Hydrogen peroxide induces contraction and raises [Ca2+]i in canine cerebral arterial smooth muscle: participation of cellular signaling pathways

Perivascular Adipose Tissue and Vascular Smooth Muscle Tone: Friends or Foes?

Perivascular adipose tissue (PVAT) is a specialized type of adipose tissue that surrounds most mammalian blood vessels. PVAT is a metabolically active, endocrine organ capable of regulating blood vessel tone, endothelium function, vascular smooth muscle cell growth and proliferation, and contributing critically to cardiovascular disease onset and progression. In the context of vascular tone regulation, under physiological conditions, PVAT exerts a potent anticontractile effect by releasing a plethora of vasoactive substances, including NO, H₂S, H₂O₂, prostacyclin, palmitic acid methyl ester, angiotensin 1-7, adiponectin, leptin, and omentin. However, under certain pathophysiological conditions, PVAT exerts pro-contractile effects by decreasing the production of anticontractile and increasing that of pro-contractile factors, including superoxide anion, angiotensin II, catecholamines, prostaglandins, chemerin, resistin, and visfatin. The present review discusses the regulatory effect of PVAT on vascular tone and the factors involved. In this scenario, dissecting the precise role of PVAT is a prerequisite to the development of PVAT-targeted therapies.

Oxidative Regulation of Vascular Cav1.2 Channels Triggers Vascular Dysfunction in Hypertension-Related Disorders

Blood pressure is determined by cardiac output and peripheral vascular resistance. The L-type voltage-gated Ca²⁺ (Ca_v1.2) channel in small arteries and arterioles plays an essential role in regulating Ca²⁺ influx, vascular resistance, and blood pressure. Hypertension and preeclampsia are characterized by high blood pressure. In addition, diabetes has a high prevalence of hypertension. The etiology of these disorders remains elusive, involving the complex interplay of environmental and genetic factors. Common to these disorders are oxidative stress and vascular dysfunction. Reactive oxygen species (ROS) derived from NADPH oxidases (NOXs) and mitochondria are primary sources of vascular oxidative stress, whereas dysfunction of the Ca_v1.2 channel confers increased vascular resistance in hypertension. This review will discuss the importance of ROS derived from NOXs and mitochondria in regulating vascular Ca_v1.2 and potential roles of ROS-mediated Ca_v1.2 dysfunction in aberrant vascular function in hypertension, diabetes, and preeclampsia.

NADPH oxidase in the vasculature: Expression, regulation and signalling pathways; role in normal cardiovascular physiology and its dysregulation in hypertension

The last 20-25 years have seen an explosion of interest in the role of NADPH oxidase (NOX) in cardiovascular function and disease. In vascular smooth muscle and endothelium, NOX generates reactive oxygen species (ROS) that act as second messengers, contributing to the control of normal vascular function. NOX activity is altered in response to a variety of stimuli, including G-protein coupled receptor agonists, growth-factors, perfusion pressure, flow and hypoxia. NOX-derived ROS are involved in smooth muscle constriction, endothelium-dependent relaxation and smooth muscle growth, proliferation and migration, thus contributing to the fine-tuning of blood flow, arterial wall thickness and vascular resistance. Through reversible oxidative modification of target proteins, ROS regulate the activity of protein tyrosine phosphatases, kinases, G proteins, ion channels, cytoskeletal proteins and transcription factors. There is now considerable, but somewhat contradictory evidence that NOX contributes to the pathogenesis of hypertension through oxidative stress. Specific NOX isoforms have been implicated in endothelial dysfunction, hyper-contractility and vascular remodelling in various animal models of hypertension, pulmonary hypertension and pulmonary arterial hypertension, but also have potential protective effects, particularly NOX4. This review explores the multiplicity of NOX function in the healthy vasculature and the evidence for and against targeting NOX for antihypertensive therapy.

Role of calcium channels and endothelial factors in nickel induced aortic hypercontraction in Wistar rats

Aim: To investigate the mechanism of nickel augmented phenylephrine (PE)-induced contraction in isolated segments of Wistar rat aorta. Materials and Methods: Effect of varying concentrations of nickel on PE-induced contraction were investigated in isolated segments of Wistar rat aorta using an organ bath system. Aortic rings were pre-incubated with verapamil (1 µM and 20 µM), gadolinium, apocynin, indomethacin or N-G-nitro-L-arginine methyl ester (L-NAME) separately before incubation with nickel. Results: Endothelium intact aortic rings incubated with 100 nM, 1 µM or 100 µM of nickel exhibited 80%, 43% and 28% increase in PE-induced contraction, respectively, while no such enhancing responses were observed in endothelium denuded aorta. Incubation of aortic rings with 1 µM and 20 µM verapamil suggested an involvement of influx of calcium through T-type calcium channels in smooth muscle cells, while aortic rings pre-incubated with gadolinium showed no role of store operated calcium channels in the nickel effect on PE-induced contractions. The enhancing effect of nickel on PE-induced contractions was inhibited by apocynin, indomethacin or L-NAME. Conclusion: Nickel has caused augmentation of PE-induced contractions as a result of the endothelial generation of reactive oxygen species (ROS) and cyclooxygenase 2 (COX2) dependent endothelium contracting factors (EDCFs), which increases the influx of extracellular calcium through T-type Ca²⁺ channels in smooth muscle cells.

Dental resin curing blue light induces vasoconstriction through release of hydrogen peroxide

Dental resin curing blue light (BL) is frequently used during treatments in dental clinics. However, little is known about the influence of BL irradiation on pulpal blood vessels. The aim of the present study was to investigate the mechanism of effect of BL irradiation on vascular tone. Rat aorta (RA) rings were irradiated with a BL source in organ baths, and the responses were recorded isometrically. Effect of BL irradiation on phenylephrine (PE) -precontraction and acetylcholine (ACh) -induced relaxation after PE -precontraction were obtained and compared in BL -irradiated and control RA rings. Effect of 20 min preincubation with catalase (enzyme that breaks down hydrogene peroxide, 1200 u/ml) on PE -precontraced and BL-irradiated rings was also evaluated. Total oxidative stress (TOS) and total antioxidant capacity (TAC) in BL-irradiated and control RA preparations were measured with special assay kits and spectrophotometry. BL slightly decreased ACh -induced endothelium -dependent relaxations in PE (1 μM) -precontracted RA rings (n = 6, p > 0.05 vs. control). BL induced marked contraction 23.88 + 3.10% of PE (maximum contraction) in isolated RA ring segments precontracted with PE (p < 0.05 vs. control). The contractile effect of BL was inhibited by 1200 u/ml catalase (n = 6, p < 0.05 vs. control). BL irradiation increased the level of TOS in RA rings (n = 6, p < 0.05 vs. control). TAC levels were similar in BL-irradiated and control preparations. These results suggest that BL induces contraction in RA, and the mechanism of this effect may to be through release of hydrogen peroxide.

Hydrogen Peroxide as a Paracrine Vascular Mediator: Regulation and Signaling Leading to Dysfunction

Numerous studies have demonstrated the ability of a variety of vascular cells, including endothelial cells, smooth muscle cells, and fibroblasts, to produce reactive oxygen species (ROS). Until recently, major emphasis was placed on the production of superoxide anion (O2–) in the vasculature as a result of its ability to directly attenuate the biological activity of endothelium-derived nitric oxide (NO). The short half-life and radius of diffusion of O2– drastically limit the role of this ROS as an important paracrine hormone in vascular biology. On the contrary, in recent years, the O2– metabolite hydrogen peroxide (H2O2) has increasingly been viewed as an important cellular signaling agent in its own right, capable of modulating both contractile and growth-promoting pathways with more far-reaching effects. In this review, we will assess the vascular production of H2O2, its regulation by endogenous scavenger systems, and its ability to activate a variety of vascular signaling pathways, thereby leading to vascular contraction and growth. This discussion will include the ability of H2O2 to (i) Initiate calcium flux as well as (ii) stimulate pathways leading to sensitization of contractile elements to calcium. The latter involves a variety of protein kinases that have also been strongly implicated in vascular hypertrophy. Previous Intensive study has emphasized the ability of NADPH oxidase-derived O2– and H2O2 to activate these pathways in cultured smooth muscle cells. However, growing evidence indicates a considerably more complex array of unique oxidase systems in the endothelium, media, and adventitia that appear to participate in these deleterious effects in a sequential and temporal manner. Taken together, these findings seem consistent with a paracrine effect of H2O2 across the vascular wall.

Effect of oxidative stress on Rho kinase II and smooth muscle contraction in rat stomach

Recent studies have shown that both Rho kinase signaling and oxidative stress are involved in the pathogenesis of a number of human diseases, such as diabetes mellitus, hypertension, and atherosclerosis. However, very little is known about the effect of oxidative stress on the gastrointestinal (GI) smooth muscle Rho kinase pathway. The aim of the current study was to investigate the effect of oxidative stress on Rho kinase II and muscle contraction in rat stomach. The peroxynitrite donor 3-morpholinosydnonimine (SIN-1), hydrogen peroxide (H2O2), and peroxynitrite were used to induce oxidative stress. Rho kinase II expression and ACh-induced activity were measured in control and oxidant-treated cells via specifically designed enzyme-linked immunosorbent assay (ELISA) and activity assay kits, respectively. Single smooth muscle cell contraction was measured via scanning micrometry in the presence or absence of the Rho kinase blocker, Y-27632 dihydrochloride. All oxidant agents significantly increased ACh-induced Rho kinase II activity without affecting its expression level. Most important, oxidative stress induced by all three agents augmented ACh-stimulated muscle cell contraction, which was significantly inhibited by Y-27632. In conclusion, oxidative stress activates Rho kinase II and enhances contraction in rat gastric muscle, suggesting an important role in GI motility disorders associated with oxidative stress.

