Endothelin in human congestive heart failure

Activation of cardiorenal and pulmonary tissue endothelin-1 in experimental heart failure

Endothelin-1 (ET-1) is a peptide that has been implicated in congestive heart failure (CHF). Although increased concentrations of circulating ET-1 have been repeatedly demonstrated, the activation of local ET-1 in target tissues of CHF remains poorly defined. Our objective was to characterize ET-1 tissue concentrations and gene expression of prepro ET-1 in myocardial, renal, and pulmonary tissue in rapid ventricular pacing-induced canine CHF. Progressive rapid ventricular pacing (38 days) resulted in impaired cardiovascular hemodynamics, increased atrial and left ventricular mass, decreased renal sodium excretion, and increased ET-1 plasma concentrations (all P < 0.05). Tissue analysis revealed significant increases in local ET-1 during CHF in left ventricular, renal, and pulmonary tissue, whereas a moderate increase in left atrial ET-1 did not reach statistical significance. In contrast, prepro-ET-1 gene expression was increased more than threefold in pulmonary tissue and more than twofold in left atrial myocardium with no increase in left ventricular or renal gene expression. The present studies demonstrate a differential pattern of ET-1 activation in cardiorenal and pulmonary tissue with a strong accumulation of ET-1 in kidney and lung during CHF. Although the observed increase in left ventricular and renal ET-1 in association with unaltered gene expression is consistent with increased uptake, pulmonary and atrial tissue may contribute to increased circulating and local ET-1 in CHF.

Endothelin A receptor blockade prevents capillary/myocyte mismatch in the heart of uremic animals

In the heart of uremic animals and patients, the number of capillaries per volume of myocardium is reduced. Immunohistochemical studies demonstrated increased cardiac endothelin-1 (ET-1) expression in the left ventricle of uremic animals. Therefore, whether treatment with a selective ET(A)-receptor antagonist prevented such capillary-myocyte mismatch was investigated. Twenty-four h after subtotal nephrectomy, rats were left untreated or started on treatment with the ET(A)-receptor antagonist LU 135252 (20 mg/kg per d) and with the angiotensin-converting enzyme (ACE) inhibitor trandolapril (0.3 mg/kg per d), respectively. BP was monitored by telemetry. Myocardial capillary length density was analyzed by stereologic techniques that avoid anisotropy artifacts. In addition, cardiac ET-1 protein and mRNA were measured using immunohistochemistry, in situ hybridization, and quantitative reverse transcription-PCR. Changes in cardiac ET(A)-and ET(B)-PCR. receptor mRNA were measured using reverse transcription-PCR. Fifteen wk after subtotal nephrectomy, significantly reduced left ventricular capillary length density (3307 +/- 535 mm/mm(3)) was found compared with sham-operated controls (3995 +/- 471 mm/mm(3)); this was also seen in animals that were treated with trandolapril (3503 +/- 533 mm/mm(3)) but not in animals that were treated with LU 135252 (3800 +/- 303 mm/mm(3)). The results support a role of ET-1 in the genesis of left ventricular capillary/myocyte mismatch in uremia.

Cardiomyopathy in AIDS: a pathophysiological perspective

This report addresses issues of pathogenesis, pathophysiology, and epidemiology of an increasingly prevalent cardiomyopathy in acquired immunodeficiency syndrome (AIDS). As patient survival increases with more effective antiretroviral therapy, cardiomyopathy in AIDS will become more apparent. The interactions of cellular and organism factors in AIDS and their relationships to the development of cardiomyopathy are reviewed herein. Amongst the factors addressed in this review are: (1) comorbid conditions found with AIDS, (2) the role of inflammatory heart disease and cytokines in the development of AIDS cardiomyopathy, (3) the pathogenetic role of vascular cells and myocardial cells in the development of cardiomyopathy, (4) the role of myocardial retroviral infection in AIDS, and (5) the impact of toxicity from antiretroviral therapy on the development of cardiomyopathy. Because it is possible that more than 1 of these factors is present in a given patient inflicted with AIDS, a multifactorial pathogenesis in AIDS cardiomyopathy must be considered.

Localization and function of ET-1 and ET receptors in small arteries post-myocardial infarction: upregulation of smooth muscle ET(B) receptors that modulate contraction

Endothelin-1 (ET-1) has been implicated as a mediator of increased vascular tone during development of heart failure post-myocardial infarction (MI). In the present study, expression and pharmacology of ET-1 and its receptors were studied in small mesenteric arteries from rats at 5 and 12 weeks after coronary artery ligation for induction of MI, or sham-operation. In vessels from sham-operated and 5 week post-MI rats preproET-1mRNA, immunoreactive (ir) ET-1, ET(B) receptor mRNA and irET(B) receptor were confined to the endothelium, while ET(A) receptor mRNA was distributed throughout the media. At 12 weeks post-MI, preproET-1 and irET(A) receptor localization was similar but ET(B) receptor mRNA and immunoreactivity were detectable in the media, as well as the endothelium. The ET-1 concentration-response curve (CRC) was progressively shifted to the right in pressurized third generation mesenteric arteries from 5 and 12 week post-MI rats relative to sham-operated rats, with no change in the maximum. The ET(A) receptor antagonist BQ-123 (10(-6) M) induced a rightward shift of the ET-1 CRC in all vessels. Desensitization of ET(B) receptors, by exposure to SRTX S6c (3x10(-8) M), had no effect on the ET-1 CRC in vessels from 5 week post-MI or sham-op rats but induced a leftward shift in vessels from 12 week post-MI rats. These results identify the endothelium as the primary site of ET-1 synthesis in small arteries and the ET(A) receptor as mediating the effects of ET-1 in these vessels. However, ET(B) receptor expression increases in vascular smooth muscle post-MI and is linked to mechanisms that inhibit the contractile response to ET-1.

Hemostatic abnormalities in patients with congestive heart failure: diagnostic significance and clinical challenge

Knowledge of the pathogenesis of congestive heart failure (CHF) has improved greatly in recent years. However, this disease continues to cause one of the highest morbidities and mortalities in the Western world. The pathophysiology of heart failure is complex and much of our understanding revolves strictly around the neurohormonal mechanisms involved. Various pharmacologic interventions have significantly improved morbidity and include ACE inhibitors, beta-blockers, diuretics, and inotropic agents. Yet, no consensus has been reached regarding the use of anticoagulants or antiplatelet agents. It has been suggested that CHF is associated with altered hemostasis, but whether this prothrombotic state contributes to the pathogenesis and progression of the disease is unknown. The purpose of this review article is to discuss our current knowledge of platelet activation, thrombin generation, fibrinolysis, and endothelial dysfunction in CHF patients, and the potential role of anticoagulants and/or antiplatelet agents in preventing these hemostatic abnormalities.

Neuropeptide variability in man

BACKGROUND

Previous studies have established short-term variability in the circulating plasma levels of cardiac peptides such as atrial natriuretic peptide (ANP) and brain natriuretic peptide (BNP). Our aim was to investigate whether such variable patterns could be observed in other vasoactive peptides.

METHODS

We measured the immunoreactivity of vasoactive intestinal polypeptide (VIP), neuropeptide Y (NPY), endothelin-1 (ET-1) and calcitonin gene-related peptide (CGRP) in peripheral venous plasma collected at 2-min intervals over a 20-min period from patients with chronic cardiac failure (CCF) and from control subjects. In a second study, blood samples were obtained at 2-min intervals from the pulmonary artery, femoral artery and antecubital vein from patients with normal cardiac function while right atrial pressure and heart rate were constant.

RESULTS

Peripheral blood VIP, NPY and ET-1 had peaks and troughs (levels > 2SD from the mean) in both patients and controls, with approximate intervals of 10 min. Levels of CGRP showed little variation. The overall levels [median (range); pmol L-1] of VIP [patients 27 (2.1-85.5); controls 9.8 (0-34)] and NPY [patients 20 (0-110); controls 12 (5-19)] were higher in patients (P < 0.05). Circulating plasma levels of ET-1 and CGRP were about the same in both groups [ET-1: patients 18 (2-84); controls 18 (0-48); CGRP: patients 4 (1-18.5), controls 5.5 (1-15); P = NS]. Levels of CGRP, VIP and ET-1 were similar in the pulmonary and femoral arteries, whereas systemic arterial levels of NPY were higher than in the pulmonary artery.

