Potential involvement of EGF-like growth factors and phosphodiesterases in initiation of equine oocyte maturation

Human chorionic gonadotropin (hCG) was administered to mares in estrus with large, dominant ovarian follicles to initiate follicular and oocyte maturation. Follicular contents were collected at 0, 2, 4 and 6 h after hCG. Epiregulin, amphiregulin and phosphodiesterase (PDE) mRNA contents of granulosa cells (PDE 4D) were determined by reverse transcription and real-time PCR; PDE 3A mRNA content of single oocytes was determined similarly. Copy numbers of mRNA did not increase for PDE 3A or 4D over the time interval studied. Amounts of epiregulin and amphiregulin mRNA were correlated (r = 0.98) when log transformed. Epiregulin and amphiregulin mRNA increased (P < 0.01) from controls by 4 h after hCG administration, with amphiregulin increasing (P < 0.01) by 2 h after hCG administration. Epiregulin and amphiregulin mRNA levels remained elevated (P < 0.01) at 6 h after hCG. These results indicate that EGF-like growth factors are likely paracrine mediators of the LH signal in the horse.