Characteristics of evodiamine-exerted stimulatory effects on rat jejunal contractility

This study was designed to characterise the effects of evodiamine on intestinal contractility and reveal the correlated mechanisms. Evodiamine (2.5-80.0 μM) increased normal jejunal contractility and jejunal hypocontractility established under a variety of experimental conditions. Evodiamine-exerted stimulatory effects were blocked by the L-type Ca(2+) channel blocker nifedipine or abolished in the Ca(2+)-free assay condition. The stimulatory effects of evodiamine on jejunal contractility were partially blocked in the presence of neurotoxin tetrodotoxin or endogenous acetylcholine synthesis blocker hemicholinium-3 or muscarinic receptor antagonist atropine, respectively. Evodiamine-exerted stimulatory effects were blocked by c-kit receptor tyrosine kinase inhibitor imatinib. Evodiamine increased myosin phosphorylation in jejunal smooth muscle of constipation-prominent rats. These results showed that evodiamine-exerted stimulatory effects on jejunal segments are Ca(2+)-dependent, need the presence of interstitial cell of Cajal, requirement of cholinergic neuron and correlate with increased myosin phosphorylation, implicating the potential value of evodiamine in relieving hypo-motility disorders.

Hydrogen peroxide elicits constriction of skeletal muscle arterioles by activating the arachidonic acid pathway

Aims

The molecular mechanisms of the vasoconstrictor responses evoked by hydrogen peroxide (H₂O₂) have not been clearly elucidated in skeletal muscle arterioles.

Methods and Results

Changes in diameter of isolated, cannulated and pressurized gracilis muscle arterioles (GAs) of Wistar-Kyoto rats were determined under various test conditions. H₂O₂ (10–100 µM) evoked concentration-dependent constrictions in the GAs, which were inhibited by endothelium removal, or by antagonists of phospholipase A (PLA; 100 µM 7,7-dimethyl-(5Z,8Z)-eicosadienoic acid), protein kinase C (PKC; 10 µM chelerythrine), phospholipase C (PLC; 10 µM U-73122), or Src family tyrosine kinase (Src kinase; 1 µM Src Inhibitor-1). Antagonists of thromboxane A2 (TXA2; 1 µM SQ-29548) or the non-specific cyclooxygenase (COX) inhibitor indomethacin (10 µM) converted constrictions to dilations. The COX-1 inhibitor (SC-560, 1 µM) demonstrated a greater reduction in constriction and conversion to dilation than that of COX-2 (celecoxib, 3 µM). H₂O₂ did not elicit significant changes in arteriolar Ca²⁺ levels measured with Fura-2.

Conclusions

These data suggest that H₂O₂ activates the endothelial Src kinase/PLC/PKC/PLA pathway, ultimately leading to the synthesis and release of TXA2 by COX-1, thereby increasing the Ca²⁺ sensitivity of the vascular smooth muscle cells and eliciting constriction in rat skeletal muscle arterioles.

Characteristics of nobiletin-induced effects on jejunal contractility

Nobiletin, a citrus polymethoxylated flavone, exhibits multiple biological properties including anti-inflammatory, anti-carcinogenic, and anti-insulin resistance effects. The present study found that nobiletin exerted significant stimulatory effects on the contractility of isolated rat jejunal segments in all 6 different low contractile states, and meanwhile significant inhibitory effects in all 6 different high contractile states, showing characteristics of bidirectional regulation (BR). Nobiletin-exerted BR on jejunal contractility was abolished in the presence of c-kit receptor tyrosine kinase inhibitor imatinib or Ca(2+) channel blocker verapamil. In the presence of neuroxin tetrodotoxin, nobiletin only exerted stimulatory effects on jejunal contractility in both low and high contractile states. Hemicholinium-3 and atropine partially blocked nobiletin-exerted stimulatory effects on jejunal contractility in low-Ca(2+)-induced low contractile state. Phentolamine or propranolol or l-NG-nitro-arginine significantly blocked nobiletin-exerted inhibitory effects on jejunal contractility in high-Ca(2+)-induced high contractile state respectively. The effects of nobiletin on myosin light chain kinase (MLCK) mRNA expression, MLCK protein content, and myosin light chain phosphorylation extent were also bidirectional. In summary, nobiletin-exerted BR depends on the contractile states of rat jejunal segments. Nobiletin-exerted BR requires the enteric nervous system, interstitial cell of Cajal, Ca(2+), and myosin phosphorylation-related mechanisms.

Signaling pathways involved in the H2O2-induced vasoconstriction of rat coronary arteries

Hydrogen peroxide (H2O2) is an endogenous endothelium-derived hyperpolarizing factor released by flow and involved in the regulation of coronary blood flow. Because opposing vasoactive effects have been reported for H2O2 depending on the vascular bed and experimental conditions, the aim of this study was to assess whether H2O2 may act as a coronary vasoconstrictor and if so to determine the underlying signaling mechanisms. Intramyocardial arteries from male Wistar rats were mounted on microvascular myographs for simultaneous measurements of intracellular Ca(2+) ([Ca(2+)]i) and tension. On coronary arteries precontracted with the thromboxane A2 (TxA2) analogue U46619, H2O2 (1-300μM) elicited further moderate contractions in the proximal arterial segments and relaxed the more distal coronary branches, the contractions being markedly augmented in arteries depolarized by raising extracellular K(+). H2O2-elicited vasoconstriction on K(+)30-precontracted coronary arteries was blunted by catalase and significantly reduced by endothelial cell removal and by inhibitors of cyclooxygenase (COX) and of the TxA2 receptor (TP). H2O2 (50μM) increased by about 10-fold basal superoxide anion (O2(-)) production in coronary arteries measured by lucigenin-enhanced chemiluminescence, and H2O2-elicited contractions were reduced by the superoxide dismutase mimetic tempol and by NADPH oxidase inhibition. Furthermore, blockade of the ERK and p38 mitogen-activated protein (MAP) kinases significantly reduced the contractions elicited by high and low concentrations of peroxide, respectively, whereas Rho kinase inhibition nearly abolished these responses. H2O2 (50μM) elicited simultaneous and similar sustained increases in [Ca(2+)]i and tension that were blunted by blockade of voltage-dependent L-type channels, but resistant to the nonselective Ca(2+) channel blocker 2-aminoethoxydiphenyl borate. Moreover, endothelial cell removal reduced the increases in [Ca(2+)]i and contraction elicited by peroxide. The present data demonstrate that H2O2 is an endothelium-dependent vasoconstrictor in rat coronary arteries that activates smooth muscle Ca(2+) entry through L-type and non-L-type channels and various intracellular signaling pathways including the release of a COX-derived TP agonist, stimulation of the MAP and Rho kinase pathways, and production of NADPH oxidase-derived superoxide.

Antioxidants condition pleiotropic vascular responses to exogenous H(2)O(2): role of modulation of vascular TP receptors and the heme oxygenase system

AIMS

Hydrogen peroxide (H(2)O(2)), a nonradical oxidant, is employed to ascertain the role of redox mechanisms in regulation of vascular tone. Where both dilation and constriction have been reported, we examined the hypothesis that the ability of H(2)O(2) to effect vasoconstriction or dilation is conditioned by redox mechanisms and may be modulated by antioxidants.

RESULTS

Exogenous H(2)O(2) (0.1-10.0 μM), dose-dependently reduced the internal diameter of rat renal interlobular and 3rd-order mesenteric arteries (p<0.05). This response was obliterated in arteries pretreated with antioxidants, including tempol, pegylated superoxide dismutase (PEG-SOD), butylated hydroxytoluene (BHT), and biliverdin (BV). However, as opposed to tempol or PEG-SOD, BHT & BV, antioxidants targeting radicals downstream of H(2)O(2), also uncovered vasodilation.

INNOVATIONS

Redox-dependent vasoconstriction to H(2)O(2) was blocked by inhibitors of cyclooxygenase (COX) (indomethacin-10 μM), thromboxane (TP) synthase (CGS13080-10 μM), and TP receptor antagonist (SQ29548-1 μM). However, H(2)O(2) did not increase vascular thromboxane B(2) release; instead, it sensitized the vasculature to a TP agonist, U46619, an effect reversed by PEG-SOD. Antioxidant-conditioned dilatory response to H(2)O(2) was accompanied by enhanced vascular heme oxygenase (HO)-dependent carbon monoxide generation and was abolished by HO inhibitors or by HO-1 & 2 antisense oligodeoxynucleotides treatment of SD rats.

CONCLUSION

These results demonstrate that H(2)O(2) has antioxidant-modifiable pleiotropic vascular effects, where constriction and dilation are brought about in the same vascular segment. H(2)O(2)-induced oxidative stress increases vascular TP sensitivity and predisposes these arterial segments to constrictor prostanoids. Conversely, vasodilation is reliant upon HO-derived products whose synthesis is stimulated only in the presence of antioxidants targeting radicals downstream of H(2)O(2).

Inflammation in subarachnoid hemorrhage and delayed deterioration associated with vasospasm: a review

Delayed deterioration associated with vasospasm (DDAV) after subarachnoid hemorrhage (SAH), (often called vasospasm) continues to be both a difficult entity to treat and a leading cause of morbidity in patients. Until recently, attention was focused on alleviating the vascular spasm. Recent evidence shows that vascular spasm may not account for all the morbidity of DDAV. There is renewed interest in looking for other potential targets for therapy. Inflammation has become a promising area of research for new treatments. This review explores the evidence that inflammation is a driver of DDAV by asking three questions: (1) If inflammation is important in the pathogenesis of the disease, what part or parts of the inflammatory response are involved? (2) When does inflammation occur in SAH? (3) In what compartment of the skull does the inflammation occur, the cerebrospinal fluid and meninges, the cerebral arteries, or the brain itself?

