tissue acidosis increased as preischemia blood glucose concentration increased. Among hyperglycemic BB rats, similar ischemia-induced changes were found for subgroups with blood glucose levels of 13.7 +/- 1.2 and 20.3 +/- 0.6 mM, in keeping with the known decrease in hexose binding sites associated with chronic hyperglycemia. Decline in PCr level during ischemia was not significantly different between groups. With reperfusion, both Pi and pH values rapidly returned to preischemia values. PCr levels, however, did not recover in hyperglycemic diabetic animals, with the degree of residual impairment dependent on the preischemia glucose level. Results suggest that optimal management of diabetes may lessen the degree of injury within the ischemic penumbra in diabetic patients who suffer a stroke.


Further defects in counterregulatory responses induced by recurrent hypoglycemia in IDDM.

We evaluated the effect of previous experimental hypoglycemia on counterregulatory responses to hypoglycemia in 13 IDDM patients. These patients had defects in counterregulatory responses to hypoglycemia compared with 7 nondiabetic control subjects. Plasma EPI and glucagon responses to hypoglycemia in IDDM patients were approximately 60% of levels in nondiabetic subjects (P less than 0.02 and P less than 0.001, respectively). Hepatic glucose output ([3-3H]glucose) was reduced by approximately 60% of normal (P less than 0.005), and the glucose infusion rate required to maintain plasma glucose was correspondingly greater in people with IDDM (P less than 0.001). With a modified glucose clamp (plasma insulin approximately 330 pM), the diabetic subjects underwent two sequential 120-min periods of hypoglycemia (approximately 3.0 mM) with an intervening 60-min euglycemic recovery period. In the IDDM patients, there were 30-50% decreases in plasma GH (P less than 0.005) and cortisol (P less than 0.001) responses during the second hypoglycemic period compared with the first. In addition, glucose output, already defective compared with that in nondiabetic subjects, was further reduced by 33% (P = 0.03) during the second period of experimental hypoglycemia. There was no effect of repeated hypoglycemia on the responses of plasma glucagon, EPI, or NE, though plasma EPI was correlated directly with glucose output (P less than 0.001) and inversely with glucose uptake (P less than 0.05). There was no correlation between the rise in glucose output during hypoglycemia and antecedent glycemic control as measured by HbA1.(ABSTRACT TRUNCATED AT 250 WORDS)


Inverse relationship between serum Lp(a) levels and first-phase insulin secretion.

Relationships between serum Lp(a) levels and insulin metabolism were investigated in 147 healthy nonobese men attending an executive health-screening program. Each subject received an IVGTT with measurement of plasma levels of glucose, insulin, and C-peptide. An inverse relationship was seen with the first-phase plasma insulin response when subjects were stratified into quartile ranges of the serum Lp(a) distribution. This relationship was supported by mathematical modeling analyses of these data, which revealed an inverse relationship between serum Lp(a) levels and first-phase pancreatic insulin secretion and plasma insulin responsiveness to glucose.


Insulin secretory profiles and C-peptide clearance kinetics at 6 months and 2 years after kidney-pancreas transplantation.

Glucose, insulin secretion, and insulin secretory pulses were measured by deconvolution of peripheral C-peptide concentrations in 10 IDDM recipients of a combined kidney-pancreas allograft 6 mo post-transplantation and were compared with 10 matched nondiabetic control subjects. Seven of the 10 recipients were restudied 2 yr post-transplantation. To control for immunosuppressive therapy, 6 patients with a kidney allograft also were studied. Pancreatic insulin secretion rates were evaluated over a 24-h period with three mixed meals. Six months post-transplantation, fasting (5.3 +/- 0.1 vs. 5.3 +/- 0.1 mM), average 24-h (6.0 +/- 0.1 vs. 5.7 +/- 0.1 mM), and meal-related (6.1 +/- 0.3 vs. 5.8 +/- 0.2 mM) plasma glucose levels were not different in control subjects and recipients, respectively. Total 24-h insulin secretion rates were similar between the two groups (150 +/- 15 vs. 182 +/- 24 nmol.m-2.24 h-1). However, post-transplantation, the relationship between basal and meal-stimulated insulin secretion was altered with increased basal insulin secretion (52.2 +/- 6.4 vs. 97.4 +/- 12.5 pmol.m-2.min-1, P less than 0.004) and reduced meal-related secretion. The proportion of total 24-h insulin secretion comprised by basal secretion was 44 +/- 4% in the control subjects vs. 73 +/- 5% in recipients. The number of ultradian oscillations of insulin secretion identified in each 24-h period by pulse analysis was similar in control subjects and recipients (11.9 +/- 0.9 vs. 10.4 +/- 0.5 oscillations/24 hr).(ABSTRACT TRUNCATED AT 250 WORDS)


Recombinant glutamic acid decarboxylase (representing the single isoform expressed in human islets) detects IDDM-associated 64,000-M(r) autoantibodies.

GAD is an autoantigen in IDDM. Molecular cloning and specific antibodies allowed us to demonstrate that only the lower M(r) GAD64 isoform is expressed in human islets, in contrast to human brain, rat islets, and rat brain, all of which express both GAD64 and GAD67. Expression of the human islet GAD64 isoform in COS-7 and BHK cells resulted in an enzymatically active rGAD64, which is immunoreactive with diabetic sera comparable with that of the islet 64,000-M(r) autoantigen. Immunoprecipitation analyses showed that 21/28 (75%) IDDM sera had rGA D64 antibodies compared with only 1/59 (1.7%) of the healthy control sera. In immunoblot analyses, an SMS serum--but only 1/10 randomly selected IDDM sera--recognized the blotted rGAD64 without relation to immunoprecipitation titers. In conclusion, only the GA D64 isoform is expressed in human islets, in contrast to rat islets, which also express the GAD67 isoform. The immunological properties of human rGAD64 are comparable with the native 64,000-M(r) islet autoantigen, allowing further studies of the immunopathogenesis of IDDM.


Human small intestine facilitative fructose/glucose transporter (GLUT5) is also present in insulin-responsive tissues and brain. Investigation of biochemical characteristics and translocation.

A recent study by C.F. Burant et al. (13) demonstrates that GLUT5 is a high-affinity fructose transporter with a much lower capacity to transport glucose. To characterize the potential role of GLUT5 in fructose and glucose transport in insulin-sensitive tissues, we investigated the distribution and insulin-stimulated translocation of the GLUT5 protein in human tissues by immunoblotting with an antibody to the COOH-terminus of the human GLUT5 sequence. GLUT5 was detected in postnuclear membranes from the small intestine, kidney, heart, four different skeletal muscle groups, and the brain, and in plasma membranes from adipocytes. Cytochalasin-B photolabeled a 53,000-M(r) protein in small intestine membranes that was immunoprecipitated by the GLUT5 antibody; labeling was inhibited by D- but not L-glucose. N-glycanase treatment resulted in a band of 45,000 M(r) in all tissues. Plasma membranes were prepared from isolated adipocytes from 5 nonobese and 4 obese subjects. Incubation of adipocytes from either group with 7 nM insulin did not recruit GLUT5 to the plasma membrane, in spite of a 54% insulin-stimulated increase in GLUT4 in nonobese subjects. Thus, GLUT5 appears to be a constitutive sugar transporter that is expressed in many tissues. Further studies are needed to define its overall contribution to fructose and glucose transport in insulin-responsive tissues and brain.


Glucokinase and NIDDM. A candidate gene that paid off.

