Differential Excretion of Cobalt-containing Products Following Administration of Co 60 -labelled Vit. B 12,to Rats

Summary

1) The excretion pattern of radioactive substance following parenteral administration of 0.25 μg of Cobalt⁶⁰-labelled Vit. B₁₂ to the young rat has been studied. 2) Urinary excretion of radioactivity reaches a maximum during the first 8 hours after labelled Vit. B₁₂ administration, then rapidly declines; fecal excretion rises progressively through the 3rd day. Moreover, administration of a large dose of unlabelled Vit. B₁₂ subsequent to radioactive B₁₂ significantly increases urinary but not fecal excretion of radioactivity. From this differential excretion pattern, it is inferred that labelled vitamin is altered prior to its excretion into the intestinal tract. 3) The fecal route is the major excretory pathway for radioactivity resultant from parenteral introduction of Co⁶⁰-labelled Vit. B₁₂; after the 1st 8 hours, the ratio of radioactivity excreted for a 10-day period via fecal and urinary pathway is 7:1, respectively. 4) Sex does not appear to influence excretion of Co⁶⁰-tagged products. Similarly, administration of large quantities of testosterone propionate to either females or males does not alter the excretion pattern.