Extracellular calcium-sensing receptor is critical in hypoxic pulmonary vasoconstriction

AIMS

The initiation of hypoxic pulmonary vasoconstriction (HPV) involves an increase in cytosolic calcium ([Ca(2+)](i)) in pulmonary artery (PA) smooth muscle cells (PASMCs). Both the processes depend on extracellular Ca(2+). Extracellular Ca(2+) can be sensed by extracellular calcium-sensing receptor (CaSR). This study aims at determining whether CaSR is pivotal in the initiation of HPV.

RESULTS

Experiments were performed in cultured PASMCs, isolated PAs, and rats including CaSR knockdown preparations. Both hypoxia and H(2)O(2) equivalent to the level achieved by hypoxia increased [Ca(2+)](i) in an extracellular Ca(2+)-dependent manner in PASMCs, and this was inhibited by CaSR knockdown or its negative allosteric modulator, Calhex231. Hypoxia-increased H(2)O(2) generation was diminished by mitochondria depletion. Mitochondria depletion abolished hypoxia-induced [Ca(2+)](i) increase (HICI), which was reversed by H(2)O(2) repletion. CaSR knockdown or Calhex231, however, prevented the reversible effect of H(2)O(2). HICI was abolished by catalase-polyethylene glycol (PEG-Catalase), not superoxide dismutase-polyethylene glycol (PEG-SOD) pretreatment, attenuated by ryanodine receptor3-knockdown or inhibition of store-operated Ca(2+) entry. HPV in vitro and in vivo was inhibited by Calhex231 and by CaSR knockdown.

INNOVATION

A novel mechanism underlying HPV is revealed by the role of CaSR in orchestrating reactive oxygen species and [Ca(2+)](i) signaling.

CONCLUSIONS

The activation of mitochondrial H(2)O(2)-sensitized CaSR by extracellular Ca(2+) mediates HICI in PASMCs and, thus, initiates HPV.

Redox regulation of protein kinases as a modulator of vascular function

Reactive oxygen species (ROS) are continuously generated in vascular tissues by various oxidoreductase enzymes. They contribute to normal cell signaling, and modulate vascular smooth muscle tone and endothelial permeability in response to physiological agonists and to various cellular stresses and environmental factors, such as hypoxia. While concentrations of ROS are normally tightly controlled by cellular redox buffer systems, if produced in excess they may contribute to vascular disease. Protein kinases are essential components of most cell signaling pathways, including those involving ROS. The functioning of several members of this highly diverse group of enzymes, which include receptor and nonreceptor tyrosine kinases, protein kinase C, mitogen-activated kinases, and Rho-kinase, are modified by ROS, either through direct oxidative modification or indirectly through modification of associated proteins such as tyrosine phosphatases and monomeric G proteins. In this review, we discuss the molecular mechanisms of redox modification of these proteins, the downstream pathways affected, the often complex interaction between major kinase pathways, and feedback to ROS production itself. We also discuss complicating factors such as differential actions of superoxide anion and hydrogen peroxide, questions concerning concentration dependence, and the significance of signaling microdomains.

Omega-3 fatty acids and metabolic syndrome: effects and emerging mechanisms of action

Epidemiological, human, animal, and cell culture studies show that n-3 fatty acids, especially α-linolenic acid (ALA), eicosapentaenoic acid (EPA), and docosahexaenoic acid (DHA), reduce the risk factors of cardiovascular diseases. EPA and DHA, rather than ALA, have been the focus of research on the n-3 fatty acids, probably due to the relatively inefficient conversion of ALA to EPA and DHA in rodents and humans. This review will assess our current understanding of the effects and potential mechanisms of actions of individual n-3 fatty acids on multiple risk factors of metabolic syndrome. Evidence for pharmacological responses and the mechanism of action of each of the n-3 fatty acid trio will be discussed for the major risk factors of metabolic syndrome, especially adiposity, dyslipidemia, insulin resistance and diabetes, hypertension, oxidative stress, and inflammation. Metabolism of n-3 and n-6 fatty acids as well as the interactions of n-3 fatty acids with nutrients, gene expression, and disease states will be addressed to provide a rationale for the use of n-3 fatty acids to reduce the risk factors of metabolic syndrome.

Receptor tyrosine and MAP kinase are involved in effects of H(2)O(2) on interstitial cells of Cajal in murine intestine

Hydrogen peroxide (H(2)O(2)) is involved in intestinal motility through changes of smooth muscle activity. However, there is no report as to the modulatory effects of H(2)O(2) on interstitial cells of Cajal (ICC). We investigated the H(2)O(2) effects and signal transductions to determine whether the intestinal motility can be modulated through ICC. We performed whole-cell patch clamp in cultured ICC from murine intestine and molecular analyses. H(2)O(2) hyperpolarized the membrane and inhibited pacemaker currents. These effects were inhibited by glibenclamide, an inhibitor of ATP-sensitive K+ (K(ATP)) channels. The free-radical scavenger catalase inhibited the H(2)O(2)-induced effects. MAFP and AACOCF3 (a cytosolic phospholipase A2 inhibitors) or SC-560 and NS-398 (a selective COX-1 and 2 inhibitor) or AH6809 (an EP2 receptor antagonist) inhibited the H(2)O(2)-induced effects. PD98059 (a mitogen activated/ERK-activating protein kinase inhibitor) inhibited the H(2)O(2)-induced effects, though SB-203580 (a p38 MAPK inhibitor) or a JNK inhibitor did not affect. H(2)O(2)-induced effects could not be inhibited by LY-294002 (an inhibitor of PI3-kinases), calphostin C (a protein kinase C inhibitor) or SQ-22536 (an adenylate cyclase inhibitor). Adenoviral infection analysis revealed H2O2 stimulated tyrosine kinase activity and AG 1478 (an antagonist of epidermal growth factor receptor tyrosine kinase) inhibited the H(2)O(2)-induced effects. These results suggest H(2)O(2) can modulate ICC pacemaker activity and this occur by the activation of K(ATP) channels through PGE(2) production via receptor tyrosine kinase-dependent MAP kinase activation.

High-carbohydrate high-fat diet–induced metabolic syndrome and cardiovascular remodeling in rats

The prevalence of metabolic syndrome including central obesity, insulin resistance, impaired glucose tolerance, hypertension, and dyslipidemia is increasing. Development of adequate therapy for metabolic syndrome requires an animal model that mimics the human disease state. Therefore, we have characterized the metabolic, cardiovascular, hepatic, renal, and pancreatic changes in male Wistar rats (8-9 weeks old) fed on a high-carbohydrate, high-fat diet including condensed milk (39.5%), beef tallow (20%), and fructose (17.5%) together with 25% fructose in drinking water; control rats were fed a cornstarch diet. During 16 weeks on this diet, rats showed progressive increases in body weight, energy intake, abdominal fat deposition, and abdominal circumference along with impaired glucose tolerance, dyslipidemia, hyperinsulinemia, and increased plasma leptin and malondialdehyde concentrations. Cardiovascular signs included increased systolic blood pressure and endothelial dysfunction together with inflammation, fibrosis, hypertrophy, increased stiffness, and delayed repolarization in the left ventricle of the heart. The liver showed increased wet weight, fat deposition, inflammation, and fibrosis with increased plasma activity of liver enzymes. The kidneys showed inflammation and fibrosis, whereas the pancreas showed increased islet size. In comparison with other models of diabetes and obesity, this diet-induced model more closely mimics the changes observed in human metabolic syndrome.

Mitochondrial aldehyde dehydrogenase prevents ROS-induced vascular contraction in angiotensin-II hypertensive mice

Mitochondrial aldehyde dehydrogenase (ALDH2) is an enzyme that detoxifies aldehydes to carboxylic acids. ALDH2 deficiency is known to increase oxidative stress, which is the imbalance between reactive oxygen species (ROS) generation and antioxidant defense activity. Increased ROS contribute to vascular dysfunction and structural remodeling in hypertension. We hypothesized that ALDH2 plays a protective role to reduce vascular contraction in angiotensin-II (AngII) hypertensive mice. Endothelium-denuded aortic rings from C57BL6 mice, treated with AngII (3.6 μg/kg/min, 14 days), were used to measure isometric force development. Rings treated with daidzin (10 μmol/L), an ALDH2 inhibitor, potentiated contractile responses to phenylephrine (PE) in AngII mice. Tempol (1 mmol/L) and catalase (600 U/mL) attenuated the augmented contractile effect of daidzin. In normotensive mice, contraction to PE in the presence of the daidzin was not different from control, untreated values. AngII aortic rings transfected with ALDH2 recombinant protein decreased contractile responses to PE compared with control. These data suggest that ALDH2 reduces vascular contraction in AngII hypertensive mice. Because tempol and catalase blocked the contractile response of the ALDH2 inhibitor, ROS generation by AngII may be decreased by ALDH2, thereby preventing ROS-induced contraction.

