Vascular Superoxide Production Research Articles

Peroxisome Proliferator‐Activated Receptor gamma (PPARgamma) ligand, Rosiglitazone, attenuates vascular oxidative stress in a mouse model of Type 2 Diabetes

Purpose The current study was designed to determine if PPARgamma ligands modulate vascular endothelial superoxide generation in vivo through suppressing expression of selected subunits of NADPH oxidase and/or by increasing the expression and activity of Cu/Zn superoxide dismutase. Methods Lean control (db+/db−) and obese, leptin receptor-deficient (db−/db−) mice were treated with either vehicle or rosiglitazone (3 mg/kg/day) by gavage for 7 days. Results Compared to db+/db− mice, obese, db−/db− mice had higher serum glucose, insulin, leptin, triglyceride, and fatty acid levels and lower adiponectin levels. Rosiglitazone had no effect on these metabolic derangements. Aortic superoxide generation measured with ESR spectroscopy was significantly increased in db−/db− mice. Aortic tissue from these mice also demonstrated higher relative mRNA levels of the NADPH oxidase subunits, Nox-1 and Nox-4, as measured by real time PCR analysis and lower mRNA levels of PPARgamma. Rosiglitazone treatment decreased superoxide generation and mRNA levels of Nox homologues in db−/db− mice. Conclusions These data indicate that short-term treatment with the rosiglitazone suppressed vascular NADPH oxidase expression and superoxide production in an animal model of vascular oxidative stress. This work is supported by grants from the Veterans Affairs Research Service

Elevated abdominal visceral fat is associated with vascular endothelial oxidative stress and inflammation among overweight and obese humans

We hypothesized that elevated abdominal visceral fat (AVF) is associated with oxidative stress and altered vascular endothelial cell protein expression (VECPE) of pro-oxidant and pro-inflammatory factors. VECPE (quantitative immunofluorescence analysis of antecubital venous endothelial cells) was measured in healthy, non-diabetic, overweight and obese (body mass index [BMI] 25–35), middle-aged and older (35–70 years) adults with high AVF (HAVF≥100cm2, computed tomography) and in age-, BMI-, total body fat-, and abdominal subcutaneous fat-matched peers with low AVF (LAVF<100cm2). VECPE of nitrotyrosine, a protein marker of oxidative stress, was greater (P<0.05) in HAVF (n=7, 0.90±0.10 VECPE/human umbilical vein endothelial cell [HUVEC] intensity) vs. LAVF (n=7, 0.46±0.11). HAVF (n=6, 0.99±0.15) had greater (P<0.05) VECPE of NADPH oxidase p47phox, a key source of vascular superoxide anion production, than LAVF (n=5, 0.44±0.08), but there were no differences in VECPE of the antioxidant enzymes CuZn superoxide dismutase (SOD), Mn SOD or catalase. VECPE of nuclear factor-κB (NFκB), a key pro-inflammatory transcription factor, was greater (P<0.05) in HAVF (n=7, 0.65±0.12) than in LAVF (n=6, 0.33±0.03), and was positively related to AVF (r=0.48, P<0.01, n=27). In overweight and obese, middle-aged and older adults, elevated AVF is associated with a vascular endothelial phenotype featuring oxidative stress and upregulation of inflammation that may predispose to atherosclerosis. Supported by NIH AG006537, AG013038, AG022241, AG025194 and RR00051.

Evidences for prevention of nitroglycerin tolerance by carvedilol

Carvedilol, a β-blocker has shown clinically to attenuate the development of nitroglycerin (NTG) tolerance. The present study was designed to investigate the possible mechanisms whereby carvedilol could prevent NTG tolerance, particularly at the level of vascular superoxide anion (O 2 −) production (an important factor in nitrate tolerance) as well as modulation of certain aortic antioxidants. Rabbits were treated with NTG patch (1.5 μg/kg/min) and/or cavedilol (10 mg/kg/day) for 3 days. Relaxation of aortic segments was studied in organ chamber and rate of vascular O 2 − production was determined. In addition, aortic glutathione (GSH) level and superoxide dismutase (SOD) activity was also assessed. Aortic segments from NTG-treated rabbits showed a significant decrease in maximal relaxation in response to various vasodilators. Also, NTG treatment increased vascular O 2 − production by two-fold as compared with untreated control group. The potential source of O 2 − production was found to be the adventitia. In addition, treatment of rabbits with NTG induced a significant decrease in total GSH level and SOD activity by 46 and 53%, respectively, as compared with the control values. Concomitant treatment of NTG with carvedilol significantly prevented the development of NTG tolerance and normalized the rate of vascular O 2 − production. Moreover, carvedilol restored the normal level of aortic antioxidants mainly, total GSH and SOD.