Glucokinase, the major enzyme that phosphorylates glucose upon entry into liver and islet beta-cells, has been considered a prime candidate for inherited defects predisposing to NIDDM. Now that the human gene has been isolated, this question has been addressed directly. Polymorphic markers flanking the gene were identified. These markers (microsatellites) are composed of variable numbers of dinucleotide repeats that vary in size, resulting in different alleles. Variably sized alleles can be typed rapidly from genomic DNA of individuals by the PCR. Studies of inheritance of glucokinase genes have revealed significant linkage in families with early-onset NIDDM, or MODY, and mutations have been identified within the coding region of the gene in some families. These studies are extremely encouraging, as they indicate that genes can be identified even in this heterogeneous genetic disorder. This study considers the phenotypes that result from glucokinase defects and the relationship of MODY to NIDDM, and it estimates the role of glucokinase defects in NIDDM in general.


Beta-cell antigen-specific lysis of macrophages by CD4 T-cell clones from newly diagnosed IDDM patient. A putative mechanism of T-cell-mediated autoimmune islet cell destruction.

Immunophenotyping of the early lesion in the pancreatic islets of Langerhans demonstrates a predominance of CD4+ lymphocytes, which may be preceded by an increase in islet macrophages. This observation implies that both types of cells may be involved in autoimmune-mediated beta-cell destruction leading to IDDM. In an attempt to attribute a role to beta-cell antigen-specific CD4-expressing T-cell clones recently isolated from a newly diagnosed IDDM patient, we investigated whether such CD4 T-cells may be pathogenic in an in vitro cytotoxicity assay with HLA-DR-matched antigen-presenting macrophages as target. We report herein that, indeed, beta-cell antigen-specific CD4+ T-cells are capable of lysing macrophages in an antigen-specific fashion. This cytotoxicity is HLA-DR restricted, T-cell receptor complex mediated, and CD4 dependent. These observations imply that both helper T-cells and macrophages may be involved in the disease process via interaction between T-cells and macrophages pulsed with beta-cell antigen.


Features of insulin-resistance syndrome in men from French Caribbean Islands. The Telecom Study.

The prevalence of diabetes is known to be high in the West Indies, whereas CVD seems relatively rare. This apparently contradicts the existence of the insulin-resistance syndrome, a cluster of metabolic abnormalities supposedly favoring both diabetes and cardiovascular complications. To address the question of whether this contradiction could be accounted for by specific features of this syndrome, we compared 1505 Caucasian and 181 Afro-Caribbean men, all participants in the French Telecom Study. The Afro-Caribbeans were of the same age and had the same BMI as the Caucasians; they also had significantly higher subscapular skin-fold thickness and fasting insulin level, but similar BP and blood glucose level, and significantly lower plasma triglyceride level. Thus, although some features of the insulin-resistance syndrome were present (central adiposity and high insulin levels), none of the associated metabolic abnormalities were present. However, within the Afro-Caribbean group, subjects with plasma insulin concentrations above the median (> 52 pM) had higher mean BP and glucose and triglyceride levels compared with subjects with insulin concentrations < or = 52 pM (P < 0.001). After adjustment for age and BMI, these differences, though smaller, still were statistically significant. These findings confirm that higher insulin concentrations are associated with higher levels of potentially atherogenic and diabetogenic metabolic parameters. However, depending on ethnic origin, the mean levels of these parameters seem to be different, with the consequence that, even if they are elevated with increasing insulin levels, they may not reach values high enough to determine a substantial risk of disease.


Metabolic effects of suppression of nonesterified fatty acid levels with acipimox in obese NIDDM subjects.

NEFAs characteristically are elevated in obese NIDDM patients in both the basal state and after insulin. This elevation might aggravate glycemic control both by decreasing peripheral glucose disposal (glucose-fatty acid cycle), and by increasing HGO. Thus, lowering plasma NEFA levels might improve carbohydrate metabolism. We therefore measured HGO and fuel use (by indirect calorimetry) both in the basal state and during the last 30 min of a hyperinsulinemic clamp (0.025U.kg-1.h-1) in 8 obese NIDDM patients (BMI 34.8 +/- 1.0 kg/m2) after complete overnight suppression of plasma NEFA levels with acipimox, a new nicotinic acid analogue. After acipimox, mean basal plasma NEFA and glycerol levels were lower than control values (0.11 +/- 0.02 vs. 0.65 +/- 0.04 mM, P < 0.001; and 16 +/- 3 vs. 68 +/- 7 microM, P = 0.004, respectively) and were accompanied by a fall in lipid oxidation (acipimox vs. placebo: 16.1 +/- 1.2 vs. 38.8 +/- 2.4 mg.m-2 x min-1; P < 0.001) and a rise in glucose oxidation (91.1 +/- 6.2 vs. 54.1 +/- 9.0 mg.m-2 x min-1; P = 0.002). Basal HGO and fasting plasma glucose levels were lower (94.1 +/- 9.2 vs. 118.5 +/- 9.5 mg.m-2 x min-1, P = 0.01; and 8.3 +/- 1.2 vs. 9.8 +/- 1.2 mM; P < 0.001), respectively.(ABSTRACT TRUNCATED AT 250 WORDS)


Glycation of albumin, not glomerular basement membrane, alters permeability in an in vitro model.

The effects of glycation of either albumin, a plasma protein, or GBM were examined in an in vitro model of GBM permeability. Albumin was incubated with glucose in vitro, and nonglycated and glycated albumin were separated by affinity chromatography. Rat GBM was glycated either in vivo after the induction of diabetes or in vitro after incubation with 25 mM glucose. 150 micrograms of GBM was consolidated in an ultrafiltration cell, and albumin permeability across the GBM filter was assessed at an applied pressure (50 mmHg) selected to approximate glomerular capillary pressure in vivo. The sieving coefficient of glycated albumin was greater than the sieving coefficient of nonglycated albumin (0.25 +/- 0.03 vs. 0.10 +/- 0.02; P < 0.05). GBM glycated in vivo in diabetic rats exhibited native albumin and water permeability that was indistinguishable from that for GBM from control rats. Similarly, GBM glycated in vitro by incubation with 25 mM glucose exhibited water and albumin permeability identical to that for GBM incubated in buffer. Thus, the glycation of albumin, but not of GBM, leads to enhanced permeability in an in vitro GBM filtration system. Increased permeability of glycated albumin may contribute to albuminuria and/or renal injury in states of increased circulating glycated albumin such as diabetes and experimental galactosemia.


Spontaneous long-term hyperglycemic rat with diabetic complications. Otsuka Long-Evans Tokushima Fatty (OLETF) strain.

A spontaneously diabetic rat with polyuria, polydipsia, and mild obesity was discovered in 1984 in an outbred colony of Long-Evans rats, which had been purchased from Charles River Canada (St. Constant, Quebec, Canada) in 1982. A strain of rats developed from this rat by selective breeding has since been maintained at the Tokushima Research Institute (Otsuka Pharmaceutical, Tokushima, Japan) and named OLETF. The characteristic features of OLETF rats are 1) late onset of hyperglycemia (after 18 wk of age); 2) a chronic course of disease; 3) mild obesity; 4) inheritance by males; 5) hyperplastic foci of pancreatic islets; and 6) renal complication (nodular lesions). Histologically, the changes of pancreatic islets can be classified into three stages: 1) an early stage (6-20 wk of age) of cellular infiltration and degeneration; 2) a hyperplastic stage (20-40 wk of age); and 3) a final stage (at > 40 wk of age). These clinical and pathological features of disease in OLETF rats resemble those of human NIDDM.


Human GLUT4/muscle-fat glucose-transporter gene. Characterization and genetic variation.