Rapamycin inhibits hydrogen peroxide-induced loss of vascular contractility

Rapamycin, an inhibitor of the mammalian target of rapamycin (mTOR) pathway, has been shown to extend the life span of mice, and oxidative stress plays critical roles in vascular aging involving loss of compliance of arteries. We examined, therefore, whether rapamycin has protective effects on the inhibition of vascular contractility by hydrogen peroxide (H₂O₂). Prolonged (3 h) exposure to H₂O₂ induced complete loss of contraction of mouse aortic rings and mesenteric (resistance) arteries to either KCl or phenylephrine, which was attenuated by pretreatment with rapamycin. H₂O₂-induced loss of contractility was unaffected by treatment with actinomycin D or cycloheximide, inhibitors of gene transcription and protein synthesis, respectively. Western blot analysis showed that there was no increase in phosphorylation of S6 kinase 1 (S6K) or factor 4E binding protein 1 (4EBP1) in response to H₂O₂ treatment, suggesting involvement of the mTOR complex-2 (mTORC2) rather than mTORC1. H₂O₂ treatment inhibited phosphorylation of the 20-kDa regulatory light chains of myosin (LC₂₀), which was partially blocked by rapamycin treatment. Interestingly, the calcineurin inhibitors cyclosporine A and FK506 were found to mimic the rapamycin effect, and rapamycin inhibited calcineurin activation induced by H₂O₂. We conclude that rapamycin inhibits H₂O₂-induced loss of vascular contractility, likely through an mTORC2-calcineurin pathway.

Mitochondrial monoamine oxidase-A-mediated hydrogen peroxide generation enhances 5-hydroxytryptamine-induced contraction of rat basilar artery

BACKGROUND AND PURPOSE

We evaluated the role(s) of monoamine oxidase (MAO)-mediated H₂O₂ generation on 5-hydroxytryptamine (5-HT)-induced tension development of isolated basilar artery of spontaneously hypertensive rats (SHR) and normotensive Wistar-Kyoto (WKY) rats.

EXPERIMENTAL APPROACH

Basilar artery (endothelium-denuded) was isolated for tension measurement and Western blots. Enzymically dissociated single myocytes from basilar arteries were used for patch-clamp electrophysiological and confocal microscopic studies.

KEY RESULTS

Under resting tension, 5-HT elicited a concentration-dependent tension development with a greater sensitivity (with unchanged maximum tension development) in SHR compared with WKY (EC(50) : 28.4 ± 4.1 nM vs. 98.2 ± 9.4 nM). The exaggerated component of 5-HT-induced tension development in SHR was eradicated by polyethylene glycol-catalase, clorgyline and citalopram whereas exogenously applied H₂O₂ enhanced the 5-HT-elicited tension development in WKY. A greater protein expression of MAO-A was detected in basilar arteries from SHR than in those from WKY. In single myocytes and the entire basilar artery, 5-HT generated (clorgyline-sensitive) a greater amount of H₂O₂ in SHR compared with WKY. Whole-cell iberiotoxin-sensitive Ca(2+) -activated K(+) (BK(Ca) ) amplitude measured in myocytes of SHR was approximately threefold greater than that in WKY (at +60 mV: 7.61 ± 0.89 pA·pF(-1) vs. 2.61 ± 0.66 pA·pF(-1) ). In SHR myocytes, 5-HT caused a greater inhibition (clorgyline-, polyethylene glycol-catalase- and reduced glutathione-sensitive) of BK(Ca) amplitude than in those from WKY.

CONCLUSIONS AND IMPLICATIONS

5-HT caused an increased generation of mitochondrial H₂O₂ via MAO-A-mediated 5-HT metabolism, which caused a greater inhibition of BK(Ca) gating in basilar artery myocytes, leading to exaggerated basilar artery tension development in SHR.

Angiotensin II upregulates Ca(V)1.2 protein expression in cultured arteries via endothelial H(2)O(2) production

BACKGROUND

We previously reported that angiotensin II caused an endothelial-dependent increase in L-type voltage-dependent Ca(2+) channel (Ca(V)1.2) in cultured arteries, but the signaling pathways are not clear.

METHODS

Endothelial damage was generated by brief intra-arterial perfusion with 0.3% CHAPS. Ca(V)1.2 expression, function and H(2)O(2) were measured by Western blot, tension recording and Amplex Red H(2)O(2) assay kit, respectively.

RESULTS

Angiotensin II dose-dependently upregulated Ca(V)1.2 expression in endothelium-intact arteries. The angiotensin II upregulation of Ca(V)1.2 expression in endothelium-intact arteries was blocked by NAD(P)H oxidase inhibitor diphenyleneiodonium (DPI), apocynin, a more specific NAD(P)H oxidase inhibitor gp91ds-tat and also by catalase. H(2)O(2) similarly upregulated Ca(V)1.2 expression in endothelium-intact and endothelium-damaged arteries, and the latter effect was also blocked by DPI and apocynin. Angiotensin II increased H(2)O(2) production by endothelium-intact but not by endothelium-damaged arteries, and this effect was blocked by apocynin, catalase and gp91ds-tat. The upregulation of Ca(V)1.2 by angiotensin II and H(2)O(2) is accompanied by an increased tension response to KCl and the Ca(2+) channel activator FPL 64176, and this effect was also attenuated by gp91ds-tat.

CONCLUSION

These results suggest that angiotensin II stimulates endothelial NAD(P)H oxidase-produced H(2)O(2,) which may additionally act through vascular smooth muscle NAD(P)H oxidase, to upregulate vascular Ca(V)1.2 protein.

Ethanol-induced vasoconstriction is mediated via redox-sensitive cyclo-oxygenase-dependent mechanisms

The present study investigated the role of ROS (reactive oxygen species) and COX (cyclo-oxygenase) in ethanol-induced contraction and elevation of [Ca2+]i (intracellular [Ca2+]). Vascular reactivity experiments, using standard muscle bath procedures, showed that ethanol (1-800 mmol/l) induced contraction in endothelium-intact (EC50: 306+/-34 mmol/l) and endothelium -denuded (EC50: 180+/-40 mmol/l) rat aortic rings. Endothelial removal enhanced ethanol-induced contraction. Preincubation of intact rings with L-NAME [NG-nitro-L-arginine methyl ester; non-selective NOS (NO synthase) inhibitor, 100 micromol/l], 7-nitroindazole [selective nNOS (neuronal NOS) inhibitor, 100 micromol/l], oxyhaemoglobin (NO scavenger, 10 micromol/l) and ODQ (selective inhibitor of guanylate cyclase enzyme, 1 micromol/l) increased ethanol-induced contraction. Tiron [O2- (superoxide anion) scavenger, 1 mmol/l] and catalase (H2O2 scavenger, 300 units/ml) reduced ethanol-induced contraction to a similar extent in both endothelium-intact and denuded rings. Similarly, indomethacin (non-selective COX inhibitor, 10 micromol/l), SC560 (selective COX-1 inhibitor, 1 micromol/l), AH6809 [PGF2alpha (prostaglandin F2alpha)] receptor antagonist, 10 micromol/l] or SQ29584 [PGH2(prostaglandin H2)/TXA2 (thromboxane A2) receptor antagonist, 3 micromol/l] inhibited ethanol-induced contraction in aortic rings with and without intact endothelium. In cultured aortic VSMCs (vascular smooth muscle cells), ethanol stimulated generation of O2- and H2O2. Ethanol induced a transient increase in [Ca2+]i, which was significantly inhibited in VSMCs pre-exposed to tiron or indomethacin. Our data suggest that ethanol induces vasoconstriction via redox-sensitive and COX-dependent pathways, probably through direct effects on ROS production and Ca2+ signalling. These findings identify putative molecular mechanisms whereby ethanol, at high concentrations, influences vascular reactivity. Whether similar phenomena occur in vivo at lower concentrations of ethanol remains unclear.

Measurement of selected ions related to oxidative stress and energy metabolism in Saudi autistic children

OBJECTIVES

Autism is a developmental disorder characterized by social and emotional deficits, language impairments and stereotyped behaviors that manifest in early postnatal life. This study aims to clarify the role of selected ions related to energy metabolism as a consequence of oxidative stress in the deterioration accompanied autism.

MATERIALS AND METHODS

Malonaldehyde as measure of lipid peroxidation, Na(+)/K(+) ion pump (ATPase), together with the concentrations of Na(+), K(+), Mg(2+), Ca(2+) and Pb(2+) were determined in plasma of 30 Saudi autistic patients and compared to 30 age-matching control samples.

RESULTS

The obtained data recorded that Saudi autistic patients have a remarkable higher activities of Na(+)/K(+) ATPase and high levels of lipid peroxidation compared to control. In addition, they have significantly elevated levels of K(+) and Pb(2+) while Ca(2+) recorded a significantly lower level compared to age-matching control subjects. On the other hand both Mg(2+) and Na(+) were non-significantly changed in autistic patients.

CONCLUSION

Alteration of the selected measured ions confirms that oxidative stress and defective mitochondrial energy production could represent the primary causative factor in the pathogenesis of autism.

NADPH oxidases and angiotensin II receptor signaling

Over the last decade many studies have demonstrated the importance of reactive oxygen species (ROS) production by NADPH oxidases in angiotensin II (Ang II) signaling, as well as a role for ROS in the development of different diseases in which Ang II is a central component. In this review, we summarize the mechanism of activation of NADPH oxidases by Ang II and describe the molecular targets of ROS in Ang II signaling in the vasculature, kidney and brain. We also discuss the effects of genetic manipulation of NADPH oxidase function on the physiology and pathophysiology of the renin-angiotensin system.

Constriction of pulmonary artery by peroxide: role of Ca2+ release and PKC

Reactive oxygen species are implicated in pulmonary hypertension and hypoxic pulmonary vasoconstriction. We examined the effects of low concentrations of peroxide on intrapulmonary arteries (IPA). IPAs from Wistar rats were mounted on a myograph for recording tension and estimating intracellular Ca2+ using Fura-PE3. Ca2+ sensitization was examined in alpha-toxin-permeabilized IPAs, and phosphorylation of MYPT-1 and MLC(20) was assayed by Western blot. Peroxide (30 microM) induced a vasoconstriction with transient and sustained components and equivalent elevations of intracellular Ca2+. The transient constriction was strongly suppressed by indomethacin, the TP-receptor antagonist SQ-29584, and the Rho kinase inhibitor Y-27632, whereas sustained constriction was unaffected. Neither vasoconstriction nor elevation of intracellular Ca2+ was affected by removal of extracellular Ca2+, whereas dantrolene suppressed the former and ryanodine abolished the latter. Peroxide-induced constriction of permeabilized IPAs was unaffected by Y-27632 but abolished by PKC inhibitors; these also suppressed constriction in intact IPAs. Peroxide caused translocation of PKCalpha, but had no significant effect on MYPT-1 or MLC(20) phosphorylation. We conclude that in IPAs peroxide causes transient release of vasoconstrictor prostanoids, but sustained constriction is associated with release of Ca2+ from ryanodine-sensitive stores and a PKC-dependent but Rho kinase- and MLC(20)-independent constrictor mechanism.

