RFamide-related peptide 3 signaling via neuropeptide FF receptor stimulates prolactin secretion in female rats.

The RF-amide peptides comprise a family of neuropeptides that includes the kisspeptin (Kp), the natural ligand of kisspeptin receptor (Kiss1r), and the RFamide-related peptide 3 (RFRP-3) that binds preferentially to the neuropeptide FF receptor 1 (Npffr1). Kp stimulates prolactin (PRL) secretion through the inhibition of tuberoinfundibular dopaminergic (TIDA) neurons. Because Kp has also affinity to Npffr1, we investigated the role of Npffr1 in the control of PRL secretion by Kp and RFRP-3. Intracerebroventricular (i.c.v.) injection of Kp increased PRL and luteinizing hormone (LH) secretion in ovariectomized, estradiol-treated rats (OVX+E). The unselective Npffr1 antagonist RF9 prevented these responses, whereas the selective antagonist GJ14 altered PRL but not LH levels. The i.c.v. injection of RFRP-3 in OVX+E rats increased PRL secretion, associated with a rise in the dopaminergic activity in the median eminence, and had no effect on LH levels. The RFRP-3-induced increase in PRL secretion was prevented by GJ14. Moreover, the estradiol-induced PRL surge in female rats was blunted by GJ14, alongside the amplification of the LH surge. Nevertheless, whole-cell patch clamp recordings showed no effect of RFRP-3 on the electrical activity of TIDA neurons in dopamine transporter-Cre recombinase transgenic female mice. We provide evidence that RFRP-3 binds to Npffr1 to stimulate PRL release, which plays a role in the estradiol-induced PRL surge. This effect of RFRP-3 is apparently not mediated by a reduction in the inhibitory tone of TIDA neurons but possibly involves the activation of a hypothalamic PRL-releasing factor.