Scudamore, Harold H.

This study was undertaken to determine the site of maximal absorption of Co60-labeled vitamin B12 in the small intestine of the male albino rat. Animals were sacrificed at intervals after ingestion of the labeled vitamin. The highest concentration of radioactivity was found in the wall of the upper and mid-ileum 1/2–3 hours after ingestion. Accordingly, the absorption of tagged vitamin B12 was estimated by fecal and urinary excretion methods in animals with resections of portions of the small intestine, including the portion containing the ileocecal valve, and in normal controls. Resection of the middle half of the small bowel (the upper and mid-ileum) was found to produce significant impairment of vitamin B12 absorption. It is concluded that in the male albino rat the upper and mid-ileum is specifically adapted to most efficient absorption of vitamin B12.

Urinary-excretion and fecal-recovery methods were employed in the study of intestinal absorption of cobalt60-labeled vitamin B12 in the normal male albino rat. a) The logarithm of the fecal excretion, as well as of the urinary excretion augmented by an intraperitoneal flushing dose of unlabeled vitamin, increased linearly with the logarithm of the oral dose. This same relation of fecal excretion to oral dose is also apparently true in man. b) Increasing the intraperitoneal flushing dose over a wide range brought about a progressive increase in the percentage of the labeled oral dose excreted in the urine, but this increase was of small magnitude. c) The optimal time for administration of the intraperitoneal flushing dose in the rat appeared to be about 2 hours after administration of the labeled oral dose. d) The male albino rat seems to be an excellent experimental animal for use in the study of vitamin B12 absorption.