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

Prostaglandin production by intra-uterine tissues from periparturient sheep: use of a superfusion technique

A technique for the continuous superfusion of small tissue samples in vitro has been applied to the study of prostaglandin production by ovine intra-uterine tissues. Basal and oxytocin-stimulated production of prostaglandins was studied at 120-125 days of pregnancy and after dexamethasone-induced delivery. In general, the relative rate of prostaglandin production by tissues was: foetal cotyledon=maternal cotyledon>myometrium and in quantitative order the prostaglandins produced were prostaglandin E (PGE)>prostaglandin F (PGF)=13,14-dihydro-15-oxo-prostaglandin F (PGFM). Considerable variation was found between the rates of prostaglandin production in individual sheep. Oxytocin had no effect on the production of prostaglandins by tissues obtained before labour but myometrium and maternal cotyledon obtained at delivery exhibited a significant increase in production of PGE and PGF (though not PGFM) in response to oxytocin. Administration of arachidonic acid increased the production of PGE and PGF by the foetal cotyledon