Four overlapping DNA fragments spanning 32 kb containing the human GLUT4 facilitative glucose-transporter gene were isolated and characterized. The sequence of the GLUT4 gene (approximately 6.3 kb) and 2.0 kb of the promoter region was determined. The sequence of the promoter revealed potential binding sites for transcription factors known to regulate gene expression in muscle cells and adipocytes. However, transfection of constructs including 2 kb of the GLUT4 promoter fused to the bacterial CAT gene into 3T3-L1 adipocytes displayed only weak promoter activity. Because insulin resistance plays a prominent role in the development of NIDDM, genetic variation in the sequence of GLUT4 also was evaluated. Oligonucleotide primer pairs were selected that allowed the protein-coding region of the human GLUT4 gene to be amplified by PCR. The sequence of the protein-coding region of the GLUT4 gene and all intron-exon junctions was determined for a single diabetic Pima Indian and was identical to that of the cloned gene and cDNA. SSCP analysis was used to screen patients with diabetes mellitus and normal, healthy nondiabetic individuals for mutations at the GLUT4 locus. In addition to the silent substitution in the codon for Asn130 (AAC or AAT) and a Val383 (GTC)-->Ile(ATC) replacement described previously, two new variants were identified. One was a T-->A substitution in intron 1 that was found in 1 of 36 NIDDM patients who were typed for this variant. The second was a Ile385(ATT)-->Thr(ACT) replacement that occurred in 1 normal individual and was not found in any of 676 other normal and diabetic subjects. A large and racially diverse group of normal and diabetic individuals also was screened for the Ile383 polymorphism. It occurred in both diabetic and nondiabetic subjects. There is no indication from our data that these polymorphisms are associated with NIDDM.


Effects of acute and chronic counterregulatory hormone infusions on glucose tolerance and insulin sensitivity in diabetic dogs.

The effects of elevated EPI and CORT levels on KG, SI, and SG were studied in dogs with alloxan-induced diabetes. Conscious dogs received SAL, EPI 20 ng.kg-1.min-1 for 30 min (short EPI) or 72 h (long EPI), or CORT 200 micrograms.kg-1.min-1 for 60 min (short CORT) or 72 h (long CORT) before assessment of glucose metabolism by rapid sampling for glucose and insulin levels after 300 mg/kg i.v. glucose and exogenous insulin infusion designed to simulate the normal secretory pattern. With EPI infusion, KG fell acutely from 2.9 +/- 0.4 to 2.0 +/- 0.2%/min (SAL vs. short EPI, P < 0.05), but rose to 3.4 +/- 0.4%/min during long EPI. Minimal-model analysis of the glucose response with the insulin data as input showed that SI decreased acutely from 4.7 +/- 1.8 to 2.5 +/- 0.6 x 10(-5) min-1/pM (SAL vs. short EPI, P < 0.05), but rose to 4.5 +/- 2.5 x 10(-5) min-1/pM during long EPI. The effects of EPI on SG paralleled the results for KG and SI, with acute decline from 3.9 +/- 0.4 to 2.1 +/- 0.4 x 10(-2) min-1 (SAL vs. short EPI, P < 0.05) and recovery to 3.3 +/- 0.3 x 10(-2) min-1 during long EPI. During CORT infusion, KG tended to fall (SAL 2.9 +/- 0.4 vs. short CORT 2.5 +/- 0.5 vs. long CORT 2.2 +/- 0.5%/min).(ABSTRACT TRUNCATED AT 250 WORDS)


Hyperglycemia markedly enhances skeletal muscle glycogen synthase activity in diabetic, but not in normal conscious rats.

Both hyperinsulinemia and hyperglycemia stimulate skeletal muscle glucose uptake. However, the intracellular metabolic fate of the phosphorylated glucose may be different when the prevalent stimulus for glucose uptake is hyperinsulinemia or hyperglycemia. To define the impact of hyperglycemia on the intracellular glucose disposal, we studied control and diabetic conscious rats under four experimental conditions: 1) basal insulin and basal glucose; 2) basal insulin and high glucose; 3) high insulin and basal glucose; and 4) high insulin and high glucose. Under both basal insulin (130 pM) and high insulin (2500 pM), hyperglycemia (15 mM) increased glucose uptake and muscle and liver glycogen synthesis similarly in control and diabetic rats. Hyperglycemia resulted in a more significant decline in the muscle G-6-P concentration in diabetic rats than in control rats, suggesting activation of intracellular glucose metabolism. The diabetic skeletal muscle glycogen synthase was severely resistant to insulin stimulation compared with control (FV0.1 = 0.31 +/- 0.04 vs. 0.49 +/- 0.03; Km = 0.19 +/- 0.05 vs. 0.10 +/- 0.01 mM; P < 0.01), but it was markedly responsive to glucose stimulation under both basal (FV0.1 = 0.38 +/- 0.03 vs. 0.21 +/- 0.03; Km = 0.10 +/- 0.01 vs. 0.35 +/- 0.08 mM) and high insulin (FV0.1 = 0.65 +/- 0.07 vs. 0.31 +/- 0.04; Km = 0.11 +/- 0.02 vs. 0.19 +/- 0.05 mM). By contrast, in control rats, hyperglycemia did not exert any stimulatory effect on skeletal muscle glycogen synthase. Thus, some metabolic alteration associated with the diabetic state renders the skeletal muscle glycogen synthase selectively responsive to glucose stimulation. This may represent a compensatory mechanism for the severe impairment in insulin's activation of this enzyme in diabetes.


Characterization of glucose-induced in situ protein kinase C activity in cultured vascular smooth muscle cells.

The VSMC is an important target for the injurious effects of hyperglycemia in vivo. PKC plays a key role in the regulation of VSMC contraction and growth. This study examines whether elevated extracellular glucose concentrations (10-30 mM [180-540 mg/dl]) activate PKC in cultured rat VSMCs in vitro. A new, rapid, and highly specific assay was used to determine in situ PKC activity in digitonin-permeabilized VSMCs. PKC activity in VSMCs responded rapidly to variations in extracellular glucose concentrations. PKC was activated significantly within 10 min of exposure to D-glucose (20 mM) versus glucose (5 mM). Moreover, with continued exposure to D-glucose (20 mM), PKC activation was sustained for up to 48 h. Reducing D-glucose concentrations to 5 mM restored PKC activity to control values within 1 h. PKC activation was also glucose-concentration dependent. A threshold of only 15 mM (270 mg/dl) was required to significantly and maximally activate PKC in VSMC. PKC was not activated in the presence of osmotic control media that contained either elevated mannitol or L-glucose concentrations. In marked contrast to the sustained PKC activation induced by D-glucose in VSMCs, the normal physiological PKC response to the pressor hormones, AII and AVP, was short-lived and returned to base line within minutes. Sustained PKC activation in the presence of elevated D-glucose concentrations in vitro could disturb the normal physiological regulation of VSMC function and growth and thereby may contribute to the apparent vasotoxicity of hyperglycemia in vivo.


1,25-Dihydroxyvitamin D3 prevents insulitis in NOD mice.

The active form of vitamin D, 1,25(OH)2D3, can prevent various forms of experimentally induced autoimmune disorders. The aim of this study was to confirm these findings in NOD mice that spontaneously develop an autoimmune type of diabetes mellitus. Therefore, the effect of a long-term 1,25(OH)2D3 treatment on the incidence of insulitis, the histological lesion preceding diabetes, was studied. Forty-three NOD mice were treated with 1,25(OH)2D3 (5 micrograms/kg) i.p. every other day from age 21 days on, when no insulitis was present yet. At day 100, 16 control mice receiving the treatment vehicle (arachis oil) had an incidence of insulitis of 75%, whereas only 41% of the 1,25(OH)2D3-treated animals developed insulitis (P < 0.025). Calcemia, determined 24 h after the last 1,25(OH)2D3 injection was 2.5 +/- 0.1 mM, which was higher than in control animals (2.3 +/- 0.1 mM), but was well tolerated. Cellular immunity, as assessed with the mixed lymphocyte reaction performed at day 100, was not impaired significantly. This study demonstrates that long-term treatment with high doses of 1,25(OH)2D3 is able to decrease the incidence of insulitis in spontaneous autoimmune diabetes without major side effects.


