The role of estradiol 17β in the activation of the uterus during premature labor and the effect of naproxen, an inhibitor of prostaglandin synthesis

Abstract

Fifty-two pregnant rats were ovariectomized on day 16 of gestation to induce estrogen and progesterone deficiencies and the animals were divided into four Groups. Ovariectomy alone (Group A) resulted in the premature delivery of 21% of the fetuses. When ovariectomy was followed by estrogen treatment restoring normal estrogen levels (Group B), premature delivery of the fetuses increased to 96%. Daily injections of 25mg/kg b.w. Naproxen (Group C), given from the day of ovariectomy to reduce prostaglandin synthesis, completely prevented premature delivery if the animals received no estradiol treatment and reduced prematurity to 50% if estradiol had been administered (Group D). It is concluded that the estrogen and progesterone deficiency, induced by ovariectomy, provokes a regulatory imbalance which promotes premature delivery. This imbalance is enhanced when the estradiol levels are restored to normal values, probably because estradiol increases the synthesis of prostaglandin, the intrinsic myometrial stimulant. Naproxen, an inhibitor of prostaglandin synthesis, restores the regulatory balance, partially or completely, depending on the estrogen levels.