Angiotensin converting enzyme inhibition modulates endogenous endothelin in chronic canine thoracic inferior vena caval constriction

Systematic Evaluation of Endothelin 1 Measurement Relative to Traditional and Modern Biomarkers for Clinical Assessment and Prognosis in Patients With Chronic Systolic Heart Failure: Serial Measurement and Multimarker Testing

OBJECTIVES

To define the role of single or serial measurement of endothelin 1 (ET-1) for prognostication beyond traditional and modern markers of risk in heart failure (HF).

METHODS

In total, 115 patients with chronic systolic HF were followed for 10 months. Clinical assessment and ET-1, N-terminal pro-B-type natriuretic peptide (NT-proBNP), highly sensitive troponin I (hsTnI), soluble ST2 (sST2), and galectin 3 were measured at each visit.

RESULTS

Elevated ET-1 was associated with worse HF, lower right ventricular function, higher pulmonary pressure, and higher left atrial volume index despite similar left ventricular function. ET-1 correlated with angiotensin-converting enzyme inhibitor use. A model containing traditional risk factors, ET-1, NT-proBNP, hsTnI, and sST2 best predicted cardiovascular events, and ET-1 improved reclassification. In an adjusted time-integrated model, percent time spent with ET-1 of 5.90 pg/mL or less was predictive of fewer cardiovascular events (odds ratio, 0.75; 95% confidence interval, 0.62-0.91). ET-1 reduction over time was associated with a lower rate of cardiovascular events compared with increasing or stable ET-1 (24.4% vs 50.0%).

CONCLUSIONS

ET-1 may be a unique predictor of HF prognosis, complementing other biomarkers in a multimarker profile. Serial measurement of ET-1 may provide additional prognostic information.

Hepatic and Plasma Endothelin-1 in Dogs with Chronic Hepatitis

BACKGROUND

Endothelin (ET)-1 is a 21-amino-acid peptide with potent vasoactive properties, which increases intrahepatic resistance in patients with chronic hepatitis (CH) or cirrhosis. ET-1 concentrations have not been investigated in dogs with CH.

HYPOTHESIS/OBJECTIVES

This study compared hepatic and plasma ET-1 levels in healthy dogs and in dogs with CH, and examined the relationship between the plasma ET-1 level and portal vein pressure in dogs with CH.

ANIMALS

Fourteen healthy dogs and twenty dogs with CH were used in this study.

METHODS

Prospective case-control study. Hepatic ET-1 mRNA expression was determined by real-time reverse transcription polymerase chain reaction, and hepatic and plasma ET-1 levels were assessed using ELISA. Splenic pulp pressure (SPP), as an indicator of portal vein pressure, was measured laparoscopically.

RESULTS

Hepatic ET-1 mRNA levels were 3.7 times higher in dogs with CH than in healthy dogs (P = .008). The median hepatic and plasma ET-1 protein levels were significantly higher in dogs with CH than in healthy dogs (13.20 pg/mg wet liver vs. 3.42 pg/mg wet liver, P = .004, and 0.99 pg/mL vs. 0.71 pg/mL, P = .013, respectively). Moreover, there was a weak but significant correlation between plasma ET-1 level and SPP in dogs with CH (P = .036; r_s = 0.53).

CONCLUSIONS AND CLINICAL IMPORTANCE

The results indicate that ET-1 might play an important role in the pathogenesis of portal hypertension caused by CH.

Onset of peripheral arterial disease: role of endothelin in endothelial dysfunction

OBJECTIVES

Endothelial dysfunction and inflammation are understood to contribute to the onset of peripheral arterial disease (PAD), and endothelin (ET) may play an important role in this process. This study investigated the role of ET in PAD, and its relationships with symptoms, endothelial dysfunction and inflammation.

METHODS AND RESULTS

This cross-sectional study enrolled 141 participants: 66 patients with PAD and intermittent claudication, 37 patients with PAD and critical ischemia, and 38 healthy controls aged under 35 years. There were no gender distribution differences between control and diseased groups. Moreover, no differences were observed in age or cardiovascular risk factors distribution between patients with critical ischemia and patients with claudication. Plasma ET concentrations were significantly higher in patients vs. controls (8.76+/-77.1 vs. 6.45+/-0.89 pmol/l, respectively; P=0.002). Nevertheless, patients with claudication exhibited significantly higher plasma ET concentrations vs. patients with critical ischemia (10.97+/-7.9 vs. 4.82+/-2.57 pmol/l, respectively; P<0.001). Otherwise, significantly greater serum concentrations of C-reactive protein (CRP) were observed in patients with critical ischemia vs. patients with claudication (16.94 vs. 4.73 mg/l, respectively; P=0.001) and controls (0.96 mg/l; P=0.001). Plasma concentrations of ET had a modest negative correlation with serum concentrations of CRP (-0.165; P=0.095).

CONCLUSION

Plasma concentrations of ET in patients with PAD are greatest in early disease; ET concentrations decrease substantially and inflammation arises as disease advances. Serum CRP concentrations exhibit a modest negative correlation with those of ET.

Endothelins in health and disease

Endothelins are powerful vasoconstrictor peptides that also play numerous other roles. The endothelin (ET) family consists of three peptides produced by a variety of tissues. Endothelin-1 (ET-1) is the principal isoform produced by the endothelium in the human cardiovascular system, and it exerts its actions through binding to specific receptors, the so-called type A (ET(A)) and type B (ET(B)) receptors. ET-1 is primarily a locally acting paracrine substance that appears to contribute to the maintenance of basal vascular tone. It is also activated in several diseases, including congestive heart failure, arterial hypertension, atherosclerosis, endothelial dysfunction, coronary artery diseases, renal failure, cerebrovascular disease, pulmonary arterial hypertension, and sepsis. Thus, ET-1 antagonists are promising new agents. They have been shown to be effective in the management of primary pulmonary hypertension, but disappointing in heart failure. Clinical trials are needed to determine whether manipulation of the ET system will be beneficial in other diseases.

Cloning of cDNA encoding canine endothelin receptors and their expressions in normal tissues

The receptors for endothelin (ET) family, ETA and ETB, were molecularly cloned and the expression of ETA and ETB as well as preproendothelin-1 (PPET-1, precursor of ET-1) was examined in normal canine tissues by RT-PCR. The entire open reading frames of the canine ETA and ETB were shown to encode 427 and 442 amino acid residues, respectively, showing from 87.4 to 97.3% sequence similarity to human, mouse, and rat counterparts. ETA and ETB mRNAs were ubiquitously expressed in a variety of canine tissues in this study and PPET-1 mRNA was detected in the tissues except for heart and liver. It was speculated that ET could play an important role in physiological events in most of the organs.

Vascular Remodeling in the Internal Mammary Artery Graft and Association With In Situ Endothelin-1 and Receptor Expression

Background— The vasoconstricting peptide endothelin-1 (ET-1) has been associated with atherosclerotic cardiovascular disease, vascular smooth muscle cell (VSMC) growth stimulation, and intimal thickening. ET-1 binds 2 receptor subtypes, endothelin A and B, and the ET A receptor mediates vasoconstriction and VSMC growth. This study aims to quantitatively assess arterial remodeling variables and compare them with changes in ET-1, ET A , and ET B expression in the internal mammary artery (IMA).

