Placental transfer of ruthenium in rat and guinea-pig

Ruthenium-106 in citrate solution was administered intravenously to rat at different stages of pregnancy and to guinea-pig either before conception or in late pregnancy. The results for rat showed that retention in the embryo/foetus measured at 3-5 days after administration increased from about 0.0002% of injected activity per embryo/foetus on day 12 of gestation to about 0.05% at birth. The relative concentrations of ¹⁰⁶ Ru in embryo/foetus and mother (C(f)/C(m) ratio) were about 0.1 in each case. Concentrations in the yolk sac on day 12 were about 1% g^-1 compared with 0.01% g^-1 in the foetus. Retention in the guinea-pig foetus in late gestation at 7 days after administration (days 50-57) was about 0.2% injected activity per foetus, corresponding to a C(f)/C(m) = 0.2. Retention in each foetoplacental unit was 2% of injected ¹⁰⁶Ru with 50% in the yolk sac, 35% in the placenta and 10% in the foetus. For administration 4 weeks prior to conception, the level of ¹⁰⁶Ru retained in the foetus on day 57 of gestation was two orders of magnitude lower than after short-term administration, with a C(f)/C(m) about 0.004.