Factors controlling B₁₂ uptake by intestinal sacs in vitro

Abstract

Sacs of everted small intestine were incubated in bicarbonate-saline containing radioactive vitamin B 12 with or without a source of gastric intrinsic factor (IF). In both the hamster and guinea pig the lowest ileum was most active in B 12 uptake in the presence of intrinsic factor, the upper jejunum showing little or no uptake. Low temperature and anaerobic conditions completely abolished the stimulatory effect of IF on B 12 uptake. Intrinsic factor did not bind to the intestinal wall in the absence of B 12 (even in the presence of calcium ion) as the IF activity could be completely removed by gentle washing of the tissue. The vitamin and intrinsic factor must be present together to cause intestinal uptake of B 12 .