Hydrogen peroxide is an endothelium-derived hyperpolarizing factor in mice

Impaired vasodilation in the pathogenesis of hypertension: focus on nitric oxide, endothelial-derived hyperpolarizing factors, and prostaglandins

Under resting conditions the arterial vasculature exists in a vasoconstricted state referred to as vascular tone. Physiological dilatation in response to increased flow, a function of normal endothelium is necessary to maintain normal blood pressure. Endothelial dysfunction in vascular smooth muscle cells thus results in loss of normal vasorelaxant function and the inability of arteries to appropriately dilate in response to increased blood flow in either a systemic or regional vascular bed, resulting in increased blood pressure, a sequence that may represent a common pathway to hypertension. Normal vasorelaxation is mediated by a number of endothelial systems including nitric oxide (NO), prostaglandins (PGI2 and PGE2), and a family of endothelial-derived hyperpolarizing factors (EDHF). In response to hemodynamic shear stress, endothelium continuously releases NO, EDHF, and PGI2 to provide vasodilatation. EDHF, not a single molecule but rather a group of molecules that includes epoxyeicosatrienoic acids, hydrogen peroxide, carbon monoxide, hydrogen sulfide, C-natriuretic peptide, and K+ itself, causes vasodilatation by activation of vascular smooth muscle cell K+ channels, resulting in hyperpolarization and thus vasorelaxation. The understanding and effective management of blood pressure requires an understanding of both physiologic and pathophysiologic regulation of vascular tone. This review describes molecular mechanisms underlying normal endothelial regulation and pathological states, such as increased oxidative stress, which cause loss of vasorelaxation. Possible pharmacological interventions to restore normal function are suggested.

Physiological implications of hydrogen sulfide: a whiff exploration that blossomed

The important life-supporting role of hydrogen sulfide (H(2)S) has evolved from bacteria to plants, invertebrates, vertebrates, and finally to mammals. Over the centuries, however, H(2)S had only been known for its toxicity and environmental hazard. Physiological importance of H(2)S has been appreciated for about a decade. It started by the discovery of endogenous H(2)S production in mammalian cells and gained momentum by typifying this gasotransmitter with a variety of physiological functions. The H(2)S-catalyzing enzymes are differentially expressed in cardiovascular, neuronal, immune, renal, respiratory, gastrointestinal, reproductive, liver, and endocrine systems and affect the functions of these systems through the production of H(2)S. The physiological functions of H(2)S are mediated by different molecular targets, such as different ion channels and signaling proteins. Alternations of H(2)S metabolism lead to an array of pathological disturbances in the form of hypertension, atherosclerosis, heart failure, diabetes, cirrhosis, inflammation, sepsis, neurodegenerative disease, erectile dysfunction, and asthma, to name a few. Many new technologies have been developed to detect endogenous H(2)S production, and novel H(2)S-delivery compounds have been invented to aid therapeutic intervention of diseases related to abnormal H(2)S metabolism. While acknowledging the challenges ahead, research on H(2)S physiology and medicine is entering an exponential exploration era.

Concomitant activation of functionally opposing prostacyclin and thromboxane prostanoid receptors by cyclo-oxygenase-1-mediated prostacyclin synthesis in mouse arteries

This study aimed to determine whether cyclo-oxygenase-1 (COX-1) mediates dilatation of mouse arteries via synthesis of prostacyclin (PGI(2)) and, if so, how PGI(2) (IP) receptors contribute and whether thromboxane prostanoid (TP) receptors are implicated in the process. Mesenteric arteries were isolated from wild-type mice or mice with COX-1 deficiency (COX-1(-/-)). The vasomotor reaction to the COX substrate arachidonic acid (AA) was determined with isometric force measurement, while the in vitro production or the plasma level of the PGI(2) metabolite 6-keto-PGF(1α) was analysed with high-performance liquid chromatography-mass spectroscopy or enzyme immunoassay, respectively. Results showed that AA, which evoked endothelium-dependent 6-keto-PGF(1α) production, elicited relaxation that was inhibited or enhanced by antagonizing IP or TP receptors, respectively. Also, IP receptor blockade resulted in contraction in response to AA (following NO synthase inhibition), which was prevented by a concomitant TP receptor antagonism. Meanwhile, COX-1(-/-) or COX-1 inhibition abolished the in vitro 6-keto-PGF(1α) production and reduced the relaxation or contraction observed with AA. Real-time PCR showed that whereas TP receptor mRNAs were detected at similar levels, IP receptor mRNAs were present at higher levels in the branches than in the main stem of the mesenteric artery. In addition, antagonizing the IP receptors enhanced the contraction evoked by PGI(2) in the carotid artery. Also, we noted that COX-1(-/-) mice had a reduced basal plasma 6-keto-PGF(1α) level. These results demonstrate an explicit vasodilator role for COX-1-mediated endothelial PGI(2) synthesis and suggest that the functionally opposing IP and TP receptors concomitantly mediate the vasomotor reaction to PGI(2), with the dilator activity of IP receptors being compromised by the vasoconstrictor effect of TP receptors and vice versa.

The endothelium: influencing vascular smooth muscle in many ways

The endothelium, although only a single layer of cells lining the vascular and lymphatic systems, contributes in multiple ways to vascular homeostasis. Subsequent to the 1980 report by Robert Furchgott and John Zawadzki, there has been a phenomenal increase in our knowledge concerning the signalling molecules and pathways that regulate endothelial - vascular smooth muscle communication. It is now recognised that the endothelium is not only an important source of nitric oxide (NO), but also numerous other signalling molecules, including the putative endothelium-derived hyperpolarizing factor (EDHF), prostacyclin (PGI(2)), and hydrogen peroxide (H(2)O(2)), which have both vasodilator and vasoconstrictor properties. In addition, the endothelium, either via transferred chemical mediators, such as NO and PGI(2), and (or) low-resistance electrical coupling through myoendothelial gap junctions, modulates flow-mediated vasodilatation as well as influencing mitogenic activity, platelet aggregation, and neutrophil adhesion. Disruption of endothelial function is an early indicator of the development of vascular disease, and thus an important area for further research and identification of potentially new therapeutic targets. This review focuses on the signalling pathways that regulate endothelial - vascular smooth muscle communication and the mechanisms that initiate endothelial dysfunction, particularly with respect to diabetic vascular disease.

Essential role of bone marrow for microvascular endothelial and metabolic functions in mice

RATIONALE

We have previously demonstrated that the importance of endothelium-derived hyperpolarizing factor (EDHF) increases as the vessel size decreases and that endothelium-derived hydrogen peroxide (H(2)O(2)) is an EDHF in animals and humans, for which endothelial nitric oxide synthase (eNOS) is the major source. Recent studies have suggested the important role of the bone marrow (BM) in modulating cardiovascular and metabolic functions.

OBJECTIVE

We aimed to examine whether BM plays a role in modulating microvascular endothelial and metabolic functions in mice, and if so, to elucidate the mechanisms involved.

