Endothelin in chronic heart failure: current position and future prospects.

Though much has still to be learned about the various actions of endothelin-1 in human physiology, current evidence suggests an important role for the peptide in the pathophysiology of CHF. The development of novel and more effective therapeutic strategies for CHF is an important priority in cardiovascular medicine, and anti-endothelin drugs appear to offer promise in this regard. The impact of ACE inhibitors has been such that for a new treatment modality to be of real value in CHF, it will need to offer haemodynamic benefit over and above that already obtained with an ACE inhibitor; anti-endothelin drugs seem to have this potential [57,98]. Ongoing studies with agents which inhibit either the generation or actions of endothelin-1 will clarify its role in the pathophysiology of CHF and determine whether anti-endothelin drugs represent a further therapeutic advance in the treatment of this disease.

Endothelin receptor antagonism in patients with chronic heart failure.

OBJECTIVE: The relative importance of ETA and ETB receptors in mediating the constrictor effects of endogenous endothelin-1 in patients with chronic heart failure is not known. The primary purpose of this study was to compare the acute effects of selective ETA and ETB receptor antagonists in vivo in healthy subjects and patients with chronic heart failure. Our secondary aim was to examine more closely the effect of chronic heart failure on endothelin biosynthesis. METHODS: We studied the effects of BQ-123 (a selective ETA antagonist) and BQ-788 (a selective ETB antagonist) in ten healthy subjects and ten patients with chronic heart failure. Locally active doses of each antagonist were infused into the non-dominant brachial artery for 90 min on separate days at least 1 week apart. Changes in forearm blood flow were measured by venous occlusion plethysmography. Venous blood samples were obtained prior to antagonist infusion for assay of total endothelin, big endothelin-1 and C-terminal fragment immunoreactivity. RESULTS: BQ-123 (100 nmol/min) increased blood flow by 54+/-10% (P<0.001) and 30+/-5% (P<0.001) in controls and heart failure patients, respectively. BQ-788 (1 nmol/min) reduced blood flow by 15+/-5% (P=0. 036) and 9+/-4% (P=0.001) in controls and heart failure patients, respectively. Total endothelin immunoreactivity was non significantly greater in heart failure patients than controls (6. 8+/-1.4 vs. 4.6+/-0.5 pM; P=0.13). Big endothelin-1 (2.6+/-0.4 vs. 1. 7+/-0.1 pM; P=0.04) and C-terminal fragment immunoreactivity (2. 1+/-0.3 vs. 0.6+/-0.1 pM; P<0.0001) were each significantly greater in heart failure patients than controls. CONCLUSIONS: Selective ETA receptor antagonism caused vasodilatation in the peripheral circulation of healthy subjects and patients with chronic heart failure while selective ETB receptor antagonism caused vasoconstriction in each group. ETB receptor antagonism may therefore cause potentially deleterious vasoconstriction in chronic heart failure. Chronic heart failure is associated with a significant increase in plasma big endothelin-1 and C-terminal fragment immunoreactivity.

Even low-dose aspirin inhibits arachidonic acid-induced vasodilation in heart failure.

BACKGROUND: There is some evidence that aspirin may be harmful to patients with congestive heart failure treated with angiotensin-converting enzyme (ACE) inhibitors, but there has never been any direct examination of the vascular effects of aspirin in these patients. We sought to determine whether there is an arachidonic acid-dependent vasodilator pathway in resistance arteries in humans, whether it is affected by congestive heart failure, and whether it is inhibited by low-dose aspirin. METHODS: A locally active dose of arachidonic acid was infused into the nondominant brachial artery while forearm blood flow was measured by venous occlusion plethysmography in 10 healthy subjects in a control group and 15 patients with congestive heart failure treated with ACE inhibitor. Patients with congestive heart failure were studied after administration of 0 mg, 75 mg, and 300 mg aspirin for 14 days. RESULTS: Arachidonic acid produced progressive and incremental vasodilation (up to 64%). There was no significant difference between patients and healthy control subjects studied after administration of 0 mg aspirin. In patients, however, administration of 75 mg and 300 mg aspirin inhibited mean vasodilation by 55% and 59%, respectively. CONCLUSIONS: There is an arachidonic acid-dependent vasodilator pathway in humans. This pathway is not significantly affected by congestive heart failure. It is significantly inhibited by even low-dose aspirin therapy. These results imply that even the very lowest dose of aspirin in common use for cardioprotection has potentially detrimental vasoconstrictor effects.

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 in heart failure: a promising therapeutic target?

