Endocrine correlates of placental permeability during gestation in the pig.

1. Hormone and electrolyte concentrations were determined in amniotic and allantoic fluid collected from sows at 47-112 days of gestation and correlated with placental and fetal membrane electrolyte permeability. 2. Significant differences between the electrolyte and endocrine gestational profiles of amniotic and allantoic fluid were identified. 3. The principal endocrine correlate (r > 0.62; P < 0.01) of gestational changes in the sodium and chloride permeabilities of the porcine placenta and fetal membranes was found to be the concentration of oestrogen in the amniotic fluid.