METHODS AND RESULTS

Male eNOS(-/-) mice were transplanted with BM cells from wild-type (WT) or eNOS(-/-) mice and were maintained for 6 weeks. Endothelium-dependent relaxations and hyperpolarizations of mesenteric arteries to acetylcholine were reduced in eNOS(-/-) mice and were markedly improved when transplanted with WT-BM but not with eNOS(-/-)-BM. The enhanced component of endothelium-dependent relaxations was abolished by catalase, indicating that the improved responses were mediated by H(2)O(2). In contrast, no such beneficial effect was noted in the aorta. Reduced plasma adiponectin levels and impaired glucose tolerance in eNOS(-/-) mice were also improved by WT-BM transplantation. Neuronal nitric oxide synthase (nNOS) in mesenteric arteries of eNOS(-/-) mice was significantly upregulated only when transplanted with WT-BM. Importantly, the beneficial effects of WT-BM transplantation were absent in eNOS(-/-)/adiponectin(-/-) or eNOS(-/-)/nNOS(-/-) mice.

CONCLUSIONS

These results provide the first evidence that BM plays an important role in modulating microvascular endothelial and metabolic functions, for which adiponectin and nNOS may be involved.

Hydrogen peroxide enhances vasodilatation by increasing dimerization of cGMP-dependent protein kinase type Iα

BACKGROUND

cGMP-dependent protein kinase type I (PKG I) plays a key role in vasodilatation caused by cGMP-elevating agents. It is a homodimer in mammalian cells, existing as 2 isoforms, Iα and Iβ. The aim of the present study was both to determine whether PKG I dimerization and activity are modulated by hydrogen peroxide (H(2)O(2)) and its influence on vasodilatation.

METHODS AND RESULTS

The dimers and monomers of total PKG I and PKG Iβ were analyzed by Western blotting. PKG I activity was assayed by measuring the incorporation of (32)P into BPDEtide. Changes in vessels tension were determined by organ chamber technique. In isolated porcine coronary arteries, H(2)O(2) increased the dimers of total PKG I in a concentration-dependent manner, but had no effect on dimerization of PKG Iβ. The dimerization of PKG I caused by H(2)O(2) was prevented by catalase but not by deferoxamine and tiron. H(2)O(2) promoted the translocation of PKG I from cytoplasm to membrane. H(2)O(2) enhanced the activity of PKG I and relaxations of porcine coronary arteries to the nitric oxide donor and 8-Br-cGMP. Inhibition of catalase under in vivo conditions significantly decreased rat mean arterial pressure, which was associated with increased dimerization of PKG I.

CONCLUSIONS

The present study suggests that H(2)O(2) may enhance the activity of PKG Iα-and PKG I-dependent vasodilatation via increased dimerization of the enzyme.

Emergence of the erythropoietin/erythropoietin receptor system as a novel cardiovascular therapeutic target

Although hypoxia and ischemia are known to be involved in the pathogenesis of cardiovascular disease, specific therapeutic targets still remain elusive. To address this important issue, we have performed 2 series of experimental studies, aiming at erythropoietin (Epo)/Epo receptor (EpoR) based on the following backgrounds. Epo has long been regarded as a hematopoietic hormone that acts exclusively in the proliferation and differentiation of erythroid progenitors. Although recent studies have demonstrated that EpoR is expressed in the cardiovascular system, the potential protective role of the vascular Epo/EpoR system in vivo remains to be examined. We hypothesized that the vascular Epo/EpoR system plays an important protective role against the development of cardiovascular disease. Using vascular EpoR-deficient mouse, we demonstrated that the vascular Epo/EpoR system plays a crucial role for endothelial function and vascular homeostasis. The vascular Epo/EpoR system is important for the activation of the vascular endothelial growth factor/vascular endothelial growth factor receptor-2 system, inhibits hypoxia-induced pulmonary endothelial damage and promotes ischemia-induced angiogenesis in vivo. These results indicate that the vascular Epo/EpoR system plays an important protective role against hypoxia/ischemia, demonstrating that this system is a novel therapeutic target in cardiovascular medicine.

Mice lacking macrophage 12/15-lipoxygenase are resistant to experimental hypertension

In mouse arteries, Alox15 [leukocyte-type 12/15-lipoxygenase (LO)] is assumed to regulate vascular function by metabolizing arachidonic acid (AA) to dilator eicosanoids that mediate the endothelium-dependent relaxations to AA and acetylcholine (ACh). We used Alox15(-/-) mice, made by targeted disruption of the Alox15 gene, to characterize its role in the regulation of blood pressure and vascular tone. Systolic blood pressures did not differ between wild-type (WT) and Alox15(-/-) mice between 8-12 wk of age, but Alox15(-/-) mice exhibited resistance toward both N(G)-nitro-L-arginine-methyl ester (L-NAME)- and deoxycorticosterone acetate (DOCA)/high-salt-induced hypertension. ACh relaxed mesenteric arteries and abdominal aortas of WT and Alox15(-/-) mice to an identical extent. The LO inhibitor nordihydroguaiaretic acid attenuated the ACh relaxations by 35% in arteries from both WT and Alox15(-/-) mice. Reverse-phase HPLC analysis of [(14)C]AA metabolites in aorta and peritoneal macrophages (PM) revealed differences. Unlike PM, aorta tissue did not produce detectable amounts of 15-hydroxyeicosatetraenoic acid. Although Alox15 mRNA was detected in aorta, high-resolution gel electrophoresis with immunodetection revealed no Alox15 protein expression. Unlike aorta, Alox15 protein was detected in PM, intestine, fat, lung, spleen, and skin from WT, but not Alox15(-/-), mice. Injection of WT PM, a primary source of Alox15 protein, into Alox15(-/-) mice abolished their resistance toward L-NAME-induced hypertension. On the other hand, WT mice acquired resistance to L-NAME-induced hypertension after depletion of macrophages by clodronate injection. These studies indicate that Alox15 is involved in development of experimental hypertension by altering macrophage functions but not via synthesis of the vasoactive LO metabolites in mouse arteries.

NADPH oxidase-derived ROS and the regulation of pulmonary vessel tone

Pulmonary vessel constriction results from an imbalance between vasodilator and vasoconstrictor factors released by the endothelium including nitric oxide, endothelin, prostanoids, and reactive oxygen species (ROS). ROS, generated by a variety of enzymatic sources (such as mitochondria and NADPH oxidases, a.k.a. Nox), appear to play a pivotal role in vascular homeostasis, whereas elevated levels effect vascular disease. The pulmonary circulation is very sensitive to changes in the partial pressure of oxygen and differs from the systemic circulation in its response to this change. In fact, the pulmonary vessels contract in response to low oxygen tension, whereas systemic vessels dilate. Growing evidence suggests that ROS production and ROS-related pathways may be key factors that underlie this differential response to oxygen tension. A major emphasis of our laboratory is the role of Nox isozymes in cardiovascular disease. In this review, we will focus our attention on the role of Nox-derived ROS in the control of pulmonary vascular tone.

