Abstract
For the purpose of clarifying the mechanism of B12 absorption, Co60- or Co58-B12 was given intravenously or into the three sites of gastrointestinal lumen of albino rats, and tissue distribution of the vitamin was studied. The effects of the agents such as hog IF, D-sorbitol, D-glucosamine, and lyophilized saline extract of rat gastric mucosa were also studied.
1. It was interesting to note that B12 could be absorbed even from the ileum in the rats.
2. The higher the site of B12 administration, the more B12 was absorbed. But, generally speaking, the main site of B12 absorption appeared to be in the middle portion of the small intestine in the rat.
3. It was observed that the chief site of B12 localization was in the kidneys and the liver in the rat, suggesting that these organs may be the B12-storage organs.
4. Hog IF inhibited B12 absorption in the rat, presumably because of species difference. Some discussions were made on the problem of species difference as well. However, when hog IF was given intravenously, the agent exceedingly enhanced B12 uptake by the liver with concomitant decrease in the uptake by other organs.
5. In contrast, the agents other than hog IF resulted in increased B12 uptake by the kidneys, not by the liver, when given intravenously.
6. Based on these results obtained, the present author has put forward a hypothesis concerning the mechanism of B12 absorption. Two mechanisms may possibly exist: B12 absorption itself across the intestinal mucosa and the subsequent uptake of the vitamin by the organs. Finally, according to the hypothesis, some comments were made regarding the effects of various agents used in this study on B12 absorption.
