Alterations in cardiac beta-adrenoceptor responsiveness and adenylate cyclase system by congestive heart failure in dogs

Right heart dysfunction and failure in heart failure with preserved ejection fraction: mechanisms and management. Position statement on behalf of the Heart Failure Association of the European Society of Cardiology

There is an unmet need for effective treatment strategies to reduce morbidity and mortality in patients with heart failure with preserved ejection fraction (HFpEF). Until recently, attention in patients with HFpEF was almost exclusively focused on the left side. However, it is now increasingly recognized that right heart dysfunction is common and contributes importantly to poor prognosis in HFpEF. More insights into the development of right heart dysfunction in HFpEF may aid to our knowledge about this complex disease and may eventually lead to better treatments to improve outcomes in these patients. In this position paper from the Heart Failure Association of the European Society of Cardiology, the Committee on Heart Failure with Preserved Ejection Fraction reviews the prevalence, diagnosis, and pathophysiology of right heart dysfunction and failure in patients with HFpEF. Finally, potential treatment strategies, important knowledge gaps and future directions regarding the right side in HFpEF are discussed.

Effect of hypertension at presentation on prognosis in patients with dilated cardiomyopathy presenting with normal renal angiogram

Background & objectives:

Dilated cardiomyopathy (DCM) is a progressive disease of heart with systolic and diastolic dysfunction carrying a poor long-term prognosis. The prognostic index and predictors of mortality are considered to be useful in guiding the treatment. This study was undertaken to evaluate the effects of hypertension at presentation on prognosis in patients with DCM presenting with normal renal and coronary angiogram.

Methods:

An observational, analytical, non-interventional and a combination of retrospective and prospective study was conducted in patients between 15 and 75 yr of age with DCM having on and off symptoms while receiving treatment in a cardiology outpatient department for more than a year. Sixty patients who fulfilled the inclusion criteria were enrolled in the study. Left ventricular systolic and diastolic functions were assessed by echocardiography along with New York Heart Association (NYHA) functional class prospectively and at baseline retrospectively. Patients were grouped into two categories: DCM with hypertension at presentation (HTNAP, Category 1) and DCM without hypertension at presentation (NHTNAP, Category 2). The primary end-points were the number and dose of parenteral drugs at hospitalization, duration of hospital stay and change in the left ventricular (LV) systolic function expressed as LV ejection fraction, and the secondary end-points included overall mortality, change in LV and right ventricular systolic and diastolic functions and change in the NYHA functional class between baseline and three month follow up in patients.

Results:

Thirty five and 25 patients presented with HTNAP and NHTNAP, respectively (total 60). The overall mortality was 10 per cent (6/60). The number of hospitalizations was less in HTNAP category and of days of hospital stay was 6.3 in HTNAP and 9.8 in NHTNAP, the difference being significant (P < 0.001). The HTNAP category required less parenteral diuretics and inotropes compared with the NHTNAP category. The echocardiographic parameters showed better improvements in the HTNAP group as compared to the NHTNAP group. Overall, the patients in the <35 yr of age showed the best prognosis (P < 0.001).

Interpretation & conclusions:

Normal or high blood pressure response at acute presentation of DCM leads to better prognosis which may be due to an intact renovascular and an active sympathetic system and can depict the stage of DCM.

Effects of Single Drug and Combined Short-term Administration of Sildenafil, Pimobendan, and Nicorandil on Right Ventricular Function in Rats With Monocrotaline-induced Pulmonary Hypertension

This study was designed to assess the progression of pulmonary arterial hypertension (PAH) and the effectiveness of therapy using recently investigated echocardiographic parameters. PAH is characterized by the progressive elevation of pulmonary artery pressure and right ventricular hypertrophy and dysfunction, which ultimately results in right-sided heart failure and death. Echocardiography results and invasive measurements of right and left ventricular systolic pressures were compared after 3-week administrations of sildenafil (S group), pimobendan (P group), nicorandil (N group), and their combinations (SP and SPN groups) in male rats with monocrotaline (MCT)-induced pulmonary hypertension (M group) and without this condition (C group). The groups that received pimobendan alone and in combinations (SP and SPN groups) showed improvement in their echocardiographic parameters of systolic function. A significant improvement of diastolic function was achieved in the SPN group. Invasive measurements showed the most significant decreases of right ventricular systolic pressure in the N and SPN groups, and the use of pimobendan resulted in a comparatively low risk of adverse hemodynamic effects (left ventricular systolic pressure). Although our results suggested the attenuation of PAH severity in all treatment groups, PAH could not be reversed.

Sympathetic nervous system activation and β-adrenoceptor blockade in right heart failure

Right heart failure may develop from pulmonary arterial hypertension or various forms of congenital heart disease. Right ventricular adaptation to the increased afterload is the most important prognostic factor in pulmonary hypertension and congenital heart disease, which share important pathophysiological mechanisms, despite having different aetiologies. There is substantial evidence of increased sympathetic nervous system activation in right heart failure related to both pulmonary hypertension and congenital heart disease. It is unknown to which degree this activation is an adaptive response, a maladaptive response, or if it mainly reflects disease progression. Several experimental studies and clinical trials have been conducted to answer these questions. Here, we review the existing knowledge on sympathetic nervous system activation and the effects of β-adrenoceptor blockade in experimental and clinical right heart failure. This review identifies important gaps in our understanding of the right ventricle and discusses the potential of β-blockers in the treatment of right heart failure.

The right ventricle in pulmonary arterial hypertension: disorders of metabolism, angiogenesis and adrenergic signaling in right ventricular failure

