Molecular cloning and gonadotropin-dependent regulation of equine prostaglandin F2α receptor in ovarian follicles during the ovulatory process in vivo

The progressive rise in gonadotropins prior to ovulation triggers a marked increase in intrafollicular levels of prostaglandin F2α(PGF2α), which is known to interact with PGF2α receptor (FP). Little is known about the regulation of FP during ovulation. This study was undertaken to characterize the equine FP and its gonadotropin-dependent regulation in preovulatory follicles prior to ovulation. The full-length equine FP encodes a 366-amino acid protein that is 82-93% homologous to other species. Using semi-quantitative RT-PCR/Southern blot, we showed that FP mRNA expression was low in follicles obtained before hCG treatment (0 h) and at 24, but increased at 12 and 36 h post-hCG (P < 0.05). This expression was regulated in both follicular cells, with high levels of the transcript at 33 and 36 h post-hCG in granulosa cells, and at 12, 30 and 33 h post-hCG in theca cells (P < 0.05). Immunohistochemistry confirmed the induction of FP protein in both follicular cells after hCG, and immunoblotting revealed the increase of FP protein in preovulatory follicles 36 h post-hCG. High levels of FP mRNA were detected in the corpora lutea and heart, but very low or undetectable in other tissues. This study reports for the first time the expression of FP and its up-regulation by hCG in preovulatory follicles prior to ovulation. FP regulation was occurred in different pattern than that observed in other species, suggesting a distinct and species-specific follicular control of FP expression during ovulation, and a potential involvement of PGF2α, acting on granulosa and theca cells, in the ovulatory process.