CONCLUSIONS

The data demonstrate marked variability in circulating levels of the neuropeptides studied. In addition, peaks and troughs were observed every 10-15 min from all three vascular beds. If these peptides are secreted in a pulsatile pattern, then interpretations of single measurements should be guarded. Furthermore, this study raises interesting questions about the physiology of hormone secretion in man.

Pharmacokinetics and pharmacodynamic effects of ABT-627, an oral ETA selective endothelin antagonist, in humans

AIMS

Endothelins (ETs) may play a role in the pathogenesis of a variety of cardiovascular diseases. The present study was designed to investigate the pharmacokinetic and pharmacodynamic effects of the orally active ETA selective receptor antagonist ABT-627 in healthy humans.

METHODS

Healthy volunteers were included in two studies with cross-over design. Subjects received single or multiple dose (an 8 day period) administration of oralABT-627 or matched placebo, in a dose range of 0.2-40 mg. The pharmacokinetics of ABT-627 were described and its effects on systemic haemodynamics under resting conditions and on forearm vasoconstriction in response to ET-1 were assessed.

RESULTS

ABT-627 was generally well tolerated in both studies, with transient headache being the most reported adverse event (in 62% vs 4% during placebo, P < 0.05, for Study 1 and in 42% vs 60%, P = 0.2, for Study 2). ABT-627 was rapidly absorbed, reaching maximum plasma levels at approximately 1 h post dose. Single dose ABT-627, at a dose of 20 and 40 mg, inhibited ET-1 induced forearm vasoconstriction at 8 h post dose. Eight days ABT-627 treatment, at a dose level of 5 mg and above, also effectively blocked forearm vasoconstriction to ET-1. ABT-627 caused a significant reduction in peripheral resistance as compared with placebo (16 +/- 1 vs 19 +/- 1, 18 +/- 2 vs 23 +/- 3, 15 +/- 1 vs 17 +/- 1 AU at 1, 5, 20 mg in Study 2) with only a mild decrease in blood pressure (79 +/- 2 vs 84 +/- 3, 80 +/- 4 vs 90 +/- 5, 75 +/- 3 vs 79 +/- 1 at 1, 5, 20 mg in Study 2). ABT-627 caused a moderate dose-dependent increase in circulating immunoreactive ET levels (a maximal increase of 50% over baseline at the 20 mg dose level).

CONCLUSIONS

The oral ETA receptor blocker ABT-627 is well tolerated, rapidly absorbed, effectively blocks ET-1 induced vasoconstriction and causes a decrease in total peripheral resistance and mean arterial pressure. Our data suggest that ABT-627 may be a valuable tool in treatment of cardiovascular disease.

ET-1 in the myocardial interstitium: relation to myocyte ECE activity and expression

Increased plasma levels of endothelin-1 (ET-1) have been identified in congestive heart failure (CHF), but local myocardial interstitial ET-1 levels and the relation to determinants of ET-1 synthesis remain to be defined. Accordingly, myocardial interstitial ET-1 levels and myocyte endothelin-converting enzyme (ECE)-1 activity and expression with the development of CHF were examined. Pigs were instrumented with a microdialysis system to measure myocardial interstitial ET-1 levels with pacing CHF (240 beats/min, 3 wk; n = 9) and in controls (n = 14). Plasma ET-1 was increased with CHF (15 +/- 1 vs. 9 +/- 1 fmol/ml, P < 0.05) as was total myocardial ET-1 content (90 +/- 15 vs. 35 +/- 5 fmol/g, P < 0.05). Paradoxically, myocardial interstitial ET-1 was decreased in CHF (32 +/- 4 vs. 21 +/- 2 fmol/ml, P < 0.05), which indicated increased ET-1 uptake by the left ventricular (LV) myocardium with CHF. In isolated LV myocyte preparations, ECE-1 activity was increased by twofold with CHF (P < 0.05). In LV myocytes, both ECE-1a and ECE-1c mRNAs were detected, and ECE-1a expression was upregulated fivefold in CHF myocytes (P < 0.05). In conclusion, this study demonstrated compartmentalization of ET-1 in the myocardial interstitium and enhanced ET-1 uptake with CHF. Thus a local ET-1 system exists at the level of the myocyte, and determinants of ET-1 biosynthesis are selectively regulated within this myocardial compartment in CHF.

Effects of long-term treatment with nonselective endothelin receptor antagonist, TAK-044, on remodeling of cardiovascular system with sustained volume overload

To assess the role of endothelin-1 (ET-1) on cardiovascular remodeling, nonselective endothelin-receptor antagonist TAK-044 was administered for the long term to rabbits with or without arteriovenous (A-V) shunt formation. Six weeks after sham operation (n = 12) or carotid-jugular shunt formation (n = 21), TAK-044 (30 mg/day) or saline was infused subcutaneously using osmotic mini pumps for another 6 weeks. Twelve weeks after operation, left ventricular (LV) diameter was enlarged with the presence of an A-V shunt; however, the levels of LV diameter and arterial pressure or the postmortem weight of LVs of shunt rabbits were similar between saline and TAK-044 groups. A linear relation of the luminal diameter and the medial cross-sectional area of the left and right carotid arteries was similar between shunt + saline and shunt + TAK-044 groups. In saline groups, myocardial ET-1 levels were higher in shunt than in sham rabbits (217+/-22 vs. 136+/-19 pg/g tissue; p < 0.01 between rabbit groups) without changes in plasma ET-1 concentrations during saline infusion for 6 weeks. Differences in plasma ET-1 levels before and 6 weeks after the administration of TAK-044 were 0.32+/-0.78 and 0.16+/-0.28 pg/ml (NS between periods) in shunt and sham groups, respectively. In TAK-044 groups, myocardial ET-I levels 12 weeks after operation were similarly lower in both sham (105+/-7.4 pg/g tissue) and shunt rabbits (126+/-9.2 pg/g tissue) than in those with saline administration; however, the plasma ET-1 concentrations were increased significantly 6 weeks after TAK-044 administration by 5.0+/-0.6-fold and 3.5 +/-0.3-fold (p < 0.01) of the levels 6 weeks after operation in shunt and sham groups (NS between groups), respectively. Accordingly, myocardial but not plasma ET-1 levels were increased by a long-term burden of volume overload and were attenuated by a long-term administration of TAK-044 without altering drastically the hemodynamics or vascular remodeling. These results suggest that endogenous ET-1 does not play a major role in the compensatory stage of cardiovascular remodeling in the present volume-overload model.

Regulation of ET: pulmonary release of ET contributes to increased plasma ET levels and vasoconstriction in CHF

Endothelin (ET) contributes to the increased systemic vascular resistance and elevated cardiac filling pressures seen in congestive heart failure (CHF). We investigated to what extent ET-mediated vasoconstriction in CHF occurs through an endocrine action of elevated plasma ET or by an autocrine/paracrine mechanism related to induction of vascular ET gene expression. Three weeks of pacing (225 beats/min) induced a marked release of ET-1 from the pulmonary circulation with a sixfold elevation of arterial plasma ET in CHF pigs compared with sham-operated pigs. Arterial plasma ET was the strongest and only independent predictor of systemic vascular resistance. In contrast, vascular preproET-1 and ET-receptor mRNA expression were unaltered or decreased in CHF pigs and did not correlate with indexes of vascular tone. However, myocardial preproET-1 mRNA expression increased twofold in CHF pigs. PreproET-2 and preproET-3 mRNAs were not detectable in cardiovascular tissues. In conclusion, plasma ET was markedly increased because of an augmented release from the pulmonary circulation during CHF, and arterial plasma ET correlated with systemic vascular resistance. The absence of ET induction in the peripheral vasculature suggests that ET increases vascular tone during CHF by an endocrine, not an autocrine/paracrine, mechanism.

