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Central Orexin-A stimulates pancreatic exocrine secretion via the vagus
Kyoko Miyasaka1, Masao Masuda, Setsuko Kanai
1Department of Clinical Physiology, Tokyo Metropolitan Institute of Gerontology, Tokyo, Japan. miyasaka@tmig.or.jp
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.