The right ventricle (RV) is the major determinant of functional state and prognosis in pulmonary arterial hypertension. RV hypertrophy (RVH) triggered by pressure overload is initially compensatory but often leads to RV failure. Despite similar RV afterload and mass some patients develop adaptive RVH (concentric with retained RV function), while others develop maladaptive RVH, characterized by dilatation, fibrosis, and RV failure. The differentiation of adaptive versus maladaptive RVH is imprecise, but adaptive RVH is associated with better functional capacity and survival. At the molecular level, maladaptive RVH displays greater impairment of angiogenesis, adrenergic signaling, and metabolism than adaptive RVH, and these derangements often involve the left ventricle. Clinically, maladaptive RVH is characterized by increased N-terminal pro-brain natriuretic peptide levels, troponin release, elevated catecholamine levels, RV dilatation, and late gadolinium enhancement on MRI, increased (18)fluorodeoxyglucose uptake on positron emission tomography, and QTc prolongation on the ECG. In maladaptive RVH there is reduced inotrope responsiveness because of G-protein receptor kinase-mediated downregulation, desensitization, and uncoupling of β-adrenoreceptors. RV ischemia may result from capillary rarefaction or decreased right coronary artery perfusion pressure. Maladaptive RVH shares metabolic abnormalities with cancer including aerobic glycolysis (resulting from a forkhead box protein O1-mediated transcriptional upregulation of pyruvate dehydrogenase kinase), and glutaminolysis (reflecting ischemia-induced cMyc activation). Augmentation of glucose oxidation is beneficial in experimental RVH and can be achieved by inhibition of pyruvate dehydrogenase kinase, fatty acid oxidation, or glutaminolysis. Therapeutic targets in RV failure include chamber-specific abnormalities of metabolism, angiogenesis, adrenergic signaling, and phosphodiesterase-5 expression. The ability to restore RV function in experimental models challenges the dogma that RV failure is irreversible without regression of pulmonary vascular disease.

Interventricular differences in β-adrenergic responses in the canine heart: role of phosphodiesterases

Background

RV and LV have different embryologic, structural, metabolic, and electrophysiologic characteristics, but whether interventricular differences exist in β‐adrenergic (β‐AR) responsiveness is unknown. In this study, we examine whether β‐AR response and signaling differ in right (RV) versus left (LV) ventricles.

Methods and Results

Sarcomere shortening, Ca²⁺ transients, I_Ca,L and I_Ks currents were recorded in isolated dog LV and RV midmyocytes. Intracellular [cAMP] and PKA activity were measured by live cell imaging using FRET‐based sensors. Isoproterenol increased sarcomere shortening ≈10‐fold and Ca²⁺‐transient amplitude ≈2‐fold in LV midmyocytes (LVMs) versus ≈25‐fold and ≈3‐fold in RVMs. FRET imaging using targeted Epac2camps sensors revealed no change in subsarcolemmal [cAMP], but a 2‐fold higher β‐AR stimulation of cytoplasmic [cAMP] in RVMs versus LVMs. Accordingly, β‐AR regulation of I_Ca,L and I_Ks were similar between LVMs and RVMs, whereas cytoplasmic PKA activity was increased in RVMs. Both PDE3 and PDE4 contributed to the β‐AR regulation of cytoplasmic [cAMP], and the difference between LVMs and RVMs was abolished by PDE3 inhibition and attenuated by PDE4 inhibition. Finally LV and RV intracavitary pressures were recorded in anesthetized beagle dogs. A bolus injection of isoproterenol increased RV dP/dt_max≈5‐fold versus 3‐fold in LV.

Conclusion

Canine RV and LV differ in their β‐AR response due to intrinsic differences in myocyte β‐AR downstream signaling. Enhanced β‐AR responsiveness of the RV results from higher cAMP elevation in the cytoplasm, due to a decreased degradation by PDE3 and PDE4 in the RV compared to the LV.

The right ventricle: biologic insights and response to disease: updated

Despite ample evidence that right ventricular function is a critical determinant of the clinical response to a spectrum of cardiovascular diseases, there has been only a limited analysis of the unique and distinguishing physiologic properties of the RV under normal circumstances and in response to pathologic insults. This knowledge deficit is increasingly acknowledged. This review highlights some of these features and underscores the fact that rational therapy in RV failure needs to acknowledge its unique physiology and ought to be chamber specific. That is proven therapies for LV dysfunction do not necessarily apply to the RV. The updated version of this review now acknowledges recent advances in the understanding of metabolic, inflammatory and gender-specific influences on the right ventricle.

GRK2-mediated inhibition of adrenergic and dopaminergic signaling in right ventricular hypertrophy: therapeutic implications in pulmonary hypertension

BACKGROUND

The cause and consequences of impaired adrenergic signaling in right ventricular failure/hypertrophy (RVH) are poorly understood. We hypothesized that G protein-coupled receptor kinase-2 (GRK2)-mediated uncoupling of β-adrenergic receptor signaling impairs inotropic reserve. The implications of right ventricular (RV) adrenergic remodeling for inotrope selection and the therapeutic benefit of interrupting Gβγ-GRK2 interaction, using gallein, were tested.

METHODS AND RESULTS

Chamber-specificity and cellular localization of adrenergic remodeling were compared in rodent RVH associated with pulmonary arterial hypertension (PAH-RVH; SU5416+chronic-hypoxia or Monocrotaline) versus pulmonary artery banding-induced RVH (PAB-RVH). Results were corroborated in RV arrays from 10 PAH patients versus controls. Inotropic reserve was assessed in RV- and left ventricular-Langendorff models and in vivo. Gallein therapy (1.8 mg/kg/day ×2-weeks) was assessed. Despite similar RVH, cardiac output (58.3±4.9 versus 82.9±4.8 mL/min; P<0.001) and treadmill distance (41.5±11.6 versus 244.1±12.4 m; P<0.001) were lower in PAH-RVH versus PAB-RVH. In PAH-RVH versus PAB-RVH there was greater downregulation of β1-, α1- and dopamine-1 receptors, more left ventricular involvement, and greater impairment of RV contractile reserve. RV GRK2 activity increased in parallel with a reduction in both adrenergic receptor expression and inotrope-stimulated cAMP levels (P<0.01). β1-receptor downregulation also occurred in human PAH-RVH. Dobutamine was superior to dopamine as an RV inotrope, both ex vivo and in vivo.

CONCLUSIONS

GRK2-mediated desensitization-downregulation of adrenergic and dopaminergic receptors impairs inotropic reserve in PAH-RVH. Acute inotropic support in RVH is best accomplished by dobutamine, reflecting its better coupling to adenylyl cyclase and the reliance of dopamine on dopamine-1-receptor signaling, which is impaired in RVH. Inhibiting Gβγ-GRK2 interactions has therapeutic benefit in RVH.

