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)

Previous studies have demonstrated hepatic cytochrome P-450-dependent biotransformation of organic nitrates. We assessed whether this biotransformation resulted in the formation of an activator of guanylyl cyclase using the 100,000 x g supernatant of rat aorta as a source of crude enzyme. Incubation of aortic supernatant with rat hepatic microsomes and glyceryl trinitrate (GTN) resulted in concentration-dependent increases in guanylyl cyclase activity provided that the incubations were performed anaerobically and that reduced nicotinamide adenine phosphate was added. Cysteine-dependent activation of guanylyl cyclase by GTN was greater under anaerobic compared to aerobic conditions. Guanylyl cyclase activation by GTN was increased using hepatic microsomes from phenobarbital-treated but not beta-naphthoflavone (BNF)-treated rats and was decreased when microsomes from cimetidine-treated rats were used. The hepatic microsome-dependent activation of guanylyl cyclase by GTN was inhibited by in vitro treatment of microsomes with carbon monoxide, SKF 525A, metyrapone and cimetidine, but not by ranitidine. The sensitivity of isolated rat aorta to the relaxant effects of GTN was increased under low oxygen conditions or when aortae were obtained from phenobarbital- or beta-naphthoflavone-treated rats. Treatment of rats with cimetidine did not affect GTN-induced relaxation. The vascular biotransformation of GTN was increased greater than 3-fold when performed anaerobically, and this increase was prevented by pretreatment of the tissues with carbon monoxide. Together, these data provide strong evidence for the involvement of hepatic cytochromes P-450 in the formation from GTN of an activator of guanylyl cyclase (presumably NO or some closely related compound), and suggest that at least a portion of the vascular biotransformation of GTN is mediated by hemoproteins.
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PMID:Hepatic cytochrome P-450-mediated activation of rat aortic guanylyl cyclase by glyceryl trinitrate. 134 46

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

We examined the effect of the cytochrome P-450 substrate, 7-ethoxyresorufin (7-ER), and its corresponding product, resorufin, on nitrovasodilator- and endothelium-dependent relaxation of isolated rat aorta. The EC50 value for glyceryl trinitrate (GTN) induced relaxation was increased over 100-fold by 7-ER and less than 3-fold by resorufin. The EC50 value for sodium nitroprusside (SNP) induced relaxation was increased approximately 12-fold by 7-ER, acetylcholine (ACh) induced relaxation was abolished, and relaxation induced by isopropylnorepinephrine was not significantly affected. GTN-, SNP-, and ACh-induced increases in cyclic GMP accumulation were inhibited by 7-ER, as were basal cyclic GMP levels in endothelium-intact, but not endothelium-denuded tissues. 7-ER decreased GTN biotransformation in intact aorta and decreased the regioselective formation of glyceryl-1,2-dinitrate. The activation by GTN and SNP of aortic guanylyl cyclase in broken cell preparations was not affected by 7-ER, indicating that the inhibitory effect of 7-ER is probably not due to a direct interaction with guanylyl cyclase. The inhibitory effect of 7-ER on GTN-induced relaxation was not altered by the addition of superoxide dismutase, suggesting that 7-ER does not act by increasing superoxide anion concentration (which would serve to increase the degradation of nitric oxide (NO) formed during vascular GTN biotransformation). Our data provide further evidence for the role of the cytochrome P-450--cytochrome P-450 reductase system in the biotransformation of GTN to an activator (presumably nitric oxide) of guanylyl cyclase. The data are consistent with a mode of action of 7-ER involving either competitive inhibition of vascular cytochrome P-450 or uncoupling of vascular cytochrome P-450 reductase from cytochrome P-450. The data also suggest that the cytochrome P-450 system facilitates NO release from SNP and that 7-ER has an inhibitory effect on endothelial nitric oxide synthase.
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PMID:Inhibition of nitrovasodilator- and acetylcholine-induced relaxation and cyclic GMP accumulation by the cytochrome P-450 substrate, 7-ethoxyresorufin. 136 24