Methods and Results— Specimens from 55 coronary artery disease (CAD) patients (45 men, 10 women; mean age 65 years) and 14 control IMA specimens (from 7 men and 7 women; mean age 45 years) were collected. IMA cross sections were assessed by histochemical and immunohistochemical staining methods to quantify the levels of medionecrosis, fibrosis, VSMC growth, ET-1, ET A , ET B , and macrophage infiltration. The percentage area of medionecrosis in the patients was almost double that in the controls (31.85±14.52% versus 17.10±9.96%, P =0.0006). Total and type 1 collagen was significantly increased compared with controls (65.8±18.3% versus 33.7±13.7%, P =0.07, and 14.2±10.0% versus 4.8±2.8%, P =0.01, respectively). Despite ACE and/or statin therapy, ET-1 expression and cell cycling were significantly elevated in the patient IMAs relative to the controls (46.27±18.46 versus 8.56±8.42, P =0.0001, and 37.29±12.88 versus 11.06±8.18, P =0.0001, respectively). ET A and ET B staining was elevated in the patient vessels (46.88±11.52% versus 18.58±7.65%, P =0.0001, and 42.98±7.08% versus 34.73±5.20%, P =0.0067, respectively). A mild presence of macrophages was noted in all sections.

Conclusions— Elevated distribution of collagen indicative of fibrosis coupled with increased cell cycling and high levels of ET-1 and ET A expression in the absence of chronic inflammation suggests altered IMA VSMC regulation is fundamental to the remodeling process.

Increased endothelin-1 production in patients with chronic heart failure

Endothelin-1 (ET-1) concentrations are elevated in patients with congestive heart failure (CHF), although the cause of this increase remains uncertain. We hypothesized that abnormalities in ET-1 production, clearance, or a combination of these may be the cause of elevated ET-1 concentrations in chronic CHF. The kinetics of clearance of ET-1 were measured with (125)I-labeled ET-1 in eight patients with CHF and five age-matched normal individuals. In both normal subjects and the CHF group, the kinetics of ET-1 clearance were best described by a three-compartment model. The steady-state volume of distribution of ET-1 was significantly greater in the CHF group compared with normal subjects (25.2 +/- 3.9 vs. 13.8 +/- 2.1 l/kg; P < 0.05). The total clearance rate from plasma was greater in the CHF group (0.119 +/- 0.018 vs. 0.047 +/- 0.013 l.kg(-1).min(-1); P = 0.05). The total body production rate of ET-1 was also significantly higher in patients with CHF (0.21 +/- 0.03. vs. 0.06 +/- 0.02 ng.kg(-1).min(-1); P < 0.05). It appears that increased ET-1 production rather than decreased clearance is the cause of elevated ET-1 concentrations in patients with chronic CHF.

Decreased cardiac output in humans during laparoscopic antireflux surgery: direct measurements

OBJECTIVE

In a porcine model, we demonstrated that laparoscopic Nissen fundoplication causes a significant drop in cardiac output (30%) because it exposes both the peritoneal cavity and the mediastinum to CO(2) under pressure. To determine if this occurs in humans, we examined cardiovascular physiology during laparoscopic Nissen fundoplication. Because of invasiveness required in this pilot trial, only six patients were studied.

METHODS

The arterial blood pressure (via radial arterial catheter) and the pulmonary artery diastolic pressure and cardiac index (via pulmonary artery thermodilution catheter) were measured at seven points in time during each laparoscopic Nissen fundoplication.

RESULTS

The systolic blood pressure decreased in all patients, and the cardiac index decreased in all but one patient. The exception was a patient with Huntington disease, in whom the cardiac output did not decrease. In four of the five patients, the cardiac output was lowest during hiatal dissection, and in the fifth, it was lowest after reverse Trendelenburg positioning. No significant change in the pulmonary artery diastolic pressure was noted. All patients received adequate intravenous fluid replacement (average, 58 +/- 16 mL/kg) to support blood pressure. In one patient, with a particularly large paraesophageal hernia, profound hypotension (40/25 mm Hg) developed during the mediastinal phase of the procedure, and this patient required alpha-adrenergic support followed by laparotomy to eliminate a surgical cause (none found).

CONCLUSIONS

Although it is a tremendous advance for patients, laparoscopic Nissen fundoplication can be associated with a significant reduction in cardiac output and blood pressure. Surgeons and anesthesiologists must be alert to changes reflecting these decreases during procedures, which violate both the peritoneal cavity and the mediastinum. We propose careful hemodynamic monitoring during these procedures, especially in patients with coronary artery disease or significant left ventricular dysfunction.

ACE inhibition increases expression of the ETB receptor in kidneys of mice with unilateral obstruction

Unilateral ureteral obstruction (UUO) is a well-established model for the study of interstitial fibrosis in the kidney. It has been shown that the renin-angiotensin system plays a central role in the progression of interstitial fibrosis. Recent studies indicate that endothelin, a powerful vasoconstrictive peptide, may play an important role in some types of renal disease. To investigate the effects of angiotensin II on endothelin and its receptors in the kidney, mice were subjected to UUO and treated with or without enalapril, an orally active angiotensin-converting enzyme inhibitor, in their drinking water (100 mg/l). The animals were killed 5 days later. Using RT coupled with PCR, we measured the levels of endothelin-1, endothelin A, and endothelin B (ET(B)) along with transforming growth factor-beta, TNF-alpha, and collagen type IV mRNA expression in the kidney with UUO and the contralateral kidney along with interstitial expansion in the kidney cortex by a standard point counting method. We found that enalapril administration ameliorated the increased expression of ET-1 mRNA in the obstructed kidney by 44% (P < 0.02). Although the level of endothelin A mRNA expression was significantly increased in the obstructed kidney, it was not affected by enalapril. We found that enalapril treatment increased ET(B) mRNA expression by 115% (P < 0.05) and protein expression (measured by Western blot) in the kidney with an obstructed ureter. Enalapril treatment alone inhibited the expansion of interstitial volume due to UUO by 52%. Cotreatment with enalapril and the ET(B) receptor antagonist BQ-788 inhibited the expression of interstitial volume by only 19%. This study confirms that enalapril inhibits the interstitial fibrosis in UUO kidneys. It also suggests a beneficial and unforeseen effect of enalapril on the obstructed kidney by potentially stimulating the production of nitric oxide through an increased expression of the ET(B) receptor.

Long-term survival and hemodynamics after endothelin-a receptor antagonism and angiotensin-converting enzyme inhibition in rats with chronic heart failure: monotherapy versus combination therapy

BACKGROUND

In patients with congestive heart failure (CHF) receiving ACE inhibitors, acute administration of selective endothelin (ET) antagonists additionally improves systemic and cardiac hemodynamics. We investigated, in a rat model of CHF, whether such acute synergistic effects are sustained and accompanied, in the long term, by an additional limitation of left ventricular remodeling or an increase in survival.

METHODS AND RESULTS

Rats were subjected to coronary artery ligation and treated for 3 or 9 months with vehicle or with the ACE inhibitor trandolapril (Tr) (0.3 mg/kg(-1) per day(-1)), the ET(A) antagonist LU 135252 (LU, 30 mg/kg(-1) per day(-1)), or their combination starting 7 days after ligation. After 3 months, the combination decreased LV systolic- and end-diastolic pressures (-32% and -80%, respectively) more markedly than Tr (-21% and -61%, respectively) or LU alone (-14% and -48%, respectively). Echocardiographic studies revealed that all treatments limited LV dilatation and increased LV fractional shortening and cardiac index. All treatments equally reduced left ventricular collagen density, whereas only Tr or the combination reduced LV weight. Finally, although LU did not modify long-term survival, Tr and the combination of Tr with LU induced a similar improvement of survival.

CONCLUSIONS

In this rat model, long-term combined administration of an ET(A) antagonist and an ACE inhibitor induces additional effects in terms of systemic and cardiac hemodynamics; however, this is not associated with an additional increase in long-term survival.

Chronic endothelin receptor antagonism prevents coronary vasa vasorum neovascularization in experimental hypercholesterolemia

OBJECTIVES

The purpose of this study was to test the hypothesis that endothelin (ET) receptor antagonism reduces coronary vasa vasorum neovascularization in experimental hypercholesterolemia.