Linkage analysis of glucokinase gene with NIDDM in Caucasian pedigrees.

NIDDM has a strong genetic component, as evidenced by the high level of concordance between identical twins. The nature of the genetic predisposition has remained largely unknown. Recently, the glucokinase gene locus on chromosome 7p has been shown to be linked to a subtype of NIDDM known as MODY in French and British pedigrees, and glucokinase mutations have been identified. To study the relationship between the glucokinase gene and NIDDM, we performed a linkage analysis in 12 Caucasian pedigrees ascertained through a proband with classical NIDDM. The LINKAGE program was used under four models, including autosomal dominant and recessive, with individuals with glucose intolerance counted as either affected or of unknown status. Linkage was significantly rejected with the dominant models (LOD scores -4.65, -4.25), and was unlikely with the recessive model when glucose intolerance was considered as affected (LOD score -1.38). These findings suggest that mutations in or near the glucokinase gene are unlikely to be the major cause of the inherited predisposition to NIDDM in Caucasian pedigrees, but do not exclude a role for this locus with a polygenic model, or a major role in some pedigrees.


Cerebral arterial and venous flow-velocity measurements in post-haemorrhagic ventricular dilatation and hydrocephalus.

Simultaneous anterior cerebral artery (ACA) and internal cerebral vein (ICV) flow-velocities were measured in 18 babies with post-haemorrhagic ventricular dilatation (PHVD) and hydrocephalus (PHH). Compared with a control group matched for post-conceptional age, the resistance index of the ACA was increased. This was shown to occur at an early stage of PHVD in a longitudinal study of seven of the babies. There were no significant changes in ACA or ICV time-averaged velocities. Eight babies with PHH had ventricular taps on 18 occasions to relieve raised intracranial pressure. There was a significant decrease in the resistance index of the ACA, accompanied by an increase in the ACA time-averaged velocity, but no change in the ICV time-averaged velocity.


Assessment of post-traumatic amnesia in young children.

To assess the duration of post-traumatic amnesia (PTA) in children, a new procedure is described, derived from a method described previously for adults. The procedure was tested on 70 healthy children between 3.5 and 10 years of age, then applied in a longitudinal prospective study of 54 children with brain damage resulting from closed head-injury. The procedure consistently measured PTA in children of various ages. The duration of PTA was found to be as good a prognostic indicator for the occurrence of long-term residual sequelae as is duration of coma.


Rolandic spikes in the inter-ictal EEG of children: contribution to diagnosis, classification and prognosis of epilepsy.

The clinical correlates of Rolandic spikes were studied in 47 children to determine the significance of this EEG finding to the diagnosis and classification of epilepsy. The children were classified into 'functional' and 'organic' groups, with and without epilepsy. Children with epilepsy were further subdivided into those with Rulandic and those with non-Rulandic seizures. In children without neurological abnormalities, the EEG finding of Rolandic spikes plays a decisive role in the diagnosis of an epileptic syndrome as benign focal epilepsy of childhood with centro-temporal spikes (BECT), a diagnosis with an excellent prognosis. Neurological and neuroradiological examinations of the 'functional' group revealed that the Rolandic spike may occur as a true 'functional' spike. The frequency of a family history of epilepsy among neurologically normal children with Rolandic spikes suggests, in addition to the inheritance of BECT and the EEG trait, the existence of a hereditary susceptibility to epilepsy.


Planning an outing from hospital for ventilator-dependent children.

Returning ventilator-dependent children to the home environment has become a well-accepted occurrence. The success of a home program depends on careful pre-discharge planning in order to ensure the child's medical safety, and adequate preparation to ensure the child's and family's adjustment to an active community life after discharge. To achieve this, involvement in community activities must begin while the child is still in hospital. As part of a complete rehabilitation program, nine ventilator-dependent children were taken on an inpatient outing to Disneyland. The planning and goals of the outing are described.


Medical cure of a brainstem abscess and serial brainstem auditory evoked potentials.

The brainstem abscess of a nine-year-old girl with tetralogy of Fallot was cured after six weeks of parenteral antibiotic therapy, without surgical intervention. Serial studies of brainstem auditory evoked potentials were undertaken until the patient was clinically normal. To the authors' knowledge, this is only the second medically cured case reported in the literature, and it is the first case studied with serial brainstem auditory evoked potentials. If the clinical status allows, medical treatment of a brainstem abscess with appropriate antibiotics could be tried before surgical intervention such as stereotactic aspiration for reducing the mass.


Effect of phospholipase A2 and ethanol on the survival of acinar cells isolated from the rat pancreas.

The study was undertaken to investigate the effect of phospholipase A2 (PLA2) on the viability of isolated pancreatic acinar cells (PACs) and its possible synergy with ethanol. The survival of PACs may be reduced by PLA2 in a dose-dependent manner. In the presence of 0.25 microgram PLA2.(10(6) cells)-1, all cells died within less than 4 h of incubation at 37 degrees C. A quantity of 180 mM ethanol, which alone was not lethal for PACs, increased the rate of cell death induced by PLA2 at a certain concentration of this enzyme. The present results imply that (1) PLA2 is able to damage PACs in the absence of additional substrates, and (2) at an appropriate activity of PLA2, ethanol may amplify the toxic effects of this lytic enzyme and force autodigestion of the pancreas.


Effect of duodenal mucosal blood flow on duodenal alkaline secretion in rats.

To investigate the role of duodenal mucosal blood flow (DMBF) in the regulation of duodenal alkaline secretion (DAS), both parameters were measured before and after the administration of various drugs in rats. The DMBF was determined using an electrolytically generated hydrogen gas clearance technique, and the DAS was measured by the perfusion method. The administration of dulcerozine, a potent duodenal ulcerogenic agent, at a dose of 250 mg/kg and serotonin at a dose of 20 mg/kg, which produces duodenal ulcerations with an acid load, decreased both DMBF and DAS. On the other hand, the administration of secretin at a dose of 10 U/kg increased both parameters. There were parallel changes in DMBF and DAS. It is concluded, therefore, that DAS may be regulated by DMBF and that both parameters may be involved in the defense mechanism of duodenal mucosa.


Induction of duodenal ulcers in sensory deafferented rats following histamine infusion.

We used capsaicin as a selective probe for sensory neuronal mechanisms and examined in rats whether defunctionalization of the sensory nerves caused duodenal ulcers in the presence of acid hypersecretion. Chemical deafferentation was performed by subcutaneous injection of capsaicin for 3 days (total dose: 100 mg/kg) 2 weeks before the experiment. This treatment did not cause by itself any damage in the duodenum. However, intravenous infusion of histamine (4, 8 and 16 mg/kg/h) in these animals caused hemorrhagic lesions in the proximal duodenum within 6 h in a dose-dependent manner with an incidence of 100%. Histamine alone in the control animals did not induce macroscopically visible lesions at lower doses and caused only slight damage at the highest dose (16 mg/kg/h), although acid secretion was stimulated to the maximal degree at 8 mg/kg/h. Ablation of capsaicin-sensitive sensory neurons did not have any effect on acid secretion induced by histamine (8 mg/kg/h), but significantly inhibited the increase in duodenal HCO3- secretion in response to mucosal acidification. We conclude that functional ablation of capsaicin-sensitive sensory nerves impairs duodenal HCO3- secretory response to acid and results in duodenal ulcers if acid hypersecretion is present. These sensory nerves may be important in the defense mechanism of the duodenum against luminal acid.


