Factors affecting steroid and prostaglandin secretion by reproductive tissues of cycling and pregnant sows in vitro.

The secretion of prostaglandin E2 and prostaglandin F2 alpha by endometrial and corpus luteum tissues of cycling and pregnant sows in vitro has been measured and the effects of arachidonic acid and steroids on prostaglandin secretion studied. In general, both types of tissues in vitro exhibited a gradually increasing capacity to secrete prostaglandin as the cycle progressed, although the most significant increase was in prostaglandin F2 alpha secretion. An inverse relationship between prostaglandin and progesterone secretion was observed, and, while indomethacin inhibited prostaglandin secretion, it was without effect on progesterone. A much lower capacity for prostaglandin secretion was observed with tissues from pregnant sows. Prostaglandin secretion by endometrial and corpus luteum tissues of the cycle were stimulated by exogenous arachidonic acid which also stimulated prostaglandin E2 secretion in pregnant sows. This clearly suggests that phospholipase A2 activity which controls substrate availability is of considerable importance in pig reproductive tissues. The effects of steroid hormones on prostaglandin secretion by pig reproductive tissues was more complex although in general oestradiol appeared to be inhibitory while progesterone was stimulatory.