Role of mitochondrial aldehyde dehydrogenase in nitrate tolerance

Glyceryl trinitrate (GTN) is used in the treatment of angina pectoris and cardiac failure, but the rapid onset of GTN tolerance limits its clinical utility. Research suggests that a principal cause of tolerance is inhibition of an enzyme responsible for the production of physiologically active concentrations of NO from GTN. This enzyme has not conclusively been identified. However, the mitochondrial aldehyde dehydrogenase (ALDH2) is inhibited in GTN-tolerant tissues and produces NO2- from GTN, which is proposed to be converted to NO within mitochondria. To investigate the role of this enzyme in GTN tolerance, cumulative GTN concentration-response curves were obtained for both GTN-tolerant and -nontolerant rat aortic rings treated with the ALDH inhibitor cyanamide or the ALDH substrate propionaldehyde. Tolerance to GTN was induced using both in vivo and in vitro protocols. The in vivo protocol resulted in almost complete inhibition of ALDH2 activity and GTN biotransformation in hepatic mitochondria, indicating that long-term GTN exposure results in inactivation of the enzyme. Treatment with cyanamide or propionaldehyde caused a dose-dependent increase in the EC50 value for GTN-induced relaxation of similar magnitude in both tolerant and nontolerant aorta, suggesting that although cyanamide and propionaldehyde inhibit GTN-induced vasodilation, these inhibitors do not affect the enzyme or system involved in tolerance development to GTN. Treatment with cyanamide or propionaldehyde did not significantly inhibit 1,1-diethyl-2-hydroxy-2-nitrosohydrazine-mediated vasodilation in tolerant or nontolerant aorta, indicating that these ALDH inhibitors do not affect the downstream effectors of NO-induced vasodilation. Immunoblot analysis indicated that the majority of vascular ALDH2 is present in the cytoplasm, suggesting that mitochondrial biotransformation of GTN by ALDH2 plays a minor role in the overall vascular biotransformation of GTN by this enzyme.     

Role of hydrogen peroxide in bactericidal action of catechin

Catechin (epicatechin (EC), epicatechin gallate (ECg), epigallocatechin (EGC) and epigallocatechin gallate (EGCg)), which occur in green tea and black tea, possess strong bactericidal action. We observed a reactive oxygen species that was generated from the catechins as the active mechanism: and this reactive oxygen was identified. EGCg reacted with the dissolved oxygen in aqueous solution, resulting in the generation of hydrogen peroxide. Hydrogen peroxide production derived from EGCg rose with increasing pH. EGCg (0.22 mmol/l) in neutral solution (0.1 mol/l phosphate buffer pH 7.0: PBS) quantitatively generated 0.2 mmol/l hydrogen peroxide after 60 min incubation. The bactericidal effect of EGCg is dependent on hydrogen peroxide levels produced by EGCg; moreover, EGCg action was inhibited by treatment with catalase. Both bactericidal effects correlated closely when the effects of EGCg and hydrogen peroxide for the bacterium (9 of 10 kinds of bacterial strains) were examined. Therefore, hydrogen peroxide, which is generated by EGCg, appears to be involved in the bactericidal action of EGCg.     

Role of endogenous hydrogen peroxide in cardiovascular ischaemia/reperfusion function: studies in mouse hearts with catalase-overexpression in the vascular endothelium.

