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 B 12 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 B 12 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 B 12 binders precipitable by centrifugation. Human jejunal mucosa homogenate uptake was not enhanced by intrinsic factor, supporting the concept that the active process of vitamin B 12 uptake is localized to the ileum. Nonspecific uptake of vitamin B 12 , unrelated to intrinsic factor, appeared to be uniform in jejunal and ileal mucosa homogenates, and to be unaffected by p H or cations. Poor vitamin B 12 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 B 12 complex. This awaits further studies, correlating this technique with in vivo absorption studies.