Hypertension increases contractile responses to hydrogen peroxide in resistance arteries through increased thromboxane A2, Ca2+, and superoxide anion levels

This study investigated the mechanisms underlying the response to hydrogen peroxide (H(2)O(2)) in mesenteric resistance arteries from spontaneously hypertensive rats (SHRs) and normotensive Wistar Kyoto (WKY) rats. Arteries were mounted in microvascular myographs for isometric tension recording and for simultaneous measurements of intracellular Ca(2+) concentration ([Ca(2+)](i)), superoxide anion (O(2)(.)) production was evaluated by dihydroethidium fluorescence and confocal microscopy, and thromboxane A(2) (TXA(2)) production was evaluated by enzyme immunoassay. H(2)O(2) (1-100 microM) induced biphasic responses characterized by a transient endothelium-dependent contraction followed by relaxation. Simultaneous measurements of tension and Ca(2+) showed a greater effect of H(2)O(2) in arteries from hypertensive than normotensive rats. The cyclooxygenase (cox) inhibitor, indomethacin [1-(4-chlorobenzoyl)-5-methoxy-2-methyl-1-H-indole-3-acetic acid] (1 microM); the COX-1 inhibitor, SC-58560 [5-(4-chlorophenyl)-1-(4-methoxyphenyl)-3-trifluoromethyl pyrazole] (1 microM); the thromboxane (TXA(2)) synthase inhibitor, furegrelate [5-(3-pyridinylmethyl)-2-benzofurancarboxylic acid, sodium salt] (10 microM); and the TXA(2)/prostaglandin H(2) receptor antagonist, SQ 29,548 ([1S-[1.alpha.,2.alpha.(Z),3.alpha.,4.alpha.]]-7-[3-[[2-[(phenylamino) carbonyl] hydrazino] methyl]-7-oxabicyclo[2.2.1]hept-2-yl]-5-heptenoic acid)) (1 microM) abolished H(2)O(2) contraction in arteries from WKY rats but only reduced it in SHRs. The O(2)(.) scavenger, tiron (4,5-dihydroxy-1,3-benzenedisulfonic acid disodium salt) (1 mM), and the NADPH oxidase inhibitor, apocynin (4'-hydroxy-3'-methoxyacetophenone) (0.3 mM), decreased H(2)O(2) contraction in arteries from SHRs but not in WKY rats. H(2)O(2) induced TXA(2) and O(2)(.) production that was greater in SHRs than in WKY rats. The TXA(2) analog, U46619 [9,11-di-deoxy-11 alpha,9 alpha-epoxymethano prostaglandin F(2 alpha) (0.1 nM-1 microM)], also increased O(2)(.) production in SHR vessels. H(2)O(2)-induced TXA(2) production was decreased by SC-58560. H(2)O(2)-induced O(2)(.) production was decreased by tiron, apocynin, and SQ 29,548. In conclusion, the enhanced H(2)O(2) contraction in resistance arteries from SHRs seems to be mediated by increased TXA(2) release from COX-1 followed by elevations in vascular smooth muscle [Ca(2+)](i) levels and O(2)(.) production. This reveals a new mechanism of oxidative stress-induced vascular damage in hypertension.

Postnatal Intermittent Hypoxia and Developmental Programming of Hypertension in Spontaneously Hypertensive Rats

Obstructive and central apneas during sleep are associated with chronic intermittent hypoxia (CIH) and increased cardiovascular morbidity. Spontaneously hypertensive rats exposed to CIH during postnatal days 4 to 30 develop exaggerated hypertension as adults. We hypothesized that reactive oxygen species and altered L-Ca 2+ channel activity may underlie the postnatal programming of exaggerated blood pressure and cardiac remodeling. Newborn male spontaneously hypertensive rats were exposed to CIH (10% and 21% O 2 alternating every 90 seconds, 12 h/d, for postnatal days 4 to 30) or normoxia (room air). In each condition, spontaneously hypertensive rats received daily (SC) 1 of 3 treatments: l -calcium channel blocker nifedipine (5 mg/kg), superoxide dismutase mimetic MnTMPyP pentachloride (10 mg/kg), or vehicle (polyethylene glycol). Blood pressure was evaluated monthly for 6 months after birth, and echocardiographic assessments were conducted at 6 months of age. CIH vehicle-treated rats presented higher systolic blood pressure (187±5 mm Hg) as compared with normoxic vehicle treated controls (163±2 mm Hg; P <0.001). Postnatal CIH elicited marked increases in left ventricular wall thickness in a pattern of concentric hypertrophy with augmented systolic contractility. The treatment with nifedipine in the CIH group attenuated blood pressure (159±2 mm Hg; P <0.001) and normalized left ventricular wall thickness and systolic function, whereas the treatment with SOD mimetic decreased blood pressure (165±2 mm Hg; P <0.001) and reduced left ventricular wall thickness without changes in the systolic function. We conclude that Ca 2+ and reactive oxygen species–mediated signaling during intermittent hypoxia are critical mechanisms underlying postnatal programming of an increased severity of hypertension and hypertrophic cardiac remodeling in a genetically susceptible rodent model.

Preconditioning with levosimendan prevents contractile dysfunction due to H2O2-induced oxidative stress in human myocardium

We studied the inotropic and possible antioxidant effects of levosimendan in human atrial strips, before and after induction of oxidative stress induced by H2O2. Levosimendan (10(-9) to 10(-6) M) increased contractions induced by electrical stimulation (ES) in human atrial strips. The maximal positive inotropic effect of levosimendan was 145.6 +/- 4.6% of predrug values. H2O2 (10(-6) to 10(-3) M) significantly reduced contractions induced by ES. The maximum inhibition by H2O2 on the ES induced contraction was 47.2 +/- 3.5%. Levosimendan significantly increased the isometric contractions induced by ES when compared with the values obtained in the presence of 10 M H2O2 by 89.0 +/- 4.7%, 98.9 +/- 3.4%, and 111.2 +/- 3.7% at 10(-8), 10(-7), and 10(-6) M concentrations, respectively. In concentrations of 10(-7) and 10(-6) M levosimendan, the maximum responses to ES increased when compared with the values obtained in the presence of 10(-3) M H2O2 by 87.1 +/- 3.6% and 95.1 +/- 5.3%, respectively. The cumulatively applied H2O2 (10(-6)-10(-3) M) did not change the positive inotropic response to levosimendan. In conclusion, levosimendan reverses the myocardial dysfunction induced by oxidative stress in human right atrial strips. Levosimendan prevents myocardial dysfunction if administered before oxidative stress.

Comparison of H2O2-induced vasoconstriction in the abdominal aorta and mesenteric artery of the mouse

Hydrogen peroxide (H(2)O(2)) is generally perceived as an arterial vasodilator. Due to the emerging importance of H(2)O(2) as a possible vasoconstrictor, we examined whether H(2)O(2) constricts both the abdominal aorta and superior mesenteric artery and postulated that H(2)O(2) is a ubiquitous constrictor of quiescent mouse arteries. Moreover, we postulated that KCl depolarization discloses and/or exaggerates H(2)O(2)-induced constriction. Under quiescent conditions, H(2)O(2) constricted the mouse abdominal aorta but not the mesenteric artery. Vessel depolarization (a) exaggerated this constrictor response in the aorta, and (b) unmasked a contractile response in the mesenteric artery. Our final hypothesis tested whether tyrosine kinases, mitogen-activated protein kinases (MAPKs), and/or Rho-kinase are uniformly involved in H(2)O(2)-induced vasoconstriction. We observed a marked difference in the ability of tyrosine kinase inhibitor to block H(2)O(2)-induced vasoconstriction. p38 and ERK 1/2MAPK inhibitors reduced the maximal response to H(2)O(2), whereas JNK inhibitor had no effect. Finally, Rho-kinase inhibitor decreased the H(2)O(2) response in the mesenteric artery but not in the aorta. These data demonstrate a variable yet tightly regulated H(2)O(2) vasoconstrictor effect. Furthermore, we found that p38, ERK 1/2 and Rho-kinase play a role in H(2)O(2) constriction, which may be critical pathways involved in H(2)O(2)-induced constriction across vascular beds.

Renin-angiotensin-aldosterone system and oxidative stress in cardiovascular insulin resistance

Hypertension commonly occurs in conjunction with insulin resistance and other components of the cardiometabolic syndrome. Insulin resistance plays a significant role in the relationship between hypertension, Type 2 diabetes mellitus, chronic kidney disease, and cardiovascular disease. There is accumulating evidence that insulin resistance occurs in cardiovascular and renal tissue as well as in classical metabolic tissues (i.e., skeletal muscle, liver, and adipose tissue). Activation of the renin-angiotensin-aldosterone system and subsequent elevations in angiotensin II and aldosterone, as seen in cardiometabolic syndrome, contribute to altered insulin/IGF-1 signaling pathways and reactive oxygen species formation to induce endothelial dysfunction and cardiovascular disease. This review examines currently understood mechanisms underlying the development of resistance to the metabolic actions of insulin in cardiovascular as well as skeletal muscle tissue.

