Plutonium movements across the haemochorial placenta of the guinea pig.

In order to measure transplacental movements of plutonium without the complications of fetal accumulation, the fetal circulation of the guinea pig placenta (at 59 to 61 days of gestation) was perfused in situ. Dams were administered trace quantities of tritiated water (to indicate changes in maternal blood flow to the placenta) and 30 mu Ci/kg (i.e., approximately 500 micrograms/kg) of citrated 239Pu by intravenous injection. Plutonium-239 doses were large, approaching the LD50/30 (20 to 80 mu Ci/kg) for other species. Perfusion pressure, maternal cardiac rate, electrocardiogram, blood pressure, and respiratory rate were monitored continuously during each perfusion. Our measurements show that the clearance of plutonium from mother to fetus is small--2.5 +/- 0.5 microliter/min--an amount that is less than 20 per cent of the clearance of inorganic mercury. The indirect measurements of maternal blood flow to the placenta indicate that placental blood flow is greatly diminished in dams dosed with plutonium, which may partially account for the low clearance of plutonium.