Stimulation and inhibition of food intake in sheep by centrally-administered hypothalamic releasing factors.

Short-term effects of hypothalamic releasing factors on feeding behavior and digestive motility patterns were assessed in hay-fed sheep trained to eat more than half the total amount eaten over 8 h within the first 3 h after food presentation. Thyrotropin-releasing hormone (TRH) given intracerebroventricularly (ICV, 30 ng/kg) or intravenously at higher doses (IV, 3 micrograms/kg) reduced food consumption by 20 p. cent. The ICV or IV TRH-induced reduction was associated with behavioral excitation and stimulation of antroduodenal motor activity without changes in water intake. The ovine corticotropin releasing factor (oCRF 41) decreased food and water intake by 30-50% when administered ICV (60 ng/kg) but was not active when given systemically at doses up to 6 micrograms/kg. The synthetic human growth hormone releasing factor (hGRF 44) administered centrally (60 ng/kg) increased the amount of food intake and the antral motor activity without behavioral excitation. The results indicate a centrally-mediated facilitation of food intake by GRF and its inhibition by CRF which also affect water consumption. The presence of digestive motor effects suggests that extrapituitary pathways may be involved, as for TRH, in the action of both GRF and CRF.