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

BACKGROUND/AIMS: Nitric oxide (NO) has recently been shown to be a neurotra nsmitter in nonadrenergic non-cholinergic (NANC) inhibitory nerves in the g astrointestinal tract. To clarify the role of NO in the human pyloric sphin cter, enteric nerve responses in pyloric tissue specimens obtained from pat ients with gastric cancer were investigated. METHODOLOGY: Fresh specimens of normal pylorus obtained from 18 patients wi th 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 eva luate in, vitro pyloric sphincter muscle responses to electrical field stim ulation (EFS) of adrenergic and cholinergic nerves before and after treatme nt with various autonomic nerve blockers, and N-G-nitro-L-arginine (L-NNA) and L-arginine. RESULTS: Cholinergic nerves were mainly involved in the regulation of enter ic nerve responses to EFS in the basal condition of the study, and NANC inh ibitory nerves acted on human pylorus. L-NNA concentration dependently inhi bited the relaxation in response to EFS in the human pylorus, and this inhi bitory effect in the pylorus was reversed by L-arginine. CONCLUSIONS: These findings suggest that the cholinergic/adrenergic and NAN C inhibitory nerves play important roles in regulating contraction and rela xation of the human pylorus, and that NO plays an important role as a neuro transmitter in NANC inhibitory nerves of the human pylorus.