DESPITE A MASSIVE INCREASE IN CORTISOL SECRETION IN WOMEN DURING PARTURITION, THERE IS AN EQUALLY MASSIVE INCREASE IN PROSTAGLANDIN SYNTHESIS - A PARADOX

The apparent paradox that is posed by the fact that there is a simultaneous increase in the production of prostaglandin and cortisol in women during labor was studied. A paradox obtains, since in most tissues, cortisol acts to inhibit prostaglandin formation. Using previously characterized model systems for the in vitro study of arachidonic acid metabolism in amnion, decidua and myometrium, prostaglandin production by amnion and endometrial stromal cells in monolayer culture was not shown to decrease by glucocorticosteroid treatment. Prostaglandin production by myometrial smooth muscle cells in culture was inhibited by > 90% in response to dexamethasone (10-7 M) treatment. Importantly, the major prostaglandin produced by myometrium, as well as myometrial smooth muscle cells in culture, is prostacyclin, a prostaglandin that acts to cause uterine quiescence. The immunity of amnion and decidua to the action of glucocorticosteroids may allow for the accelerated production of prostaglandins E2 and F2.alpha., which act to cause myometrial contractions; simultaneously, glucocorticosteroid produced in large quantitites in women in labor may lead to decreased production of prostacyclin by myometrium, thereby reducing uterine quiescence. In this coordinated manner, the uterine contractions that culminate in delivery of the fetus may proceed uninterrupted in the face of increased cortisol production.