Propofol improves endothelial dysfunction and attenuates vascular superoxide production in septic rats

To determine the effects of propofol on vascular functions, plasma and endothelium-derived nitric oxide (EDNO), vascular NO, and cyclic guanosine monophosphate (cGMP), as well as vascular production of superoxide anion (O2*-), in septic animals. Prospective, multiexperimental, randomized, controlled studies. University research laboratory. Male adult Sprague-Dawley rats weighing 350-400 g. Cecal ligation and puncture (CLP), with and without propofol (25 mg/kg/hr) infusion, after sham or CLP (24 hrs postsurgery). Plasma NOx, basal aortic NOx, and cGMP concentrations all increased, whereas acetylcholine-induced endothelium-dependent relaxation (EDR), contractile response, and EDNO all decreased in CLP vs. sham rats (p < .001). Acetylcholine stimulated aortic NOx and cGMP significantly in sham and CLP-propofol (p < .01) but not CLP rats. Thus, propofol ameliorated the CLP-induced increases in plasma NOx, basal aortic NOx, and cGMP. It restored the CLP-induced impairment of EDR, EDNO, and acetylcholine-stimulated aortic NOx and cGMP levels. More O2*- production (measured by lucigenin-enhanced chemiluminescence) was noted in carotid arteries from CLP vs. sham rats (p < .001). Nicotinamide adenine dinucleotide (NADH; 1 mM) stimulated O2*- production in all rings, with significantly more increase in CLP vs. sham (p < .001). Propofol attenuated the excessive increase in O2*- production of CLP rings. Propofol treatment attenuated the overproduction of NO and O2*-, thus restoring the acetylcholine-responsive NO-cGMP pathway in CLP-induced sepsis. It also significantly improved the CLP-impaired EDR and EDNO in a parallel manner. These beneficial effects of propofol could be accounted for by improvement of the disturbed NO/O2*- balance in sepsis.

Arginase: a modulator of myocardial function

when nitric oxide (NO) donors were first administered to isolated, normal cardiomyocytes, a negative, cGMP-dependent inotropic effect was observed, whereas inhibitors of NO synthases (NOS) had no effect. Further studies then demonstrated a biphasic contractile response to exogenous NO and cGMP,

Vitamin E deficiency accelerates nitrate tolerance via a decrease in cardiac P450 expression and increased oxidative stress

Organic nitrates, such as nitroglycerin (NTG), have been used to relieve the symptoms of angina pectoris. However, their biochemical mechanisms of action, particularly in relation to the development of tolerance, are incompletely defined. It has been reported that supplemental antioxidants such as vitamin E attenuate the development of nitrate tolerance. Therefore, we examined the role of vitamin E in the regulation of nitrate tolerance. Continuous NTG infusion induced nitrate tolerance in rats after 48 h, and vitamin E concentrations decreased in a time-dependent manner in tissues and plasma. Vitamin E supplementation (0.5 g/kg diet) maintained higher concentrations of vitamin E during NTG infusion. The onset and extent of the tolerance, estimated by the decrease in blood pressure following NTG bolus injection during the infusion of NTG, were accentuated in the vitamin E-deficient group. Vitamin E supplementation inhibited nitrate tolerance 48 h after NTG infusion. Cardiac P450 expression (CYP1A2) assessed by immunoblotting, markedly decreased 48 h after NTG administration in control rats. The supplementation of vitamin E significantly attenuated the decrease in P450. Treatment of NTG enhanced vascular superoxide production (L-012 chemiluminescence, DHE fluorescence). The peak of lipid peroxidation and free radical generation in the heart was reached before tolerance developed. In contrast, vitamin E-deficient hearts had lower P450 expression and higher free radical generation than control hearts. To evaluate other vitamin E-inhibitable mechanisms of nitrate tolerance, we studied the NO-cGMP pathway. NTG markedly reduced the vasodilator-stimulated phosphoprotein (VASP) serine 239 phosphorylation (specific substrate of cGMP-activated protein kinase I; cGK-I) in tolerant hearts. Vitamin E inhibited the depletion of pVASP. In conclusion, because continuous NTG infusion causes vitamin E depletion as well as nitrate tolerance, vitamin E deficiency may further accelerate nitrate tolerance via an increase in oxidative stress, the reduced bioconversion because of decreased P450 expression, and impairment of the NO/cGMP pathway in tolerant heart tissues.