Hydrogen peroxide (H2O2) has been implicated as a component of oxidative ischaemia/reperfusion stress. We investigated the role of H2O2 in cardiovascular ischaemia/reperfusion stress in hearts from mice overexpressing catalase in their endothelial cells. Hearts of transgenic (TG, n = 9) and age-matched wild-type (WT, n = 7) mice were perfused at constant flow (2.2 mlmin(-1)) and subjected to brief ischaemia and reperfusion. Intrinsic function and the effects of norepinephrine (3 nM-3 microM) were determined. Left ventricular pressure (LVDevP; balloon method), end-diastolic pressure (LVEDP), maximum rates of pressure development (+dP/dt, -dP/dt), coronary perfusion pressure (index of vascular function) and heart rate were recorded. Apart from a slightly higher recovery of LVDevP during reperfusion (+6 mmHg), neither systolic nor diastolic function was improved during ischaemia or reperfusion in TG hearts. However, hearts from TG mice exhibited a significantly better contractile response to noradrenergic stimulation (LVDevP: +20 mHg or 1.15-fold increase; +dP/dt: +1476 mmHgs(-1) or 1.2-fold increase) (P < 0.05). Norepinephrine relaxed the coronary microvasculature and increased heart rate, but no differences were detected between groups. We conclude that overexpressing catalase in endothelial cells is only weakly protective against myocardial or vascular ischaemia/reperfusion injury, but preserves the responsiveness of the heart to adrenergic stimulation.     

Role of superoxide dismutase in in vivo and in vitro nitrate tolerance.

We assessed whether pharmacological inhibition of CuZn-superoxide dismutase (SOD) mimics the molecular mechanism of either in vitro or in vivo nitrovasodilator tolerance. In endothelium-intact aortic rings from in vivo tolerant rabbits the GTN- and acetylcholine (ACh)-induced maximal relaxation was attenuated by 36 and 23%, respectively. In vitro treatment of control rings with GTN (1 h 10 microM) similarly attenuated the vasorelaxant response to GTN, but not to ACh. Formation of superoxide radicals (*O2-) in endothelium-intact rings (lucigenin-chemiluminescence) increased 2.5 fold in in vivo tolerance, but significantly decreased in in vitro tolerance. The membrane associated NADH oxidase activity was increased 2.5 fold in homogenates of in vivo tolerant aortae, but was not changed in in vitro tolerant aorta. Conversely, SOD activity and protein expression was halved in in vivo tolerance, but SOD activity was not altered by in vitro tolerance. The *O2- scavenger tiron (10 mM) effectively restored the vasorelaxant response to GTN in in vivo tolerant aortic rings, but not the reduced response to GTN in in vitro tolerant rings. Pretreatment (1 h) of vessels with diethyldithiocarbamate (DETC; 10 mM) attenuated vasorelaxant responses to GTN and ACh, increased vascular *O2- production, and inhibited SOD activity in vessel homogenates to a similar degree as observed in in vivo tolerance. DETC-treatment of in vivo-tolerant vessels induced an additional increase in *O2- production. Increased *O2- production in in vivo nitrate tolerant aorta is associated with activation of vascular NADH oxidase and inactivation of CuZnSOD. Therefore, in vivo tolerance can be mimicked by in vitro inhibition of CuZnSOD, but not by in vitro exposure to GTN, which does not affect vascular *O2- production, NADH oxidase and CuZnSOD.     

Role of hydrogen peroxide in the aetiology of Alzheimer's disease: implications for treatment

Hydrogen peroxide (H(2)O(2)) is a stable, uncharged and freely diffusable reactive oxygen species (ROS) and second messenger. The generation of H(2)O(2) in the brain is relatively high because of the high oxygen consumption in the tissue. Alzheimer's disease is a neurodegenerative disorder characterised by the appearance of amyloid-beta (Abeta)-containing plaques and hyperphosphorylated tau-containing neurofibrillary tangles. The pathology of Alzheimer's disease is also associated with oxidative stress and H(2)O(2) is implicated in this and the neurotoxicity of the Abeta peptide. The ability for Abeta to generate H(2)O(2), and interactions of H(2)O(2) with iron and copper to generate highly toxic ROS, may provide a mechanism for the oxidative stress associated with Alzheimer's disease. The role of heavy metals in Alzheimer's disease pathology and the toxicity of the H(2)O(2) molecule may be closely linked.Drugs that prevent oxidative stress include antioxidants, modifiers of the enzymes involved in ROS generation and metabolism, metal chelating agents and agents that can remove the stimulus for ROS generation. In Alzheimer's disease the H(2)O(2) molecule must be considered a therapeutic target for treatment of the oxidative stress associated with the disease. The actions of H(2)O(2) include modifications of proteins, lipids and DNA, all of which are effects seen in the Alzheimer's disease brain and may contribute to the loss of synaptic function characteristic of the disease. The effectiveness of drugs to target this component of the disease pathology remains to be determined; however, metal chelators may provide an effective route and have the added bonus in the case of clioquinol of potentially reducing the Abeta load. Future research and development of agents that specifically target the H(2)O(2) molecule or enzymes involved in its metabolism may provide the future route to Alzheimer's disease therapy.     

