Prolactin and hypertension.

Progesterone (2.5 mg per kilogram) caused sustained hypertension in rabbits. When the same dose of progesterone was administered together with prolactin (1.25 mg. per kilogram), there was no increase in the blood pressure. In rabbits with progesterone-induced hypertension, the addition of prolactin caused a sharp drop in blood pressure. It is suggested that prolactin acts by reducing the sensitivity of the blood vessels to circulating pressor substances and further that a reduced prolactin response may be the cause of heightened sensitivity to pressor substances observed in pre-eclampsia.