Effects of prostaglandin inhibitors on angiotensin, oxytocin and prostaglandin F2 alpha contractile effects on the rat uterus during the oestrous cycle.

1 In the rat isolated uterus maximal spontaneous contractions and maximal sensitivity to angiotensin II, oxytocin and prostaglandin F(2alpha) 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(2alpha) 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(2alpha). Polyphloretin phosphate at a concentration of 10 mug/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(2alpha) induced the reappearance of spontaneous contractions.4 Prostaglandin F(2alpha) had a potentiating effect on angiotensin-elicited contractions which persisted after washing out prostaglandin F(2alpha).