Critical role of hydrogen peroxide signaling in the sequential activation of p38 MAPK and eNOS in laminar shear stress

Laminar shear stress (LSS) is a protective hemodynamic regulator of endothelial function and limits the development of atherosclerosis and other vascular wall diseases related to pathophysiological generation of reactive oxygen species. LSS activates several endothelial signaling responses, including the activation of MAPKs and eNOS. Here, we explored the mechanisms of activation of these key endothelial signaling pathways. Using the cone/plate model we found that LSS (12 dyn/cm(2)) rapidly promotes endothelial intracellular generation of superoxide and hydrogen peroxide (H(2)O(2)). Physiological concentrations of H(2)O(2) (flux of 0.1 nM/min and 15 μM added extracellularly) significantly activated both eNOS and p38 MAPK. Pharmacological inhibition of NADPH oxidases (NOXs) and specific knockdown of NOX4 decreased LSS-induced p38 MAPK activation. Whereas the absence of eNOS did not alter LSS-induced p38 MAPK activation, pharmacological inhibition and knockdown of p38α MAPK blocked H(2)O(2)- and LSS-induced eNOS phosphorylation and reduced (•)NO levels. We propose a model in which LSS promotes the formation of signaling levels of H(2)O(2), which in turn activate p38α MAPK and then stimulate eNOS, leading to increased (•)NO generation and protection of endothelial function.

Decreased production of neuronal NOS-derived hydrogen peroxide contributes to endothelial dysfunction in atherosclerosis

BACKGROUND AND PURPOSE

Reduced NO availability has been described as a key mechanism responsible for endothelial dysfunction in atherosclerosis. We previously reported that neuronal NOS (nNOS)-derived H(2)O(2) is an important endothelium-derived relaxant factor in the mouse aorta. The role of H(2)O(2) and nNOS in endothelial dysfunction in atherosclerosis remains undetermined. We hypothesized that a decrease in nNOS-derived H(2)O(2) contributes to the impaired vasodilatation in apolipoprotein E-deficient mice (ApoE(-/-)).

EXPERIMENTAL APPROACH

Changes in isometric tension were recorded on a myograph; simultaneously, NO and H(2)O(2) were measured using carbon microsensors. Antisense oligodeoxynucleotides were used to knockdown eNOS and nNOS in vivo. Western blot and confocal microscopy were used to analyse the expression and localization of NOS isoforms.

KEY RESULTS

Aortas from ApoE(-/-) mice showed impaired vasodilatation paralleled by decreased NO and H(2)O(2) production. Inhibition of nNOS with L-Arg(NO2) -L-Dbu, knockdown of nNOS and catalase, which decomposes H(2)O(2) into oxygen and water, decreased ACh-induced relaxation by half, produced a small diminution of NO production and abolished H(2)O(2) in wild-type animals, but had no effect in ApoE(-/-) mice. Confocal microscopy showed increased nNOS immunostaining in endothelial cells of ApoE(-/-) mice. However, ACh stimulation of vessels resulted in less phosphorylation on Ser852 in ApoE(-/-) mice.

CONCLUSIONS AND IMPLICATIONS

Our data show that endothelial nNOS-derived H(2)O(2) production is impaired and contributes to endothelial dysfunction in ApoE(-/-) aorta. The present study provides a new mechanism for endothelial dysfunction in atherosclerosis and may represent a novel target to elaborate the therapeutic strategy for vascular atherosclerosis.

Effect of exercise training on nitric oxide and superoxide/H₂O₂ signaling pathways in collateral-dependent porcine coronary arterioles

Endothelial nitric oxide (NO) synthase (NOS) has been shown to contribute to enhanced vascular function after exercise training. Recent studies have revealed that relatively low concentrations of reactive oxygen species can contribute to endothelium-dependent vasodilation under physiological conditions. We tested the hypothesis that exercise training enhances endothelial function via endothelium-derived vasodilators, NO and superoxide/H(2)O(2), in the underlying setting of chronic coronary artery occlusion. An ameroid constrictor was placed around the proximal left circumflex coronary artery to induce gradual occlusion in Yucatan miniature swine. At 8 wk postoperatively, pigs were randomly assigned to sedentary (pen-confined) or exercise-training (treadmill-run: 5 days/wk for 14 wk) regimens. Exercise training significantly enhanced concentration-dependent, bradykinin-mediated dilation in cannulated collateral-dependent arterioles (∼130 μm diameter) compared with sedentary pigs. NOS inhibition reversed training-enhanced dilation at low bradykinin concentrations in collateral-dependent arterioles, although increased dilation persisted at higher bradykinin concentrations. Total and phosphorylated (Ser(1179)) endothelial NOS protein levels were significantly increased in arterioles from collateral-dependent compared with the nonoccluded region, independent of exercise. The H(2)O(2) scavenger polyethylene glycol-catalase abolished the training-enhanced bradykinin-mediated dilation in collateral-dependent arterioles; similar results were observed with the SOD inhibitor diethyldithiocarbamate. Fluorescence measures of bradykinin-stimulated H(2)O(2) levels were significantly increased by exercise training, independent of occlusion. The NADPH inhibitor apocynin significantly attenuated bradykinin-mediated dilation in arterioles of exercise-trained, but not sedentary, pigs and was associated with significantly increased protein levels of the NADPH subunit p67phox. These data provide evidence that, in addition to NO, the superoxide/H(2)O(2) signaling pathway significantly contributes to exercise training-enhanced endothelium-mediated dilation in collateral-dependent coronary arterioles.

Hydrogen peroxide mediates oxidant-dependent stimulation of arterial smooth muscle L-type calcium channels

Changes in calcium and redox homeostasis influence multiple cellular processes. Dysregulation of these signaling modalities is associated with pathology in cardiovascular, neuronal, endocrine, and other physiological systems. Calcium and oxidant signaling mechanisms are frequently inferred to be functionally related. To address and clarify this clinically relevant issue in the vasculature we tested the hypothesis that the ubiquitous reactive oxygen molecule hydrogen peroxide mediates oxidant-dependent stimulation of cerebral arterial smooth muscle L-type calcium channels. Using a combinatorial approach including intact arterial manipulations, electrophysiology, and total internal reflection fluorescence imaging, we found that application of physiological levels of hydrogen peroxide to isolated arterial smooth muscle cells increased localized calcium influx through L-type calcium channels. Similarly, oxidant-dependent stimulation of L-type calcium channels by the vasoconstrictor ANG II was abolished by intracellular application of catalase. Catalase also prevented ANG II from increasing localized subplasmalemmal sites of increased oxidation previously associated with colocalized calcium influx through L-type channels. Furthermore, catalase largely attenuated the contractile response of intact cerebral arterial segments to ANG II. In contrast, enhanced dismutation of superoxide to hydrogen peroxide with SOD had no effect on ANG II-dependent stimulation of L-type calcium channels. From these data we conclude that hydrogen peroxide is important for oxidant-dependent regulation of smooth muscle L-type calcium channels and arterial function. These data also support the emerging concept of hydrogen peroxide as a biologically relevant oxidant second messenger in multiple cell types with a diverse array of physiological functions.

