INDUCTION OF PROSTAGLANDIN ENDOPEROXIDE SYNTHASE ISOFORM-2 IN OVINE COTYLEDONARY TISSUES DURING LATE-GESTATION

The present study was designed to characterize the developmental patte rn of specific prostaglandin endoperoxide synthase (PGS) isoform immun oreactivity and activity in tissues of fetal origin during the last ha lf of gestation in sheep. Fetal amnion, allantochorion, and cotyledons were collected under halothane general anesthesia on days 79-80, 105- 108, 120-122, 128-131, and 140-145 (term) of pregnancy. Solubilized ex tracts were prepared and analyzed by immunoblots using anti-PGS antibo dies previously shown to recognize PGS isoform-1 and -2 (PGS-1 and PGS -2). PGS activity from cotyledon microsomes was assayed by the measure ment of prostaglandin E2 (PGE2) production under All fetal tissues con tained PGS-1 at each of the stages of gestation examined, with minimal regulation of this isoform from 79-144 days gestation. In contrast, P GS-2 increased gradually in the cotyledons from 120-139 days gestation , with the most marked expression observed at term. PGS-2 was not dete cted in amnion or allantochorion. PGS activity in cotyledons increased (P < 0.01) in parallel with immunoreactive PGS-2 levels; indicating t hat PGS-2, rather than PGS-1, is associated with increased PG synthesi s in this tissue. Both the activity (n = 5/group) and the amount of PG S-2 increased significantly from 105-108 days gestation to term (P < 0 .01). We conclude that the increase in PGS that occurs at term in shee p is predominantly active PGS-2 localized to fetal cotyledons.