The role of gonadotropin-releasing hormone in murine preimplantation embryonic development

Previous studies have established the presence of an extrahypothalamic GnRH in a variety of tissues. GnRH receptor is known to be present in the place nta, which produces and secretes the decapeptide from the very early stages of placentation. We hypothesized that GnRH may play a role in the preimpla ntation development of embryos. To examine this hypothesis, we assessed GnR H and GnRH receptor messenger RNA (mRNA; RT-PCR) and protein expression (Im munohistochemistry) in preimplantation murine embryos at various developmen tal stages. Furthermore, preimplantation murine embryos were cultured with GnRH agonist and antagonist in vitro to assess the influence of GnRH analog s on embryo development. GnRH is expressed in the developing mouse embryo f rom morula to hatching blastocyst stages at the mRNA and protein levels. Gn RH receptor mRNA is also present in the developing embryos studied. Preimpl antation embryonic development was significantly enhanced by incubation wit h increasing concentrations of GnRH agonist and is significantly decreased by GnRH antagonist compared with that in the control group. Moreover, GnRH antagonist (5 and 10 mu M) was able to completely block embryo development. The deleterious effect of GnRH antagonist on embryo development was revers ed by increasing concentrations of the agonist, as determined by the number of embryos reaching the blastocyst stage.