Bisphenol A Disposition in the Sheep Maternal-Placental-Fetal Unit: Mechanisms Determining Fetal Internal Exposure

The widespread human exposure to bisphenol A (BPA), a xenoestrogen interfering with developmental processes, raises the question of the mechanisms determining fetal exposure to BPA. A physiological model was developed in ewes to determine whether the pregnancy-associated physiological changes and the metabolic specificities of the fetal-placental unit can influence BPA toxicokinetics (TK) and fetal exposure to BPA. In a first longitudinal study, BPA was infused (2 mg/[kg.day] i.v. for 1 day) into ewes before breeding, at early and late stages of gestation, and after lambing. In a second study, BPA and BPA-glucuronide (BPA-G) were infused intravenously into pregnant ewes or into fetuses at 4 mo of gestation. BPA and its metabolites were assayed in maternal and fetal plasma and amniotic fluid sampled at steady state and after the end of the infusion. The pregnancy status did not modify the TK parameters of BPA and of BPA-G. Five percent of the BPA dose infused into the pregnant ewe was transferred across the placenta to the fetus. The fetal-placental unit was very efficient in metabolizing BPA into conjugated compounds; those metabolites remained trapped in the fetal-placental compartment, leading to a high fetal exposure to BPA conjugates. Taking into account a body weight adjustment, the ovine fetus in late pregnancy is exposed to a BPA dose similar to that of its mother. In contrast to its mother, the fetus exhibits much higher and sustained exposure to BPA metabolites without evidence of their hydrolysis.