Endothelium-dependent and -independent vasoreactivity of rat basilar artery in chronic heart failure

Alterations of vasoreactivity are a well-known phenomenon in chronic heart failure (CHF), and activation of the endogenous endothelin (ET) system is suspected to contribute significantly. Regional differences in alterations of vasoreactivity exist; however, nothing is known about cerebrovascular reactivity in CHF. This is of interest in view of increased stroke risk in CHF. Therefore, 12 weeks after coronary artery ligation to induce CHF in rats, studies of vasoreactivity of the isolated basilar artery (BA) were performed and compared with third-order branches (MA-A3) and the main trunk (MA) of the superior mesenteric artery. Some of the animals received long-term ET-receptor antagonism by 11 weeks of treatment with the selective ET(A)-receptor antagonist LU 135252 or the mixed ET(A)/ET(B)-receptor antagonist bosentan. In rats with CHF, endothelium-dependent relaxation by acetylcholine and A23187 as well as endothelium-independent relaxation by sodium nitroprusside (SNP) was largely unaffected in BA or MA. However, in MA-A3, potency of SNP was diminished without change of maximal effect. ET-1-induced contraction did not differ in arteries from CHF and control rats, either in placeboor ET-receptor antagonist-treated animals. In summary, there was essentially no change of vascular reactivity in similar sized arteries obtained from brain and mesentery. This is in contrast to results on arteries from a variety of vascular regions published previously, thus supporting the concept of organ- and probably time-related changes of vascular function in the development of CHF. The absence of significant alteration of cerebral vasoreactivity may be taken to indicate that changes in cerebral blood flow and increased incidence of ischemic stroke in patients with CHF are caused not by local alterations of vascular function.

Insights into pathogenesis and treatment of cytokines in cardiomyopathy

Our understanding of the pathophysiology of chronic heart failure is rapidly expanding. recent investigations suggest a role for various proinflammatory and vasoconstrictive cytokines in the development and progression of the disease. In particular, tumor necrosis factor-alpha, interlukin-6, and endothelin have all been implicated in heart failure desease progression. These cytokines appear to be activated in response to a remodeling, induction of programmed cell death, neurohormonal activation, and hemodynamics, these agents cause a variety of deleterious effects in the setting of ventricular dysfunction. Investigational inhibitors and antagonists of these substances show promise for the future treatment of heart failure.

Neurohormones in an ovine model of compensated postinfarction left ventricular dysfunction

Clinical heart failure, often the result of myocardial infarction, may be preceded by a period of compensated left ventricular impairment. There is substantial need for an experimental model that reflects this human condition. In sheep, coronary artery ligation produced consistent left ventricular anteroapical myocardial infarctions resulting in chronic (5 wk), stable hemodynamic changes compared with sham controls, including reductions in ejection fraction (51 +/- 2 vs. 30 +/- 5%, P < 0.001), cardiac output (6.3 +/- 0.2 vs. 5.1 +/- 0.2 l/min, P < 0.01), and arterial pressure (93 +/- 2 vs. 79 +/- 3 mmHg, P < 0.001), and increases in cardiac preload (left atrial pressure, 3.3 +/- 0.1 vs. 8.3 +/- 1.3 mmHg, P < 0.001). These changes were associated with acute and sustained increases in plasma concentrations of atrial natriuretic peptide (ANP; 5 wk, 11 +/- 2 vs. 27 +/- 5 pmol/l, P < 0.001), brain natriuretic peptide (BNP; 3 +/- 0.2 vs. 11 +/- 2 pmol/l, P < 0.001), and amino-terminal pro-brain natriuretic peptide (NT-BNP; 17 +/- 3 vs. 42 +/- 12 pmol/l, P < 0.001). Significant correlations were observed between plasma levels of the natriuretic peptides (ANP, day 7 to week 5 samples; BNP and NT-BNP, day 1 to week 5 samples) and changes in left ventricular volumes and ejection fraction. In contrast, renin activity, aldosterone, catecholamines, and endothelin were not chronically elevated postinfarction and were not related to indexes of ventricular function. Coronary artery ligation in sheep produces the pathological, hemodynamic, and neurohormonal characteristics of compensated left ventricular impairment secondary to myocardial infarction. Plasma concentrations of the cardiac natriuretic peptides are sensitive markers of left ventricular dysfunction. This is a reproducible model that reflects the clinical condition and should prove suitable for investigating the pathophysiology of, and experimental therapies in, early left ventricular dysfunction.

The role of inflammatory mediators in chronic heart failure: cytokines, nitric oxide, and endothelin-1

There is now considerable evidence to suggest that neurohormonal and immune mechanisms may play a central role in the pathogenesis of chronic heart failure (CHF), which is likely to have important implications for the management of this condition. It has been proposed that CHF is a state of immune activation with inflammatory cytokines contributing to both the central and the peripheral manifestations of this syndrome. The immune system is the body's natural defence mechanism against infection and other stresses, which has several different components that interact with each other in a complex manner. The main components which are thought to be relevant to the pathogenesis of CHF are: cytokines, adhesion molecules, autoantibodies, nitric oxide, and endothelin-1, and this review will concentrate on these factors. This article will also discuss the potential role of anti-cytokine therapies in the treatment of CHF.

Surviving heart failure: Robert L. Frye lecture

Heart failure is increasing in both incidence and prevalence and is associated with a high mortality. In patients with heart failure, coronary artery disease is the cause for about two thirds. Pathophysiologic changes have been linked to altered muscle function and hemodynamics, elevated neurohormones, and, more recently, cellular mechanisms, including apoptosis. Standard triple therapy for symptomatic heart failure consists of an angiotensin-converting enzyme (ACE) inhibitor, digoxin, and a diuretic. In patients with severe heart failure, spironolactone should be added. In large clinical trials, ACE inhibitors, spironolactone, and beta-blockers have reduced mortality. Other drugs may be helpful in the treatment of heart failure. Amiodarone is the antiarrhythmic drug of choice in patients with symptomatic arrhythmias and also has a role in the treatment of dilated cardiomyopathy. Angiotensin II receptor blockers are being compared with ACE inhibitors and appear promising. Newer agents being tested include antagonists to endothelin and tumor necrosis factor. Overall, it is clear that polypharmacy is the standard of care for patients with heart failure. A future challenge will be to prevent heart failure from occurring.

Brain blood flow patterns after the development of congestive heart failure: effects of treadmill exercise

OBJECTIVE

Congestive heart failure (CHF) is associated with left ventricular (LV) failure, neurohormonal system activation, and diminished exercise capacity. Although alterations in systemic vascular resistive properties have been recognized to occur with CHF, whether and to what degree perfusion abnormalities occur within the brain after the development of CHF remain poorly understood. Accordingly, the present study measured brain blood flow patterns in pigs after the development of pacing-induced CHF at rest and after treadmill-induced exercise.

MEASUREMENTS AND MAIN RESULTS

Adult pigs (n = 6) were studied before and after the development of pacing-induced CHF (240 beats/min, 3 wks) at rest and with treadmill exercise (3 mph, 15 degrees incline, 10 mins). At rest, LV stroke volume was reduced nearly 45% with CHF compared with normal (20+/-2 vs. 36+/-3 mL; p<.05) and was associated with a more than four-fold increase in plasma catecholamines, renin activity, and endothelin concentration. At rest, global brain blood flow was reduced with CHF compared with the normal state (1.06+/-0.13 vs. 0.81+/-0.06 mL/min/g; p<.05). At rest, blood flow to the frontal lobe, cerebellum, and medullary regions was reduced by approximately 30% in the CHF group (p<.05). With treadmill exercise, LV stroke volume remained lower and neurohormonal concentrations remained higher in the pacing CHF state. Global brain blood flow increased significantly with treadmill exercise in both the normal and CHF states (4.58+/-1.36 and 2.01+/-0.29 mL/min/g; p<.05) but remained reduced in the CHF state compared with normal values (p<.05). In the CHF group, the relative increase in blood flow with exercise was significantly blunted in the parietal and occipital regions of the cerebrum and the suprapyramidal region of the medulla.

CONCLUSIONS

The development of pacing-induced CHF was associated with diminished brain perfusion under resting conditions and with treadmill exercise. These perfusion abnormalities with pacing CHF were pronounced in specific regions of the brain. The defects in brain perfusion with the development of CHF may contribute to abnormalities in centrally mediated processes of cardiovascular regulation.

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.

