Central vagal activation by an analogue of TRH stimulates gastric nitric oxide release in rats

In the stomach nitric oxide (NO) appears to be involved in vagally induced cholinergic vasodilation and nonadrenergic, noncholinergic relaxation of the fundus. We investigated whether central vagal activation by intracisternal injection of a thyrotropin-releasing hormone (TRH) analogue stimulates gastric NO release in anesthetized rats. To quantitate gastric NO production, the luminal release of NO breakdown products, nitrite (NO2-) and nitrate (NO3-), were measured by the Griess method. Intracisternal injection of RX-77368 (30-300 ng) dose dependently stimulated gastric NO2- and NO3- release (P < 0.05) along with a significant acid secretory response (P < 0.05). The specific inhibitor of NO synthesis, NG-nitro-L-arginine methyl ester (10 mg/kg ip), completely blocked gastric luminal NO2- and NO3- release without affecting the acid secretory response to the highest dose of RX-77368. Either bilateral cervical vagotomy, hexamethonium (15 mg/kg ip), or atropine (1 mg/kg ip) abolished both gastric luminal release of NO-derived metabolites and the acid secretory responses to RX-77368. These results indicate that intracisternal injection of RX-77368 stimulates gastric release of NO through vagal nicotinic pathways and peripheral activation of muscarinic receptors. These findings provide evidence for central nervous system regulation of NO-mediated functions in the rat stomach through TRH-sensitive vagal pathways.