Mechanisms of Increased Vascular Superoxide Production in an Experimental Model of Idiopathic Dilated Cardiomyopathy

In the present study, we sought to identify mechanisms underlying increased oxidative stress in vascular tissue in an experimental animal model of chronic congestive heart failure (CHF). Superoxide and nitric oxide (NO) was measured in vessels from cardiomyopathic hamsters (CHF hamsters) and golden Syrian hamsters. We also determined expression of endothelial nitric oxide synthase (NOSIII), the soluble guanylyl cyclase, the cGMP-dependent kinase, and the NADPH oxidase. To analyze the contribution of the renin-angiotensin system to oxidative stress, CHF hamsters were treated with the angiotensin-converting enzyme inhibitor captopril for 200 days (120 mg . kg(-1) . d(-1)). CHF led to increased superoxide production by NOSIII and the NADPH oxidase. Decreased NO production in CHF was associated with a decrease in the expression of NOSIII and an inhibition of NO downstream signaling in the aorta. NOSIII expression was increased within the left ventricle. Captopril treatment normalized NOSIII expression in vessels and the myocardium, reduced superoxide levels, and prevented NOSIII uncoupling. Accordingly, endothelial function, NO production, and downstream signaling were improved in CHF vessels. Oxidative stress in CHF is mediated by NADPH oxidase and an uncoupled NOSIII secondary to an activation of the renin-angiotensin system leading to impaired NO downstream signaling.

Explaining the Phenomenon of Nitrate Tolerance

During the last century, nitroglycerin has been the most commonly used antiischemic and antianginal agent. Unfortunately, after continuous application, its therapeutic efficacy rapidly vanishes. Neurohormonal activation of vasoconstrictor signals and intravascular volume expansion constitute early counter-regulatory responses (pseudotolerance), whereas long-term treatment induces intrinsic vascular changes, eg, a loss of nitrovasodilator-responsiveness (vascular tolerance). This is caused by increased vascular superoxide production and a supersensitivity to vasoconstrictors secondary to a tonic activation of protein kinase C. NADPH oxidase(s) and uncoupled endothelial nitric oxide synthase have been proposed as superoxide sources. Superoxide and vascular NO rapidly form peroxynitrite, which aggravates tolerance by promoting NO synthase uncoupling and inhibition of soluble guanylyl cyclase and prostacyclin synthase. This oxidative stress concept may explain why radical scavengers and substances, which reduce oxidative stress indirectly, are able to relieve tolerance and endothelial dysfunction. Recent work has defined a new tolerance mechanism, ie, an inhibition of mitochondrial aldehyde dehydrogenase, the enzyme that accomplishes bioactivation of nitroglycerin, and has identified mitochondria as an additional source of reactive oxygen species. Nitroglycerin-induced reactive oxygen species inhibit the bioactivation of nitroglycerin by thiol oxidation of aldehyde dehydrogenase. Both mechanisms, increased oxidative stress and impaired bioactivation of nitroglycerin, can be joined to provide a new concept for nitroglycerin tolerance and cross-tolerance. The consequences of these processes for the nitroglycerin downstream targets soluble guanylyl cyclase, cGMP-dependent protein kinase, cGMP-degrading phosphodiesterases, and toxic side effects contributing to endothelial dysfunction, such as inhibition of prostacyclin synthase, are discussed in this review.

