Role of NO in pyloric, antral, and duodenal motility and its interaction with other inhibitory mediators.

The antroduodenal region represents a crucial mechanism for the regulation of gastric emptying and prevention of duodenogastric reflux. The pylorus is characterized by a cholinergic excitation from the duodenum to the pylorus and by a potent nonadrenergic noncholinergic (NANC) inhibitory innervation, which can be activated by antral field stimulation and by extrinsic vagal stimulation. The inhibitory effect of both vagal stimulation and antral field stimulation can be abolished in vivo by inhibitors of the L-arginine-NO pathway (L-NAME). During complete blockade of nitric oxide (NO) synthesis in vivo, the contractile response to intraarterial acetylcholine is enhanced and the direct inhibitory effect of vasoactive intestinal peptide (VIP) is still present. Basal or vagally stimulated VIP release was not influenced by L-NAME. NO is a NANC inhibitory transmitter in the pylorus that exerts a tonic inhibition in the pyloric region in vivo.