Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:4.6.1.2 (guanylate cyclase)
 8,497 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The cellular mechanism of bioactivation underlying guanylate cyclase activation by organic nitrates was investigated. In cultured rat lung fibroblasts (RFL-6 cells), the inhibitor of cytochrome P-450 proadifen (0.1 mM) decreased cyclic GMP stimulation by glyceryl trinitrate (GTN, 1-100 microM) by up to 81%. Cyclic GMP stimulation by isoidide dinitrate was inhibited to a similar degree under these conditions. However, proadifen did not affect cyclic GMP stimulation by sodium nitroprusside that spontaneously releases nitric oxide. Cyclic GMP stimulation in RFL-6 cells by GTN remained unaltered in the presence of the inhibitor of glutathione S-transferase sulfobromophthalein. In the same cell type, a 24-hr pretreatment with the inducer of cytochrome P-450 3-methylcholanthrene (10 microM) augmented cyclic GMP stimulation by GTN or isoidide dinitrate by up to 102%. Cultured porcine aortic endothelial cells were found to be without a cyclic GMP response to GTN, although sodium nitroprusside produced a marked cyclic GMP elevation in these cells. The endothelial cells remained unresponsive to GTN even in the presence of N-acetylcysteine (5 mM). Moreover, in a cell-free preparation from rat liver, glutathione-dependent biotransformation of GTN was not accompanied by activation of soluble guanylate cyclase. These findings suggest that in intact cells bioactivation of, i.e., nitric oxide formation from organic nitrates is mediated by a cytochrome P-450 enzyme system rather than by glutathione S-transferase or free thiols.
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PMID:Cytochrome P-450 mediates bioactivation of organic nitrates. 135 50

Several cellular constituents of the lung have the capacity to synthesize a factor capable of relaxing smooth muscle which has the physicochemical properties of nitric oxide (NO). In other systems, it has been shown that NO may be stabilized in the plasma and cellular milieu by reduced thiol in the form of an S-nitrosothiol (RS-NO). These compounds have half-lives that are significantly greater than that of NO, and also retain the vasorelaxant activity of NO, which is mediated by activating guanylate cyclase and raising cyclic GMP levels. The effects of RS-NO and their potential mechanism of action on airways, however, have not been previously investigated. In this study, we have examined the smooth muscle relaxant properties of several biological and synthetic RS-NO on guinea pig trachea. Our data reveal that RS-NO are generally potent airway smooth muscle relaxants with at least a partial effect through stimulation of cyclic GMP. Relaxations were attenuated significantly by the guanylate cyclase inhibitor methylene blue (P less than .05), and RS-NO-induced increases in cyclic GMP were demonstrated (P less than .0005). The IC50 values for S-nitroso-glutathione, S-nitroso-cysteine, S-nitroso-homocysteine, S-nitroso-N-acetylcysteine, S-nitroso-penicillamine and S-nitroso-captopril were 0.99 +/- 0.09, 3.2 +/- 0.2, 2.1 +/- 0.3, 2.1 +/- 0.8, 1.8 +/- 0.8 and 20 +/- 0.7 microM (mean +/- S.E.M.), respectively. In this system isoproterenol has an IC50 of 0.016 microM and theophylline an IC50 of 74 microM, making the relaxant properties of these NO derivatives of potential pharmacological and physiological relevance.
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PMID:The relaxant properties in guinea pig airways of S-nitrosothiols. 156 Mar 60