Nervous control of distension-induced relaxation of the porcine lower oesophageal sphincter.

The mechanisms involved in the relaxation of the lower oesophageal sphincter induced by distension of the oesophagus and different parts of the stomach, were studied in an anaesthetized porcine model. A computer technique was developed allowing on-line digitizing of lower oesophageal sphincter (sleeve device) and intragastric pressures. Basal sphincter tone was slightly reduced by truncal vagotomy, an effect which seemed to be reversed by sectioning of the vagosympathetic trunks in the neck. Balloon distension of the body of the oesophagus, relaxed the sphincter irrespective of the denervation procedures carried out. Distension of the whole stomach with increasing amounts of air induced a dose-dependent relaxatory lower oesophageal sphincter response, which was also closely associated with the subsequent increases in intragastric pressure. Denervation procedures did not alter this dose-response relationship. The importance of intramural mechanisms was illustrated by the abolition of distension-induced effects in most animals studied after transection of the gastro-oesophageal junction distal to the sphincter. Balloon distension of the antrum elicited a smaller but significant sphincter relaxation, but the mechanisms behind this response seemed to be more complex than after insufflation of air.


Clinical significance of hypergastrinaemia: relevance to gastrin monitoring during omeprazole therapy.

During the early experience with omeprazole, it was recommended that plasma gastrin levels be monitored to identify patients with 4-5-fold increases above baseline. Such patients were thought to be at an increased risk of developing gastric carcinoid tumours. Studies have established that plasma gastrin levels usually rise 2-4-fold during omeprazole therapy, there being considerable inter- and intra-individual variation. Approximately 3.3% of patients have plasma gastrin levels above 400 pg/ml when treated continuously for 1 year. In clinical practice, it is not cost-effective to screen all patients to detect such a small percentage, particularly given the paucity of realistic treatment options in such patients, and the growing evidence that hypergastrinaemia during omeprazole treatment is of little, if any, clinical significance.


Helicobacter pylori, peptic ulcer disease and inhibition of gastric acid secretion.

Recent studies have been reviewed to establish the possible importance of the interaction between Helicobacter pylori infection and gastric acid secretion. H. pylori infection results in increased gastrin release, but this does not lead to gastric acid hypersecretion and gastrin normalizes after eradication of the infection. An optimal, well-tolerated treatment strategy against H. pylori infection has not yet been clearly defined. One potentially useful approach may be to improve the antibacterial efficacy of antibiotics by effectively regulating gastric acidity. H2-receptor antagonists have no effect against H. pylori infection, while omeprazole (an acid pump inhibitor) appears to have a bacteriostatic action. Combination therapy with omeprazole and amoxycillin has been found to eradicate H. pylori in 50-80% of patients with duodenal ulcer, leading to a significant reduction in ulcer recurrence.


Is endoscopy helpful in patient monitoring?

The safety issues involved in patients on long-term treatment with omeprazole will determine whether endoscopic monitoring is necessary. In a review of 646 patients who have undergone regular gastric biopsies during continuous treatment with omeprazole, 10-120 mg daily, for periods of up to 5.5 years, there were no overall patterns to the changes in gastric endocrine cells. Apparent gastric endocrine cell hyperplasia in 72% of patients correlated with the development of chronic atrophic corpus gastritis. The only macroscopic changes to be reported were endocrine tumours in 4 out of 184 patients on long-term omeprazole for Zollinger-Ellison syndrome, and at least 3 of these patients had multiple endocrine neoplasia (MEN) type 1 syndrome. In patients with other low acid states, such as pernicious anaemia or after gastric irradiation or gastric surgery, in which drug therapy is not a confounding factor, there is a very low risk of developing macroscopic lesions within the stomach, and endoscopic surveillance is not routine practice. In conclusion, upper gastrointestinal endoscopic monitoring to identify microscopic or macroscopic changes cannot be justified during at least the first 5 years of continuous treatment with omeprazole.


The potential clinical role of intravenous omeprazole.

The efficacy of intravenous omeprazole has been investigated in a number of clinical applications. In critically ill patients with bleeding peptic ulcer, which developed despite prophylactic measures for stress ulcer, bleeding stopped in 16 out of 19 patients treated with omeprazole given as a 40-mg i.v. bolus twice daily for up to 5 days. By contrast, bleeding stopped in only 3 out of 20 such patients given a continuous infusion of ranitidine, 400 mg daily for the same time period. Dose-finding studies in volunteers showed that an initial bolus of omeprazole, 80 mg, followed by continuous infusion for 48 hours (8 mg/hour for the first 24 hours and 4 mg/hour for the subsequent 24 hours) produced elevation of gastric pH to 6 or above. This high-dose regimen when combined with infusion of large amounts of fluid was accompanied by peripheral oedema in three females, but did not occur when the dose was reduced to 4 mg/hour. In patients with non-bleeding ulcers who were unable to take oral medication, treatment with an intravenous bolus of omeprazole, 40 mg twice daily, healed 91% of gastric ulcers and 88% of duodenal ulcers in 2 weeks. In patients with temporary impairment of gastric emptying, resulting from pyloric oedema secondary to an ulcer in this region, an intravenous bolus of omeprazole, 40 mg three times daily, led to resolution of pyloric stenosis in seven out of nine patients with pre- and intra-pyloric ulcers, and in three out of five patients with post-pyloric ulcers.(ABSTRACT TRUNCATED AT 250 WORDS)


Epidemiology and natural history of gastro-oesophageal reflux disease.

Epidemiological studies of gastro-oesophageal reflux disease (GORD) are confounded by the lack of a standardized definition and a diagnostic 'gold-standard' for the disorder. In Western countries, 20-40% of the adult population experience heartburn, which is the cardinal symptom of GORD, but only some 2% of adults have objective evidence of reflux oesophagitis. The incidence of GORD increases with age, rising dramatically after 40 years of age. There is also wide geographical variation in prevalence. Complications, including oesophageal ulcer and stricture, and Barrett's oesophagus, are found in up to 20% of patients with verified reflux oesophagitis. The signs and symptoms of GORD often wax and wane in intensity, and spontaneous remissions have been reported. In most cases, however, GORD is a chronic condition that returns shortly after discontinuing therapy. Although GORD causes substantial morbidity, the annual mortality rate due to GORD is very low (approximately 1 death per 100,000 patients), and even severe GORD has no apparent effect on longevity, although the quality of life can be significantly impaired. There are data to suggest that the use of non-steroidal anti-inflammatory drugs (NSAIDs) contributes to oesophagitis and stricture formation in patients with GORD. Although these data are not conclusive, it seems prudent, if possible, to avoid the use of NSAIDs in patients with GORD, particularly those with oesophageal stricture.


Long-term aims of treatment of reflux disease, and the role of non-drug measures.

Recent opinion about the long-term aims of treatment of reflux disease has been influenced substantially by the development of highly effective drugs that have minimal side-effects. The success of these drugs has emphasized the importance of gains in lifestyle resulting from relief of heartburn and other reflux-induced symptoms. Such relief is seldom achieved by traditional non-drug measures, which can also significantly impair lifestyle. In many patients with reflux disease, the effective relief of symptoms is a major aim. Oesophagitis, particularly when severe, carries a risk of developing peptic stricture or Barrett's oesophagus, but the risk factors associated with the development of these significant complications are not well identified. There is also no direct evidence that successful healing of oesophagitis by drug therapy is associated with prevention of local complications of oesophagitis, although many anecdotes regarding the resolution of peptic stricture by successful anti-reflux surgery support this possibility. Similarly, the linkage between development of Barrett's oesophagus and severe oesophagitis suggests that in some patients maintained healing of oesophagitis will prevent development or progression of Barrett's oesophagus. These considerations support the aim of healing of severe oesophagitis (i.e. more than patchy erosions), quite independently of the need to achieve effective symptom relief.


