Factors controlling B12 uptake by intestinal sacs in vitro

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Abstract
Sacs of everted small intestine were incubated in bicarbonate-saline containing radioactive vitamin B12 with or without a source of gastric intrinsic factor (IF). In both the hamster and guinea pig the lowest ileum was most active in B12 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 B12 uptake. Intrinsic factor did not bind to the intestinal wall in the absence of B12 (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 B12.