Effects of sustained-release moxonidine, an imidazoline agonist, on plasma norepinephrine in patients with chronic heart failure

Presynaptic Adrenoceptors

Presynaptic α2-adrenoceptors are localized on axon terminals of many noradrenergic and non-noradrenergic neurons in the peripheral and central nervous systems. Their activation by exogenous agonists leads to inhibition of the exocytotic release of noradrenaline and other transmitters from the neurons. Most often, the α2A-receptor subtype is involved in this inhibition. The chain of molecular events between receptor occupation and inhibition of the exocytotic release of transmitters has been determined. Physiologically released endogenous noradrenaline elicits retrograde autoinhibition of its own release. Some clonidine-like α2-receptor agonists have been used to treat hypertension. Dexmedetomidine is used for prolonged sedation in the intensive care; It also has a strong analgesic effect. The α2-receptor antagonist mirtazapine increases the noradrenaline concentration in the synaptic cleft by interrupting physiological autoinhibion of release. It belongs to the most effective antidepressive drugs. β2-Adrenoceptors are also localized on axon terminals in the peripheral and central nervous systems. Their activation leads to enhanced transmitter release, however, they are not activated by endogenous adrenaline.

Normal and excessive muscle sympathetic nerve activity in heart failure: implications for future trials of therapeutic autonomic modulation

AIMS

Patients with sympathetic excess are those most likely to benefit from novel interventions targeting the autonomic nervous system. To inform such personalized therapy, we identified determinants of augmented muscle sympathetic nerve activity (MSNA) in heart failure, versus healthy controls.

METHODS AND RESULTS

We compared data acquired in 177 conventionally-treated, stable non-diabetic patients in sinus rhythm, aged 18-79 years (149 males; 28 females; left ventricular ejection fraction [LVEF] 25 ± 11% [mean ± standard deviation]; range 5-60%), and, concurrently, under similar conditions, in 658 healthy, normotensive volunteers (398 males; aged 18-81 years). In heart failure, MSNA ranged between 7 and 90 bursts·min^-1 , proportionate to heart rate (p < 0.0001) and body mass index (BMI) (p = 0.03), but was unrelated to age, blood pressure, or drug therapy. Mean MSNA, adjusted for age, sex, BMI, and heart rate, was greater in heart failure (+14.2 bursts·min^-1 ; 95% confidence interval [CI] 12.1-16.3; p < 0.0001), but lower in women (-5.0 bursts·min^-1 ; 95% CI 3.4-6.6; p < 0.0001). With spline modeling, LVEF accounted for 9.8% of MSNA variance; MSNA related inversely to LVEF below an inflection point of ∼21% (p < 0.006), but not above. Burst incidence was greater in ischaemic than dilated cardiomyopathy (p = 0.01), and patients with sleep apnoea (p = 0.03). Burst frequency correlated inversely with stroke volume (p < 0.001), cardiac output (p < 0.001), and peak oxygen consumption (p = 0.002), and directly with norepinephrine (p < 0.0001) and peripheral resistance (p < 0.001).

CONCLUSION

Burst frequency and incidence exceeded normative values in only ∼53% and ∼33% of patients. Such diversity encourages selective deployment of sympatho-modulatory therapies. Clinical characteristics can highlight individuals who may benefit from future personalized interventions targeting pathological sympathetic activation.

Role of the sympathetic nervous system in cardiometabolic control: implications for targeted multiorgan neuromodulation approaches

Sympathetic overdrive plays a key role in the perturbation of cardiometabolic homeostasis. Diet-induced and exercise-induced weight loss remains a key strategy to combat metabolic disorders, but is often difficult to achieve. Current pharmacological approaches result in variable responses in different patient cohorts and long-term efficacy may be limited by medication intolerance and nonadherence. A clinical need exists for complementary therapies to curb the burden of cardiometabolic diseases. One such approach may include interventional sympathetic neuromodulation of organs relevant to cardiometabolic control. The experience from catheter-based renal denervation studies clearly demonstrates the feasibility, safety and efficacy of such an approach. In analogy, denervation of the common hepatic artery is now feasible in humans and may prove to be similarly useful in modulating sympathetic overdrive directed towards the liver, pancreas and duodenum. Such a targeted multiorgan neuromodulation strategy may beneficially influence multiple aspects of the cardiometabolic disease continuum offering a holistic approach.

Alpha2-adrenoceptors in adrenomedullary chromaffin cells: functional role and pathophysiological implications

Chromaffin cells from the adrenal medulla participate in stress responses by releasing catecholamines into the bloodstream. Main control of adrenal catecholamine secretion is exerted both neurally (by the splanchnic nerve fibers) and humorally (by corticosteroids, circulating noradrenaline, etc.). It should be noted, however, that secretory products themselves (catecholamines, ATP, opioids, ascorbic acid, chromogranins) could also influence the secretory response in an autocrine/paracrine manner. This form of control is activity-dependent and can be either inhibitory or excitatory. Among the inhibitory influences, it stands out the one mediated by α₂-adrenergic autoreceptors activated by released catecholamines. α₂-adrenoceptors are G protein-coupled receptors capable to inhibit exocytotic secretion through a direct interaction of Gβγ subunits with voltage-gated Ca²⁺ channels. Interestingly, upon intense and/or prolonged stimulation, α₂-adrenergic receptors become desensitized by the intervention of G protein-coupled receptor kinase 2 (GRK2). In several experimental models of heart failure, there has been reported the up-regulation of GRK2 and the loss of functioning of inhibitory α₂-adrenoceptors resulting in enhanced release of adrenomedullary catecholamines. Given the importance of circulating catecholamines in the pathophysiology of heart failure, the recovery of α₂-adrenergic modulation of the secretory response from chromaffin cells appears as a novel strategy for a better control of the patients with this cardiac disease.

Sympathetic Overactivity in Chronic Kidney Disease: Consequences and Mechanisms

The incidence of chronic kidney disease (CKD) is increasing worldwide, with more than 26 million people suffering from CKD in the United States alone. More patients with CKD die of cardiovascular complications than progress to dialysis. Over 80% of CKD patients have hypertension, which is associated with increased risk of cardiovascular morbidity and mortality. Another common, perhaps underappreciated, feature of CKD is an overactive sympathetic nervous system. This elevation in sympathetic nerve activity (SNA) not only contributes to hypertension but also plays a detrimental role in the progression of CKD independent of any increase in blood pressure. Indeed, high SNA is associated with poor prognosis and increased cardiovascular morbidity and mortality independent of its effect on blood pressure. This brief review will discuss some of the consequences of sympathetic overactivity and highlight some of the potential pathways contributing to chronically elevated SNA in CKD. Mechanisms leading to chronic sympathoexcitation in CKD are complex, multifactorial and to date, not completely understood. Identification of the mechanisms and/or signals leading to sympathetic overactivity in CKD are crucial for development of effective therapeutic targets to reduce the increased cardiovascular risk in this patient group.

