Whole-body retetion of 60CoCl2 and 58Co-cyanocobalamin in young and adult rats

Whole-body retention of 60CoCl2 and 58Co-cyanocobalamin after oral and intravenous administration was investigated in young and adult rats. Whole-body retention of 58Co-cyanocobalamin was considerably higher than that of 60CoCl2 in rats of all age groups. Younger rats showed higher retention of both CoCl2 and cyanocobalamin than did the adult rats. The biological half life in the slowly decreasing phase after oral administration of 60CoCl2 and 58Co-cyanocobalamin was approximately equal in all age groups and was estimated to be about 10 and 25 days, respectively. These results suggested that the whole-body retention of orally administered 60CoCl2 and 58Co-cyanocobalamin in rats of various ages depends mainly on intestinal absorption rather than endogenous excretion rate. The excretion pattern of 58Co-cyanocobalamin, i.e., F/U ratio etc., is very different from that of inorganic cobalt, and it is therefore assumed that 58Co-cyanocobalamin is rather stable in the body. (auth.)