Interaction between endothelin-1 and endothelium-derived relaxing factor in human arteries and veins

Immune and Metabolic Mechanisms of Endothelial Dysfunction

Endothelial dysfunction is a strong prognostic factor in predicting the development of cardiovascular diseases. Dysfunctional endothelium loses its homeostatic ability to regulate vascular tone and prevent overactivation of inflammation, leading to vascular dysfunction. These functions are critical for vascular homeostasis and arterial pressure control, the disruption of which may lead to hypertension. Hypertension itself can also cause endothelial dysfunction, as endothelial cells are susceptible to haemodynamic changes. Although it is unclear which of those factors appear first, they create a vicious circle further damaging multiple organs, including the heart and vessels. There are also sex-specific differences in homeostatic functions of the endothelium regarding vessel tone regulation, which may contribute to differences in arterial blood pressure between men and women. Even more importantly, there are sex-differences in the development of endothelial dysfunction and vessel remodelling. Hence, an understanding of the mechanisms of endothelial dysfunction and its contribution to pathological vascular remodelling during hypertension is of critical importance. This review addresses immunological and metabolic aspects in mechanisms of endothelial dysfunction and the resulting mechanisms in vascular remodelling with respect to arterial hypertension, including the potential role of sex-specific differences.

Osteoporosis under psychological stress: mechanisms and therapeutics

Psychological stress has been associated with the onset of several diseases, including osteoporosis. However, the underlying pathogenic mechanism remains unknown, and effective therapeutic strategies are still unavailable. Growing evidence suggests that the sympathetic nervous system regulates bone homeostasis and vascular function under psychological stress, as well as the coupling of osteogenesis and angiogenesis in bone development, remodeling, and regeneration. Furthermore, extracellular vesicles (EVs), particularly mesenchymal stem cell extracellular vesicles (MSC-EVs), have emerged as prospecting therapies for stimulating angiogenesis and bone regeneration. We summarize the role of sympathetic regulation in bone homeostasis and vascular function in response to psychological stress and emphasize the relationship between vessels and bone. Finally, we suggest using MSC-EVs as a promising therapeutic method for treating osteoporosis in psychological stress.

UV-B filter octylmethoxycinnamate-induced vascular endothelial disruption on rat aorta: In silico and in vitro approach

Throughout human life, an extensive and varied range of emerging environmental contaminants, called endocrine disruptors (EDCs), cause adverse health effects, including in the cardiovascular (CV) system. Cardiovascular diseases (CVD) are worryingly one of the leading causes of all mortality and mobility worldwide. The UV-B filter octylmethoxycinnamate (also designated octinoxate, or ethylhexyl methoxycinnamate (CAS number: 5466-77-3)) is an EDC widely present in all personal care products. However, to date, there are no studies evaluating the OMC-induced effects on vasculature using animal models to improve human cardiovascular health. This work analysed the effects of OMC on rat aorta vasculature and explored the modes of action implicated in these effects. Our results indicated that OMC relaxes the rat aorta by endothelium-dependent mechanisms through the signaling pathways of cyclic nucleotides and by endothelium-independent mechanisms involving inhibition of L-Type voltage-operated Ca²⁺ channels (L-Type VOCC). Overall, OMC toxicity on rat aorta may produce hypotension via vasodilation due to excessive NO release and blockade of L-Type VOCC. Moreover, the OMC-induced endothelial dysfunction may also occur by promoting the endothelial release of endothelin-1. Therefore, our findings demonstrate that exposure to OMC alters the reactivity of the rat aorta and highlight that long-term OMC exposure may increase the risk of human CV diseases.

Endothelial Cells and the Cerebral Circulation

Endothelial cells form the innermost layer of all blood vessels and are the only vascular component that remains throughout all vascular segments. The cerebral vasculature has several unique properties not found in the peripheral circulation; this requires that the cerebral endothelium be considered as a unique entity. Cerebral endothelial cells perform several functions vital for brain health. The cerebral vasculature is responsible for protecting the brain from external threats carried in the blood. The endothelial cells are central to this requirement as they form the basis of the blood-brain barrier. The endothelium also regulates fibrinolysis, thrombosis, platelet activation, vascular permeability, metabolism, catabolism, inflammation, and white cell trafficking. Endothelial cells regulate the changes in vascular structure caused by angiogenesis and artery remodeling. Further, the endothelium contributes to vascular tone, allowing proper perfusion of the brain which has high energy demands and no energy stores. In this article, we discuss the basic anatomy and physiology of the cerebral endothelium. Where appropriate, we discuss the detrimental effects of high blood pressure on the cerebral endothelium and the contribution of cerebrovascular disease endothelial dysfunction and dementia. © 2022 American Physiological Society. Compr Physiol 12:3449-3508, 2022.

Indoxyl sulfate enhances endothelin-1-induced contraction via impairment of NO/cGMP signaling in rat aorta

The microbiome-derived tryptophan metabolite, indoxyl sulfate, is considered a harmful vascular toxin. Here, we examined the effects of indoxyl sulfate on endothelin-1 (ET-1)-induced contraction in rat thoracic aortas. Indoxyl sulfate (10-3 M, 60 min) increased ET-1-induced contraction but did not affect isotonic high-K+-induced contraction. The ET-1-induced contraction was enhanced by endothelial denudation in both control and indoxyl sulfate-treated groups. BQ123 (10-6 M), an ETA receptor antagonist, reduced the ET-1-induced contraction in both control and indoxyl sulfate groups. BQ788 (10-6 M), an ETB receptor antagonist, increased the contraction in the control group but had no effect on the indoxyl sulfate group. Conversely, indoxyl sulfate inhibited relaxation induced by IRL1620, an ETB receptor agonist. L-NNA, an NO synthase (NOS) inhibitor, increased the ET-1-induced contractions in both the control and indoxyl sulfate groups, whereas L-NPA (10-6 M), a specific neuronal NOS inhibitor, did not affect the ET-1-induced contraction in both groups. However, ODQ, an inhibitor of soluble guanylyl cyclase, increased the ET-1-induced contraction in both groups. Organic anion transporter (OAT) inhibitor probenecid (10-3 M) and antioxidant N-acetyl-L-cysteine (NAC; 5 × 10-3 M) inhibited the effects of indoxyl sulfate. A cell-permeant superoxide scavenger reduced the ET-1-induced contraction in the indoxyl sulfate group. The aortic activity of SOD was reduced by indoxyl sulfate. The present study revealed that indoxyl sulfate augments ET-1-induced contraction in rat aortae. This enhancement may be due to the impairment of NO/cGMP signaling and may be attributed to impairment of the antioxidant systems via cellular uptake through OATs.

