The Intraluminal Transport of Vitamin B12 and the Exocrine Pancreatic Insufficiency

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Abstract
The vitamin B12-binding proteins saturated or unsaturated with endogenous vitamin B12 in human gastric and intestinal juice were characterized in terms of molecular size, reaction with specific anti-intrinsic factor and R-binder (also called non-IF, Cobalophilin) sera and reaction with specific porcine intrinsic factor receptor. The intestinal juice contains only intrinsic factor whereas gastric juice contains in addition R-binders. The absence of R-binders in intestinal juice may be due to degradation by pancreatic enzymes. The vitamin B12 malabsorption in exocrine pancreatic insufficiency may be due to the presence of undegraded R-binders. The presence of free and biologically active intrinsic factor in intestinal juice suggests that enterohepatic circulation may play an important role in vitamin B12 homeostasis.