Fetal uptake of 60CoCl2 and 57Co-cyanocobalamin in different gestation stages of rats

Fetal uptake of 60CoCl2 and 57Co-cyanocobalamin was investigated in different gestation stages of rats. The fetal uptake of 60CoCl2 24 hrs after administration to pregnant rat slightly increased with the progress of gestation age at the administration but taking account of the growth of the fetus the value expressed in terms of concentration of 60Co 24 hrs after injection decreased on the contrary. In the case of 57Co-cyanocobalamin the fetal uptake 24 hrs after administration to pregnant rat increased markedly when the time of injection was in later stage of pregnancy. Fetal accumulation of 57Co-cyanocobalamin increased with time after injection and the retrograde transfer from fetus to mother was not observed. The amount of 57Co-cyanocobalamin in the placenta is the greatest immediately after administration followed by a gradual decrease thereafter. Since the amount of radiocobalt transferred through placenta in both chemical forms is greater than that accumulated in placenta, this organ does not seem to play a role as a barrier to both forms of radiocobalt. It was observed that 1 - 2% of maternal dose of 57Co-cyanocobalamin were transferred to sucklings via milk. The amount of milk-born cyanocobalamin in sucklings is dependent on the gestation age at the time of dosing. (author)