L-Arginine-Nitric Oxide-Asymmetric Dimethylarginine Pathway and the Coronary Circulation: Translation of Basic Science Results to Clinical Practice

By 1980, it was thought that we already knew most of the major mechanisms regulating vascular tone. However, after the somewhat serendipity discovery that endothelium is involved in mediation of relaxation to acetylcholine, a whole new world opened up and we had to rewrite our concept regarding vascular function and its regulation (not to mention many other fields). The new player was an endothelium derived relaxing factor, which molecular constitution has been identified to be nitric oxide (NO). This review summarizes the major molecular steps concerning how NO is synthetized from L-arginine. Also, the fate of L-arginine is described via the arginase and methylation pathways; both of them are affecting substantially the level and efficacy of NO. In vitro and in vivo effects of L-arginine are summarized and controversial clinical findings are discussed. On the basis of the use of methylated L-arginines, the vasomotor effects of endothelial NO released to agonists and increases in flow/wall shear stress (a major biological stimulus) is summarized. In this review the role of NO in the regulation of coronary vascular resistance, hence blood flow, is delineated and the somewhat questionable clinical use of NO donors is discussed. We made an attempt to summarize the biosynthesis, role, and molecular mechanisms of endogenously produced methylated L-arginine, asymmetric dimethylarginine (ADMA) in modulating vascular resistance, affecting the function of the heart. Additionally, the relationship between ADMA level and various cardiovascular diseases is described, such as atherosclerosis, coronary artery disease (CAD), ischemia/reperfusion injuries, and different types of coronary revascularization. A novel aspect of coronary vasomotor regulation is identified in which the pericardial fluid ADMA and endothelin play putative roles. Finally, some of the open possibilities for future research on L-arginine-NO-ADMA signaling are highlighted.

Modulation of the coronary tone in the expanding scenario of Chromogranin-A and its derived peptides

The cardiac function critically depends on an adequate myocardial oxygenation and on a correct coronary blood flow. Endothelial, hormonal and extravascular factors work together generating a fine balance between oxygen supply and oxygen utilization through the coronary circulation. Among the regulatory factors that contribute to the coronary tone, increasing attention is paid to the cardiac endocrines, such as chromogranin A, a prohormone for many biologically active peptides, including vasostatin and catestatin. In this review, we will summarize the available evidences about the coronary effects of these molecules, and their putative mechanism of action. Laboratory and clinical data on chromogranin A and its derived fragments will be analyzed in relation to the scenario of the endocrine heart, and of its putative clinical perspectives.

The importance of comorbidities in ischemic stroke: Impact of hypertension on the cerebral circulation

Comorbidities are a hallmark of stroke that both increase the incidence of stroke and worsen outcome. Hypertension is prevalent in the stroke population and the most important modifiable risk factor for stroke. Hypertensive disorders promote stroke through increased shear stress, endothelial dysfunction, and large artery stiffness that transmits pulsatile flow to the cerebral microcirculation. Hypertension also promotes cerebral small vessel disease through several mechanisms, including hypoperfusion, diminished autoregulatory capacity and localized increase in blood-brain barrier permeability. Preeclampsia, a hypertensive disorder of pregnancy, also increases the risk of stroke 4-5-fold compared to normal pregnancy that predisposes women to early-onset cognitive impairment. In this review, we highlight how comorbidities and concomitant disorders are not only risk factors for ischemic stroke, but alter the response to acute ischemia. We focus on hypertension as a comorbidity and its effects on the cerebral circulation that alters the pathophysiology of ischemic stroke and should be considered in guiding future therapeutic strategies.

Vascular endothelium - Gatekeeper of vessel health

The vascular endothelium is an interface between the blood stream and the vessel wall. Changes in this single cell layer of the artery wall are believed of primary importance in the pathogenesis of vascular disease/atherosclerosis. The endothelium responds to humoral, neural and especially hemodynamic stimuli and regulates platelet function, inflammatory responses, vascular smooth muscle cell growth and migration, in addition to modulating vascular tone by synthesizing and releasing vasoactive substances. Compromised endothelial function contributes to the pathogenesis of cardiovascular disease; endothelial 'dysfunction' is associated with risk factors, correlates with disease progression, and predicts cardiovascular events. Therapies for atherosclerosis have been developed, therefore, that are directed towards improving endothelial function.

Tissue engineering the cardiac microenvironment: Multicellular microphysiological systems for drug screening

The ability to accurately detect cardiotoxicity has become increasingly important in the development of new drugs. Since the advent of human pluripotent stem cell-derived cardiomyocytes, researchers have explored their use in creating an in vitro drug screening platform. Recently, there has been increasing interest in creating 3D microphysiological models of the heart as a tool to detect cardiotoxic compounds. By recapitulating the complex microenvironment that exists in the native heart, cardiac microphysiological systems have the potential to provide a more accurate pharmacological response compared to current standards in preclinical drug screening. This review aims to provide an overview on the progress made in creating advanced models of the human heart, including the significance and contributions of the various cellular and extracellular components to cardiac function.

Polyphenol fraction of extra virgin olive oil protects against endothelial dysfunction induced by high glucose and free fatty acids through modulation of nitric oxide and endothelin-1

Epidemiological and clinical studies have reported that olive oil reduces the incidence of cardiovascular disease. However, the mechanisms involved in this beneficial effect have not been delineated. The endothelium plays an important role in blood pressure regulation through the release of potent vasodilator and vasoconstrictor agents such as nitric oxide (NO) and endothelin-1 (ET-1), respectively, events that are disrupted in type 2 diabetes. Extra virgin olive oil contains polyphenols, compounds that exert a biological action on endothelial function. This study analyzes the effects of olive oil polyphenols on endothelial dysfunction using an in vitro model that simulates the conditions of type 2 diabetes. Our findings show that high glucose and linoleic and oleic acids decrease endothelial NO synthase phosphorylation, and consequently intracellular NO levels, and increase ET-1 synthesis by ECV304 cells. These effects may be related to the stimulation of reactive oxygen species production in these experimental conditions. Hydroxytyrosol and the polyphenol extract from extra virgin olive oil partially reversed the above events. Moreover, we observed that high glucose and free fatty acids reduced NO and increased ET-1 levels induced by acetylcholine through the modulation of intracellular calcium concentrations and endothelial NO synthase phosphorylation, events also reverted by hydroxytyrosol and polyphenol extract. Thus, our results suggest a protective effect of olive oil polyphenols on endothelial dysfunction induced by hyperglycemia and free fatty acids.

The Relationship between Vascular Function and the Autonomic Nervous System

Endothelial dysfunction and autonomic nervous system dysfunction are both risk factors for atherosclerosis. There is evidence demonstrating that there is a close interrelationship between these two systems. In hypertension, endothelial dysfunction affects the pathologic process through autonomic nervous pathways, and the pathophysiological process of autonomic neuropathy in diabetes mellitus is closely related with vascular function. However, detailed mechanisms of this interrelationship have not been clearly explained. In this review, we summarize findings concerning the interrelationship between vascular function and the autonomic nervous system from both experimental and clinical studies. The clarification of this interrelationship may provide more comprehensive risk stratification and a new effective therapeutic strategy against atherosclerosis.

