Transfer of plutonium to rat embryos in vivo and in vitro.

The 239Pu distribution in the 12.5-day-old rat conceptus was compared between in vivo and in vitro experimental systems to establish a possible mechanism of cross-placental transfer of this radionuclide. In the in vivo study, plutonium citrate solution was injected intravenously to pregnant Wistar rats. In the in vitro study, either plutonium citrate or plutonium hydroxide colloid was administered, as a solution of Eagle MEM and FCS containing 239Pu at the concentration used in the maternal serum in the in vivo experiments, to rat conceptuses maintained by the whole-embryo culture method. The concentration of 239Pu in the yolk sac (239Pu activity per gram wet weight) were much higher than in the embryo in both the in vivo and in vitro experiments, suggesting that the yolk sac may be an effective barrier against the transfer of plutonium to the embryos. The ratios of the 239Pu concentration in the yolk sac to that in the embryo were relatively constant with time after administration in the in vitro system; 18-27 for plutonium citrate and 67-84 for plutonium hydroxide. In the in vivo experiment, these ratios changed with time after injection; 15 at 5 min and 62 and 60 min after injection. This suggests that in the in vivo system, the chemical form of 239Pu changed with time after injection, probably to a macromolecular form such as the hydroxide colloid or plutonium-protein complex although 239Pu was injected to the maternal blood as citrate.