Blockade of nitric oxide synthase inhibits nerve-mediated contraction in the rat small intestine

Inhibitors of nitric oxide (NO) synthase inhibit nerve-mediated non-adrenergic, non-cholinergic (NANC) smooth muscle relaxation in the gastrointestinal tract. In this study, the effect of a NO synthase inhibitor, NG-nitro-L-arginine, was examined on the tetrodotoxin-sensitive NANC contractile response of the rat isolated ileal myenteric plexus-longitudinal muscle evoked by electrical field stimulation. This contraction was concentration-dependently inhibited by NG-nitro-L-arginine (1-3 x 10(-5) M). The inhibition was partly or entirely reversed by L-arginine. The NO synthase inhibitor did not exhibit any non-specific smooth-muscle depressant action or local anaesthetic effect. Sodium nitroprusside, a putative donor of NO also caused a transient contraction of the rat ileal strip. This response was resistant to tetrodotoxin. It is concluded that an NO synthase product is involved in the mechanism of the nerve-mediated NANC primary contraction due to field stimulation in the rat small intestine.