Advertisement
Mayo Clinic Proceedings Home

The Role of Endothelin in Coronary Atherosclerosis

      During the evolution of coronary atherosclerosis, growth factors, cytokines, and other molecules are involved in cell recruitment, migration, and proliferation. Endothelin is an endothelial-derived vasoconstrictor peptide that possesses mitogenic properties. In this review, current evidence is provided that suggests that endothelin fulfills proposed criteria to be considered an atherogenic peptide because of its mitogenic and proliferative properties, as well as its interactions with known atherogenic factors. In addition, a proposed role of endothelin in the evolution of atherosclerosis is outlined.
      EDRF (endothelium-derived relaxing factor), ET (endothelin), LDL (low-density lipoprotein), PDGF (platelet-derived growth factor), PTCA (percutaneous transluminal coronary anaioelasty)
      Atherosclerosis results from an excessive inflammatory and fibroproliferative response to numerous potential vascular insults. During atherogenesis, growth factors, cytokines, lipids, and enzymes modulate critical cell functions in a manner that induces lipid accumulation and oxidation, cellmediated inflammatory response, smooth muscle proliferation, vasoconstriction, and a prothrombotic environment within the vascular wall.
      • Fuster V
      • Badimon L
      • Badimon JJ
      • Chesebro JH
      The patho-genesis of coronary artery disease and the acute coronary syndromes (first of two parts).
      • Ip JH
      • Fuster V
      • Badimon L
      • Badimon J
      • Taubman MB
      • Chesebro JH
      Syndromes of accelerated atherosclerosis: role of vascular injury and smooth muscle cell proliferation.
      • Ross R
      The pathogenesis of atherosclerosis: a perspective for the 1990s.
      ? Endothelin (ET) is an endothelial-derived peptide that exerts profound vasoconstrictive activity in vitro and in vivo. Although the role of ET as a potent systemic and coronary vasoconstrictor has been well established and reviewed extensively, an increasing body of evidence suggests that ET may have a major role in the pathogenesis and the pathophysiologic processes of coronary atherosclerosis.
      • Yanagisawa M
      • Kurihara H
      • Kimura S
      • Tomobe Y
      • Kobayashi M
      • Mitsui Y
      • et al.
      A novel potent vasoconstrictor peptide produced by vascular endothelial cells.
      • Luscher TF
      • Oemar BS
      • Boulanger CM
      • Hahn AWA
      Molecular and cellular biology of endothelin and its receptors. Part I. Part II.
      Whether ET is responsible for the initiation of these pathophysiologic changes is still unclear, but ET may well be a cofactor or marker of these alterations.
      For a peptide to have a major role in atherogenesis, it should possess certain characteristics that initiate or propagate the steps critical to the pathogenesis of atherosclerosis. (1) The peptide should participate in the pathophysiologic processes leading to atherogenesis on the cellular level. This participation includes mitogenic and proliferative properties that are mediated through specific receptors. (2) The production and activity of the peptide are enhanced by known atherogenic factors, and the circulating levels and tissue immunoreactivity are enhanced in human and animal models of atherosclerosis. (3) The peptide should also interact with these known atherogenic factors, thereby being integrated into the milieu leading to the initiation and progression of atherosclerosis.
      This review provides current evidence that suggests that ET fulfills the criteria to be considered an atherogenic peptide. The role of ET during the evolution of atherosclerosis and during the various clinical stages of atherosclerosis, such as endothelial dysfunction, unstable angina, acute myocardial infarction, and restenosis after percutaneous transluminal coronary angioplasty (PTCA), is outlined. Insofar as these factors may ultimately lead to left ventricular dysfunction, the role of ET in heart failure and cardiac transplantation is also briefly discussed. For a better understanding of the role of ET, the conventional knowledge of the morphologic changes and pathogenesis of atherosclerosis is examined first, and ET in the atherogenic process is discussed subsequently.

      Morphology of Atherosclerosis

      Vascular endothelial injury is a critical initiating event in atherogenesis; it leads to lipid accumulation and adhesion of monocytes and platelets that, in concert with the endothelium, release various growth factors, causing migration and proliferation of smooth muscle cells. Fuster and associates
      • Fuster V
      • Badimon L
      • Badimon JJ
      • Chesebro JH
      The patho-genesis of coronary artery disease and the acute coronary syndromes (first of two parts).
      proposed a pathophysiologic classification of vascular injury that puts these morphologic changes into the context of the progression of atherosclerosis and the pathogenesis of acute coronary syndromes (unstable angina, myocardial infarction, and sudden cardiac death). Type I injury consists of functional alterations in the endothelium in the absence of morphologic changes, which have been described in the setting of chronic endothelial injury as a result of disturbances in blood flow, hypertension, hypercholesterolemia, and cigarette smoking.
      • Ip JH
      • Fuster V
      • Badimon L
      • Badimon J
      • Taubman MB
      • Chesebro JH
      Syndromes of accelerated atherosclerosis: role of vascular injury and smooth muscle cell proliferation.
      Although characteristic macroscopic features of atherosclerosis are not present at this stage, ample evidence suggests that this stage of endothelial dysfunction is the earliest detectable stage in the spectrum of atherosclerosis. Accumulation of lipids and monocytesmacrophages results from type I injury. In type II injury, the release of various factors by macrophages leads to the accumulation of platelets
      • Ross R
      The pathogenesis of atherosclerosis: a perspective for the 1990s.
      with ensuing endothelial denudation and damage to the intima. These cells, along with the endothelium, stimulate the migration and proliferation of smooth muscle cells and may form either a fibrointimal lesion or an outer capsule on a predominantly lipid-rich lesion. A lipid lesion surrounded by a thin capsule can be disrupted to expose an extremely thrombogenic matrix and leads to type III injury, manifest by endothelial denudation with damage to the intima and media. During the evolution of atherosclerosis, growth factors, cytokines, and other molecules such as lipids are involved in cell recruitment, migration, and proliferation, as well as lipid and protein synthesis. These molecules are also intimately involved in vasomotor regulation, vascular remodeling, and coagulation. This humoral-cellular “cross-talk” has been eloquently discussed by Ross.
      • Ross R
      The pathogenesis of atherosclerosis: a perspective for the 1990s.
      The role of ET and its potential importance in this series of elaborate humoral-cellular interactions are discussed in the subsequent sections.

      ET in the Pathogenesis of Atherosclerosis

      Background on ET

      ET is a potent vasoconstrictor that was first described by Yanagisawa and colleagues in 1988.
      • Yanagisawa M
      • Kurihara H
      • Kimura S
      • Tomobe Y
      • Kobayashi M
      • Mitsui Y
      • et al.
      A novel potent vasoconstrictor peptide produced by vascular endothelial cells.
      ET is primarily secreted by endothelial cells. A prepropeptide is cleaved to form “big” ET (39 amino acids) and then further cleaved by an ET-converting enzyme to form the 21-amino acid active peptide. The three structurally and pharmacologically distinct isopeptides-ET −1, ET−2, and ET−3-are each encoded by a different gene.
      • Lerman A
      • Hildebrand Jr, FL
      • Margulies KB
      • O'Murchu B
      • Perrella MA
      • Heublein DM
      • et al.
      Endothelin: a new cardiovascular regulatory peptide.
      Two distinct ET receptors exist-ET-A and ET-B. The ET-A receptor, expressed in vascular smooth muscle cells, binds ET−1, biologically active form of and is believed to mediate the profound vasoconstrictive effect associated with ET−1 through increases in intracellular calcium.
      • Luscher TF
      • Oemar BS
      • Boulanger CM
      • Hahn AWA
      Molecular and cellular biology of endothelin and its receptors. Part I. Part II.
      A specific competitive antagonist of the ET-A receptor has been shown to cause arterial vasodilatation, a finding that demonstrates that ET exerts an effect on basal arterial vasomotor tone.
      • Haynes WG
      • Webb DJ
      Contribution of endogenous generation of endothelin-l to basal vascular tone.
      The ET-B receptor, expressed on endothelial cells and smooth muscle cells, has been reported to be associated with a dual vasodilating
      • Hirata Y
      • Emori T
      • Eguchi S
      • Kanno K
      • Imai T
      • Ohta K
      • et al.
      Endothelin receptor subtype B mediates synthesis of nitric oxide by cultured bovine endothelial cells.
      and vasoconstrictive
      • Seo B
      • Oemar BS
      • Siebenmann R
      • von Segesser L
      • Luscher TF
      Both ETA and ETB receptors mediate contraction to endothelin-l in human blood vessels.
      • Rigel DF
      • Lappe RW
      Differential responsiveness of conduit and resistance coronary arteries to endothelin A and B receptor stimulation in anesthetized dogs.
      response.

