Site of absorption of Co⁶⁰-labeled vitamin B₁₂ in the male albino rat

¹ Section of Medicine and Section of Biochemistry, Mayo Clinic and Mayo Foundation, Rochester, Minnesota

This study was undertaken to determine the site of maximal absorption of Co⁶⁰-labeled vitamin B₁₂ in the small intestine of the male albino rat. Animals were sacrificed at intervals after ingestion of the labeled vitamin. The highest concentration of radioactivity was found in the wall of the upper and mid-ileum 1/2–3 hours after ingestion. Accordingly, the absorption of tagged vitamin B₁₂ was estimated by fecal and urinary excretion methods in animals with resections of portions of the small intestine, including the portion containing the ileocecal valve, and in normal controls. Resection of the middle half of the small bowel (the upper and mid-ileum) was found to produce significant impairment of vitamin B₁₂ absorption. It is concluded that in the male albino rat the upper and mid-ileum is specifically adapted to most efficient absorption of vitamin B₁₂.