Role of endothelium in vasomotor responses to endothelin system and protein kinase C activation in porcine retinal arterioles

PURPOSE

Endothelial cells synthesize vasodilator nitric oxide (NO) and vasoconstrictor endothelin-1 (ET-1) from NO synthase (eNOS) and endothelin-converting enzyme-1 (ECE-1), respectively. Protein kinase C (PKC) and Rho kinase (ROCK) are major signaling molecules mediating vasoconstriction. Although endothelial cells express eNOS, ECE-1, endothelin B (ET(B)) receptors, PKC, and ROCK, their influences on ET-1-induced vasoconstriction remain elusive. We studied whether these endothelial signaling molecules modulate retinal arteriolar constriction to ET-1.

METHODS

Porcine retinal arterioles were isolated and pressurized for vasomotor study, under conditions with intact or denuded endothelium, using videomicroscopic techniques.

RESULTS

Retinal arterioles developed similar resting tone (≈45% of maximum diameter) with or without endothelium. Endothelial denudation attenuated vasoconstriction to ET-1 precursor, big ET-1, by almost equal to 50%, but did not affect vasoconstrictions to ET-1, ET(B) agonist sarafotoxin S6c, or PKC activator phorbol-12, 13-dibutyrate (PDBu). The ROCK inhibitor H-1152 caused vasodilation, and abolished vasoconstrictions to ET-1 and PDBu independent of endothelium. With L-type voltage-operated calcium channel (L-VOCC) blocker nifedipine, PDBu-induced vasoconstriction was abolished and converted to NO-mediated vasodilation in the presence of endothelium. The ET-1-induced vasoconstriction was unaffected by NO released from endothelium during flow elevation.

CONCLUSIONS

Endothelial and smooth muscle ECE-1 contribute equally to synthesis of vasoactive ET-1 in retinal arterioles, with nominal role of endothelial ETB receptors in vasoconstriction to ET-1. The PKC activation leads to endothelium-dependent NO-mediated vasodilation when smooth muscle contraction is ablated by L-VOCC blockade. Endothelial cells and NO appear to have modest roles in modulating ROCK-dependent vasoconstriction, and are insufficient to counteract smooth muscle contractions to ET-1 and PKC activation.

Effects of arginine and antioxidant vitamins on pulmonary artery reactivity to phenylephrine in the broiler chicken

The effects of supplemental l-arginine (Arg), vitamin E (VE), and vitamin C (VC) on vascular reactivity to phenylephrine (PE) were examined in clinically healthy hypoxemic male broiler chickens. One-day-old chicks were housed in wire cages and randomly allocated to 1 of 3 dietary treatments: control (CTL; n = 80; 3,200 kcal of ME/kg, 23% CP, 1.55% Arg and 40 IU of VE/kg of feed), high-Arg (HA; n = 40; CTL + 0.8% Arg), or high-Arg and high antioxidant-vitamin diet (AEC; n = 40; HA + 200 IU of VE/kg of feed and 500 mg of VC/kg of feed). At d 14, 40 CTL birds and all the HA and AEC birds had a primary pulmonary bronchus surgically occluded (PBO). Forty CTL broilers underwent surgery without occluding the bronchus (SHAM). Pulmonary artery (PA) rings were mounted for isometric tension recordings 14 to 21 d postsurgery. The HA-PBO and AEC-PBO PA were immersed in Krebs-Henseleit buffer plus a vehicle (VehCtl) or Krebs-Henseleit buffer plus supplemental Arg, or Arg, VE, and VC (A-E-C). Maximal contractile response to PE of the CTL-SHAM PA (16 ± 14 mg/mg of dry tissue) was one-tenth compared with that of the CTL-PBO PA (159 ± 13 mg/mg), whereas the PA contractility in the supplemented groups was one-ninth compared with those of the CTL-PBO (17.9 ± 13.0 mg/mg, 17.90 ± 13.0 mg/mg for the HA-PBO+Arg and AEC-PBO+A-E-C treatments, respectively). Supplementing the bath with Arg did not change the maximal response to PE compared with the vehicle control (16.7 ± 12.2 mg/mg for HA-PBO-VehCtl). However, supplementing the bath with A-E-C produced a one-fourth reactivity compared with that of the vehicle control (80.7 ± 13.0 mg/mg for AEC-PBO-VehCtl). The PBO increased PA reactivity to PE, but supplemental Arg plus VE and VC significantly reduced it. Differential reactivity responses to PE may have been the result of protective effects of Arg, VE, and VC, implicating oxidative stress in endothelial dysfunction as well as in the upregulation of smooth muscle contractility.

The vascular endothelium in diabetes--a therapeutic target?

Insulin resistance affects the vascular endothelium, and contributes to systemic insulin resistance by directly impairing the actions of insulin to redistribute blood flow as part of its normal actions driving muscle glucose uptake. Impaired vascular function is a component of the insulin resistance syndrome, and is a feature of type 2 diabetes. On this basis, the vascular endothelium has emerged as a therapeutic target where the intent is to improve systemic metabolic state by improving vascular function. We review the available literature presenting studies in humans, evaluating the effects of metabolically targeted and vascular targeted therapies on insulin action and systemic metabolism. Therapies that improve systemic insulin resistance exert strong concurrent effects to improve vascular function and vascular insulin action. RAS-acting agents and statins have widely recognized beneficial effects on vascular function but have not uniformly produced the hoped-for metabolic benefits. These observations support the notion that systemic metabolic benefits can arise from therapies targeted at the endothelium, but improving vascular insulin action does not result from all treatments that improve endothelium-dependent vasodilation. A better understanding of the mechanisms of insulin's actions in the vascular wall will advance our understanding of the specificity of these responses, and allow us to better target the vasculature for metabolic benefits.

Thromboxane modulates endothelial permeability

The study tests the role of thromboxane in modulating microvascular permeability in vitro. Cultured monolayers of bovine aortic endothelial cells were challenged with the thromboxane (Tx) mimic U46619. This led to disassembly of actin microfilaments, cell rounding, border retraction and interendotheHal gap formation. Pretreatment with the Tx receptor antagonist SQ 29,548 prevented the Tx mimic-induced cytoskeletal changes. The Tx mimic also altered endothelial cell barrier function. Increased permeability was indicated by the increased passage of labelled albumin across monolayers cultured on microcarriers, relative to untreated endothelial cells (p < 0.05). Furthermore, electron microscopy of endothelial cells cultured on the basement membrane of human placental amnion indicated increased permeability based on wide, interendotheHal gap formation and transit of the tracer horseradish peroxidase. Quantification of interendothelial gaps revealed an eleven-fold increase with the Tx mimic relative to untreated endothial cells (p < 0.05) and prevention by pretreatment with the Tx receptor antagonist (p < 0.05). These data indicate that Tx directly modulates the permeability of endothelial cell in vitro.

