The relative transfer of estrogens and their sulfates across the guinea pig placenta: sulfurylation of estrogens by the placenta.

In a recent report from these laboratories (2), an in situ perfusion method was described which could be used to measure the transfer of substances in either direction across the guinea pig placenta. When the procedure was applied to the estrogens, it was found that the unconjugated hormones, estrone, estradiol170, and estriol were transferred quickly under conditions in which the placenta posed an effective barrier to their glucuronide conjugates. However, it was found that when estrogens were administered to the mother, conjugates other than glucosiduronates were detected in the umbilical circulation. In the present report, evidence is presented indicating that these conjugates are estrogen sulfates, that the placenta is impermeable to these conjugates, but that the placenta can sulfurylate estrogens and release them into the umbilical circulation.