INTRODUCTION: Digestive organs are controlled from the central nervous system, and the vagus nerve plays an important role. Orexins are recently purified neuropeptides localized in neurons within the lateral hypothalamus. AIM: To examine the effects of centrally injected Orexin-A and B on pancreatic exocrine secretion in conscious rats. METHODOLOGY: Rats were prepared with cannulae draining bile and pancreatic juice separately. The experiments were conducted without anesthesia on day 4 or 5 after the operation. RESULTS: Intracerebroventricular administration of Orexin-A (0.25, 0.5, and 1.0 nmol) significantly increased pancreatic fluid and protein output in a dose-dependent manner. A significant stimulatory effect of Orexin-B was not observed. Pretreatment with the ganglion blocker hexamethonium and with atropine completely abolished the stimulatory effect of central Orexin-A. Central Orexin-A significantly increased pancreatic secretion after pretreatment with omeprazole. Intravenous injection of Orexin-A had no effect. Centrally administered Orexin-A stimulated the vagal efferent nerve in anesthetized rats. CONCLUSIONS: Centrally administered Orexin-A stimulates pancreatic exocrine secretion through the vagal efferent nerve, and the stimulatory action is independent of gastric acid secretion.
INTRODUCTION: Digestive organs are controlled from the central nervous system, and the vagus nerve plays an important role. Orexins are recently purified neuropeptides localized in neurons within the lateral hypothalamus. AIM: To examine the effects of centrally injected Orexin-A and B on pancreatic exocrine secretion in conscious rats. METHODOLOGY:Rats were prepared with cannulae draining bile and pancreatic juice separately. The experiments were conducted without anesthesia on day 4 or 5 after the operation. RESULTS: Intracerebroventricular administration of Orexin-A (0.25, 0.5, and 1.0 nmol) significantly increased pancreatic fluid and protein output in a dose-dependent manner. A significant stimulatory effect of Orexin-B was not observed. Pretreatment with the ganglion blocker hexamethonium and with atropine completely abolished the stimulatory effect of central Orexin-A. Central Orexin-A significantly increased pancreatic secretion after pretreatment with omeprazole. Intravenous injection of Orexin-A had no effect. Centrally administered Orexin-A stimulated the vagal efferent nerve in anesthetized rats. CONCLUSIONS: Centrally administered Orexin-A stimulates pancreatic exocrine secretion through the vagal efferent nerve, and the stimulatory action is independent of gastric acid secretion.