Ovarian and hormonal responses to single or continuous peripheral administration of senktide, a neurokinin 3 receptor agonist, during the follicular phase in goats

• Senktide is a highly selective agonist of neurokinin 3 receptor.
• We report the effects of senktide on hormonal secretion in follicular phase goats.
• Continuous infusion of senktide caused a sustained increase in LH secretion.
• The increase in LH secretion advanced the timing of ovulation in more than half cases.

The present study aimed to investigate the effects of single or continuous administration of a neurokinin 3 receptor agonist, senktide, on hormonal and follicular dynamics in follicular phase goats. Goats were injected with PGF2α in the luteal phase and treated with an intravaginal progesterone device for 10 d. At 12 h after the cessation of progesterone treatment, the goats received a single intravenous injection of senktide (200 nmol, n = 4) or vehicle (n = 4), or continuous intravenous infusion of senktide (20 nmol/min, n = 6) or vehicle (n = 6) for 6 h. Blood sampling and ovarian ultrasonography were performed during the experiment. A single injection of senktide did not influence the number of luteinizing hormone (LH) pulses and mean LH concentration. On the other hand, continuous injection of senktide caused a sustained increase in LH secretion, and mean LH concentration in samples collected at 10-min intervals for 6 h after the start of infusion was higher than that of vehicle-treated goats (2.8 ± 1.3 vs 1.0 ± 0.6 ng/mL, P < 0.01). In 4 of 6 goats, LH concentrations reached their peaks during the 6-h senktide infusion, and ovulation was observed at 48 h after the start of infusion without estrous behavior. The remaining 2 senktide-treated goats and all vehicle-treated goats showed estrus and ovulated at 72 or 96 h after treatment. These results suggest that continuous infusion of senktide in follicular phase goats can cause a sustained increase in LH and advance the time of ovulation.