Pretreatment of phenylephrine (0.5 microM)-preconstricted, isolated perfused kidneys of the male rat with indomethacin (2.8 microM) or BM 13.177 (20 microM) abolished the vasoconstrictor response to arachidonic acid (AA), uncovering a vasodilator response. BW 755C (25 microM), a dual cyclooxygenase/lipoxygenase inhibitor, did not modify the vasodilator effect of AA, whereas 5,8,11,14-eicosatetraynoic acid (10 microM), which blocks all pathways of AA metabolism, abolished AA-induced vasodilation, thus suggesting the involvement of nonlipoxygenase AA metabolites. Clotrimazole (0.7 microM) and 7-ethoxyresorufin (1 microM), both considered to be specific inhibitors of the cytochrome P-450 monooxygenase enzymes, inhibited the vasodilator effect, suggesting that AA-induced renal vasodilation is mediated by one or more cytochrome P-450-derived AA metabolites. None of these interventions affected the vasodilator responses to acetylcholine (100 ng) and nitroprusside (1 microgram). Denudation of the endothelium with CHAPS (10 mg/l) reduced the vasodilator responses to AA, suggesting a requirement of an intact endothelium, whereas inhibition of guanylate cyclase with methylene blue (10(-4) M) was without effect, suggesting that cGMP was not involved in the vasodilator response to AA. The AA-induced renal vasodilation was accompanied by the generation of biologically active material or materials released into the renal effluent, which relaxed endothelium-intact and endothelium-denuded rings of isolated aorta and mesenteric and celiac arteries of the rabbit. These results suggest that in the rat kidney, AA is metabolized by endothelial cytochrome P-450-dependent enzymes to vasodilator metabolites.
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PMID:Cytochrome P-450-dependent vasodilator responses to arachidonic acid in the isolated, perfused kidney of the rat. 190 Dec 56

1. An epithelium-derived inhibitory factor (EpDIF) released by guinea-pig tracheal epithelium was evaluated in a co-axial bioassay system consisting of an epithelium-intact guinea-pig tracheal tube surrounding endothelium-denuded rat aortic strip. 2. Histamine and several muscarinic agonists induced concentration-dependent relaxation of phenylephrine-contracted rat aorta via the release of EpDIF. However, several other agonists did not induce the release of EpDIF from guinea-pig trachea. These included the nicotinic cholinoceptor agonists nicotine (25 microM), 1,1-dimethyl-4-phenylpiperazinium (DMPP) (25 microM), calcium ionophore A23187 (0.5 microM), bradykinin (0.05-0.5 microM), substance P (5 microM), platelet activating factor (PAF, 1-100 nM), the leukotrienes (LT) LTC4, LTD4 and LTE4 (0.1-10 nM) as well as hyperosmotic stimuli. 3. Prostaglandin E2 (PGE2) induced concentration-dependent contraction of endothelium-denuded rat aortic preparations, indicating that this prostanoid could not be EpDIF. Furthermore, relaxation to histamine and methacholine, mediated via EpDIF, was not significantly altered in the presence of phenidone (50 microM) the cyclo-oxygenase/lipoxygenase inhibitor with radical scavenging properties or the cytochrome P-450 inhibitors metyrapone (1 mM) and SKF 525A (25 microM). This suggests that EpDIF is neither a prostanoid nor a cytochrome P-450 metabolite of arachidonic acid. 4. The soluble guanylate cyclase inhibitor, methylene blue (50 microM), caused small but significant increases in the potencies of both histamine and methacholine in co-axial assemblies, indicating that EpDIF did not activate this enzyme and therefore was not NO or a related substance. The beta-adrenoceptor antagonist, (-)-propranolol (1 microM), and the PAF-receptor antagonist, WEB 2086 (50 microM), also failed to alter significantly EpDIF-modulated relaxations. These data suggest that EpDIF is neither a stimulant of fiadrenoceptors nor of PAF receptors. 5. The present study provides some evidence that this vascular smooth muscle-sensitive EpDIF may not be related to the putative EpDIF previously hypothesized to modulate directly spasmogen-induced airway smooth muscle tone.
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PMID:Pharmacological evaluation of a guinea-pig tracheal epithelium-derived inhibitory factor (EpDIF). 239 Jun 83

