GnRH mRNA and protein expression in human preimplantation embryos

Gonadotrophin-releasing hormone (GnRH) regulates gonadotrophin biosynthesis and release in the anterior pituitary via specific receptors. Extrapituitary expression and action of GnRH have been demonstrated in several species. A possible role for GnRH in preimplantation embryonic development, endometrial preparation, and the implantation process has been previously suggested. Moreover, the presence of an immunoreactive GnRH in preimplantation embryos has been demonstrated in different species; however, there are no data for human embryos. We postulate that in humans GnRH may play a role in preimplantation embryonic development as well as in the implantation process. To examine this hypothesis, we assessed GnRH and GnRH-receptor mRNA and protein expression in human preimplantation embryos with three pronuclei. GnRH is expressed in peri-implantation human embryos at both the mRNA and protein level. GnRH-receptor mRNA is also present in the embryos studied. Immunohistochemical localization of GnRH showed intense staining in all the blastomeres at morula stage as well as in the trophectoderm and inner cell mass of the blastocysts. The results of the present study challenge the widely held view that GnRH has a predominantly central action, and suggests a pathway to describe a local role for the GnRH system in successful preimplantation embryonic development and implantation.