NITRERGIC-INHIBITORY INNERVATION OF PORCINE RECTAL CIRCULAR SMOOTH-MUSCLE

This study was performed to determine whether nitric oxide contributes to inhibitory non-adrenergic noncholinergic (NANC) neurotransmission in the circular smooth muscle layer of pig mean(s.e.m.) 86.5(2.6) per cent (P=0.0003) at concentration of 3 x 10(-5) mol/l L-NOArg. The resp onse was restored by the addition of L-arginine. Sodium nitroprusside, an exogenous donor of nitric oxide, mimicked the relaxant response. R esponses to EFS were abolished by tetrodotoxin. These results suggest that inhibitory NANC neurotransmission in this tissue is mediated, at least in part, by nitric oxide. The failure of L-NOArg to completely a bolish the relaxant response Suggests that additional neurotransmitter s may be involved.rectum. Smooth muscle strips were mounted for isomet ric tension recording in superfusion organ baths. In the presence of a tropine Sulphate and guanethidine, transmural electrical field stimula tion (EFS) produced frequency-dependent relaxation of precontracted mu scle strips. N omega-nitro-L-arginine (L-NOArg), a powerful competitiv e antagonist of nitric oxide Synthase, reduced the relaxant response i n dose-dependent fashion; this response was maximally reduced by