1. Acetylcholine, ionophore A23187 and melittin induced endothelium-dependent relaxations of preconstricted strips of rabbit aorta. These relaxations are likely to be mediated by endothelium-derived relaxing factor (EDRF). 2. Relaxations in response to acetylcholine (1 microM) were inhibited by the following lipoxygenase inhibitors, with the approximate IC50 values indicated in parentheses: gossypol (1.5 microM), nordihydroguairetic acid (NDGA, 5 microM), AA 861 (20 microM), phenidone (30 microM), quercetin (40 microM), BW 755C (300 microM), and piriprost (500 microM); with cirsiliol 50% inhibition was not achieved. Acetylcholine-induced relaxations were also blocked by the cytochrome P-450-mono-oxygenase inhibitors proadifen (SKF 525A, 4 microM), metyrapone (300 microM), and cimetidine (300 microM); 7,8 benzoflavone had no effect up to 100 microM. 3. The more potent inhibitors were also tested against relaxations induced by A23187 (0.1 microM) and melittin (1 microM) and produced partial inhibition of these relaxations. 4. The mechanism of action of the more potent inhibitors was investigated in a bioassay system. EDRF was produced in columns filled with cultured human endothelial cells. The factor was bioassayed with endothelium denuded segments of rabbit femoral artery. When added to effluent of the column, NDGA, AA861, proadifen and metyrapone inhibited the EDRF-induced vasodilatation, whereas gossypol had no effect. Gossypol, however, blocked EDRF production when infused through the column. 5. The more potent inhibitors were also tested to determine their effect on purified soluble guanylate cyclase. While gossypol, NDGA and proadifen had no appreciable effects, basal and nitroprusside (50 microM)-stimulated guanylate cyclase activity was inhibited by AA861 and metyrapone. 6. These data suggest that many of the above compounds inhibit EDRF by mechanisms other than lipoxygenase- or cytochrome P-450-mono-oxygenase inhibition.
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PMID:Mechanisms of action of lipoxygenase and cytochrome P-450-mono-oxygenase inhibitors in blocking endothelium-dependent vasodilatation. 289 18

The mechanism of biotransformation of nitroglycerin into the pharmacologically active radical nitric oxide (NO) or a related compound is still unclear. Different enzymes have been discussed to be involved in the bioactivation process. The effects of inhibition of glutathione-S-transferase and cytochrome P-450 enzymes were investigated on nitroglycerin-induced relaxation of bovine and porcine coronary arteries and on nitroglycerin-induced activation of guanylyl cyclase in cultivated porcine aortic smooth muscle cells. The glutathione-S-transferase inhibitor sulfobromophthalein had no effect on nitroglycerin-induced vascular relaxation, nor on nitroglycerin-induced elevation of cGMP levels in porcine coronary artery smooth muscle cells. The modulation of cytochrome P-450 activity by selective inhibitors as well as inducers did not alter the bioactivity of nitroglycerin in both systems. The data demonstrate that the isoenzymes of both enzyme families, which have been shown to be involved in the metabolism of nitroglycerin in different non-vascular tissues, do not play a role in bioactivation of nitroglycerin in the vascular system.
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PMID:Bioactivation of nitroglycerin in vascular smooth muscle cells is different from that in non-vascular tissue. 760 Dec 9

