Evidence that part of the NANC relaxant response of guinea‐pig trachea to electrical field stimulation is mediated by nitric oxide

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Abstract
1 The nitric oxide (NO) synthesis inhibitors NG-monomethyl l-arginine (l-NMMA) and l-nitroarginine methyl ester (l-NAME) reduced relaxations of guinea-pig tracheal smooth muscle elicited by stimulation of intramural non-adrenergic, non-cholinergic (NANC) nerves, but d-NMMA had no effect. l-NAME was 10–30 times more potent than l-NMMA. Relaxations produced by sodium nitroprusside and vasoactive intestinal polypeptide (VIP) were not affected by l-NMMA or l-NAME. 2 The inhibitory effect of l-NMMA on NANC-mediated relaxations was partially reversed by l-arginine but was not affected by d-arginine. 3 VIP antibody and α-chymotrypsin abolished or greatly reduced the relaxant action of VIP and reduced relaxations elicited by stimulation of NANC nerves; the residual NANC relaxation was further reduced by l-NAME. 4 The results suggest that NO and VIP are mediators of NANC-induced relaxations of guinea-pig tracheal smooth muscle. We propose the term ‘nitrergic’ to describe transmission processes which are mediated by NO.