Nitric oxide formation is involved in vagal inhibition of the stomach of the trout (Salmo gairdneri).

Stimulation of the vagus nerves to isolated stomach preparations from trout (Salmo gairdneri) caused both excitation and inhibition of smooth muscle activity. Excitatory responses were partly reduced by atropine, suggesting that cholinergic neurons are involved. The atropine-resistant excitation could not readily be ascribed to a 'rebound' from preceding inhibition, to the production of prostaglandins, or to the activation of either adrenergic or capsaicin-sensitive fibres. Inhibitory responses were reduced by the nicotinic antagonist d-tubocurarine and more profoundly reduced by an inhibitor of nitric oxide synthase, NG-nitro-L-arginine. The latter effect was reversed by excess L-arginine. The nitric oxide donors sodium nitroprusside and nitroglycerine caused inhibition of the muscle. It is concluded that the vagal inhibitory postganglionic neurons are nitergic in this tissue.