BACKGROUND

Experimental hypercholesterolemia is associated with increased expression of ET-1, an endothelium-derived peptide with vasoconstricting, mitogenic and angiogenic properties, in the coronary arterial wall as well as with vasa vasorum neovascularization. A pathomechanistic role of the endogenous ET system in vasa vasorum neovascularization in hypercholesterolemia has, however, remained uncertain so far.

METHODS

Female domestic pigs were placed on a normal diet (N; n = 7) or on a hypercholesterolemic diet without (HC; n = 6) or with ET-A receptor antagonism (ABT-627, 4 mg/kg/day; HC + ET-A; n = 6). After 12 weeks, coronary vasa vasorum structure was assessed by three-dimensional microscopic computed tomography, expression of vascular endothelial growth factor (VEGF) within the coronary arterial wall by Western blotting and immunostaining.

RESULTS

Compared with the N group, plasma concentrations of low-density lipoprotein cholesterol were higher in both the HC and HC + ET-A groups (36 +/- 3 mg/dl vs. 312 +/- 153 mg/dl and 303 +/- 113 mg/dl, p < 0.01). Vasa vasorum density was higher in the HC group compared with the N group (4.7 +/- 1.8 per mm(2) vs. 2.5 +/- 1.5 per mm(2); p < 0.05) and was preserved in the HC + ET-A group (3.2 +/- 0.7 per mm(2)). In parallel, increase in VEGF expression in the coronary arterial wall in the HC group was preserved in the HC + ET-A group.

CONCLUSIONS

The current study demonstrates that chronic endothelin receptor antagonism prevents the increase in VEGF expression and vasa vasorum density of coronary arteries in experimental hypercholesterolemia. These findings support a role for the endogenous ET system in vasa vasorum neovascularization in early coronary atherosclerosis.

Therapeutic role of bosentan in hypertension: lessons from the model of perinephritic hypertension

Since its discovery in 1988, there has been increasing evidence that endothelin-1 (ET-1) plays an important role in the pathophysiology of hypertension and its related end-organ damages. First studies, using ET-1 administration in animals or in humans suspected this role by demonstrating the hypertensive properties of ET-1. The latter, due to stimulation of ET(A) receptors inducing sustained vasoconstriction have been reported to follow transient vasodilation linked with activation of an endothelial ET(B) receptor releasing nitric oxide (NO). In certain instances, ET(B) smooth-muscle receptors might also induce contraction. Cloning of these receptors helped to develop ET-1 receptor antagonists. As soon as one of them became available, bosentan, a dual (ET(A) and ET(B)) ET-1 receptor antagonist, we tested its effects in the canine model of perinephritic hypertension. Bosentan was found to exert striking hypotensive effects, due to peripheral vasodilation but without affecting cardiac function. In further experiments, we observed that effects of bosentan were additional to those of ACE inhibitors or angiotensin II antagonists. This opened new therapeutic perspectives and also suggested a proper role of ET-1 in hypertension, independent of the renin-angiotensin system. To explain this role, we demonstrated a real imbalance characterized by an impairment of the NO system in favor of the ET-1 pathway. Recent studies suggest that such an imbalance may also occur in human hypertension. Furthermore, the contribution of ET-1 to human hypertension appears more convincing since bosentan was shown to decrease blood pressure in hypertensive subjects. Finally, ET-1 receptor antagonists might be of therapeutic interest to prevent hypertension induced end-organ damages. Whether or not these compounds are able to prevent or to reverse target organ injuries in man remains to be investigated.

Vasopeptidase inhibition and endothelial function in hypertension

Vasopeptidase inhibitors are a new class of drugs capable of inhibiting both angiotensin-converting enzyme and neutral endopeptidase 24.11. This involves simultaneous inhibition with a single molecule of two key enzymes, ACE and NEP, which are both involved in the regulation of cardiovascular homeostasis in many ways. This includes metabolism of several vasoactive peptides and their clearance from the circulation, therefore contributing to neurohumoral modulation, which might have therapeutic advantages in the prevention of endothelial dysfunction in hypertension.

Angiotensin II activates collagen type I gene in the renal cortex and aorta of transgenic mice through interaction with endothelin and TGF-beta

Hypertension is frequently associated with the development of renal vascular fibrosis. This pathophysiologic process is due to the abnormal formation of extracellular matrix proteins, mainly collagen type I. In previous studies, it has been observed that the pharmacologic blockade of angiotensin II (Ang II) or endothelin (ET) blunted the development of glomerulo- and nephroangiosclerosis in nitric oxide-deficient hypertensive animals by inhibiting collagen I gene activation. The purpose of this study was to investigate whether and how AngII interacts with ET to activate the collagen I gene and whether transforming growth factor-beta (TGF-beta) could be a player in this interaction. Experiments were performed in vivo on transgenic mice harboring the luciferase gene under the control of the collagen I-alpha 2 chain promoter (procol alpha 2[I]). Bolus intravenous administration of AngII or ET produced a rapid, dose-dependent activation of collagen I gene in aorta and renal cortical slices (threefold increase over control at 2 h, P < 0.01). The AngII-induced effect on procol alpha 2(I) was completely inhibited by candesartan (AngII type 1 receptor antagonist) and substantially blunted by bosentan (dual ET receptor antagonist) (P < 0.01), whereas the ET-induced activation of collagen I gene was blocked only by bosentan. In subsequent experiments, TGF-beta (also administered intravenously) produced a rapid increase of procol alpha 2(I) in aorta and renal cortical slices (twofold increase over control at 1 h, P < 0.01) that was completely blocked by decorin (scavenger of the active form of TGF-beta). In addition, decorin attenuated the activation of collagen I gene produced by AngII (P < 0.01). These data indicate that AngII can activate collagen I gene in aorta and renal cortex in vivo by a mechanism(s) requiring participation and/or cooperation of ET and TGF-beta.

Regulation of cardiac adrenomedullin in heart failure

Adrenomedullin (ADM), a potent natriuretic and vasorelaxing peptide with inotropic properties, is elevated in plasma in human and experimental congestive heart failure (CHF). Recent studies suggest that angiotensin II stimulates ADM production and secretion from cardiac myocytes and fibroblasts. In the present study, we investigated cardiac ADM in experimental CHF, and tested the hypothesis that angiotensin converting enzyme (ACE) inhibition modulates cardiac ADM in CHF. Cardiac tissue ADM immunoreactivity and gene expression were assessed by radioimmunoassay, immunohistochemistry, in situ hybridization and Northern blot analysis in normal and CHF dogs in the presence and absence of ACE inhibition. Experimental CHF was produced by progressive rapid ventricular pacing and characterized by increased ventricular ADM concentrations as well as increased ventricular ADM gene expression. ACE inhibition abolished the increases in ventricular ADM concentrations and ventricular ADM gene expression in CHF. Ventricular ADM gene expression was localized to ventricular myocytes and correlated with left ventricular mass index, suggesting that ventricular ADM is a marker for ventricular hypertrophy. In contrast, atrial ADM concentrations and gene expression did not change in CHF with or without ACE inhibition. Increased plasma ADM concentrations in CHF were also abolished with ACE inhibition. The present study demonstrates that circulating and ventricular ADM are activated in pacing-induced experimental CHF and that ACE inhibition reverses ventricular ADM activation in CHF. This study also indicates that cardiac ADM gene expression is differently regulated between atrium and ventricle in CHF.

Endothelin receptor antagonists and cardiovascular diseases of aging

Our understanding of the role of the endothelin system in human cardiovascular physiology and pathophysiology has evolved very rapidly since the initial description of its constituent parts in 1988. Endothelin-1 (ET-1) is the predominant endothelin isoform in the human cardiovascular system and has potent vasoconstrictor, mitogenic and antinatriuretic properties which have implicated it in the pathophysiology of a number of cardiovascular diseases. The effects of ET-1 have been shown to be mediated by 2 principal endothelin receptor subtypes: ET(A) and ET(B). The development of a range of peptidic and nonpeptidic endothelin receptor antagonists represents an exciting breakthrough in human cardiovascular therapeutics. Two main classes of endothelin receptor antagonist have been developed for possible human therapeutic use: ET(A)-selective and nonselective antagonists. Extensive laboratory and clinical research with these agents has highlighted their promise in various cardiovascular diseases. Randomised, placebo-controlled clinical trials have yielded very encouraging results in patients with hypertension and chronic heart failure with more preliminary data suggesting a possible role in the treatment and prevention of atherosclerosis and stroke. Much more research is needed, however, before endothelin receptor antagonists can be considered for clinical use.