Role of reactive oxygen and nitrogen species in the vascular responses to inflammation

Inflammation is a complex and potentially life-threatening condition that involves the participation of a variety of chemical mediators, signaling pathways, and cell types. The microcirculation, which is critical for the initiation and perpetuation of an inflammatory response, exhibits several characteristic functional and structural changes in response to inflammation. These include vasomotor dysfunction (impaired vessel dilation and constriction), the adhesion and transendothelial migration of leukocytes, endothelial barrier dysfunction (increased vascular permeability), blood vessel proliferation (angiogenesis), and enhanced thrombus formation. These diverse responses of the microvasculature largely reflect the endothelial cell dysfunction that accompanies inflammation and the central role of these cells in modulating processes as varied as blood flow regulation, angiogenesis, and thrombogenesis. The importance of endothelial cells in inflammation-induced vascular dysfunction is also predicated on the ability of these cells to produce and respond to reactive oxygen and nitrogen species. Inflammation seems to upset the balance between nitric oxide and superoxide within (and surrounding) endothelial cells, which is necessary for normal vessel function. This review is focused on defining the molecular targets in the vessel wall that interact with reactive oxygen species and nitric oxide to produce the characteristic functional and structural changes that occur in response to inflammation. This analysis of the literature is consistent with the view that reactive oxygen and nitrogen species contribute significantly to the diverse vascular responses in inflammation and supports efforts that are directed at targeting these highly reactive species to maintain normal vascular health in pathological conditions that are associated with acute or chronic inflammation.

Single atom substitution in mouse protein kinase G eliminates oxidant sensing to cause hypertension

Blood pressure regulation is crucial for the maintenance of health, and hypertension is a risk factor for myocardial infarction, heart failure, stroke and renal disease. Nitric oxide (NO) and prostacyclin trigger well-defined vasodilator pathways; however, substantial vasorelaxation in response to agents such as acetylcholine persists when the synthesis of these molecules is prevented. This remaining vasorelaxation activity, termed endothelium-derived hyperpolarizing factor (EDHF), is more prevalent in resistance than in conduit blood vessels and is considered a major mechanism for blood pressure control. Hydrogen peroxide (H2O2) has been shown to be a major component of EDHF in several vascular beds in multiple species, including in humans. H2O2 causes the formation of a disulfide bond between the two α subunits of protein kinase G I-α (PKGI-α), which activates the kinase independently of the NO-cyclic guanosine monophosphate (cGMP) pathway and is coupled to vasodilation. To test the importance of PKGI-α oxidation in the EDHF mechanism and blood pressure control in vivo, we generated a knock-in mouse expressing only a C42S 'redox-dead' version of PKGI-α. This amino acid substitution, a single-atom change (an oxygen atom replacing a sulfur atom), blocked the vasodilatory action of H2O2 on resistance vessels and resulted in hypertension in vivo.

Differential roles of NADPH oxidases in vascular physiology and pathophysiology

Reactive oxygen species (ROS) are produced by all vascular cells and regulate the major physiological functions of the vasculature. Production and removal of ROS are tightly controlled and occur in discrete subcellular locations, allowing for specific, compartmentalized signaling. Among the many sources of ROS in the vessel wall, NADPH oxidases are implicated in physiological functions such as control of vasomotor tone, regulation of extracellular matrix and phenotypic modulation of vascular smooth muscle cells. They are involved in the response to injury, whether as an oxygen sensor during hypoxia, as a regulator of protein processing, as an angiogenic stimulus, or as a mechanism of wound healing. These enzymes have also been linked to processes leading to disease development, including migration, proliferation, hypertrophy, apoptosis and autophagy. As a result, NADPH oxidases participate in atherogenesis, systemic and pulmonary hypertension and diabetic vascular disease. The role of ROS in each of these processes and diseases is complex, and a more full understanding of the sources, targets, cell-specific responses and counterbalancing mechanisms is critical for the rational development of future therapeutics.

Hypoxic pulmonary vasoconstriction

It has been known for more than 60 years, and suspected for over 100, that alveolar hypoxia causes pulmonary vasoconstriction by means of mechanisms local to the lung. For the last 20 years, it has been clear that the essential sensor, transduction, and effector mechanisms responsible for hypoxic pulmonary vasoconstriction (HPV) reside in the pulmonary arterial smooth muscle cell. The main focus of this review is the cellular and molecular work performed to clarify these intrinsic mechanisms and to determine how they are facilitated and inhibited by the extrinsic influences of other cells. Because the interaction of intrinsic and extrinsic mechanisms is likely to shape expression of HPV in vivo, we relate results obtained in cells to HPV in more intact preparations, such as intact and isolated lungs and isolated pulmonary vessels. Finally, we evaluate evidence regarding the contribution of HPV to the physiological and pathophysiological processes involved in the transition from fetal to neonatal life, pulmonary gas exchange, high-altitude pulmonary edema, and pulmonary hypertension. Although understanding of HPV has advanced significantly, major areas of ignorance and uncertainty await resolution.

H2O2-induced dilation in human coronary arterioles: role of protein kinase G dimerization and large-conductance Ca2+-activated K+ channel activation

RATIONALE

Hydrogen peroxide (H(2)O(2)) serves as a key endothelium-derived hyperpolarizing factor mediating flow-induced dilation in human coronary arterioles (HCAs). The precise mechanisms by which H(2)O(2) elicits smooth muscle hyperpolarization are not well understood. An important mode of action of H(2)O(2) involves the oxidation of cysteine residues in its target proteins, including protein kinase G (PKG)-Iα, thereby modulating their activities.

OBJECTIVE

Here we hypothesize that H(2)O(2) dilates HCAs through direct oxidation and activation of PKG-Iα leading to the opening of the large-conductance Ca(2+)-activated K(+) (BK(Ca)) channel and subsequent smooth muscle hyperpolarization.

METHODS AND RESULTS

Flow and H(2)O(2) induced pressure gradient/concentration-dependent vasodilation in isolated endothelium-intact and -denuded HCAs, respectively. The dilation was largely abolished by iberiotoxin, a BK(Ca) channel blocker. The PKG inhibitor Rp-8-Br-PET-cGMP also markedly inhibited flow- and H(2)O(2)-induced dilation, whereas the soluble guanylate cyclase inhibitor ODQ had no effect. Treatment of coronary smooth muscle cells (SMCs) with H(2)O(2) elicited dose-dependent, reversible dimerization of PKG-Iα, and induced its translocation to the plasma membrane. Patch-clamp analysis identified a paxilline-sensitive single-channel K(+) current with a unitary conductance of 246-pS in freshly isolated coronary SMCs. Addition of H(2)O(2) into the bath solution significantly increased the probability of BK(Ca) single-channel openings recorded from cell-attached patches, an effect that was blocked by the PKG-Iα inhibitor DT-2. H(2)O(2) exhibited an attenuated stimulatory effect on BK(Ca) channel open probability in inside-out membrane patches.