Effects of long-term therapy with bosentan on the progression of left ventricular dysfunction and remodeling in dogs with heart failure

OBJECTIVES

In this study, we examined the effects of long-term therapy with bosentan on the progression of LV dysfunction and remodeling in dogs with moderate HF.

BACKGROUND

Acute intravenous administration of bosentan, a mixed endothelin-1 type A and type B receptor antagonist, was shown to improve left ventricular (LV) function in patients and dogs with heart failure (HF).

METHODS

Left ventricular dysfunction was induced by multiple, sequential intracoronary microembolizations in 14 dogs. Embolizations were discontinued when LV ejection fraction (EF) was between 30% and 40%. Dogs were randomized to three months of therapy with bosentan (30 mg/kg twice daily, n = 7) or no therapy at all (control, n = 7).

RESULTS

In untreated dogs, EF decreased from 35 +/- 1% before initiating therapy to 29 +/- 1% at the end of three months of therapy (p = 0.001), and LV end-diastolic volume (EDV) and end-systolic volume (ESV) increased (EDV: 71 +/- 3 vs. 84 +/- 8 ml, p = 0.08; ESV: 46 +/- 2 vs. 60 +/- 6 ml, p = 0.03). By contrast, in dogs treated with bosentan, EF tended to increase from 34 +/- 2% before initiating therapy to 39 +/- 1% at the end of three months of therapy (p = 0.06), and EDV and ESV decreased (EDV: 75 +/- 3 vs. 71 +/- 4 ml, p = 0.05; ESV: 48 +/- 2 vs. 43 +/- 3 ml, p = 0.01). Furthermore, compared with untreated dogs, dogs treated with bosentan showed significantly less LV cardiomyocyte hypertrophy and LV volume fraction of interstitial fibrosis.

CONCLUSIONS

In dogs with moderate HF, long-term therapy with bosentan prevents the progression of LV dysfunction and attenuates LV chamber remodeling. The findings support the use of mixed endothelin-1 receptor antagonists as adjuncts to the long-term treatment of HF.

Impaired endothelium-mediated vasodilation is not the principal cause of vasoconstriction in heart failure

The extent to which abnormal endothelium-dependent vasodilator mechanisms contribute to abnormal resting vasoconstriction and blunted reflex vasodilation seen in heart failure is unknown. The purpose of this study was to test the hypothesis that the resting and reflex abnormalities in vascular tone that characterize heart failure are mediated by abnormal endothelium-mediated mechanisms. Thirteen advanced heart-failure patients (New York Heart Association III-IV) and 13 age-matched normal controls were studied. Saline, acetylcholine (20 microg/min), or L-arginine (10 mg/min) was infused into the brachial artery, and forearm blood flow was measured by venous plethysmography at rest and during mental stress. At rest, acetylcholine decreased forearm vascular resistance in normal subjects, but this response was blunted in heart failure. During mental stress with intra-arterial acetylcholine or L-arginine, the decrease in forearm vascular resistance was not greater than during saline control in heart failure [saline control vs. acetylcholine (7 +/- 3 vs. 6 +/- 3, P = NS) or vs. L-arginine (9 +/- 2 units, P = NS)]. The increase in forearm blood flow was not greater than during saline control in heart failure [saline control vs. acetylcholine (1. 2 +/- 0.3 vs. 1.3 +/- 0.3, P = NS), or vs. L-arginine (1.2 +/- 0.2 ml x min(-1) x 100 ml(-1), P = NS)]. Furthermore, during mental stress with nitroprusside, the decrease in forearm vascular resistance was not greater than during saline control [saline control vs. nitroprusside (7 +/- 3 vs. 5 +/- 4 ml x min(-1) x 100 g(-1), P = NS)], and the increase in forearm blood flow was not greater than during saline control [saline control vs. nitroprusside (1.2 +/- 0.3 vs. 1.3 +/- 0.5 ml x min(-1) x 100 g(-1), P = NS)]. Because the endothelial-independent agent nitroprusside was unable to restore resting and reflex vasodilation to normal in heart failure, we conclude that impaired endothelium-mediated vasodilation with acetylholine-nitric oxide cannot be the principal cause of the attenuated resting- or reflex-mediated vasodilation in heart failure.

Contribution of the endothelin system to the renal hypoperfusion associated with experimental congestive heart failure

The objective of this study was to define further the local activation of endothelin-1 (ET-1) and the ETA receptor as well as the functional consequences of activated ET-1 for renal hypoperfusion associated with experimental congestive heart failure (CHF). We studied eight rabbits permanently instrumented with Doppler flow probes around the renal arteries before and after the induction of epinephrine-induced CHF. CHF was characterized by left-ventricular dysfunction (fractional shortening 34+/-2% vs. 46+/-3%; p < or = 0.05) and dilatation (LVEDd 13.6+/-0.3 vs. 11.5+/-0.4 mm; p < or = 0.05), decreased mean arterial pressure (59.4+/-2.9 vs. 74.6+/-3.7 mm Hg; p < or = 0.05), increased heart rate (236+/-11 vs. 216+/-8 beats/min; p < or = 0.05) and renal vasoconstriction (vascular resistance 49.65 +/-8.55 vs. 24.61+/-5.85 U; p < 0.05; blood flow velocity, 1.58+/-0.21 vs. 3.63+/-0.31 kHz; p < 0.05). ET-1 concentrations were significantly increased not only in plasma (7.67+/-0.47 vs. 4.56 +/-0.69 pg/ml; p < 0.05) but also in renal tissue (4.8+/-0.5 vs. 3.5 +/-0.64 pg/mg; p < 0.05). Northern analysis revealed an unchanged expression of ETA receptor messenger RNA (0.79+/-0.05 vs. 0.77+/-0.04 arbitrary units; NS) in renal tissue, whereas expression of prepro-ET-1 was below the range of detection. In CHF, selective ETA-receptor antagonism with BQ-123 (1 mg/ kg bolus, i.v.) significantly increased renal blood flow velocity (3.07+/-0.38 vs. 1.33+/-0.19 kHz; p < 0.05) and reduced renal vascular resistance (29.63+/-6.22 vs. 58.17+/-8.75 U; p < 0.05) without significant effects on mean arterial pressure or heart rate. These studies demonstrate activation of the renal ET system, unaltered gene expression, and functional integrity of the renal ETA receptor in CHF. They indicate a principal functional role for the ETA receptor in renal vasoconstriction and suggest blockade of the renal ETA receptor as an important strategy to attenuate renal hypoperfusion in CHF.

Role of endothelin-1 in myocardial failure

Endothelin-1 (ET-1) is a potent molecule produced throughout the cardiovascular system; it can exert important effects on both the structure and function of vascular smooth muscle cells and cardiac myocytes. ET-1 appears to play a central role in the physiological regulation of cardiovascular function, particularly in the vasculature. The known actions of ET-1 and the demonstration that plasma ET-1 is elevated in patients with heart failure has raised the possibility that this molecule could play a role in the pathophysiology of heart failure. This thesis has been supported and furthered by studies in animal models of heart failure that demonstrate the salutary, short-term effects of ET-1 receptor antagonists on hemodynamic function, as well as improved ventricular remodeling and survival with long-term administration. Early clinical trials with these ET receptor blockers have demonstrated systemic vasodilation. Long-term trials to determine the effects of ET-1 blockade on symptoms and survival are under way.

