Discussion of Session on Prostaglandins in Female Reproductive Physiology

The effects of prostaglandins (PGs) on the ovary are contradictory; in vivo studies with PGF2alpha have shown evident luteolytic effects, while in vitro studies have shown that PGs are usually steroidogenic. It is difficult to reconcile these differences, and a clearer understanding of the mechanism of action of PGs is needed. How PGs work in the induction of labor or for abortion is not very clear. The most simple explanation would indicate a direct muscle stimulating effect. While there is evidence that plasma progestin and estrogen levels are unchanged during PG infusion during delivery at term, there is some suggestion that the mechanism in early pregnancy may be related to an effect on the corpus luteum. Initial studies indicate that plasma progestin level during PG infusion for the induction of abortion does not change until after passage of the placenta; on the other hand it has been found that plasma estrogen levels consistently drop during infusion, especially with high doses of PGs. Also, it is doubtful whether PGs induce oxytocin secretion or enhance the effect of endogenous or administered oxytocin. PGs will induce labor, but it is still not known whether there are any advantages over oxytocic preparations in terms of efficiency. There are 3 major areas of investigation on PGs which require a concentrated effort: 1) the development of a sensitive and specific assay which would allow the measurement of endogenous levels of PGs, 2) clearer ideas about doses and systems of delivery, and 3) the safety level of the drug.