The first-in-man randomized trial of a beta3 adrenoceptor agonist in chronic heart failure: the BEAT-HF trial

AIMS

The third isotype of beta adrenergic receptors (β3 ARs) has distinctly different effects on cardiomyocytes compared with β1 and β2 ARs. Stimulation of β3 ARs may reduce cardiomyocyte Na⁺ overload and reduce oxidative stress in heart failure (HF). We examined if treatment with the β3 AR agonist mirabegron increases LVEF in patients with HF.

METHODS AND RESULTS

In a double-blind trial we randomly assigned 70 patients with NYHA class II-III HF and LVEF <40% at screening-echocardiography to receive mirabegron or placebo for 6 months as add-on to optimized standard therapy. The primary endpoint was an increase in LVEF after 6 months as measured by computed tomography (CT). Changes in LVEF after 6 months between treatment groups were not significantly different (0.4%, -3.5 to 3.8%, P = 0.82). In an exploratory analysis, based on an expectation that the pathophysiological substrate targeted with treatment is dependent on the baseline LVEF, patients with LVEF <40% by CT given mirabegron had a significant increase in LVEF while no increase was seen in patients given placebo. The changes were significantly different between groups (5.5%, 0.6-10.4%, P < 0.03). Additionally, there was interaction between baseline LVEF and change in LVEF in the entire group of patients treated with mirabegron (R²  = 0.40, β  = -0.63, P < 0.001), but not in the placebo group (R²  = 0.00, β  = -0.01, P = 0.95). Treatment was generally well tolerated. Three patients in each group had fatal or life-threatening events.

CONCLUSIONS

The primary endpoint was not reached. Exploratory analysis indicated that β3 AR stimulation by mirabegron increased LVEF in patients with severe HF. Treatment appeared safe. Additional studies in severe HF are needed.

TRIAL REGISTRATION

NCT01876433.

Drugs That May Cause or Exacerbate Heart Failure: A Scientific Statement From the American Heart Association

Heart failure is a common, costly, and debilitating syndrome that is associated with a highly complex drug regimen, a large number of comorbidities, and a large and often disparate number of healthcare providers. All of these factors conspire to increase the risk of heart failure exacerbation by direct myocardial toxicity, drug-drug interactions, or both. This scientific statement is designed to serve as a comprehensive and accessible source of drugs that may cause or exacerbate heart failure to assist healthcare providers in improving the quality of care for these patients.

Carotid body modulation in systolic heart failure from the clinical perspective

Augmented sensitivity of peripheral chemoreceptors (PChS) is a common finding in systolic heart failure (HF). It is related to lower left ventricle systolic function, higher plasma concentrations of natriuretic peptides, worse exercise tolerance and greater prevalence of atrial fibrillation compared to patients with normal PChS. The magnitude of ventilatory response to the activation of peripheral chemoreceptors is proportional to the level of heart rate (tachycardia) and blood pressure (hypertension) responses. All these responses can be measured non-invasively in a safe and reproducible fashion using different methods employing either hypoxia or hypercapnia. Current interventions aimed at modulation of peripheral chemoreceptors in HF are focused on carotid bodies (CBs). There is a clear link between afferent signalling from CBs and sympathetic overactivity, which remains the priority target of modern HF treatment. However, CB modulation therapies may face several potential obstacles: (1) As evidenced by HF trials, an excessive inhibition of sympathetic system may be harmful. (2) Proximity of critical anatomical structures (important vessels and nerves) makes surgical and transcutaneous interventions on CB technically demanding. (3) Co-existence of atherosclerosis in the area of carotid artery bifurcation increases the risk of central embolic events related to CB modulation. (4) The relative contribution of CBs vs. aortic bodies to sympathetic activation in HF patients is unclear. (5) Choosing optimal candidates for CB modulation from the population of HF patients may be problematic. (6) There is a risk of nocturnal hypoxia following CB ablation - mostly after bilateral procedures and in patients with concomitant obstructive sleep apnoea.

Alpha-1-adrenergic receptors in heart failure: the adaptive arm of the cardiac response to chronic catecholamine stimulation

Alpha-1-adrenergic receptors (ARs) are G protein-coupled receptors activated by catecholamines. The alpha-1A and alpha-1B subtypes are expressed in mouse and human myocardium, whereas the alpha-1D protein is found only in coronary arteries. There are far fewer alpha-1-ARs than beta-ARs in the nonfailing heart, but their abundance is maintained or increased in the setting of heart failure, which is characterized by pronounced chronic elevation of catecholamines and beta-AR dysfunction. Decades of evidence from gain and loss-of-function studies in isolated cardiac myocytes and numerous animal models demonstrate important adaptive functions for cardiac alpha-1-ARs to include physiological hypertrophy, positive inotropy, ischemic preconditioning, and protection from cell death. Clinical trial data indicate that blocking alpha-1-ARs is associated with incident heart failure in patients with hypertension. Collectively, these findings suggest that alpha-1-AR activation might mitigate the well-recognized toxic effects of beta-ARs in the hyperadrenergic setting of chronic heart failure. Thus, exogenous cardioselective activation of alpha-1-ARs might represent a novel and viable approach to the treatment of heart failure.

Time and technology will tell: the pathophysiologic basis of neurohormonal modulation in heart failure

The central roles of neurohormonal abnormalities in the pathobiology of heart failure have been defined in recent decades. Experiments have revealed both systemic involvement and intricate subcellular regulation by circulating effectors of the sympathetic nervous system, the renin-angiotensin-aldosterone system, and others. Randomized clinical trials substantiated these findings, establishing neurohormonal antagonists as cornerstones of heart failure pharmacotherapy, and occasionally offering further insight on mode of benefit. This review discusses the use of β-blockers, angiotensin-converting enzyme inhibitors, angiotensin receptor blockers, and aldosterone receptor antagonists in the treatment of heart failure, with particular attention to the pathophysiologic basis and mechanisms of action.

