PROSTAGLANDIN-H SYNTHASE ACTIVITY IN THE SHEEP PLACENTA DURING CORTISOL-INDUCED LABOR AT 128-131 DAYS OF GESTATION AND DURING SPONTANEOUS DELIVERY AT TERM

This study investigated whether the prostaglandin H synthase (PGHS) en zyme activity of sheep fetal placental cotyledon can be induced by cor tisol at 128-131 days of gestation (dga) as compared to gestational ag e matched controls, before PGHS's normal gestational increase would oc cur (experiment 1), This study also investigated whether active PGHS i s diminished following prostanoid synthesis in the labor process (expe riment 2), A PGHS activity assay was employed in which PGE(2) product was measured under initial velocity conditions, Labor was induced befo re term by continuous infusion of 10 mg of cortisol succinate per day (day 1) followed by 15 mg per day (days 2-4, or until delivery) of cor tisol succinate administered through the fetal saphenous vein, Cotyled onary tissue was collected from sheep at term (142-145 dga), as judged by the absence of labor-type myometrial electromyogram (EMG) activity , and during cortisol induction at 128-131 dga, Tissue was also collec ted from term laboring animals immediately after fetal delivery while the fetus was still attached to the umbilicus and before placental del ivery, At 128-131 dga, cortisol had no significant effect on PGHS acti vity as compared to gestational age matched saline-infused controls; t hus, it is unlikely that cortisol directly induces PGHS, In experiment 2, normal progression of active spontaneous labor led to a significan t diminution of PGHS activity (p < 0.05) that may be partially explain ed, based on thin-layer chromatography (TLC) results, as a significant decrease in PGE(2) (p < 0.05) production coincident with a lesser com pensatory increase in PGD(2) (p = 0.06) output.