The role of nitric oxide (NO) in the human pyloric sphincter

Nitric oxide (NO) has recently been shown to be a neurotransmitter in non-adrenergic non-cholinergic (NANC) inhibitory nerves in the gastrointestinal tract. To clarify the role of NO in the human pyloric sphincter, enteric nerve responses in pyloric tissue specimens obtained from patients with gastric cancer were investigated.

Fresh specimens of normal pylorus obtained from 18 patients with gastric cancer were used. The subjects consisted of 12 men and 6 women, aged from 45-74 years (average: 60.1 years). A mechanograph was used to evaluate in vitro pyloric sphincter muscle responses to electrical field stimulation (EFS) of adrenergic and cholinergic nerves before and after treatment with various autonomic nerve blockers, and N(G)-nitro-L-arginine (L-NNA) and L-arginine.

Cholinergic nerves were mainly involved in the regulation of enteric nerve responses to EFS in the basal condition of the study, and NANC inhibitory nerves acted on human pylorus. L-NNA concentration dependently inhibited the relaxation in response to EFS in the human pylorus, and this inhibitory effect in the pylorus was reversed by L-arginine.

These findings suggest that the cholinergic/adrenergic and NANC inhibitory nerves play important roles in regulating contraction and relaxation of the human pylorus, and that NO plays an important role as a neurotransmitter in NANC inhibitory nerves of the human pylorus.