Functional role of endogenous endothelin-1 in congestive heart failure treated with angiotensin II receptor antagonist

Interactions between angiotensin (ANG) II and endothelin (ET)-1 receptor transduction pathways have been unclear in congestive heart failure (CHF). Therefore the objects of this study are, in CHF, whether production of ET-1 is modulated by ANG II and/or whether hemodynamic effects of endogenous ET-1 are modulated by ANG II. Twelve dogs were randomly assigned to two groups: untreated (n = 6) and treated with ANG II type 1 (AT1) receptor antagonist (TCV116, 1.5 mg/kg/d) (n = 6). After rapid ventricular pacing (240 bpm) for 4 weeks, plasma and cardiac ET-1 levels were compared between the two groups. Acute hemodynamic effects of a nonspecific ET(A&B) receptor antagonist, TAK044 (3 mg/kg plus 3 mg/kg/h i.v.) were examined in both groups by a conductance catheter and a micromanometer. After 4 weeks of pacing, plasma and cardiac tissue ET-1 levels were elevated in both groups to a similar degree. In the group treated with TCV116, TAK044 produced an increase in stroke volume and a decrease in total systemic resistance; heart rate was unchanged. The time constant of left ventricular (LV) relaxation was significantly decreased. The slope of LV end-systolic pressure-volume relation (E(ES)) was increased (p < 0.05), indicating an increased LV contractility. Thus endogenous ET-1 produces an arterial vasoconstriction and impairs LV contractility and relaxation in CHF with AT1 receptor antagonism. These hemodynamic responses to TAK044 in CHF treated with TCV116 were similar in untreated CHF. These results suggest that the production of ET-1 and the cardiac effects of endogenous ET-1 in CHF may be unaffected by ANG II acting through AT1 receptors.

Differential effects of angiotensin II versus endothelin-1 inhibitions in hypertrophic left ventricular myocardium during transition to heart failure

BACKGROUND

In view of their mutual crosstalk, the roles of angiotensin II (Ang II) and endothelin-1 (ET-1) in the myocardium are assumed to be synergistic and supplemental.

METHODS AND RESULTS

In the phase of compensated left ventricular (LV) hypertrophy of Dahl salt-sensitive rats, Ang II peptide and the ACE mRNA in the LV were increased by 1.6- and 3.8-fold, respectively. In contrast, ET-1 peptide and the preproET-1 mRNA remained unchanged. In subsequent congestive heart failure (CHF), Ang II and ACE mRNA did not show further increases. But ET-1 and the mRNA were increased de novo by 5.3- and 4.1-fold, respectively. In ascending aorta-banded rats, the local activations of Ang II and ET-1 also showed a differential time course between LV hypertrophy and CHF. Long-term treatments of Dahl salt-sensitive rats with temocapril (an ACE inhibitor) and with bosentan (a mixed ET receptor blocker) equally improved long-term survival. Temocapril reduced the LV/body weight ratio and ameliorated LV fractional shortening. Conversely, although bosentan equally improved fractional shortening, it did not reduce the increase in LV mass. Combined treatment with these 2 drugs further ameliorated the animal's survival without additional decreases in systolic pressure.

CONCLUSIONS

The pathophysiological roles in the myocardium during the transition to CHF differ qualitatively between Ang II and ET-1. Thus, long-term therapy with a combination of ACE inhibition and ET antagonism may provide a new approach for heart failure in humans.

Coronary endothelial function in health and disease

The endothelium participates in the control of coronary vascular tone and growth through the release of vasodilating and growth-inhibiting factors such as nitric oxide (NO) and C-type natriuretic peptide (CNP), and vasoconstricting and growth-promoting substances such as endothelin-1 (ET-1). Abnormalities in NO and/or CNP generation or actions have been demonstrated in various cardiovascular pathophysiological states, specifically atherosclerosis, congestive heart failure, hypertension and hypercholesterolaemia. Moreover, an increase in plasma ET-1 levels has also been reported in these disease states. When these observations are considered together, these states may be characterised by an attenuated release or action of NO and/or CNP, together with an augmented release of ET-1. Thus, an imbalance between these opposing factors may contribute to the alteration in vascular tone and the vascular remodelling characteristics of cardiovascular disease. The following article summarises the present knowledge of endothelial control of the coronary circulation and derangements associated with coronary endothelial dysfunction.

Effect of valsartan and captopril in rabbit carotid injury. Possible involvement of bradykinin in the antiproliferative action of the renin-angiotensin blockade

The effects of the specific angiotensin II (Ang II) AT1-receptor blocker valsartan on events related to restenosis were investigated in rabbits after common carotid balloon injury. Six animals were given valsartan from two days prior to injury until 14 days post-injury. Three control groups (n=6 in each group) were either sham-operated, untreated or treated with the angiotensin-converting enzyme (ACE) inhibitor,captopril. Both ACE inhibition and AT,-receptor blockade had marked effects on plasma levels of endothelin ET1, thromboxane TXB2 and 6-keto-PGF1-alpha. The most dramatic effects on ET, levels were seen in rabbits treated with valsartan, where levels were reduced to values close to those for sham-operated animals (96.85 vs. 86.45 pg/ml). Captopril treatment led to a statistically significant (p<0.01) reduction in ET1 levels compared with untreated animals, but the reduction was only about half that seen with AT1-receptor blockade. TXB2 levels doubled (202.58 vs.413.28 pg/ml) upon arterial injury in control animals but rose by only 20-35% in rabbits treated with captopril (246.45 pg/ml) or valsartan (268.13). In untreated animals, 6-keto-PGF1-alpha levels decreased slightly after injury, but for both the captopril and valsartan groups, there were significant increases in levels of this prostaglandin derivative, effects attributed to the action of bradykinins. Levels were highest in the captopril-treated animals. Valsartan and captopril treatment led to a significant reduction in neointimal thickness and the extent of lumen stenosis compared with untreated animals. Both treatments were effective in reducing neointimal area and significantly (p<0.05)reduced cell proliferation. The differences between treatments can be attributed to the different actions of the agents, as valsartan leaves the AT2-receptor unblocked, while captopril, through inhibition of Ang II synthesis, prevents stimulation of both receptors.A combination of both treatments may be a possible way forward in the clinical prevention of restenosis.

Endothelins and endothelin receptor antagonists: therapeutic considerations for a novel class of cardiovascular drugs

The 21-amino acid peptide endothelin-1 (ET-1) is the predominant isoform of the endothelin peptide family, which includes ET-2, ET-3, and ET-4. It exerts various biological effects, including vasoconstriction and the stimulation of cell proliferation in tissues both within and outside of the cardiovascular system. ET-1 is synthesized by endothelin-converting enzymes (ECE), chymases, and non-ECE metalloproteases; it is regulated in an autocrine fashion in vascular and nonvascular cells. ET-1 acts through the activation of G(i)-protein-coupled receptors. ET(A) receptors mediate vasoconstriction and cell proliferation, whereas ET(B) receptors are important for the clearance of ET-1, endothelial cell survival, the release of nitric oxide and prostacyclin, and the inhibition of ECE-1. ET is activated in hypertension, atherosclerosis, restenosis, heart failure, idiopathic cardiomyopathy, and renal failure. Tissue concentrations more reliably reflect the activation of the ET system because increased vascular ET-1 levels occur in the absence of changes in plasma. Experimental studies using molecular and pharmacological inhibition of the ET system and the first clinical trials have demonstrated that ET-1 takes part in normal cardiovascular homeostasis. Thus, ET-1 plays a major role in the functional and structural changes observed in arterial and pulmonary hypertension, glomerulosclerosis, atherosclerosis, and heart failure, mainly through pressure-independent mechanisms. ET antagonists are promising new agents in the treatment of cardiovascular diseases.

