Abstract
The absorption of B_<12> was studied in Mongrel dogs using ^<57>Co-cyanocobalamin. It was found that the main absorptive site is the terminal ileum, and that absorption of small doses (0.005〜0.03μg) from isolated ileum, is usually poor with considerable fluctuation, while that of doses above 0.1μg is greater percentage-wise. Dog gastric juice contains one or two B_<12> binding proteins which are relatively resistant to proteases with respect to binding capacity, and when placed in intestinal loops with the test dose, it inhibits absorption. Under the same conditions, rat stomach mucosa extract rather promoted absorption of the small dose. Dog duodenal fluid collected after pancreatic secretion stimulation, enhanced absorption of small doses of B_<12>, whether it waa used in the intestinal loop or in the small intestine without the supply of pancreatic juice. It seems that the gastric binder has an unknown role and that pancreatic juice has a prime function in B_<12> absorption in the dog.
