The involvement of oxytocin in ovulation and in the outputs of cyclo-oxygenase and 5-lipoxygenase products from isolated rat ovaries

The effects on ovulation of a specific anti-oxytocin rabbit serum (anti-OT) (50.0 μl) given by intrabursal injection into the right ovaries of etherized adult female rats at proestrus, were explored by counting the number of ovulated ova present within the right oviducts. Left ovaries were not treated and served as control ovaries. Control rats were treated with male normal rabbit serum (NRS) (50.0 μl) given by intrabursal injections into the right ovaries of animals at proestrus. Ovulation was induced by injection of human chorionic gonadotrophin (hCG). Anti-OT administered into the right ovarian bursae of proestrous rat ovaries evoked a significant 51% inhibition of ovulation in comparison with that observed in control non-injected left ovaries (p<0.01). Also, when the ovulation of right ovaries injected with anti-OT was compared with that of left ovaries injected with NRS, the number of ovulated ova in the right side was significantly smaller (30%) than on the contralateral side (p<0.02). However, in rats pre-treated with hCg the intrabursal injection of oxytocin (OT) (50.0 mU/ml) into right and left ovaries failed to alter the number of ovulated ova compared with that of rats receiving intrabursal injections of saline. The basal control and the OT-evoked synthesis and release of endogenous prostaglandin E2 (PGE2) and PGF2α were explored in ovaries isolated from prepuberal rats injected with pregnant mare's serum gonadotrophin (PMSG), two days prior to sacrifice. OT augmented the basal release of PGF2α but did not influence that of PGE. Moreover, the conversion of exogenous 14C-arachidonic acid (214C-AA) into different prostanoids and into 5-HETE, in the presence and in the absence of added OT (50.0 mU/ml), was studied in rat ovaries isolated in proestrus. The challenge with OT augmented the basal synthesis and release of PGF2α and of 5-HETE from 14C-AA, but failed to influence the formation of products generated via the cyclo-oxygenase pathway, namely 6-keto-PGF1α, PGE2 and thromboxane B2 (TXB2). Therefore, the present results suggest that ovarian OT may play a role in the ovulatory process, via generation of PGF2α to enhance contractions of ovarian smooth muscle and of 5-HETE to promote follicular collagenolysis.