Mechanism of Intrinsic Factor Action in the Gastrectomized Rat. ∗

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.