Chronic sympathetic activation promotes downregulation of β-adrenoceptor-mediated effects in the guinea pig heart independently of structural remodeling and systolic dysfunction

It is uncertain if downregulation of β-adrenoceptor signaling pathway is promoted by an enhanced adrenergic tone at an early stage of cardiac disease, or it develops secondary to detrimental local myocardial changes in advanced heart failure. We examined the integrity of β-adrenoceptor signaling pathway upon chronic infusion of isoproterenol, a β-adrenoceptor agonist, at a dose producing no structural left ventricular (LV) remodeling and systolic dysfunction. Subcutaneous isoproterenol infusion (400 μg kg(-1) h(-1) over 16 days) to guinea pigs using osmotic minipumps produced no change in cardiac weights, LV internal dimensions, myocyte cross-sectional area, extent of interstitial fibrosis, and basal contractile function. Isolated, perfused heart preparations from isoproterenol-treated guinea pigs exhibited attenuated responsiveness to acute β-adrenoceptor stimulation, as evidenced by reduced LV developed pressure increase, less shortening of LV epicardial monophasic action potential and effective refractory period, and less myocardial cyclic adenosine monophosphate elevation, in response to isoproterenol exposure, when compared to saline-treated controls. Pharmacological responses to forskolin, an activator of the adenylate cyclase catalytic subunit, were well preserved in isoproterenol-treated hearts. Downregulation of β-adrenoceptor-mediated effects upon chronic isoproterenol infusion was associated with markedly reduced stimulatory G-protein α-subunit (G(sα)) myocardial expression levels. No change in expression levels of β-adrenoceptors, G-protein-coupled receptor kinase 2, inhibitory G-protein α-subunit (G(iα2)), and Ca(v)1.2 and K(v)7.1 ion channels was determined in isoproterenol-treated hearts. We therefore conclude that sustained adrenergic overstimulation may promote downregulation of myocardial β-adrenoceptor-mediated effects independently of structural LV remodeling and systolic failure, an effect attributed to β-adrenoceptor uncoupling from adenylate cyclase due to reduced G(sα)-protein expression.

The right ventricle: biologic insights and response to disease

Despite ample evidence that right ventricular function is a critical determinant of the clinical response to a spectrum of cardiovascular diseases, there has been only a limited analysis of the unique and distinguishing physiologic properties of the RV under normal circumstances and in response to pathologic insults. This review highlights some of these features and underscores the fact that rational therapy in RV failure should acknowledge this physiology and ought to be chamber specific.

Role of the excessive amounts of circulating catecholamines and glucocorticoids in stress-induced heart disease

Various stressful stimuli are known to activate the sympathetic nervous system to release catecholamines and the hypothalamic-pituitary-adrenal axis to release glucocorticoids in the circulation. Although initial actions of both catecholamines and glucocorticoids are beneficial for the function of the cardiovascular system, their delayed effects on the heart are deleterious. Glucocorticoids not only increase plasma levels of catecholamines by inhibiting their extraneuronal uptake, but they have also been shown to induce supersensitivity to catecholamines in the heart by upregulating different components of the betta-adrenoceptor signal transduction system. Low concentrations of catecholamines stimulate the heart by promoting Ca2+ movements, whereas excessive amounts of catecholamines produce cardiac dysfunction by inducing intracellular Ca2+ overload in cardiomyocytes. Several studies have shown, however, that under stressful conditions high concentrations of catecholamines become oxidized to form aminolutins and generate oxyradicals. These oxidation products of catecholamines have been demonstrated to produce coronary spasm, arrhythmias, and cardiac dysfunction by inducing Ca2+-handling abnormalities in both sarcolemmal and sarcoplasmic reticulum, defects in energy production by mitochondria, and myocardial cell damage. In this article we have focused the discussion to highlight the interrelationship between catecholamines and glucocorticoids and to emphasize the role of oxidation products of catecholamines in the development of stress-induced heart disease.

Pulmonary hypertension in heart failure

BACKGROUND

Pulmonary hypertension occurs in 60% to 80% of patients with heart failure and is associated with high morbidity and mortality.

METHODS AND RESULTS

Pulmonary artery pressure correlates with increased left ventricular end-diastolic pressure. Therefore, pulmonary hypertension is a common feature of heart failure with preserved as well as reduced systolic function. Pulmonary hypertension is partially reversible with normalization of cardiac filling pressures. Pulmonary vasculature remodeling and vasoconstriction create a second component, which does not reverse immediately, but has been shown to improve with vasoactive drugs and especially with left ventricular assist devices.

CONCLUSION

Many drugs used for idiopathic pulmonary arterial hypertension are being considered as treatment options for heart failure-related pulmonary hypertension. This is of particular significance in the heart transplant population. Randomized clinical trials with interventions targeting heart failure patients with elevated pulmonary artery pressure would be justified.

Cardiac sympathetic nerve terminal function in congestive heart failure

Increased cardiac release of norepinephrine (NE) and depleted cardiac stores of NE are two salient features of the human failing heart. Researches from my laboratory have shown that these changes are accompanied by a functional defect of NE uptake in the cardiac sympathetic nerve terminals. Our studies have shown that the decrease of NE uptake is caused by reduction of NE transporter density in the sympathetic nerve endings, and this change is responsible, at least in part, for the increased myocardial interstitial NE, decreased myocardial adrenoceptor density, and increased myocyte apoptosis in experimental cardiomyopathies. We have also provided evidence in both intact animals and cultured PC12 cells that the decrease of NE transporter is induced by the actions of oxidative metabolites of exogenous NE, involving endoplasmic reticulum stress and impaired N-glycosylation of the NE transporter. This change in the cardiac sympathetic NE uptake function, as demonstrated by [123I] metaiodobenzylguanidine in human studies, may not only serve as an important prognostic variable in patients with congestive heart failure, but also be used as a surrogate for the efficacies of various therapeutic interventions for heart failure. Finally, increasing evidence suggests and further studies are needed to show that the cardiac sympathetic nerve terminal function may be a direct target for pharmacologic treatment of congestive heart failure.

Dependence of changes in β-adrenoceptor signal transduction on type and stage of cardiac hypertrophy

To examine whether cardiac hypertrophy is associated with changes in β-adrenoceptor signal transduction mechanisms, pressure overload (PO) was induced by occlusion of the abdominal aorta and volume overload (VO) by creation of an aortocaval shunt for 4 and 24 wk in rats. After hemodynamic assessment of the animals, the left ventricular (LV) particulate fraction was isolated for measurement of β1-adrenoceptors and adenylyl cyclase activity, and cardiomyocytes were isolated for monitoring of the intracellular Ca2+ concentration. Although PO and VO produced cardiac hypertrophy and increased LV end-diastolic pressure at 4 wk, cardiac function was increased in animals subjected to PO but remained unaltered in animals subjected to VO. Cardiac hypertrophy and increased LV end-diastolic pressure were associated with depressed cardiac function at 24 wk of PO or VO, but clinical signs of congestive heart failure were evident only in animals subjected to VO. Isoproterenol-induced increases in cardiac function, activation of adenylyl cyclase activity, and increase in intracellular Ca2+ concentration, as well as β1-adrenoceptor density, were unaltered by PO at 4 wk, augmented by VO at 4 wk, and attenuated by PO and VO at 24 wk. These results suggest that alterations in β1-adrenoceptor signal transduction are dependent on the type and stage of cardiac hypertrophy.