Pulmonary release and coronary and peripheral consumption of big endothelin and endothelin-1 in severe heart failure: acute effects of vasodilator therapy

BACKGROUND

We investigated plasma endothelin (ET) levels in patients with congestive heart failure (CHF) during treatment for acute decompensation; we also measured imbalances in ET peptides across the pulmonary, coronary, and peripheral circulation. Methods and Results-In patients with severe CHF (n=21; cardiac index [CI], 1.9+/-0.2 L. min(-1). m(-2); pulmonary capillary wedge pressure [PCWP], 31+/-1 mm Hg), vasodilation was achieved with the nitric oxide donor sodium nitroprusside (n=11) or with the alpha(1)-antagonist urapidil (nitric oxide-independent, n=10). ET concentrations were determined from arterial blood and blood from the pulmonary artery, coronary sinus, and antecubital vein. Depending on sites of measurement, baseline big ET and ET-1 levels were, respectively, 12 to 16 times and 5 to 11 times higher than in controls (n=11), and 4 to 6 times and 2 to 3 times higher than in patients with moderate CHF (n=10; CI, 2.7+/-0.3 L. min(-1). m(-2); PCWP, 14+/-2 mm Hg). Patients with severe CHF demonstrated pulmonary net release and coronary and peripheral net consumption of both peptides (ie, arterial levels [big ET, 7.3+/-1.3 pmol/L; ET-1, 1.8+/-0.1 pmol/L] were higher than levels in the pulmonary artery [6.7+/-1.2 pmol/L; 1. 3+/-0.1 pmol/L], coronary sinus [6.4+/-1.0 pmol/L; 1.4+/-0.1 pmol/L], and antecubital vein [6.6+/-1.1 pmol/L; 1.3+/-0.1 pmol/L]). In these patients, sodium nitroprusside (SNP) and urapidil resulted in comparable hemodynamic improvement after 6 hours (CI: SNP, 63+/-2%; urapidil, 72+/-3%; PCWP: SNP, -50+/-2%; urapidil, -47+/-2%) and a maximum decrease in ET peptides by >50%. After 3 hours, pulmonary net release and coronary and peripheral net consumption were no longer detectable.

CONCLUSIONS

In patients with severe CHF, the lungs act as a producer and the heart and the periphery act as consumers of elevated circulating ETs. Short-term vasodilator therapy decreases ETs and restores their pulmonary, coronary, and peripheral balance.

Mechanical unloading versus neurohumoral stimulation on myocardial structure and endocrine function In vivo

BACKGROUND-Mechanical load and humoral stimuli such as endothelin (ET) and angiotensin II (Ang II) are potent modulators of cardiac structure and endocrine function, specifically gene expression and production and release of atrial natriuretic peptide (ANP). We define the contribution of mechanical load compared with neurohumoral stimulation in vivo with specific focus on myocardial and circulating ANP during chronic myocardial unloading produced by thoracic inferior vena caval constriction (TIVCC). METHODS AND RESULTS-TIVCC was produced by banding the IVC for 10 days in 7 dogs, whereas in the 6 control dogs, the band was not constricted. TIVCC was characterized by a decrease in cardiac output, right atrial pressure, and left ventricular (LV) end-diastolic diameter and marked activation of ET and Ang II in plasma and atrial and ventricular myocardium. Despite neurohumoral stimulation, LV mass index and myocyte diameters in unloaded hearts decreased, reflecting myocyte atrophy. The total number of myocytes in the LV remained unchanged. Atrial stores of ANP increased, but plasma ANP did not change, in association with a trend toward ANP gene expression to decrease in unloaded hearts. CONCLUSIONS-Chronic mechanical unloading of the heart results in myocardial atrophy and lack of activation of ANP synthesis despite marked neurohumoral stimulation by the growth promoters ET and Ang II.

Endothelin-1 attenuates bradykinin-induced hypotension in rats

Endothelin-1 has vasoconstrictor and mitogenic properties and may contribute to the pathogenesis of hypertension by enhancing vasoconstrictor mechanisms. In this study, we investigated the ability of endothelin-1 decrease the hypotensive effects of the vasodilator bradykinin in anesthetized rats. We also studied the effects a two-week oral pre-treatment with losartan (10 mg/kg/day) or enalapril (25 mg/kg/day) on endothelin-1-induced changes in the hypotensive responses to bradykinin. Bradykinin (0.4, 1.6, 6.4, and 25 mcg/kg, i.v.) induced dose-dependent hypotensive responses which were attenuated (P<0.05) by endothelin-1 (2 mcg/kg, i.v.). This effect of endothelin-1 was abolished by the mixed endothelin receptor antagonist N-Acetyl-alpha-[10,11-Dihydro-5H-dibenzo[a, d]cycloheptadien-5-yl]-D-Gly-Leu-Asp-Ile-Ile-Trp (PD145065, 1 mg/kg, i.v.). Endothelin-1 also decreased (P<0.05) the responses to bradykinin in rats pre-treated with losartan, but had no effect in rats pre-treated with enalapril. These results suggest that endothelin-1 may contribute to the development of hypertension by decreasing the responses to bradykinin through a mechanism not involving angiotensin AT(1) receptors, although the inhibition of angiotensin converting enzyme blunted the effect of endothelin-1.

Endothelin and renal vascular fibrosis: of mice and men

The present review focuses on recent data regarding the role of endothelin as a mediator of renal vascular fibrosis. Following a brief description of the endothelin system, the question of whether endothelin is involved in hypertensive mechanisms is examined in experimental, genetic and transgenic animal models. Evidence is provided that implicates endothelin as an important factor of the development of tissue fibrosis and end-organ damage associated with hypertension, with particular emphasis on renal vascular fibrosis. Data indicating that endothelin interacts with other vasoconstrictor systems, such as angiotensin II, are also considered. Finally, results from preliminary clinical studies using endothelin receptor antagonists to treat cardiac and renal pathologies are briefly discussed.

Inhibition by calcium antagonism of circulating and renal endothelin in experimental congestive heart failure

Endothelin (ET) is a potent vasoconstrictor and sodium-regulating peptide whose tissue and plasma concentrations are increased in congestive heart failure (CHF). ET may mediate its vasoconstrictor and sodium-regulatory actions secondary to an increase in intracellular calcium. Calcium influx may augment ET synthesis. Although felodipine, a dihydropyridine calcium-channel antagonist, is effective in reducing vascular resistance in generalized vasoconstriction, its actions in CHF on circulating and local tissue ET remain undefined. The current studies were designed to determine the modulating actions of felodipine (oral, 40 mg/day for 7 days; n = 6) in an experimental canine model of CHF produced by chronic thoracic inferior vena caval constriction (TIVCC) compared with normal (n = 7) and TIVCC-alone (n = 7) dogs. We hypothesized that felodipine would decrease circulating and renal ET. Plasma ET was significantly increased in TIVCC compared with normal dogs (26 +/- 0. 5 vs. 12 +/- 0.7 pg/ml, P < 0.05) and was markedly decreased by felodipine compared with TIVCC alone (14 +/- 3 vs. 26 +/- 0.5 pg/ml, P < 0.05). Renal ET immunohistochemical staining demonstrated the presence of ET in normal kidney, which was markedly increased in renal cortex and medulla in TIVCC dogs. Renal cortical and medullary ET staining densities were markedly decreased with felodipine compared with those with TIVCC alone. In the TIVCC + felodipine group, cardiovascular hemodynamics also was markedly improved compared with the TIVCC-alone group [systemic vascular resistance: 27 +/- 2 vs. 44 +/- 3 resistance units (RU), P < 0.05; pulmonary vascular resistance: 3.3 +/- 0.1 vs. 5.7 +/- 0.4 RU, P < 0.05; cardiac output: 2.9 +/- 0.2 vs. 1.7 +/- 0.1 l/min, P < 0.05]. This study demonstrates important modulating inhibitory actions of felodipine on renal and plasma ET in an experimental model of CHF.