CONCLUSIONS

H(2)O(2) dilates HCAs through a novel mechanism involving protein dimerization and activation of PKG-Iα and subsequent opening of smooth muscle BK(Ca) channels.

Hydrogen peroxide as a mediator of vasorelaxation evoked by N-oleoylethanolamine and anandamide in rat small mesenteric arteries

Hydrogen peroxide (H(2)O(2)) has been shown to participate in endothelium-derived hyperpolarising factor (EDHF)-mediated mechanisms. Vasorelaxation to the endocannabinoid-like N-oleoylethanolamine (OEA) and anandamide has been shown to be endothelium-dependent. Therefore, the principal aim was to investigate whether H(2)O(2) plays a role in vasorelaxation to endocannabinoids in rat mesenteric arteries. We have also investigated the effects of catalase on endothelium-dependent relaxations and vascular responses to H(2)O(2). First- (G1) and third- (G3) order branches of the superior mesenteric artery from male, Wistar rats were mounted in a wire myograph, contracted with methoxamine, and concentration-response curves to anandamide, OEA carbachol or H(2)O(2), were constructed. The influence of nitric oxide production and H(2)O(2) breakdown on these responses were then investigated using L-NAME (300 μM), and catalase (1000 Uml(-1)) respectively. In G1 mesenteric arteries, vasorelaxations to carbachol and H(2)O(2) were inhibited by L-NAME, but not by catalase. Responses to both anandamide and OEA were also unaffected by catalase. In G3 mesenteric arteries, endothelium-dependent relaxations to carbachol were modestly affected by L-NAME, unaffected by catalase alone, but their combination greatly inhibited vasorelaxation. Similarly, catalase inhibited vasorelaxation to anandamide and OEA, and combined treatment with L-NAME further reduced this response. In G1 mesenteric arteries, vasorelaxation to H(2)O(2) is predominantly mediated by nitric oxide. We conclude that in G3 arteries H(2)O(2) activity contributes towards EDHF-type responses and vasorelaxation to endocannabinoids, either directly or indirectly. Given the association between vascular pathophysiology and H(2)O(2), these findings may provide a mechanism whereby disease states may influence responses to endocannabinoid and related mediators.

Endothelium-derived hyperpolarizing factor in the brain: influence of sex, vessel size and disease state

The endothelial layer of cells lining the intimal surface of blood vessels is essential for vascular function. The endothelium releases multiple vasodilator and protective factors, including nitric oxide, prostacyclin and endothelium-derived hyperpolarizing factor; an imbalance in these factors predisposes individuals to vascular diseases such as stroke. These factors are differentially regulated by vessel size, sex hormones and disease state, therefore playing differential roles in different tissues following vascular injury. In particular, the endothelium-derived hyperpolarizing factor candidate termed epoxyeicosatrienoic acid, plays a prominent role in microvessel function, especially after ischemia, thereby making this signaling pathway an attractive target for therapy in vascular disease, including stroke.

Endothelial dysfunction in the apolipoprotein E-deficient mouse: insights into the influence of diet, gender and aging

Since the early 1990s, several strains of genetically modified mice have been developed as models for experimental atherosclerosis. Among the available models, the apolipoprotein E-deficient (apoE⁻/⁻) mouse is of particular relevance because of its propensity to spontaneously develop hypercholesterolemia and atherosclerotic lesions that are similar to those found in humans, even when the mice are fed a chow diet. The main purpose of this review is to highlight the key achievements that have contributed to elucidating the mechanisms pertaining to vascular dysfunction in the apoE⁻/⁻ mouse. First, we summarize lipoproteins and atherosclerosis phenotypes in the apoE⁻/⁻ mouse, and then we briefly discuss controversial evidence relative to the influence of gender on the development of atherosclerosis in this murine model. Second, we discuss the main mechanisms underlying the endothelial dysfunction of conducting vessels and resistance vessels and examine how this vascular defect can be influenced by diet, aging and gender in the apoE⁻/⁻ mouse.

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.

Regulation of endothelial function by mitochondrial reactive oxygen species

Mitochondria are well known for their central roles in ATP production, calcium homeostasis, and heme and steroid biosynthesis. However, mitochondrial reactive oxygen species (ROS), including superoxide and hydrogen peroxide, once thought to be toxic byproducts of mitochondrial physiologic activities, have recently been recognized as important cell-signaling molecules in the vascular endothelium, where their production, conversion, and destruction are highly regulated. Mitochondrial reactive oxygen species appear to regulate important vascular homeostatic functions under basal conditions in a variety of vascular beds, where, in particular, they contribute to endothelium-dependent vasodilation. On exposure to cardiovascular risk factors, endothelial mitochondria produce excessive ROS in concert with other cellular ROS sources. Mitochondrial ROS, in this setting, act as important signaling molecules activating prothrombotic and proinflammatory pathways in the vascular endothelium, a process that initially manifests itself as endothelial dysfunction and, if persistent, may lead to the development of atherosclerotic plaques. This review concentrates on emerging appreciation of the importance of mitochondrial ROS as cell-signaling molecules in the vascular endothelium under both physiologic and pathophysiologic conditions. Future potential avenues of research in this field also are discussed.

Reactive oxygen species and the regulation of hyperproliferation in a colonial hydroid

Colonies of Podocoryna carnea circulate gastrovascular fluid among polyps via tubelike stolons. At polyp-stolon junctions, mitochondrion-rich cells in part regulate this gastrovascular flow. During competition, colonies hyperproliferate nematocytes and stolons; nematocysts are discharged until one colony is killed. Hyperproliferation then ceases, and normal growth resumes. Here, competing colonies were treated with azide, which inhibits respiration and upregulates reactive oxygen species (ROS). After the cessation of competition, azide-treated colonies continued to hyperproliferate. In azide-treated competing colonies, however, mitochondrion-rich cells were found to produce similar amounts of ROS as those in untreated competing colonies. Subsequent experiments showed that both azide treatment and competition diminished the lumen widths at polyp-stolon junctions, where mitochondrion-rich cells are found. In competing colonies, these diminished widths may also diminish the metabolic demand on these cells, causing mitochondria to enter the resting state and emit more ROS. Indeed, results with two fluorescent probes show that mitochondrion-rich cells in competing colonies produce more ROS than those in noncompeting colonies. In sum, these results suggest that competition perturbs the usual activity of mitochondrion-rich cells, altering their redox state and increasing ROS formation. Via uncharacterized pathways, these ROS may contribute to hyperproliferation.

Effect of hypoxia in mice mesenteric arteries surrounded by adipose tissue

AIM

To investigate the influence of hypoxia on the vasoactive effect of peri-vascular white adipose tissue.