Inhaled Nitric Oxide Counterbalances ET-1 Dependent Pulmonary Hypertension and Bronchoconstriction in the Pig

In anaesthetized, paralysed, ventilated pigs the ability of inhaled nitric oxide (80 ppm in 0(2)) to reduce the haemodynamic and respiratory effects of endothelin-1 administration (200 pmol/kg, i.v.) was evaluated. The mechanical properties of the respiratory system were evaluated by the rapid airway occlusion technique. The overall respiratory resistance, the interrupter resistance and the additional resistance that reflects the viscoelastic properties of tissues and the inequality of the time constant within the system were also evaluated. The results show that inhaled nitric oxide can act as a selective pulmonary vasodilator and as a bronchodilator to counteract the vasoconstrictor and bronchoconstrictor activity of endothelin-1. In the pig, nitric oxide inhaled at 80 ppm for 6 mitt reduced the changes in respiratory-, interrupter- and additional resistance due to endothelin-1 administration without significantly changing the static and dynamic elastance of the respiratory system.

Comparison of vascular and respiratory effects of endothelin-1 in the pig

The haemodynamic and respiratory responses caused by i.v. administration of endothelin-1 (ET-1) (20–100 pmol/kg) were studied in anaesthetized spontaneously breathing pigs. Intravenous bolus administration of synthetic ET-1 (40–100 pmol/kg) caused a transient decrease followed by a long-lasting increase in mean pulmonary arterial pressure and dose dependent vasoconstriction both in the systemic and pulmonary circulations. The effect on pulmonary arterial pressure was biphasic, with an initial transient fall followed by a long-lasting dose dependent increase. A biphasic response of the systemic mean arterial pressure was demonstrated only at a high dose of ET-1 (100 pmol/kg). ET-1 administration did not significantly change breathing pattern or phasic vagal input, but caused a significant decrease in passive compliance. Passive resistances or active compliance and resistances of the respiratory system were not modified. These results suggest that in the pig ET-1 is a more potent constrictor of vascular than of bronchial smooth muscle. The vasoconstrictor activity was greater in the pulmonary than the systemic circulations.

Modulatory Role of Nitric Oxide/cGMP System in Endothelin-1-Induced Signaling Responses in Vascular Smooth Muscle Cells

Nitric oxide (NO) is an important vasoprotective molecule that serves not only as a vasodilator but also exerts antihypertrophic and antiproliferative effects in vascular smooth muscle cells (VSMC). The precise mechanism by which the antihypertrophic and antiproliferative responses of NO are mediated remains obscure. However, recent studies have suggested that one of the mechanisms by which this may be achieved includes the attenuation of signal transduction pathways responsible for inducing the hypertrophic and proliferative program in VSMC. Endothelin-1 is a powerful vasoconstrictor peptide with mitogenic and growth stimulatory properties and exerts its effects by activating multiple signaling pathways which include ERK 1/2, PKB and Rho-ROCK. Both cGMP-dependent and independent events have been reported to mediate the effect of NO on these pathways leading to its vasoprotective response. This review briefly summarizes some key studies on the modulatory effect of NO on these signaling pathways and discusses the possible role of cGMP system in this process.

Effects of chronic mental stress and atherogenic diet on the immune inflammatory environment in mouse aorta

Inflammation and stress are regarded as two important atherogenic factors. Because stress can affect leukocyte distribution, we hypothesized that stress-mediated leukocyte extravasation can modify the inflammatory environment of the arterial wall possibly contributing to atherogenesis. To test this hypothesis we evaluated the inflammatory environment of the aorta in C57Bl/6 mice subjected to 3 and 12 months of chronic stress and compared it to age matched non-stressed animals. Experiments were carried out in mice fed regular chow or atherogenic diets. Both treatments increased the expression of vascular and leukocyte adhesion molecules and leukocyte accumulation. At 3 months, stress but not an atherogenic diet elevated the number of CD4 cells, CD8 cells, macrophages, dendritic cells and neutrophils. These changes were associated with elevation of transcripts for ICAM-1 and VCAM-1, E-selectin and neuropeptide Y. At 12 months, stress or high cholesterol acted similarly to elevate the number of CD8 and macrophages, and synergistically on the number of all cell types investigated. At this time-point, strong synergism was also observed on the level of E-selectin and NPY in the aorta, but not in the circulation. Despite these effects, histological and morphological alterations of the arterial wall were severe in the atherogenic diet, but not in the stress groups. Thus, although stress and an atherogenic diet may both affect leukocyte accumulation in the aorta, they may contribute differently to atherogenesis.

Calcitonin Gene-Related Peptide Terminates Long-Lasting Vasopressor Responses to Endothelin 1 In Vivo

Slow dissociation of endothelin 1 from its endothelin A receptors is responsible for the long-lasting vasoconstrictor effects of the peptide. We showed recently that calcitonin gene-related peptide selectively terminates long-lasting contractile responses to endothelin 1 in isolated rat mesenteric arteries. Here we assessed whether the antiendothelinergic effect of calcitonin gene-related peptide is vascular bed specific and may terminate long-lasting pressor responses to exogenous and locally produced endothelin 1 in vivo. Regional heterogeneity of the calcitonin gene-related peptide/endothelin A receptor cross-talk was explored in arteries isolated from various rat organs. Endothelin A receptor-mediated arterial contractions were terminated by calcitonin gene-related peptide in rat mesenteric, renal, and spermatic arteries but not in basilar, coronary, epigastric, gastric, splenic, and saphenous arteries. Endothelin A receptor antagonism only ended endothelin 1–induced contractions in spermatic arteries. In anesthetized rats, instrumented with Doppler flow probes to record regional blood flows, long-lasting pressor and vasoconstrictor responses to an intravenous bolus injection of endothelin 1 or big endothelin 1 were transiently reduced by sodium nitroprusside (NO donor) but terminated by intravenously administered calcitonin gene-related peptide. In conscious rats, calcitonin gene-related peptide but not sodium nitroprusside terminated prolonged (>60-minute) pressor responses to endothelin 1 but not those to intravenous infusion of phenylephrine. In conclusion, pressor responses to circulating and locally produced endothelin 1 that are resistant to endothelin receptor antagonism and NO can be terminated by a regionally selective effect of calcitonin gene-related peptide. Calcitonin gene related peptide receptor agonism may represent a novel strategy to treat endothelin 1–associated cardiovascular pathologies.