Hydrogen peroxide-induced Ca2+ mobilization in pulmonary arterial smooth muscle cells

Reactive oxygen species (ROS) generated from NADPH oxidases and mitochondria have been implicated as key messengers for pulmonary vasoconstriction and vascular remodeling induced by agonists and hypoxia. Since Ca2+ mobilization is essential for vasoconstriction and cell proliferation, we sought to characterize the Ca2+ response and to delineate the Ca2+ pathways activated by hydrogen peroxide (H2O2) in rat intralobar pulmonary arterial smooth muscle cells (PASMCs). Exogenous application of 10 μM to 1 mM H2O2 elicited concentration-dependent increase in intracellular Ca2+ concentration in PASMCs, with an initial rise followed by a plateau or slow secondary increase. The initial phase was related to intracellular release. It was attenuated by the inositol trisphosphate (IP3) receptor antagonist 2-aminoethyl diphenylborate, ryanodine, or thapsigargin, but was unaffected by the removal of Ca2+ in external solution. The secondary phase was dependent on extracellular Ca2+ influx. It was unaffected by the voltage-gated Ca2+ channel blocker nifedipine or the nonselective cation channel blockers SKF-96365 and La3+, but inhibited concentration dependently by millimolar Ni2+, and potentiated by the Na+/Ca2+ exchange inhibitor KB-R 7943. H2O2 did not alter the rate of Mn2+ quenching of fura 2, suggesting store- and receptor-operated Ca2+ channels were not involved. By contrast, H2O2 elicited a sustained inward current carried by Na+ at −70 mV, and the current was inhibited by Ni2+. These results suggest that H2O2 mobilizes intracellular Ca2+ through multiple pathways, including the IP3- and ryanodine receptor-gated Ca2+ stores, and Ni2+-sensitive cation channels. Activation of these Ca2+ pathways may play important roles in ROS signaling in PASMCs.

Reduction in extracellular superoxide dismutase activity in African-American patients with hypertension

Superoxide anions react with nitric oxide to form peroxynitrite and hence reduce the bioavailability of nitric oxide in the arteries. Extracellular superoxide dismutase (EC-SOD) is a major superoxide scavenger in human plasma and vascular tissues. The objective of this study is to assess whether essential hypertension is associated with an alteration in EC-SOD activity. In this report, blood samples were obtained from hypertensive (n=39) and normotensive (n=37) African-Americans. Plasma EC-SOD activity was measured using in-gel activity staining and spectrophotometric assays, EC-SOD protein level was measured using Western blotting, nitrotyrosine was measured using slot blotting, 8-isoprostane was measured with an enzyme immunoassay, and plasma copper and zinc concentrations were measured using an atomic absorption assay. Our data demonstrate that the copper, zinc, and plasma EC-SOD protein concentrations in the hypertensive and normotensive subjects are indistinguishable. Compared to normotensive controls, hypertensive patients have significantly reduced plasma EC-SOD activity. Plasma nitrotyrosine and 8-isoprostane levels are significantly higher in the hypertensive patients than in normotensive controls. Results from this study suggest that a reduction in EC-SOD activity in hypertensive patients is not due to a down-regulation of the SOD3 gene (encoding EC-SOD) or deficiency in mineral cofactors. Furthermore, the reduced EC-SOD activity might be at least partially responsible for the increased oxidative stress, as reflected by increased plasma nitrotyrosine and 8-isoprostane, in hypertensive subjects.

Pleiotropic Effects of Hydrogen Peroxide in Arteries and Veins From Normotensive and Hypertensive Rats

Hydrogen peroxide causes vascular contraction and relaxation and contributes to the pathogenesis of hypertension. We hypothesized that the contractile state of blood vessels governs whether H 2 O 2 causes contraction or relaxation. Hydrogen peroxide (1 μmol/L to 1 mmol/L) concentration-dependently contracted thoracic aorta and vena cava from sham normotensive and deoxycorticosterone acetate (DOCA)-salt hypertensive rats. The maximal contraction to H 2 O 2 was 3 times greater in DOCA aorta compared with sham aorta but unchanged in DOCA vena cava compared with sham vena cava. In prostaglandin F 2α (20 μmol/L)–contracted aorta and vena cava from sham and DOCA rats, H 2 O 2 (1 μmol/L to 1 mmol/L) induced a concentration-dependent relaxation that was impaired in DOCA aorta but not DOCA vena cava. In contrast, in KCl (30 mmol/L)-contracted vessels, maximal H 2 O 2 -induced contraction was enhanced 15-fold in sham aorta and 5-fold in DOCA aorta but only 2-fold in sham vena cava. Tetraethylammonium (10 mmol/L), BAY K 8644 (100 nmol/L), and ouabain (1 mmol/L) all enhanced maximal aortic H 2 O 2 -induced contraction, whereas only ouabain enhanced venous H 2 O 2 -induced contraction. The removal of extracellular Ca 2+ reduced H 2 O 2 -induced contraction in KCl-contracted aorta, whereas maximal venous H 2 O 2 -induced contraction (under basal conditions) was unchanged. Our data suggest that differences in arterial and venous K + channel activity and extracellular Ca 2+ influx are responsible for differences in arterial and venous contraction to H 2 O 2 . In DOCA-salt hypertension, arterial but not venous contraction to H 2 O 2 is enhanced, and relaxation to H 2 O 2 is reduced.

Halothane does not protect against vascular injury in isolated cerebral and mesenteric arteries

PURPOSE

This study was designed to examine regional differences in the vascular injury induced by hydrogen peroxide (H2O2) and to determine its modulation by halothane in canine basilar and mesenteric arteries.

METHODS

Rings of canine basilar and mesenteric arteries with intact endothelium were mounted in Krebs bicarbonate solution for isometric tension recording. The relaxation responses to substance P (10(-8) M) and sodium nitroprusside (SNP; 10(-8) to 10(-5) M) were examined before and after exposure to H2O2 (1 mM) for eight minutes in the presence or absence of halothane (2%), to evaluate the effects of oxidative injury on the endothelium-dependent and -independent relaxation. The contractile responses to KCl (30 mM) and prostaglandin (PG) F(2alpha) (3 x 10(-6) M) were also compared in rings with and without exposure to H2O2.

RESULTS

After exposure to H2O2 the relaxant responses to substance P were significantly inhibited in basilar arteries (P < 0.01), but not in mesenteric arteries. Exposure to H2O2 also attenuated SNP-induced relaxation in basilar (P < 0.05), but not in mesenteric arteries. The attenuation of the contractile responses to KCl and PGF(2alpha) after H2O2 exposure was observed only in basilar arteries (P < 0.01). Simultaneous exposure to halothane did not affect the attenuation of these relaxant and contractile responses. Scanning electron microscopy revealed that H2O2 resulted in marked disruption of the endothelial layer in basilar arteries, compared to almost no morphological changes in mesenteric arteries.

CONCLUSION

These results indicate that the endothelium and vascular smooth muscle of the basilar artery are more susceptible to oxidative stress than those of the mesenteric artery. Halothane, at clinically relevant concentrations, exerts no significant influence on this vascular injury.

Angiotensin II, reactive oxygen species, and Ca2+signaling in afferent arterioles

In afferent arteriolar vascular smooth muscle cells, ANG II induces a rise in cytosolic Ca2+([Ca2+]i) via inositol trisphosphate receptor (IP3R) stimulation and by activation of the adenine diphosphate ribose (ADPR) cyclase to form cyclic ADPR, which sensitizes the ryanodine receptor (RyR) to Ca2+. We hypothesize that ANG II stimulation of NAD(P)H oxidases leads to the formation of superoxide anion (O2−·), which, in turn, activates ADPR cyclase. Afferent arterioles were isolated from rat kidney with the magnetized microsphere and sieving technique and loaded with fura-2 to measure [Ca2+]i. ANG II rapidly increased [Ca2+]iby 124 ± 12 nM. In the presence of apocynin, a specific inhibitor of NAD(P)H oxidase assembly, the [Ca2+]iresponse was reduced to 35 ± 5 nM ( P < 0.01). Tempol, a superoxide dismutase mimetic, did not alter the [Ca2+]iresponse to ANG II at a concentration of 10−4M (99 ± 12 nM), but 10−3M tempol reduced the response to 32 ± 3 nM ( P < 0.01). The addition of nicotinamide, an inhibitor of ADPR cyclase, to apocynin or tempol (10−3M) resulted in no further inhibition. Measurement of superoxide production with the fluorescent probe tempo 9-AC showed that ANG II caused an increase of 48 ± 20 arbitrary units; apocynin or diphenyl iodonium (an inhibitor of flavoprotein oxidases) inhibited the response by 94%. Hydrogen peroxide (H2O2) was studied at physiological (10−7M) and higher concentrations. In the presence of H2O2(10−7M), neither baseline [Ca2+]inor the response to ANG II was altered (125 ± 15 nM), whereas H2O2(10−6and 10−5M) inhibited the [Ca2+]iresponse to ANG II by 35 and 46%, respectively. We conclude that ANG II rapidly activates NAD(P)H oxidases of afferent arterioles, leading to the formation of O2−·, which then stimulates ADPR cyclase to form cADPR. cADPR, by sensitizing the RyR to Ca2+, augments the Ca2+response (calcium-induced calcium release) initiated by activation of the IP3R.

Endogenous Vascular Hydrogen Peroxide Regulates Arteriolar Tension In Vivo

Background— Although many studies suggested direct vasomotor effects of hydrogen peroxide (H 2 O 2 ) in vitro, little is known about the vasomotor effects of H 2 O 2 in vivo.