      Cellular Activity of ET in the Pathophysiology of Atherosclerosis

      ET is released in response to vascular injury (Fig. 1), is a strong chemoattractant for circulating monocytes, and activates macrophages.
      • Haller H
      • Schaberg T
      • Lindschau C
      • Lode H
      • Distler A
      Endothelin increases [Ca], protein phosphorylation, and 0; production in human alveolar macrophages.
      Macrophages, in tum, can then cause further injury to the overlying endothelium and also produce platelet-derived growth factor (PDGF), interleukin 1, and tumor necrosis factor-α, which can result in secondary up-regulation of PDGF production by smooth muscle cells and endothelium.
      • Ross R
      The pathogenesis of atherosclerosis: a perspective for the 1990s.
      Oxidized low-density lipoprotein (LDL), one of the major participants in the atherogenic process, is a strong stimulus for ET production and secretion.
      • Boulanger CM
      • Tanner FC
      • Bea ML
      • Hahn AW
      • Werner A
      • Luscher TF
      Oxidized low density lipoproteins induce mRNA expression and release of endothelin from human and porcine endothelium.
      Figure thumbnail gr1
      Fig. 1Proposed model of role of endothelin (ET) in the atherogenic process. Top, Stage I: role of ET in early stage of coronary atherosclerosis. Coronary artery disease risk factors, especially oxidized lowdensity lipoprotein (Ox-LDL), lead to endothelial injury and release of ET. Release of ET into lumen mediates activation of circulating monocytes and macrophages. Accumulation of platelets also promotes further ET release. Release of ET into vascular wall mediates smooth muscle cell proliferation and vasoconstriction. ET also opposes activity of endothelium-derived relaxing factor (EDRF). IEL = internal elastic lamina; IL-1 = interleukin-1; PLT = platelets; SMC = smooth muscle cell. Bottom, Stage II: role of ET in progression of coronary atherosclerosis. ET interacts with other cytokines and growth factors to stimulate smooth muscle cell proliferation. ET induces chemotaxis and replication of fibroblasts and also activates fibroblasts to secrete collagen matrix.
      Smooth muscle cells are the predominant cell type in fibrous plaques, migrating to the intima and proliferating in response to cytokines released after endothelial injury.
      • Ross R
      The pathogenesis of atherosclerosis: a perspective for the 1990s.
      At least two phenotypes of smooth muscle cells have been found. In the contractile phenotype, cells respond to vasomodulating agents such as ET,
      • Lerman A
      • Hildebrand Jr, FL
      • Margulies KB
      • O'Murchu B
      • Perrella MA
      • Heublein DM
      • et al.
      Endothelin: a new cardiovascular regulatory peptide.
      nitric oxide,

      Moncada S, Higgs EA, editors. Nitric oxide from L-arginine: a bioregulatory system. Excerpta Medica International Congress Series No. 897,1990

