151 Is kisspeptin a mediator of nerve growth factor-induced ovulation in South American camelids?

Nerve growth factor (NGF) is a neurotrophin present in the seminal plasma of camelids that is the main trigger for ovulation. The mediators of NGF-induced ovulation remain unknown; however, the hypothalamic neuropeptide kisspeptin is a potential candidate. We showed previously that intravenous administration of kisspeptin induces a transient elevation in circulating LH concentrations in llamas, and the effect was mediated upstream of the pituitary. In the present study, we tested the hypothesis that kisspeptin is a hypothalamic mediator of NGF-induced ovulation. In Experiment 1, adult, nonpregnant, non-lactating llamas (n = 10) were surgically implanted with an intracerebroventricular (ICV) catheter attached to a subcutaneous port. After a week of rest, llamas were given gonadotrophin-releasing hormone to synchronise ovarian function, and the ovaries were monitored every other day by transrectal ultrasonography. When a growing ovarian follicle ≥ 7 mm was detected in all llamas, a jugular catheter was put in place and, the following day, llamas were assigned to two groups and given an ICV infusion of a kisspeptin receptor antagonist (p271, dissolved in 10% DMSO; loading dose of 300 μg, and constant infusion of 300 μg/hr for 4 h), or left untreated (n = 5 per group). An hour after the start of the ICV infusion, llamas in both groups were given 500 μg NGF intravenously. Blood samples were collected every 30 min from the start of the infusion until 4 h after treatment for measurement of plasma LH concentration. The ovaries were examined by transrectal ultrasonography 48 h after treatment to detect ovulation. In Experiment 2, the functionality of the kisspeptin antagonist was tested in two groups of female llamas (n = 3 per group), as described for Experiment 1. At 60 min after the start of infusion of the kisspeptin blocker, both groups were given 150 μg kisspeptin ICV. Blood samples were collected every 15 min from the start of blocker infusion to 75 min after kisspeptin treatment. Ovulation rate was compared by chi-square, serial data were analysed by analysis of variance for repeated measures, and single-point measurements were compared by paired t-tests. In Experiment 1, no differences between the kisspeptin receptor blocker and control groups were detected in the ovulatory response (3/5 and 5/5, respectively), or plasma LH concentrations in response to NGF (time, P < 0.05; treatment, P = 0.85; interaction, P = 0.59). In Experiment 2, plasma LH concentrations in response to a kisspeptin ICV bolus were lower in llamas pre-treated with the kisspeptin receptor antagonist (P < 0.05), confirming the functionality of the kisspeptin blocker. Results of the present study do not support the hypothesis that NGF-induced ovulation is mediated by kisspeptin neurons in the arcuate nucleus or preoptic area directly. Instead, our results suggest that a different mechanistic route or neuronal system is involved in NGF-induced ovulation.

This research was supported by the Natural Science and Engineering Research Council.