The Oxidative Stress Concept of Nitrate Tolerance and the Antioxidant Properties of Hydralazine

The hemodynamic and anti-ischemic effects of nitroglycerin (NTG) are rapidly blunted as a result of the development of nitrate tolerance. With initiation of NTG therapy, it is possible to detect neurohormonal activation and intravascular volume expansion. These so-called pseudotolerance mechanisms may compromise the vasodilatory effects of NTG. Long-term nitrate treatment also is associated with decreased vascular responsiveness caused by changes in intrinsic mechanisms of the tolerant vasculature itself. According to the oxidative stress concept, increased vascular superoxide (O2-) production and an increased sensitivity to vasoconstrictors secondary to activation of protein kinase C contribute to the development of tolerance. Nicotinamide adenine dinucleotide phosphate oxidase and the uncoupled endothelial nitric oxide synthase may be O2- -producing enzymes. Nitric oxide (NO) and O2-, both derived from NTG and the vessel wall, form peroxynitrite in a diffusion-limited rapid reaction. Peroxynitrite, O2-, or both may be responsible for the development of nitrate tolerance and cross-tolerance to direct NO donors (eg, sodium nitroprusside, sydnonimines) and endothelium-dependent NO synthase-activating vasodilators. Hydralazine is an efficient reactive oxygen species (ROS) scavenger and an inhibitor of O2- generation. When given concomitantly with NTG, hydralazine prevents the development of nitrate tolerance and normalizes endogenous rates of vascular O2- production. Recent experimental work has defined new tolerance mechanisms, including inhibition of the enzyme that bioactivates NTG (ie, mitochondrial aldehyde dehydrogenase isoform 2 [ALDH2]) and mitochondria as potential sources of ROS. NTG-induced ROS inhibit the bioactivation of NTG by ALDH2. Both mechanisms increase oxidative stress and impair NTG bioactivation, and now converge at the level of ALDH2 to support a new theory for NTG tolerance and NTG-induced endothelial dysfunction. The consequences of these processes for NTG downstream targets (eg, soluble guanylyl cyclase, cyclic guanosine monophosphate-dependent protein kinase), toxic effects contributing to endothelial dysfunction (eg, prostacyclin synthase inhibition) and novel applications of the antioxidant properties of hydralazine are discussed.

Genetic modification of vascular endothelial function as therapeutic strategy in heart failure

in patients with chronic heart failure, endothelial dysfunction contributes to increased systemic vascular resistance, decreased exercise tolerance, and reduced tissue perfusion. One of the better-characterized mechanisms responsible for endothelial dysfunction is the increased production of

Endothelial Nitric Oxide Production Stimulated by the Bioflavonoid Chrysin in Rat Isolated Aorta

In the present study, the effects of the bioflavonoid chrysin (5,7-dihydroxyflavone) were analysed on nitric oxide (NO) production from vascular endothelium. In aortic rings, incubation with chrysin or acetylcholine (both at 10 microM) increased L-NAME-sensitive endothelial NO release as measured using the fluorescent probe 4,5-diaminofluorescein diacetate (DAF-2 DA). Moreover, chrysin increased cGMP accumulation only in aortic rings with endothelium. However, at this concentration, chrysin had no effect either on basal or on NADPH-stimulated vascular superoxide production. Moreover, at this low concentration, chrysin, similar to acetylcholine, induced aortic relaxation, which was abolished by both endothelial deprivation and NO synthase inhibition. Endothelium-dependent relaxation induced by chrysin was unaltered by removal of extracellular calcium and incubation with the intracellular calcium chelator BAPTA, while the phosphatidylinositol (PI)-3 kinase inhibitor wortmannin suppressed the endothelial dependence. In conclusion, chrysin stimulated NO release from endothelial cells leading to vascular cGMP accumulation and subsequent endothelium dependent aortic relaxation. Chrysin-stimulated NO release is calcium independent and possibly mediated via PI3-kinase.

