Use of meclofenamic acid to investigate the role of prostaglandin biosynthesis during induced parturition in sheep.

The maternal administration of meclofenamic acid (a prostaglandin synthetase inhibitor) to pregnant sheep prevented the dexamethasone-induced delivery of live lambs and delayed delivery after foetal death in utero. Administration of meclofenamic acid had no effect on the changes in the levels of progesterone and oestrogen in the plasma which occur before lambing in response to foetal glucocorticoid. Despite normal maternal endocrine changes, increased uterine activity did not occur at the expected time, although it could be elicited by vaginal distension or by administration of oxytocin. The rates of cervical ripening and dilatation were reduced by meclofenamic acid and lambing was frequently associated with some degree of cervical dystocia. Withdrawal of meclofenamic acid did not immediately result in an increase in the level of prostaglandin F in the plasma despite the appearance of co-ordinated uterine contractions; the concentration of prostaglandin in the plasma was not raised until vaginal passage of the lambs. It is concluded that the synthesis or release of prostaglandins mediates the effects of changes in the levels of steroids in the maternal plasma on uterine contractility in sheep.