Leukotoxin (Lx), a cytochrome P-450-dependent metabolite of linoleate synthesized by neutrophils or synthesized by OH- and linoleate in neutrophil cell membranes, has been recovered in lung lavages of patients with the adult respiratory distress syndrome. We studied the direct vasoactive effects of Lx and linoleate, its parent compound, in the rat pulmonary circulation. In isolated rat lungs perfused at constant flow with a physiological salt solution, Lx (but not linoleate) caused a biphasic response, an initial transient vasoconstriction followed by a more prolonged vasodilation. The latter response was only evident when the pulmonary vascular tone was increased with either alveolar hypoxia (0% O2) or KCl (20 mM). The pressor response to angiotensin II was also attenuated in the presence of Lx. The vasodilatory response in perfused lungs was attenuated by methylene blue (2 x 10(-5) M), a putative inhibitor of the soluble guanylate cyclase but not by pretreatment with meclofenamate (10(-5) M), a cyclooxygenase inhibitor. In isolated pulmonary arterial (PA) rings preconstricted either with phenylephrine (5 x 10(-9) M), endothelin-1 (10(-8) M), or KCl (30 mM), Lx (but not linoleate) caused dose-dependent relaxation. The relaxing effect of Lx on endothelium-intact rings was attenuated by NG-monomethyl-L-arginine or methylene blue. The magnitude of the hypoxic contraction of PA rings was attenuated in the presence of Lx. Whereas the mechanism of Lx-induced vasoconstriction is not clear, we conclude that Lx causes vasodilation in rat lungs and that the vasodilatory component is to a large degree endothelium-derived relaxing factor-dependent.
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PMID:Leukotoxin, 9,10-epoxy-12-octadecenoate causes pulmonary vasodilation in rats. 784 Feb 18

Glyceryl trinitrate, isosorbide dinitrate, and isosorbide-5-mononitrate are organic nitrate esters commonly used in the treatment of angina pectoris, myocardial infarction, and congestive heart failure. Organic nitrate esters have a direct relaxant effect on vascular smooth muscles, and the dilation of coronary vessels improves oxygen supply to the myocardium. The dilation of peripheral veins, and in higher doses peripheral arteries, reduces preload and afterload, and thereby lowers myocardial oxygen consumption. Inhibition of platelet aggregation is another effect that is probably of therapeutic value. Effects on the central nervous system and the myocardium have been shown but not scrutinized for therapeutic importance. Both the relaxing effect on vascular smooth muscle and the effect on platelets are considered to be due to a stimulation of soluble guanylate cyclase by nitric oxide derived from the organic nitrate ester molecule through metabolization catalyzed by enzymes such as glutathione S-transferase, cytochrome P-450, and possibly esterases. The cyclic GMP produced by the guanylate cyclase acts via cGMP-dependent protein kinase. Ultimately, through various processes, the protein kinase lowers intracellular calcium; an increased uptake to and a decreased release from intracellular stores seem to be particularly important.
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PMID:Mechanisms of action of nitrates. 787 67

Considerable evidence suggests that nitric oxide (NO) acts as a nonadrenergic noncholinergic (NANC) transmitter at autonomic neuroeffector junctions. NO is generated enzymatically from L-arginine by a constitutive, cytosolic, Ca2+/calmodulin-activated NO synthase (NOS): NADPH- and tetrahydrobiopterin-dependent cytochrome P-450-type hemoprotein. Electrophysiological and pharmacological data indicate that NO fulfils most of the criteria for a neurotransmitter. It is released from axon terminals when invaded by action potentials and mimics the effect of nerve stimulation. The changes in the mechanical and/or electrical activity of smooth muscle preparations in response to transmural stimulation of NANC nerves are antagonized by inhibitors of NO synthesis or oxyhemoglobin, an NO scavenger. NO acts principally by stimulating soluble guanylate cyclase. Studies on the histochemical localization of NOS point to the involvement of the neural L-arginine-NO pathway in the regulation of vascular tone and of several aspects of respiratory, gastrointestinal, and genitourinary tract functions.
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PMID:Nitric oxide--a novel autonomic neurotransmitter. 797 84


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