Cardiovascular effects of a phosphodiesterase III inhibitor in the presence of carvedilol in dogs

The aim of this study was to determine whether dobutamine, dopamine, or milrinone (a phosphodiesterase [PDE] III inhibitor) would support cardiac function that had been attenuated by administration of the beta-blocker, carvedilol (0.2, 0.4, or 0.8 mg/kg). Hemodynamic and cardiac parameters including the heart rate (HR), left-ventricular fractional shortening (FS), and arterial pressure were measured in six healthy dogs without cardiac disease. Carvedilol did not affect FS or arterial pressure, but decreased the HR significantly. The positive inotropic and chronotropic responses to dobutamine and dopamine were attenuated by carvedilol, whereas arterial pressure was unaffected. Milrinone did not affect the HR and decreased arterial pressure, whereas FS was significantly greater both in the control and carvedilol-treated groups. Although milrinone affect the negative chronotropic effects of carvedilol, milrinone increased FS and prevented the decrease in arterial pressure. These results suggest that inhibition of PDE III preserves cardiac contractility and hemodynamic function in the presence of carvedilol.

Differential functional expression of human myocardial G protein receptor kinases in left ventricular cardiac diseases

The relationship between myocardial G protein receptor kinase (GRK) expression and beta-adrenoceptor signalling in human left heart diseases has not been fully elucidated yet. In this study, we characterized and compared the GRK2-7 expression in patients with left ventricular volume overload disorders and dilated cardiomyopathic hearts, and evaluated the relationship of this expression with alterations in myocardial beta-adrenoceptor signalling in volume overload, in order to test the notion that GRK functional expression is influenced in a disease-specific and selective fashion. We established that GRK2, GRK3, and GRK5 are well expressed, while GRK4, GRK6, and GRK7 are only scarcely detectable in the healthy human heart. Compared to control hearts (n=8), GRK2 mRNA expression was elevated by 71% (P<0.005) in the left ventricle, 110% (P<0.05) in the right ventricle, 130% (P<0.05) in the left atrium, and 1300% (P<0.005) in the right atrium (RA) of the dilated cardiomyopathy hearts (n=6). In the volume overload group (n=10), it was increased by approximately 40% (P<0.05) in the left ventricle, 38% in the right ventricle, 81% (P<0.05) in the left atrium, and 850% (P<0.005) in the right atrium. On the other hand, GRK5 was significantly elevated only in the left ventricle by 68% (P<0.05) in the dilated cardiomyopathy hearts and by 48% (P<0.01) in volume overload patients, while in contrast, GRK3 remained unchanged in dilated cardiomyopathy, but was slightly elevated by 36% (P=0.05) in the right ventricle of the volume overload patients. The alterations in GRK expression were accompanied with a decrease in myocardial beta(1)-adrenoceptor mRNA in all four chambers, and these trends in gene expression were paralleled with those of their immunodetectable protein levels. Furthermore, these changes were in association with a decrease in downstream receptor-stimulated, adenylyl cyclase-mediated functional expression and an increase in ventricular protein kinase A activity. The results point to differences in which myocardial GRKs are regulated in cardiac disease, whereby changes in GRK2 expression may be related to the global effects of the disease on myocardial adrenoceptor function and those in GRK5 may be localized to the ventricles, depending on the nature of the myocardial load.

Differential pre- and postsynaptic effects of desipramine on cardiac sympathetic nerve terminals in RHF

Right heart failure (RHF) is characterized by chamber-specific reductions of myocardial norepinephrine (NE) reuptake, beta-receptor density, and profiles of cardiac sympathetic nerve ending neurotransmitters. To study the functional linkage between NE uptake and the pre- and postsynaptic changes, we administered desipramine (225 mg/day), a NE uptake inhibitor, to dogs with RHF produced by tricuspid avulsion and progressive pulmonary constriction or sham-operated dogs for 6 wk. Animals receiving no desipramine were studied as controls. We measured myocardial NE uptake activity using [(3)H]NE, beta-receptor density by [(125)I]iodocyanopindolol, inotropic responses to dobutamine, and noradrenergic terminal neurotransmitter profiles by glyoxylic acid-induced histofluorescence for catecholamines, and immunocytochemical staining for tyrosine hydroxylase and neuropeptide Y. Desipramine decreased myocardial NE uptake activity and had no effect on the resting hemodynamics in both RHF and sham animals but decreased myocardial beta-adrenoceptor density and beta-adrenergic inotropic responses in both ventricles of the RHF animals. However, desipramine treatment prevented the reduction of sympathetic neurotransmitter profiles in the failing heart. Our results indicate that NE uptake inhibition facilitates the reduction of myocardial beta-adrenoceptor density and beta-adrenergic subsensitivity in RHF, probably by increasing interstitial NE concentrations, but protects the cardiac noradrenergic nerve endings from damage, probably via blockade of NE-derived neurotoxic metabolites into the nerve endings.

Early effects of right ventricular volume overload on ventricular performance and beta-adrenergic signaling

OBJECTIVE

Right ventricular dysfunction is a poorly understood but persistent clinical problem. This study was undertaken to evaluate ventricular performance and beta-adrenergic receptor signaling in a tricuspid regurgitation model of right ventricular overload.

METHODS

Seventeen dogs were chronically instrumented with epicardial dimension transducers. By means of the shell-subtraction model, right ventricular pressure-volume relationships were evaluated in normal and right ventricular overload states. Right ventricular chamber performance was quantified by the stroke work at an end-diastolic volume relationship.

RESULTS

Right ventricular volume overload caused a 28% +/- 11% and 31% +/- 9% decline in chamber performance acutely and at 1 week, respectively, whereas end-diastolic volume increased from 45 +/- 21 to 60 +/- 30 mL (P =. 019). beta-Adrenergic receptor signaling in myocardial samples was assessed, examining adenylyl cyclase and G-protein-coupled receptor kinase activity. Stimulated adenylyl cyclase activity significantly decreased, and G-protein-coupled receptor kinase activity significantly increased in both left and right ventricular samples caused by increased levels of beta-adrenergic receptor kinase 1. No change in beta-adrenergic receptor density was seen at 1 week.

