BackgroundCyclooxygenases (COXs) are the rate limiting enzymes in the process of prostaglandins (PGs) synthesis, which are critical regulators of a number of reproductive processes, including ovulation, implantation, decidualization and parturition. The aim of the present study was to investigate the expression and regulation of COX-1 and COX-2 and levels of prostaglandins during rat pregnancy, in a model of pseudopregnancy and estrous cycle.MethodsUteri were collected from the cyclic rats on each day of estrous cycle, after every two days for pregnant (days 2 to 22) and pseudopregnant rats (days 1 to 9). In vitro primary endometrial stromal cells were cultured in the presence of steroid hormones and their respective inhibitors for the possible modulation of COX-1 and COX-2. Endometrial protein extracts were used for western blot analysis and tissue sections were prepared for protein localization using immunofluorescence. Measurements of PGF2alpha and PGE2 metabolites in serum were performed by enzyme immunoassay (EIA).ResultsCOX-1 expression was found to be elevated during implantation and parturition, however, the levels of COX-1 decreased during decidualization periods. COX-2 was detected during early pregnancy from day 2 to 5, increased during decidual regression, and was also expressed at the time of parturition. COX-2 protein expression was found to be increased at estrus phase in cyclic rats. Both enzymes were found to be modulated in the endometrium of pseudopregnant rats, suggesting that they are regulated by 17beta-estradiol and progesterone. A significant increase in PGE2 metabolite levels was observed on day 10, 12 and 14 of pregnancy. However, an increase in PGF2alpha metabolite levels was observed only on day 14. The concentration of both these metabolites changed during pseudopregnancy and maximum levels were observed at day 7. Significant increase in PGE2 metabolite was observed at proestrus phase, on the other hand, PGF2alpha metabolite was significantly increased at proestrus and metestrus phase. COX-2 protein was regulated by 17beta-estradiol in cultured endometrial stromal cells which was blocked in the presence of ICI-182,780.ConclusionsTaken together, these results suggest that COX-1 and COX-2 could be differentially regulated by steroid hormones and might be the key factors involved in embryo implantation, decidualization, decidua basalis regression and parturition in rats.

Prostaglandins (PGs) are critical regulators of a number of reproductive processes. To date, the presence and regulation of PGS in the rat endometrium have not yet been described. The objective of the present study was to investigate the expression of PGD synthase (PGDS) and prostacyclin synthase (PGIS) in the endometrium. Endometrial proteins and tissues were collected from cyclic non-pregnant, pregnant, and steroid-induced pseudopregnant rats. PGIS and PGDS were detected in the endometrium of cyclic, pregnant, and pseudopregnant rats but were not influenced by the estrous cycle. During early pregnancy, PGIS was significantly higher at day 5 and was gradually decreased from day 5 . 5 to 6 . 5. Later during pregnancy, PGIS was maximal on day 12 and gradually decreased to the end of pregnancy. PGDS expression was high during early and was maximal at the end of pregnancy. During pseudopregnancy, PGDS and PGIS were increased in a time-dependent manner and were maximal at day 5. Immunohistochemical analysis revealed that PGDS and PGIS were found in luminal as well as glandular epithelial cells and in stroma during late pregnancy. We also found a significant increase of PGD 2 serum metabolite at days 21 and 22 of pregnancy. During steroidinduced pseudopregnancy, PGI 2 serum metabolite was increased in a time-dependent manner and was maximal at day 7. These results suggest that PGDS and PGIS are present and could be regulated by steroids in the rat uterus during pregnancy, and that the endometrium could be a significant source of PGD 2 and PGI 2 at specific times during pregnancy.

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