Nitroglycerin and the organic nitrates (RONO2) can be considered prodrugs that require conversion to an active intracellular moiety that initiates vascular smooth muscle relaxation. Vasodilation of veins and arteries occurs when the enzyme guanylate cyclase (GC) is activated, initiating the conversion of guanosine triphosphate (GTP) to cyclic guanosine monophosphate (cGMP); this is the final pathway for vascular dilation caused by the nitrovasodilators (organic nitrates, sodium nitroprusside, and molsidomine) as well as endothelium-derived relaxing factor (EDRF). The common denominator appears to be the intracellular production of nitric oxide (NO), which is the activated product of organic nitrate denitration. Nitrate tolerance has been associated with a relative depletion or unavailability of thiol groups that are involved in the initial step of denitration of RONO2. Sulfhydryl groups (SH) are oxidized during this process; with continuous nitrate exposure, decreased nitrate metabolism within the vascular smooth muscle cell occurs as a direct result of the depletion of reduced SH groups. Thus, less NO is formed and cGMP production is diminished, with a subsequent decrease or absence of vasodilation. In addition, SH groups or thiols are required for the production of S-nitrosothiols (RSNO). These short-lived compounds have been identified as an end product of organic nitrate metabolism and as possibly obligatory for the induction of GC. It is unclear, however, as to whether S-nitrosothiols are a necessary by-product of NO production from organic nitrates. It appears that RSNO can be formed outside the cell membrane and may be able to induce vasorelaxation after penetrating the cell and initiating GC activation. Exogenous SH donors, particularly N-acetylcysteine (NAC), have been employed to provide intracellular thiols in efforts to prevent or reverse nitrate tolerance. Nitrate physiologic actions are accentuated following NAC administration in the absence of tolerance. Although controversial, the concept that NAC or other thiols might be able to prevent the development of nitrate tolerance is being actively studied in laboratories around the world. Methionine has also been utilized as an SH donor with some success. Not all data are consistent, however, and the ultimate role of thiol donors for the prevention or reversal of nitrate tolerance remains uncertain. Finally, there has been considerable interest in supplying thiols by use of the SH-containing angiotensin converting enzyme inhibitors, such as captopril. This approach does not seem promising, probably because insufficient thiol can be supplied by therapeutic dosages of these drugs.
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PMID:Interactions between organic nitrates and thiol groups. 192

The development of unstable angina pectoris and acute myocardial infarction is a process of platelet aggregation and thrombus formation associated with local coronary vasoconstriction. Regional deficiencies in endothelial vasodilator function, due to reduced formation of endothelium-derived relaxing factor (EDRF), may predispose to platelet aggregation and coronary vasoconstriction. Nitroglycerin (NTG), frequently utilized in the management of unstable angina pectoris and acute myocardial infarction, undergoes bioconversion, via a sulfhydryl-dependent process, to nitric oxide, which is identical or closely related to EDRF. Other products of the nitrate bioconversion "cascade" are various S-nitrosothiols, which, like nitric oxide, activate soluble guanylate cyclase, inducing increased formation of cyclic guanosine monophosphate. NTG potentially may act to correct a localized deficiency of EDRF effect, at both the vasculature and platelet levels. In patients with unstable angina, hemodynamic effects and therapeutic efficacy of intravenously infused NTG may be attenuated within hours. Combined therapy with NTG and intravenously infused N-acetylcysteine (NAC) results in potentiation of hemodynamic responses to NTG, markedly augments the effects of NTG on platelet aggregation, and reduces the incidence of acute myocardial infarction in patients with severe unstable angina pectoris. The combination of NTG with intermittent NAC infusion may increase the risk of hypotensive episodes in such patients, whereas continuous coinfusion of the drugs is better tolerated. The combination of NTG with thiol-containing agents, such as NAC, may be of therapeutic value in unstable angina pectoris and in evolving acute myocardial infarction. This is currently under investigation.
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PMID:Thiol-containing agents in the management of unstable angina pectoris and acute myocardial infarction. 192 1

Nitrovasodilators have been found to relax vascular smooth muscle by stimulating soluble guanylate cyclase and thus by increasing the formation of cyclic GMP (cGMP). This nucleotide is responsible for relaxation, most likely by decreasing cytosolic free Ca2+ by one or several mechanisms. Repeated administration of organic nitrates causes tolerance development characterized by a diminished relaxing effect and an attenuated rise in cGMP. Experiments in isolated circular strips from bovine coronary arteries were performed in order to study the mechanism of tolerance development. It was found that after nitroglycerin (NG) pretreatment the response of the coronary strips to NG was less sensitive with respect to relaxation and increases in cGMP. These strips were also cross-tolerant against isosorbide-5-mononitrate, which by itself caused only little tolerance. With NG, the degree of tolerance development depended on the time and the concentration of NG pre-exposure. NG was found to stimulate guanylate cyclase (GC) in coronary supernatant provided that cysteine was added to the incubation medium. As in the intact strips, activation of GC by NG was attenuated when supernatants were preincubated with NG. It was found that addition of cysteine during incubation lessened the degree of desensitization but did not prevent it completely. Similarly, in coronary strips, tolerance development was lower when N-acetylcysteine was present during pre-exposure of the strips with NG. Considerably more effective in preventing tolerance development by about 50% was L-2-oxothiazolidine-4-carboxylate (OTC), a substance that easily penetrates into the cell and is transformed into cysteine by 5-oxo-prolinase.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Mechanisms of nitrate-induced vasodilatation and tolerance. 197 61