METHODS

Isometric tension recordings were performed on mesenteric arteries from Swiss male mice with or without adherent adipose tissue.

RESULTS

Hypoxia (bubbling with 95% N(2), 5% CO(2)) induced a biphasic response, i.e. vasoconstriction followed by vasorelaxation, in pre-contracted (noradrenaline, 10 μm) mesenteric arteries with adipose tissue in the presence of indomethacin (10 μm) and N(ω) -nitro-l-arginine (0.1 mm). Only a small vasorelaxation was observed in arteries without adipose tissue. Pre-contraction with 60 or 120 mm K(+) , incubation with tetraethylammoniumchloride (1 and 3 mm), apamin (1 μm) combined with charybdotoxin (0.1 μm) or 1-[(2-chlorophenyl) diphenylmethyl]-1H-pyrazole (TRAM-34) (10 μm) significantly impaired the hypoxic vasorelaxation. Removal of the endothelium only reduced the hypoxic vasorelaxation. Apamin (1 μm) and charybdotoxin (0.1 μm) did not influence the vasorelaxation of sodium hydrosulfide hydrate. Zinc protoporphyrin IX (10 μm), miconazole (10 μm), 8-(p-sulfophenyl)theophylline (0.1 mm), 1 H-[1, 2, 4]oxadiazolo[4,3- A]quinoxalin-1-one (10 μm), apocynin (0.3 mm), diphenyliodonium (1 μm), catalase (2500 U mL(-1)) and tempol (0.1 mm) did not influence the hypoxic vasorelaxation. In contrast to losartan (0.1 mm), indomethacin (10 μm) and SQ-29548 (10 μm) significantly reduced the hypoxic vasoconstriction.

CONCLUSIONS

Moderate hypoxia induces a biphasic vasomotor response in mice mesenteric arteries surrounded by adipose tissue. The hypoxic vasoconstriction is endothelium independent, whereas the vasodilation is endothelium dependent, soluble guanylyl cyclase independent and in part mediated by opening K(Ca) channels. Cyclooxygenase metabolites mediate the hypoxic vasoconstriction, while endothelium-derived hyperpolarizing factor plays a small role in the hypoxic vasorelaxation.

Endothelium-derived hyperpolarizing factor and vascular function

Endothelial function refers to a multitude of physiological processes that maintain healthy homeostasis of the vascular wall. Exposure of the endothelium to cardiac risk factors results in endothelial dysfunction and is associated with an alteration in the balance of vasoactive substances produced by endothelial cells. These include a reduction in nitric oxide (NO), an increase in generation of potential vasoconstrictor substances and a potential compensatory increase in other mediators of vasodilation. The latter has been surmised from data demonstrating persistent endothelium-dependent vasodilatation despite complete inhibition of NO and prostaglandins. This remaining non-NO, non-prostaglandin mediated endothelium-dependent vasodilator response has been attributed to endothelium-derived hyperpolarizing factor/s (EDHF). Endothelial hyperpolarization is likely due to several factors that appear to be site and species specific. Experimental studies suggest that the contribution of the EDHFs increase as the vessel size decreases, with a predominance of EDHF activity in the resistance vessels, and a compensatory up-regulation of hyperpolarization in states characterized by reduced NO availability. Since endothelial dysfunction is a precursor for atherosclerosis development and its magnitude is a reflection of future risk, then the mechanisms underlying endothelial dysfunction need to be fully understood, so that adequate therapeutic interventions can be designed.

Interaction between nitric oxide signaling and gap junctions: effects on vascular function

Nitric oxide signaling, through eNOS (or possibly nNOS), and gap junction communication are essential for normal vascular function. While each component controls specific aspects of vascular function, there is substantial evidence for cross-talk between nitric oxide signaling and the gap junction proteins (connexins), and more recently, protein-protein association between eNOS and connexins. This review will examine the evidence for interaction between these pathways in normal and diseased arteries, highlight the questions that remain about the mechanisms of their interaction, and explore the possible interaction between nitric oxide signaling and the newly discovered pannexin channels. This article is part of a Special Issue entitled: The Communicating junctions, composition, structure and characteristics.

Soluble epoxide hydrolase contamination of specific catalase preparations inhibits epoxyeicosatrienoic acid vasodilation of rat renal arterioles

Cytochrome P-450 metabolites of arachidonic acid, the epoxyeicosatrienoic acids (EETs) and hydrogen peroxide (H(2)O(2)), are important signaling molecules in the kidney. In renal arteries, EETs cause vasodilation whereas H(2)O(2) causes vasoconstriction. To determine the physiological contribution of H(2)O(2), catalase is used to inactivate H(2)O(2). However, the consequence of catalase action on EET vascular activity has not been determined. In rat renal afferent arterioles, 14,15-EET caused concentration-related dilations that were inhibited by Sigma bovine liver (SBL) catalase (1,000 U/ml) but not Calbiochem bovine liver (CBL) catalase (1,000 U/ml). SBL catalase inhibition was reversed by the soluble epoxide hydrolase (sEH) inhibitor tAUCB (1 μM). In 14,15-EET incubations, SBL catalase caused a concentration-related increase in a polar metabolite. Using mass spectrometry, the metabolite was identified as 14,15-dihydroxyeicosatrienoic acid (14,15-DHET), the inactive sEH metabolite. 14,15-EET hydrolysis was not altered by the catalase inhibitor 3-amino-1,2,4-triazole (3-ATZ; 10-50 mM), but was abolished by the sEH inhibitor BIRD-0826 (1-10 μM). SBL catalase EET hydrolysis showed a regioisomer preference with greatest hydrolysis of 14,15-EET followed by 11,12-, 8,9- and 5,6-EET (V(max) = 0.54 ± 0.07, 0.23 ± 0.06, 0.18 ± 0.01 and 0.08 ± 0.02 ng DHET·U catalase(-1)·min(-1), respectively). Of five different catalase preparations assayed, EET hydrolysis was observed with two Sigma liver catalases. These preparations had low specific catalase activity and positive sEH expression. Mass spectrometric analysis of the SBL catalase identified peptide fragments matching bovine sEH. Collectively, these data indicate that catalase does not affect EET-mediated dilation of renal arterioles. However, some commercial catalase preparations are contaminated with sEH, and these contaminated preparations diminish the biological activity of H(2)O(2) and EETs.

