Evidence for a role of nitric oxide in the neurotransmitter system mediating relaxation of the rat anococcygeus musclec

1. The nitric oxide (NO) synthesis inhibitor N^G‐monomethyl‐l‐arginine (l‐NMMA), but not d‐NMMA, inhibited the NANC‐mediated relaxations of the rat anococcygeus muscle, but did not affect the relaxation produced by sodium nitroprusside. 2. The inhibitory effect of l‐NMMA was reversed by l‐arginine but not by d‐arginine, and prior exposure to l‐arginine blocked the effect of l‐NMMA. 3. The noradrenergically mediated contractions of the anococcygeus elicited by field stimulation were slightly enhanced by l‐NMMA, but the response to noradrenaline was not affected. 4. The results suggest that NANC transmission in the rat anococcygeus muscle involves the generation of NO from arginine.