Gonadotropin-Releasing Response to Kisspeptin-10 and Its Modulation by Progesterone in Postpartum Cyclic Cows

The present study aimed to evaluate the effect of kisspeptin-10 (Kp10), a shorter variant of kisspeptin re-taining full biological activity, on the release of luteinizing hormone (LH) and follicle stimulating hormone (FSH) in cyclic adult cows, and the effect of plasma progesterone (P4) concentration on the response to Kp10 administration. The experiments were performed using five postpartum cows (4-5 years old) treated with a progesterone-releasing intravaginal device (PRID) for 7 days. The animals received a single intrave-nous (i.v.) injection of Kp10 (5 ?g/kg b.w.: 3.85 nmol/kg b.w.) for three consecutive days after the device’s removal. Plasma concentrations of P4 were higher on the day of the PRID’s removal (day 0: 7.3±1.1 ng/mL) than 1 (day 1: 0.8±0.1 ng/mL) and 2 (day 2: 0.6±0.1 ng/mL) days later (P < 0.05). Kp10 did not alter plasma LH concentrations significantly at day 0. However, it significantly stimulated the release of LH on day 1 and day 2 (P < 0.05). Kp10 tended to stimulate the release of FSH at day 2; however, it did not alter the con-centrations of FSH in plasma significantly throughout the experiment. The results showed that Kp10 stimu-lates the release of LH in postpartum cyclic cows, and suggested that high concentrations of P4 in plasma may reduce the effect of kisspeptin on the secretion of gonadotropins.