The neuropeptide kisspeptin and its receptor, KiSS1R, govern the reproductive timeline of mammals by triggering puberty onset and promoting ovulation by stimulating gonadotrophin-releasing hormone (GnRH) secretion. To overcome the drawback of kisspeptin short half-life we designed kisspeptin analogs combining original modifications, triazole peptidomimetic and albumin binding motif, to reduce proteolytic degradation and to slow down renal clearance, respectively. These analogs showed improved in vitro potency and dramatically enhanced pharmacodynamics. When injected intramuscularly into ewes (15 nmol/ewe) primed with a progestogen, the best analog (compound 6, C6) induced synchronized ovulations in both breeding and non-breeding seasons. Ovulations were fertile as demonstrated by the delivery of lambs at term. C6 was also fully active in both female and male mice but was completely inactive in KiSS1R KO mice. Electrophysiological recordings of GnRH neurons from brain slices of GnRH-GFP mice indicated that C6 exerted a direct excitatory action on GnRH neurons. Finally, in prepubertal female mice daily injections (0.3 nmol/mouse) for five days significantly advanced puberty. C6 ability to trigger ovulation and advance puberty demonstrates that kisspeptin analogs may find application in the management of livestock reproduction and opens new possibilities for the treatment of reproductive disorders in humans.

The neuropeptide RFamide-related peptide 3 (RFRP-3) has been implicated in the control of gonadotropin secretion in both birds and mammals. However, in mammals, depending on species, sex and photoperiod, inhibitory, excitatory, or no effect of RFRP-3 on the plasma concentration of LH has been reported. In the ewe, treatment with RFRP-3 either reduced LH concentration or had no effect, and treatment with an RFRP-3 receptor antagonist (ie, RF9) resulted in increased concentration of plasma LH. To clarify these conflicting results in the present study, a set of experiments was performed in ewes. Multiple iv injections of RFRP-3 (6 × 50 μg) in ovariectomized ewes had no effect on plasma LH pulsatility. In intact ewes a bolus injection (500 μg) or an injection (250, 500, or 1000 μg) followed by a 4-hour perfusion (250, 500, or 1000 μg · h(-1)) of RFRP-3 had no effect on the LH pulse induced by kisspeptin (6.5 μg). In ovariectomized, estrogen-replaced ewes, the LH surge induced by estradiol benzoate was not modified by a 24-hour perfusion of RFRP-3 (500 μg h(-1)). Finally, although treatment with RF9 induced a robust release of LH, treatment with a more selective RFRP-3 receptor antagonist, GJ14, resulted in no evident increase of LH. In contrast to the inhibitory effect previously suggested, our data are more consistent with the concept that RFRP-3 has no direct effect on LH secretion in ewes and that RF9 effect on LH release is likely not RFRP-3 receptor mediated. Hence, RFRP-3 probably has a minor role on the control of LH secretion in the ewe.