Augmented basal nitric oxide production contributes to maintenance of coronary blood flow in dogs with pacing-induced heart failure

It remains controversial whether basal nitric oxide (NO) production in coronary resistance vessels in heart failure is enhanced or not. A transonic Doppler flow probe was placed around the left anterior descending coronary artery, and complete atrioventricular block was produced in fifteen dogs. The coronary pressure-flow relationships during long diastole were analyzed without and with pacing-induced heart failure. Three weeks after pacing at 240/min, plasma norepinephrine and renin activity significantly rose. Right atrial pressure and left ventricular end-diastolic pressure increased, and cardiac output and coronary perfusion pressure decreased; however, mean coronary blood flow did not change after pacing (55 +/- 5 to 52 +/- 5 ml/min/100 g, mean +/- SEM). The slope of the diastolic coronary pressure-flow relationship became steeper (1.22 +/- 0.13 to 1.62 +/- 0.09 ml/min/100 g/mmHg, p < 0.05) with a slight increase in the measured zero-flow pressure (29.5 +/- 1.1 to 32.8 +/- 1.5 mmHg, p < 0.05) after pacing. After pretreatment with indomethacin, administration of NG-nitro-L-arginine methyl ester caused an equal increase in the zero-flow pressure before (31.4 +/- 1.7 to 39.2 +/- 2.2 mmHg, p < 0.05) and after heart failure (33.9 +/- 2.5 to 41.6 +/- 2.2 mmHg, p < 0.05), and more decline of the slope of the coronary pressure-flow relationship in heart failure (1.86 +/- 0.22 to 1.20 +/- 0.05 ml/min/100 g/mmHg, p < 0.05) than before heart failure (1.11 +/- 0.12 to 1.05 +/- 0.11 ml/min/100 g/mmHg, N.S.). This indicates that in failing hearts the vasodilatory action of NO in small vessels predominates despite the presence of several vasoconstricting factors. These results suggest that coronary blood flow is maintained despite detrimental hemodynamic and activated neurohumoral factors in the initial stage of heart failure, and that increased basal NO production plays a central role in the maintenance of basal coronary blood flow.

Amlodipine therapy in congestive heart failure: hemodynamic and neurohormonal effects at rest and after treadmill exercise

This study examined the acute effects of amlodipine treatment on left ventricular pump function, systemic hemodynamics, neurohormonal status, and regional blood flow distribution in an animal model of congestive heart failure (CHF), both at rest and with treadmill exercise. A total of 14 pigs were studied under control conditions and after the development of pacing-induced CHF (240 beats per minute, 3 weeks, n = 7) or with CHF and acute amlodipine treatment for the last 3 days of pacing (1.5 mg/kg per day, n = 7). Under resting conditions, left ventricular stroke volume (mL) was reduced with CHF compared with the normal state (15+/-2 vs. 31+/-1, p<0.05) and increased with amlodipine treatment (23+/-4, p<0.05). At rest, systemic vascular resistance increased with CHF compared with the normal state (3,078+/-295 vs. 2,131+/-120 dyne x s cm(-5), p<0.05) and was reduced after amlodipine treatment (2,472+/-355 dyne x s cm(-5), p<0.05). With exercise, left ventricular stroke volume remained lower and systemic vascular resistance higher in the CHF group, but was normalized with amlodipine treatment. With exercise, left ventricular myocardial blood flow increased from resting values, but was reduced from the normal state with CHF (normal: 1.69+/-0.12 to 7.62+/-0.74 mL/min per gram vs. CHF: 1.26+/-0.12 to 4.77+/-0.45 mL/min per gram, both p<0.05) and was normalized with acute amlodipine treatment (1.99+/-0.35 to 6.29+/-1.23 mL/min per gram). Resting plasma norepinephrine was increased by >5-fold in the CHF group at rest and was not affected by amlodipine treatment. However, with exercise, amlodipine treatment blunted the increase in plasma norepinephrine by >50% when compared with untreated CHF values. Resting plasma endothelin levels increased with CHF compared with the normal state (10.9+/-0.9 vs. 2.8+/-0.4 fmol/mL, p<0.05) and was reduced with amlodipine treatment (7.5+/-1.5 fmol/mL, p<0.5). In other vascular beds, acute amlodipine treatment with CHF improved pulmonary and renal blood flow both at rest and with exercise; however, there were no effects observed on skeletal muscle blood flow. With the development of CHF, acute amlodipine treatment does not negatively influence left ventricular pump function, but rather may provide favorable hemodynamic and neurohormonal effects.

Potential role of the microvasculature in progression of heart failure

After cardiac injury, there are changes in the cardiac myocyte morphology, function, matrix, and molecular gene expression. These all play an important role in remodeling of the injured heart, contributing to the progression toward heart failure. The role of the microvasculature in the progression toward heart failure is less well characterized. However, laboratory studies have established that there are important interactions between the microvascular endothelium and the myocyte. Furthermore, in a multitude of animal models of heart failure and cardiomyopathy, there is always an association with microvascular abnormalities. Reversal of these abnormalities is also associated with improvement in the cardiomyopathy. Major mediators that likely play an important role in the microvasculature include endothelin and nitric oxide. These are elaborated by both endothelium and myocyte compartments of the myocardium. Preliminary clinical studies already demonstrate that microvascular ischemia may have prognostic power in patients with nonischemic dilated cardiomyopathy. Results from these studies showed a reduction in mortality from treatment with amlodipine, suggesting a possible benefit based on changes in the microvasculature.

Specificity of glycosaminoglycan suppression of endothelin-1 production by human umbilical vein endothelial cells

Endothelin-1 (ET-1) is the most potent vasoconstrictor peptide found in nature. Its production is stimulated by thrombin. By inhibiting thrombin we have previously shown that heparin, a highly negatively-charged glycosaminoglycan (GAG), suppresses the production of ET-1 by cultured human umbilical vein endothelial cells (HUVEC). The purpose of our study is to determine the effect of other GAGs and related compounds on ET-1 production. The GAGs and related compounds used in the study were: chondroitin sulfate A, chondroitin sulfate B, chondroitin sulfate C, fucoidin, low molecular weight dextran sulfate, high molecular weight dextran sulfate, and hyaluronan. HUVEC were incubated for 48 hr with media containing these GAGs and related compounds and with media without GAG as control. ET-1 levels were measured by radioimmunoassay. GAGs and related molecules with higher sulfate content, heparin, chondroitin sulfate B, low and high molecular weight dextran sulfates significantly suppressed ET-1 production by HUVEC. Fucoidin also suppressed ET-1 production despite its lower sulfate content, probably because of its structural similarity to heparin. These compounds may be useful for future in vivo studies.

Aggravated renal dysfunction during intensive therapy for advanced chronic heart failure

BACKGROUND

Chronic heart failure is associated with impaired renal function, which may worsen during therapy. The incidence, predictors, and consequences of aggravated renal dysfunction (ARD) in patients undergoing intensive therapy for advanced chronic heart failure are unknown.

METHODS

We reviewed the experience of 48 consecutive patients hospitalized for treatment of advanced chronic heart failure who underwent intravenous diuretic therapy with a weight loss of >/=2 kg. Evaluation included baseline renal function and echocardiography in all patients and hemodynamic measurements in 38 (79%) patients.

RESULTS

ARD, defined as >/=25% increase in serum creatinine concentration to >/=2 mg/dL, developed in 10 (21%) patients. Patients with ARD developing were older (aged 58 +/- 16 years vs 51 +/- 13 years; P =.006) and had lower baseline creatinine clearance (49 +/- 21 mL/min vs 74 +/- 26 mL/min; P =.01) but had the same serum creatinine at baseline. They were more likely to have atrial fibrillation (70% vs 29%, P =.02) but did not have lower filling pressures, cardiac output, or estimated renal perfusion pressure. Length of stay was longer if ARD developed (median 17 vs 9 days, P =.02). Mortality rate after discharge was increased in the patients with ARD (relative risk 5.3, P =.002).

CONCLUSIONS

In patients undergoing intensive treatment for heart failure, ARD is common and clinically significant. The relation among baseline factors, ARD, and worsened outcome may reflect complex cardiorenal interactions. Better understanding of the causes and prevention of ARD during heart failure therapy may in the future lead to better outcomes.

Increased p53 protein expression in human failing myocardium

BACKGROUND

The p53 gene is a tumor-suppressor gene which involves apoptosis and cell-cycle arrest under certain stress stimulate. However, the status of the p53 gene expression in human myocardium in congestive heart failure (CHF) remains unclear. Therefore, the current study was designed to investigate the expression of the p53 protein in human myocardium in normal subjects and in patients with severe CHF.

METHODS

Human ventricular cardiac tissue was obtained from 7 normal subjects and 7 end-stage CHF patients during cardiac transplantation. The expression of p53 protein was determined by immunohistochemical staining. The cardiac apoptosis was determined by TUNEL staining.

RESULTS

The p53 protein was minimally stained in normal human ventricular cardiomyocytes. In contrast, the staining density and positive stained nuclear (%) of p53 was significantly increased in ventricular cardiomyocytes of patients with severe CHF. Apoptosis in CHF human myocardium also markedly increased.

