THE INFLUENCE OF OVARIAN HORMONES UPON THE MOTILITY AND PROSTAGLANDIN PRODUCTION OF THE PREGNANT RAT UTERUS IN VITRO

Abstract

SUMMARY The output of prostaglandin-like material and the spontaneous contractions of the pregnant rat uterus in vitro have been studied during the last 6 days of pregnancy and for 3 days post partum. Both prostaglandin release and uterine activity were minimal on days 17–18 of pregnancy but both parameters gradually increased, reaching a peak on day 22, the expected day of delivery. Post partum both uterine prostaglandin release and spontaneous activity declined. Progesterone (25 mg, i.m.) given to rats from days 16–21 of pregnancy did not alter uterine activity or prostaglandin output when compared with uteri taken on day 22 from animals which had received ethyl oleate over the same period. On day 22 the spontaneous activity of uteri in vitro taken from animals ovariectomized on day 17 was very low compared with that seen in preparations from sham-operated controls, although prostaglandin release in these groups was not significantly different. Oestrogen (1 μg, i.m.) was given to one group of ovariectomized animals on days 19 and 20; uterine activity was determined on day 21 of pregnancy and found to be of greater intensity and amplitude than that seen in an ovariectomized control group. Prostaglandin output was similar in these groups. Thus although exogenous progesterone and oestrogen do not influence uterine prostaglandin release at term, oestrogen appears essential for the occurrence of spontaneous contractions. It is concluded that, in the pregnant rat uterus in vitro, prostaglandin release may contribute to uterine activity but oestrogen is essential for this to become apparent.