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

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.