Role of endogenous nicotinic signaling in guiding neuronal development

Spontaneous nicotinic cholinergic activity is widespread in the developing nervous system. One of the major components mediating this activity is the nicotinic acetylcholine receptor with alpha7 subunits (alpha7-nAChR) and high relative calcium permeability. We recently reported that alpha7-nAChRs co-localize in part with GABA(A) receptors during development, and the sites become co-innervated by cholinergic and GABAergic terminals. Patch-clamp recording either from embryonic chick ciliary ganglion neurons or from early postnatal mouse hippocampal interneurons reveals that alpha7-nAChR activation can impose a rapid and reversible decrease in GABA(A) receptor responses. The effect extends to GABAergic synaptic currents, and depends on intracellular calcium, calcium/calmodulin-dependent protein kinase II, and MAP kinase in the postsynaptic cell. Over the longer term, nicotinic activity has a more profound effect: it determines the time during development when GABAergic signaling converts from excitation to inhibition. It does this by changing the pattern of chloride transporters to establish the mature chloride gradient required for inhibitory GABAergic responses. The excitatory phase of GABAergic signaling is critical for proper development and integration of neurons into circuits. By driving the conversion of GABAergic signaling, nicotinic activity not only terminates one set of developmental instructions, but also initiates another by collaborating with GABAergic inhibition to impose new instructions. The results reveal a multi-layered pattern of activity-dependent controls in development and indicate the significance of nicotinic signaling in shaping these events.     

硝酸酯类药物耐药的研究进展

硝酸酯类药物在临床上广泛用于冠心病和充血性心力衰竭的治疗；但硝酸酯耐药的出现，使其临床应用受到一定限制。目前有关硝酸酯耐药的机制、预防等方面的研究已取得了一定的进展，本文对此进行综述。     

Role of endogenous hydrogen sulfide in neurogenic relaxation of rat corpus cavernosum

Relaxation of corpus cavernosum during penile erection is mediated by a non-adrenergic non-cholinergic (NANC) neurotransmission and by the endothelium via the release of nitric oxide. Hydrogen sulfide (H(2)S) is an endogenous gaseous mediator which is a potent vasodilator and a neurotransmitter. This study was initiated to characterize the role of H(2)S in NANC neurogenic transmission in rat corpus cavernosum. The expression of H(2)S producing enzymes was assessed using RT-PCR as well as Western blotting and showed the expression of cystathionine γ-lyase (CSE) in rat corporal tissue. Homogenates from rat corpus cavernosum convert l-cysteine to H(2)S and this was partially inhibited by a CSE inhibitor, propargylglycine. Electrical stimulation of corporal tissue strips caused NANC relaxation. This neurogenic relaxation was significantly enhanced by inhibition of CSE by propargylglycine indicating that endogenously produced H(2)S may have a negative regulatory role in neurogenic relaxation of rat corpus cavernosum. To investigate this further we used physiologically relevant concentrations of exogenous NaHS, and showed that nanomolar concentrations could inhibit corporal relaxation induced by a nitroxyl (HNO) donor (Angeli's salt) but not with nitrosonium (NO(+)) or NO donors. This suggests that an interaction between endogenously produced H(2)S and nitroxyl (HNO) might be involved in erectile function.     

