The effect of intracerebroventricular infusions of ghrelin on the secretory activity of the GnRH/LH system in peripubertal ewes

Ghrelin is a 28-amino acid orexigenic peptide, synthesized mainly by cells located in the stomach mucosa, that can be also engaged in modulation of reproductive functions. The aim of this study was to investigate the effect of intracerebroventricular (icv) infusion of ghrelin on the secretory activity of the gonadotropin hormone releasing hormone/luteinizing hormone (GnRH/LH) system in peripubertal ewes. The animals were randomly divided into three groups: 1. standard fed, 2. starved for 72 h, and 3. standard fed + icv infused with ghrelin. Infusions were performed during three consecutive days; blood samples were collected on day 0 and day 3. Ghrelin infusions and short-term starvation increased the accumulation of immunoreactive (ir) GnRH material in the median eminence (P < 0.001) and ir LH material in the secretory granules of pituitary cells (P < 0.001) in the fasted and ghrelin-infused groups. The short starvation resulted in a decrease of mean LH plasma concentrations (P < 0.05) between days 0 and 3 of infusion, which was related to a lower pulse amplitude. After the icy ghrelin infusion, significant (P < 0.05) changes in LH pulse amplitude and frequency, but not in LH concentrations were observed. The obtained results revealed that in peripubertal ewes, exogenous ghrelin administration affects the GnRH/LH axis mainly at the level of neurohormone/protein accumulation and LH pulsatility modifications. Ghrelin action at the hypothalamus-pituitary axis is likely involved in the endocrine network that integrates energy balance and fertility in immature sheep.