Vasodilation or altered perfusion pressure moves 15-micrometers spheres trapped in the gut wall

Abstract

To determine whether the microsphere method for measuring the intramural distribution of intestinal blood flow is affected by perfusion pressure or vasodilation, radioactive 9- and 15-.mu.m spheres were infused into adjacent segments of isolated canine small bowel. After sphere infusion the blood supply of the control loop was occluded, and the vasculature of the experimental loop was either dilated by infusing isoproterenol or subjected to increased perfusion pressure. Intestinal segments were dissected into mucosal, submucosal and muscularis samples. Venous blood was collected during sphere infusions and experimental perturbations. Accumulations of spheres in tissue samples and venous blood were assessed in a .gamma.-radioactivity counter. Isoproterenol caused previously infused spheres to leave submucosa and redistributed them primarily to mucosa, with few additional spheres reaching venous blood. An increase in perfusion pressure also dislodged spheres from submucosa, but these did reach venous blood. The combined estimate of mucosal plus submucosal blood flow was relatively unaffected by isoproterenol infusion but was significantly altered by increased perfusion pressure. The following implications for microsphere studies of the intramural distribution of intestinal blood flow were made: tissue must be sampled after each sphere infusion unless the possibility of sphere migration has been experimentally eliminated, and even a 2-compartment fractionation of blood flow into muscularis and mucosal-plus-submucosal compartments is not valid under some experimental conditions.