Angiotensin II activates collagen type I gene in the renal vasculature of transgenic mice during inhibition of nitric oxide synthesis: evidence for an endothelin-mediated mechanism

BACKGROUND

Hypertension is frequently associated with renal vascular fibrosis. The purpose of this study was to investigate whether angiotensin II (Ang II) is involved in this fibrogenic process.

METHODS AND RESULTS

Experiments were performed on transgenic mice harboring the luciferase gene under the control of the collagen I-alpha(2) chain promoter [procolalpha(2)(I)]. Hypertension was induced by chronic inhibition of NO synthesis (N(G)-nitro-L-arginine methyl ester, L-NAME). Procolalpha(2)(I) activity started to increase in the renal vasculature after 4 weeks of L-NAME treatment (P<0.01) and at 14 weeks reached 3- and 8-fold increases over control in afferent arterioles and glomeruli, respectively (P<0.001). Losartan, an AT(1) receptor antagonist, given simultaneously with L-NAME prevented the increase of procolalpha(2)(I) levels and attenuated the development of renal vascular fibrosis without normalizing systolic pressure increase. Because we found previously that endothelin mediated renal vascular fibrosis in the L-NAME model, the interaction between Ang II, endothelin, and procolalpha(2)(I) was investigated in ex vivo and short-term in vivo experiments. In both conditions, the Ang II-induced activation of procolalpha(2)(I) in renal cortex was blocked by an endothelin receptor antagonist.

CONCLUSIONS

During chronic inhibition of NO, the collagen I gene becomes activated, leading to the development of renal vascular fibrosis. Ang II is a major player in this fibrogenic process, and its effect on collagen I gene is independent of systemic hemodynamics and is at least partly mediated by the profibrogenic action of endothelin.

Chronic endothelin receptor antagonism preserves coronary endothelial function in experimental hypercholesterolemia

BACKGROUND

Endothelin-1 (ET-1) is an endothelium-derived peptide that constricts coronary vessels through stimulation of the ET-A and ET-B receptors. Experimental porcine hypercholesterolemia is associated with impaired coronary endothelial function and elevated ET-1 concentrations. This study was designed to test the hypothesis that chronic endothelin receptor antagonism preserves coronary endothelial function in experimental hypercholesterolemia.

METHODS AND RESULTS

Acetylcholine (10(-6) to 10(-4) mol/L) was serially infused into the left anterior descending coronary artery in pigs at baseline and after 12 weeks of a high-cholesterol diet. In the interim, the animals were randomized to 3 groups: Group 1 received no therapy, group 2 received 3 mg/kg per day RO 48-5695, a combined ET-A/ET-B receptor antagonist, and group 3 received 4 mg/kg per day ABT-627, a selective ET-A receptor antagonist. Percent change in coronary artery diameter, coronary blood flow, and coronary vascular resistance were calculated on the basis of quantitative coronary angiography and intracoronary Doppler. At 12 weeks, total cholesterol was significantly and similarly increased in all groups. Chronic endothelin receptor antagonism significantly increased coronary blood flow in response to acetylcholine at 12 weeks (group 1: -41.6%+/-10.7%, group 2: -4.7%+/-11.9%, group 3: 11.4%+/-7.4%).

CONCLUSIONS

Chronic endothelin receptor antagonism preserves coronary endothelial function in experimental hypercholesterolemia. This study supports the role for ET-1 in the pathogenesis of endothelial function. Moreover, endothelin receptor antagonists may have a therapeutic role by maintaining coronary endothelial function in pathophysiological states.

Effects of hypertension, diabetes mellitus, and hypercholesterolemia on endothelin type B receptor-mediated nitric oxide release from rat kidney

BACKGROUND

Although endothelin-1 is a potent vasoconstrictor peptide, stimulation of endothelin type B receptor (ETBR) causes bidirectional changes in vascular tone, ie, vasodilation and vasoconstriction. Roles of ETBR in pathological conditions are largely unknown.

METHODS AND RESULTS

We studied the effect of BQ-3020, a highly selective ETBR agonist, on renal vascular resistance and nitric oxide (NO) release in the isolated, perfused kidney of rats with hypertension, diabetes mellitus, and hypercholesterolemia. Immunohistochemistry of endothelial NO synthase and ETBR was also examined. Infusion of BQ-3020 at concentrations of </=10(-10) mol/L reduced renal perfusion pressure in Dahl salt-resistant (R) rats but increased renal perfusion pressure in Dahl salt-sensitive (S) rats (10(-10) mol/L: -10.3+/-0. 6% versus 11.2+/-1.5%, R versus S; P<0.01). BQ-3020 caused a dose-dependent release of NO in both R and S rats, although the level of NO release in S rats was lower, as detected by chemiluminescence (10(-10) mol/L: 10.7+/-0.7 versus 3.1+/-0.4 fmol/min per gram of kidney, R versus S; P<0.01). Similar effects of BQ-3020 were observed in streptozotocin-induced diabetic rats and diet-induced hypercholesterolemic rats. Expression of endothelial NO synthase decreased in S rats but not in diabetic or hypercholesterolemic rats. In contrast, expression of ETBR in the endothelium was decreased in all 3 disease models compared with that in the vascular smooth muscle cell.

CONCLUSIONS

These results suggest that impaired NO release in response to stimulation of ETBR is due, at least in part, to a decrease in endothelial ETBR and may play a role in vascular dysfunction usually associated with arteriosclerosis-related diseases.

Maintenance of blood pressure in normotensive dogs by endothelin

The role of endothelin (ET)-1 in blood pressure homeostasis and the interaction with the renin-angiotensin system (RAS) was investigated in normotensive conscious dogs. ETA receptors were blocked by LU-135252 (1-30 mg/kg); trandolapril (2 mg/kg) or losartan (10 mg/kg) was used to inhibit the RAS. LU-135252 in oral doses of 3-30 mg/kg significantly reduced mean arterial pressure (MAP) by approximately 10 mmHg maximally, whereas trandolapril or losartan were without any effect. MAP reduction was more pronounced when LU-135252 was combined with either losartan (-15.5 +/- 3.2 mmHg; 2 h postadministration; P < 0.05) or trandolapril (-30.9 +/- 3.6 mmHg; P < 0.05). When endogenous nitric oxide (NO) generation was blocked but NO concomitantly infused, this synergistic effect on MAP was prevented. The data show that ET-1 contributes to the maintenance of blood pressure via ETA receptors. Furthermore, ET-1 and ANG II play a prominent role in the control of blood pressure by opposing the effects of NO. The pronounced blood pressure fall after combined blockade of ETA receptors and the RAS may be mediated by an enhanced release of NO.

