Effect of estrus induction on prostaglandin content and prostaglandin synthesis enzyme expression in the uterus of early pregnant pigs.

Prostaglandins (PGs) play a pivotal role in maternal recognition of pregnancy and implantation in pigs. In the present study, PGE(2), PGF(2alpha), and PGFM (PGF(2alpha) metabolite) content, as well as PGE(2) synthase (mPGES-1) and PGF(2alpha) synthase (PGFS) expression was investigated in early pregnant gilts with natural (n=21) and PMSG/hCG-stimulated (n=19) estrus. Endometrial tissue samples, uterine luminal flushings (ULFs), and blood serum were collected on days 10-11, 12, and 15 after insemination. Additionally, day 15 conceptuses were collected for mPGES-1 and PGFS protein expression. Effect of estrus induction was observed on day 15 of pregnancy, when the content of PGE(2) in the uterine lumen was fourfold lower in gonadotropin-stimulated gilts in comparison to controls (P<0.001). Decreased PGE(2) content in ULFs of gonadotropin-treated pigs was preceded by lower endometrial mPGES-1 gene expression in hormonally-stimulated animals in comparison to control gilts (P<0.01). On the other hand, estrus induction with PMSG/hCG resulted in higher PGE(2) accumulation in the endometrial tissue on day 15 of pregnancy (P<0.01). Furthermore, PGF(2alpha) content in the endometrium and PGFM levels in blood serum were lower in gonadotropin-treated gilts, especially on day 12 after insemination when compared to control gilts (P<0.01). Finally, PGFS expression in day 15 conceptuses was decreased in animals with hormonally-induced estrus. We conclude that PMSG/hCG stimulation of prepubertal gilts to induce estrus results in changes of PG production and secretion during early pregnancy, which, in turn, may affect conceptus development, implantation, and the course of pregnancy.