Chronic intracerebroventricular administration of orexin-A to rats increases food intake in daytime, but has no effect on body weight

Orexins are recently identified neuropeptides, and have been shown to incre ase food intake when administered intracerebroventricularly. We examined th e effects of chronic administration of orexin in rats by continuous intrace rebroventricular administration by means of an osmotic minipump. Continuous administration of orexin-A (0.5 nmol/h) for 7 days in rats resulted in a s ignificant increase in food intake in the daytime. Daytime food intake incr eased to 180% of the control value. However, it resulted in a slight decrea se nighttime food intake as compared with vehicle-treated rats. The total a mount of food intake per day was almost comparable with that of vehicle-adm inistered rats. The gain of body weight and blood glucose, total cholestero l and free fatty acid levels were normal. Chronic orexin-A treatment did no t cause obesity in rats. We observed abnormal behavior during the daytime a fter starting administration of orexin-A: these rats kept awake during the daytime. Our present observation showed that continuous administration of o rexin-A could not overcome the regulation of energy homeostasis and body we ight. However, orexin-A might be implicated in short-term, immediate regula tion of feeding behavior. (C) 1999 Elsevier Science B.V. All rights reserve d.