Substance P is a vasoactive peptide. Nerve fibers containing substance P are present in the media of pulmonary arteries but the physiologic function of substance P in the pulmonary vasculature is unknown. Several doses of substance P were infused intravenously in the anesthetized dog to ascertain its effects on the pulmonary vasculature, both during normoxia and following preconstriction with hypoxia (F1O2 0.1) or prostaglandin F2 alpha (PGF2 alpha 5 mug/kg/min). Substance P resulted in systemic vasodilation during normoxia but had minimal effect on the pulmonary vasculature. During hypoxia and PGF2 alpha-induced pulmonary vasoconstriction, substance P significantly lowered pulmonary artery pressure, pulmonary vascular resistance, mean aortic pressure, and total systemic resistance. It had no effect on cardiac output, wedge pressure, and arterial blood gases. To investigate possible mechanisms for substance P-induced vasodilation, substance P was studied following pretreatment with N-acetylcysteine (a radical scavenging agent), methylene blue (an inhibitor of guanylate cyclase), meclofenamate (a cyclooxygenase inhibitor), and atropine (a muscarinic receptor antagonist). None of these agents impaired substance P-induced vasodilation. Substance P given intravenously is a nonselective vasodilator in the dog but the mechanism of its action remains uncertain.
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PMID:The effects of substance P on the preconstricted pulmonary vasculature of the anesthetized dog. 242 48

The same factors that regulate the activation of purified hepatic soluble guanylate cyclase by diverse agents possessing distinct requirements for enzyme activation were found to modulate cyclic GMP formation in intact viable hepatic cells. A comparison was made between activation of heme-deficient or heme-reconstituted guanylate cyclase and stimulation of cyclic GMP formation in mouse hepatic slices that were 95% viable and showed no active efflux of cyclic GMP. Heme-dependent activators of guanylate cyclase elicited a greater -fold increase in hepatic cyclic GMP levels in slices from phenobarbital-pretreated than control mice. Brilliant cresyl blue and KCN inhibited both enzyme activation and hepatic cyclic GMP accumulation caused by agents that generate nitric oxide. Hepatic slices from 3,5-diethoxycarbonyl-1,4-dihydrocollidine-treated mice, which are known to develop sharp increases in hepatic protoporphyrin IX/heme concentration ratios, showed elevated resting cyclic GMP levels whereas phenobarbital pretreatment produced decreased resting cyclic GMP levels compared to controls. Guanylate cyclase activation by azide required added catalase, and both enzyme activation and hepatic cyclic GMP formation were inhibited by aminotriazole. Enzyme activation by glyceryl trinitrate and NaNO2 required added thiols. Hepatic slices from acetaminophen-pretreated mice showed marked depletion of sulfhydryls and decreased cyclic GMP formation in response to these enzyme activators. Both effects were completely restored by treatment of thiol-depleted mice with N-acetylcysteine. These observations lend support to the general view that information gained from studies on the regulatory properties of purified soluble guanylate cyclase bears a close relationship to studies on regulatory mechanisms that modulate cyclic GMP formation in intact cells.
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PMID:Hepatic cyclic GMP formation is regulated by similar factors that modulate activation of purified hepatic soluble guanylate cyclase. 243 23

