EFFECTS OF PROSTAGLANDIN INHIBITORS ON ANGIOTENSIN, OXYTOCIN AND PROSTAGLANDIN F2α CONTRACTILE EFFECTS ON THE RAT UTERUS DURING THE OESTROUS CYCLE

Abstract

1 In the rat isolated uterus maximal spontaneous contractions and maximal sensitivity to angiotensin II, oxytocin and prostaglandin F_2α were observed in di- and proestrus. Minimal sensitivity to the three agonists was observed in metoestrus. Maximal contractile effects of angiotensin II, oxytocin and prostaglandin F_2α were thus observed when the ratio oestrogen/ progesterone levels was high. 2 The oestrogen-dependent sensitivity of the rat uterus is partially mediated by endogenous prostaglandins. Indomethacin suppressed the increased sensitivity to angiotensin and oxytocin present in dioestrus and proestrus but did not affect that to prostaglandin F_2α. Polyphloretin phosphate at a concentration of 10μg/ml resulted in complete identity of dioestrus and metoestrus dose-response curves to angiotensin and oxytocin. 3 Spontaneous uterine contractions observed when oestrogen levels are high are also dependent on intramural prostaglandins as they were inhibited by indomethacin and polyphloretin phosphate. In the metoestrus uterus, prostaglandin F_2α induced the reappearance of spontaneous contractions. 4 Prostaglandin F_2α had a potentiating effect on angiotensin-elicited contractions which persisted after washing out prostaglandin F_2α.