Distribution of intrinsic factor-vitamin B12 receptors in human intestine.

A new rapid and accurate method for detecting vitamin B12-intrinsic factor (IF-B12) receptors was used to study the distribution of mucosal IF-B12 receptors in three human small intestines. IF-B12 receptors in human intestine are present in significant amounts in the entire distal three-fifths of intestine. Triokinase activity is absent in the distal two-fifths of intestine, and tryptophan oxygenase is present only in the distal one-sixth, or most terminal part of the ileum. These data suggest (1) biochemical functions in the ileum have different anatomical distributions, (2) IF-B12 receptors correspond most closely with the accepted anatomical definitions of the ileum, and (3) vitamin B12 malabsorption seen in resection or disease of terminal ileum may not be attributable solely to a deficiency of ileal receptors.