Endocrine Abstracts

Hypothalamic regulation of the appetite and reproductive neuroendocrine axes is modulated by nutritional feedback from the periphery, potentially via shared mechanisms. Ghrelin is a recently identified orexigenic hormone secreted by the stomach that has been implicated in meal-time hunger, energy homeostasis and body weight regulation. In rodents, intracerebroventricular (ICV) injection acutely stimulates food intake and one study has shown that it can also transiently suppress luteinising hormone (LH) output. It is unknown whether ghrelin, also secreted by the gut in sheep, elicits the same responses in this ruminant species with its contrasting digestive physiology. Nine castrated male Suffolk x Greyface sheep, with subcutaneous oestradiol implants and surgically prepared with cannulae into the third cerebral ventricle, were fed complete forage-based diet ad libitum, with fresh food provided in two meals at 0830h and 1600h. On two consecutive days, blood samples were taken at 15 minute intervals 0800h - 1600h for LH analysis, and voluntary food intake (VFI) was measured at 0930h, 1130h, 1330h and the following 0830h. Each sheep received a single ICV injection at 0830h of 0.9% saline control (0.1 ml) on day 1 and of ghrelin (rat) (0.1 mg in 0.1 ml saline) on day 2. Ghrelin ICV immediately increased VFI during the first hour compared with control treatment (6 vs 13% total daily intake; sed 2.3, P<0.01), but there was no difference remaining after 3 h (18 vs 20%; sed 3.2) or 5 h (26% vs 28%; sed 4.6). Mean plasma LH concentration was reduced following ICV ghrelin compared with control treatment for 4 h (8.9 vs 11.8 ng/ml; sed 1.58, P<0.01) and for 8 h (8.9 vs 11.2 ng/ml; sed 1.67, P<0.05). These data suggest that ghrelin acts acutely within the ovine hypothalamus both to stimulate food intake and to inhibit reproductive neuroendocrine output.