The effect of high-dose pentaerythritol tetranitrate on the development of nitrate tolerance in rabbits

Experimental studies with therapeutic doses of pentaerythritol tetranitrate (PETN) have shown unexpected actions such as a lack of nitrate tolerance and vasoprotective effects in atherosclerosis. We investigated the effect of a 3-week treatment with low- (6 mg kg(-1) day(-1), n=10) and high-dose (100 mg kg(-1) day(-1), n=10) oral PETN given twice daily on the development of nitrate tolerance in rabbits. We measured aortic relaxation in response to acetylcholine, S-nitroso-N-acetyl-D,L-penicillamine and PETN, constriction in response to phenylephrine and production of reactive oxygen species (ROS). Mean aortic pressure (AOPmean) and heart rate were measured after a single oral dose of PETN (50 mg kg(-1), n=6) and after increasing doses of pentaerythritol dinitrate (PEDN, n=5) and pentaerythritol mononitrate (PEMN, n=5) in anaesthetized rabbits. Oral PETN, even at high dosage, was not associated with nitrate tolerance. None of the aortic ring studies showed a difference in the responses to the vasodilators, while the vasoconstriction to phenylephrine was slightly reduced in both PETN groups. The production of vascular ROS was also not different. Oral PETN reduced AOPmean transiently (-19.3+/-4.4%, P<0.01 vs. controls) and i.v. administration of both PEMN and PEDN reduced AOPmean dose dependently (P<0.05, ANOVA). These results suggest that oral PETN elicits minor nitrate tolerance. This unique feature might be due to the slow onset of vasodilator activity of the predominantly active metabolites PEDN and PEMN and might contribute to the vasoprotective activity of PETN in atherosclerosis.     

Ascorbic acid induces redifferentiation and growth inhibition in human hepatoma cells by increasing endogenous hydrogen peroxide

The mechanisms of redifferentiation and growth inhibition induced in human hepatoma cells by ascorbic acid (AA) were studied. After treatment with AA, the content of hydrogen peroxide (H2O2) and the activity of superoxide dismutase (SOD) increased in a concentration- and time-dependent manner, while the activity of catalase (CAT) decreased in a concentration- and time-dependent manner. Using 6 mM AA as a positive control, after treatment by 50 microM hydrogen peroxide, the malignant characteristics of human hepatoma cells were alleviated; for example as cell surface charge markedly decreased, the electrophoresis rate dropped from 1.68 microns.s-1.V-1.cm-1 to 0.97, the average of alpha-fetoprotein content decreased from 327 micrograms.g-1 protein to 193, and gamma-glutamyl-transpeptidase activity fell from 0.84 U.g-1 protein to 0.30. The indexes related to cell differentiation were promoted, such as tyrosine-alpha-ketoglutarate transaminase activity increased from 17.1 mumol.g-1 protein to 33.1, and the colonogenic potential decreased by 79.3%. SOD and 3-amino-1,2,4-triazole (AT) exhibited some effects, but there were statistically significant differences between the SOD, AT and H2O2 or AA groups. AA induced growth inhibition and redifferentiation of human hepatoma cells through the production of hydrogen peroxide, since addition of SOD (200 units/ml), an enzyme that dismutates superoxide and generates hydrogen peroxide, and AT (1.5 mM), a CAT inhibitor that inhibits the activity of CAT and leads to an increase in H2O2 content, showed some inducing changes emphasizing the involvement of reactive oxygen species (ROS) in redifferentiation of hepatoma cells. AA can cause the content of H2O2 to increase, and the factor H2O2 showed a similar effect to AA on growth and redifferentiation suggests that H2O2 is involved in hepatoma cell redifferentiation. In conclusion, these results suggest that AA inhibits tumor growth and induces tumor redifferentiation by virtue of producing H2O2.     

