The present study was designed to characterize the developmental pattern of specific prostaglandin endoperoxide synthase (PGS) isoform immunoreactivity and activity in tissues of fetal origin during the last half of gestation in sheep. Fetal amnion, allantochorion, and cotyledons were collected under halothane general anesthesia on days 79-80, 105108, 120-122, 128-131, and 140-145 (term) of pregnancy. Solubilized extracts were prepared and analyzed by immunoblots using anti-PGS antibodies previously shown to recognize PGS isoform-1 and -2 (PGS-1 and PGS-2). PGS activity from cotyledon microsomes was assayed by the measurement of prostaglandin E2 (PGE2) production under initial velocity conditions. All fetal tissues contained PGS-1 at each of the stages of gestation examined, with minimal regulation of this isoform from 79-144 days gestation. In contrast, PGS-2 increased gradually in the cotyledons from 120-139 days gestation, with the most marked expression observed at term. PGS-2 was not detected in amnion or allantochorion. PGS activity in cotyledons increased (P < 0.01) in parallel with immunoreactive PGS-2 levels; indicating that PGS-2, rather than PGS-1, is associated with increased PG synthesis in this tissue. Both the activity (n = 5/group) and the amount of PGS-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 sheep is predominantly active PGS-2 localized to fetal cotyledons.
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