Methods and Results— We have generated mice overexpressing human catalase driven by the Tie-2 promoter to specifically target this transgene to the vascular tissue. Vessels of these mice (cat ++ ) expressed significantly higher levels of catalase mRNA, protein, and activity. The overexpression was selective for vascular tissue, as evidenced by immunohistochemistry in specimens of aorta, heart, lung, and kidney. Quantification of reactive oxygen species by fluorescence signals in cat ++ versus catalase-negative (cat n ) mice showed a strong decrease in aortic endothelium and left ventricular myocardium but not in leukocytes. Awake male cat ++ at 3 to 4 months of age had a significantly lower systolic blood pressure (sBP, 102.7±2.2 mm Hg, n=10) compared with their transgene-negative littermates (cat n , 115.6±2.5 mm Hg, P =0.0211) and C57BL/6 mice (118.4±3.06 mm Hg, n=6). Treatment with the catalase inhibitor aminotriazole increased sBP of cat ++ to 117.3±4.3 mm Hg ( P =0.0345), while having no effect in cat n (118.4±2.4 mm Hg, n=4, P >0.05). In contrast, treatment with the NO-synthase inhibitor nitro- l -arginine methyl ester (100 mg · kg BW −1 · d −1 ) increased sBP in cat ++ and C57Bl/6 to a similar extent. Likewise, phosphorylation of vasodilator-stimulated phosphoprotein in skeletal muscle, left ventricular myocardium, and lung was identical in cat ++ and cat n . Endothelium- and NO-dependent aortic vasodilations were unchanged in cat ++ . Aortic KCl contractions were significantly lower in cat ++ and exogenous H 2 O 2 (10 μmol/L)–induced vasoconstriction.

Conclusions— These data suggest that endogenous H 2 O 2 may act as a vasoconstrictor in resistance vessels and contribute to the regulation of blood pressure.

Reactive oxygen species as mediators of calcium signaling by angiotensin II: implications in vascular physiology and pathophysiology

Reactive oxygen species (ROS), including superoxide anion, hydrogen peroxide, and hydroxyl radical, and reactive nitrogen species, such as nitric oxide and peroxynitrite, are biologically relevant O2 derivatives increasingly being recognized as important in vascular biology through their oxidation/reduction (redox) potential. All vascular cell types produce ROS primarily via membrane-associated NAD(P)H oxidase. ROS influence vascular function by modulating contraction/dilation, cell growth, apoptosis/anoikis, migration, inflammation, and fibrosis. An imbalance in redox state where prooxidants overwhelm antioxidant capacity results in oxidative stress. Oxidative excess and associated oxidative damage are mediators of altered vascular tone and structural remodeling in many cardiovascular diseases. ROS elicit these effects by influencing intracellular signaling events. In addition to modulating protein tyrosine kinases, protein phosphatases, mitogen-activated protein kinases, and transcription factors, ROS are important regulators of intracellular Ca2+ homeostasis and RhoA/Rho kinase signaling. ROS increase vascular [Ca2+]i by stimulating inositol trisphosphate-mediated Ca2+ mobilization, by increasing cytosolic Ca2+ accumulation through sarcoplasmic/endoplasmic reticulum Ca2+-ATPase inhibition, and by stimulating Ca2+ influx through Ca2+ channels. Increased ROS generation enhances Ca2+ signaling and up-regulates RhoA/Rho kinase, thereby altering vascular contractility and tone. The present review discusses the importance of ROS in angiotensin II signaling in vascular biology and focuses specifically on the role of oxidative stress in Ca2+ signaling in the vasculature.

Cooling and response to hydrogen peroxide in human saphenous vein: role of the endothelium

In the present work we studied the responses of human saphenous vein to H2O2 and effects of moderate cooling on these responses with analysis of the role of endothelium. H2O2 (10(-7)-10(-2) M) induced concentration-dependent contraction in the intact human saphenous vein strips at both temperatures. At 28 degrees C, the maximal contraction induced by H2O2 was significantly lower than that at 37 degrees C. Compared with intact strips, the sensitivity and the maximal contraction to H2O2 were significantly enhanced in endothelium-denuded strips at 37 and 28 degrees C. However, pD2 values and maximal contractions were not significantly different in endothelium-denuded strips at different temperatures. Pretreatment with N(G)-nitro-L-arginine methyl ester (L-NAME) increased significantly the maximal contraction and sensitivity to H2O2 at 37 and 28 degrees C. The contractions increased by L-NAME were restored by the pre-incubation of l-arginine (10(-3) M) at every temperature studied. The contractile responses of intact human saphenous veins to H2O2 were reduced significantly by 10(-5) M indomethacin at both temperatures. Our results suggest that H2O2-induced contraction of human saphenous vein are mediated by its direct effect on the smooth muscle and by the generation of products of the cyclooxygenase pathway from the endothelium. Signalling pathways of these contractile effects are the same at 37 and 28 degrees C. Under normal temperature conditions, the contraction to H2O2 is possibly modulated by endothelial nitric oxide. Cooling reduces the contraction to H2O2 by increasing release of nitric oxide.

The pulmonary biology of isoprostanes

Isoprostanes were first recognized as convenient markers of oxidative stress, but their powerful effects on a variety of cell functions are now also being increasingly appreciated. This is particularly true of the lung, which is comprised of a wide variety of different cell types (smooth muscle, innervation, epithelium, lymphatics, etc.), all of which have been shown to respond to exogenously applied isoprostanes. In this review, we summarize these biological responses in the lung, and also consider the roles that isoprostanes might play in a range of pulmonary clinical disorders.

Activation of Rho/Rho kinase signaling pathway by reactive oxygen species in rat aorta

Evidence indicates that both the Rho/Rho kinase signaling pathway and reactive oxygen species (ROS) such as superoxide and H(2)O(2) are involved in the pathogenesis of hypertension. This study aimed to determine whether ROS-induced vascular contraction is mediated through activation of Rho/Rho kinase. Rat aortic rings (endothelium denuded) were isolated and placed in organ chambers for measurement of isometric force development. ROS were generated by a xanthine (X)-xanthine oxidase (XO) mixture. The antioxidants tempol (3 mM) and catalase (1,200 U/ml) or the XO inhibitor allopurinol (400 microM) significantly reduced X/XO-induced contraction. A Rho kinase inhibitor, (+)-(R)-trans-4-(1-aminoethyl-N-4-pyridil)cyclohexanecarboxamide dihydrochloride (Y-27632), decreased the contraction in a concentration-dependent manner; however, the Ca(2+)-independent protein kinase C inhibitor rottlerin did not have an effect on X/XO-induced contraction. Phosphorylation of the myosin light chain phosphatase target subunit (MYPT1) was increased by ROS, and preincubation with Y-27632 blocked this increased phosphorylation. Western blotting for cytosolic and membrane-bound fractions of Rho showed that Rho was increased in the membrane fraction by ROS, suggesting activation of Rho. These observations demonstrate that ROS-induced Ca(2+) sensitization is through activation of Rho and a subsequent increase in Rho kinase activity but not Ca(2+)-independent PKC.

Mechanisms involved in the early increase of serotonin contraction evoked by endotoxin in rat middle cerebral arteries

The present study investigated the mechanisms involved in the increased 5-hydroxytryptamine (5-HT) vasoconstriction observed in rat middle cerebral arteries exposed in vitro to lipopolysaccharide (LPS, 10 microg x ml-1) for 1-5 h. Functional, immunohistochemical and Western blot analysis and superoxide anion measurements by ethidium fluorescence were performed. LPS exposure increased 5-HT (10 microm) vasoconstriction only during the first 4 h. In contrast to control tissue, indomethacin (10 microm), the COX-2 inhibitor NS 398 (10 microm), the TXA2/PGH2 receptor antagonist SQ 29548 (1 microm) and the TXA2 synthase inhibitor furegrelate (1 microm) reduced 5-HT contraction of LPS-treated arteries from hour one. The iNOS inhibitor aminoguanidine (0.1 mm) increased 5-HT contraction from hour three of LPS incubation. The superoxide anion scavenger superoxide dismutase (SOD, 100 U ml-1) and the H2O2 scavenger catalase (1000 U ml-1), as well as the respective inhibitors of NAD(P)H oxidase and xanthine oxidase, apocynin (0.3 mm) and allopurinol (0.3 mm), reduced 5-HT contraction after LPS incubation. LPS induced an increase in superoxide anion levels that was abolished by PEG-SOD. Subthreshold concentrations of the TXA2 analogue U 46619, xanthine/xanthine oxidase and H2O2 potentiated, whereas those of sodium nitroprusside inhibited, the 5-HT contraction. COX-2 expression was increased at 1 and 5 h of LPS incubation, while that of iNOS, Cu/Zn-SOD and Mn-SOD was only increased after 5 h. All the three vascular layers expressed COX-2 and Cu/Zn-SOD. iNOS expression was detected in the endothelium and adventitia after LPS. In conclusion, increased production of TXA2 from COX-2, superoxide anion and H2O2 enhanced vasoconstriction to 5-HT during the first few hours of LPS exposure; iNOS and SOD expression counteracted that increase at 5 h. These changes can contribute to the disturbance of cerebral blood flow in endotoxic shock.