CONCLUSIONS

Early right ventricular overload is associated with impaired right ventricular chamber contractility, dilation, and, importantly, a biventricular alteration of beta-adrenergic receptor signaling.

Alterations by norepinephrine of cardiac sympathetic nerve terminal function and myocardial beta-adrenergic receptor sensitivity in the ferret: normalization by antioxidant vitamins

BACKGROUND

Chronic excessive norepinephrine (NE) causes cardiac sympathetic nerve terminal abnormalities, myocardial beta-adrenergic receptor downregulation, and beta-adrenergic subsensitivity. The present study was carried out to determine whether these changes could be prevented by antioxidants.

METHODS AND RESULTS

Ferrets were administered either NE (1.33 mg/d) or vehicle by use of subcutaneous pellets for 4 weeks. Animals were simultaneously assigned to receive either antioxidant vitamins (beta-carotene, ascorbic acid, and alpha-tocopherol) or placebo pellets. NE increased plasma NE 4- to 5-fold but had no effect on heart rate, heart weight, arterial pressure, or left ventricular systolic function. However, myocardial NE uptake activity and NE uptake-1 site density were reduced, as well as cardiac neuronal NE, tyrosine hydroxylase, and neuropeptide Y. In addition, there was a decrease in myocardial beta-adrenergic receptor density with a selective decrease of the beta(1)-receptor subtype, reduction of the high-affinity site for isoproterenol, decreased basal adenylyl cyclase activity, and the adenylyl cyclase responses to isoproterenol, Gpp(NH)p, and forskolin. All of these changes were prevented by antioxidant vitamins. The effects of NE on myocardial beta-adrenergic receptor density, NE uptake-1 carrier site density, and neuronal NE were also prevented by superoxide dismutase or Trolox C.

CONCLUSIONS

The toxic effects of NE on the sympathetic nerve terminals are mediated via the formation of NE-derived oxygen free radicals. Preservation of the neuronal NE reuptake mechanism is functionally important, because the antioxidants also prevented myocardial beta-adrenergic receptor downregulation and postreceptor abnormalities. Thus, antioxidant therapy may be beneficial in heart failure, in which cardiac NE release is increased.

Alterations in cardiac adrenergic terminal function and beta-adrenoceptor density in pacing-induced heart failure

Congestive heart failure is associated with cardiac adrenergic nerve terminal changes and beta-adrenoceptor density downregulation. To study the temporal sequence of these changes, we performed studies in rabbits at 2, 4, and 8 wk of cardiac pacing (360 beats/min) and at 1, 2, and 4 wk after cessation of pacing. Rapid pacing produced left ventricular (LV) dysfunction and an increase in plasma norepinephrine (NE) in 1-2 wk. At week 2, NE uptake activity, NE uptake-1 density, and adenylyl cyclase responses to isoproterenol, 5'-guanylyl imidodiphosphate [Gpp(NH)p], and forskolin reduced. However, immunostained tyrosine hydroxylase profile, beta-adrenoceptor density, and NE histofluorescence did not reduce until 4-8 wk of pacing. After cessation of cardiac pacing, LV function normalized quickly, followed by return of tyrosine hydroxylase and NE profiles in 1 wk and adenylyl cyclase responses to agonists and NE uptake activity in 2 wk. Myocardial beta-adrenoceptor density returned to normal by 4 wk after cessation of pacing. Our results suggest that there is no permanent structural neuronal damage in the myocardium within the first 8 wk of rapid cardiac pacing. Abnormal myocardial NE reuptake mechanism may play an important pathophysiological role in heart failure.

Myocardial beta-adrenoceptor down-regulation by norepinephrine is linked to reduced norepinephrine uptake activity

Chronic administration of norepinephrine for 8 weeks has been shown to reduce neuronal norepinephrine uptake activity and increase interstitial norepinephrine concentration in the heart. To determine whether the changes could lead to myocardial beta-adrenoceptor down-regulation or beta-adrenergic subsensitivity, we measured left ventricular contractile responses to dobutamine, myocardial beta-adrenoceptor density, beta subtype distribution, competitive inhibition agonist binding, and adenylyl cyclase activity activation by isoproterenol, 5'-guanylylimidodiphosphate, and forskolin in dogs after a norepinephrine or saline infusion for 8 weeks. We found that norepinephrine infusion reduced myocardial beta-adrenoceptor density, beta(1)-adrenoceptor subtype density, and high-affinity site for isoproterenol. Left ventricular contractile responses to dobutamine were reduced in the norepinephrine-infused animals. In addition, norepinephrine infusion decreased the basal adenylyl cyclase activity and the adenylyl cyclase responses to isoproterenol, 5'-guanylylimidodiphosphate, and forskolin. The findings indicate that a decrease in cardiac norepinephrine uptake predisposes the heart to norepinephrine-induced myocardial beta-adrenoceptor down-regulation, and that norepinephrine, when present in a sufficient amount over a long period as it is in chronic heart failure, can reduce myocardial beta-adrenergic responsiveness by both homologous and heterologous desensitization.

ACE inhibition improves cardiac NE uptake and attenuates sympathetic nerve terminal abnormalities in heart failure

Cardiac sympathetic nerve terminal dysfunction plays an important role in the downregulation of myocardial beta-adrenoceptors in heart failure. To determine whether chronic angiotensin-converting enzyme (ACE) inhibition improved cardiac sympathetic nerve terminal function and hence increased myocardial beta-adrenergic responsiveness, we administered ACE inhibitors to dogs with chronic right-sided heart failure (RHF) produced by tricuspid avulsion and pulmonary artery constriction. The RHF animals exhibited fluid retention, elevated right heart filling pressures, blunted inotropic response to isoproterenol, and reduced beta-adrenoceptor density. These changes were accompanied by decreases in right ventricular norepinephrine (NE) uptake and neuronal NE histofluorescence and tyrosine hydroxylase immunoreactive profiles. ACE inhibitors had no effect on the production of heart failure but greatly reduced the attenuation of cardiac NE uptake, neuronal NE histofluorescence, and tyrosine hydroxylase immunoreactive profiles. ACE inhibition also improved the inotropic response to isoproterenol and restored myocardial beta-adrenoceptor density. The changes probably are caused by reduction of cardiac NE release by ACE inhibition and may contribute to the beneficial effects of ACE inhibitor therapy in patients with chronic heart failure.