Preservation of platelet responsiveness to nitroglycerine despite development of vascular nitrate tolerance

AIMS: Organic nitrates, via nitric oxide (NO) release, induce vasodilatation and inhibit platelet aggregation. Development of nitrate tolerance in some vascular preparations may be associated with diminished responsiveness to NO. To date it is not known to what extent vascular tolerance to organic nitrates is associated with acquired platelet hypo-responsiveness to NO. In the current study we compared the acute and chronic effects of sustained release (SR) isosorbide 5' mono-nitrate (ISMN) and transdermal nitroglycerine (TD-NTG) on blood vessels (effects on apparent arterial stiffness) and platelets (effects on responsiveness to NO donors) in patients with stable angina pectoris (SAP). METHODS: Patients (n = 34) with SAP entered a blinded randomized crossover study of ISMN (120 mg) vs. intermittent TD-NTG (15 mg 24 h(-1)). Effects of each nitrate on pulse wave reflection (augmentation index (AIx)), platelet response to adenosine di-phosphate (ADP 1 micromol l(-1)), nitroglycerine (NTG 100 micromol l(-1)) and the non-nitrate NO donor sodium nitroprusside (SNP 10 micromol l(-1)), were measured pre-dose, 4 and 8 h post dose, on three occasions: 1) at the end of a pre-nitrate phase, 2) after dosing for 7 days and 3) following 14 days of full dose therapy with either nitrate. RESULTS: Acutely, both ISMN and TD-NTG markedly reduced AIx. After 14 days, these effects were significantly attenuated (ANOVA, P = 0.018) but not abolished, indicating development of nitrate tolerance. Neither nitrate preparation affected ADP (1 micromol l(-1))-induced platelet aggregation. Platelet responsiveness to NTG (100 micromol l(-1)) and SNP (10 micromol l(-1)) was not diminished during chronic nitrate therapy, and there was no evidence of 'rebound' hyper-aggregability during 'nitrate-free' periods. CONCLUSIONS: Chronic therapy with either ISMN or TD-NTG is associated with development of vascular tolerance. Despite the induction of vascular tolerance, platelet responsiveness to NTG and SNP remains unaffected. Therefore, development of vascular tolerance is unlikely to compromise the anti-aggregatory effects of organic nitrates, or those of endogenous NO.     

Role of hydrogen peroxide in cyclosporine-induced renal tubular cell (LLC-PK1) injury

We examined the role of hydrogen peroxide production in cyclosporine A (CsA)-induced LLC-PK1 injury. After exposure to CsA (0.1 microM - 100 microM), cytotoxicity assessed by lactate dehydrogenase release to the media increased dose-dependently. LLC-PK1 cells produced hydrogen peroxide, visualized by 2,7-dichlorodihydrofluorescein assay by the treatment with 100 microM CsA, that was blocked by the treatment with catalase. The cytotoxicity of CsA significantly decreased either by the treatment with catalase, mannitol, or deferoxamine, but not with superoxide dismutase. These results suggest the role of hydrogen peroxide as the source of hydroxyl radical, which mainly contributes to CsA-induced LLC-PK1 injury.     

Role of endogenous hydrogen sulfide on renal damage induced by adriamycin injection

A single injection of adriamycin (ADR) induces marked and persistent proteinuria in rats that progress to glomerular and tubulointerstitial lesions. It has been shown that ADR-induced nephrotoxicity is mediated, at least in part, by oxidative stress that lead to inflammation. Endogenous hydrogen sulfide (H₂S) is synthesized from l-cysteine and is an important signaling molecule in inflammation. This study evaluates the effect of DL-propargylglycine (PAG), an inhibitor of endogenous H₂S formation, on the evolution of renal damage induced by ADR. The rats were injected i.p. with 0.15 M NaCl or PAG (50 mg/kg) 2 h after ADR injection (3.5 mg/kg). Control rats were injected with 0.15 M NaCl or PAG only. Twenty hours urine samples were collected for albuminuria and creatinine measurements on days 1 and 14 after saline or ADR injections and on days 2 and 15 blood samples were collected to measure plasma creatinine, then the rats were killed. The kidneys were removed for H₂S formation evaluation, renal lipid peroxidation and glutathione levels, and histological and immunohistochemical analysis. On day 2 after ADR injection the rats presented increase in oxidative stress associated with neutrophils and macrophages influx in renal tissue. On day 15 the rats also presented increased desmin expression at glomerular edge and vimentin in cortical tubulointerstitium, as well as albuminuria. All these alterations were reduced by PAG injection. The protective effect of PAG on ADR nephrotoxicity was associated to decreased H₂S formation and to restriction of oxidative stress and inflammation in the renal cortex.     

