Absorption, excretion and tissue distribution of oral cyano-cobalamin in rabbits

¹ Department of Physiological Chemistry, Washington University School of Dentistry, St. Louis, Missouri

The appearance of radioactivity in plasma, following an oral dose of Co⁶⁰ cyanocobalamin, reached maximum values after 7 hours. The plasma activity during the succeeding 26-day experimental period decreased in a logarithmic fashion which was resolved into three components with biological half-lives of 29 hours, 7.1 days and 15.8 days. The 7.1-day half-life component is significantly longer than the 4-day half-life found in rabbits following intramuscular or intravenous administration of Co⁶⁰ cyanocobalamin. This indicates a different, more stable, protein-cyanocobalamin complex formed during absorption. The excretion of radioactivity in urine and feces following oral dosage of Co⁶⁰ cyanocobalamin demonstrates the limited absorption of cyanocobalamin from the gut of rabbits. The urinary excretion of the radioactive dose increased from 2.2% to 20.7% in animals previously injected with nonradioactive cyanocobalamin and liver tissue retained more radioactivity following nonradioactive cyanocobalamin supplementation. It is concluded that the cyanocobalamin absorption mechanism of rabbits is similar to that of human subjects and other laboratory animals.

Note:
With the Technical Assistance of Paul R. Myers and Mari Lou Pfluke