THE INFLUENCE OF L-N(G)-NITRO-ARGININE ON SYMPATHETIC-NERVE INDUCED CONTRACTION AND NORADRENALINE RELEASE IN THE RAT ISOLATED ANOCOCCYGEUS MUSCLE

1 The possibility of an interaction between the motor sympathetic and inhibitory non-adrenergic, non-cholinergic (NANC) nerves in the rat an ococcygeus was investigated using L-NG-nitro-arginine (L-NOARG), an in hibitor of L-arginine: NO synthase. 2 L-NOARG (50 muM) increased contr actions induced by field stimulation (20 s trains; 0.5-40 Hz); overall , the frequency-response curve was displaced six-fold to the left. D-N OARG (50 muM) was without effect. 3 The potentiation produced by L-NOA RG was reversed by 200 muM L-, but not D-, arginine. 4 L-NOARG had no effect on contractions induced by exogenous noradrenaline (NA) or on f ield stimulation-induced overflow of tritium from muscles previously l oaded With [H-3]-NA. 5 It is concluded that the endogenous nitrate NAN C transmitter does not influence release of NA from the sympathetic ne rves and the potentiation of contractions induced by field stimulation in the presence of L-NOARG most probably results from removal of the opposing relaxing influence of concomitantly released-NANC transmitter .