Role of superoxide and hydrogen peroxide in hypertension induced by an antagonist of adenosine receptors

Treatment of Wistar rats for 7 days with 1,3-dipropyl-8-sulfophenylxanthine (DPSPX), an antagonist of adenosine receptors, induces long-lasting hypertension associated with marked changes in vascular structure and reactivity and renin-angiotensin system activation. This study aimed at evaluating the role of oxidative stress in the development of DPSPX-induced hypertension and also at identifying the relative contribution of superoxide radical (O2.-) vs hydrogen peroxide (H2O2). Vascular and systemic prooxidant/antioxidant status was evaluated in sham (saline, i.p., 7 days) and DPSPX (90 microg/kg/h, i.p., 7 days)-treated rats. Systolic blood pressure was determined by invasive and non-invasive methods. The activity of vascular NADPH oxidase, superoxide dismutase (SOD), catalase and glutathione peroxidase was assayed by fluorometric/spectrophotometric methods. H2O2 levels were measured using an Amplex Red Hydrogen Peroxide kit. Plasma thiobarbituric acid reactive substances and plasma antioxidant capacity were also measured. In addition we tested the effects of antioxidants or inhibitors of reactive oxygen species generation on blood pressure, vascular hyperplasia and oxidative stress parameters. DPSPX-hypertensive rats showed increased activity of vascular NADPH oxidase, SOD, catalase and glutathione peroxidase, as well as increased H2O2 generation. DPSPX-hypertensive rats also had increased plasma lipid peroxidation and decreased plasma antioxidant capacity. Treatment with apocynin (1.5 mmol/l, per os, 14 days), or with polyethylene glycol (PEG)-catalase (10,000 U/kg/day, i.p., 8 days), prevented the DPSPX-induced effects on blood pressure, vascular structure and H2O2 levels. Tempol (3 mmol/l, per os, 14 days) failed to inhibit these changes, unless PEG-catalase was co-administered. It is concluded that O2.- generation with subsequent formation of H2O2 plays a major role in the development of DPSPX-induced hypertension.     

Nitroglycerin-induced release of calcitonin gene-related peptide from sensory nerves attenuates the development of nitrate tolerance

