The expression of cytosolic phospholipase A2 and prostaglandin endoperoxide synthase in ovine maternal uterine and fetal tissues during late gestation and labor

Gene expression of cytosolic phospholipase A2 (cPLA2) and prostaglandin endoperoxide synthase (PGHS) 1 and 2 was studied in ovine maternal uterine and fetal tissues during glucocorticoid induced premature labor and spontaneous labor and compared with gestational age matched controls not in labor. Northern blot analysis demonstrated that the messenger RNA (mRNA) abundance of cPLA2 and PGHS-2, but not PGHS-1, increased significantly in the endometrium during both glucocorticoid induced premature labor and spontaneous labor. Protein levels of the two enzymes measured by Western blot analyses were also elevated in the endometrium during glucocorticoid induced premature labor. cPLA2 mRNA was detected in the myometrium, but no difference was observed between ewes in labor and their gestational age matched controls not in labor. While the level of PGHS-2 mRNA was below detection in the myometrium with the methods used, the enzyme protein for PGHS-2 in the myometrium was significantly increased in both glucocorticoid induced premature labor and spontaneous labor. Using immunocytochemical methods, PGHS-2 enzyme protein was identified in the endometrial gland epithelial cells and myometrial cells. PGHS-2 mRNA was also detected in the ovine fetal cotyledons in which no differences for PGHS-2 mRNA existed between tissues collected from ewes in labor and ewes not in labor. In contrast, there were no detectable signals for cPLA2 or PGHS-2 mRNA in either amnion or chorion. We conclude that the ovine endometrium and myometrium, but not fetal membranes, are important tissue sites of prostaglandin biosynthesis involved in the process of ovine parturition.