PARTICIPATION OF NITRIC-OXIDE IN THE NICOTINE-INDUCED RELAXATION OF THE CAT LOWER ESOPHAGEAL SPHINCTER

The participation of nitric oxide in the relaxation of the cat lower e sophageal sphincter muscle strip in response to electrical field stimu lation or administration of nicotine was studied. The nicotine-induced relaxation was mediated via a neuronal pathway, since it was inhibite d by administration of hexamethonium or tetrodotoxini Inhibition of ni tric oxide biosynthesis by N-nitro-L-arginine decreased the relaxation induced by nicotine (50 mu M) or field stimulation. With the maximal concentration of N-nitro-L-arginine (1 mM) electrical field stimulatio n-induced relaxation was abolished, while nicotine-induced relaxation decreased by 70%. L-Arginine (1 mM) partly restored this relaxation. D esensitization of P-2x receptors by alpha,beta methylene-adenosine 5-t riphosphate (alpha,beta(o)-m-ATP) did not change the relaxation induce d by either electrical field stimulation or administration of nicotine . It is therefore suggested that the field stimulation-induced relaxat ion is mediated by the release of nitric oxide, but in the nicotine-pr oduced relaxation is only partly due to nitric oxide, other factor(s) might be also be involved.