The present study was designed to determine if endogenous calcitonin gene-related peptide (CGRP) affects the process of nitrate tolerance development in blood vessels. Rat aortic rings were suspended in organ chambers and relaxations to nitroglycerin (10(-9) -10(-6) M) were obtained in nitrate tolerant and nontolerant rings contracted with norepinephrine (10(-7) M). Tolerance was induced by incubating the rings with (tolerant) or without (nontolerant) nitroglycerin (10(-4) M) for 90 minutes, followed by repeated rinsing for 1 hour. Some rings were treated with CGRP8-37 (10(-6) M), glyburide (10(-6) M), or iberiotoxin (10(-7) M) during the 90-minute desensitization period with nitroglycerin (10(-4) M), and were then washed out during the 1-hour rinsing period. Other rings were treated with capsaicin (10(-5) M) prior to the 90-minute desensitization period. Calcitonin gene-related peptide release was measured by radioimmunoassay. Relaxation to nitroglycerin was markedly reduced in tolerant rings, as compared with nontolerant. Incubation with CGRP8-37 (10(-6) M) specifically during the 90-minute desensitization period with nitroglycerin resulted in even greater impairment in the response to nitroglycerin in tolerant rings, even though the calcitonin gene-related peptide antagonist had been washed out before completion of the nitroglycerin dose-response curve. Similar results were obtained following depletion of calcitonin gene-related peptide stores in sensory nerves by treatment with capsaicin (10(-5) M) prior to the 90-minute desensitization period with nitroglycerin. Prior treatment with CGRP8-37 or capsaicin had no effect on the response to nitroglycerin in nontolerant rings. Incubation with glyburide (10(-6) M), but not iberiotoxin (10(-7) M), specifically during the 90-minute desensitization period, mimicked the effect of CGRP8-37 and capsaicin in tolerant rings, suggesting a role for KATP channels in the effect of calcitonin gene-related peptide. Nitroglycerin (10(-4) M) caused a greater than twofold increase over basal levels in calcitonin gene-related peptide release in nontolerant rings, which was abolished in rings treated with capsaicin and in nitrate tolerant rings. These results suggest that nitroglycerin releases calcitonin gene-related peptide from sensory nerves during the process of desensitization to nitrovasodilators, and that interference with either the release or action of endogenous calcitonin gene-related peptide during this period enhances the extent to which nitrate tolerance occurs. The finding that nitroglycerin-induced release of calcitonin gene-related peptide from sensory nerves attenuates the desensitizing effect of nitroglycerin represents a heretofore unknown event in the development of nitrate tolerance, and demonstrates a novel role for calcitonin gene-related peptide in the vasculature.     

Role of L-arginine in the vascular actions and development of tolerance to nitroglycerin

The goal of this work was to test the role of nitric oxide synthase (NOS) and its substrate L-arginine in development of tolerance to nitroglycerin's (GTN) vasodilator actions. GTN's effects on NOS activity and NO formation were tested in cultured bovine aortic endothelial cells (BAECs). The arginine to citrulline conversion assay showed that GTN stimulated NOS basal activity in BAECs by approximately 40%, comparable with acetylcholine (ACh)-treated controls. Both effects were blocked by L-NMMA. Photometric assays showed that both GTN and ACh-stimulated NO formation. Both effects were potentiated by L-arginine and inhibited by L-NAME. L-NAME inhibited ACh responses approximately 80% compared with approximately 40% for GTN responses. The aortic ring assay showed that 2 h pretreatment with GTN caused substantial tolerance to GTN's vasodilating effects as evidenced by a 38 fold rightward shift of the concentration-relaxation curve. In contrast to D-arginine, addition of L-arginine substantially inhibited this effect, reducing the rightward shift to 4.4 fold of control values. GTN tolerance was associated with a 40% reduction in L-arginine tissue levels. GTN had a biphasic effect on BAEC uptake of L-arginine, stimulating uptake at 5 and 15 min, and suppressing uptake after 1 and 4 h In summary, acute GTN treatment stimulates endothelial NOS activity in producing NO and increases cellular uptake of L-arginine. Prolonged GTN exposure reduces GTN's vasodilator actions, decreases L-arginine tissue levels and depresses BAECs uptake of L-arginine. Supplementation of L-arginine reduces development of GTN tolerance. These data indicate that GTN tolerance depends in part on activation of the NOS pathway.     

硝酸酯类的生物转化及其耐受机制的研究进展

硝酸酯类的生物转化涉及谷胱甘肽转移酶、细胞色素P450代谢酶、黄嘌呤氧化酶和线粒体醛脱氢酶等多种酶,其中线粒体醛脱氢酶的作用引人注目;硝酸酯类耐受的机制包括巯基耗竭学说、神经激素激活学说和氧化应激学说等,其中氧化应激学说比较流行;对于硝酸酯类耐受的防治除补充巯基供体等传统方法外,一些具有抗氧化特性的药物如肼屈嗪和硫辛酸等具有良好的抗硝酸酯耐受作用,其机制与恢复被抑制的线粒体醛脱氢酶活性有关。因此,抗氧化治疗特别是寻找和开发针对恢复线粒体醛脱氢酶活性的抗氧化药物成为目前防治硝酸酯类耐受的新策略。