Abstract
Disclosure: A. Lomniczi: None. M. Appleman: None. H.F. Urbanski: None. It has been known for many years that rhesus macaques express two forms of gonadotropin-releasing hormone (GnRH-I and GnRH-II) in the medial basal hypothalamus (MBH), and that both forms are capable of stimulating the release of luteinizing hormone (LH) in vivo. However, while much has been published about the role of GnRH-I in reproduction, very little is known about the function of GnRH-II. To shed light on this issue, we studied the expression pattern of these two genes in different parts of the monkey hypothalamus, median eminence and pituitary gland. Quantitative PCR (qPCR) analysis revealed that while GnRH-I is preferentially expressed in the Arcuate Nucleus (ARC), Median Eminence (ME), Supraoptic Nucleus (SON) and Suprachiasmatic Nucleus (SCN); GnRH-II was highly expressed in the SON, ARC-ME and Paraventricular Nucleus (PVN), confirming our previously published in situ hybridization studies. Strikingly, GnRH-II mRNA was also detected in the pituitary gland, a site where GnRH-I was not found. We have previously demonstrated that maximum hypothalamic GnRH-II expression occurs around the time of the preovulatory LH surge, when estrogen (E2) levels are maximal, but no significant changes in GnRH-I mRNA levels occur. Here using an ovariectomized (OVX) macaque model subjected to E2 replacement paradigm, designed to mimic the plasma E2 levels observed during the preovulatory estradiol peak, we performed RNAseq and qPCR from the PVN and pituitary gland to identify genes differentially regulated by E2. While GnRH-I mRNA was not affected by E2 treatment in any of the tissues studied, pituitary GnRH-II expression highly correlated with estrogen levels (r>0.8; p<0.01), with over a hundred-fold increase in mRNA expression. Taken together, these data suggest that pituitary GnRH-II (but not GnRH-I) gene expression is induced by a positive feedback action of estradiol. This novel finding raises the possibility that GnRH-II plays a major role in triggering the preovulatory LH surge in primates, not only at the ARC-ME but also at the pituitary level. Presentation Date: Saturday, June 17, 2023