In this study we investigated the relative vascular response of different locations of the gastrointestinal tract to continuous intravenous infusion of isoproterenol (0.1 microgram kg-1 min-1 for 10 min). The vascular response of some nonsplanchnic organs was also examined. Blood flow of the arteries was measured by electromagnetic flowmetry and that of the tissues by 15-micron microspheres. Isoproterenol increased (P less than 0.05) blood flow of the axillary artery (+52%), and the superior mesenteric artery (+45%), but not that of the inferior mesenteric artery. In the nongastrointestinal tissues, isoproterenol increased (P less than 0.05) the blood flow of the left (+46%), and right ventricle (+85%), and the skeletal muscle (+100%). In the gastrointestinal tract, isoproterenol increased (P less than 0.05) blood flow in the esophagogastric junction (+505%) and antrum (+1511%) only, but not in the gastric body or in any location of the small or large intestine. The drug also caused a large fall in resistance in the esophagogastric junction (-74%) and antrum (-94%), and a small, but significant fall in the duodenum, jejunum, and in the mid-small intestine. It had no significant effect on vascular resistance in the gastric body, ileum, or colon. In those locations of the gastrointestinal tract where isoproterenol caused an increase in blood flow, this effect was confined to the combined mucosal plus submucosal layer, and the drug had no effect on the muscularis. These data suggest that different locations of the gastrointestinal tract respond differently to the same circulating concentration of isoproterenol. The mechanism of this difference in response merits further investigation.(ABSTRACT TRUNCATED AT 250 WORDS)
Animals Colon