Placental Transfer of 110Agm in Rats

Wistar strain pregnant rats were used to determine the uptake of 110 Ag m by the conceptus in relation to its gestational stages, measuring retention in the placenta, fetal membranes and fetus. The transfer of 110 Ag m into the fetuses on the 20th day of gestation, 24 h after injection, was about 9% of the initial maternal dose. The relative concentration in the placenta and fetal membranes was much higher than in the fetus and decreased with time after injection. These results indicate that the placenta and fetal membranes play significant roles as barriers to the transfer of 110 Ag m into the fetus. It is proposed that a C P :C M ratio of 2 is used in calculations of doses to the human fetus following maternal intakes of radioactive silver. It was also observed that about 10% of the maternal dose of 110 Ag m was transferred to suckling rats through milk. The amount of milk-born 110 Ag m transferred to suckling rats was dependent on the gestation age at the time of the dose.