RFamide-related peptide-3 (RFRP-3) has been acknowledged as the mammalian ortholog of avian gonadotrophin-inhibitory hormone (GnIH), which is a major suppressive neuropeptide of the avian reproductive system. Previous studies have shown that central administration of RFRP-3 induced a net decrease in the mean circulating levels of luteinizing hormone (LH) in rats. However, the physiological role played by RFRP-3 in the control of gonadotrophin-releasing hormone (GnRH) pulse generator frequency remains to be fully elucidated. Furthermore, psychological stress increases hypothalamic expression of RFRP in rats1. Myriad stressors, including psychogenic, suppress the pulsatile release of GnRH/LH via corticotrophin-releasing factor (CRF)2. We hypothesise that RFRP-3 mediates stress-induced suppression of the GnRH pulse generator via CRF mediated mechanisms. Since endogenous opioid peptides (EOPs) are also involved in basal and stress-induced suppression of pulsatile LH release, we will test the hypothesis that EOPs mediate the effects of RFRP-3 on LH pulses. Adult female rats were ovariectomised (OVX) and chronically implanted with intracerebroventricular (icv) cannulae and cardiac catheters. Serial blood samples (25 µl) were taken every 5 min for 6 h for measurement of LH. Central administration of rat RFRP-3 induced a dose-dependent inhibition of LH pulse frequency. Antagonism of RFRP-3 receptors (GPR147) with icv administration of RF-9 blocked the effects of RFRP-3 on LH pulses. RF-9 also partially blocked CRF and stress (lipopolysaccharide or restraint) induced inhibition of pulsatile LH secretion. Furthermore, RFRP-3 induced suppression of LH pulse frequency is partially blocked by the µ-opioid receptor antagonist naloxone, but not by selective kappa- or delta-receptor antagonists. In conclusion, RFRP-3 suppresses pulsatile LH release in female rats and this effect may involve, at least in part, EOPs. Furthermore, RFRP-3 plays an important role in stress-induced suppression of pulsatile LH release.