Working under pressure: coronary arteries and the endothelin system

Endogenous endothelin-1-dependent (ET-1) tone in coronary arteries depends on the balance between ET(A) and ET(B) receptor-mediated effects and on parameters such as receptor distribution and endothelial integrity. Numerous studies highlight the striking functional interactions that exist between nitric oxide (NO) and ET-1 in the regulation of vascular tone. Many of the cardiovascular complications associated with cardiovascular risk factors and aging are initially attributable, at least in part, to endothelial dysfunction characterized by a dysregulation between NO and ET-1. The contribution of the imbalance between smooth muscle ET(A/B) and endothelial ET(B) receptors to this process is poorly understood. An increased contribution of ET-1 that is associated with a proportional decrease in that of NO accompanies the development of coronary endothelial dysfunction, coronary vasospasm, and atherosclerosis. These data form the basis for the rationale of testing therapeutic approaches counteracting ET-1-induced cardiovascular dysfunction. It remains to be determined whether the beneficial role of endothelial ET(B) receptors declines with age and risk factors for cardiovascular diseases, revealing smooth muscle ET(B) receptors with proconstricting and proinflammatory activities.

The cardiovascular physiology and pharmacology of endothelin-1

One year after the discovery in 1980 that the endothelium was obligatory for acetylcholine to relax isolated arteries, it was clearly shown that the endothelium could also promote contraction. In 1988, Dr Yanagisawa's group identified endothelin-1 (ET-1) as the first endothelium-derived contracting factor. The circulating levels of this short (21 amino acids) peptide were quickly determined in humans and it was reported that in most cardiovascular diseases, circulating levels of ET-1 were increased and ET-1 was then recognized as a likely mediator of pathological vasoconstriction in human. The discovery of two receptor subtypes in 1990, ET(A) and ET(B), permitted optimization of bosentan, which entered clinical development in 1993, and was offered to patients with pulmonary arterial hypertension in 2001. In this report, we discuss the physiological and pathophysiological role of endothelium-derived ET-1, the pharmacology of its two receptors, focusing on the regulation of the vascular tone and as much as possible in humans. The coronary bed will be used as a running example, but references to the pulmonary, cerebral, and renal circulation will also be made. Many of the cardiovascular complications associated with aging and cardiovascular risk factors are initially attributable, at least in part, to endothelial dysfunction, particularly dysregulation of the vascular function associated with an imbalance in the close interdependence of NO and ET-1, in which the implication of the ET(B) receptor may be central.

Endothelium-derived endothelin-1

One year after the revelation by Dr. Furchgott in 1980 that the endothelium was obligatory for acetylcholine to relax isolated arteries, it was clearly shown that the endothelium could also promote contraction. In 1988, Dr. Yanagisawa's group identified endothelin-1 (ET-1) as the first endothelium-derived contracting factor. The circulating levels of this short (21-amino acid) peptide were quickly determined in humans, and it was reported that, in most cardiovascular diseases, circulating levels of ET-1 were increased, and ET-1 was then tagged as "a bad guy." The discovery of two receptor subtypes in 1990, ET(A) and ET(B), permitted optimization of the first dual ET-1 receptor antagonist in 1993 by Dr. Clozel's team, who entered clinical development with bosentan, which was offered to patients with pulmonary arterial hypertension in 2001. The revelation of Dr. Furchgott opened a Pandora's box with ET-1 as one of the actors. In this brief review, we will discuss the physiological and pathophysiological role of endothelium-derived ET-1 focusing on the regulation of the vascular tone, and as much as possible in humans. The coronary bed will be used as a running example in this review because it is the most susceptible to endothelial dysfunction, but references to the cerebral and renal circulation will also be made. Many of the cardiovascular complications associated with aging and cardiovascular risk factors are initially attributable, at least in part, to endothelial dysfunction, particularly dysregulation of the vascular function associated with an imbalance in the close interdependence of nitric oxide and ET-1.

Endothelin-1 impairs nitric oxide signaling in endothelial cells through a protein kinase Cdelta-dependent activation of STAT3 and decreased endothelial nitric oxide synthase expression

In an ovine model of persistent pulmonary hypertension of the newborn (PPHN), endothelin-1 (ET-1) expression is increased, while endothelial nitric oxide synthase (eNOS) expression is decreased. However, the molecular mechanisms by which ET-1 attenuates eNOS expression in endothelial cells are not completely understood. Thus, the goal of this study was to determine if the overexpression of ET-1 decreases eNOS expression in pulmonary arterial endothelial cells isolated from fetal lambs. To increase the ET-1 expression, cells were transfected with a plasmid coding for Prepro-ET-1, a precursor of ET-1. After overexpression of Prepro-ET-1, ET-1 levels in the culture medium were significantly increased (control = 805.3 +/- 69.8; Prepro-ET-1 overexpression = 1351 +/- 127.9). eNOS promoter activity, protein levels, and NO generation were all significantly decreased by the overexpression of Prepro-ET-1. The decrease in transcription correlated with increased activity of protein kinase Cdelta (PKCdelta) and STAT3. Further, DNA binding activity of STAT3 was also increased by Prepro-ET-1 overexpression. The increase in STAT3 activity and decrease in eNOS promoter activity were inhibited by the overexpression of dominant negative mutants of PKCdelta or STAT3. Further, a 2 bp mutation in the STAT3 binding site in the eNOS promoter inhibited STAT3 binding and led to enhanced promoter activity in the presence of Prepro-ET-1 overexpression. In conclusion, ET-1 secretion is increased by Prepro-ET-1 overexpression. This results in activation of PKCdelta, which phosphorylates STAT3, increasing its binding to the eNOS promoter. This in turn decreases eNOS promoter activity, protein levels, and NO production. Thus, ET-1 can reduce eNOS expression and NO generation in fetal pulmonary artery endothelial cells through PKCdelta-mediated activation of STAT3.

Relationship between endogenous concentrations of vasoactive substances and measures of peripheral vasodilator function in patients with coronary artery disease

1. The aim of the present study was to determine the relationship between plasma concentrations of nitrite/nitrate (NO(x)) and endothelin (ET)-1 and non-invasive measures of peripheral vasodilator function in patients with coronary artery disease (CAD). 2. Twenty-two patients with angiographic CAD underwent non-invasive measurement of peripheral vasodilator function in the brachial conduit artery (flow-mediated dilation (FMD) testing via ultrasound) and in the forearm resistance arteries (via venous occlusion plethysmography) during reactive hyperaemia after 5 min ischaemia. In addition, plasma NO(x) and ET-1 concentrations were determined. 3. The plasma concentration of NO(x) was related to the peak brachial FMD response when expressed as either the relative (%) or absolute (mm) change in diameter (r = 0.73, P < 0.001; and r = 0.64, P < 0.01, respectively). Moreover, plasma concentrations of NO(x) demonstrated a relationship with forearm vasodilation estimated by total forearm blood flow following 5 min ischaemia (r = 0.63, P < 0.01) and the flow debt repayment of the forearm (r = 0.54, P < 0.01). Finally, ET-1 concentrations were inversely related to FMD% (r = -0.45, P < 0.05). 4. The findings of the present study demonstrate a relationship between the plasma concentrations of NO(x) and measures of vascular reactivity in conduit and resistance arteries in patients with CAD. Therefore, measurement of plasma NO(x) may serve as a reliable marker for peripheral vasodilator dysfunction in patients with CAD.

