Placental transmission and foetal distribution of 3H-ouabain

Placental transfer and foetal distribution of 3H-ouabain were studied in eight pregnant women undergoing legal termination of pregnancy during the first half of gestation. The 3H activity in maternal and foetal plasma, in foetal tissues and amniotic fluid was estimated using the oxidation method. The intactness of the labelled drug was determined by thin-layer chromatography. 3H-ouabain rapidly disappeared from the maternal blood-steam, and a measurable amount of 3H activity was already present in the umbilical blood of the foetus two min. after the administration of the drug into the maternal blood. The foetal plasma 3H values were lower than the maternal values during the time interval 2 to 120 min. after injection, and the foetal 3H plasma concentrations approximated the maternal values five hours after drug administration. The 3H concentrations found in the amniotic fluid were lower than those in the corresponding maternal or foetal plasma samples. The distribution of ouabain in the foetal tissues was relatively uniform, with the highest 3H concentrations found in the heart and placenta, the lowest in the brain. The results suggest that the human foetal heart has some capacity to bind ouabain even during the first half of gestation.