      and angiotensin H,
      • Weber H
      • Webb ML
      • Serafino R
      • Taylor DS
      • Moreland S
      • Norman J
      • et al.
      Endothelin-I and angiotensin-II stimulate delayed mitogenesis in cultured rat aortic smooth muscle cells: evidence for common signaling mechanisms.
      whereas in the synthetic phenotype, they express several regulatory molecules,
      • Sjolund M
      • Hedin D
      • Sejersen T
      • Heldin CH
      • Thyberg J
      Arterial smooth muscle cells express platelet-derived growth factor (PDGF) A chain mRNA, secrete a PDGF-like mitogen, and bind exogenous PDGF in a phenotype- and growth state-dependent manner.
      respond to growth factors by expressing appropriate receptors, and synthesize extracellular matrix. Evidence suggests that, in the development of atherosclerosis, the contractile phenotype transforms into the synthetic phenotype,
      • Sjolund M
      • Hedin D
      • Sejersen T
      • Heldin CH
      • Thyberg J
      Arterial smooth muscle cells express platelet-derived growth factor (PDGF) A chain mRNA, secrete a PDGF-like mitogen, and bind exogenous PDGF in a phenotype- and growth state-dependent manner.
      a phenomenon suggesting that the vasomotor influences in early atherosclerosis are later replaced by a predominantly cellular and fibroproliferative phase. An abundance of in vitro and in vivo data have demonstrated the mitogenic effect of ET on smooth muscle cells.
      • Weissberg PL
      • Witchell C
      • Davenport AP
      • Hesketh TR
      • Metcalfe Je
      The endothelin peptides ET-l, ET-2, ET-3 and sarafotoxin S6b are co-mitogenic with platelet-derived growth factor for vascular smooth muscle cells.
      • Resink TJ
      • Hahn AW
      • Scott-Burden T
      • Powell J
      • Weber E
      • Buhler FR
      Inducible endothelin mRNA expression and pep-tide secretion in cultured human vascular smooth muscle cells.
      ET has been shown to stimulate vascular smooth muscle hypertrophy and hyperplasia in cell culture systems,
      • Alberts GF
      • Peifley KA
      • Johns A
      • Kleha JF
      • Winkles JA
      Constitutive endothelin-l overexpression promotes smooth muscle cell proliferation via an external autocrine loop.
      and smooth muscle cells may also produce and secrete ET.
      • Resink TJ
      • Hahn AW
      • Scott-Burden T
      • Powell J
      • Weber E
      • Buhler FR
      Inducible endothelin mRNA expression and pep-tide secretion in cultured human vascular smooth muscle cells.
      Moreover, constitutive ET−1 overexpression can promote smooth muscle cell proliferation,
      • Alberts GF
      • Peifley KA
      • Johns A
      • Kleha JF
      • Winkles JA
      Constitutive endothelin-l overexpression promotes smooth muscle cell proliferation via an external autocrine loop.
      and exogenous short-term and long-term administration of ET-1 augments neointima formation in vivo.
      • Douglas SA
      • Louden C
      • Vickery-Clark LM
      • Storer BL
      • Hart T
      • Feuerstein GZ
      • et al.
      A role for endogenous endothelin-l in neointimal formation after rat carotid artery balloon angio-plasty: protective effects of the novel nonpeptide endothelin receptor antagonist SB 209670.
      • Douglas SA
      • Ohlstein EH
      Endothelin-1 promotes neointima formation after balloon angioplasty in the rat.
      Recent studies have suggested that ET exerts its mitogenic effect, in large part, through protein kinase C activation.
      • Lonchampt MO
      • Pinelis S
      • Goulin J
      • Chabrier PE
      • Braquet P
      Proliferation and Na+/H+ exchange activation by endothelin in vascular smooth muscle cells.
      Furthermore, in vitro studies in early-passaged, cultured aortic smooth muscle cells have shown that ET-inducedsmooth muscle cell mitogenesis and proliferation are mediated through the ET-A, but not the ET-B, receptor subtype
      • Douglas SA
      • Louden C
      • Vickery-Clark LM
      • Storer BL
      • Hart T
      • Feuerstein GZ
      • et al.
      A role for endogenous endothelin-l in neointimal formation after rat carotid artery balloon angio-plasty: protective effects of the novel nonpeptide endothelin receptor antagonist SB 209670.
      and that the mitogenic activity of ET correlates with ET-A receptor binding and density.
      • Kanse SM
      • Wijelath E
      • Kanthou C
      • Newman P
      • Kakkar VV
      The proliferative responsiveness of human vascular smooth muscle cells to endothelin correlates with endothelin receptor density.
      These results are underscored by a recent report that selective blockade of the ET-A receptor subtype decreases early atherosclerosis in hypercholesterolemic hamsters.
      • Kowala MC
      • Rose PM
      • Stein PD
      • Goller N
      • Reece R
      • Beyer S
      • et al.
      Selective blockade of the endothelin subtype A receptor decreases early atherosclerosis in hamsters fed cholesterol.
      This mitogenic response seems to be subject to phenotypic modulation; however, investigators have also demonstrated that, in repeated passaging of smooth muscle cells into the synthetic phenotype, ET-B receptor expression is increased to the extent that selective ET-A antagonism no longer inhibits the mitogenic action of ET−1.
      • Serradeil-Le Gal C
      • Herbert JM
      • Garcia C
      • Boutin M
      • Maffrand IP
      Importance of the phenotypic state of vascular smooth muscle cells on the binding and the mitogenic activity of endothelin.
      Further definition of the factors modulating this phenotypic change would be important relative to potential therapeutic implications of ET receptor antagonists. In addition, ET acts in concert with other mitogenic factors such as PDGF to induce proliferation of smooth muscle cells.
      • Weissberg PL
      • Witchell C
      • Davenport AP
      • Hesketh TR
      • Metcalfe Je
      The endothelin peptides ET-l, ET-2, ET-3 and sarafotoxin S6b are co-mitogenic with platelet-derived growth factor for vascular smooth muscle cells.
      • Senior RM
      • Huang JS
      • Griffin GL
      • Deuel TF
      Dissociation of the chemotactic and mitogenic activities of platelet-derived growth factor by human neutrophil elastase.
      During the progression of the atherosclerotic lesion (Fig. 1), fibroblasts and the formation of extracellular matrix have a substantial role. ET has been shown in vitro to induce chemotaxis and replication of fibroblasts;
      • Peacock AJ
      • Dawes KE
      • Shock A
      • Gray AJ
      • Reeves JT
      • Laurent GJ
      Endothelin-l and endothelin-3 induce chemo-taxis and replication of pulmonary artery fibroblasts.
      this effect has been demonstrated to be mediated through the ET -A receptor subtype.
      • Kikuchi K
      • Kadono T
      • Sato S
      • Tamaki K
      • Takehara K
      Impaired growth response to endothelin-1 in scleroderma fibro-blasts.
      The proliferative effect of ET has been shown to be synergistic with the effect of insulinlike growth factor in human placental cells
      • Fant ME
      • Nanu L
      • Word RA
      A potential role for endothelin-1 in human placental growth: interactions with the insulin-like growth factor family of peptides.
      and synergistic with transforming growth factor and epidermal growth factor in mouse fibroblasts.
      • Yeh YC
      • Bums ER
      • Yeh J
      • Yeh HW
      Synergistic effects of endothelin-1 (ET-1) and transforming growth factor alpha (TGF-alpha) or epidermal growth factor (EGF) on DNA replication and Gl to S phase transition.
      ET has also been shown to promote the production and contraction of collagen fibro blasts.
      • Guidry C
      • Hook M
      Endothelins produced by endothelial cells promote collagen gel contraction by fibroblasts.
      ET has been shown to promote microvascular platelet thrombus formation
      • Halim A
      • Kanayama N
      • el Maradny E
      • Maehara K
      • Terao T
      Coagulation in vivo microcirculation and in vitro caused by endothelin-1.
      and therefore may contribute to acute coronary syndromes in this manner. Of interest, however, the ET-B receptor subtype has been demonstrated to have an antiaggregatory effect on platelets,
      • Leadley Jr, RJ
      • Lee P
      • Erickson LA
      • Shebuski RJ
      The snake venom peptide sarafotoxin S6b inhibits repetitive platelet thrombus formation in the stenosed canine coronary artery.
      • McMurdo L
      • Lidbury PS
      • Thiemermann C
      • Vane JR
      Mediation of endothelin-l-induced inhibition of platelet aggregation via the ETB receptor.
      suggesting that the prothrombotic effects of ET on platelets are ET-A mediated. This evidence implies that ET has an important role in the initiation and progression of cellular pathways leading to atherogenesis. In addition, the potent coronary vasoconstrictive properties of ET
      • Cannan CR
      • Burnett Jr, JC
      • Brandt RR
      • Lerman A
      Endothelin at pathophysiological concentrations mediates coronary vasoconstriction via the endothelin-A receptor.
      may potentiate the atherosclerotic process by reducing blood flow and subsequently enhancing platelet aggregation and thrombus formation.

      Production and Activity of ET in the Atherogenic Process and Interaction With Clinical Risk Factors

      Several atherogenic risk factors have been found to be associated with ET activity. Conventional modifiable risk factors for atherosclerotic vascular disease include hyperlipidemia, smoking, hypertension, and diabetes. Investigators have demonstrated that ET production and secretion are enhanced in the presence of oxidized LDL, specifically in cultured endothelial cells, intact blood vessels, and macrophages.
      • Boulanger CM
      • Tanner FC
      • Bea ML
      • Hahn AW
      • Werner A
      • Luscher TF
      Oxidized low density lipoproteins induce mRNA expression and release of endothelin from human and porcine endothelium.
      • Martin-Nizard F
      • Houssaini HS
      • Lestavel-Delattre S
      • Duriez P
      • Fruchart Je
      Modified low density lipoproteins activate human macrophages to secrete immunoreactive endothelin.
      Oxidized LDL has also been shown to increase superoxide production by human alveolar macrophages.
      • Haller H
      • Schaberg T
      • Lindschau C
      • Lode H
      • Distler A
      Endothelin increases [Ca], protein phosphorylation, and 0; production in human alveolar macrophages.
      Uptake of oxidized LDL by the macrophages results in formation of foam cells and may alter expression of various regulatory hormones.
      Enhanced plasma levels and tissue ET immunoreactivity have been demonstrated in the early stage of coronary atherosclerosis in experimental models and in humans. ET-l has been shown to be increased in hypercholesterolemic rats before the onset of morphologic changes in the vasculature.
      • Horio T
      • Kohno M
      • Murakawa K
      • Yasunari K
      • Yokokawa K
      • Ueda M
      • et al.
      Increased plasma immunoreactive endothelin-1 concentration in hypercholesterolemic rats.
      A high cholesterol diet in pigs resulted in coronary endothelial dysfunction, an increase in circulating ET concentrations, and enhanced coronary artery ET tissue immunoreactivity (Fig. 2); moreover, the administration of intracoronary acetylcholine resulted in a further increase in plasma ET concentrations that correlated with the degree of coronary vasoconstriction.
      • Lerman A
      • Webster MW
      • Chesebro JH
      • Edwards WD
      • Wei CM
      • Fuster V
      • et al.
      Circulating and tissue endothelin immu-noreactivity in hypercholesterolemic pigs.
      Patients with increased total serum cholesterol and Lp(a) lipoprotein levels have been shown to have elevated circulating levels of ET.
      • Haak T
      • Marz W
      • Jungmann E
      • Hausser S
      • Siekmeier R
      • Gross W
      • et al.
      Elevated endothelin levels in patients with hyperlipoproteinemia.
      Circulating levels and tissue ET immunoreactivity are enhanced in advanced atherosclerosis in humans and correlate with the severity of disease.
      • Lerman A
      • Edwards BS
      • Hallett JW
      • Heublein DM
      • Sandberg SM
      • Burnett Jr, JC
      Circulating and tissue endothelin immu-noreactivity in advanced atherosclerosis.
      ET has been shown to be increased in association with cigarette smoking,
      • Haak T
      • Jungmann E
      • Raab C
      • Usadel KH
      Elevated endothelin-1 levels after cigarette smoking.
      and enhanced vasoconstriction in response to low-dose exogenously administered ET has been demonstrated in smokers.
      • Kiowski W
      • Linder L
      • Stoschitzky K
      • Pfisterer M
      • Burckhardt D
      • Burkart F
      • et al.
      Diminished vascular response to inhibition of endothelium-derived nitric oxide and enhanced vaso-constriction to exogenously administered endothelin-l in clinically healthy smokers.
      In contrast, the role of ET in essential hypertension is still controversial and may be related to the degree of vascular disease associated with hypertension.
      • Schiffrin EL
      Endothelin in hypertension.
      Figure thumbnail gr2
      Fig. 2Left, Photomicrograph showing distribution of endothelin immunoreactivity in 6-µm sections of left anterior descending coronary artery from hypercholesterolemic pig. Immunoreactivity can be seen in endothelial cells and in subendothelial myointimal cells. (Original magnification, ×400.) Right, Sections of left anterior descending coronary artery from pig receiving normal diet show absence of immunoreactivity. (Original magnification, ×200.) No immunoreactivity was detected in sections treated with nonimmune rabbit serum (not shown).
      (From Lerman and associates.
      • Lerman A
      • Webster MW
      • Chesebro JH
      • Edwards WD
      • Wei CM
      • Fuster V
      • et al.
      Circulating and tissue endothelin immu-noreactivity in hypercholesterolemic pigs.
      By permission.)