The autonomic nervous system and heart failure

The pathophysiology of heart failure (HF) is characterized by hemodynamic abnormalities that result in neurohormonal activation and autonomic imbalance with increase in sympathetic activity and withdrawal of vagal activity. Alterations in receptor activation from this autonomic imbalance may have profound effects on cardiac function and structure. Inhibition of the sympathetic drive to the heart through β-receptor blockade has become a standard component of therapy for HF with a dilated left ventricle because of its effectiveness in inhibiting the ventricular structural remodeling process and in prolonging life. Several devices for selective modulation of sympathetic and vagal activity have recently been developed in an attempt to alter the natural history of HF. The optimal counteraction of the excessive sympathetic activity is still unclear. A profound decrease in adrenergic support with excessive blockade of the sympathetic nervous system may result in adverse outcomes in clinical HF. In this review, we analyze the data supporting a contributory role of the autonomic functional alterations on the course of HF, the techniques used to assess autonomic nervous system activity, the evidence for clinical effectiveness of pharmacological and device interventions, and the potential future role of autonomic nervous system modifiers in the management of this syndrome.

Adrenal adrenoceptors in heart failure

Heart failure (HF) is a chronic clinical syndrome characterized by the reduction in left ventricular (LV) function and it represents one of the most important causes of morbidity and mortality worldwide. Despite considerable advances in pharmacological treatment, HF represents a severe clinical and social burden. Sympathetic outflow, characterized by increased circulating catecholamines (CA) biosynthesis and secretion, is peculiar in HF and sympatholytic treatments (as β-blockers) are presently being used for the treatment of this disease. Adrenal gland secretes Epinephrine (80%) and Norepinephrine (20%) in response to acetylcholine stimulation of nicotinic cholinergic receptors on the chromaffin cell membranes. This process is regulated by adrenergic receptors (ARs): α2ARs inhibit CA release through coupling to inhibitory Gi-proteins, and β ARs (mainly β2ARs) stimulate CA release through coupling to stimulatory Gs-proteins. All ARs are G-protein-coupled receptors (GPCRs) and GPCR kinases (GRKs) regulate their signaling and function. Adrenal GRK2-mediated α2AR desensitization and downregulation are increased in HF and seem to be a fundamental regulator of CA secretion from the adrenal gland. Consequently, restoration of adrenal α2AR signaling through the inhibition of GRK2 is a fascinating sympatholytic therapeutic strategy for chronic HF. This strategy could have several significant advantages over existing HF pharmacotherapies minimizing side-effects on extra-cardiac tissues and reducing the chronic activation of the renin–angiotensin–aldosterone and endothelin systems. The role of adrenal ARs in regulation of sympathetic hyperactivity opens interesting perspectives in understanding HF pathophysiology and in the identification of new therapeutic targets.

Adrenergic signaling in heart failure: a balance of toxic and protective effects

Heart failure with reduced ejection fraction involves activation of the sympathetic nervous system and chronic hyperactivation of the sympatho-adrenergic receptors (ARs) β-ARs and α1-ARs, which are thought to be cardiotoxic and worsen pathological remodeling and function. Concurrently, the failing heart manifests significant decreases in sympathetic nerve terminal density, decreased cardiac norepinephrine levels, and marked downregulation of β-AR abundance and signaling. Thus, a state of both feast and famine coexist with respect to the adrenergic state in heart failure. For the failing heart, the hyperadrenergic state is toxic. However, the role of hypoadrenergic mechanisms in the pathophysiology of heart failure is less clear. Cardiotoxic effects are known to arise from the β1-AR subtype, and use of β-AR blockers is a cornerstone of current heart failure therapy. However, cardioprotective effects arise from the β2-AR subtype that counteract hyperactive β1-AR signaling, but unfortunately, β2-AR cardioprotective signaling in heart failure is inhibited by β-AR blocker therapy. In contrast to current dogma, recent research shows β1-AR signaling can also be cardioprotective. Moreover, for some forms of heart failure, β2-AR signaling is cardiotoxic. Thus for both β-AR subtypes, there is a balance between cardiotoxic versus cardioprotective effects. In heart failure, stimulation of α1-ARs is widely thought to be cardiotoxic. However, also contrary to current dogma, recent research shows that α1-AR signaling is cardioprotective. Taken together, recent research identifies cardioprotective signaling arising from β1-AR, β2-AR, and α1-ARs. A goal for future therapies will to harness the protective effects of AR signaling while minimizing cardiotoxic effects. The trajectory of heart failure therapy changed radically from the previous and intuitive use of sympathetic agonists, which unfortunately resulted in greater mortality, to the current use of β-AR blockers, which initially seemed counterintuitive. As a cautionary note, if the slow adoption of beta-blocker therapy in heart failure is any guide, then new treatment strategies, especially counterintuitive therapies involving stimulating β-AR and α1-AR signaling, may take considerable time to develop and gain acceptance.

Cardiac alpha1-adrenergic receptors: novel aspects of expression, signaling mechanisms, physiologic function, and clinical importance

Adrenergic receptors (AR) are G-protein-coupled receptors (GPCRs) that have a crucial role in cardiac physiology in health and disease. Alpha1-ARs signal through Gαq, and signaling through Gq, for example, by endothelin and angiotensin receptors, is thought to be detrimental to the heart. In contrast, cardiac alpha1-ARs mediate important protective and adaptive functions in the heart, although alpha1-ARs are only a minor fraction of total cardiac ARs. Cardiac alpha1-ARs activate pleiotropic downstream signaling to prevent pathologic remodeling in heart failure. Mechanisms defined in animal and cell models include activation of adaptive hypertrophy, prevention of cardiac myocyte death, augmentation of contractility, and induction of ischemic preconditioning. Surprisingly, at the molecular level, alpha1-ARs localize to and signal at the nucleus in cardiac myocytes, and, unlike most GPCRs, activate "inside-out" signaling to cause cardioprotection. Contrary to past opinion, human cardiac alpha1-AR expression is similar to that in the mouse, where alpha1-AR effects are seen most convincingly in knockout models. Human clinical studies show that alpha1-blockade worsens heart failure in hypertension and does not improve outcomes in heart failure, implying a cardioprotective role for human alpha1-ARs. In summary, these findings identify novel functional and mechanistic aspects of cardiac alpha1-AR function and suggest that activation of cardiac alpha1-AR might be a viable therapeutic strategy in heart failure.

Effects of moxonidine on sympathetic nervous system activity: An update on metabolism, cardio, and other target-organ protection

Moxonidine is the newest, second-generation, centrally acting antihypertensive agent. It has selective agonist activity at imidazoline I1 receptors and less adverse effects than the other centrally acting drugs. This fact authorizes the frequent use of moxonidine in clinical practice, as monotherapy or in combination with other antihypertensive agents. Also, moxonidine has beneficial effects in obese and metabolic syndrome and in target-organs, such as heart and kidneys.

