title: Spontaneous liberation of nitric oxide cannot account for in vitro vascular relaxation by S-nitrosothiols.
abstract: S-nitrosothiols are potent vasodilators in vivo and in vitro, and have recently been proposed as possible endogenous precursors of endothelium-derived nitric oxide (NO). NO release from S-nitrosothiols has generally been assumed to be spontaneous, but this has not been proven. This hypothesis was examined by altering the NO release profiles of two S-nitrosothiols, those of S-nitroso-N-acetylpenicillamine (SNAP) and S-nitroso-glutathione (GSNO), and observing their relaxation potency on isolated endothelium-denuded rat aortic rings. Spontaneous degradation of SNAP and GSNO in tissue bathing medium (monitored by high-performance liquid chromatography) and the associated NO release (assessed by chemiluminescence detection of headspace NO) were enhanced in the presence of 100 microM N-acetylpenicillamine and inhibited in the presence of 100 U/ml superoxide dismutase. However, the relaxant effects of SNAP and GSNO were enhanced in the presence of superoxide dismutase, and diminished in the presence of N-acetylpenicillamine. In addition, the relaxation potencies of SNAP, GSNO, S-nitrosocystein, S-nitroso-N-acetylcysteine and S-nitroso-coenzyme A were not correlated with spontaneous NO generation. These findings therefore argue against spontaneous liberation of NO as a predominant mechanism of S-nitrosothiol action. The highly polar SNAP, GSNO, S-nitrosocysteine and S-nitroso-N-acetylcysteine (octanol, pH 7.4 buffer partition coefficient from less than .025-.052) and the bulky and polar S-nitroso-coenzyme A (MW 797) have similar relaxation potencies, indicating that intracellular penetration of intact S-nitrosothiols may not be required for activity. NO generation from SNAP was examined in subcellular fractions of bovine coronary arterial smooth muscle cells.(ABSTRACT TRUNCATED AT 250 WORDS)
authors.affiliation: Department of Pharmaceutics, School of Pharmacy, State University of New York, Buffalo.
authors.forename: E A
authors.initials: EA
authors.lastname: Kowaluk
authors.forename: H L
authors.initials: HL
authors.lastname: Fung
mesh_terms: D000818:Animals; D001011:Aorta / Q000187:drug effects / Q000502:physiology; D002417:Cattle; D002478:Cells, Cultured; D003331:Coronary Vessels / Q000187:drug effects / Q000502:physiology; D005978:Glutathione / Q000031:analogs & derivatives / Q000378:metabolism / Q000494:pharmacology; D007700:Kinetics; D008623:Mercaptoethanol; D009126:Muscle Relaxation / Q000187:drug effects*; D009131:Muscle, Smooth, Vascular / Q000166:cytology / Q000187:drug effects* / Q000502:physiology; D009566:Nitrates; D017942:Nitric Acid; D009569:Nitric Oxide / Q000378:metabolism*; D009603:Nitroso Compounds / Q000378:metabolism / Q000494:pharmacology*; D010396:Penicillamine / Q000031:analogs & derivatives / Q000378:metabolism / Q000494:pharmacology; D026423:S-Nitroso-N-Acetylpenicillamine; D026422:S-Nitrosoglutathione; D026403:S-Nitrosothiols; D013347:Subcellular Fractions / Q000378:metabolism; D014665:Vasodilator Agents / Q000378:metabolism / Q000494:pharmacology
chemical_list: D009566:Nitrates; D009603:Nitroso Compounds; D026403:S-Nitrosothiols; D014665:Vasodilator Agents; D009569:Nitric Oxide; D017942:Nitric Acid; D026422:S-Nitrosoglutathione; D008623:Mercaptoethanol; C032635:S-nitrosomercaptoethanol; D026423:S-Nitroso-N-Acetylpenicillamine; D005978:Glutathione; D010396:Penicillamine