      Clinical and Pathophysiologic Implications of ET in the Evolution of Atherosclerosis

      ET may have a pivotal role in the clinical stages of coronary atherosclerosis, from the early stage of coronary endothelial dysfunction that progresses to myocardial ischemia, acute myocardial infarction, heart failure, and cardiac transplantation (Fig. 3).
      Figure thumbnail gr3
      Fig. 3Clinical stages of coronary atherosclerosis. Endothelin activity is enhanced in various stages of coronary atherosclerosis. Endothelin may have a pivotal role in clinical stages of coronary atherosclerosis, from early stage of coronary endothelial dysfunction that progresses to myocardial ischemia, acute myocardial infarction, heart failure, and cardiac transplantation.

      ET in Early Atherosclerosis

      ET may have a role as a marker or as a participant in early coronary atherosclerosis. The endothelium functions as the principal modulator of vascular tone by producing and releasing vasoactive substances such as endothelium-derived relaxing factor (EDRF) with its vasodilating and antiproliferative properties, as well as ET with its vasoconstrictive and mitogenic properties. Thus, maintenance of coronary vasomotor tone implies a balance between these factors. Imbalances between these factors have been implicated in cardiovascular disease states such as hypercholesterolemia, atherosclerosis, hypertension, and congestive heart failure.
      • Lerman A
      • Burnett Jr, JC
      Intact and altered endothelium in regulation of vasomotion.
      Such imbalance may stem from a relative lack of EDRF activity, excess of ET, or both. Regardless, the observed net effect has been a relative increase in coronary vasomotor tone and a relative decrease in coronary blood flow.
      Endothelial injury is the stimulus that triggers atherogenesis based on the response to injury hypothesis.' A precise definition of endothelial injury is difficult because changes in integrity of the endothelial lining may not be manifest morphologically. Endothelial dysfunction has been demonstrated in disease states such as hypercholesterol emia,
      • Flavahan NA
      Atherosclerosis or lipoprotein-induced endo-thelial dysfunction: potential mechanisms underlying reduction in EDRF/nitric oxide activity.
      • Zeiher AM
      • Drexler H
      • Saurbier B
      • Just H
      Endothelium-mediated coronary blood flow modulation in humans: effects of age, atherosclerosis, hypercholesterolemia, and hypertension.
      atherosclerosis, heart failure, and hypertension,
      • Zeiher AM
      • Drexler H
      • Saurbier B
      • Just H
      Endothelium-mediated coronary blood flow modulation in humans: effects of age, atherosclerosis, hypercholesterolemia, and hypertension.
      which are also characterized by increased plasma ET concentrations. The assessment of endothelial function in the human coronary vascular bed with use of acetylcholine has been previously described.
      • Zeiher AM
      • Drexler H
      • Saurbier B
      • Just H
      Endothelium-mediated coronary blood flow modulation in humans: effects of age, atherosclerosis, hypercholesterolemia, and hypertension.
      • Cannan CR
      • McGoon M
      • Holmes Jr, DR
      • Lerman A
      Altered coronary endothelial function in a patient with asymptomatic left ventricular dysfunction.
      Patients with endothelial dysfunction who do not have significant angiographically detectable atherosclerosis are characterized by a decrease in coronary blood flow in response to the endothelial-dependent vasodilator acetylcholine.
      • Zeiher AM
      • Drexler H
      • Saurbier B
      • Just H
      Endothelium-mediated coronary blood flow modulation in humans: effects of age, atherosclerosis, hypercholesterolemia, and hypertension.
      • Cannan CR
      • McGoon M
      • Holmes Jr, DR
      • Lerman A
      Altered coronary endothelial function in a patient with asymptomatic left ventricular dysfunction.
      In a recent study, Lerman and coworkers
      • Lerman A
      • Holmes Jr, DR
      • Bell MR
      • Garratt KN
      • Nishimura RA
      • Burnett Jr, JC
      Endothelin in coronary endothelial dysfunction and early atherosclerosis in humans.
      demonstrated that ET immunoreactivity is enhanced in the coronary and systemic circulation in humans with coronary endothelial dysfunction; moreover, acetylcholine further increased coronary ET concentrations in patients with coronary endothelial dysfunction and was associated with coronary vasoconstriction.