The science of endothelin-1 and endothelin receptor antagonists in the management of pulmonary arterial hypertension: current understanding and future studies

Pathological vascular remodelling is a key contributor to the symptomatology of pulmonary arterial hypertension (PAH), and reversing this process may offer the best hope for improving this debilitating condition. The vascular remodelling process is believed to be due to endothelial cell dysfunction and to involve altered production of endothelial cell-derived vasoactive mediators. The observation that circulating plasma levels of the vasoactive peptide endothelin (ET)-1 are raised in patients with PAH, and that ET-1 production is increased in the pulmonary tissue of affected individuals, makes it a particularly interesting target for a therapeutic intervention in PAH. Clinical trials with ET receptor antagonists (ETRAs) show that they provide symptomatic benefit in patients with PAH, thereby proving the clinical relevance of the ET system as a therapeutic target. In this paper, we review the role of ET-1 together with the available data on the roles of the specific ET receptors and ETRAs in PAH. In particular, we discuss the possible role of ET receptor selectivity in the vascular remodelling process in PAH and whether selective ET(A) or nonselective ET(A)/ET(B) blockade offers the greatest potential to improve symptoms and alter the clinical course of the disease.

Endothelin receptor antagonism: role in the treatment of pulmonary arterial hypertension related to scleroderma

Pulmonary arterial hypertension (PAH) is a devastating disease, which is associated with a 1-year survival of about 50% without specific treatment. Pulmonary vascular remodelling, thrombosis and vasoconstriction are thought to be directly involved in increasing pulmonary vascular resistance (PVR), which, left untreated, ultimately leads to right ventricular failure and death. A total of 10-12% of patients with systemic sclerosis (SSc) develop PAH, which is a leading cause of mortality in these patients. Targeted treatment regimens involving oral therapies, in particular endothelin receptor antagonists (ERAs), such as bosentan, sitaxsentan (sitaxentan) and ambrisentan, are now being used and this approach has improved symptoms as well as survival. 1-Year survival has improved to about 80%, while 3-year survival in advanced SSc-PAH has improved from 44% to 65% since the introduction of ERAs. Subanalysis of BREATHE-1, a pilot study and the STRIDE-2X randomized controlled trials has reported improvements in time to clinical worsening, 6-minute walk distance (6mwd) and right heart haemodynamics in SSc-PAH patients given bosentan and sitaxsentan, respectively, compared with placebo. The ARIES studies have also demonstrated a delay in the time to clinical worsening and improvement in 6mwd in connective tissue associated-PAH patients given ambrisentan compared with placebo. Unfortunately, these drugs are expensive and also have the potential for adverse interactions with other PAH and supportive therapies. Mandatory monthly liver function tests are required for safe administration of bosentan, ambrisentan and sitaxsentan, while dose adjustment of warfarin and careful monitoring are required when sitaxsentan is initiated. Earlier diagnosis and treatment of PAH may further improve outcomes with current ERAs. WHO functional class (FC) has traditionally been used to determine which patients with PAH will start therapy. The EARLY study has reported significant reductions in PVR and time to clinical worsening in mildly symptomatic PAH patients treated with bosentan, and many PAH clinicians now believe WHO FC should be used as a monitoring tool once targeted therapies have been initiated and not as a tool for deciding when to start PAH specific therapies.Many pathways are thought to be involved in the pathophysiology of the PAH. There is growing evidence that combination therapies targeting different pathophysiological steps may be necessary to effectively treat SSc-PAH. The COMPASS-1 study has reported an acute haemodynamic benefit in PAH when a single-dose of sildenafil is used in combination with bosentan and COMPASS-2 will investigate whether this acute response translates into long-term benefit. Well designed morbidity and mortality trials in SSc-PAH should help increase our understanding and treatment of this orphan disease.

Interleukin-10 attenuates vascular responses to endothelin-1 via effects on ERK1/2-dependent pathway

Interleukin-10 (IL-10) is an anti-inflammatory cytokine with protective actions on the vasculature. On the other hand, endothelin (ET)-1 has potent vasoconstrictor, mitogenic, and proinflammatory activities, which have been implicated in the pathophysiology of a number of cardiovascular diseases. We hypothesized that, in a condition where ET-1 expression is upregulated, i.e., on infusion of TNF-alpha, IL-10 confers vascular protection from ET-1-induced injury. Aortic rings and first-order mesenteric arteries from male C57BL/6 (WT) and IL-10-knockout (IL-10(-/-)) mice were treated with human recombinant TNF-alpha (220 ng x kg(-1) x day(-1)) or vehicle (saline) for 14 days. TNF-alpha infusion significantly increased blood pressure in IL-10(-/-), but not WT, mice. TNF-alpha augmented vascular ET-1 mRNA expression in arteries from WT and IL-10(-/-) mice. ET type A (ET(A)) receptor expression was increased in arteries from IL-10(-/-) mice, and TNF-alpha infusion did not change vascular ET(A) receptor expression in control or IL-10(-/-) mice. Aorta and mesenteric arteries from TNF-alpha-infused IL-10(-/-) mice displayed increased contractile responses to ET-1, but not the ET type B receptor agonist IRL-1620. The ET(A) receptor antagonist atrasentan completely abolished responses to ET-1 in aorta and mesenteric vessels, whereas the ERK1/2 inhibitor PD-98059 abrogated increased contractions to ET-1 in arteries from TNF-alpha-infused IL-10(-/-) mice. Infusion of TNF-alpha, as well as knockdown of IL-10 (IL-10(-/-)), induced an increase in total and phosphorylated ERK1/2. These data demonstrate that IL-10 counteracts ET(A)-mediated vascular responses to ET-1, as well as activation of the ERK1/2 pathway.

Correlation between vascular responsivensss and expression of novel transcripts of the ETA-receptor in human vascular tissue

Alternatively spliced endothelin (ET-1) receptor transcripts have been identified, but their significance to the functional effects of ET-1 has not been established. We have investigated the presence and influence of alternatively spliced ET(A) receptor transcripts on ET-1 mediated contraction of segments of human saphenous vein. The expression of ET(A) receptor transcripts was examined with quantitative reverse transcription-polymerase chain reaction (qPCR) studies, while the response of veins to ET-1 was tested with in vitro organ bath techniques. The expression of four different transcripts for the ET(A) receptor, in which either exon 3 is spliced out (Delta3), exon 4 is spliced out (Delta4), both 3 and 4 spliced out (Delta3,4) and when both exons 2 and 4 (Delta2,4) are spliced out were identified. Functional studies showed that a lack of efficacy and potency of ET-1 is associated with a significantly lower expression of the Delta3,4 transcript. ET(A) receptor antagonism was insurmountable in samples that had lower levels of the Delta3,4 transcript, while samples from patients with higher expression of the Delta3,4 showed surmountable antagonism with BQ123. These results suggest that there is a genetic basis for the variability between individuals for the contractile effect of ET-1 at ET(A) receptors.