Chamber-specific regulation of heme oxygenase-1 (heat shock protein 32) in right-sided congestive heart failure

Heme oxygenase (HO)-1 is a stress protein (HSP 32) and, together with HO-2, catalyses oxidation of the heme molecule to generate carbon monoxide, a gas with vasodilatory properties, and bilirubin, an antioxidant. Right-sided heart failure (RHF) resulted in a two-fold increase in the HO-1 transcript (;1.8 kb) in the right ventricle (RV) of RHF dogs compared to that of controls. In contrast, the left ventricle showed no increase in HO-1 mRNA in RHF. The change in HO was unique to HO-1, because neither the HO-2 transcripts (;1.3 and 1.9 kb) nor the HSP 70 mRNA was altered in either ventricle. This increase in HO-1 mRNA in RV was accompanied by a two-fold increase in immunoreactive HO-1 protein, as judged by Western blot analysis, as well as by a significant increase in cGMP levels. There was, however, no significant increase in RV total nitric oxide synthase activity in RHF. Furthermore, since norepinephrine infusion also increased HO-1 transcript and protein levels, the HO-1 system probably was induced in RHF by the increased interstitial norepinephrine levels known to occur in failing myocardium. This differential regulation and induction of HO-1 gene in the failing ventricle might be one of the defense mechanisms by which the heart attempts to protect from stress caused by congestive heart failure.

Overexpression of nerve growth factor in the heart alters ion channel activity and beta-adrenergic signalling in an adult transgenic mouse

1. The electrophysiological and pharmacological properties of cardiac myocytes from the hearts of adult transgenic mice engineered to overexpress nerve growth factor (NGF) in the heart were studied. 2. There was a 12% increase in the ventricular myocyte capacitance in NGF myocytes consistent with cardiac hypertrophy, and action potential duration at 90% repolarization (APD90) was prolonged by 142 % compared with wild-type (WT) myocytes. This was due, at least in part, to a decrease in the density of two K+ currents, Ito and IK(ur), which were significantly reduced in NGF mice with no change in their electrophysiological characteristics. We found no change in the current density or electrophysiological properties of the L-type Ca2+ current. 3. The effect on Ito and IK(ur) of TEA and 4-aminopyridine (4-AP) was not different in cells isolated from WT and NGF mice. The prolongation of APD observed in NGF cells was mimicked in WT cells by exposure to 1 mM 4-AP, which partially blocked Ito, completely blocked IK(ur) and increased APD90 by 157%. 4. The isoprenaline-induced increase in ICa was significantly smaller in NGF myocytes than in WT myocytes. This was not due to a decrease in beta-adrenergic receptor (beta-AR) density, as this was increased in NGF tissue by 55%. Analysis of beta-AR subtypes showed that this increase was entirely due to an increase in beta2-AR density with no change in beta1-ARs. 5. The response of the beta-AR-coupled adenylyl cyclase system to isoprenaline, Gpp(NH)p and forskolin was studied by measuring cAMP production. In NGF tissue, isoprenaline elicited a significantly smaller response than in WT myoyctes and this was not due to reduced adenylyl cyclase activity as the responses of NGF tissue to guanylylimidodiphosphate (Gpp(NH)p) and forskolin were unaffected. 6. In conclusion, the overexpression of NGF in the mouse heart resulted in a decrease in the current density of two K+ channels, which contributed to the prolongation of the cardiac action potential. Despite an increase in beta2-AR density in the hearts of the NGF mice, the response to isoprenaline was diminished, and this was due to an uncoupling of the beta-ARs from the intracellular signalling cascade. These potentially pathological changes may be involved in the occurrence of ventricular arrhythmias in cardiac hypertrophy and failure, and this mouse provides a novel model in which to study such changes.

Dissociation between regional dysfunction and beta-adrenergic receptor signaling in heart failure

We have previously shown that left ventricular (LV) pacing-induced heart failure is associated with preserved wall thickening in the interventricular septum (IVS) compared with the posterolateral wall (PLW). The current study focuses on the relationship between regional myocardial function and altered beta-adrenergic receptor (beta-AR) signaling. We studied 15 pigs: 6 controls and 9 paced from the left ventricle (225 beats/min, 26 +/- 3 days). Heart failure was documented by decreased LV fractional shortening (P < 0.0001) and increased left atrial pressure (P < 0.0001). In heart failure, despite marked differences in basal regional function (percent wall thickening: IVS, 33 +/- 10% vs. PLW, 13 +/- 7%; P = 0.0003), there were no differences between the two regions in beta-AR responsiveness, measured by regional wall thickening in response to dobutamine infusion and any measurement of adrenergic signaling. Adenylyl cyclase activity, beta-AR number, and beta-AR/Gs coupling were markedly reduced in failing LV without regional differences. In animals with heart failure, LV G protein receptor kinase (GRK) isoform 2 content was unchanged and GRK5, the other major GRK isoform, was increased more than threefold (IVS, 0.51 +/- 0.20 vs. 0. 12 +/- 0.12 arbitrary densitometric units, P = 0.01; PLW, 0.47 +/- 0. 15 vs. 0.13 +/- 0.09 arbitrary densitometric units, P = 0.03), but again, there were no regional differences. These data indicate that systemic rather than regional factors govern LV adrenergic signaling and that regional adrenergic signaling abnormalities poorly predict wall thickening in the same regions.

Abnormal beta-adrenergic transmembrane signaling in rabbits with adriamycin-induced cardiomyopathy

We investigated alterations in the beta-adrenergic receptor-adenylate cyclase system in rabbits with congestive heart failure induced by adriamycin cardiotoxicity. A dose of 24 mg/kg adriamycin was administered over 16 weeks in 16 rabbits. Five of them died and 4 of them could not tolerate the full dose of adriamycin. Complete data were obtained in the remaining 7 rabbits. Another 7 rabbits received physiological saline for the same period and served as controls. Plasma norepinephrine concentration increased in adriamycin-treated rabbits, but not in the control rabbits. Cardiac output was lower in the adriamycin-treated group than in the control group. Both the left and right ventricular end-diastolic pressure were higher in the adriamycin-treated group. The density of myocardial beta-adrenergic receptors and the norepinephrine content were reduced in both ventricles in the adriamycin-treated group. Basal and isoproterenol-, sodium fluoride- and forskolin-stimulated adenylate cyclase activities were lower in the adriamycin-treated group. Thus, alterations in beta-adrenergic signaling occurred in both ventricles in animals with chronic biventricular failure induced by adriamycin. These may be the result of post-receptor abnormalities, including abnormalities of guanine nucleotide-binding proteins or of the catalytic unit of adenylate cyclase.