      ET in Unstable Angina and Acute Myocardial lnfarction

      Although myocardial ischemia may occur in the setting of type I injury, most patients with acute coronary syndromes have type II and type III lesions. In patients with stable and unstable angina, circulating ET levels have been shown to be increased in clinical studies.
      • Yasuda M
      • Kohno M
      • Tahara A
      • Itagane H
      • Toda I
      • Akioka K
      • et al.
      Circulating immunoreactive endothelin in ischemic heart disease.
      • Ray SG
      • McMurray LL
      • Morton LL
      • Dargie HI
      Circulating endothelin in acute ischaemic syndromes.
      Of interest, Zeiher and associates
      • Zeiher AM
      • Goebel H
      • Schachinger V
      • Ihling C
      Tissue endothelin-l immunoreactivity in the active coronary atherosclerotic plaque: a clue to the mechanism of increased vasoreactivity of the culprit lesion in unstable angina.
      demonstrated that ET−1 immunoreactivity was detected in atherectomy specimens from 86% of the patients in their series and that the degree of immunostaining was significantly higher in patients with unstable angina in comparison with those with stable angina. Toyooka and colleagues
      • Toyo-oka T
      • Aizawa T
      • Suzuki N
      • Hirata Y
      • Miyauchi T
      • Shin WS
      • et al.
      Increased plasma level of endothelin-l and coronaryspasm induction in patients with vasospastic angina pectoris.
      reported increased venous and coronary sinus levels of ET in patients with variant angina and coronary vasospasm. These findings offer a potential explanation for the recently described increase in coronary vasoreactivity associated with the culprit lesion in acute coronary syndromes.
      • Bogaty P
      • Hackett D
      • Davies G
      • Maseri A
      Vasoreactivity of the culprit lesion in unstable angina.
      ET levels have consistently been shown to be increased in the setting of acute myocardial infarction, especially when the clinical course was complicated by congestive heart failure.
      • Miyauchi T
      • Yanagisawa M
      • Tomizawa T
      • Sugishita Y
      • Suzuki N
      • Fujino M
      • et al.
      Increased plasma concentrations of endothelin-I and big endothelin-I in acute myocardial infarction [letter].
      • Nakamura M
      • Arakawa N
      • Yoshida H
      • Funakoshi T
      • Chiba M
      • Abe Y
      • et al.
      Increased plasma endothelin concentrations in patients with acute heart failure after myocardial infarction.
      The l-year mortality rate of patients with myocardial infarction strongly correlates with the concentration of plasma ET-1 measured 3 days after infarction.
      • Omland T
      • Lie RT
      • Aakvaag A
      • Aarsland T
      • Dickstein K
      Plasma endothelin determination as a prognostic indicator of I-year mortality after acute myocardial infarction.
      In experimental models of acute infarction created by ligation of a coronary artery in rats and dogs, infarct size was reduced 40 to 45% by infusion of ET antibodies
      • Watanabe T
      • Suzuki N
      • Shimamoto N
      • Fujino M
      • Imada A
      Contribution of endogenous endothelin to the extension of myocardial infarct size in rats.
      and a receptor antagonist before ligation.
      • Grover GJ
      • Dzwonczyk S
      • Parham CS
      The endothelin-I receptor antagonist BQ-123 reduces infarct size in a canine model of coronary occlusion and reperfusion.
      In addition, animal models of experimentally induced myocardial ischemia have shown that ET-1 release is greatly enhanced during reperfusion,
      • Grover GJ
      • Dzwonczyk S
      • Parham CS
      The endothelin-I receptor antagonist BQ-123 reduces infarct size in a canine model of coronary occlusion and reperfusion.
      a finding suggesting that ET-1 may have a role in reperfusion injury. Although Velasco and coworkers
      • Velasco CE
      • Turner M
      • Inagami T
      • Atkinson JB
      • Virmani R
      • Jackson EK
      • et al.
      Reperfusion enhances the local release of endothelin after regional myocardial ischemia.
      demonstrated that myocardial tissue levels of ET-1 and messenger RNA for ET-l are increased in the ischemic zone concomitantly with increased levels of ET-1 in the coronary sinus and aorta, increased myocardial production and release of ET may not completely account for the increased plasma levels, and other organs such as the kidney may also be involved.
      • Margulies KB
      • Hildebrand Jr, FL
      • Lerman A
      • Perrella MA
      • Burnett Jr, JC
      Increased endothelin in experimental heart failure.
      The mechanism for increased ET immunoreactivity in acute myocardial syndromes may be multifactorial. Vascular injury, reduced EDRF activity, ischemia, and decreased shear stress all stimulate ET release,
      • Kourembanas S
      • Marsden PA
      • McQuillan LP
      • Faller DV
      Hypoxia induces endothelin gene expression and secretion in cultured human endothelium.
      • Yoshizumi M
      • Kurihara H
      • Sugiyama T
      • Takaku F
      • Yanagisawa M
      • Masaki T
      • et al.
      Hemodynamic shear stress stimulates endothelin production by cultured endothelial cells.
      • Pearson PJ
      • Lin PJ
      • Schaff HV
      Global myocardial ischemia and reperfusion impair endothelium -dependent relaxations to aggregating platelets in the canine coronary artery: a possible cause of vasospasm following cardiopulmonary bypass.
      which, in tum, results in vasoconstriction that leads to vasospasm and continuing ischemia with extension of myocardial infarct size. Thrombin, which plays a seminal role in acute myocardial syndromes including unstable angina, is a strong stimulus for ET release.
      • Lerman A
      • Mruk JS
      • Webster MWI
      • Burnett Jr, JC
      • Chesebro JH
      Activation of endothelin during arterial thrombosis and ENDOTHELINAND CORONARY ATHEROSCLEROSIS 777 thrombolysis [abstract].
      The role of thrombin is further supported by the observation that thrombin-stimulated release of ET is inhibited by inactivation of thrombin with hirudin, a specific thrombin inhibitor.
      • Boulanger CM
      • Luscher TF
      Hirudin and nitrates inhibit the thrombin-induced release of endothelin from the intact porcine aorta.
      These studies also underscore the hypothesis that circulating levels of ET may not be representative of the enhanced local circulating levels and tissue E'I immunoreactivity in acute myocardial syndromes due to the fact that most ET secretion is abluminal. The increased circulating ET concentrations may represent generalized activation or hemodynamic compensation and may reflect poor prognosis.

      ET in PTCA and Restenosis

      PTCA was developed during the late 1970s;
      • Gruntzig AR
      • Senning A
      • Siegenthaler WE
      Nonoperative dilatation of coronary-artery stenosis: percutaneous transluminal coronary angioplasty.
      the major factor limiting the success of this procedure is the high incidence of neointima formation, resulting in clinically apparent restenosis. Multiple vasoactive peptides and growth factors are thought to be involved in the restenotic process. Recent studies have implicated ET as a component in what is probably a multifactorial cascade of vascular reactivity and neointimal growth after balloon angioplasty. Tahara and associates
      • Tahara A
      • Kohno M
      • Yanagi S
      • Itagane H
      • Toda I
      • Akioka K
      • et al.
      Circulating immunoreactive endothelin in patients undergoing percutaneous transluminal coronary angioplasty.
      demonstrated that circulating immunoreactive ET was significantly increased in the coronary sinus of patients undergoing PTCA; femoral arterial levels also tended to be increased but were not statistically significant. This finding was further proved by Lerman and colleagues
      • Lerman A
      • Holmes Jr, DR
      • Garratt KN
      • Reeder GS
      • Bell MR
      • Burnett Jr, JC
      Local release of endothelin in human coronary arteries in response to balloon angioplasty [abstract].
      who demonstrated a significant increase in intracoronary ET levels measured distal to the dilated stenosis in patients undergoing PTCA; the increase also correlated to the degree of mechanical stress (pressure of inflation multiplied by the duration of inflation). Furthermore, the immediate detectable increase in ET levels in both studies supports the recent discovery that ET is stored in secretory vesicles within endothelial cells and is available for rapid release in high concentrations into the vasculature; this finding is in contrast to the previously held notion that ET release is a strictly constitutive process occurring at an essentially constant rate regulated mainly at the level of protein synthesis.
      • Harrison VJ
      • Bames K
      • Turner AJ
      • Wood E
      • Corder R
      • Vane JR
      Identification of endothelin I and big endothelin I in secretory vesicles isolated from bovine aortic endothelial cells.
      To date, an effective pharmacologic intervention to minimize restenosis does not exist; however, therole of ET in this process is being studied. Investigators have shown that longterm administration of the nonpeptide ET-A/ET-B receptor antagonist SB 209670 ameliorates the neointima formation observed in the rat carotid artery balloon angioplasty model.
      • Douglas SA
      • Louden C
      • Vickery-Clark LM
      • Storer BL
      • Hart T
      • Feuerstein GZ
      • et al.
      A role for endogenous endothelin-l in neointimal formation after rat carotid artery balloon angio-plasty: protective effects of the novel nonpeptide endothelin receptor antagonist SB 209670.
      In addition, the selective ET -A receptor antagonist BQ-123 was found to be ineffective in this role, an outcome that implicates the ET-B receptor subtype in the pathogenesis of neointima formation.
      • Douglas SA
      • Vickery-Clark LM
      • Louden C
      • Ohlstein EH
      Selective ETA receptor antagonism with BQ-123 is insufficient to inhibit angioplasry induced neointima formation in the rat.
      Furthermore, investigators have shown that ET-B receptor density receptor density doubles in the intima of hyperplastic carotid arteries of rabbits 4 weeks after angioplasty.
      • Azuma H
      • Hamasaki H
      • Niimi Y
      Endothelin-l (ET- l ) plays a role in the intimal hyperplasia after endothelial removal [abstract].
      This occurrence also expresses the increased relative importance of the ET-B receptor subtype in the synthetic phenotype of smooth muscle cells that comprise the fibroproliferative stages of atherosclerosis, particularly restenosis. This may have ramifications for the development of selective antagonists to ET receptor subtypes for the prevention and treatment of restenosis.

