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. Extrapituita ry expression and action of GnRH have been demonstrated in several species. A possible role for GnRH in preimplantation embryonic development, endomet rial preparation, and the implantation process has been previously suggeste d. Moreover, the presence of an immunoreactive GnRH in preimplantation embr yos 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 prei mplantation embryonic development as well as in the implantation process. T o examine this hypothesis, we assessed GnRH and GnRH-receptor mRNA and prot ein expression in human preimplantation embryos with three pronuclei. GnRH is expressed in peri-implantation human embryos at both the mRNA and protei n level. GnRH-receptor mRNA is also present in the embryos studied. Immunoh istochemical localization of GnRH showed intense staining in all the blasto meres at morula stage as well as in the trophectoderm and inner cell mass o f the blastocysts. The results of the present study challenge the widely he ld view that GnRH has a predominantly central action, and suggests a pathwa y to describe a local role for the GnRH system in successful preimplantatio n embryonic development and implantation.