Controlled clinical trials of omeprazole in the long-term management of reflux disease.

Reflux oesophagitis is a chronic relapsing disorder. When treatment is stopped after successful short-term healing of oesophagitis, high relapse rates (80% within 6 months) indicate that prolonged treatment is necessary in order to maintain remission. The results of three long-term, multicentre, controlled, double-blind clinical trials comparing different regimens of omeprazole with ranitidine are reviewed. Omeprazole, 20 mg daily, was found to be a highly effective maintenance therapy in patients with ulcerative oesophagitis, keeping 67-89% of patients in remission for 1 year, compared with 10-25% of patients treated with ranitidine, 150 mg twice daily. Weekend omeprazole therapy, 20 mg daily every Friday, Saturday and Sunday, was, as with daily ranitidine, relatively ineffective. All treatment regimens were well tolerated and gastric mucosal biopsies showed no qualitative changes in gastric enterochromaffin-like cells.


Appropriate acid suppression for the management of gastro-oesophageal reflux disease.

Gastro-oesophageal reflux disease (GORD) results from an abnormally prolonged dwell time of acidic gastric contents in the oesophagus. Although GORD is primarily a motor disorder, the injurious effects of gastric acid are central to the pathogenic process of oesophagitis, and the severity of disease correlates with the degree and duration of oesophageal acid exposure. In the majority of patients with mild disease, oesophageal acid exposure occurs predominantly during post-prandial periods. Conventional doses of H2-receptor antagonists cannot overcome the integrated stimulus to acid secretion resulting from a meal, and are thus relatively ineffective in preventing daytime, post-prandial oesophageal acid exposure. In patients with more severe grades of oesophagitis, there are abnormally high levels of nocturnal acid exposure, with the intra-oesophageal pH being less than 4.0 for 36% of the time, compared with 5% of the time in patients with mild GORD. Control of nocturnal acid secretion thus becomes increasingly important. This may be made worse by relative gastric acid hypersecretion in some patients with severe GORD. The long duration of action and effective inhibition of meal-stimulated acid secretion probably explains the superiority of omeprazole in treating GORD. Preliminary meta-analysis shows that the healing rate of erosive oesophagitis at 8 weeks by antisecretory agents is directly related to the duration of suppression of gastric acid secretion achieved over a 24-hour period (r = 0.87; p less than 0.05).


Natural history of gastritis and its relationship to peptic ulcer disease.

Chronic gastritis is a common inflammatory disease. In a number of patients, the inflamed gastric mucosa shows a gradual tendency to become atrophic (atrophic gastritis). Gastritis tends to be lifelong, and spontaneous healing is rare. With very few exceptions (e.g. in patients with autoimmune chronic corpus gastritis), gastritis is associated with the presence of the bacterium Helicobacter pylori. Inflammation and atrophy of the gastric mucosa result in impairment of gastric secretory functions (e.g. secretion of gastric acid, pepsin and gastrin). Such impairment is dependent on the topographic type of gastritis; i.e. whether the inflammation and atrophy occur in the antrum (chronic antral gastritis), corpus (chronic corpus gastritis) or in both the antrum and corpus simultaneously (chronic pangastritis). Gastritis of different topographic types associates with different gastric diseases. In patients with H. pylori-related antral or pangastritis, peptic ulcer disease, and in particular duodenal ulcer, is common (with an incidence exceeding 20% after 10 years' follow-up), as compared with peptic ulcer disease, which is very rare in patients with a normal stomach. Gastric ulcer may sometimes occur in patients with a rather atrophic stomach, but both gastric and duodenal ulcers are extremely rare in patients in whom the gastritis accompanies severe atrophic changes in the corpus mucosa. Routine biopsies from the antrum and corpus, and interpretation of the results in the light of the data on gastritis and its atrophic sequelae, allow the gastroenterologist to predict the risk and likelihood of peptic ulcer disease in patients with gastritis.


Inter-relationship between serum gastrin levels, gastric mucosal histology and gastric endocrine cell growth.

The development of gastric enterochromaffin-like (ECL)-cell hyperplasia in humans may be associated with extreme hypergastrinaemia, as occurs in Zollinger-Ellison syndrome (ZES) and pernicious anaemia (type A gastritis). More recently, endocrine cell hyperplasia has been found in all forms of chronic atrophic gastritis and even in cases of focal atrophy. Serum gastrin levels, non-antral gastric endocrine (argyrophil) cell growth, and the severity and type of concomitant gastritis were monitored in 66 unoperated and 8 antrectomized patients with poorly responsive peptic ulcer or reflux oesophagitis during up to 5 years' treatment with high-dose omeprazole, 40 mg daily. A small subgroup of patients (23%) had serum gastrin concentrations of more than four times the normal upper limit. These patients also had hyperplasia of the gastric argyrophil cells. More importantly, the same subgroup of patients had high-grade (atrophic) gastritis. Micronodular hyperplasia of argyrophil cells was significantly more frequent in biopsies showing atrophic gastritis (48%) than in biopsies showing only superficial gastritis (3.6%). It is concluded that, as previously demonstrated in untreated patients with gastric ulcer, the argyrophil cell hyperplasia observed during high-dose omeprazole therapy is related to the progression of chronic atrophic gastritis rather than to serum gastrin levels.


Gastric endocrine cells and gastritis in patients receiving long-term omeprazole treatment.

Both argyrophil endocrine cells and gastritis were investigated in 2,120 biopsies of gastric corpus mucosa from 443 out of 448 patients receiving long-term (for periods ranging from several months to 4 years) omeprazole treatment. None of the patients showed neoplasia or dysplasia, either endocrine or non-endocrine. In 123 out of 443 patients (27.8%), endocrine hyperplasia of diffuse (9.3%), linear (4.1%) or micronodular (14.4%) type was detected either before or at some time during treatment. Chronic atrophic gastritis was found in 45 (10.2%) patients, 60% of whom also showed micronodular hyperplasia. In patients with chronic atrophic gastritis, micronodular hyperplasia occurred in 49% of 96 biopsies, compared with 6% of 1,083 biopsies from patients with non-atrophic chronic gastritis and 2% of 941 biopsies from patients with no evidence of gastritis. In 202 patients treated with omeprazole for at least 330 days, the incidence of micronodular hyperplasia increased from 2.5% at the first biopsy to 10.4% at the final biopsy, while the incidence of chronic atrophic gastritis increased from 1.0% to 13.0%. The present and parallel studies suggest that progression of gastritis is inherent in the natural history of acid-related diseases, while endocrine cell changes are mostly secondary to gastritis-related gland atrophy and have no tumorigenic potential.


Safety experience from long-term treatment with omeprazole.

Omeprazole was administered for up to 6 years in 859 patients for 'prevention of relapse in patients with poorly responsive peptic ulcer or reflux oesophagitis'. The pattern of adverse events reported during long-term treatment was similar to the adverse-event profile in short-term treatment with omeprazole (n = 2,818), ranitidine (n = 1,572) and cimetidine (n = 891). Omeprazole had essentially the same adverse-event profile as the two H2-receptor antagonists. The adverse-event profile for omeprazole during long-term treatment did not differ from that seen during short-term treatment with either omeprazole or the H2-receptor antagonists. The rate of occurrence of any specific adverse event decreased with time, and no previously unidentified adverse event occurred with long-term omeprazole therapy. There were no serious adverse events that were considered to be causally related to omeprazole therapy. Thus, omeprazole has been shown to be well tolerated in both short- and long-term treatment.