CONCLUSIONS

The significantly increased expression of p53 in CHF human cardiomyocytes suggests that p53 may play an important pathophysiological role in the process of CHF through mechanisms involving myocardial apoptosis.

Detection of anthracycline-induced cardiotoxicity

The use of anthracyclines, a group of potent anti-cancer agents incorporated into the treatment of a wide variety of solid and haematological tumours, is limited by its cardiotoxicity that can result in congestive heart failure (CHF). The best method to detect cardiotoxicity at an early stage in order to prevent severe deterioration, is still an unsolved problem. Although endomyocardial biopsy is considered to be the most sensitive and specific test for this purpose, its use is limited by its invasiveness. In daily practice, oncologists make use of parameters of systolic function (left ventricular ejection fraction, or fractional shortening) to detect cardiotoxicity, but these methods are not able to identify cardiotoxicity at an early stage. Based on increasing knowledge into the pathophysiology of anthracycline-induced cardiotoxicity and heart failure in general, new methods including the determination of diastolic function parameters, anti-myosin scintigraphy, assessment of heart rate variability, and the determination of biochemical markers have been proposed to identify patients at risk of the development of CHF in an early stage. However, most of these newer methods have not yet been adequately evaluated to allow them to be recommended for use in routine clinical practice.

[Endothelin-1 and cardiovascular diseases]

INTRODUCTION

Endothelins are peptides released from endothelial cells. According to both their structure and receptor affinity, three isoforms may be identified. Endothelin-1 is secreted abluminally by endothelial cells, and binds ETA and ETB2 receptors expressed on vascular smooth muscle cells, and ETB1 expressed on endothelial cells. ETA and ETB2 receptors stimulation induces smooth muscle contraction and proliferation, whereas ETB1 receptors stimulation induces relaxation.

CURRENT KNOWLEDGE AND KEY POINTS

Endothelin-1 plays an important role in maintaining peripheral vascular tone and systemic blood pressure. It is recognized to have a role in various diseases associated with vasoconstriction and vascular hypertrophy.

FUTURE PROSPECTS AND PROJECTS

Recent development of endothelin receptor antagonists seems promising for the treatment of heart failure and systemic hypertension, with interesting results obtained from short-term clinical trials. However, better evaluation of these drugs requires further long-term studies regarding not only the above mentioned diseases but also ischemic heart disease or pulmonary hypertension. Endothelin antagonists are therefore new therapeutic agents able to inhibit a vasoconstricting system that has been recently discovered. Results of ongoing clinical studies are awaited with interest.

Ascorbic acid prevents cigarette smoke injury to endothelium-dependent arterial relaxation

BACKGROUND

Arterial endothelium-dependent acetylcholine relaxation is impaired by smoking, and this injury may be mediated by oxygen free radicals. The purpose of this study was to examine the effect of ascorbic acid (AA) treatment on this injury.

MATERIALS AND METHODS

New Zealand White rabbits (n = 6, each group) were placed in a 240-ft3 airflow chamber for 3 h per day, 5 days per week over an 8-week period. Animals were divided into four groups and fed rabbit chow and water or rabbit chow and AA (250 ml/kg)-supplemented water. The control-smoke rabbit group and the ascorbic acid-smoke rabbit group were exposed to mainstream cigarette smoke from a robotic smoke generator for the 3-h period, while the control-no smoke rabbit group and ascorbic acid-no smoke rabbit group were similarly placed in the chamber without smoke. At the end of 8 weeks, rabbits were sacrificed and segments of their superficial femoral arteries were suspended from tension transducers and the maximal contraction was determined. The remaining rings were contracted to 50% of the maximum and relaxation was determined by adding acetylcholine. Groups were compared using one-way ANOVA.

RESULTS

Rings from control-smoke (5.13 +/- 0.21 g) and AA-smoke rabbits (6. 24 +/- 0.46 g) exhibited increased mean contraction to KCl (P < 0. 05) compared to control-no smoke rabbits (3.86 +/- 0.40 g). Acetylcholine-dependent relaxation was significantly reduced in the rings from the control-smoke rabbits compared to control-no smoke rabbits (acetylcholine, 5 x 10(-7) M: 24.7 +/- 2.7% versus 55.3 +/- 8.0%; acetylcholine, 7 x 10(-7) M: 27.5 +/- 2.3% versus 56.3 +/- 9. 2%). The AA-smoke group (acetylcholine, 5 x 10(-7) M: 61.8 +/- 12. 4%; 7 x 10(-7) M: 67.9 +/- 11.4%) had significantly increased relaxation compared to the control-smoke group (P < 0.05). There was no statistical difference in the mean percentage ring relaxation between the control-no smoke, AA-no smoke, and AA-smoke groups.

CONCLUSIONS

Ascorbic acid protected the artery from cigarette smoke-induced endothelial injury.

Endothelin concentrations in monochorionic twins with severe twin-twin transfusion syndrome

The objective of this study was to determine endothelin (ET-1) concentrations in monochorionic twin fetuses with and without twin-twin transfusion syndrome (TTTS). Fourteen monochorionic twin pregnancies complicated by TTTS and six without TTTS were studied. Matched maternal and fetal blood samples were obtained both in utero and at birth. Amniotic fluid samples were also collected from twin pairs. ET-1 concentrations were measured by radio-immunoassay. ET-1 concentrations in recipient fetuses were higher than in the donors both in utero(P < 0.001) and at birth (P < 0.01). Fetal concentrations of ET-1 in donors were similar to non-TTTS twins. Plasma ET-1 concentrations were significantly higher (P < 0.01) in recipient fetuses with severe hydrops than those with mild/no hydrops. Maternal concentrations of ET-1 were comparable in the two groups. Endothelin concentrations in recipient twins were 2(1/2) times higher than in their co-twins and this was related to the severity of hydrops.

Heart failure and endothelin receptor antagonists

Cardiac myocytes and vascular endothelial cells produce endothelin-1, which increases the contractility of cardiac muscles and of vascular smooth muscles. Endothelin-1 also exerts long-term effects, such as myocardial hypertrophy, and causes cellular injury in cardiac myocytes. In heart failure, the production of endothelin-1 is markedly increased in the failing heart. Here, evidence that an endothelin receptor antagonist is a useful new drug for the treatment of heart failure is discussed. Long-term treatment with an endothelin receptor antagonist greatly improves the survival rate of animals (rat, hamster, etc.) with chronic heart failure. This beneficial effect is accompanied by amelioration of left ventricular dysfunction. The myocardial endothelin system appears to be a novel and important target for therapeutic intervention in heart failure.

Characterisation of constrictor endothelin receptors in the human internal thoracic artery and saphenous vein

We studied the endothelin receptors mediating contraction in the human saphenous vein (SV) and internal thoracic artery (ITA). In the SV, the ET(A)-receptor antagonist BQ123 (1 microM) did not significantly shift the ET-1 concentration-response curve but did cause a parallel shift in the ITA. In the SV, the ET(A)-receptor agonist sarafotoxin 6b (S6b) produced a monophasic concentration-response curve that was antagonised biphasically by BQ123 (0.1-1 microM). In the ITA, S6b was an ineffective agonist with contractions seen only at 3 x 10(-9) M upward. The ET(B)-receptor agonist sarafotoxin 6c (S6c) caused constrictions in only 74% of SV rings and 42% of ITA rings. In the tissues that did respond, S6c caused a monophasic concentration-response curve with a lower maximal response than ET-1. The ET(B) antagonist BQ788 did not antagonise the responses to ET-1 in either the SV or the ITA but did antagonise the responses to S6c in the SV. The results from this study suggest that mainly ET(A) receptors mediate the contractile responses in the human SV and ITA. There is also evidence for an ET(B)-mediated response, although the contractions were much smaller than those elicited by ET-1. We also conclude that the ET(A) receptors mediating responses in these human vessels are atypical because of the different effects of BQ123 on the two vessels.

Endothelin B receptors are functionally important in mediating vasoconstriction in the systemic circulation in patients with left ventricular systolic dysfunction

OBJECTIVES

This study was designed to assess the functional importance of endothelin (ET)B receptors in patients with left ventricular systolic dysfunction (LVSD) by comparing the hemodynamic effects of ET-1, a nonselective ET(A) and ET(B) agonist, with ET-3, a selective ET(B) receptor agonist.

