Absorption of Liver-bound Vitamin B₁₂ in Relation to Intrinsic Factor

Rat liver containing radioactive native B₁₂ was prepared by repeated injections of ⁵⁷Co-OH-B₁₂, and absorption of liver B₁₂ was measured in patients with pernicious anemia and in subjects without stomach, using physiologic doses. It was found that absorption of liver B₁₂ was very poor, not superior to that of free OH-B₁₂, and coadministration of IFC markedly enhanced absorption.

In vitro digestion of rat liver with several enzymes, as determined from liberation of dialyzable radioactivity, suggested its easy digestibility. Biochemical studies of the dialyzable products of liver containing ⁵⁷Co-B₁₂ failed to demonstrate any detectable quantities of radioactivity other than free ⁵⁷Co-OH-B₁₂. A study in which cow liver powder mixed with a small quantity of ⁵⁷Co-CN-B₁₂ was fed to humans and digestion of liver was estimated from the reduction in absorption of radioactivity, indicated that most of the extractable liver B₁₂ was liberated free in the intestine. Thus, no evidence has been obtained for the production of B₁₂-peptide complexes from liver by digestion that require no IF for absorption.