Porcine trophoblast attachment to the uterine surface is associated with increased conceptus and endometrial production of prostaglandins. Conceptus secretion of estrogen on Day 12 of gestation is important for establishment of pregnancy; however, early (Days 9 and 10) exposure to exogenous estrogens results in embryonic mortality. Present studies established the temporal and spatial pattern of endometrial PTGS1 (prostaglandin-endoperoxide synthase 1) and PTGS2 expression during the estrous cycle and early pregnancy and determined the effect of early estrogen treatment on endometrial PTGS expression in pregnant gilts. Endometrial PTGS1 mRNA expression increased 2- to 3-fold after Day 10 of the estrous cycle and pregnancy, whereas PTGS2 mRNA expression increased 76-fold between Days 5 and 15 of the estrous cycle and pregnancy. Increased expression of the PTGS2 transcript was detected in the lumenal epithelium after Day 10 in both cyclic and pregnant gilts. There was a 10- and 20-fold increase in endometrial PTGS2 protein expression between Days 5 and 18 of the estrous cycle and pregnancy respectively. Administration of estrogen on Days 9 and 10 of gestation increased endometrial PTGS2 mRNA and protein on Day 10, but decreased PTGS2 mRNA and protein in lumenal epithelium (LE) on Day 12 of gestation compared to vehicle-treated gilts. The present study demonstrates that an increase in uterine epithelial PTGS2 expression occurs after Day 10 of the estrous cycle and early pregnancy in the pig. The conceptus-independent increase in the uterine LE indicates that a novel pathway exists for endometrial induction PTGS2 expression before conceptus elongation and attachment to the uterine surface. Epithelial expression of PTGS2 may serve as one of the signals for placental attachment and embryo survival in the pig. Early administration of estrogen on Days 9 and 10 of pregnancy alters endometrial PTGS2 mRNA and protein expression, which may, at least in part, represent a mechanism by which endocrine disruption of pregnancy causes total embryonic loss during implantation in the pig.
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