The role of renal denervation in the treatment of heart failure

The heart and kidney interact in terms of hemodynamics and neurohumoral regulatory mechanisms, and this helps to maintain circulatory homeostasis under normal conditions. However, the normal regulatory mechanisms become inappropriate in the setting of congestive heart failure (CHF), and significant renal dysfunction often develops in CHF patients. Activation of renal sympathetic efferent nerves causes renin release, sodium and water retention, and reduced renal blood flow, all hallmarks of the renal manifestations of CHF. An increase in plasma levels of angiotensin II that is mediated in part by renal sympathetic activation has an effect on the central nervous system to further increase global sympathetic tone. Renal sympathetic activity can be assessed clinically by renal norepinephrine spillover, and an increase in renal norepinephrine spillover in CHF predicts reduced survival. In addition to efferent sympathetic activation, activation of renal sensory nerves in CHF may cause a reflex increase in sympathetic tone that contributes to elevated peripheral vascular resistance and vascular remodeling as well as left ventricular remodeling and dysfunction. In animal models of heart failure, surgical renal denervation has been shown to improve both renal and ventricular function. Although surgical renal denervation has long been known to lower blood pressure and improve survival in patients with hypertension, the invasive nature of this approach and its associated complications has limited its appeal. However, a novel catheter-based device has recently been introduced that specifically interrupts both efferent and afferent renal nerves, and there is significant interest in the use of this device to treat both hypertension and CHF. Several ongoing clinical trials are investigating the safety and efficacy of renal denervation in patients with CHF.

Blockade of β-adrenoceptors restores the GRK2-mediated adrenal α(2) -adrenoceptor-catecholamine production axis in heart failure

BACKGROUND AND PURPOSE

Sympathetic nervous system (SNS) hyperactivity is characteristic of chronic heart failure (HF) and significantly worsens prognosis. The success of β-adrenoceptor antagonist (β-blockers) therapy in HF is primarily attributed to protection of the heart from the noxious effects of augmented catecholamine levels. β-Blockers have been shown to reduce SNS hyperactivity in HF, but the underlying molecular mechanisms are not understood. The GPCR kinase-2 (GRK2)-α(2) adrenoceptor-catecholamine production axis is up-regulated in the adrenal medulla during HF causing α(2) -adrenoceptor dysfunction and elevated catecholamine levels. Here, we sought to investigate if β-blocker treatment in HF could lower SNS activation by directly altering adrenal GRK2 levels.

EXPERIMENTAL APPROACH

Four weeks after myocardial infarction-induced HF, adult rats were randomized to 10-week treatment with vehicle (HF/C) or bisoprolol (HF/B). Cardiac function and dimensions were measured. In heart and adrenal gland, GRK2 levels were assessed by RT-PCR and Western blotting and adrenoceptors studied with radioligand binding. Catecholamines and α(2) adrenoceptors in adrenal medulla chromaffin cell cultures were also measured.

KEY RESULTS

Bisoprolol treatment ameliorated HF-related adverse cardiac remodelling and reduced plasma catecholamine levels, compared with HF/C rats. Bisoprolol also attenuated adrenal GRK2 overexpression as observed in HF/C rats and increased α(2) adrenoceptor density. In cultures of adrenal medulla chromaffin cells from all study groups, bisoprolol reversed HF-related α(2) adrenoceptor dysfunction. This effect was reversed by GRK2 overexpression.

CONCLUSION AND IMPLICATIONS

Blockade of β-adrenoceptors normalized the adrenal α(2) adrenoceptor-catecholamine production axis by reducing GRK2 levels. This effect may contribute significantly to the decrease of HF-related sympathetic overdrive by β-blockers.

Are the pharmacology and physiology of α₂ adrenoceptors determined by α₂-heteroreceptors and autoreceptors respectively?

α(2)-Adrenoceptors are important mediators of physiological responses to the endogenous catecholamines noradrenaline and adrenaline. In addition, α(2)-adrenoceptors are pharmacological targets for the treatment of hypertension, sympathetic overactivity and glaucoma. α(2)-Adrenoceptors are also targeted to induce sedation and analgesia in anaesthesia and intensive care. α(2)-Adrenoceptors were first described as presynaptic receptors inhibiting the release of various transmitters from neurons in the central and peripheral nervous systems. In addition to these presynaptic neuronal receptors, α(2)-adrenoceptors were also identified in many non-neuronal cell types of the body. Gene-targeting in mice provided a comprehensive assignment of the physiological and pharmacological functions of these receptors to specific α(2A)-, α(2B) - and α(2C)-adrenoceptor subtypes. However, the specific cell types and signalling pathways involved in these subtype-specific α(2)-adrenoceptor functions were largely unexplored until recently. This review summarizes recent findings from transgenic mouse models, which were generated to define the role of α(2)-adrenoceptors in adrenergic neurons, that is, α(2)-autoreceptors, versus α(2)-adrenoceptors in non-adrenergic neurons, termed α(2)-heteroreceptors. α(2)-Autoreceptors are primarily required to limit release of noradrenaline from sympathetic nerves and adrenaline from adrenal chromaffin cells at rest. These receptors are desensitized upon chronic activation as it may for instance occur due to enhanced sympathetic activity during chronic heart failure. In contrast, pharmacological effects of acutely administered α(2)-adrenoceptor agonist drugs essentially require α(2)-heteroreceptors in non-adrenergic neurons, including analgesia, sedation, hypothermia and anaesthetic-sparing as well as bradycardia and hypotension. Thus a clear picture has emerged of the significance of auto- versus heteroreceptors in mediating the physiological functions of α(2)-adrenoceptors and the pharmacological functions of α(2)-adrenoceptor agonist drugs respectively.

