Intestinal absorption of intrinsic factor and B12-intrinsic factor complex

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Abstract
Evidence is presented which suggests that the vitamin B12-intrinsic factor (B12-IF) complex is absorbed into the intestinal epithelial cell. Following incubation of sacs of hamster ileum with B12-IF complex, the tissue was washed, the mucosa was homogenized and assayed for the complex. The soluble fraction from such a mucosal homogenate was found to possess significant amounts of the B12-IF complex. The exit of vitamin B12 from the basal surface of the epithelial cells was investigated by studying its appearance in the intestinal lymphatics. In a series of rats it was found that 3–9% of the absorbed B12 entered the lymphatic capillaries while the remaining fraction (91–97%) passed into the blood capillaries. Vitamin B12 present in lymph, although not dialyzable, was not bound to intrinsic factor. It is inferred from these studies that B12-IF complex enters the intestinal epithelial cells where it is converted into some other B12-protein complex. Following the exit of this B12-protein complex from the epithelial cell, it enters both lymphatic and blood capillaries, the latter being a quantitatively more important route.