Response of large and small vessels to alpha and beta adrenoceptor stimulation in heart failure: effect of angiotensin converting enzyme inhibition

The increased sympathetic drive in chronic heart failure (CHF) might provoke vascular adrenoceptor desensitization, which, together with endothelial dysfunction, could contribute to the altered vasomotor tone seen in CHF. We investigated 1) whether CHF alters the responses mediated by alpha and beta adrenoceptors in small and large peripheral arteries, and 2) the effect of angiotensin-converting enzyme (ACE) inhibition. Rats with CHF (coronary artery ligation) were treated with placebo or the ACE inhibitor lisinopril (10 mg/kg/d) starting 7 days after ligation. Responses to phenylephrine (alpha 1 agonist), salbutamol (beta 2 agonist) as well as acetylcholine (endothelium-dependent), were assessed after 3 months in isolated and pressurized segments of the abdominal aorta, the femoral and the mesenteric arteries. In animals with hemodynamic signs of CHF, neither the vasoconstrictor responses to phenylephrine nor the vasodilator response to salbutamol were affected. In contrast, the dilator response to acetylcholine of both small arteries, but not that of the aorta, was impaired. Furthermore, CHF did not modify vessel structure. While lisinopril did not modify the responses to adrenergic agonists, it normalized the response to acetylcholine. Furthermore, ACE inhibition reduced vascular media cross sectional area and collagen density. Thus, the unchanged arterial responsiveness to adrenoceptor agonists does not indicate any vascular adrenoceptor desensitization, while endothelial dependent vasodilation of small arteries is impaired in CHF. ACE inhibition does not modify the response to adrenergic stimuli, prevents endothelial dysfunction and induces both cardiac and vascular remodeling, which probably contribute to the effect ACE inhibitors have on exercise tolerance and survival.

Myocardial sympathetic denervation prevents chamber-specific alteration of beta-adrenergic transmembrane signaling in rabbits with heart failure

OBJECTIVES

The purpose of this study was to assess the effect of myocardial sympathetic denervation on the chamber-specific alteration of beta-adrenergic signaling in left ventricular failure in rabbits.

BACKGROUND

Local abnormalities in sympathetic nerve terminals, including the neuronal reuptake of norepinephrine, are thought to be responsible for the chamber-specific regulation of beta-adrenergic signaling in heart failure.

METHODS

Sixteen rabbits were given 6-hydroxydopamine, 25 mg/kg body weight intravenously on days 1 and 2 and 50 mg/kg intravenously on days 7 and 8. Another 16 rabbits received vehicle. Aortic regurgitation was induced in eight of the 6-hydroxydopamine-treated and eight of the vehicle-treated rabbits on day 14. Another eight of the 6-hydroxydopamine-treated and eight of the vehicle-treated rabbits underwent a sham operation. The hearts were excised for biochemical analysis on day 21.

RESULTS

Hemodynamic characteristics on day 21 showed left ventricular failure in both the aortic regurgitation groups. The plasma norepinephrine concentration on day 21 was higher in both the aortic regurgitation groups than in the sham groups. The beta-adrenoceptor densities and isoproterenol plus 5'-guanylylimidodiphosphate-, 5'-guanylylimidodiphosphate- and sodium fluoride-stimulated adenylyl cyclase activities were decreased only in the failing left ventricle of the vehicle-pretreated aortic regurgitation group, but in both ventricles of the 6-hydroxydopamine-pretreated aortic regurgitation group. The basal and forskolin-stimulated adenylyl cyclase activities were similar in both the aortic regurgitation groups and in the sham groups.

CONCLUSIONS

Sympathetic denervation prevented chamber-specific alterations in beta-adrenergic signaling in acute left ventricular failure. Local loss of sympathetic nerve endings, and especially the defective neuronal norepinephrine reuptake, are likely to be responsible for the chamber-specific alteration of the beta-adrenoceptor-G protein-adenylyl cyclase system in heart failure in rabbits.

Differential changes of myocardial beta-adrenoceptor subtypes and G-proteins in dogs with right-sided congestive heart failure

We have shown previously in dogs with right heart failure that the reduction of myocardial beta-adrenoceptor density occurs only in the failing right ventricle, while cardiac inotropic responses to beta-adrenergic stimulation are reduced in both the right and left ventricles. The purpose of the present study was to determine whether a post-receptor defect in the guanine nucleotide-binding regulatory proteins (G-proteins) existed which would explain, at least in part, the adrenergic subsensitivity in both ventricles of the heart failure dogs. Using both immunoblotting technique and the bacterial toxin-mediated ADP ribosylation assays, we found that the stimulatory G-protein (Gs) was reduced in both ventricles of the heart failure dogs. In contrast, there were no changes in the inhibitory G-protein (Gi). In addition, receptor subtype analysis showed that only beta(1)-adrenoceptors were reduced in the failing right ventricle of the heart failure animals. This study demonstrated that the reduction of beta-adrenoceptors in right heart failure was chamber-specific whereas the reduction of Gs was non-selective, occurring in both ventricles of right heart failure dogs. The findings further suggest that the reduction of Gs probably was caused by systemic neurohormonal activation, independent of local ventricular stress.

Physiological and biochemical evidence for coordinate increases in muscarinic receptors and Gi during pacing-induced heart failure

BACKGROUND

It is not clear whether the increase in the myocardial guanylyl nucleotide inhibitory protein (Gi), frequently observed in heart failure, is associated with any functional effects.

METHODS AND RESULTS

Eight sham-operated dogs and 10 dogs were studied with pacing-induced heart failure (240 bpm for 4 to 7 weeks), characterized by reduced (P<.05) left ventricular dP/dt (from 2926+/-99 to 1303+/-126 mm Hg/s). The muscarinic agonist acetylcholine (10 micrograms/kg IV) in the presence of ganglionic blockade reduced left ventricular dP/dt more (P<.05) in heart failure (-23+/-2%) than before heart failure (-8+/-2%), despite lesser reductions in arterial pressure. Gi alpha2 was increased by 55% in heart failure. Dose-response curves for carbachol (10-8 to 10-3 mol/L) inhibition of isoproterenol-stimulated adenylyl cyclase demonstrated significantly greater (P<.05) inhibition in heart failure compared with sham-operated dogs. These changes were associated with a coordinate increase in muscarinic receptor density, determined by antagonist binding with 3H-quinuclidinyl benzilate, in heart failure (153+/-6.2 fmol/mg protein) compared with sham-operated dogs (124+/-7.4 fmol/mg protein). Agonist binding with carbachol also revealed an increase in total muscarinic receptors in heart failure without a change in fraction of high- and low-affinity receptors.

