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.

The purpose of the present study was to investigate the distribution in the small bowel wall of intracardially injected microspheres with different diameters, and to find a sphere size that could be used for determination of blood flow to the different layers of the bowel wall. Microspheres were injected into the left ventricle of the hearts of cats in the following order of succession, 8–10, 15 + 5, 25 + 5 and 50 + 5 µm. Samples of the proximal part of the jejunum and the distal part of the ileum were examined microscopically, and the size and the location of the spheres recorded. The following distribution of the microspheres was found: villi 6–16 µm, crypt layer 6–20 µm, propria below the crypts and the muscularis mucosa 11–24 µm, submucosa 9–66 µm and muscularis 6–30 µm. Spheres between 8 and 13 µm appeared to be fairly uniformly distributed in the different layers of the intestinal wall.