Regulation of prostacyclin synthase expression and prostacyclin content in the pig endometrium

Prostaglandins (PGs) are critical regulators of a number of reproductive processes, including embryo development and implantation. In the present study, prostacyclin (PGI(2)) synthase (PGIS) mRNA and protein expression, as well as 6-keto PGF(1α) (a PGI(2) metabolite) concentration, were investigated in the pig uterus. Endometrial tissue and uterine luminal flushings were obtained on Days 4 to 18 of the estrous cycle and pregnancy. Additionally, conceptuses were collected and examined for PGIS mRNA expression and 6-keto PGF(1α) concentration. Regulation of PGI(2) synthesis in the porcine endometrium by steroids, conceptus products, and cytokines was studied in vitro and/or in vivo. Endometrial PGIS protein level increased on Days 12 and 16 in pregnant but not in cyclic gilts. Moreover, higher PGIS protein expression on Day 12 of pregnancy was accompanied by a greater content of 6-keto PGF(1α) in the endometrium. The concentration of 6-keto PGF(1α) in uterine luminal flushings increased substantially on Days 16 and 18 in pregnant gilts and was higher than in cyclic animals. Greater PGIS mRNA expression and PGI(2) metabolite concentration were detected in Day 12 and 14 conceptuses, respectively. Incubation of endometrial explants with conceptus-conditioned medium resulted in upregulation of PGIS protein expression and increased PGI(2) secretion. Moreover, PGIS mRNA and protein expression were upregulated in the endometrium collected from gravid uterine horn on Day 14 of pregnancy. In summary, PGIS is differentially expressed in the endometrium of cyclic and pregnant gilts resulting in higher PGI(2) synthesis in pregnant animals. Porcine conceptuses are important regulators of endometrial PGIS expression and PGI(2) release during the implantation period.