Contribution of endothelin to renal vascular tone and autoregulation in the conscious dog

Exogenous endothelin-1 (ET-1) is a strong vasoconstrictor in the canine kidney and causes a decrease in renal blood flow (RBF) by stimulating the ETA receptor subtype. The aim of the present study was to investigate the role of endogenously generated ET-1 in renal hemodynamics under physiological conditions. In six conscious foxhounds, the time course of the effects of the selective ETA receptor antagonist LU-135252 (10 mg/kg iv) on mean arterial blood pressure (MAP), heart rate (HR), RBF, and glomerular filtration rate (GFR), as well as its effects on renal autoregulation, were examined. LU-135252 increased RBF by 20% (from 270 +/- 21 to 323 +/- 41 ml/min, P < 0.05) and HR from 76 +/- 5 to 97 +/- 8 beats/min (P < 0. 05), but did not alter MAP, GFR, or autoregulation of RBF and GFR. Since a number of interactions between ET-1 and the renin-angiotensin system have been reported previously, experiments were repeated during angiotensin converting enzyme (ACE) inhibition by trandolaprilat (2 mg/kg iv). When ETA receptor blockade was combined with ACE inhibition, which by itself had no effects on renal hemodynamics, marked changes were observed: MAP decreased from 91 +/- 4 to 80 +/- 5 mmHg (P < 0.05), HR increased from 85 +/- 5 to 102 +/- 11 beats/min (P < 0.05), and RBF increased from 278 +/- 23 to 412 +/- 45 ml/min (P < 0.05). Despite a pronounced decrease in renal vascular resistance over the entire pressure range investigated (40-100 mmHg), the capacity of the kidneys to autoregulate RBF was not impaired. The GFR remained completely unaffected at all pressure levels. These results demonstrate that endogenously generated ET-1 contributes significantly to renal vascular tone but does not interfere with the mechanisms of renal autoregulation. If ETA receptors are blocked, then the vasoconstrictor effects of ET-1 in the kidney are compensated for to a large extent by an augmented influence of ANG II. Thus ET-1 and ANG II appear to constitute a major interrelated vasoconstrictor system in the control of RBF.

Relationship between endothelin-1 extraction in the peripheral circulation and systemic vascular resistance in patients with severe congestive heart failure

OBJECTIVES

This study was done to determine the spillover and extraction of endothelin-1 (ET-1) in the peripheral circulation, and to evaluate the factors that regulate local ET-1 extraction in the peripheral circulation in patients with congestive heart failure (CHF).

BACKGROUND

The relationship between the spillover and extraction of the ET-1 in the peripheral circulation and systemic vascular resistance (SVR) has not been fully clarified.

METHODS

We measured plasma levels of ET-1 both in femoral artery (FA) and femoral vein (FV) in 93 patients with CHF.

RESULTS

Plasma ET-1 was significantly higher in FV than in FA in New York Heart Association (NYHA) functional class II patients, but there was no difference of ET-1 between FA and FV in functional class III patients. In patients with functional class IV, plasma ET-1 was significantly lower in FV than in FA, and SVR was significantly higher than in patients with NYHA class II or class III. Moreover, a significant positive correlation existed between plasma ET-1 extraction across the lower leg and SVR in these patients. Among the various neurohumoral factors and hemodynamics, plasma levels of ET-1, angiotensin II in the FA showed an independent and significant relationship with the plasma arteriovenous difference of ET-1 in the lower limb.

CONCLUSIONS

Circulating ET-1 is extracted in peripheral circulation in patients with severe CHF, suggesting the possibility of upregulation of ET receptors of vascular beds in the lower limb in these patients. The peripheral extraction of ET-1 correlates with SVR in severe CHF patients and is mainly regulated by the local ET-1 and renin angiotensin systems.

Neurohormonal markers of clinical outcome in cardiovascular disease: is endothelin the best one?

Endothelin-1 (ET-1) is the most potent vasoconstrictor yet described. The active 21-amino-acid peptide is derived from the conversion of the inactive precursor "Big ET-1" by an enzyme called endothelin-converting enzyme. In addition to its potent action as a vasoconstrictor, endothelin promotes growth and proliferation of smooth muscle and myocardial hypertrophy. ET-1 levels are elevated in acute myocardial infarction (MI), atherosclerosis, renal failure, diabetes, pulmonary hypertension, and congestive heart failure (CHF). ET-1 levels correlate extremely well with the seriousness of the pathophysiologic condition. ET-1 levels at 72 h post MI accurately predict long-term survival. In patients with heart failure, ET-1 levels also predict long-term outcome, with the prognosis being severely compromised in patients with elevated ET-1 levels. Levels of plasma big ET-1 have been demonstrated to predict 1-year mortality and have been shown to be a better predictor of 1-year outcome than plasma atrial natriuretic peptide and norepinephrine, NYHA class, age, and echocardiographic left ventricular parameters. Although a small number of studies have reported beneficial effects of ACE inhibitors on ET-1 levels in animal models, most reports in humans have not found an effect of ACE inhibitors on ET-1 levels. Only one ACE inhibitor, fosinopril, has been shown to be effective in normalizing ET-1 levels in clinically relevant situations, such as the long-term study of patients with CHF. This observation may point to a superior role of fosinopril compared with other ACE inhibitors in CHF patients and may indicate beneficial effects of fosinopril beyond blood pressure control.

Impact of neuroendocrine activation on coronary artery disease

Several independent predictors of the risk of atherosclerosis are known including plasma cholesterol concentration, cigarette smoking, elevated blood pressure, as well as genetic factors such as non-insulin-dependent diabetes and plasma fibrinogen. Also known are the 3 major elements of the pathogenesis of atherosclerosis, involving modification of endothelial function, changes in vascular tone, and clinical sequelae of hyperplasia of smooth muscle cells in the intima of the affected blood vessels. This article further examines vasoconstrictor/vasodilator balance, the role of angiotensin II, and the significant role played by the endothelium in the complex events and interactions that occur both with smooth muscle cells and platelets. Clinical evidence of endothelial dysfunction in coronary artery disease is presented. The importance of the association of the progression of coronary artery disease with signs of neuroendocrine activation, the relation of endothelin-1 to mechanisms of neuroendocrine activation, and how the counteraction of this activation may have beneficial effects on disease progression are discussed.

Autocrine/paracrine determinants of strain-activated brain natriuretic peptide gene expression in cultured cardiac myocytes

The application of mechanical strain leads to activation of human brain natriuretic peptide gene promoter activity, a marker of hypertrophy, in cultured neonatal rat ventricular myocytes. We have used a combination of transient transfection analysis and reverse transcriptase-polymerase chain reaction to examine the role of locally produced factors in contributing to this activation. Conditioned media from strained, but not static, cultures led to a dose-dependent increase in human brain natriuretic peptide gene promoter activity. This increase was completely blocked by losartan or BQ-123, implying a role for angiotensin and endothelin as autocrine/paracrine mediators of the response to strain. Inclusion of the same antagonists in the cultures themselves led to only partial inhibition (approximately 60%), whereas inclusion of exogenous endothelin or angiotensin II resulted in amplification of the strain response. Angiotensin II and endothelin appear to be arrayed in series in the regulatory circuitry; the angiotensin response was blocked by BQ-123, whereas the endothelin response was unaffected by losartan. Mechanical strain was also shown to stimulate expression of the endogenous angiotensinogen, angiotensin-converting enzyme, and endothelin genes in this system. Collectively, these data indicate that locally generated angiotensin II and endothelin, acting in series, play an important autocrine/paracrine role in mediating strain-dependent activation of cardiac-specific gene expression.

Losartan but not verapamil inhibits angiotensin II-induced tissue endothelin-1 increase: role of blood pressure and endothelial function

Endothelin partially mediates angiotensin (Ang) II-induced vascular changes in vivo. This study investigated the effects of the angiotensin type 1 receptor antagonist losartan and the calcium channel blocker verapamil on vascular reactivity and tissue endothelin-1 levels in aortas of Wistar-Kyoto rats treated for 2 weeks with Ang II (200 ng x kg(-1) x min(-1)). Ang II increased systolic blood pressure (39+/-4 mm Hg, P<0.05). Concomitant treatment with losartan abolished the Ang II-induced pressure increase (P<0.05), whereas verapamil reduced it only partially (P<0.05). In the aortas of rats with Ang II-induced hypertension, tissue endothelin-1 content was increased threefold and contractions to endothelin-1 were impaired (P<0.05). Interestingly, these alterations were normalized by losartan (P<0.05) but not by verapamil. Hence, there was a strong, negative correlation between contractions to endothelin-1 and tissue endothelin-1 content (r=-0.733, P<0.0001). In contrast, both antihypertensive drugs normalized impaired endothelium-dependent relaxations to acetylcholine and reduced the sensitivity of vascular smooth muscle to sodium nitroprusside compared with Ang II-treated rats (P<0.05). Ang II-induced hypertension enhanced endothelium-dependent contractions to acetylcholine, and these were normalized by either drug. In conclusion, these findings suggest that long-term treatment with Ang II modulates endothelin-1 protein expression in the rat aorta. Although both antihypertensive agents lowered blood pressure and normalized endothelial function, only losartan prevented the increase in tissue endothelin-1 content, suggesting that angiotensin type 1 receptor antagonists but not calcium antagonists modulate tissue endothelin-1 in vivo.