Treatment with raloxifene and 17beta-estradiol differentially modulates nitric oxide and prostanoids in venous endothelium and platelets of ovariectomized pigs

Oral treatment with raloxifene, a synthetic estrogen receptor modulator (SERM), or 17beta-estradiol (E2) increases risk for venous thrombosis in women. Acute application of either substance releases endothelium-derived factors from isolated femoral veins but it is not known how their chronic use affects venous functions or the interaction of platelets with veins. This study tested the hypothesis that treatment of ovariectomized animals with oral raloxifene or E2 would increase release of proaggregatory factors from venous endothelium and platelets. Ovariectomized (OVX) pigs were either untreated or treated with oral raloxifene (60 mg/day) or E2 (2 mg/day) for 4 weeks. Plasma concentrations of nitric oxide were comparable in both treatment groups and greater than in OVX pigs. Ratio of plasma thromboxane to prostacyclin was twofold greater in raloxifene compared to E2-treated pigs. In isolated femoral veins, NG-monomethyl-L-arginine (L-NMMA; 10(-4) M) augmented endothelium-dependent relaxations to adenosine diphosphate in veins from E2-treated pigs but inhibited relaxations in veins from raloxifene-treated pigs. Addition of indomethacin (10(-5) M) reversed these effects. Endothelium-dependent relaxations to thrombin were inhibited by L-NMMA only in OVX and raloxifene-treated pigs. Autologous platelets contracted veins in all groups; the magnitude of contractions depended upon the number of platelets and existing tone. Basal release of thromboxane from platelets was greatest in raloxifene compared to OVX or E2-treated pigs. Raloxifene treatment compared to E2 increased production of contractile and proaggregatory prostanoids from venous endothelium and platelets. These differences, if found in humans, may contribute to varying degrees of thrombotic risk with the SERM compared to the natural hormone.

Lack of Endothelial Nitric Oxide Synthase Promotes Endothelin-Induced Hypertension: Lessons from Endothelin-1 Transgenic/Endothelial Nitric Oxide Synthase Knockout Mice

Endothelin-1 (ET-1) is one of the most potent biologic vasoconstrictors. Nevertheless, transgenic mice that overexpress ET-1 exhibit normal BP. It was hypothesized that vascular effects of ET-1 may be antagonized by an increase of the endothelial counterpart of ET-1, nitric oxide (NO), which is produced by the endothelial NO synthase (eNOS). Therefore, cross-bred animals of ET transgenic mice (ET+/+) and eNOS knockout (eNOS-/-) mice and were generated, and BP and endothelial function were evaluated in these animals. Endothelium-dependent and -independent vascular function was assessed as relaxation/contraction of isolated preconstricted aortic rings. The tissue ET and NO system was determined in aortic rings by quantitative real-time PCR and Western blotting. Systolic BP was similar in ET+/+ and wild-type (WT) mice but was significantly elevated in eNOS-/- mice (117 +/- 4 mmHg versus 94 +/- 6 mmHg in WT mice; P < 0.001) and even more elevated in ET+/+ eNOS-/- cross-bred mice (130 +/- 4 mmHg; P < 0.05 versus eNOS-/-). Maximum endothelium-dependent relaxation was enhanced in ET+/+ mice (103 +/- 6 versus 87 +/- 4% of preconstriction in WT littermates; P < 0.05) and was completely blunted in eNOS-/- (-3 +/- 4%) and ET+/+ eNOS-/- mice (-4 +/- 4%), respectively. Endothelium-independent relaxation was comparable among all groups. Quantitative real-time PCR as well as Western blotting revealed an upregulation of the aortic ET(A) and ET(B) receptors in ET+/+ eNOS-/-, whereas eNOS was absent in aortic rings of eNOS-/- and ET+/+ eNOS-/- mice. ET-1 aortic tissue concentrations were similar in WT mice and ET+/+ eNOS-/- mice most probably as a result of an enhanced clearance of ET-1 by the upregulated ET(B) receptor. These data show for the first time that in transgenic mice that overexpress human ET-1, additional knockout of eNOS results in a further enhancement of BP as compared with eNOS-/- mice. The human ET+/+ eNOS-/- mice therefore represent a novel model of hypertension as a result of an imbalance between the vascular ET-1 and NO systems.

The vascular endothelium in hypertension

The vascular endothelium plays a fundamental role in the basal and dynamic regulation of the circulation. Thus, it has a crucial role in the pathogenesis of hypertension. A spectrum of vasoactive substances is synthesised in the endothelium; of these, nitric oxide (NO), prostacyclin (PGI2) and endothelin (ET)-1 are the most important. There is a continuous basal release of NO determining the tone of peripheral blood vessels. Systemic inhibition of NO synthesis or scavenging of NO through oxidative stress causes an increase in arterial blood pressure. Also, the renin-angiotensin-aldosterone system has a major role in hypertension as it has a direct vasoconstrictor effect and important interactions with oxygen free radicals and NO. Prostacyclin, in contrast to NO, does not contribute to the maintenance of basal vascular tone of conduit arteries, but its effect on platelets is most important. ET acts as the natural counterpart to endothelium-derived NO and has an arterial blood pressure-raising effect in man. Anti-hypertensive therapy lowers blood pressure and may influence these different mediators, thus influencing endothelial function. In summary, due to its position between the blood pressure and smooth muscle cells responsible for peripheral resistance, the endothelium is thought to be both victim and offender in arterial hypertension. The delicate balance of endothelium-derived factors is disturbed in hypertension. Specific anti-hypertensive and anti-oxidant treatment is able to restore this balance.

Oxidative and nitrosative stress in pediatric pulmonary hypertension: roles of endothelin-1 and nitric oxide

An increasing number of studies implicate oxidative stress in the development of endothelial dysfunction and the pathogenesis of cardiovascular disease. Further, this oxidative stress has been shown to be associated with alterations in both the endothelin-1 (ET-1) and nitric oxide (NO) signaling pathways such that bioavailable NO is decreased and ET-1 signaling is potentiated. However, recent data, from our groups and others, have shown that oxidative stress, ET-1, and NO are co-regulated in a complex fashion that appears to be dependent on the cellular levels of each species. Thus, when ROS levels are transiently elevated, NO signaling is potentiated through transcriptional, post-transcriptional, and post-translational mechanisms. However, in pediatric pulmonary hypertensive disorders, when reactive oxygen species (ROS) increases are sustained by ET-1 mediated activation of smooth muscle cell ET(A) subtype receptors, NOS gene expression and NO signaling are reduced. Further, increases in oxidative stress can stimulate both the expression of the ET-1 gene and the secretion of the ET-1 peptide. Finally, the addition of exogenous NO, and increasingly utilized therapy for pulmonary hypertension, can also lead to increases ROS generation via the activation of ROS generating enzymes and through the induction of mitochondrial dysfunction. Thus, this manuscript will review the available data regarding the interaction of oxidative and nitrosative stress, endothelial dysfunction, and its role in the pathophysiology of pediatric pulmonary hypertension. In addition, we will suggest avenues of both basic and clinical research that will be important to develop novel pulmonary hypertension treatment and prevention strategies, and resolve some of the remaining clinical issues regarding the use of NO augmentation.

