Effect of progesterone antagonist RU486 on uterine progesterone receptor mRNA expression, embryonic development and ovarian function during early pregnancy in pigs.

Porcine peri-implantation development and maternal recognition of pregnancy is temporally associated with down-regulation of progesterone receptor (PGR) in the endometrial epithelium on days 10 to 12 (Geisert et al. 2006). One theory for down-regulation of uterine epithelial PGR is progesterone stimulates epithelial PGRto induce expression of RANKL [receptor activator for nuclear factor-kappa B (NF-KB) ligand or TNESF11]. RANKL binds to its receptor, RANK (TNERSF11A) to activate NF-KB. NE-KB and PGR are mutually antagonistic to one another. Activation of NE-KB, therefore, may inhibit PGR expression and induce the increase in endometrial prostaglandinendoperoxide synthase 2 (PTGS2 or COX2) expression that occurs in the endometrium of cyclic and pregnant pigs on days 10 to 12. The PGRantagonist, RU486, could be usedto determine if blocking PGRdown-regulation in the uterine epithelium prevents RANKL expression and NE-KB activation. To test this hypothesis, gilts were inseminated at estrus (d 0) and assigned to one of three treatments: RU486 (400 mg/d) on d 3, 4, and 5 (T1; n = 10); RU486 on d 6 and 7 (T2; n = 9); or control (n = 9). Blood was collected daily for plasma progesterone analysis, and the uterus and ovaries were harvested after slaughter on d 8 or d 12. Endometrial total RNA was isolated and analyzed with specific primers for RANKL, PTGS2, PGR isoform B (PGR-B) or the region common to PGR isoforms A and B (PGR-AB)by real-time reverse transcriptase PCR (RTPCR).NF-KBactivation was measured by immunohistochemistry and scored objectively by three independent individuals. Gilts treated with RU486 (T1 and 12) had heavier ovaries (17.9, 19.8 and 16.1 g [SEM = 1.1]; T1, 12 and control; P < 0.05), greater average follicular diameters (5.6, 4.9 and 3.6 mm [SEM = 0.5]; P < 0.01), a tendency for a greater number of corpora lutea (16.8, 15.0 and 13.7 [SEM = 1.0]; P < 0.07) and greater mid-cycle plasma progesterone concentration (25.2, 28.0 and 20.6 ng/mL; P < 0.05; d 9 to 11). Uterine weight (g) was reduced (P < 0.05) for T1 (608 ± 46) compared with T2 (780 ± 49) or control (785 ± 44). Treatment of giRswith RU486 affected early embryonic development. The proportion of gilts with normal early embryonic development was lowest for gilts in T1 (chi-square= 11.2; P < 0.01; Table 1). There was a treatment effect (P < 0.01) on log-transformed RANKL mRNA expression (fold change relative to internal assaycontrol) because compared with the control gilts, RANKL expression was greater in T1 (d 8 and d 12) and greater in T2 on d 12. Treatment affected both endometrial PGR-B (P < 0.0W) and PGR-AB (P < 0.001) mRNA abundance. The PGR-BmRNA was more abundant in T1 (9.1 ± 1.0) compared with control (3.1+ 1.0) with mRNA expression intermediate (6.0 ± 1.0) for T2 pigs. Likewise, the