A role for prostaglandins in the regulation of the placental blood flows.

A model is proposed for the regulation of the placental blood flows to the near-term pregnancy. The model has three features. 1) The maternal uterine and fetal placental tissues can synthesize constrictor and dilator prostaglandins. 2) Prostaglandins can cross the placenta. 3) There must exist a prostaglandin which has a vascodilating action in one of the placental circulations and a vasoconstricting action in the other circulation. Evidence is provided to indicate that the sheep, prostaglandin E2 (PGE2) can cross the placenta and has a vasodilating action in the uterine placental circulation and a vasoconstricting action in the umbilical placental circulation. The placenta and the lung are compared and PGE2 is shown to have similar actions in each of these organs.