      ET in Congestive Heart Failure

      In patients with acute coronary syndromes in whom timely reperfusion is not achieved, left ventricular dysfunction occurs as a result of a loss of functioning myocardium; large infarctions or repeated ischemic syndromes may ultimately result in clinical heart failure. The role of ET in heart failure has been extensively discussed previously
      • Clavell A
      • Stingo A
      • Margulies K
      • Lerman A
      • Underwood D
      • Burnett Jr, JC
      Physiological significance of endothelin: its role in congestive heart failure.
      it is mentioned herein briefly because of the interaction of ET, ischemic syndromes, and left ventricular dysfunction.
      Plasma ET levels have been shown to be increased up to fourfold in patients with moderate to severe congestive heart failure; the level seems to correlate with the severity of the symptoms regardless of the cause of left ventricular dysfunction.
      • Wei CM
      • Lerman A
      • Rodeheffer RJ
      • McGregor CGA
      • Brandt RR
      • Wright S
      • et al.
      Endothelin in human congestive heart failure.
      • Rodeheffer RJ
      • Lerman A
      • Heublein DM
      • Burnett Jr, JC
      Increased plasma concentrations of endothelin in congestive heart failure in humans.
      In patients with severe heart failure, ET receptor blockade results in a decrease in mean arterial pressure, mean pulmonary pressure, and pulmonary capillary wedge pressure and a significant increase in cardiac index.
      • Kiowski W
      • Sutsch G
      • Hunziker P
      • Muller P
      • Kim J
      • Oechslin E
      • et al.
      Evidence for endothelin-I-mediated vasoconstriction in severe chronic heart failure.
      These findings indicate that ET contributes to the maintenance of vascular tone in such patients, and thus ET antagonism may prove beneficial and have implications in the development of future therapeutic options.

      ET in Cardiac Transplantation

      Intractable heart failure can be treated effectively in selected patients by using orthotopic cardiac transplantation. Increased ET levels and endothelial dysfunction have been well documented in patients who have undergone orthotopic cardiac transplantation.
      • Lerman A
      • Kubo SH
      • Tschumperlin LK
      • Burnett Jr, JC
      Plasma endothelin concentration s in humans with end-stage heart failure and after cardiac transplantation.
      • Berkenboom G
      • Giot C
      • Unger P
      • Vachiery JL
      • Antoine M
      • LeClerc JL
      Plasma endothelin and early coronary endothelial dysfunction in recipients of a cardiac transplant.
      Furthermore, it is widely accepted that atherogenesis after transplantation is accelerated, perhaps as a result of the immunosuppressive regimens required. It is interesting to postulate that increased levels of ET with resultant endothelial dysfunction may have a pivotal role in the acceleration of the atherosclerotic process in these patients and that ET receptor antagonism may retard this process. The issue of smooth muscle cell proliferation may also be important; conceivably, the rapid acceleration of atherosclerosis in these patients may parallel the cellular changes noted in restenosis after PTCA and may affect the treatment of transplant-related vasculopathy if similar mechanisms can be demonstrated.

      Conclusion

      The morphologic changes of the vasculature associated with atherosclerosis have been well defined previously. The conventional understanding of atherogenesis revolves around the interaction of various cell types, cytokines, and growth factors, which are stimulated to act in response to endothelial injury. To date, review of studies suggests that ET is an important peptide in the atherogenic process. ET affects cell chemotaxis and proliferation and interacts with other cytokines and growth factors to potentiate the atherogenic process. Its production and activity seem to be enhanced by known atherosclerotic risk factors, and circulating levels and tissue immunoreactivity of ET have been shown to be increased in vitro and in vivo in experimental models of atherosclerosis and in patients with advanced atherosclerosis. Of note, evidence at this point is insufficient to state that ET is primarily responsible for the pathogenesis of atherosclero sis, but sufficient evidence exits to conclude that ET is involved as a mediator or cofactor in this process. Future basic science and clinical work in this area will likely center around the ET receptorsubtypes, particularly the ET-B subtype, and further define their relative roles during the atherogenic process, as well as the role of selective ET receptor antagonists in preventing and treating the consequences of coronary atherosclerosis and myocardial ischemic syndromes.

      References

        • Fuster V
        • Badimon L
        • Badimon JJ
        • Chesebro JH
        The patho-genesis of coronary artery disease and the acute coronary syndromes (first of two parts).
        N Engl J Med. 1992; 326: 242-250
        • Ip JH
        • Fuster V
        • Badimon L
        • Badimon J
        • Taubman MB
        • Chesebro JH
        Syndromes of accelerated atherosclerosis: role of vascular injury and smooth muscle cell proliferation.
        JAm Coil Cardiol. 1990; 15: 1667-1687
        • Ross R
        The pathogenesis of atherosclerosis: a perspective for the 1990s.
        Nature. 1993; 362: 801-809
        • Yanagisawa M
        • Kurihara H
        • Kimura S
        • Tomobe Y
        • Kobayashi M
        • Mitsui Y
        • et al.
        A novel potent vasoconstrictor peptide produced by vascular endothelial cells.
        Nature. 1988; 332: 411-415
        • Lerman A
        • Hildebrand Jr, FL
        • Margulies KB
        • O'Murchu B
        • Perrella MA
        • Heublein DM
        • et al.
        Endothelin: a new cardiovascular regulatory peptide.
        Mayo Clin Proc. 1990; 65: 1441-1455
        • Luscher TF
        • Oemar BS
        • Boulanger CM
        • Hahn AWA
        Molecular and cellular biology of endothelin and its receptors. Part I. Part II.
        J Hypertens. 1993; 11 (121–126): 7-11
        • Haynes WG
        • Webb DJ
        Contribution of endogenous generation of endothelin-l to basal vascular tone.
        Lancet. 1994; 344: 852-854
        • Hirata Y
        • Emori T
        • Eguchi S
        • Kanno K
        • Imai T
        • Ohta K
        • et al.
        Endothelin receptor subtype B mediates synthesis of nitric oxide by cultured bovine endothelial cells.
        J Clin Invest. 1993; 91: 1367-1373
        • Seo B
        • Oemar BS
        • Siebenmann R
        • von Segesser L
        • Luscher TF
        Both ETA and ETB receptors mediate contraction to endothelin-l in human blood vessels.
        Circulation. 1994; 89: 1203-1208
        • Rigel DF
        • Lappe RW
        Differential responsiveness of conduit and resistance coronary arteries to endothelin A and B receptor stimulation in anesthetized dogs.
        J Cardiovasc Pharmacol. 1993; 22: S243-S247
        • Haller H
        • Schaberg T
        • Lindschau C
        • Lode H
        • Distler A
        Endothelin increases [Ca], protein phosphorylation, and 0; production in human alveolar macrophages.
        Am J Physiol. 1991; 261: L478-L484
        • Boulanger CM
        • Tanner FC
        • Bea ML
        • Hahn AW
        • Werner A
        • Luscher TF
        Oxidized low density lipoproteins induce mRNA expression and release of endothelin from human and porcine endothelium.
        Circ Res. 1992; 70: 1191-1197
      1. Moncada S, Higgs EA, editors. Nitric oxide from L-arginine: a bioregulatory system. Excerpta Medica International Congress Series No. 897,1990

