AJP - Heart and Circulatory Physiology, Vol 243, Issue 1 123-H127, Copyright © 1982 by American Physiological Society
Vasodilation or altered perfusion pressure moves 15-micrometers spheres trapped in the gut wall
L. C. Maxwell, A. P. Shepherd and G. L. Riedel
To determine whether the microsphere method for measuring the intramural
distribution of intestinal blood flow is affected by perfusion pressure or
vasodilation, we infused radioactive 9- and 15-micrometers spheres 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 was
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. These results have the following
implications for microsphere studies of the intramural distribution of
intestinal blood flow: 1) tissue must be sampled after each sphere infusion
unless the possibility of sphere migration has been experimentally
eliminated and 2) even a two-compartment fractionation of blood flow into
muscularis and mucosal-plus-submucosal compartments is not valid under some
experimental conditions.
