Human oviductal gonadotropin-releasing hormone: possible implications in fertilization, early embryonic development, and implantation.

The oviduct is host to gametes and early embryos at a critical point in their lives. It is clear that the interactions of gametes/early embryo with the maternal oviduct in an autocrine and paracrine manner provide a microenvironment that enhances fertilization, early embryonic development, and implantation. Moreover, there is considerable evidence that an extrahypothalamic GnRH may play a substantial role as a molecular autocrine/paracrine regulator in these events. Gametes and preimplantation embryos express GnRH and GnRH receptor at both messenger ribonucleic acid (mRNA) and protein levels. However, whether GnRH is produced by the human oviduct has not yet been demonstrated. We used RT-PCR and immunohistochemical techniques to investigate GnRH mRNA and protein expression in human fallopian tubes throughout the menstrual cycle of premenopausal fertile patients. Our results, at both the mRNA and protein levels, revealed cycle-dependent production of an oviductal GnRH with expression during the luteal phase. Moreover, GnRH immunostaining was localized in the tubal epithelium during the luteal phase. On the basis of these data, we suggest that during reproductive life, oviductal GnRH may play a substantial paracrine/autocrine role in human fertilization, early embryonic development, and implantation.