Treating Mares with the Long-Acting Kisspeptin Analog C6 Increases Circulating Gonadotropins but Does Not Trigger Ovulation

The role of the neuropeptide kisspeptin (Kp) in mammalian reproduction is well established. Nevertheless, species-specific differences exist. In horse, administration shortest endogenous Kp isoform, Kp10, unable to trigger ovulation even though it increases plasma gonadotropins concentrations. To check if this issue would be dependent on Kp10 short half-life, we tested two degradation-resistant analogs. first analog was based equine sequence (eC6), second ovine (oC6). During non-breeding season, a dose 150 nmol/mare either molecule had no significant effect LH concentration, while oC6 provided better stimulation FSH than eC6 (p = 0.01). Furthermore, more effective when injected intravenously intramuscularly. Due its best pharmacodynamics profile, (150 nmol/mare) probed for induction during breeding season. preovulatory phase follicle diameter ranged from 34 37 mm and uterine oedema observed. consistently increased total amount released (FSH, p 0.01 LH, 0.02). However, as shown by transrectal ultrasonography progesterone levels, did not anticipate compared control group. Our results provide further evidence peculiar reproductive endocrinology mare but leave open questions regarding exact mare, which attempt identify discuss.