THE ROLE OF NITRIC-OXIDE IN MEDIATING NONADRENERGIC NONCHOLINERGIC RELAXATION IN LONGITUDINAL MUSCLE OF HUMAN TAENIA-COLI

Electrical field stimulation (EFS) of isolated longitudinal muscle of human taenia coli at 4Hz produced relaxation which was abolished by tetrodotoxin but not adrenergic and cholinergic blockade (NANC-relaxation). N(G)-nitro L-arginine (L-NOARG; 1-100-mu-M), an NO synthesis inhibitor, produced a concentration-dependent partial inhibition of the NANC response; 10-mu-M L-NOARG inhibited EFS-induced relaxation by 48.6 +/- 5.20% and 100-mu-M L-NOARG by 54.2 +/- 10.1%. L-Arginine (1mM), but not D-arginine (1mM) partially reversed the inhibitory effect and this was inversely proportional to the concentration of L-NOARG used. Cumulative administration of NO (acidified sodium nitrite solution; 1-100-mu-M) produced a concentration-dependent relaxation of the strips. L-NOARG (1mM) did not affect either NO or isoprenaline-induced relaxations. These results provide the first preliminary evidence that NO is partially responsible for the NANC inhibitory transmission in the longitudinal muscle of the taenia coli of human colon.