Endothelium-derived relaing factor (EDRF) activity has been attributed to the highly labile nitric oxide radical (NO). In view of the fact that the plasma and cellular mifleux contain reactive species that can rapidly inactivate NO, it has been postulated that NO is stabilized by a carrier molecule that preserves its biological activity. Reduced thiol species are candidates for this role, reacting readily in the presence of NO to yield biologically active S-nitrosothiols that are more stable than NO itself. Because sulfhydryl groups in proteins represent an abundant source of reduced thiol in biologic systems, we examined the reaction of several sulfhy--I dryl-containing proteins of diverse nature and function upon exposure to authentic NO and EDRF. We demonstrate that S-nitroso proteins form readily under physiologic conditions and possess EDRF-like effects of vasodilation and platelet inhibition. These observations suggest that S-nitrosothiol groups in proteins may serve as intermediates in the cellular metabolism ofNO and raise the possibility ofan additional type of cellular regulatory mechanism.The richest source of reduced thiol in plasma (and a particularly prevalent source in cellular cytosol) is protein sulflydryl groups (19). The reaction ofNO with protein thiols has not been previously studied, and the potential biological significance ofthis reaction has been neglected because ofthe exclusion of proteins from (bio)assays of the functional activity and half-life of EDRF and from analyses of its chemical characteristics. We therefore investigated the reaction of protein thiols exposed to NO, and we present data showing that a variety of proteins of biological significance and relative abundance can be S-nitrosylated. S-Nitrosylation of proteins endows these molecules with potent and long-lasting EDRF-like effects of vasodilation and platelet inhibition that are mediated by guanylate cyclase activation. These observations raise the possibility that S-nitrosothiol groups in proteins may serve as intermediates in the cellular metabolism or bioactivity ofNO and that their formation may represent an important cellular regulatory mechanism.The endothelium-dependent relaxation of vascular smooth muscle first observed by Furchgott and Zawadski (1) has been largely attributed to nitric oxide (NO) derived from L-arginine through the action of NO synthase (2)(3)(4). This free radical ultimately stimulates guanylate cyclase by the formation of a nitrosyl-heme complex at the activator site of the enzyme (5, 6); however, the molecular mechanism(s) by which NO is transferred from synthase to cyclase remains poorly understood. The rapidity of the reaction of NO with molecular oxygen (7), superoxide anion (8), and heme (2) as well as nonheme iron (9) and the ready availability of these inactivating reactants in the plasma and cellular milieux militate against simple diffusion-limited transport of free NO in this medium. That endothelium-derived relaxing factor (EDRE) has the relatively long half-life of the ord...

Elevated levels of homocysteine are associated with an increased risk of atherosclerosis and thrombosis. The reactivity of the sulfhydryl group of homocysteine has been implicated in molecular mechanisms underlying this increased risk. There is also increasingly compelling evidence that thiols react in the presence of nitric oxide (NO) and endothelium-derived relaxing factor (EDRF) to form S-nitrosothiols, compounds with potent vasodilatory and antiplatelet effects. We, therefore, hypothesized that S-nitrosation of homocysteine would confer these beneficial bioactivities to the thiol, and at the same time attenuate its pathogenicity. We found that prolonged (> 3 h) exposure of endothelial cells to homocysteine results in impaired EDRF responses. By contrast, brief (15 min) exposure of endothelial cells, stimulated to secrete EDRF, to homocysteine results in the formation of S-NO-homocysteine, a potent antiplatelet agent and vasodilator. In contrast to homocysteine, S-NO-homocysteine does not support H202 generation and does not undergo conversion to homocysteine thiolactone, reaction products believed to contribute to endothelial toxicity. These results suggest that the normal endothelium modulates the potential, adverse effects of homocysteine by releasing EDRF and forming the adduct S-NO-homocysteine. The adverse vascular properties of homocysteine may result from an inability to sustain S-NO formation owing to a progressive imbalance between the production of NO by progressively dysfunctional endothelial cells and the levels of homocysteine. (J.

Recent discoveries suggesting essential bioactivities of nitric oxide (NO') in the lung are difficult to reconcile with the established pulmbnary cytotoxicity of this common air pollutant. These conflicting observations suggest that metabolic intermediaries may exist in the lung to modulate the bioactivity and toxicity of NO'. We report that S-nitrosothiols (RS-NO), predominantly the adduct with glutathione, are present at nano-to micromolar concentrations in the airways of normal subjects and that their levels vary in different human pathophysiologic states. These endogenous RS-NO are longlived, potent relaxants of human airways under physiological 02 concentrations. Moreover, RS-NO form in high concentrations upon administration of NO gas. Nitrite (10-20 ,M) is found in airway lining fluid in concentrations linearly proportional to leukocyte counts, suggestive of local NO' metabolism. NO itself was not detected either free in solution or in complexes with transition metals. These observations may provide insight into the means by which NO is packaged in biological systems to preserve its bioactivity and limit its potential 02-dependent toicity and suggest an important role for NO' in regulation of airway luminal homeostasis.There is accumulating evidence that nitric oxide (NO') is produced in mammalian airways: constitutive and inducible forms of NO synthase have recently been identified in the lung (1, 2), oxides of nitrogen (NOx) are produced by airway cells (3), and exhaled NO gas can be measured in nonsmoking volunteers (4). Potential sources of NO' include the lung parenchyma itself [smooth muscle, mast cells, nerves, and epithelium (1-3, 5-8)] as well as the cellular constituents of airway lining fluid [macrophages and neutrophils (1, 2, 9-11)]. NO has well established vasodilator properties that may play a role in the physiological regulation of blood flow and pressure in the pulmonary circulation (12). Although more disputed (13), the smooth muscle relaxant effects of NO' in airways suggest that it may have an additional role as a bronchodilator (14)(15)(16).NO', a common air pollutant and component of cigarette smoke, has been viewed as highly toxic to the lung, in part as a consequence of the high ambient 02 tension (17)(18)(19)(20)(21)(22). The reactions of NO with ambient 02 and superoxide (02 ) yield more reactive NO,, including nitrogen dioxide (NO) and peroxynitrite (OONO-), which are implicated in bronchiolitis and lung edema (17,20,21,23,24). There is additional concern that the oxidative metabolism of NO may lead to formation of carcinogenic nitrosoamines (25,26). Notably, these oxidative reactions of NO also result in the rapid loss of its smooth muscle relaxant activity (27, 28).The publication costs of this article were defrayed in part by page charge payment. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. §1734 solely to indicate this fact.An alternative metabolic pathway for NOI of potential biological relevance involves the reaction wit...

Bochdalek's hernia is not rare, and the incidence of Bochdalek's hernias that contain enteric tract is higher than previously reported. This incidence likely represents a conservative estimate because some Bochdalek's hernias may have been overlooked or unreported.