Maturation of hearing aid benefit: objective and subjective measurements.

The goals of this investigation were to determine whether hearing aid benefit improved significantly over the first 10 weeks of hearing aid use and whether time-related changes in benefit (if any) were affected by the type of benefit measurement (i.e., objective or subjective). A total of 17 hearing-impaired subjects participated, with different subjects completing different phases of the study. Benefit was measured soon after the hearing aid fitting and again after 10 weeks of adjustment to hearing aid use. Objective benefit data were determined using the Connected Speech Test. No significant changes in objective benefit were noted in noisy or reverberant listening environments when visual cues were available. However, in a low-noise setting and in a noisy setting without visual cues, improvements in objective benefit were seen over time. Subjective benefit data were derived from responses to the Profile of Hearing Aid Benefit. These data indicated significant benefit improvement over time in all five types of daily life situations assessed, although the improvement was small in reverberant and noisy environments. Significant, but modest, correlations were found between objective and subjective data for low-noise and reverberant listening environments. Comparison of experienced and novice hearing aid wearers suggested that although experienced wearers obtain more benefit than novice wearers, they evidence similar time-related changes in benefit during the first 10 weeks of new hearing aid use.


Comparison of two methods for estimating the sensation level of amplified speech.

Several methods have been proposed to estimate the sensation level (SL) at which children receive amplified speech from their hearing aids. The present study compared the SL estimates obtained with two such methods: (1) a sound field aided audiogram approach, and (2) an electroacoustic approach that incorporated the use of a probe tube microphone system (Seewald, Ross, & Stelmachowicz, 1987). Sound field aided thresholds were obtained for 13 hearing-impaired subjects at eight audiometric frequencies. For the electroacoustic approach, in situ thresholds were obtained using a button-type hearing aid receiver attached to a custom earmold. Real ear aided responses were measured using a 70 dB RMS speech-weighted composite noise signal (Frye, 1986). A comparison of the frequency-specific SL estimates derived from the two different methods revealed that the sound field aided audiogram approach yielded higher SL estimates for 74% of the individual comparisons. A detailed analysis of the findings obtained from two subjects suggested that when the results of the two methods did not agree, the differences were due to an interaction between signal level and the unique input/output characteristics of the subjects' hearing aids. A precautionary measure is suggested for those who wish to use sound field aided threshold data to estimate the SLs at which children receive amplified conversational speech.


Spectral distribution of /s/ and the frequency response of hearing aids.

The purpose was to determine a target for the upper frequency limit of a hearing aid that will provide access to the important spectral cues for all the sounds of English. The sibilant /s/ was studied because of its high-frequency content. Repeated tokens of /s/ were recorded from five men and five women before and between the vowels /u/, /a/, and /i/. Using fast Fourier transform analysis, the prominent spectral peak with the lowest frequency was identified and its center frequency determined for each token. This frequency averaged around 4.9 kHz for the /u/ context, 5.6 kHz for the /a/ context, and 6.0 kHz for the /i/ context. There were dramatic differences among talkers, with subject means ranging from 3.2 to 8.4 kHz. The women generated consistently higher frequency /s/ sounds than the men, but there were also large differences within gender groups. These data suggest that the upper frequency limit of a high-fidelity hearing aid should be in the region of 10 kHz. If this cannot be accomplished with direct amplification, an alternative might be the selective use of frequency transposition.


Mismatch negativity event-related potential elicited by speech stimuli.

The mismatch negativity (MMN) is a passively elicited event-related potential that is extremely sensitive to acoustic stimulus properties. The MMN was characterized in normal adults and school-age children in response to speech stimuli differing minimally in the onset frequency of the second and third formant transitions. The speech-evoked MMN consists of a negative waveform at about 230 msec that occurs in response to the deviant stimulus when it is presented in an oddball paradigm. It is absent in response to that same stimulus when presented alone. The MMN was clearly present in all adults and children tested. Using the procedures developed in this study, this event-related potential was found to be robust enough in individual subjects to be considered a potential clinical measure for assessing central auditory function in school-age children and adults.


Threshold estimation using the "chained stimuli" auditory brain stem response technique.

The chained stimuli ABR method, which allows acquisition of data for a seven-point latency-intensity function for both ears in approximately 35 min, is described. Testing of 22 ears with a simulated conductive loss, and 20 ears with sensorineural impairment, indicates that the chained stimuli method provides equivalent threshold estimates to that obtained with the conventional ABR measurement technique.


Effect of hearing loss of cochlear origin on the auditory brain stem response.

Auditory brain stem response (ABR) testing is widely used to detect lesions of the auditory neural pathways. The ABR waves depend not only on the integrity of the neural pathways, but also on the condition of the cochlea. To properly interpret the ABR response, it is necessary to understand the effects of cochlear hearing loss on the ABR wave latencies. We studied two populations of subjects with cochlear hearing loss: one with varying degrees of high-frequency hearing loss and the other with varying degrees of flat configuration hearing loss. The degree of cochlear hearing loss was quantified in several different ways and subjected to one linear and three nonlinear regression analyses to test for accuracy in predicting ABR wave latencies and interpeak intervals (waves I, III, V, I-V, I-III, and III-V) for three click intensities. Hearing loss levels from 2 to 6 kHz, in particular 4 kHz, were superior to other audiometric test frequencies as predictors of ABR wave latencies for the group with the high-frequency losses. No particular characterization was found to be superior for the flat hearing loss configurations. From these results, modeled predictions of wave latencies as a function of degree and configuration of hearing loss were made. The modeled predictions are then used to suggest guidelines for interpretations of ABR results where hearing impaired patients are involved.


A comparison of acoustic reflex and auditory brain stem response screening of high-risk infants.

This investigation was undertaken to explore the feasibility of screening for hearing impairment in an intensive care nursery population with a combined acoustic stapedius reflex-ABR approach. Acoustic reflex threshold measurements (AR) were made on intensive care nursery patients in an existing ABR screening program. Pass-fail results were determined for the two methods, separately and in combination. AR screening identified all 10 ears that failed the ABR screen. The cost savings of screening with a combined AR-ABR approach was determined for various pass-fail criteria. The results suggest that the AR-ABR approach can produce a significant cost savings without compromising the sensitivity and specificity of the screening program.


Auditory responsiveness of premature infants utilizing visual reinforcement audiometry (VRA).

The purpose of this investigation was to study the relationship between visual reinforcement audiometry (VRA) performance and age (i.e., corrected and mental) with 60 premature infants. VRA performance was classified as unacceptable, marginal, or acceptable based on conditionability and number of responses obtained before habituation to the task. The results indicated that mental age and corrected age were significantly related to VRA performance. It was found that a corrected age of 8 mo and/or a mental age of 6 mo is typically required for acceptable performance using VRA. A lack of responsiveness to the VRA procedure at these ages would most likely be due to hearing loss as opposed to a general developmental delay. The data from this study would not support a large scale behavioral hearing screening program for premature infants below 8 mo corrected age or 6 mo mental age.


Auditory perception changes after reimplantation in a child cochlear implant user.

The ability to remove cochlear implants from children and subsequently reimplant a more complex device in the same ear was the concern of this single case study. A postlinguistically deafened child, J.L., received a single-channel cochlear implant 1 yr after contracting meningitis and suffering a profound bilateral sensorineural hearing loss. After 3 yr of successful implant use, J.L. suffered an internal coil failure. She was then explanted and reimplanted with a multichannel cochlear implant in the same ear. This case report details her speech perception skills with her single-channel cochlear implant, a vibrotactile aid, and a multichannel cochlear implant. Results from auditory perceptual measures suggest that the explantation/reimplantation process was technically feasible with no adverse effects on J.L.'s ability to utilize a more sophisticated device and to exceed her previous performance levels.