Mechanisms of hydroxyl radical-induced contraction of rat aorta

The present study was designed to investigate the effects of hydroxyl radicals (*OH), generated via the Fe2+-mediated Fenton reaction, on isolated rat aortic rings with and without endothelium. In the absence of any vasoactive agent, generation of *OH alone elicited an endothelium-independent contraction in rat aortic rings in a concentration-dependent manner. Hydroxyl radical-induced contractions of denuded rat aortic rings appeared, however, to be slightly stronger than those on intact rat aortic rings. The contractile responses to *OH were neither reversible nor reproducible in the same ring; even small concentrations of *OH radicals resulted in tachyphylaxis. Removal of extracellular calcium ions (Ca2+) or buffering intracellular Ca2+ with 10 microM acetyl methyl ester of bis(o-aminophenoxy) ethane-N,N,N',N',-tetraacetic acid (BAPTA-AM) significantly attenuated the contractile actions of *OH radicals. The presence of 1 microM staurosporine, 1 microM bisindolylmaleimide I, 1 microM Gö6976 [inhibitor of protein kinase C (PKC)], 2 microM PD-980592 (inhibitor of ERK), 10 microM genistein, and 1 microM wortmannin significantly inhibited the contractions induced by *OH. Proadifen (10 microM), on the other hand, significantly potentiated the hydroxyl radical-induced contractions. Exposure of primary cultured aortic smooth muscle cells to *OH produced significant, rapid rises of intracellular free Ca2+ ([Ca2+]i). Several, specific antagonists of possible endogenously formed vasoconstrictors did not inhibit or attenuate either hydroxyl radical-induced contractions or the elevation of [Ca2+]i. Our new results suggest that hydroxyl radical-triggered contractions on rat aortic rings are Ca2+-dependent. Several intracellular signal transduction systems seem to play some role in hydroxyl radical-induced vasoconstriction of rat aortic rings.

Differential Calcium Regulation by Hydrogen Peroxide and Superoxide in Vascular Smooth Muscle Cells from Spontaneously Hypertensive Rats

We investigated the role of reactive oxygen species (ROS), particularly hydrogen peroxide (H2O2) and superoxide anion (*O2-) in the regulation of vascular smooth muscle cell (VSMC) Ca2+ concentration ([Ca2+]i) and vascular contraction and assessed whether redox-dependent Ca2+ signaling and contraction are altered in hypertension. VSMCs and mesenteric arteries from Wistar Kyoto (WKY) and spontaneously hypertensive rats (SHR) were studied. Cells were stimulated with H2O2 (10(-4) mol/l) or LY83583 (*O2- generator, 10(-5) mol/l). [Ca2+]i and cytosolic *O2- were measured by fura-2AM and tempo-9-AC fluorescence respectively. L-type and T-type Ca2+ channels were assessed using verapamil/diltiazem and mibefradil respectively and mRNA and protein expression of these channels was assessed by real-time PCR and immunoblotting respectively. H2O2 time-dependently increased [Ca2+]i and contraction with significantly greater effects in SHR versus WKY (P < 0.001). LY83583 increased [Ca2+]i in both strains, but responses were blunted in SHR. Removal of extracellular Ca2+ abrogated [Ca2+]i responses to H2O2 and *O2-. Verapamil and diltiazem, but not mibefradil, significantly decreased H2O2 -induced [Ca2+]i responses with greater effects in SHR (P < 0.01). L-type and T-type Ca2+ channel inhibition reduced LY83583-mediated [Ca2+]i increase only in WKY cells. Both types of Ca2+ channels were expressed (mRNA and protein) in VSMCs from WKY and SHR, with greater abundance in SHR than WKY (2- to 3-fold). These results demonstrate that ROS increase vascular [Ca2+]i and contraction, primarily via extracellular Ca2+ influx. Whereas responses to H2O2 are enhanced, *O2- -mediated actions are blunted in SHR. These effects may relate to differential activation of Ca2+ channels by H2O2 and *O2-. Enhanced activation of L-type Ca2+ channels and increased Ca2+ influx by H2O2 may contribute to increased Ca2+ signaling in VSMCs from SHR.

Endothelium-derived reactive oxygen species: their relationship to endothelium-dependent hyperpolarization and vascular tone

Opinions on the role of reactive oxygen species (ROS) in the vasculature have shifted in recent years, such that they are no longer merely regarded as indicators of cellular damage or byproducts of metabolism--they may also be putative mediators of physiological functions. Hydrogen peroxide (H2O2), in particular, can initiate vascular myocyte proliferation (and, incongruously, apoptosis), hyperplasia, cell adhesion, migration, and the regulation of smooth muscle tone. Endothelial cells express enzymes that produce ROS in response to various stimuli, and H2O2 is a potent relaxant of vascular smooth muscle. H2O2 itself can mediate endothelium-dependent relaxations in some vascular beds. Although nitric oxide (NO) is well recognized as an endothelium-derived dilator, it is also well established, particularly in the microvasculature, that another factor, endothelium-derived hyperpolarizing factor (EDHF), is a significant determinant of vasodilatory tone. This review primarily focuses on the hypothesis that H2O2 is an EDHF in resistance arteries. Putative endothelial sources of H2O2 and the effects of H2O2 on potassium channels, calcium homeostasis, and vascular smooth muscle tone are discussed. Furthermore, given the perception that ROS can more likely elicit cytotoxic effects than perform signalling functions, the arguments for and against H2O2 being an endogenous vasodilator are assessed.

Red wine polyphenols induce EDHF-mediated relaxations in porcine coronary arteries through the redox-sensitive activation of the PI3-kinase/Akt pathway

Red wine polyphenolic compounds (RWPCs) are potent inducers of endothelium-dependent relaxations of coronary arteries, which involve both nitric oxide and endothelium-derived hyperpolarizing factor (EDHF). The EDHF-mediated relaxation to RWPCs is critically dependent on the formation of reactive oxygen species by a flavin-dependent enzyme. The aim of the present study was to determine the role of redox-sensitive protein kinases including p38 MAPK, ERK1/2 and PI3-kinase/Akt in RWPCs-induced EDHF-mediated relaxation. Porcine coronary artery rings were suspended in organ chambers for measurement of changes in isometric tension. Confluent cultures of porcine coronary artery endothelial cells were used to determine the phosphorylation level of p38 MAPK, ERK1/2 and Akt by Western blot analysis. All experiments were performed in the presence of indomethacin and Nomega-nitro-L-arginine. RWPCs caused pronounced endothelium-dependent relaxations, which were significantly reduced by wortmannin and LY294002, two inhibitors of PI3-kinase, and not affected by PD98059 (an inhibitor of ERK1/2 kinase kinase) and SB203580 (an inhibitor of p38 MAPK). In contrast, wortmannin did not affect relaxations to bradykinin or levcromakalim. RWPCs elicited within minutes a sustained and concentration-dependent phosphorylation of p38 MAPK, ERK1/2 and Akt in endothelial cells. The phosphorylation of Akt in response to RWPCs was abolished by wortmannin and LY294002, and by the membrane-permeant analogue of superoxide dismutase Mn(III)tetrakis(1-methyl-4-pyridyl)porphyrin. The present findings demonstrate that RWPCs cause EDHF-mediated relaxations of coronary arteries; these responses are critically dependent on the redox-sensitive activation of the PI3-kinase/Akt pathway in endothelial cells.

The pulmonary biology of isoprostanes

Isoprostanes are widely recognized as useful markers of membrane lipid peroxidation. It seems to be less well appreciated, however, that they also elicit important biological responses, even though this was first shown at the same time that they were introduced as markers of oxidative stress. The past several years have seen the list of cells/tissues which are sensitive to isoprostanes grow considerably: in fact, as we summarize here, there is now evidence that essentially every cell type in the lung responds in some pathologically relevant way to isoprostanes. In this sense, they might well be considered as not just markers of oxidative stress and inflammation, but also as a novel group of inflammatory mediators. Moreover, in addition to their pathological effects, we summarize here the evidence which has led us to hypothesize that isoprostanes could play an important role in vascular smooth muscle physiology as "endothelium-derived hyperpolarizing factors."

Peroxynitrite-induced relaxation in isolated canine cerebral arteries and mechanisms of action

The present study was undertaken to determine the vascular actions of peroxynitrite (ONOO(-)), the product of superoxide and nitric oxide (NO), in isolated canine cerebral arteries and to gain insight into its potential mechanisms of action. In the absence of any vasoactive agent, ONOO(-) (from 10(-7) to 10(-6) M) was able to reduce the basal tension. In prostaglandin F2alpha-precontracted canine basilar arterial rings, ONOO(-) elicited concentration-dependent relaxation at concentrations from 10(-8) to 10(-5) M. The effective concentrations producing approximately 50% maximal relaxation (EC(50)) to ONOO(-) were 4.06 x 10(-6) and 4.12 x 10(-6) M in intact and denuded rings, respectively (P > 0.05). No significant differences in relaxation responses were found in ring preparations with or without endothelium (P > 0.05). The presence of either 5 microM methylene blue (MB) or 5 microM 1H-[1,2,4]oxadiazolo-[4,3-alpha]quinoxalin-1-one (ODQ) significantly inhibited the relaxations induced by ONOO(-). Tetraethylammonium chloride (T-2265) significantly decreased the ONOO(-)-induced relaxations in a concentration-dependent manner. However, ONOO(-) had no effect on rings precontracted by high KCL (P > 0.05). Addition of low concentrations of calyculin A (50 nM) was able to abolish the ONOO(-)-induced relaxation. Furthermore, ONOO(-) significantly inhibited calcium-induced contractions of K(+)-depolarized canine cerebral rings in a concentration-related manner. Lastly, a variety of pharmacological agents and antagonists including L-NMMA, l-arginine, indomethacin, atropine, naloxone, diphenhydramine, cimetine, glibenclamide, haloperidol, etc., did not influence the relaxant effects of ONOO(-) on the rings. Our new results suggest that ONOO(-)-triggered relaxation, on canine cerebral arteries, is mediated by elevation of cyclic guanosine monophosphate (cGMP) levels, membrane hyperpolarization via K+ channel activation, activation of myosin light chain phosphatase activity, and interference with calcium movement and cellular membrane Ca(2+) entry.