The results of early acute haemodynamic studies with anti-endothelin agents are promising. Much still needs to be done, however, before endothelin antagonism is established as a therapeutic strategy in heart failure. We need to know, for example, whether the haemodynamic effects of anti-endothelin drugs are sustained. We need to ensure that there is no reflex activation of other neuroendocrine systems and, preferably, to demonstrate neuroendocrine suppression. Characterisation of the renal actions of endothelin receptor antagonists will also be important. Perhaps the most pressing issue in the development of these agents is elucidation of the role of the endothelial ETB receptor in heart failure. It is now clearly shown that vascular smooth muscle ETB receptors can mediate vasoconstriction in human blood vessels and that these receptors may be particularly important in heart failure. The effect of selective ETB receptor blockade in humans in vivo is not currently known, however, and whether endothelial ETB receptors might tonically offset ETA and ETB receptor mediated smooth muscle contraction remains conjectural. This question is directly relevant to whether selective ETA or non-selective ETA and ETB receptor antagonism might be the better therapeutic strategy in heart failure. ECE inhibition may become another therapeutic option in due course, but at present no specific and selective inhibitors of the enzyme have been developed. The recent demonstration that the selective ETA receptor antagonist BQ-123 improves long term survival in rats with heart failure induced by myocardial infarction suggests that anti-endothelin strategies may hold great therapeutic promise in heart failure.

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.

Endothelin in congestive heart failure.

The endothelin (ET) family of peptides have potent vascular, cardiac and renal actions which may be of pathophysiological importance in congestive heart failure (CHF). In vivo studies with selective and non-selective ET receptor antagonists are required to clarify the role of ET in the pathophysiology of CHF and determine whether anti-ET drugs may be therapeutically useful in CHF. The impact of angiotensin converting enzyme (ACE) inhibitors on the management of CHF has been such that for any new treatment to be of value it will probably have to offer hemodynamic benefit over and above that already obtained with an ACE inhibitor; anti-ET agents seem to have this potential. The recent formal cloning and characterization of endothelin converting enzyme (ECE) should hasten the development of specific and selective ECE inhibitors and thus provide an alternative investigative, and perhaps therapeutic, tool. Morbidity and mortality from CHF remain unacceptably high even in patients receiving maximal medical therapy, including an ACE inhibitor. Blockade of either the generation (through ECE inhibition) or actions (through receptor blockade) of ET warrant further investigation as potential new therapeutic strategies.

Clinical experience with endothelin receptor antagonists in chronic heart failure.

Both ET(A) selective and dual, ET(A/B), receptor antagonists have favourable short- and longer-term haemodynamic actions in patients with acute and chronic heart failure. Their effect on neurohumoral measures is not yet fully determined. Two moderately large, medium-duration studies have examined the effect of dual ET(A/B) receptor antagonists on clinical status, reaching conflicting conclusions. One large scale, long-term, morbidity mortality evaluation is underway with bosentan.

Venous endothelin receptor function in patients with chronic heart failure.

Cardiac preload reduction through venodilatation is beneficial in chronic heart failure. The recent development of endothelin receptor antagonists for possible therapeutic use in heart failure has hastened the need for a clearer understanding of the venoconstrictor actions of endothelin-1 in this disease. Two main subtypes of endothelin receptor, ET(A) and ET(B), exist in human blood vessels. We studied the venoconstrictor effects of endothelin-1 (a non-selective ET(A) and ET(B) agonist) and sarafotoxin S6c (a selective ET(B) agonist) in vivo in patients with chronic heart failure and in age-matched healthy controls. On separate days at least 1 week apart, locally active doses of endothelin-1 or sarafotoxin S6c were infused into a suitable dorsal hand vein for 1 h, and the venous internal diameter was measured using a displacement technique. Venoconstriction in response to endothelin-1 was significantly blunted in heart failure patients compared with controls (26+/-7% and 51+/-6% peak reduction in vein calibre respectively; P=0.013). Venoconstriction to sarafotoxin S6c was similar in heart failure patients and controls (17+/-5% and 17+/-4% peak reduction in vein calibre respectively). Both ET(A) and ET(B) receptors mediate venoconstriction in healthy subjects and in patients with chronic heart failure. Optimal inhibition of the venoconstrictor effects of endothelin-1 in chronic heart failure may therefore require administration of an antagonist with ET(A)- and ET(B)-receptor-blocking properties. Chronic heart failure may be associated with a selective decrease in venous ET(A) receptor sensitivity, but further studies are required to clarify the functional significance of this observation.

Vasodilator effects of endothelin-converting enzyme inhibition and endothelin ETA receptor blockade in chronic heart failure patients treated with ACE inhibitors.

