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 retaining 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 intravenous (i.v.) injection of Kp10 (5 μg/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