Mechanism of Intrinsic Factor Action in the Gastrectomized Rat.

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Abstract
Summary and Conclusion 1. In experiments with gastrectomized rats: (a) The probable species specificity of rat intrinsic factor was demonstrated by the failure of a highly purified preparation of hog intrinsic factor to increase the absorption of Co60-B12. (b) In consonance with previous observations in pernicious anemia, acidification (pH 1.85) of a mixture of Co60-B12 and homogenized rat stomach inhibited the absorption of Co60-B12. (c) In contrast to previous observations in pernicious anemia, separate serial administration of Co60-B12 and rat gastric juice failed to show that rat intrinsic factor was more effective in promoting the absorption of Co60-B12 when it preceded than when it followed the Co60-B12. Indeed, no certain effect of rat intrinsic factor was detected whether it preceded or followed the Co60-B12 by as short an interval as 30 minutes. 2. In experiments with paired isolated loops of small bowel with intact blood supply created in previously gastrectomized rats: (a) The radioactivity of the wall of the loop perfused with Co60-B12 and rat gastric juice was greater than that of the paired loop perfused with Co60-B12 and rat gastric juice previously heated to destroy its intrinsic factor activity. No consistent difference was observed with heated or unheated human gastric juice. (b) The absorption of Co60-B12 was greater when labelled rather than unlabelled vit. B12 in equal amounts had saturated the binding capacity of rat gastric juice before admixture with an equal amount of the other form of vit. B12 just before the intestinal perfusion. 3. In conclusion, binding of vit. B12 is an important, perhaps indispensable, aspect of the function of intrinsic factor.

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