        • Weber H
        • Webb ML
        • Serafino R
        • Taylor DS
        • Moreland S
        • Norman J
        • et al.
        Endothelin-I and angiotensin-II stimulate delayed mitogenesis in cultured rat aortic smooth muscle cells: evidence for common signaling mechanisms.
        Mol Endocrinol. 1994; 8: 148-158
        • Sjolund M
        • Hedin D
        • Sejersen T
        • Heldin CH
        • Thyberg J
        Arterial smooth muscle cells express platelet-derived growth factor (PDGF) A chain mRNA, secrete a PDGF-like mitogen, and bind exogenous PDGF in a phenotype- and growth state-dependent manner.
        J Cell Bioi. 1988; 106: 403-413
        • Weissberg PL
        • Witchell C
        • Davenport AP
        • Hesketh TR
        • Metcalfe Je
        The endothelin peptides ET-l, ET-2, ET-3 and sarafotoxin S6b are co-mitogenic with platelet-derived growth factor for vascular smooth muscle cells.
        Atherosclerosis. 1990; 85: 257-262
        • Resink TJ
        • Hahn AW
        • Scott-Burden T
        • Powell J
        • Weber E
        • Buhler FR
        Inducible endothelin mRNA expression and pep-tide secretion in cultured human vascular smooth muscle cells.
        Biochem Biophys Res Commun. 1990; 168: 1303-1310
        • Alberts GF
        • Peifley KA
        • Johns A
        • Kleha JF
        • Winkles JA
        Constitutive endothelin-l overexpression promotes smooth muscle cell proliferation via an external autocrine loop.
        J Bioi Chern. 1994; 269: 10112-10118
        • Douglas SA
        • Louden C
        • Vickery-Clark LM
        • Storer BL
        • Hart T
        • Feuerstein GZ
        • et al.
        A role for endogenous endothelin-l in neointimal formation after rat carotid artery balloon angio-plasty: protective effects of the novel nonpeptide endothelin receptor antagonist SB 209670.
        Circ Res. 1994; 75: 190-197
        • Douglas SA
        • Ohlstein EH
        Endothelin-1 promotes neointima formation after balloon angioplasty in the rat.
        J Cardiovasc Pharmacol. 1993; 22: S371-S373
        • Lonchampt MO
        • Pinelis S
        • Goulin J
        • Chabrier PE
        • Braquet P
        Proliferation and Na+/H+ exchange activation by endothelin in vascular smooth muscle cells.
        Am I Hypertens. 1991; 4: 776-779
        • Kanse SM
        • Wijelath E
        • Kanthou C
        • Newman P
        • Kakkar VV
        The proliferative responsiveness of human vascular smooth muscle cells to endothelin correlates with endothelin receptor density.
        Lab Invest. 1995; 72: 376-382
        • Kowala MC
        • Rose PM
        • Stein PD
        • Goller N
        • Reece R
        • Beyer S
        • et al.
        Selective blockade of the endothelin subtype A receptor decreases early atherosclerosis in hamsters fed cholesterol.
        Am J Pathol. 1995; 146: 819-826
        • Serradeil-Le Gal C
        • Herbert JM
        • Garcia C
        • Boutin M
        • Maffrand IP
        Importance of the phenotypic state of vascular smooth muscle cells on the binding and the mitogenic activity of endothelin.
        Peptides. 1991; 12: 575-579
        • Senior RM
        • Huang JS
        • Griffin GL
        • Deuel TF
        Dissociation of the chemotactic and mitogenic activities of platelet-derived growth factor by human neutrophil elastase.
        J Cell Biol. 1985; 100: 351-356
        • Peacock AJ
        • Dawes KE
        • Shock A
        • Gray AJ
        • Reeves JT
        • Laurent GJ
        Endothelin-l and endothelin-3 induce chemo-taxis and replication of pulmonary artery fibroblasts.
        Am J Respir Cell Mol Bio I. 1992; 7: 492-499
        • Kikuchi K
        • Kadono T
        • Sato S
        • Tamaki K
        • Takehara K
        Impaired growth response to endothelin-1 in scleroderma fibro-blasts.
        Biochem Biophys Res Commun. 1995; 207: 829-838
        • Fant ME
        • Nanu L
        • Word RA
        A potential role for endothelin-1 in human placental growth: interactions with the insulin-like growth factor family of peptides.
        J Clin Endocrinol Metab. 1992; 74: 1158-1163
        • Yeh YC
        • Bums ER
        • Yeh J
        • Yeh HW
        Synergistic effects of endothelin-1 (ET-1) and transforming growth factor alpha (TGF-alpha) or epidermal growth factor (EGF) on DNA replication and Gl to S phase transition.
        Biosci Rep. 1991; 11: 171-180
        • Guidry C
        • Hook M
        Endothelins produced by endothelial cells promote collagen gel contraction by fibroblasts.
        J Cell BioI. 1991; 115: 873-880
        • Halim A
        • Kanayama N
        • el Maradny E
        • Maehara K
        • Terao T
        Coagulation in vivo microcirculation and in vitro caused by endothelin-1.
        Thromb Res. 1993; 72: 203-209
        • Leadley Jr, RJ
        • Lee P
        • Erickson LA
        • Shebuski RJ
        The snake venom peptide sarafotoxin S6b inhibits repetitive platelet thrombus formation in the stenosed canine coronary artery.
        J Cardiovasc Pharmacol. 1993; 22: S199-S203
        • McMurdo L
        • Lidbury PS
        • Thiemermann C
        • Vane JR
        Mediation of endothelin-l-induced inhibition of platelet aggregation via the ETB receptor.
        Br J Pharmacol. 1993; 109: 530-534
        • Cannan CR
        • Burnett Jr, JC
        • Brandt RR
        • Lerman A
        Endothelin at pathophysiological concentrations mediates coronary vasoconstriction via the endothelin-A receptor.
        Circulation. 1995; 92: 3312-3317
        • Martin-Nizard F
        • Houssaini HS
        • Lestavel-Delattre S
        • Duriez P
        • Fruchart Je
        Modified low density lipoproteins activate human macrophages to secrete immunoreactive endothelin.
        FEBS Lett. 1991; 293: 127-130
        • Horio T
        • Kohno M
        • Murakawa K
        • Yasunari K
        • Yokokawa K
        • Ueda M
        • et al.
        Increased plasma immunoreactive endothelin-1 concentration in hypercholesterolemic rats.
        Atherosclerosis. 1991; 89: 239-246
        • Lerman A
        • Webster MW
        • Chesebro JH
        • Edwards WD
        • Wei CM
        • Fuster V
        • et al.
        Circulating and tissue endothelin immu-noreactivity in hypercholesterolemic pigs.
        Circulation. 1993; 88: 2923-2928
        • Haak T
        • Marz W
        • Jungmann E
        • Hausser S
        • Siekmeier R
        • Gross W
        • et al.
        Elevated endothelin levels in patients with hyperlipoproteinemia.
        Clin Invest. 1994; 72: 580-584
        • Lerman A
        • Edwards BS
        • Hallett JW
        • Heublein DM
        • Sandberg SM
        • Burnett Jr, JC
        Circulating and tissue endothelin immu-noreactivity in advanced atherosclerosis.
        N Engl J Med. 1991; 325: 997-1001
        • Haak T
        • Jungmann E
        • Raab C
        • Usadel KH
        Elevated endothelin-1 levels after cigarette smoking.
        Metabolism. 1994; 43: 267-269
        • Kiowski W
        • Linder L
        • Stoschitzky K
        • Pfisterer M
        • Burckhardt D
        • Burkart F
        • et al.
        Diminished vascular response to inhibition of endothelium-derived nitric oxide and enhanced vaso-constriction to exogenously administered endothelin-l in clinically healthy smokers.
        Circulation. 1994; 90: 27-34
        • Schiffrin EL
        Endothelin in hypertension.
        Curr Opin Cardiol. 1995; 10: 485-494
        • Lerman A
        • Burnett Jr, JC
        Intact and altered endothelium in regulation of vasomotion.
        Circulation. 1992; 86: IIII2-IIII9
        • Flavahan NA
        Atherosclerosis or lipoprotein-induced endo-thelial dysfunction: potential mechanisms underlying reduction in EDRF/nitric oxide activity.
        Circulation. 1992; 85: 1927-1938
        • Zeiher AM
        • Drexler H
        • Saurbier B
        • Just H