BACKGROUND: The importance of endothelin-1 in chronic heart failure (CHF) is unclear. We therefore investigated the effects of endothelin-converting enzyme (ECE) inhibition and endothelin ETA receptor blockade in CHF patients treated with ACE inhibitors. We also compared the function of ETA and ETB receptors in healthy subjects and patients with CHF. METHODS AND RESULTS: Locally active doses of study drugs were infused into the nondominant brachial artery while forearm blood flow (FBF was measured by venous occlusion plethysmography. In CHF patients (n = 10), phosphoramidon (a combined ECE and neutral endopeptidase inhibitor) and BQ-123 (an ETA receptor antagonist) increased FBF by 52 +/- 10% (P = .0006) and 31 +/- 6% (P = .002), respectively, and thiorphan (a selective neutral endopeptidase inhibitor) reduced FBF by 15 +/- 5% (P = .0007). Forearm vasoconstriction to endothelin-1 (an ETA and ETB receptor agonist) was significantly blunted in CHF patients compared with control subjects (both n = 10; CHF versus control subjects, P < .001), whereas vasoconstriction to sarafotoxin S6c (an ETB receptor agonist) was significantly enhanced in CHF patients compared with control subjects (both n = 10; CHF versus control subjects. P < .05). CONCLUSIONS: ECE inhibitors and ETA receptor antagonists may be useful as vasodilator agents in CHF patients already receiving treatment with an ACE inhibitor. Both ETA and ETB receptors can mediate agonist-induced vasoconstriction in healthy subjects and patients with CHF, but further studies are required to clarify the contribution of each receptor subtype in mediating the effects of endogenous endothelin-1.

Effect of adrenomedullin on the production of endothelin-1 and on its vasoconstrictor action in resistance arteries: evidence for a receptor-specific functional interaction in patients with heart failure.

Endothelin-1 (ET-1) and adrenomedullin (ADM) are both produced in the arterial wall, but have opposing biological actions. Evidence from experimental animals suggests a functional interaction between ET-1 and ADM. We have tested this in humans. Small resistance arteries were obtained from gluteal biopsies taken from patients with chronic heart failure (CHF) due to coronary heart disease (CHD), or with CHD and preserved ventricular function. The contractile responses to big ET-1 and to ET-1 in both sets of vessels were studied in the absence (control) and presence of ADM at 20 pmol/l (low ADM) or 200 pmol/l (high ADM), using wire myography. ADM did not affect the conversion of big ET-1 into ET-1 in vessels from patients with either CHD or CHF. Low ADM did not alter the contractile response to ET-1 in vessels from patients with CHF. Low ADM was not tested in vessels from patients with CHD, but high ADM did not affect this response in arteries from these patients. High ADM did, however, significantly reduce the vasoconstrictor effect of ET-1 in vessels from patients with CHF. The maximum response, as a percentage of the response to high potassium, was 199% (S.E.M. 25%) in the control experiments (n=14), 205% (27%) in the low-ADM (n=7) studies and 150% (17%) in the high-ADM (n=6) experiments (P<0.001). Furthermore, the Hill coefficient increased from 0.57+/-0.05 in the absence of ADM to 1.16+/-0.15 in the high-ADM experiments, indicating that ADM at 200 pmol/l specifically antagonized one receptor type in vessels from patients with CHF. We conclude that there is a one-site receptor interaction between ADM and ET-1 that is specific for vessels from patients with CHF. This functional interaction between ADM and ET-1 in resistance arteries may be of pathophysiological importance in CHF.

Importance of heart failure as a cause of death. Changing contribution to overall mortality and coronary heart disease mortality in Scotland 1979-1992.

AIMS: As heart failure is a syndrome arising from another condition, such as coronary heart disease, it is rarely officially coded as the underlying cause of death regardless of the cause recorded by the physician at the time of certification. We sought to assess the true contribution of heart failure to overall mortality and coronary heart disease mortality and to examine how this contribution has changed over time. METHODS AND RESULTS: We carried out a retrospective analysis of all death certificates in Scotland between 1979 and 1992 for which heart failure was coded as the underlying or a contributory cause of death. From a total of 833622 deaths in Scotland between 1979 and 1992, heart failure was coded as the underlying cause in only 1.5% (13695), but as a contributory cause in a further 14.3% (126073). In 1979, 28.5% of male and 40.4% of female deaths attributed to coronary heart disease (coded as the underlying cause of death) also had a coding for heart failure. In 1992 these percentages had risen significantly to 34.1% and 44.8%, respectively (both P<0.001). Mortality rates for heart failure as the underlying or contributory cause of death, standardized by age and sex, fell significantly over the period studied in all ages and in both sexes: by 31% in men and 41% in women <65 years and 15.8% in men and 5.1% in women > or =65 years, respectively (P<0.01 for all changes). CONCLUSIONS: Death from heart failure is substantially underestimated by official statistics. Furthermore, one third or more of deaths currently attributed to coronary heart disease may be related to heart failure and this proportion appears to be increasing. While the absolute numbers of deaths caused by heart failure remains constant, this study is the first to show that standardized mortality rates are declining.