Cell signaling of angiotensin II on vascular tone: novel mechanisms

Angiotensin II (Ang II) is a pleiotropic hormone that influences the function of many cell types and regulates many organ systems. In the cardiovascular system, it is a potent vasoconstrictor that increases peripheral vascular resistance and elevates arterial pressure. It also promotes inflammation, hypertrophy, and fibrosis, which are important in vascular remodeling in cardiovascular diseases. The diverse actions of Ang II are mediated via AT(1) and AT(2) receptors, which couple to many signaling molecules, including small G proteins, phospholipases, mitogen-activated protein (MAP) kinases, phosphatases, tyrosine kinases, NADPH oxidase, and transcription factors. In general, acute Ang II stimulation induces vasoconstriction through changes in the intracellular free calcium concentration [Ca(2+)](i), whereas long-term stimulation leads to cell proliferation and proinflammatory responses. This review focuses on signaling processes of vasoconstriction and highlights some new mechanisms regulating the contractile machinery in controlling vasomotor tone by Ang II, including RhoA/Rho kinase, transient receptor potential (TRP) channels, reactive oxygen species, and arachidonic acid metabolites.

ROS-induced ROS release in vascular biology: redox-redox signaling

The involvement of reactive oxygen species (ROS) in regulating vascular function both in normal vessels and as part of an adaptive response during disease has been intensively studied. From the recognition that ROS serve as important signaling molecules has emerged multiple lines of evidence that there is a functional connectivity between intracellular sites of ROS production. This cross talk has been termed ROS-induced ROS release (RIRR) and is supported by a variety of observations showing that RIRR is a common mechanism for ROS amplification and regional ROS generation. The compartmentalization of ROS production within a cell is critical to its signaling function and is facilitated by microlocalization of specific scavengers. This review will provide descriptions and examples of important mechanisms of RIRR.

Hyperhomocysteinemia impairs endothelium-derived hyperpolarizing factor-mediated vasorelaxation in transgenic cystathionine beta synthase-deficient mice

Hyperhomocysteinemia (HHcy) is associated with endothelial dysfunction (ED), but the mechanism is largely unknown. In this study, we investigated the role and mechanism of HHcy-induced ED in microvasculature in our newly established mouse model of severe HHcy (plasma total homocysteine, 169.5 μM). We found that severe HHcy impaired nitric oxide (NO)- and endothelium-derived hyperpolarizing factor (EDHF)-mediated, endothelium-dependent relaxations of small mesenteric arteries (SMAs). Endothelium-independent and prostacyclin-mediated endothelium-dependent relaxations were not changed. A nonselective Ca(2+)-activated potassium channel (K(Ca)) inhibitor completely blocked EDHF-mediated relaxation. Selective blockers for small-conductance K(Ca) (SK) or intermediate-conductance K(Ca) (IK) failed to inhibit EDHF-mediated relaxation in HHcy mice. HHcy increased the levels of SK3 and IK1 protein, superoxide (O(2)(-)), and 3-nitrotyrosine in the endothelium of SMAs. Preincubation with antioxidants and peroxynitrite (ONOO(-)) inhibitors improved endothelium-dependent and EDHF-mediated relaxations and decreased O(2)(-) production in SMAs from HHcy mice. Further, EDHF-mediated relaxation was inhibited by ONOO(-) and prevented by catalase in the control mice. Finally, L-homocysteine stimulated O(2)(-) production, which was reversed by antioxidants, and increased SK/IK protein levels and tyrosine nitration in cultured human cardiac microvascular endothelial cells. Our results suggest that HHcy impairs EDHF relaxation in SMAs by inhibiting SK/IK activities via oxidation- and tyrosine nitration-related mechanisms.

Endothelial Nox4 NADPH oxidase enhances vasodilatation and reduces blood pressure in vivo

OBJECTIVE

Increased reactive oxygen species (ROS) production is involved in the pathophysiology of endothelial dysfunction. NADPH oxidase-4 (Nox4) is a ROS-generating enzyme expressed in the endothelium, levels of which increase in pathological settings. Recent studies indicate that it generates predominantly hydrogen peroxide (H(2)O(2)), but its role in vivo remains unclear.

METHODS AND RESULTS

We generated transgenic mice with endothelium-targeted Nox4 overexpression (Tg) to study the in vivo role of Nox4. Tg demonstrated significantly greater acetylcholine- or histamine-induced vasodilatation than wild-type littermates. This resulted from increased H(2)O(2) production and H(2)O(2)-induced hyperpolarization but not altered nitric oxide bioactivity. Tg had lower systemic blood pressure than wild-type littermates, which was normalized by antioxidants.

CONCLUSION

Endothelial Nox4 exerts potentially beneficial effects on vasodilator function and blood pressure that are attributable to H(2)O(2) production. These effects contrast markedly with those reported for Nox1 and Nox2, which involve superoxide-mediated inactivation of nitric oxide. Our results suggest that therapeutic strategies to modulate ROS production in vascular disease may need to separately target individual Nox isoforms.

Balloon catheter injury abolishes phenylephrine-induced relaxation in the rat contralateral carotid

BACKGROUND AND PURPOSE

The consequences of compensatory responses to balloon catheter injury in rat carotid artery, on phenylephrine-induced relaxation and contraction in the contralateral carotid artery were studied.

EXPERIMENTAL APPROACH

Relaxation and contraction concentration-response curves for phenylephrine were obtained for contralateral carotid arteries in the presence of indomethacin (COX inhibitor), SC560 (COX-1 inhibitor), SC236 (COX-2 inhibitor) or 4-hydroxytetramethyl-L-piperidine-1-oxyl (tempol; superoxide dismutase mimetic). Reactive oxygen species were measured in carotid artery endothelial cells fluorimetrically with dihydroethidium.

KEY RESULTS

Phenylephrine-induced relaxation was abolished in contralateral carotid arteries from operated rats (E(max) = 0.01 ± 0.004 g) in relation to control (E(max) = 0.18 ± 0.005 g). Phenylephrine-induced contractions were increased in contralateral arteries (E(max) = 0.54 ± 0.009 g) in relation to control (E(max) = 0.38 ± 0.014 g). SC236 restored phenylephrine-induced relaxation (E(max) = 0.17 ± 0.004 g) and contraction (E(max) = 0.34 ± 0.018 g) in contralateral arteries. Tempol restored phenylephrine-induced relaxation (E(max) = 0.19 ± 0.012 g) and contraction (E(max) = 0.42 ± 0.014 g) in contralateral arteries, while apocynin did not alter either relaxation (E(max) = 0.01 ± 0.004 g) or contraction (E(max) = 0.54 ± 0.009 g). Dihydroethidium fluorescence was increased in contralateral samples (18 882 ± 435 U) in relation to control (10 455 ± 303 U). SC236 reduced the fluorescence in contralateral samples (8250 ± 365 U).

CONCLUSIONS AND IMPLICATIONS

Balloon catheter injury abolished phenylephrine-induced relaxation and increased phenylephrine-induced contraction in contralateral carotid arteries, through O(2) (-) derived from COX-2.