Statin therapy lowers muscle sympathetic nerve activity and oxidative stress in patients with heart failure

Despite standard drug therapy, sympathetic nerve activity (SNA) remains high in heart failure (HF) patients making the sympathetic nervous system a primary drug target in the treatment of HF. Studies in rabbits with pacing-induced HF have demonstrated that statins reduce resting SNA, in part, due to reductions in reactive oxygen species (ROS). Whether these findings can be extended to the clinical setting of human HF remains unclear. We first performed a study in seven statin-naïve HF patients (56 ± 2 yr; ejection fraction: 31 ± 4%) to determine if 1 mo of simvastatin (40 mg/day) reduces muscle SNA (MSNA). Next, to control for possible placebo effects and determine the effect of simvastatin on ROS, a double-blinded, placebo-controlled crossover design study was performed in six additional HF patients (51 ± 3 yr; ejection fraction: 22 ± 4%), and MSNA, ROS, and superoxide were measured. We tested the hypothesis that statin therapy decreases resting MSNA in HF patients and this would be associated with reductions in ROS. In study 1, simvastatin reduced resting MSNA (75 ± 5 baseline vs. 65 ± 5 statin bursts/100 heartbeats; P < 0.05). Likewise, in study 2, simvastatin also decreased resting MSNA (59 ± 5 placebo vs. 45 ± 6 statin bursts/100 heartbeats; P < 0.05). In addition, statin therapy significantly reduced total ROS and superoxide. As expected, cholesterol was reduced after simvastatin. Collectively, these findings indicate that short-term statin therapy concomitantly reduces resting MSNA and total ROS and superoxide in HF patients. Thus, in addition to lowering cholesterol, statins may also be beneficial in reducing sympathetic overactivity and oxidative stress in HF patients.

Icariin attenuates cardiac remodelling through down-regulating myocardial apoptosis and matrix metalloproteinase activity in rats with congestive heart failure

Objectives

In this study, the anti-heart failure effect of icariin, a natural flavonol glycoside, and the underlying mechanisms were investigated.

Methods

Heart failure was induced by isoproterenol in male Sprague–Dawley rats. Matrix metalloproteinase activity was determined by gelatin zymography assay. The mRNA expression was determined by real-time PCR. The protein expression was determined by Western bolt. Mitochondria structure was examined by transmission electron microscopy.

Key findings

Isoproterenol administration resulted in a severe heart failure, as shown by the increased levels of left ventricular weight index, heart rate, left ventricular end diastolic pressure, maximal rate of left ventricular pressure decline (dp/dtmin), decreased levels of left ventricular systolic pressure and maximal rate of left ventricular pressure rise (dp/dtmax). Against these, icariin dose-dependently reversed the changes of these cardiac morphometric and haemodynamic parameters. In addition, icariin significantly inhibited serum levels of tumour necrosis factor-α, noradrenaline, angiotensin II and brain natriuretic peptide in rats with congestive hear failure and improved the histological changes, including cardiocyte hypertrophy, cardiocyte degeneration, inflammatory infiltration and cardiac desmoplasia. Furthermore, the expression and activity of matrix metalloproteinase (MMP)-2 and MMP-9, which regulate collagen production, were also blocked by icariin. Moreover, myocardial apoptosis was remarkably attenuated by icariin through regulating Bcl-2/Bax axle.

Conclusions

Icariin ameliorates left ventricular dysfunction and cardiac remodelling through down-regulating matrix metalloproteinase-2 and 9 activity and myocardial apoptosis in rats with congestive heart failure.

Functional and molecular effects of imidazoline receptor activation in heart failure

AIMS

Heart failure is a progressive deterioration in heart function associated with overactivity of the sympathetic nervous system. The benefit of inhibition of sympathetic activity by moxonidine, a centrally acting imidazoline receptor agonist, was questioned based on the outcome of a failing clinical trial. The following studies measured cardiac structure and hemodynamics and mechanisms underlying moxonidine-induced changes, in cardiomyopathic hamsters, where the stage of the disease, dose, and compliance were controlled.

MAIN METHODS

Male BIO 14.6 hamsters (6 and 10 months old, with moderate and advanced heart failure, respectively) received moxonidine at 2 concentrations: low (2.4 mg/kg/day) and high (9.6 mg/kg/day), or vehicle, subcutaneously, for 1month. Cardiac function was measured by echocardiography, plasma and hearts were collected for histological determination of fibrosis and apoptosis, as well as for measurement cytokines by Elisa and cardiac proteins by Western blotting.

KEY FINDINGS

Compared to age-matched vehicle-treated BIO 14.6, moxonidine did not reduce blood pressure but significantly reduced heart rate and improved cardiac performance. Moxonidine exerted anti-apoptotic effect with differential inflammatory/anti-inflammatory responses that culminate in attenuated cardiac apoptosis and fibrosis and altered protein expression of collagen types. Some effects were observed regardless of treatment onset, although the changes were more significant in the younger group. Interestingly, moxonidine resulted in upregulation of cardiac imidazoline receptors.

SIGNIFICANCE

These studies imply that in addition to centrally mediated sympathetic inhibition, the effects of moxonidine may, at least in part, be mediated by direct actions on the heart. Further investigation of imidazolines/imidazoline receptors in cardiovascular diseases is warranted.

Alpha-1-adrenergic receptors: targets for agonist drugs to treat heart failure

Evidence from cell, animal, and human studies demonstrates that α1-adrenergic receptors mediate adaptive and protective effects in the heart. These effects may be particularly important in chronic heart failure, when catecholamine levels are elevated and β-adrenergic receptors are down-regulated and dysfunctional. This review summarizes these data and proposes that selectively activating α1-adrenergic receptors in the heart might represent a novel and effective way to treat heart failure. This article is part of a special issue entitled "Key Signaling Molecules in Hypertrophy and Heart Failure."

Quantitative evaluation of drug or device effects on ventricular remodeling as predictors of therapeutic effects on mortality in patients with heart failure and reduced ejection fraction: a meta-analytic approach

OBJECTIVES

The purpose of this study was to quantitatively assess the relationship between therapy-induced changes in left ventricular (LV) remodeling and longer-term outcomes in patients with left ventricular dysfunction (LVD).

BACKGROUND

Whether therapy-induced changes in left ventricular ejection fraction (LVEF), end-diastolic volume (EDV), and end-systolic volume (ESV) are predictors of mortality in patients with LVD is not established.

METHODS

Searches for randomized controlled trials (RCTs) were conducted to identify drug or device therapies for which an effect on mortality in patients with LVD was studied in at least 1 RCT of > or = 500 patients (mortality trials). Then, all RCTs involving those therapies were identified in patients with LVD that described changes in LVEF and/or volumes over time (remodeling trials). We examined whether the magnitude of remodeling effects is associated with the odds ratios for death across all therapies or associated with whether the odds ratio for mortality was favorable, neutral, or adverse (i.e., statistically significantly decreased, nonsignificant, or statistically significantly increased odds for mortality, respectively).