        Endothelium-mediated coronary blood flow modulation in humans: effects of age, atherosclerosis, hypercholesterolemia, and hypertension.
        I Clin Invest. 1993; 92: 652-662
        • Cannan CR
        • McGoon M
        • Holmes Jr, DR
        • Lerman A
        Altered coronary endothelial function in a patient with asymptomatic left ventricular dysfunction.
        Int J Cardiol. 1996; 53: 147-151
        • Lerman A
        • Holmes Jr, DR
        • Bell MR
        • Garratt KN
        • Nishimura RA
        • Burnett Jr, JC
        Endothelin in coronary endothelial dysfunction and early atherosclerosis in humans.
        Circulation. 1995; 92: 2426-2431
        • Yasuda M
        • Kohno M
        • Tahara A
        • Itagane H
        • Toda I
        • Akioka K
        • et al.
        Circulating immunoreactive endothelin in ischemic heart disease.
        Am Heart J. 1990; 119: 801-806
        • Ray SG
        • McMurray LL
        • Morton LL
        • Dargie HI
        Circulating endothelin in acute ischaemic syndromes.
        Br Heart J. 1992; 67: 383-386
        • Zeiher AM
        • Goebel H
        • Schachinger V
        • Ihling C
        Tissue endothelin-l immunoreactivity in the active coronary atherosclerotic plaque: a clue to the mechanism of increased vasoreactivity of the culprit lesion in unstable angina.
        Circulation. 1995; 91: 941-947
        • Toyo-oka T
        • Aizawa T
        • Suzuki N
        • Hirata Y
        • Miyauchi T
        • Shin WS
        • et al.
        Increased plasma level of endothelin-l and coronaryspasm induction in patients with vasospastic angina pectoris.
        Circulation. 1991; 83: 476-483
        • Bogaty P
        • Hackett D
        • Davies G
        • Maseri A
        Vasoreactivity of the culprit lesion in unstable angina.
        Circulation. 1994; 90: 511
        • Miyauchi T
        • Yanagisawa M
        • Tomizawa T
        • Sugishita Y
        • Suzuki N
        • Fujino M
        • et al.
        Increased plasma concentrations of endothelin-I and big endothelin-I in acute myocardial infarction [letter].
        Lancet. 1989; 2: 53-54
        • Nakamura M
        • Arakawa N
        • Yoshida H
        • Funakoshi T
        • Chiba M
        • Abe Y
        • et al.
        Increased plasma endothelin concentrations in patients with acute heart failure after myocardial infarction.
        Jpn Circ J. 1993; 57: 371-378
        • Omland T
        • Lie RT
        • Aakvaag A
        • Aarsland T
        • Dickstein K
        Plasma endothelin determination as a prognostic indicator of I-year mortality after acute myocardial infarction.
        Circulation. 1994; 89: 1573-1579
        • Watanabe T
        • Suzuki N
        • Shimamoto N
        • Fujino M
        • Imada A
        Contribution of endogenous endothelin to the extension of myocardial infarct size in rats.
        Circ Res. 1991; 69: 370-377
        • Grover GJ
        • Dzwonczyk S
        • Parham CS
        The endothelin-I receptor antagonist BQ-123 reduces infarct size in a canine model of coronary occlusion and reperfusion.
        Cardiovasc Res. 1993; 27: 1613-1618
        • Velasco CE
        • Turner M
        • Inagami T
        • Atkinson JB
        • Virmani R
        • Jackson EK
        • et al.
        Reperfusion enhances the local release of endothelin after regional myocardial ischemia.
        Am Heart J. 1994; 128: 441-451
        • Margulies KB
        • Hildebrand Jr, FL
        • Lerman A
        • Perrella MA
        • Burnett Jr, JC
        Increased endothelin in experimental heart failure.
        Circulation. 1990; 82: 2226-2230
        • Kourembanas S
        • Marsden PA
        • McQuillan LP
        • Faller DV
        Hypoxia induces endothelin gene expression and secretion in cultured human endothelium.
        J Clin Invest. 1991; 88: 1054-1057
        • Yoshizumi M
        • Kurihara H
        • Sugiyama T
        • Takaku F
        • Yanagisawa M
        • Masaki T
        • et al.
        Hemodynamic shear stress stimulates endothelin production by cultured endothelial cells.
        Biochem Biophys Res Commun. 1989; 161: 859-864
        • Pearson PJ
        • Lin PJ
        • Schaff HV
        Global myocardial ischemia and reperfusion impair endothelium -dependent relaxations to aggregating platelets in the canine coronary artery: a possible cause of vasospasm following cardiopulmonary bypass.
        J Thorac Cardiovasc Surg. 1992; 103: 1147-1154
        • Lerman A
        • Mruk JS
        • Webster MWI
        • Burnett Jr, JC
        • Chesebro JH
        Activation of endothelin during arterial thrombosis and ENDOTHELINAND CORONARY ATHEROSCLEROSIS 777 thrombolysis [abstract].
        J Am Coil Cardiol. 1991; 17: 26A
        • Boulanger CM
        • Luscher TF
        Hirudin and nitrates inhibit the thrombin-induced release of endothelin from the intact porcine aorta.
        Circ Res. 1991; 68: 1768-1772
        • Gruntzig AR
        • Senning A
        • Siegenthaler WE
        Nonoperative dilatation of coronary-artery stenosis: percutaneous transluminal coronary angioplasty.
        N Engl J Med. 1979; 301: 61-68
        • Tahara A
        • Kohno M
        • Yanagi S
        • Itagane H
        • Toda I
        • Akioka K
        • et al.
        Circulating immunoreactive endothelin in patients undergoing percutaneous transluminal coronary angioplasty.
        Metabolism. 1991; 40: 1235-1237
        • Lerman A
        • Holmes Jr, DR
        • Garratt KN
        • Reeder GS
        • Bell MR
        • Burnett Jr, JC
        Local release of endothelin in human coronary arteries in response to balloon angioplasty [abstract].
        J Am Coil Cardiol. 1994; 23: 124A
        • Harrison VJ
        • Bames K
        • Turner AJ
        • Wood E
        • Corder R
        • Vane JR
        Identification of endothelin I and big endothelin I in secretory vesicles isolated from bovine aortic endothelial cells.
        Proc Natl Acad Sci USA. 1995; 92: 6344-6348
        • Douglas SA
        • Vickery-Clark LM
        • Louden C
        • Ohlstein EH
        Selective ETA receptor antagonism with BQ-123 is insufficient to inhibit angioplasry induced neointima formation in the rat.
        Cardiovasc Res. 1995; 29: 641-646
        • Azuma H
        • Hamasaki H
        • Niimi Y
        Endothelin-l (ET- l ) plays a role in the intimal hyperplasia after endothelial removal [abstract].
        Can J Physiol Pharmacol. 1994; 72: 154
        • Clavell A
        • Stingo A
        • Margulies K
        • Lerman A
        • Underwood D
        • Burnett Jr, JC
        Physiological significance of endothelin: its role in congestive heart failure.
        Circulation. 1993; 87: V45-v50
        • Wei CM
        • Lerman A
        • Rodeheffer RJ
        • McGregor CGA
        • Brandt RR
        • Wright S
        • et al.
        Endothelin in human congestive heart failure.
        Circulation. 1994; 89: 1580-1586
        • Rodeheffer RJ
        • Lerman A
        • Heublein DM
        • Burnett Jr, JC
        Increased plasma concentrations of endothelin in congestive heart failure in humans.
        Mayo Clin Proc. 1992; 67: 719-724
        • Kiowski W
        • Sutsch G
        • Hunziker P
        • Muller P
        • Kim J
        • Oechslin E
        • et al.
        Evidence for endothelin-I-mediated vasoconstriction in severe chronic heart failure.
        Lancet. 1995; 346: 732-736
        • Lerman A
        • Kubo SH
        • Tschumperlin LK
        • Burnett Jr, JC
        Plasma endothelin concentration s in humans with end-stage heart failure and after cardiac transplantation.
        J Am Coli Cardiol. 1992; 20: 849-853
        • Berkenboom G
        • Giot C
        • Unger P
        • Vachiery JL
        • Antoine M
        • LeClerc JL
        Plasma endothelin and early coronary endothelial dysfunction in recipients of a cardiac transplant.
        Am Heart J. 1995; 129: 1178-1184