BACKGROUND

Knowledge of the functional importance of ET(B) receptors in mediating vasoconstriction in chronic heart failure will help determine whether antagonists at both ET(A) and ET(B) receptors are required to fully prevent vasoconstriction to endogenously produced ET-1.

METHODS

We infused ET-1 (5 and 15 pmol/min) and ET-3 (5 and 15 pmol/min) into two separate groups of eight patients with LVSD with similar baseline hemodynamic indices. Hemodynamics were measured using a pulmonary thermodilution catheter and an arterial line.

RESULTS

Endothelin-1 infusion led to systemic vasoconstriction, with a rise in mean arterial pressure (mean +/- SEM 100 +/- 3 to 105 +/- 3 mm Hg, p < 0.02) and systemic vascular resistance (1,727 +/- 142 to 2,055 +/- 164 dyn/s/cm(-5), p < 0.001) and a fall in cardiac index (2.44 +/- 0.21 to 2.22 +/- 0.20 liters/min/m , p < 0.01). Endothelin-3 infusion also led to systemic vasoconstriction, with a rise in mean arterial pressure (99 +/- 6 to 105 +/- 6 mm Hg, p < 0.01) and systemic vascular resistance (1,639 +/- 210 to 1,918 +/- 245 dyn/s/cm(-5), p < 0.01) and a fall in cardiac index (2.66 +/- 0.28 to 2.42 +/- 0.24 liters/min/m2, p < 0.05). Pulmonary hemodynamic measurements did not change significantly in either group.

CONCLUSIONS

Both ET-1 and ET-3 infusions led to systemic vasoconstriction; the hemodynamic changes observed were of a similar magnitude at the same molar concentration. This suggests that ET(B) receptors are functionally important in mediating vasoconstriction, at least in the systemic circulation, in patients with LVSD.

Novel neuropeptides in the pathophysiology of heart failure: adrenomedullin and endothelin-1

The clinical success of neurohumoral manipulation by ACE inhibitors and beta blockers in heart failure has led to new therapeutic approaches. New neurohumoral factors are now viewed as offering the potential for treatment interventions. Not only do we consider blocking the production of deleterious hormones, but also, more recently, consideration has been given to augmenting the actions of factors with potentially beneficial actions. Hopefully such manipulation of ADM and ET-1 can result in further improvement in the well-being of heart failure patients.

Endothelin-1 as a mediator in cardiovascular disease

1. Brachial artery infusion of endothelin (ET)-1 causes transient vasodilatation followed by sustained vasoconstriction of the forearm vascular bed, whereas ET-1 antagonists cause sustained vasodilatation. These data suggest that ET-1 contributes to basal vascular tone. 2. Systemic infusion of ET-1 increases blood pressure and total peripheral vascular resistance and reduces heart rate and cardiac output. The renal and pulmonary circulations are particularly sensitive to the vasoconstrictor effects of ET-1. Systemic infusion of the ETA/B receptor antagonist TAK-044 reduces mean arterial pressure and peripheral vascular resistance. 3. Plasma ET-1 concentrations are not elevated in essential hypertension; however, insulin resistance may be a major determinant of plasma ET-1 concentrations. Vascular sensitivity to ET-1 is normal or may be increased in essential hypertension. 4. Plasma ET-1 concentrations are increased in moderate and severe heart failure and are correlated with clinical and haemodynamic measures of severity. Endothelin-1 contributes to increased vascular tone in cardiac failure. 5. Plasma ET-1 concentrations increase following myocardial infarction and persistent elevation predicts an increased mortality within the subsequent 12 months. 6. Preliminary data suggest that interventions that reduce the activity of the endothelin system may have a beneficial effect in heart failure and myocardial infarction.

Endothelin in heart failure

Congestive heart failure is a complex disease that results from pumping failure of the cardiac muscle and adaptational processes of the cardiovascular system to correct for the reduced blood supply to the organism. It is associated with increased vasoconstriction and impaired vasodilation in response to physical activity. The elevated vasoconstrictor tone is caused by the activation of compensatory mechanisms including the sympathetic nervous system and stimulation of the release of neurohormones like angiotensin II, catecholamines, and vasopressin. Furthermore, the vascular endothelium is importantly involved in the regulation of vascular tone as it releases a variety of vasoactive substances that act locally and systemically. In congestive heart failure, there is a marked imbalance between the diminished release or the increased inactivation of vasodilators on the one hand, ie, nitric oxide, and the elevated production, release, or reduced inactivation of vasoconstrictors such as endothelin-1 on the other hand. In addition to its very potent vasoconstrictor effects, endothelin-1 possesses antinatriuretic and mitogenic properties that are a common feature of substances that are involved in development of the deleterious consequences that render congestive heart failure a lethal disease. The spectrum of action of the endothelin system and the advent of specific antagonists for its receptors have made this system a very interesting target for clinical research and possibly for future therapeutic approaches.

Upregulated expression of cardiac endothelin-1 participates in myocardial cell growth in Bio14.6 Syrian cardiomyopathic hamsters

OBJECTIVES

The purpose of this study is to investigate the role of endogenous endothelin-1 (ET-1) in myocardial growth in Bio 14.6 Syrian cardiomyopathic hamsters (Bio).

BACKGROUND

While ET-1, as a growth-promoting peptide, has been implicated in the development of secondary cardiac hypertrophy, the role of endogenous ET-1 in cardiac growth in primary myocardial disease is unknown.

METHODS

We measured left ventricular ET-1 levels by a specific sandwich enzyme-linked immunosorbent assay. Furthermore, we examined the chronic effect of T0201, an ET type A receptor-specific antagonist.

RESULTS

The ET-1 levels in the left ventricles were 1.8-fold higher (p < 0.0005) at 20 weeks and 6.4-fold higher (p < 0.0001) at 35 weeks in the Bio compared to age-matched control F1B hamsters (F1B). The Bio ET-1 levels in the lungs exhibited an only 1.3-fold elevation at 35 weeks. Immunohistochemistry demonstrated the localization of ET-1 mainly in the cardiac myocytes. The treatment with T0201 significantly reduced the heart weight/body weight ratio in the Bio, but did not affect the heart weight/body weight ratio in the F1B. Histologically, T0201 reduced the myocyte diameter of Bio to a level similar with that of F1B. However, T0201 did not affect the extent of fibrosis in Bio or F1B.

CONCLUSIONS

The ET-1 level in the heart of cardiomyopathic hamsters increases in stage-dependent and organ-specific manners. Though myocyte degeneration and subsequent replacement fibrosis do not require an ET-1 pathway, the accelerated synthesis of ET-1 in the heart may contribute to the pathological growth of remaining myocytes in this animal model.

Endothelin antagonists

The very potent endogenous vasoconstrictor endothelin was discovered in 1988. We know now that there are three isoforms (1, 2, and 3) and two receptor subtypes (A and B). A whole range of peptide and non-peptide antagonists has been developed, some selective for A or B receptors and others with non-selective A/B antagonistic activity. So far the main application of these agents has been experimental--ie, endothelin blockers are used to throw light on disease mechanisms, most notably cardiovascular and renal. However, the non-selective antagonist bosentan and a few other agents have been studied clinically. Evidence so far from preclinical studies and healthy volunteers and from the limited number of investigations in patients permits a listing of the potential areas of clinical interest. These are mainly cardiovascular (eg, hypertension, cerebrovascular damage, and possibly heart failure) and renal. Clouds on the horizon are the need to show that these new agents are better than existing drugs; the possibility of conflicting actions if mixed A/B antagonists are used; and animal evidence hinting that endothelin blockade during development could be dangerous.