RESULTS

Included were 30 mortality trials of 25 drug/device therapies (n = 69,766 patients; median follow-up 17 months) and 88 remodeling trials of the same therapies (n = 19,921 patients; median follow-up 6 months). The odds ratio for death in the mortality trials was correlated with drug/device effects on LVEF (r = -0.51, p < 0.001), EDV (r = 0.44, p = 0.002), and ESV (r = 0.48, p = 0.002). In (ordinal) logistic regressions, the odds for neutral or favorable effects in the mortality RCTs increased with mean increases in LVEF and with mean decreases in EDV and ESV in the remodeling trials.

CONCLUSIONS

In patients with LVD, short-term trial-level therapeutic effects of a drug or device on LV remodeling are associated with longer-term trial-level effects on mortality.

Adrenal GRK2 lowering is an underlying mechanism for the beneficial sympathetic effects of exercise training in heart failure

Exercise training has been reported to exert beneficial effects on cardiac function and to reduce morbidity and mortality of chronic heart failure (HF). Augmented sympathetic nervous system (SNS) activity, leading to elevated circulating catecholamine (CA) levels, is a hallmark of chronic HF that significantly aggravates this disease. Exercise training has been shown to also reduce SNS overactivity in HF, but the underlying molecular mechanism(s) remain unidentified. We recently reported that adrenal G protein-coupled receptor kinase-2 (GRK2), an enzyme that regulates the sympathoinhibitory alpha(2)-adrenoceptors (alpha(2)-ARs) present in the CA-producing adrenal medulla, is upregulated in HF, contributing to the chronically elevated CA levels and SNS activity of the disease. In the present study, we tested whether exercise training can affect the adrenal GRK2-alpha(2)-AR-CA production system in the context of HF. For this purpose, a 10-wk-long exercise training regimen of adult male Sprague-Dawley rats starting at 4 wk postmyocardial infarction (post-MI) was employed, and examination at the end of this treatment period revealed significant amelioration of beta-AR-stimulated contractility in response to exercise training, accompanied by cardiac GRK2 reduction and restoration of circulating plasma CA levels. Importantly, adrenal GRK2 expression (72 + or - 5% reduction vs. post-MI untrained) and alpha(2)-AR number were also restored after exercise training in post-MI animals. These results suggest that exercise training restores the adrenal GRK2-alpha(2)-AR-CA production axis, and this might be part of the mechanism whereby this therapeutic modality normalizes sympathetic overdrive and impedes worsening of the failing heart.

An α 2C -Adrenergic Receptor Polymorphism Alters the Norepinephrine-Lowering Effects and Therapeutic Response of the β-Blocker Bucindolol in Chronic Heart Failure

Background— Adrenergic activation is an important determinant of outcomes in chronic heart failure. Adrenergic activity is regulated in part by prejunctional α 2C -adrenergic receptors (ARs), which exhibit genetic variation in humans. Bucindolol is a novel β-AR blocking agent that also lowers systemic norepinephrine and thus is also a sympatholytic agent. This study investigated whether α 2C -AR polymorphisms affect sympatholytic effects of bucindolol in patients with heart failure.

Methods and Results— In the β-Blocker Evaluation of Survival Trial, adrenergic activation was estimated by systemic venous norepinephrine measured at baseline, 3 months, and 12 months posttreatment in patients treated with placebo or bucindolol. In the β-Blocker Evaluation of Survival Trial AR polymorphism substudy, DNA was collected from 1040 of the 2708 randomized patients, and α 2C -AR gene polymorphisms (α 2C Del322-325 or the wild-type counterpart) were measured by polymerase chain reaction and gel electrophoresis. Patients who were α 2C Del carriers (heterozygotes or homozygotes) exhibited a much greater sympatholytic response to bucindolol (decrease in norepinephrine at 3 months of 153±57 pg/mL, P =0.012 compared with placebo versus decrease of 50±13 pg/mL in α 2C wild type, P =0.0005 versus placebo; P =0.010 by interaction test). α 2C Del carriers had no evidence of a favorable survival benefit from bucindolol (mortality compared with placebo hazard ratio, 1.09; 95% CI, 0.57 to 2.08; P =0.80), whereas bucindolol-treated subjects who were wild type for the α 2C -AR had a 30% reduction in mortality (hazard ratio, 0.70; 95% CI, 0.51 to 0.96; P =0.025).

Conclusions— In the β-Blocker Evaluation of Survival Trial AR polymorphism substudy, the norepinephrine lowering and clinical therapeutic responses to bucindolol were strongly influenced by α 2C receptor genotype.

What we may expect from biomarkers in heart failure

A profusion of circulating candidate biomarkers in heart failure is currently being investigated. Although all will advance our insight into the pathophysiology of heart failure, their potential clinical utility will depend on satisfaction of three key criteria. Assays must be accessible, reliable, and affordable. Secondly, the marker must provide information about cardiac function and prognosis not otherwise available. Finally, measurement of the marker must demonstrably lead to improved management and better clinical outcomes. Despite many promising candidates requiring fuller investigation, currently, only the natriuretic peptides satisfy these requirements.

G-protein-coupled receptor kinases in cardiovascular conditions: focus on G-protein-coupled receptor kinase 2, a gain in translational medicine

With increasing knowledge of the regulatory mechanisms of G-protein-coupled receptor signaling in heart physiology, many studies have focused on the role of this system in cardiovascular disease. In recent years, scientists have moved their attention from the receptors to their regulatory proteins: the G-protein-coupled receptor kinases. This class of protein is indispensable for terminating signaling of G-protein-coupled receptors through receptor desensitization and downregulation. This article attempts to assemble the currently available information regarding G-protein-coupled receptor kinases and their role in cardiovascular disease and, in particular, the potential employment of G-protein-coupled receptor kinase 2 as biomarker of cardiac dysfunction.

{alpha}1-Adrenergic receptor subtypes in nonfailing and failing human myocardium

BACKGROUND

alpha1-adrenergic receptors (alpha1-ARs) play adaptive roles in the heart and protect against the development of heart failure. The 3 alpha1-AR subtypes, alpha1A, alpha1B, and alpha1D, have distinct physiological roles in mouse heart, but very little is known about alpha1 subtypes in human heart. Here, we test the hypothesis that the alpha1A and alpha1B subtypes are present in human myocardium, similar to the mouse, and are not downregulated in heart failure.