Performance over time with a nucleus or Ineraid cochlear implant.

This investigation determined whether the audiological performance of cochlear implant users varied with experience. Thirteen Nucleus and 14 Ineraid subjects were evaluated at 1, 9, and 18 mo after cochlear implant connection. Ten Nucleus and five Ineraid subjects were tested at 30 mo. On average, the ability of the subjects to recognize words and phonemes in an audition-only condition improved during the first 9 mo, as did their ability to recognize spondees in noise. The phoneme scores continued to improve during the next 9 mo. Environmental sound recognition improved gradually; significant improvement from the 1 mo scores was not noted until 18 mo. About half of the subjects who demonstrated poor word recognition at 1 mo showed significantly improved percent word correct scores by 18 mo. The Nucleus and Ineraid subjects did not differ in their patterns of change over time. An information transmission analysis performed on the subjects' consonant confusion matrices showed relatively little change for the nasality and place features during the first 18 mo, and relatively large change for the voice, duration, and frication features. Most improvement in the feature scores occurred during the first 9 mo.


Correlations of neuroanatomical measures to auditory brain stem response latencies.

Magnetic resonance imaging (MRI) was used to obtain measures presumed to scale the dimensions of the lower auditory pathway in humans for the purpose of further defining the relationship between length of the auditory pathway and auditory brain stem response (ABR) latencies. Specifically, measurements of soft tissue structures, that is, the eighth nerve and brain stem, were made for comparison with skull dimensions and ABR latencies. It was hypothesized that the brain stem dimensions covary significantly with skull dimensions and that the ABR parameters covary with both skull and brain stem dimensions. In general, only weak correlations were obtained with coefficients failing to reach statistical significance for most comparisons. These findings suggest that variance in ABR latencies cannot be attributed completely to variance in brain stem dimensions and raise suspicion that skull dimensions do not directly reflect brain stem dimensions.


Improving the frequency specificity of the auditory brain stem response.

Several investigators have suggested that the use of tonal stimuli shaped with nonlinear windowing functions can improve the frequency specificity of the auditory brain stem response (ABR). This study investigated the effects of different windowing functions on the ABR for 30 normal-hearing adults and 30 adults with high-frequency hearing loss. These hearing-impaired patients often produce an abnormal click-evoked ABR because of the influence of the high-frequency loss. Each subject was evaluated using a click stimulus and a 500 Hz tone burst gated with one linear and four nonlinear windowing functions. There were no significant differences in wave V latency between the groups for any of the five windowed tone burst conditions. These results suggest that any of the windowing functions used would be effective for 500 Hz tonal ABRs with this population of hearing-impaired adults.


The frequency-following response and the onset response: evaluation of frequency specificity using a forward-masking paradigm.

The onset and frequency-following response (FFR) components of the auditory brain stem response were investigated using a tone on tone forward-masking paradigm, as an alternate strategy to simultaneous masking, in an effort to further clarify the issue of place specificity of these components when elicited by a low-frequency stimulus (500 Hz tone burst). The results of this preliminary investigation suggest that both the onset and FFR components yield frequency-specific information, that is, they reflect activity along a limited apicalward region of the cochlea, but both are biased somewhat basalward to the place of the probe frequency. Also, of the two, the FFR is the relatively more place-specific response.


The effect of cochlear hearing loss on auditory brain stem response latency.

The effect of audiometric configuration on the auditory brain stem response was studied in a large patient sample, and wave I latencies, wave V latencies, and the I-V interwave intervals were compared to those from a previous report. Patients with notched hearing losses showed longer wave V latencies and I-V interwave intervals than those with other audiometric configurations, but the magnitude of the effect was relatively small, and the confidence limit for cochlear diagnosis was essentially the same as that based upon a cochlear hearing loss population without regard to audiometric configuration.


Strategies for increasing response behavior of 1- and 2-year-old children during visual reinforcement audiometry (VRA).

This study investigated strategies for increasing the number of responses that can be obtained from young children during visual reinforcement audiometry. Subjects included normal 1- and 2-yr-old children. Responses before habituation were studied as a function of age, reinforcer conditions, and test sessions. It was found that: (1) using two reinforcers led to more responses before habituation than use of a single reinforcer; (2) after habituation in test session 1 and a 10-min break, most 1-yr-olds demonstrated a minimum of five additional responses in test session 2; and (3) 2-yr-olds habituated more rapidly than 1-yr-olds.


The clinical assessment of "Obscure Auditory Dysfunction" (OAD) 2. Case control analysis of determining factors.

Obscure Auditory Dysfunction (OAD) is defined as a clinical referral for self-reported auditory disability with no audiometric abnormality by stringent criteria. In stage 2 of a case control study of OAD, we have confirmed the general finding of stage 1 that OAD is multifactorial; compared with controls, patients as a group have a genuine performance deficit for understanding speech in noise, accompanied by personality-related factors. Paired logistic regression analysis optimally differentiated the 50 patients from their 50 matched controls on the basis of variables from three different domains: masked thresholds (psychoacoustic domain), dichotic listening ability (central/cognitive domain), and underestimation of own hearing ability (personality domain). A further and influential contributing variable was understanding of speech in noise supplementing the variables in both the psychoacoustic and the cognitive domains. With this model, 82.7% of the total group deviance was explained (i.e., the binary variable of case/control). A corresponding discriminant function analysis correctly classified 80% of patients and 90% of controls. When factors underlying the performance and personality-related variables were investigated with multiple linear regression within the two groups separately, relatively little of the within-group variance among OADs was explained. This is consistent with the multifactorial nature of OAD, in that the combinations of factors leading to OAD status differ between individuals. The research findings have been used to design a clinical test package to provide diagnostic information on the basis of OAD in individuals.


Performance with an adaptive frequency response hearing aid in a sample of elderly hearing-impaired listeners.

This study assessed the efficacy of an adaptive frequency response hearing aid (AFR) for improving speech perception ability in noise among a group of elderly hearing-impaired listeners. A speech recognition task, self-assessed speech intelligibility task, and qualitative judgment task were administered to examine subtle differences in the effects of the AFR "signal processing" versus linear amplification. Group scores showed statistically significant improvement with AFR processing on the speech recognition task involving high-predictability sentences, but not on any other measures. However, there was a trend toward improved scores with AFR processing for low-predictability sentences as well. These results suggest that AFR circuitry may be most useful for enhancing recognition of speech in high-cue contexts. Wide individual subject variability was observed on all measures. This demonstrates the importance of evaluating the effectiveness of noise reduction hearing aids on an individual basis and with more than one task.


Effects of noise and noise suppression on speech perception by cochlear implant users.

The recognition of phonemes in consonant-vowel-consonant words, presented in speech-shaped random noise, was measured as a function of signal to noise ratio (S/N) in 10 normally hearing adults and 10 successful adult users of the Nucleus cochlear implant. Optimal scores (measured at a S/N of +25 dB) were 98% for the average normal subject and 42% for the average implantee. Phoneme recognition threshold was defined as the S/N at which the phoneme recognition score fell to 50% of its optimal value. This threshold was -2 dB for the average normal subject and +9 dB for the average implantee. Application of a digital noise suppression algorithm (INTEL) to the mixed speech plus noise signal had no effect on the optimal phoneme recognition score of either group or on the phoneme recognition threshold of the normal group. It did, however, improve the phoneme recognition threshold of the implant group by an average of 4 to 5 dB. These findings illustrate the noise susceptibility of Nucleus cochlear implant users and suggest that single-channel digital noise reduction techniques may offer some relief from this problem.