Regulation of endometrial fibroblast growth factor 7 (FGF-7) and its receptor FGFR2IIIb in gilts after sex steroid replacements, and during the estrous cycle and early gestation.

The aim of this study was to characterize the effect of ovarian steroids and early gestation on the expression of fibroblast growth factor 7 (FGF-7) and its receptor (FGFR2IIIb) in the porcine endometrium. In Experiment 1, gilts were ovariectomized (OVX) on day 10 of the estrous cycle and treated thereafter with vehicle (VEH), progesterone (P4), estradiol benzoate (EB), or P4+EB. Days 12 and 20 cyclic gilts (C12 and C20) were used to determine the influence of physiologically low and high plasma estradiol and progesterone concentrations on their expression. In Experiment 2, the expression of FGF-7 and FGFR2IIIB was characterized on days 1 (G 1) and 12 (G 12) of gestation. FGF-7 and FGFR2IIIb mRNA were quantified by quantitative real-time RT-PCR, and localization of FGF-7 protein in steroid-treated and early pregnant gilts was performed by immunohistochemistry. VEH-gilts expressed both FGF-7 and FGFR2IIIB mRNA. We found a significant effect of EB, but no effects of P4 or P4+EB on the mRNA expression of FGF-7. FGFR2IIIb mRNA significantly decreased after the EB and combined P4+EB treatments, compared to P4 only substituted animals. Day 12 cyclic gilts showed significantly higher FGF-7 and FGFR2IIIb mRNA expression compared with day 20 gilts. Between day 1 and 12 of gestation, FGF-7 mRNA expression differed highly while FGFR2IIIb transcripts only varied significantly. FGF-7 protein was localized in endometrial epithelia, vascular smooth muscle, and the endothelium of different types of blood vessels. Staining was weak in VEH and P4 treated gilts, whereas it was prominent following EB and P4+EB. FGF-7 antibody strongly stained the luminal epithelium on day 12 of gestation. In summary, FGF-7 and FGFR2IIIb mRNA expression is regulated differently by exogenous ovarian steroids, assuming progesterone in connection with a specific amount of 17beta-estradiol, whereas the receptor seems to be inhibited by estradiol. Both transcripts coordinately increased during the progesterone dominated phase on day 12 both in cyclic and early pregnant gilts. We conclude that estradiol and progesterone are involved in the regulation of this ligand-receptor system, which might have an important role in preparing endometrial tissue for implantation in gilts.