METHODS AND RESULTS

Hearts from transplant recipients and unused donors were failing (n=12; mean ejection fraction, 24%) or nonfailing (n=9; mean ejection fraction, 59%) and similar in age ( approximately 44 years) and sex ( approximately 70% male). We measured the alpha1-AR subtypes in multiple regions of both ventricles by quantitative real-time reverse-transcription polymerase chain reaction and radioligand binding. All 3 alpha1-AR subtype mRNAs were present, and alpha1A mRNA was most abundant ( approximately 65% of total alpha1-AR mRNA). However, only alpha1A and alpha1B binding were present, and the alpha1B was most abundant (60% of total). In failing hearts, alpha1A and alpha1B binding was not downregulated, in contrast with beta1-ARs.

CONCLUSIONS

Our data show for the first time that the alpha1A and alpha1B subtypes are both present in human myocardium, but alpha1D binding is not, and the alpha1 subtypes are not downregulated in heart failure. Because alpha1 subtypes in the human heart are similar to those in the mouse, where adaptive and protective effects of alpha1 subtypes are most convincing, it might become feasible to treat heart failure with a drug targeting the alpha1A and/or alpha1B.

Central sympathetic overactivity: maladies and mechanisms

There is growing evidence to suggest that many disease states are accompanied by chronic elevations in sympathetic nerve activity. The present review will specifically focus on central sympathetic overactivity and highlight three main areas of interest: 1) the pathological consequences of excessive sympathetic nerve activity; 2) the potential role of centrally derived nitric oxide in the genesis of neural dysregulation in disease; and 3) the promise of several novel therapeutic strategies targeting central sympathetic overactivity. The findings from both animal and human studies will be discussed and integrated in an attempt to provide a concise update on current work and ideas in these important areas.

Traditional and novel approaches to management of heart failure: successes and failures

Although considerable progress has been made in the pharmacologic and device management of chronic heart failure in recent decades, heart failure patients continue to remain symptomatic, with high hospitalization and mortality rates. A number of novel agents, including endothelin antagonists and tumor-necrosis factor blockers, have recently failed to improve the clinical outcomes of patients with heart failure. Have we reached a ceiling in preventing the progression of the disease? This article reviews successes and late-stage clinical trial disappointments in the treatment of patients with heart failure. Furthermore, the article discusses how agents that have beneficial effects in heart failure also generally attenuate or reverse ventricular remodeling, whereas the newer agents that have failed to improve clinical outcomes either had no effect on remodeling or have been associated with adverse remodeling.

Assist devices fail to reverse patterns of fetal gene expression despite beta-blockers

BACKGROUND

Heart failure is associated with reversal to a fetal gene expression pattern of contractile and metabolic genes. Substantial recovery of ventricular function with assist devices is rare. Our goal was to evaluate the effects of assist devices on fetal gene expression and hypoxia inducible factor-1 alpha (HIF-1 alpha), a transcriptional factor in hypoxic signaling.

METHODS

Human heart tissue was obtained from the left ventricular apex at the time of assist device implantation and again from the left ventricular free wall during cardiac transplantation. Non-failing tissue was obtained from unused hearts from human donors. Gene expression was measured with the Affymetrix 133 plus 2 Array. HIF-1 alpha was measured by Western blotting with commercially available antibodies.

RESULTS

Heart failure was associated with a decrease in alpha-myosin heavy chain and sarcoplasmic reticulum-Ca(2+) adenosine triphosphatase messenger RNA expression along with an increase in skeletal tropomyosin. This pattern persisted after assist device therapy. Heart failure was also associated with abnormalities in regulatory metabolic genes including glucose transporter 1 (GLUT1). These patterns also persisted after assist device therapy despite a reduction in atrial natriuretic peptide expression and normalization of HIF-1 alpha.

CONCLUSIONS

Failure of assist devices to produce sustained recovery of myocardial contractile function may be due in part to persistent fetal transcriptional patterns of contractile and metabolic genes.

Adrenal adrenoceptors in heart failure: fine-tuning cardiac stimulation

Chronic heart failure (HF) is characterized by sympathetic hyperactivity reflected by increased circulating catecholamines (CAs), which contributes significantly to its morbidity and mortality. Therefore, sympatholytic treatments, that is, treatments that reduce sympathetic hyperactivity, are being pursued currently for the treatment of HF. Secretion of CAs from the adrenal gland, which is a major source of CAs, is regulated by alpha(2)-adrenoceptors (alpha(2)ARs), which inhibit, and by beta-adrenoceptors (betaARs), which enhance CA secretion. All ARs are G-protein-coupled receptors (GPCRs), whose signaling and function are regulated tightly by the family of GPCR kinases (GRKs). Despite the enormous potential of adrenal ARs for the regulation of sympathetic outflow, elucidation of their properties has only begun recently. Here, recent advances regarding the roles of adrenal ARs in the regulation of sympathetic outflow in HF and the regulatory properties of ARs are discussed, along with the potential benefits and challenges of harnessing their function for HF therapy.

Cardiac Transplantation: Any Role Left?

The authors analyze the question of whether heart transplantation still has a role in the current era of complex technologies. To achieve this objective, the authors first discuss the known benefits of different therapeutic modalities currently available for patients who have end-stage heart failure, including pharmacologic management, electrophysiologic therapies, high-risk surgical strategies, implantation of mechanical circulatory support device therapy, and heart transplantation. The authors then evaluate the current developments and future perspectives in the field that may influence the likelihood of heart transplantation to remain the therapeutic modality of choice for end-stage heart failure.

Nesiritide for acute decompensated heart failure: does the benefit justify the risk?

Nesiritide is US Food and Drug Administration-approved for the treatment of patients with acutely decompensated heart failure who suffer from symptoms at rest or with minimal exertion. Its approval was based on a clinical development program that focused on surrogates and short-term effects on symptoms rather than clinical outcomes. The association between its use and subsequent risk of death raises the question of whether the endpoints assessed in the clinical development program were adequate, and provides the opportunity to evaluate the process of weighing risks with benefits. We conclude that with nesiritide, the risks of therapy outweigh the benefits demonstrated to date.

Adrenal GRK2 upregulation mediates sympathetic overdrive in heart failure

Cardiac overstimulation by the sympathetic nervous system (SNS) is a salient characteristic of heart failure, reflected by elevated circulating levels of catecholamines. The success of beta-adrenergic receptor (betaAR) antagonists in heart failure argues for SNS hyperactivity being pathogenic; however, sympatholytic agents targeting alpha2AR-mediated catecholamine inhibition have been unsuccessful. By investigating adrenal adrenergic receptor signaling in heart failure models, we found molecular mechanisms to explain the failure of sympatholytic agents and discovered a new strategy to lower SNS activity. During heart failure, there is substantial alpha2AR dysregulation in the adrenal gland, triggered by increased expression and activity of G protein-coupled receptor kinase 2 (GRK2). Adrenal gland-specific GRK2 inhibition reversed alpha2AR dysregulation in heart failure, resulting in lowered plasma catecholamine levels, improved cardiac betaAR signaling and function, and increased sympatholytic efficacy of a alpha2AR agonist. This is the first demonstration, to our knowledge, of a molecular mechanism for SNS hyperactivity in heart failure, and our study identifies adrenal GRK2 activity as a new sympatholytic target.