Nicorandil (SG-75) is a new organic nitrate with pronounced vasodilator properties. We studied whether nicorandil, in analogy to other nitrovasodilatators, exerted its relaxing effects on vascular smooth muscle by stimulating guanylate cyclase, and whether this effect was susceptible to tolerance development. Dose-response curves for the relaxing and cyclic guanosine monophosphate (cGMP) increasing effects of nicorandil were obtained in isolated strips of bovine coronary arteries and compared with those of other nitrovasodilatators. It was found that nicorandil dose-dependently relaxed the strips precontracted with 26.7 mM K+ and that this effect was closely associated with increases in cGMP levels (measured by RIA under various conditions). The correlation between relaxation and rises in cGMP was steeper than with other nitrovasodilatators, suggesting that nicorandil, in addition to its cGMP-mediated effect, also relaxed vascular smooth muscle by a cGMP independent mechanism. In contrast to nitroglycerin (NG), nicorandil caused little development of tolerance or cross-tolerance toward ISDN or IS-5-MN when tested after preincubation of the strips toward the respective substance. Pretreatment with N-acetylcysteine during the preincubation period prevented tolerance towards nicorandil. The results indicate that the relaxant effects of nicorandil consist of a larger cGMP-mediated component and a smaller one which is independent of this nucleotide.
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PMID:Cyclic GMP in nicorandil-induced vasodilatation and tolerance development. 244 21

Cultured rat lung fibroblasts were used to explore desensitization of guanylate cyclase to nitrovasodilators. The effect of pretreatment with glyceryl trinitrate (GTN) on the concentration-response curves of GTN and sodium nitroprusside (SNP) for cyclic GMP accumulation in intact cells and activation of guanylate cyclase in broken cell preparations was measured. Pretreatment of cells with 1 microM GTN for 3 h decreased cyclic GMP accumulation induced by GTN but had no effect on SNP-induced cyclic GMP accumulation. Pretreatment of cells with 100 microM GTN decreased the efficacy of GTN and SNP for cyclic GMP elevation by 89% and 40%, respectively. In contrast to results obtained with GTN, SNP slightly desensitized cyclic GMP accumulation induced by GTN and SNP. Pretreatment of cells with 100 nM atrial natriuretic peptide resulted in a 44% decrease in cyclic GMP accumulation induced by subsequent exposure to 10 nM atrial natriuretic peptide but had no effect on cyclic GMP elevation induced by nitrovasodilators. In experiments with crude preparations of soluble guanylate cyclase from cells pretreated with 1 mM GTN, activation of the enzyme by GTN and SNP was inhibited almost completely. Tolerance to GTN in intact cells could not be reversed by subsequent incubation with thiols such as cysteine, N-acetylcysteine or glutathione. However, overnight incubation of GTN-tolerant cells in media without added thiols resulted in complete recovery of responsiveness to GTN. Recovery of GTN-induced cyclic GMP accumulation was inhibited in a concentration-dependent manner by cycloheximide, suggesting that reversal of organic nitrate tolerance requires de novo synthesis of gyanylate cyclase.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Glyceryl trinitrate-induced desensitization of guanylate cyclase in cultured rat lung fibroblasts. 245 70

NAC has been thought to reverse nitrate tolerance by replenishing depleted intracellular sulfhydryl groups, however data on interactions between N-acetylcysteine and nitrates in patients with stable angina are controversial and disappointing. Therefore, we studied the effect of NAC on nitrate responsiveness of epicardial arteries and of the venous system (assessed as changes in effective vascular compliance) in dogs (n = 12) during long-term nitroglycerine (GTN)-treatment (1.5 micrograms/kg/min for 5 to 6 days). In dogs with GTN-specific tolerance (shift of venous or epicardial artery dilation with 15- to 17-fold higher dosages), NAC (100 mg/kg i.v.) had no dilator effect and did not alter the dose response relations of nitroglycerin. However, in nontolerant dogs (n = 7) NAC augmented (1.5- to 2-fold) the reduction of peripheral vascular resistance induced by 0.5-1.5 microgram/kg/min GTN. In vitro, the augmentation of purified guanylate cyclase activity by GTN (100 microM) was potentiated by NAC (0.01-1.0 mM) in saline or in canine plasma, whereas NAC alone was ineffective. Therefore, NAC does not restore GTN-responsiveness in epicardial arteries or veins in vivo and a small, tolerance-independent augmentation of GTN-induced dilation may result from NAC-induced extracellular formation of a stimulant of guanylate cyclase from GTN.
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PMID:Failure of the sulfhydryl donor N-acetylcysteine (NAC) to reverse nitrate tolerance in large epicardial arteries and the venous capacitance system of the dog. 251 88


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