An investigation of some S‐nitrosothiols, and of hydroxy‐arginine, on the mouse anococcygeus

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Abstract
1 The effect of five S-nitrosothiols, and of the stereoisomers of NG-hydroxy-arginine (HOARG), were investigated on the mouse anococcygeus. 2 All five S-nitrosothiols produced concentration-related (0.1–100 μm) relaxations of carbachol (50 μm)-induced tone; the order of potency was S-nitroso-l-cysteine (CYSNO) > S-nitroso-N-acetyl-d,l-penicillamine (SNAP) > S-nitrosoglutathione (GSNO) > S-nitrosocoenzyme A (CoASNO) > S-nitroso-N-acetyl-l-cysteine (NACNO). The relaxations were unaffected by the nitric oxide synthase (NOS) inhibitor, l-NG-nitro-arginine (10 μm) (l-NOARG). 3 Cold-storage of the tissue for 72 h resulted in loss of sympathetic and non-adrenergic, non-cholinergic (NANC) nerve function. NOS activity in the tissue was reduced by 97%. Despite this, relaxations induced by the S-nitrosothiols were unaffected. 4 Haemoglobin (50 μm) attenuated relaxations induced by NO and the S-nitrosothiols, although responses to 3-isobutyl-1-methyl-xanthine were unaffected. N-methyl-hydroxylamine (2 Mm) which has been shown previously to produce selective inhibition of NANC and nitrovasodilator responses in this tissue, also reduced responses to all S-nitrosothiols. 5 Hydroquinone (100 μm) greatly reduced relaxations to CYSNO (by 88%) but had no effect on those to SNAP, GSNO, CoASNO or NACNO. Since hydroquinone does not reduce responses to NANC stimulation, CYSNO is unlikely to be the NANC transmitter. 6 l-HOARG by itself (up to 100 μm) had no significant effect on carbachol-induced tone or on NANC (10 Hz; 10 s train every 100 s) relaxations. However, it produced reversal of the inhibitory effects of l-NOARG (10 μm), being only slightly less potent than l-arginine. d-HOARG was without effect. l-HOARG had no effect on relaxations induced by 1.5 μm NO. 7 The results show that S-nitrosothiols are potent relaxants of the mouse anococcygeus; they act directly on the smooth muscle with a mechanism similar to NO and other nitrovasodilators. In addition, the results are consistent with l-HOARG being an intermediate in the biosynthesis of NO from l-arginine, although there is no evidence for it acting to stabilize NO extracellularly.