Glucose-6 Phosphate Dehydrogenase Deficiency Decreases the Vascular Response to Angiotensin II

Glucose-6-phosphate dehydrogenase (G6PD) regulates production of the reduced form of NADPH through the pentose phosphate pathway. G6PD may therefore affect superoxide anion production via vascular NADPH oxidase, which is key in mediating the vascular response to angiotensin II (Ang II). We determined the hypertensive and vascular hypertrophic response to Ang II in G6PD-deficient mice. Ang II (0.7 mg/kg per day) was infused via subcutaneous osmotic pumps for 6 days in male hemizygote G6PD mutant (G6PD(mut)) and wild-type (WT) C3H mice. (1) Compared with WT, G6PD(mut) mouse aorta had 10% to 20% of G6PD activity and 50% less NADPH. (2) Basal systolic blood pressure was not significantly different in G6PD(mut) mice (WT 88+/-4 mm Hg versus G6PD(mut) 95+/-4 mm Hg), but Ang II increased blood pressure to a lower level in G6PD(mut) mice (WT 139+/-4 mm Hg versus G6PD(mut) 123+/-5 mm Hg; P<0.05). (3) Ang II increased aortic medial thickness less in G6PD(mut) mice (WT 71+/-2 mum versus G6PD(mut) 62+/-1 mum; P<0.01). (4) 3-o-Nitrotyrosine staining and dihydroethidium oxidation in the aorta was increased by Ang II less in G6PD(mut) mice. (5) Smooth muscle cells isolated from G6PD(mut) mice showed less Ang II-induced phosphorylation of Akt and p42/44 ERK. G6PD deficiency may reduce vascular superoxide anion production by limiting production of the substrate for NADPH oxidase, thereby inhibiting oxidant-mediated Ang II-induced signaling pathways that contribute to hypertension and smooth muscle hypertrophy.

Oxidative stress and vascular remodelling

Oxidative stress plays an important role in the pathophysiology of vascular diseases. Reactive oxygen species, especially superoxide anion and hydrogen peroxide, are important signalling molecules in cardiovascular cells. Enhanced superoxide production increases nitric oxide inactivation and leads to an accumulation of peroxynitrites and hydrogen peroxide. Reactive oxygen species participate in growth, apoptosis and migration of vascular smooth muscle cells, in the modulation of endothelial function, including endothelium-dependent relaxation and expression of proinflammatory phenotype, and in the modification of the extracellular matrix. All these events play important roles in vascular diseases such as hypertension, suggesting that the sources of reactive oxygen species and the signalling pathways that they modify may represent important therapeutic targets. Potential sources of vascular superoxide production include NADPH-dependent oxidases, xanthine oxidases, lipoxygenases, mitochondrial oxidases and nitric oxide synthases. Studies performed during the last decade have shown that NADPH oxidase is the most important source of superoxide anion in phagocytic and vascular cells. Evidence from experimental animal and human studies suggests a significant role of NADPH oxidase activation in the vascular remodelling and endothelial dysfunction found in cardiovascular diseases.

W02-P-015 Novel cardiovascular risk factors in individuals with family history of premature atherosclerotic disease

This study sought to determine the effects of endogenous tetrahydrobiopterin (BH4) bioavailability on endothelial nitric oxide synthase (eNOS) coupling, nitric oxide (NO) bioavailability, and vascular superoxide production in patients with coronary artery disease (CAD).GTP-cyclohydrolase I, encoded by the GCH1 gene, is the rate-limiting enzyme in the biosynthesis of BH4, an eNOS cofactor important for maintaining enzymatic coupling. We examined the associations between haplotypes of the GCH1 gene, GCH1 expression and biopterin levels, and the effects on endothelial function and vascular superoxide production.Blood samples and segments of internal mammary arteries and saphenous veins were obtained from patients with CAD undergoing coronary artery bypass grafting (n = 347). The GCH1 haplotypes were defined by 3 polymorphisms: rs8007267G<A, rs3783641A<T, and rs10483639C<G (X haplotype: A, T, G; O haplotype: any other combination). Vascular superoxide (± the eNOS inhibitor NG-nitro-L-arginine methyl ester [L-NAME]) was measured by lucigenin-enhanced chemiluminescence, whereas the vasorelaxations of saphenous veins to acetylcholine were evaluated ex vivo.Haplotype frequencies were OO 70.6%, XO 27.4%, and XX 2.0%. The X haplotype was associated with significantly lower vascular GCH1 messenger ribonucleic acid expression and substantial reductions in both plasma and vascular BH4 levels. In X haplotype carriers both vascular superoxide and L-NAME–inhibitable superoxide were significantly increased, and were associated with reduced vasorelaxations to acetylcholine.GCH1 gene expression, modulated by a particular GCH1 haplotype, is a major determinant of BH4 bioavailability both in plasma and in the vascular wall in patients with CAD. Genetic variation in GCH1 underlies important differences in endogenous BH4 availability and is a determinant of eNOS coupling, vascular redox state, and endothelial function in human vascular disease.

