Vitamin B12 Uptake by Human Small Bowel Homogenate and its Enhancement by Intrinsic Factor

Abstract

Mucosal homogenates of human ileum were demonstrated to have enhanced vitamin B12 uptake in the presence of normal human gastric juice or hog intrinsic factor concentrate. This process was demonstrated to require Ca++ or Mg++ and to be optimal at pH 6.6 and above. The enhancement was blocked by antibody to intrinsic factor. Pernicious anemia gastric juice and normal and pernicious anemia serum did not enhance B12 uptake. In fact, these substances diminished nonspecific uptake of the vitamin, presumably by binding it and rendering it unadsorbable. “Enhancement” by saliva appeared to be an artifact due to the presence of B12 binders precipitable by centrifugation. Human jejunal mucosa homogenate uptake was not enhanced by intrinsic factor, supporting the concept that the active process of vitamin B12 uptake is localized to the ileum. Nonspecific uptake of vitamin B12, unrelated to intrinsic factor, appeared to be uniform in jejunal and ileal mucosa homogenates, and to be unaffected by pH or cations. Poor vitamin B12 uptake in some but not other ileal homogenates from patients with regional ileitis suggests that the ileal homogenate technique may be useful in evaluating in vivo function of intestinal receptors for the intrinsic factor-vitamin B12 complex. This awaits further studies, correlating this technique with in vivo absorption studies. © 1969, The Williams & Wilkins Co.. All rights reserved.