EXCHANGE BETWEEN FREE AND GASTRIC JUICE-BOUND CYANOCOBALAMIN*

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Abstract
Exchange between free and gastric juice-bound radioactive cyanocobalamin was demonstrated in vitro when free and bound cyanocobalamin were separated by dialysis, by starch gel electrophoresis, or by dextran gel filtration. Absorption studies in patients with pernicious anemia and in gastrectomized rats suggested that intrinsic factor was involved in this exchange. Significant quantities of endogenous vitamin B12 were found in the intestinal lumen of rats. When rat liver or intestine was incubated, tissue vitamin B12 escaped into the incubation medium. Exchange between this endogenous vitamin B12 and gastric juice-bound radioactive cyanocobalamin was demonstrated. These findings are pertinent to the quantitative interpretation of studies concerned with in vitro tissue uptake and in vivo absorption of radioactive cyanocobalamin.