Quantitative Gonadotropin-Releasing Hormone: DISCUSSION(1)
We have shown for the first time that both GnRH and its receptor are expressed at the mRNA level in vivo by the human endometrium throughout the entire menstrual cycle of fertile patients. Isolated endometrial stromal and epithelial cells expressed both GnRH and its receptor, with greater GnRH mRNA expression in stromal cells compared to epithelial cells during proliferative phase. However, increased epithelial expression of GnRH mRNA occurred during the luteal phase. This is consistent with the immunohistochem-ical data, which showed affinity-purified antibody to GnRH bound to the endometrial stroma of each section of every patient studied both in the follicular and luteal phases of the menstrual cycle, with the most intense reactivity in the luteal phase. We also localized the GnRH staining to both the glandular and luminal epithelium, with increased signal in the luteal phase.
Human implantation is a complex series of steps that under normal circumstances begins even before the blastocyst reaches the uterine cavity and attaches to the endometrial epithelium after the loss of zona pellucida. In order to complete this series of events and to accomplish successful implantation and placentation, the embryo and the uterine endometrium must be synchronized during this limited period of uterine receptivity known as the ‘‘window of implantation”.