Metabolic Fate of <SUP>57</SUP>Co-Labeled Hydroxocobalamin and <SUP>57</SUP>Co-Labeled 5, 6-Dimethylbenzimidazolylcobamide Coenzyme in Rats

The metabolic fate of 57Co-hydroxocobalamin (57Co-OH-B12) and 57Co-5, 6-dimethyl-benzimidazolylcobamide coenzyme (57Co-DBCC) has been studied after intraperitoneal administration at the dosage of 25 μg/kg in rats. About 60% of radioactivity administered was recovered in urine during the first 24 hr after administration of 57Co-OH-B12 or 57Co-DBCC. The highest tissue uptake was found in kidney, especially after injection of 57Co-DBCC, followed by adrenal gland, pancreas, stomach and liver. The distribution in brain, muscle and adipose tissue was much lower. It is evident that 57Co-OH-B12 was converted to 57Co-DBCC and reverse conversion of 57Co-DBCC occured in liver and kidney. Furthermore, 57Co-methylcobalamin (57Co-CH3-B12) was found to be yielded from both the cobamides. The biological interconversion among 57Co-CH3-B12, 57Co-OH-B12and 57Co-DBCC was established.