Influence of Rhythmic and Tonic Contraction of Intestinal Muscle on Blood Flow and Blood Reservoir Capacity in Dog Intestine

Abstract

The influence of rhythmic and tonic contractions of intestinal muscle on intestinal blood flow and reservoir capacity were studied in isolated, perfused segments of dog intestine set up in a constant temperature plethysmographic chamber, or isolated in situ with extrinsic nerves intact. Blood flow recorded continuously by thermopile and drop methods showed that rhythmic intestinal contractions caused a reciprocal periodicity in arterial and venous flows due to a positive pumping action which can develop venous pressures well in excess of the arterial inflow and therefore contributes importantly to the active propulsion of blood through the intestine and the liver. Prolonged tonic contraction diminishes intestinal blood flow and may nullify the augmentative influence of the rhythmic contractions and/or of vascular dilatation. Decreased intestinal tonus by itself augments intestinal blood flow even in the absence of rhythmic contractions. Intestinal tonus is therefore an important determinant of the functional blood reservoir capacity of the intestine, the total peripheral resistance and the degree of intestinal hemostasis. These motor influences on intestinal blood flow are superimposed upon those of the intestinal vasculature per se, which thereby may be augmented, completely masked or even reversed. These data find ready explanation in a consideration of the peculiar anatomical features of the intestinal vasculature.