New insight into coronary endothelial dysfunction: role of endothelin

The coronary endothelium plays a central role in the modulation of coronary vascular tone via the production and release of vasoactive mediators. A number of cardiovascular disease states are associated with coronary endothelial dysfunction, which results in an imbalance between vasoactive substances. Endothelin is a potent vasoconstrictor produced by the coronary endothelium and has been implicated in the pathogenesis of coronary endothelial dysfunction. This review examines the relationship between endothelin and coronary endothelial dysfunction as it occurs in a number of cardiovascular disease states and explores potential therapeutic options.

Chronic oral endothelin type A receptor antagonism in experimental heart failure

Endothelin-1 (ET-1) is a cardiovascular peptide that binds to two distinct receptors, ET(A) and ET(B), resulting in systemic and regional vasoconstriction, alteration in sodium excretion, mitogenesis, and release of other vasoactive peptides such as atrial natriuretic peptide (ANP). A role for ET-1 has been proposed in congestive heart failure (CHF) based on the increase in circulating ET-1 in this cardiovascular disease state. The present study determined the cardiorenal and endocrine responses to chronic selective oral ETA antagonism in experimental CHF. Two groups of conscious dogs underwent 21 days of pacing-induced CHF. These groups included a control untreated group (n = 6) and a group that received an orally active ET(A) receptor antagonist (A-127722, Abbott Pharmaceuticals, 5 mg/kg PO bid, n = 6). Each group was studied at baseline before the onset of CHF and after 14 and 21 days of CHF. Compared with the CHF control group, the ET(A) receptor antagonism group at 14 days of CHF showed lower mean arterial pressure and systemic vascular resistance. Similarly, ET(A) receptor antagonism markedly attenuated the increase in circulating ANP despite similar atrial pressures. At 21 days of CHF, ET(A) receptor antagonism lowered pulmonary artery pressure, pulmonary vascular resistance, and systemic vascular resistance in association with a higher cardiac output. Plasma ANP remained suppressed. Despite the lower mean arterial pressure and circulating ANP in the ET(A) receptor antagonist group, the absolute decrease in sodium excretion from baseline was less compared with the untreated CHF control group. The present investigation supports the conclusion that endogenous ET-1 participates in the systemic and pulmonary vasoconstriction, the elevation of ANP, and the sodium retention that characterize this model of experimental CHF, suggesting a potential therapeutic role for ET(A) receptor antagonism in CHF.

Cardiovascular actions of ET-B activation in vivo and modulation by receptor antagonism

The endothelin (ET)-B receptor subtype is expressed on vascular endothelial and smooth muscle cells and participates in vasodilatation and vasoconstriction. Controversy exists regarding the role of the ET-B receptor as a mediator of systemic, pulmonary, and renal vasoconstriction in states of marked ET-1 activation. Moreover, the potential activation of endogenous ET-1 with secondary stimulation of the ET-A receptor in response to sarafotoxin S6c (S6c) remains unclear. This study was designed to assess the cardiovascular actions of ET-B activation with S6c in the presence and absence of selective ET-A antagonism with FR-139317 and dual ET-A/ET-B antagonism with SB-209670 in the anesthetized dog. Compared with time control (n = 5), S6c increased from baseline systemic vascular resistance (SVR) [28 +/- 7 vs. 14 +/- 3 resistance units (RU), P < 0.05] and pulmonary vascular resistance (PVR) (3.2 +/- 0.7 vs. 0.9 +/- 0.3 RU, P < 0.05) and decreased cardiac output (CO) (-1.7 +/- 0.3 vs. -0.5 +/- 0.1 l/min, P < 0.05), with no differences in renal vascular resistance in association with increases in plasma ET-1. S6c also decreased mixed venous oxygen saturation (SVO2) (56 +/- 6 vs. 76 +/- 5%, P < 0.05). Selective ET-A receptor antagonism did not affect the actions of S6c, with the exception that ET-A receptor antagonism blocked the increase in SVR to high-dose S6c. Dual ET-A/ET-B receptor antagonism attenuated the increase from baseline in SVR (7 +/- 1 vs. 28 +/- 7 RU, P < 0.05) and PVR (0.7 +/- 0.2 vs. 3.2 +/- 0.7 RU, P < 0.05) and decrease from baseline in CO (-0.9 +/- 0.1 vs. -1.7 +/- 0.3 l/min, P < 0.05) and SVO2 (-7 +/- 3 vs. -20 +/- 3%, P < 0.05) observed with S6c alone. In summary, this study demonstrates an important role of ET-B receptor activation in vivo, which results in increases in plasma ET-1 and systemic and pulmonary vasoconstriction and reductions in CO and SVO2. This study also supports a modest role for the ET-A receptor in mediating the systemic vasoconstrictor response to high-dose S6c.

Acute endothelin-receptor inhibition does not attenuate acetylcholine-induced coronary vasoconstriction in experimental hypercholesterolemia

Endothelin (ET) may mediate the enhanced coronary vasoconstriction associated with hypercholesterolemia. We hypothesized that short-term inhibition of ET receptors attenuates the coronary epicardial vasoconstrictor response to acetylcholine in experimental hypercholesterolemia. ET-1 (group I, n=5; 5 ng x kg[-1] x min[-1]) and acetylcholine (group III, n=7; 10[-6] to 10[-4] mol/L) were given by intracoronary infusion in pigs. ET-1 and acetylcholine were also infused with the specific ETA-receptor blocker FR-139317 (5 microg x kg[-1] x min[-1]; group II, n=6; group IV, n=6). Acetylcholine was also infused with the combined ET-receptor blocker, bosentan (0.5 mg/kg plus 1 mg x kg[-1] x h[-1], group V, n=5). The ETB-receptor agonist sarafotoxin 6c (5 ng x kg[-1] x min[-1]; n=4) was also infused. The percentage change in coronary artery diameter (%deltaCAD) to the infusions was measured at baseline and after 10 weeks of high-cholesterol diet in all animals. Sarafotoxin 6c mildly reduced %deltaCAD at baseline and 10 weeks (-10+/-2% and -12+/-3%, respectively). FR-139317 did not attenuate the epicardial vasoconstrictor response to ET-1 at baseline (%deltaCAD -18+/-8% for group I versus -12+/-6% for group II; P=NS) but did at 10 weeks (%deltaCAD -77+/-14% for group I versus -14+/-6% for group II; P<.05). FR-139317 did not affect the response to acetylcholine at baseline (%deltaCAD 5+/-2% for group III versus 7+/-3% for group IV, P=NS) or at 10 weeks (%deltaCAD -23+/-12% for group III versus -19+/-7% for group IV; P=NS). Bosentan did not affect the response to acetylcholine at baseline or 10 weeks. Short-term ET-receptor inhibition in experimental hypercholesterolemia attenuated the enhanced coronary epicardial vasoconstrictor effects of ET-1 but not acetylcholine-induced coronary epicardial vasoconstriction, suggesting that acetylcholine-induced coronary epicardial vasoconstriction may not be mediated by ET receptors.