Molecular mechanisms of myocardial remodeling

"Remodeling" implies changes that result in rearrangement of normally existing structures. This review focuses only on permanent modifications in relation to clinical dysfunction in cardiac remodeling (CR) secondary to myocardial infarction (MI) and/or arterial hypertension and includes a special section on the senescent heart, since CR is mainly a disease of the elderly. From a biological point of view, CR is determined by 1 ) the general process of adaptation which allows both the myocyte and the collagen network to adapt to new working conditions; 2) ventricular fibrosis, i.e., increased collagen concentration, which is multifactorial and caused by senescence, ischemia, various hormones, and/or inflammatory processes; 3) cell death, a parameter linked to fibrosis, which is usually due to necrosis and apoptosis and occurs in nearly all models of CR. The process of adaptation is associated with various changes in genetic expression, including a general activation that causes hypertrophy, isogenic shifts which result in the appearance of a slow isomyosin, and a new Na+-K+-ATPase with a low affinity for sodium, reactivation of genes encoding for atrial natriuretic factor and the renin-angiotensin system, and a diminished concentration of sarcoplasmic reticulum Ca2+-ATPase, beta-adrenergic receptors, and the potassium channel responsible for transient outward current. From a clinical point of view, fibrosis is for the moment a major marker for cardiac failure and a crucial determinant of myocardial heterogeneity, increasing diastolic stiffness, and the propensity for reentry arrhythmias. In addition, systolic dysfunction is facilitated by slowing of the calcium transient and the downregulation of the entire adrenergic system. Modifications of intracellular calcium movements are the main determinants of the triggered activity and automaticity that cause arrhythmias and alterations in relaxation.

Dilated cardiomyopathy: changing pathophysiological concepts and mechanisms of dysfunction

Experimental observations made over the past two decades have led to a profound shift in the conceptual paradigms about the syndrome of heart failure and dilated cardiomyopathy. As a consequence, heart failure is currently considered a complex disease and is not merely characterized by hemodynamic disturbances. It is now believed that the syndrome is governed and impelled by neurohormonal imbalances and intracardiac paracrine processes. The latter processes are mediated by activated cardiac endothelial cells and cytokines, creating a state of cardiac maladaption and leading to disease progression. Therapeutic interventions such as operative left ventricular volume reduction or mitral valve reconstruction should therefore no longer be solely interpreted in terms of hemodynamics (i.e., symptomatic improvements). Effects on neurohormonal, endothelial, and cytokine activities should be taken equally into account.

Increasing plasma neopterin and persistent plasma endothelin during follow-up after acute cerebral ischemia

Release of inflammatory mediators from leukocytes and endothelial release of vasoactive factors are both important in the pathogenesis of atherosclerosis. To evaluate the concentrations of a specific marker for macrophage activation, neopterin, and the potent endothelial derived vasoconstrictive peptide endothelin-1 (ET-1), during the acute and chronic stages of cerebral ischemia, plasma concentrations of neopterin and ET-1 were measured in 59 patients with acute cerebral infarction or transient ischemic attack (median age 73 years, range 43-93, 27 men) and after a 1-year follow-up in 57/59 (97%) of patients. Plasma neopterin was higher at follow-up (6.3 nmol/L [3.7-21.6] vs 5.6 nmol/L [3.5-17.2]; p < 0.05) than at the acute stage, whereas the plasma ET-1 concentration was unchanged. Plasma concentrations of both neopterin and ET-1 correlated directly with age both in the acute stage (r = 0.42 and r = 0.35, respectively; p < 0.01) and after follow-up (r = 0.34; p < 0.05 and r = 0.27; p = 0.05, respectively). In conclusion, plasma neopterin increased after acute cerebral ischemia, indicating chronic inflammatory activity and continuous macrophage activation in ischemic cerebrovascular diseases.

AT1 angiotensin II receptor inhibition in pacing-induced heart failure: effects on left ventricular performance and regional blood flow patterns

BACKGROUND

AT1 angiotensin II (AT1 Ang II) receptor activation has been shown to cause increased vascular resistance in the systemic (SVR), pulmonary (PVR), and coronary vasculature which may be of particular importance in the setting of congestive heart failure (CHF). The overall goal of this study was to examine the effects of acute AT1 Ang II receptor inhibition on left ventricular (LV) pump function, systemic hemodynamics, and regional blood flow patterns in the normal state and with CHF, both at rest and with treadmill-induced exercise.

METHODS AND RESULTS

Pigs (25 kg) were instrumented to measure cardiac output (CO), SVR, and PVR, and LV myocardial blood flow distribution in the conscious state and were assigned to one of two groups: (1) pacing-induced CHF (240 bpm for 3 weeks, n = 6) or (2) sham controls (n = 5). Measurements were obtained at rest and after treadmill exercise (15 degrees for 10 minutes). Studies were repeated 30 minutes after intravenous infusion of a low (1.1 mg/kg) or high (125 mg/kg) dose of the AT1 Ang II antagonist, valsartan. The low dose of valsartan reduced the Ang II pressor response by approximately 50% but had a minimal effect on arterial pressure, whereas the high dose eliminated the Ang II pressor response and reduced resting blood pressure by approximately 20%. With CHF, CO was reduced at rest (2.5+/-0.2 v 3.9+/-0.1 L/min) and with exercise (6.4+/-0.5 v 7.8+/-0.5 L/min) compared with controls (P < .05). Valsartan at the low and high dose increased resting CO by 28% in the control and CHF groups, but did not affect CO with exercise. Resting SVR in the CHF group was higher than controls (2,479+/-222 v 1,877+/-65 dyne x s x cm(-5), P < .05), but SVR fell to a similar degree with exercise (1,043+/-98 v 1,000+/-77 dyne x s x cm(-5)). The low and high dose of valsartan reduced resting SVR by more than 30% in both the control and CHF groups. PVR was increased by more than twofold in the CHF group at rest. The high dose of valsartan reduced resting PVR with CHF, but had no further effect with exercise. LV myocardial blood flow was reduced with pacing CHF, particularly with exercise. With exercise and CHF, a low or high dose of valsartan reduced coronary vascular resistance, but LV myocardial blood flow remained reduced from normal values.

CONCLUSIONS

Heightened AT1 Ang II receptor activity occurred in this model of CHF, which contributed to alterations in systemic hemodynamics and vascular resistive properties. By using a low dose of a selective AT1 Ang II receptor antagonist reduced SVR, PVR, and coronary vascular resistive properties and therefore may provide beneficial effects in a setting of CHF.

Arrhythmogenic effects induced by coronary conversion of pulmonary big endothelin to endothelin: aggravation of this phenomenon in heritable hyperlipidemia

OBJECTIVES

We investigated whether endogenous pulmonary big endothelin has arrhythmogenic properties under normal conditions and in heritable hyperlipidemia.

BACKGROUND

Endothelin (ET), one of the most potent vasoconstrictors, is known to induce ventricular arrhythmias. It is unclear, however, whether its precursor, big endothelin, released from the lung, contributes to arrhythmogenesis.

METHODS

In a lung-heart model in which a Langendorff heart is serially perfused with the effluent from the isolated lung of the same animal, we evaluated arrhythmias in control and in Watanabe heritable hyperlipidemic (WHHL) rabbits.

RESULTS

In both controls (n=12) and WHHL (n=8), serial perfusion evoked a decrease in coronary flow (controls, -11+/-3%; WHHL, -25+/-6%) and a fourfold increase of ventricular extrasystoles (VES) (controls, 40.7+/-8; WHHL, 40.2+/-5 VES/40 min, p < 0.05). However, WHHL developed more and longer nonsustained ventricular tachycardias (VT) compared with controls (incidence, 1.38+/-1.1 vs. 0.33+/-0.5 VT/40 min, p < 0.05; length, 14.36+/-3.1 vs. 7.25+/-1.5 beats/VT, p < 0.05). Arrhythmias were not ischemia-induced because corresponding mechanical flow reduction had no arrhythmogenic effect (n=6 in controls and WHHL). Although vasoconstriction disappeared entirely, arrhythmias were only partly suppressed by ET(A) antagonists (BQ-123, 2 micromol/liter; A-127722, 20 micromol/liter). The ET-converting enzyme inhibitor phosphoramidon (50 micromol/liter) completely suppressed arrhythmias and vasoconstriction. The ET(B) antagonists (IRL-1038, 4 micromol/liter; IRL-1025, 5 micromol/liter) had no effect (n=6).

CONCLUSIONS

Endogenous pulmonary big ET produces arrhythmogenic effects that are aggravated in heritable hyperlipidemia. These effects, requiring coronary conversion of big ET into ET, are partly ET(A)-mediated and ET(B)-independent.