Physical Inactivity Increases Oxidative Stress, Endothelial Dysfunction, and Atherosclerosis

Sedentary lifestyle is associated with increased cardiovascular events. The underlying molecular mechanisms are incompletely understood. Reactive oxygen species (ROS) contribute to endothelial dysfunction and atherosclerosis. An important source of vascular ROS is the NADPH oxidase. C57BL6 mice were subjected to regular housing (physical inactivity) or voluntary training on running wheels (6 weeks). Inactivity increased vascular lipid peroxidation to 148+/-9% and upregulated superoxide release to 176+/-17% (L-012 chemiluminescence) and 188+/-29% (cytochrome C reduction assay), respectively. ROS production was predominantly increased in the endothelium and the media (dihydroethidium fluorescence). Activity of the NADPH oxidase was increased to 154+/-22% in the sedentary group. Rac1 GST-PAK pull-down assays showed an upregulation of rac1 activity to 161+/-14%. Expression levels of the subunits nox1, p47phox, and p67phox were increased. To address the significance of the antioxidative effects of running, experiments were repeated in apolipoprotein E-deficient mice treated with a high-cholesterol diet. Inactivity increased vascular superoxide production and impaired endothelium-dependent vasorelaxation. Atherosclerotic lesion formation was significantly accelerated in sedentary mice. Inactivity increases vascular NADPH oxidase expression and activity and enhances vascular ROS production, which contributes to endothelial dysfunction and atherosclerosis during sedentary as opposed to physically active lifestyle.

Effects of sarpogrelate, a 5-hydroxytriptamine 2A receptor antagonist on endotoxin shock in rats

It is known that 5-hydroxytriptamine (5-HT)2A receptors have some roles in vascular constriction, platelet aggregation, and superoxide production by neutrophils. 5-HT2A receptor antagonists are therefore expected to be effective for sepsis. The present study was performed to investigate the effects of sarpogrelate, a 5-HT2A receptor antagonist on endotoxin shock in rats.

Chronic Hypoxia Accelerates the Progression of Atherosclerosis in Apolipoprotein E-Knockout Mice

The aim of this study was to investigate the effect of chronic hypoxia on the development and progression of atherosclerosis in apolipoprotein E-knockout (apoE-KO) mice. Male and female apoE-KO mice (6 weeks old) and age- and sex-matched wild-type mice were kept under hypoxic conditions (10.0 +/- 0.5% O2) in a gas chamber or in room air for 3 weeks. Aortic atherosclerotic plaque was not observed in wild-type mice under normoxic or hypoxic conditions. In the apoE-KO mice, however, hypoxia induced proliferation of smooth muscle cells and plaque formation in the aorta, which were not observed under normoxic conditions. Although sexual dimorphism of the response to hypoxia was not observed, these hypoxia-induced atherogenic changes were accompanied by a significant increase of plasma low density lipoprotein (LDL) cholesterol and NADPH-dependent vascular superoxide (O2-) production. Furthermore, matrix metalloproteinase (MMP)-9 was activated in the aorta of apoE-KO mice. In conclusion, chronic hypoxia accelerated the development of atherosclerosis in apoE-KO mice, along with increased O2- production and activated MMP-9 in the aorta.

Hyperbaric oxygen protects against lipopolysaccharide-stimulated oxidative stress and mortality in rats

