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-palcental 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.
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