Abstract
Abstract
The effects of intra-arterial administration of Met-enkephalin upon intestinal blood flow, oxygen consumption, intestinal motor activity, and distribution of blood flow to the compartments of the gut wall were measured in anesthetized dogs before and after blockade of opiate receptors with naloxone. Blood flow to a segment of distal ileum was measured with an electromagnetic blood flow meter and intestinal oxygen extraction was measured spectrophotometrically. Oxygen uptake was calculated as the product of oxygen extraction and total blood flow. Changes in blood flow distribution were estimated from the distribution of radiolabeled microspheres. Motor activity was monitored from changes in intraluminal pressure. In dogs prior to blockade of opiate receptors, Met-enkephalin induced a dose-related increase in mesenteric blood flow, oxygen extraction and consumption, and intestinal motor activity. A significant increase in blood flow to the muscularis was also observed. The intestinal vasodilator, metabolic, and motor responses to Met-enkephalin were abolished by blockade of opiate receptors with naloxone. The results of our study indicate that Met-enkephalin causes an increase in intestinal motor activity and an increase in the metabolic demand for oxygen. The primary effect probably results in smooth muscle relaxation in intestinal arterioles and precapillary sphincters, thereby increasing intestinal blood flow and oxygen consumption. We conclude that opiate receptors may be involved in the regulation of intestinal motor function.
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