Alteration in choroidal blood flow produced by local pressure

BACKGROUND

To investigate how transient pressure applied to the retinal pigment epithelium (RPE) layer and choroid affects choroidal blood flow in rabbits.

METHODS

Twelve rabbits underwent vitrectomy and local retinectomy. In nine of the rabbits a glass rod was used to exert brief pressure on the RPE layer and choroid. Three of the rabbits had no pressure indentation and were considered to be controls. The choroidal circulation was studied by indocyanine green (ICG) angiography. The retina and choroid were studied by postmortem histology.

RESULTS

Pressure on the RPE layer and choroid caused nonfluorescence in segments of retinal arteries and veins and reduced fluorescence in adjacent choroidal capillaries, producing a black region at the pressure site in the angiograms. The size of this region decreased during the angiogram, often accompanied by the appearance of fine channels considered to be flow through the partially blocked vessels; the obstructed ends of the vessels became increasingly hyperfluorescent. These changes lasted for about 24 h before the choroidal circulation recovered. Histology showed evidence of thrombotic-like material in choroidal arteries and veins at the areas of absent perfusion. After local retinectomies, there was no evidence of thrombosis in control eyes where no pressure had been applied.

CONCLUSION

Brief pressure on the RPE and choroid causes immediate reduction in flow through choroidal vessels, which appears to be due to local thrombosis in small segments of these vessels that resolves slowly. This may reflect a tendency for thrombi to form rapidly in choroidal vessels; it may also depend on neural reflexes causing vasoconstriction. The long time course of recovery could result in retinal ischemia and may underlie the pathophysiology of other pressure insults to the choroid.

Protection of endothelial function: targets for nutritional and pharmacological interventions

The vascular endothelium synthesizes and releases a spectrum of vasoactive substances and therefore plays a fundamental role in the basal and dynamic regulation of the circulation. Nitric oxide (NO)-originally described as endothelium-derived relaxing factor-is released from endothelial cells in response to shear stress produced by blood flow, and in response to activation of a variety of receptors. After diffusion from endothelial to vascular smooth muscle cells, NO increases intracellular cyclic guanosine-monophosphate concentrations by activation of the enzyme guanylate cyclase leading to relaxation of the smooth muscle cells. NO has also antithrombogenic, antiproliferative, leukocyte-adhesion inhibiting effects, and influences myocardial contractility. Endothelium-derived NO-mediated vascular relaxation is impaired in spontaneously hypertensive animals. NO decomposition by free oxygen radicals is a major mechanism of impaired NO bioavailability. The resulting imbalance of endothelium-derived relaxing and contracting substances disturbs the normal function of the vascular endothelium. Endothelin acts as the natural counterpart to endothelium-derived NO. Besides its arterial blood pressure rising effect in humans, endothelin-1 induces vascular and myocardial hypertrophy, which are independent risk factors for cardiovascular morbidity and mortality. Current therapeutic strategies concentrate mainly on lowering low-density lipoprotein cholesterol and an impressive reduction in the risk for cardiovascular morbidity and mortality has been achieved. Inflammatory mechanisms play an important role in vascular disease and inflammatory plasma markers correlate with prognosis. The production of reactive oxygen species under pathological conditions may represent an important inflammatory trigger. Novel therapeutic strategies specifically targeting inflammation thus bear great potential for the prevention and treatment of atherosclerotic vascular disease. In this context, the vascular actions of flavanol-rich cocoa, particularly with regard to enhanced NO synthesis and endothelial function observed in humans following consumption, warrants further attention. This review discusses pharmacological and dietary intervention.

Nitric oxide-endothelin-1 interactions after surgically induced acute increases in pulmonary blood flow in intact lambs

Several congenital heart defects require surgery that acutely increases pulmonary blood flow (PBF). This can lead to dynamic alterations in postoperative pulmonary vascular resistance (PVR) and can contribute to morbidity and mortality. Thus the objective of this study was to determine the role of nitric oxide (NO), endothelin (ET)-1, and their interactions in the alterations of PVR after surgically induced increases in PBF. Twenty lambs underwent placement of an aortopulmonary vascular graft. Lambs were instrumented to measure vascular pressures and PBF and studied for 4 h. Before and after shunt opening, lambs received an infusion of saline (n = 9), tezosentan, an ETA- and ETB -receptor antagonist (n = 6), or Nomega-nitro-L-arginine (L-NNA), a NO synthase (NOS) inhibitor (n = 5). In control lambs, shunt opening increased PBF by 117.8% and decreased PVR by 40.7% (P < 0.05) by 15 min, without further changes thereafter. Plasma ET-1 levels increased 17.6% (P < 0.05), and total NOS activity decreased 61.1% (P < 0.05) at 4 h. ET-receptor blockade (tezosentan) prevented the plateau of PBF and PVR, such that PBF was increased and PVR was decreased compared with controls at 3 and 4 h (P < 0.05). These changes were associated with an increase in total NOS activity (+61.4%; P < 0.05) at 4 h. NOS inhibition (L-NNA) after shunt placement prevented the sustained decrease in PVR seen in control lambs. In these lambs, PVR decreased by 15 min (P < 0.05) but returned to baseline by 2 h. Together, these data suggest that surgically induced increases in PBF are limited by vasoconstriction, at least in part by an ET-receptor-mediated decrease in lung NOS activity. Thus NO appears to be important in maintaining a reduction in PVR after acutely increased PBF.

Nitric oxide modulates renal vasoconstrictor effect of endothelin-1 in conscious lambs

To test the hypothesis that nitric oxide (NO) buffers the renal vasoconstrictor effects of endothelin-1 (ET-1) early in life, renal haemodynamic responses to ET-1 were measured in the presence and absence of endogenously produced NO in conscious lambs. Renal haemodynamic effects of ET-1 were measured for 5 min before (control) and 20 min after intraarterial injection of ET-1 before and after pretreatment with 20 mg/kg of the L-arginine analogue N(G)-nitro-L-arginine methyl ester (L-NAME), (experiment 1) and its inactive isomer D-NAME (experiment 2) in conscious lambs aged approximately 1 week (N=7) and approximately 6 weeks (N=6). The two experiments were carried out in random order at intervals of 24-48 h. In lambs aged approximately 6 weeks, a marked increase in renal vascular resistance (RVR) was elicited by ET-1 administration; this response was enhanced twofold following pretreatment with L-NAME. In 1-week-old lambs, however, an increase in RVR in response to ET-1 occurred only after pretreatment with L-NAME. Therefore, we accept our hypothesis and conclude that NO buffers the renal vasoconstrictor effects of ET-1 early in life.