Microsphere method in measurement of blood flow to wall layers of small intestine

Microspheres of 10.90 +/- 0.65 micron (SD) were injected in the superior mesenteric artery of cats and their intramural distribution and diameter in the small intestine were studied microscopically under basal conditions and after vasodilation by isoproterenol. Approximately 2% of the spheres were shunted through the small intestinal vasculature and could be recovered in the liver. Analysis of the tissue distribution suggested that all spheres arrested in villi represented villous blood flow, spheres arrested in the crypt layer represented flow to the crypts, and the majority of microspheres trapped in the submucosa also represented crypt flow. Nutritive blood flow to the submucosa constituted only 1.5% of total intestinal flow. Log-linear analyses identified factors responsible for sphere distribution, including effects of sphere size, isoproterenol treatment, and local blood flow or vascular resistance. Spheres with diameters greater than 11.08 micron had 1.35 times larger odds than smaller spheres to embolize in the muscularis rather than in the mucosa, but no consistent difference between diameter profiles in the crypts and villi was found. With this reservation, 11-micron spheres seem to be appropriate for measuring blood flow to the muscle, crypt, and villous layers of the small intestine.