β-blocker therapy of heart failure: an update

The beneficial effects of beta-blocker therapy in patients with heart failure have been consistently shown by multi-center randomised trials. These agents are effective and also relatively well tolerated in the elderly and in patients with diabetes and advanced heart failure--traditionally considered as relative contraindications to their administration. However, the use of beta-blockers in clinical practice remains low. The difficulties in their initiation and up-titration may be overcome by patient and physician education, as well as by their initiation during hospitalisation and/or the involvement of non-physician providers (i.e., a nurse facilitator). Forthcoming advances in the pharmacokinetic and pharmacodynamic characteristics of some beta-blockers, and testing of novel methods for patient and drug selection may be based on genetic testing, and may allow further improvement of beta-blocker therapy in the next future.

Beta-blockers in heart failure: are pharmacological differences clinically important?

Beta-blockers are not an homogeneous group of agents. Only three beta-blockers, carvedilol, bisoprolol and metoprolol succinate, have had favorable effects on prognosis in controlled clinical trials in the patients with chronic heart failure. However, pharmacological differences exist between them. Metoprolol and bisoprolol are selective for beta(1)-adrenergic receptors while carvedilol blocks also beta(2)-, and alpha(1)- adrenergic receptors, and has associated antioxidant, anti-endothelin and antiproliferative properties. In COMET carvedilol was associated with a significant reduction in mortality compared to metoprolol tartrate further showing that different beta-blockers may have different effects on the outcome. These differences may be related to the ancillary properties of carvedilol or to its broader antiadrenergic profile. However, also more effective and prolonged blockade of beta1 adrenergic receptors may occur with carvedilol compared to metoprolol.

Using Measures of Disease Progression to Determine Therapeutic Effect

With an increasing burden of cardiovascular disease and many promising novel treatments in development, the need for efficient systems to evaluate treatments has never been greater. To understand whether a treatment should be used in practice, we need to know whether it makes patients live longer, feel better, prevents adverse events, or does these things with better tolerability or lower cost. But therapeutic development is expensive, inefficient, and is generally focused on short-term treatment effects, rather than on prevention and on long-term impact. Could measures of disease progression, combined with trends on clinical outcomes and post-marketing surveillance to assess safety, serve as the foundation for therapeutic development? Experience and principles of clinical research tell us no. Especially in the field of heart failure, numerous treatments have appeared promising based on disease markers, yet caused harm when tested in studies that assessed clinical outcomes. The intersection of complex human disease, intended and unintended targets of therapy, and overall risk and benefit make it impossible to accurately predict the effect on clinical outcomes based on impact on a disease marker. While reliable measures of disease progression are important to guide which treatments to study in trials, clinical outcome trials must remain the basis for informing clinicians on which treatments improve clinical outcomes. Improved reliability and capacity require the development of more efficient clinical trial methods, streamlined regulatory processes, rational use of privacy protection, leveraging of electronic medical records, and recruitment of a larger proportion of the clinical community to participate in clinical trials.

Alpha1-adrenergic receptors prevent a maladaptive cardiac response to pressure overload

An alpha1-adrenergic receptor (alpha1-AR) antagonist increased heart failure in the Antihypertensive and Lipid-Lowering Treatment to Prevent Heart Attack Trial (ALLHAT), but it is unknown whether this adverse result was due to alpha1-AR inhibition or a nonspecific drug effect. We studied cardiac pressure overload in mice with double KO of the 2 main alpha1-AR subtypes in the heart, alpha 1A (Adra1a) and alpha 1B (Adra1b). At 2 weeks after transverse aortic constriction (TAC), KO mouse survival was only 60% of WT, and surviving KO mice had lower ejection fractions and larger end-diastolic volumes than WT mice. Mechanistically, final heart weight and myocyte cross-sectional area were the same after TAC in KO and WT mice. However, KO hearts after TAC had increased interstitial fibrosis, increased apoptosis, and failed induction of the fetal hypertrophic genes. Before TAC, isolated KO myocytes were more susceptible to apoptosis after oxidative and beta-AR stimulation, and beta-ARs were desensitized. Thus, alpha1-AR deletion worsens dilated cardiomyopathy after pressure overload, by multiple mechanisms, indicating that alpha1-signaling is required for cardiac adaptation. These results suggest that the adverse cardiac effects of alpha1-antagonists in clinical trials are due to loss of alpha1-signaling in myocytes, emphasizing concern about clinical use of alpha1-antagonists, and point to a revised perspective on sympathetic activation in heart failure.

Influence of central inhibition of sympathetic nervous activity on myocardial metabolism in chronic heart failure: acute effects of the imidazoline I1-receptor agonist moxonidine

Although β-adrenergic blockade is beneficial in heart failure, inhibition of central sympathetic outflow using moxonidine has been associated with increased mortality. In the present study, we studied the acute effects of the imidazoline-receptor agonist moxonidine on haemodynamics, NA (noradrenaline) kinetics and myocardial metabolism. Fifteen patients with CHF (chronic heart failure) were randomized to a single dose of 0.6 mg of sustained-release moxonidine or matching placebo. Haemodynamics, NA kinetics and myocardial metabolism were studied over a 2.5 h time period. There was a significant reduction in pulmonary and systemic arterial pressures, together with a decrease in cardiac index in the moxonidine group. Furthermore, there was a simultaneous reduction in systemic and cardiac net spillover of NA in the moxonidine group. Analysis of myocardial consumption of substrates in the moxonidine group showed a significant increase in non-esterified fatty acid consumption and a possible trend towards an increase in myocardial oxygen consumption compared with the placebo group (P=0.16). We conclude that a single dose of moxonidine (0.6 mg) in patients already treated with a β-blocker reduced cardiac and overall sympathetic activity. The finding of increased lipid consumption without decreased myocardial oxygen consumption indicates a lack of positive effects on myocardial metabolism under these conditions. We suggest this might be a reason for the failure of moxonidine to prevent deaths in long-term studies in CHF.