Sex steroids enhance endotoxin-stimulated phospholipase A2 activity in hum endometrial cells.

Growing evidence suggests an association between intra-amniotic infection and preterm labor. We recently demonstrated that some factor(s) including endotoxin produced by the organism stimulated endogenous phospholipase A2 resulting in liberation of arachidonic acid and prostaglandin formation (Takahashi et al. 1988). The studies presented in this report were designed to evaluate whether ovarian steroids alter activity of the phospholipase A2 responsive to endotoxin. Exposure of human endometrial proliferative- or secretory-phases epithelium to endotoxin from Escherichia coli increased the level of lysophosphatidylcholine (lyso-PC) by 15- and 25-fold, respectively. When the endometrial cells were preincubated with progesterone alone or progesterone and estradiol-17 beta for 16 h, the increase of lyso-PC by endotoxin was enhanced by approximately 1.5-fold. Progesterone showed a stimulatory effect on the response of phospholipase A2 to bacterial endotoxin in endometrial cells. These observations may explain the mechanism(s) by which preterm or term labor associated with intra-amniotic infection is initiated.