Vasomodulatory effect of novel peroxovanadate compounds on rat aorta: Role of rho kinase and nitric oxide/cGMP pathway

The present study was undertaken to assess the role of reactive oxygen species (ROS) in rat aortic ring vasoreactivity and integrity by using various peroxovanadate (pV) compounds. All the pV compounds (1nM-300 μM) used in the present study exerted concentration-dependent contractions on endothelium intact rat aortic rings. All compounds with an exception of DPV-asparagine (DPV-asn) significantly altered vascular integrity as shown by diminished KCl responses. Phenylephrine (PE)-mediated contractions (3nM-300 μM) were unaltered in the presence of these compounds. Acetylcholine (Ach)-mediated relaxation in PE (1μM) pre-contracted rings was significantly reduced in presence of diperoxovanadate (DPV), poly (sodium styrene sulfonate-co-maleate)-pV (PSS-CoM-pV) and poly (sodium styrene 4-sulfonate)-pV (PSS-pV). However, no significant change in Ach-mediated responses was observed in the presence of poly (acrylate)-pV (PAA-pV) and DPV-asn. DPV-asn was thus chosen to further elucidate mechanism involved in peroxide mediated modulation of vasoreactivity. DPV-asn (30nM - 300 μM) exerted significantly more stable contractions, that was found to be catalase (100U/ml) resistant in comparison with H(2)O(2) (30nM-300 μM) in endothelium intact aortic rings. These contractile responses were found to be dependent on extracellular Ca(2+) and were significantly inhibited in presence of ROS scavenger N-acetylcysteine (100 μM). Intracellular calcium chelation by BAPTA-AM (10μM) had no significant effect on DPV-asn (30nM-300 μM) mediated contraction. Pretreatment of aortic rings by rho-kinase inhibitor Y-27632 (10μM) significantly inhibited DPV-asn-mediated vasoconstriction indicating role of voltage-dependent Ca(2+) influx and downstream activation of rho-kinase. The small initial relaxant effect obtained on addition of DPV-asn (30nM-1 μM) in PE (1 μM) pre-contracted endothelium intact rings, was prevented in the presence of guanylate cyclase inhibitor, methylene blue (10 μM) and/or nitric oxide synthase (NOS) inhibitor, l-NAME (100 μM) suggesting involvement of nitric oxide and cGMP. DPV-asn, like H(2)O(2), exerted a response of vasoconstriction in normal arteries and vasodilation at low concentrations (30nM-1 μM) in PE-pre contracted rings with overlapping mechanisms. These findings suggest usefulness of DPV-asn having low toxicity, in exploring the peroxide-mediated effects on various vascular beds. The present study also convincingly demonstrates role of H(2)O(2) in the modulation of vasoreactivity by using stable peroxide DPV-asn and warrants future studies on peroxide mediated signaling from a newer perspective.

H2O2 is the transferrable factor mediating flow-induced dilation in human coronary arterioles

RATIONALE

Endothelial derived hydrogen peroxide (H(2)O(2)) is a necessary component of the pathway regulating flow-mediated dilation (FMD) in human coronary arterioles (HCAs). However, H(2)O(2) has never been shown to be the endothelium-dependent transferrable hyperpolarization factor (EDHF) in response to shear stress.

OBJECTIVE

We examined the hypothesis that H(2)O(2) serves as the EDHF in HCAs to shear stress.

METHODS AND RESULTS

Two HCAs were cannulated in series (a donor intact vessel upstream and endothelium-denuded detector vessel downstream). Diameter changes to flow were examined in the absence and presence of polyethylene glycol catalase (PEG-CAT). The open state probability of large conductance Ca(2+)-activated K(+) (BK(Ca)) channels in smooth muscle cells downstream from the perfusate from an endothelium-intact arteriole was examined by patch clamping. In some experiments, a cyanogen bromide-activated resin column bound with CAT was used to remove H(2)O(2) from the donor vessel. When flow proceeds from donor to detector, both vessels dilate (donor:68±7%; detector: 45±11%). With flow in the opposite direction, only the donor vessel dilates. PEG-CAT contacting only the detector vessel blocked FMD in that vessel (6±4%) but not in donor vessel (61±13%). Paxilline inhibited dilation of endothelium-denuded HCAs to H(2)O(2). Effluent from donor vessels elicited K(+) channel opening in an iberiotoxin- or PEG-CAT-sensitive fashion in cell-attached patches but had little effect on channel opening on inside-out patches. Vasodilation of detector vessels was diminished when exposed to effluent from CAT-column.

CONCLUSIONS

Flow induced endothelial production of H(2)O(2), which acts as the transferrable EDHF activating BK(Ca) channels on the smooth muscle cells.

Acute effects of hydrogen peroxide on skeletal muscle microvascular oxygenation from rest to contractions

Reactive oxygen species, such as hydrogen peroxide (H(2)O(2)), exert a critical regulatory role on skeletal muscle function. Whether acute increases in H(2)O(2) modulate muscle microvascular O(2) delivery-utilization (Qo(2)/Vo(2)) matching [i.e., microvascular partial pressure of O(2) (Pmv(O(2)))] at rest and following the onset of contractions is unknown. The hypothesis was tested that H(2)O(2) treatment (exogenous H(2)O(2)) would enhance Pmv(O(2)) and slow Pmv(O(2)) kinetics during contractions compared with control. Anesthetized, healthy young Sprague-Dawley rats had their spinotrapezius muscles either exposed for measurement of blood flow (and therefore QO(2)), VO(2), and Pmv(O(2)), or exteriorized for measurement of force production. Electrically stimulated twitch contractions (1 Hz, ~7 V, 2-ms pulse duration, 3 min) were evoked following acute superfusion with Krebs-Henseleit (control) and H(2)O(2) (100 μM). Relative to control, H(2)O(2) treatment elicited disproportionate increases in QO(2) and VO(2) that elevated Pmv(O(2)) at rest and throughout contractions and slowed overall Pmv(O(2)) kinetics (i.e., ~85% slower mean response time; P < 0.05). Accordingly, H(2)O(2) resulted in ~33% greater overall Pmv(O(2)), as assessed by the area under the Pmv(O(2)) curve (P < 0.05). Muscle force production was not altered with H(2)O(2) treatment (P > 0.05), evidencing reduced economy during contractions (~40% decrease in the force/VO(2) relationship; P < 0.05). These findings indicate that, although increasing the driving force for blood-myocyte O(2) flux (i.e., Pmv(O(2))), transient elevations in H(2)O(2) impair skeletal muscle function (i.e., reduced economy during contractions), which mechanistically may underlie, in part, the reduced exercise tolerance in conditions associated with oxidative stress.

Endothelium-derived hyperpolarizing factor and diabetes

In addition to its role as a barrier between blood and tissues, the vascular endothelium is responsible for the synthesis and released of a number of vasodilators including prostaglandins, nitric oxide and endothelium-derived hyperpolarizing factor (EDHF). As one of these vasodilators, the specific nature of EDHF has not been fully elucidated, although a number of roles have been proposed. Importantly, many conditions, such as hypertension, hyperlipidemia, heart failure, ischemia-reperfusion and diabetes mellitus comprise vascular endothelial dysfunction with EDHF dysregulation. This article reviews reports on the role of EDHF in diabetes-related endothelial dysfunction.