Free radicals and proinflammatory mediators have been implicated in the pathogenesis of endotoxic shock, a disease with high mortality caused by Gram-negative bacterial endotoxin. Hyperbaric oxygen is used as an adjuvant therapy for various inflammatory diseases and shows beneficial effects in lipopolysaccharide-induced shock syndrome. However, the underlying mechanisms for these effects are still to be defined. In this study, we investigated the effect of hyperbaric oxygen on inflammatory mediators, free radicals, and mortality in endotoxic rats. Wistar–Kyoto rats were injected with lipopolysaccharide (10 mg/kg) and then exposed to aminoguanidine, an inhibitor of inducible nitric oxide (NO) synthase (bolus injection 2 h after lipopolysaccharide), or hyperbaric oxygen (2 ATA for 60 min 1, 4, 9, and 24 h after lipopolysaccharide). Plasma tumor necrosis factor alpha (TNF-α), NO, and superoxide anion were detected and the vasorelaxation response and survival rate were assessed. The results demonstrated that increases in plasma TNF-α and NO, and the vasohyporeactivity induced by lipopolysaccharide treatment were significantly inhibited by hyperbaric oxygen and aminoguanidine. Mortality and vascular superoxide anion production of lipopolysaccharide treatment were also markedly reduced by hyperbaric oxygen treatment, but were not restored by aminoguanidine. None of the parameters was changed by hyperbaric oxygen treatment alone. Thus, repeated hyperbaric oxygen exposure significantly attenuated the inflammatory mediators, free radicals, and mortality in endotoxic rats.

NADPH Oxidase Inhibition Attenuates Oxidative Stress but Not Hypertension Produced by Chronic ET-1

Experiments were conducted to test the hypothesis that hypertension produced by chronic ET-1 infusion is mediated by NADPH oxidase-dependent superoxide production. Mean arterial pressure (MAP) was continuously monitored in male Sprague Dawley rats by telemetry. After baseline measurements, rats were placed on a high-salt diet (8% NaCl) and osmotic minipumps were implanted to infuse ET-1 (5 pmol/kg per minute intravenous) for 12 days. Control rats were maintained on the high-salt diet only. Separate groups of rats were also infused with ET-1 and given the superoxide dismutase mimetic, tempol (1 mmol/L), or the NADPH oxidase inhibitor, apocynin (1.5 mmol/L), in the drinking water. Infusion of ET-1 significantly increased MAP when compared with baseline values (132+/-3 versus 114+/-2 mm Hg, P<0.05). Neither tempol nor apocynin treatment had any effect on the increase in MAP produced by ET-1 when compared with baseline values (127+/-5 versus 113+/-2 and 130+/-3 versus 115+/-2 mm Hg, respectively). Plasma 8-isoprostane, an indicator of oxidative stress, was significantly increased in ET-1-infused rats compared with rats on a high-salt diet alone (128+/-33 versus 51+/-5 pg/mL; P<0.05). Both tempol and apocynin treatment significantly attenuated the ET-1-induced increase in plasma 8-isoprostane (72+/-10 and 61+/-6 pg/mL, respectively). Similarly, ET-1 infusion also significantly increased aortic superoxide production (chemiluminescence and dihydroethidium staining techniques), which was prevented by both tempol and apocynin. These data provide evidence that chronic ET-1 infusion increases vascular NADPH oxidase-dependent superoxide production but does not account for chronic ET-1-induced hypertension.

ETA Receptor Blockade Attenuates Hypertension and Decreases Reactive Oxygen Species in ETB Receptor-Deficient Rats

We hypothesize that endothelin-A receptor stimulation contributes to the elevated blood pressure and superoxide production in endothelin-B receptor-deficient rats on a high salt diet. Experiments were conducted on homozygous endothelin-B-deficient (sl/sl) and wild-type rats (wt) fed a high salt diet (8% NaCl) for 3 weeks. Separate groups were given normal drinking water or water containing the endothelin-A receptor antagonist, ABT-627 (5 mg/kg per day; n = 8-9 in all groups). On a normal salt diet, (sl/sl) rats had a significantly elevated systolic blood pressure compared with wt (138 +/- 3 vs 117 +/- 4 mmHg, respectively; P < 0.05). High salt diet caused a significant increase in systolic blood pressure in (sl/sl) rats compared with wt (158 +/- 2 vs 138 +/- 3 mmHg, respectively; P < 0.05). Endothelin-A receptor blockade decreased systolic blood pressure in (sl/sl) rats on high salt (125 +/- 5 mmHg; P < 0.05 vs without antagonist) without affecting the systolic blood pressure in wt (119 +/- 4 mmHg). Aortic superoxide production (lucigenin chemiluminescence) and plasma 8-isoprostane were elevated in sl/sl rats and were significantly reduced by endothelin-A receptor blockade in sl/sl, but not in wt rats. These findings suggest that endothelin-1, through the endothelin-A receptor, contributes to salt-induced hypertension and vascular superoxide production in endothelin-B-deficient rats.