Vitamin B12 absorption in rats, studied by a ‘loop’ technique

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Abstract
A technique to prepare an intestinal loop in situ in rats is described for the study of the effect of intrinsic factor (IF) on the absorption of vitamin B12 and of the site of absorption. It was found that a) the site of absorption of vitamin B12 is the smal intestine and, particularly, the middle portion; b) a saline extract of rat stomach mucosa, as well as rat gastric juice, when mixed with a low test dose of vitamin B12, markedly increased the absorption of vitamin B12 by the loop. A quantitative relationship was demonstrated between absorption and vitamin B12-binding power of such an extract. However, a purified hog IF did not enhance the absorption of vitamin B12 and c) two different mechanisms for the absorption of vitamin B12 are suggested. One operates when a small physiological dose is administered; the absorption can be enhanced by co-administration of IF and be inhibited by ethylenediaminetetraacetate (EDTA). The other operates when a high dose is given; the absorption under such conditions is not affected either way by the administration of IF or EDTA.