CONCLUSIONS

These data, in the aggregate, provide physiological and biochemical evidence to support the concept that the coordinate increases in muscarinic receptor number and Gi levels in heart failure are coupled to increased inhibition of adenylyl cyclase activity and an increased inhibition of myocardial contractility.

Long-term treatment with angiotensin I-converting enzyme inhibitors attenuates the loss of cardiac beta-adrenoceptor responses in rats with chronic heart failure

BACKGROUND

Cardiac contractile force in response to beta-adrenoceptor agonists and beta-adrenergic receptor density are decreased in failing human hearts. The effects of angiotensin I-converting enzyme (ACE) inhibitor on cardiac responsiveness to beta-adrenergic stimulation in failing hearts are not established. The present study was undertaken to determine whether ACE inhibitor may improve cardiac beta-adrenergic responsiveness in animals with chronic heart failure (CHF).

METHODS AND RESULTS

CHF was induced by left coronary artery ligation in rats. Cardiac output and stroke volume indices decreased 12 weeks after the operation. In sham-operated rats, dobutamine and isoprenaline increased cardiac output and stroke volume indices. In contrast, cardiac output and stroke volume responses to dobutamine and isoprenaline were severely blunted in the CHF rat. Cardiac beta 1-adrenergic receptor density was decreased while its dissociation constant (Kd) was not altered in the viable tissue of the left ventricle of the CHF rat, which is consistent with beta-adrenergic receptor downregulation. Cardiac norepinephrine content decreased in the CHF rats. Rats were treated orally with ACE inhibitors, 3 mg/kg trandolapril or 10 mg/kg enalapril once daily, or 5 mg/kg captopril twice daily from the 2nd to the 12th weeks after the operation. Treatment with ACE inhibitors attenuated the reduction in cardiac output and stroke volume indices and improved the inotropic response to dobutamine and isoprenaline and reversed partially the cardiac norepinephrine content in the CHF rat. ACE inhibitor treatment also attenuated the reduction in beta 1-adrenergic receptor density in the viable tissue of the left ventricle of the CHF rat.

CONCLUSIONS

The results suggest that ACE inhibitor treatment attenuates the blunting of cardiac responses to beta-adrenergic agonists in the CHF rat and that one of the mechanisms underlying this effect is prevention of cardiac beta 1-adrenergic receptor downregulation.

Activation and inhibition of the endogenous opioid system in human heart failure

BACKGROUND

In a canine model of congestive heart failure beta endorphin concentrations were high and opioid receptor antagonists exerted beneficial haemodynamic effects. In humans previous studies have suggested that opioid peptides may modify the perception of breathlessness and fatigue in heart failure.

METHODS

Plasma concentrations of beta endorphin were measured in patients with acute and chronic heart failure and cardiogenic shock. A subgroup of eight patients with New York Heart Association (NYHA) class III-IV heart failure was assessed for acute haemodynamic effects of naloxone, an opioid receptor antagonist. A separate group of 10 patients with class II-III heart failure, was randomised to a double blind placebo controlled study of the effects of intravenous naloxone on cardiopulmonary exercise performance.

RESULTS

Plasma concentrations of beta endorphin were usually normal in patients with chronic heart failure and did not correlate with severity as assessed by NYHA class. In 29% of patients with acute heart failure and 71% of those with cardiogenic shock beta endorphin concentrations were high. The median concentration in the cardiogenic shock group was significantly higher than in either of the two heart failure groups and there was some evidence of a relation between beta endorphin concentrations and survival. At the doses tested, naloxone was unable to modify systemic haemodynamics, exercise performance, or symptoms in patients with chronic congestive heart failure.

CONCLUSIONS

Circulating concentrations of beta endorphin are usually normal in patients with chronic congestive heart failure. Inhibition of the endogenous opioid system is unlikely to have therapeutic potential in heart failure.

Alterations in G-proteins in congestive heart failure in cardiomyopathic (UM-X7.1) hamsters

In order to explain the attenuated sympathetic support during the development of heart failure, the status of beta-adrenergic mechanisms in the failing myocardium was assessed by employing cardiomyopathic hamsters (155-170 days old) at moderate degree of congestive heart failure. The norepinephrine turnover rate was increased but the norepinephrine content was decreased in cardiomyopathic hearts. The number and the affinity of beta receptors in the sarcolemmal preparations were not changed in these hearts at moderate stage of congestive heart failure. While the basal adenylyl cyclase activity was not altered in sarcolemma, the stimulation of enzyme activity by NaF, forskolin, Gpp(NH)p or epinephrine was depressed in hearts from these cardiomyopathic hamsters. Since G-proteins are involved in modifying the adenylyl cyclase activity, the functional and bioactivities as well as contents of both Gs and Gi proteins were determined in the cardiomyopathic heart sarcolemma. The functional stimulation of adenylyl cyclase by cholera toxin, which activates Gs proteins, was markedly depressed whereas that by Pertussis toxin, which inhibits Gi proteins, was markedly augmented in cardiomyopathic hearts. The cholera toxin and pertussis toxin catalyzed ADP-ribosylation was increased by 37 and 126%, respectively; this indicated increased bioactivities of both Gs and Gi proteins in experimental preparations. The immunoblot analysis suggested 74 and 124% increase in Gs and Gi contents in failing hearts, respectively. These results suggest that depressed adenylyl cyclase activation in cardiomyopathic hamsters may not only be due to increased content and bioactivity of Gi proteins but the functional uncoupling of Gs proteins from the adenylyl cyclase enzyme may also be involved at this stage of heart failure.

Abnormalities in sympathoneuronal regulation are localized to failing myocardium in rabbit heart

OBJECTIVES

This study investigated the differences in sympathoneuronal regulation between acute left ventricular failure and chronic biventricular failure to determine whether an increase in plasma norepinephrine concentration plays a primary role in the genesis of the desensitization phenomenon in heart failure.

BACKGROUND

It remains to be determined whether plasma norepinephrine plays a primary role in the pathogenesis of sympathetic desensitization in heart failure in vivo.

METHODS

Acute left ventricular failure was induced by aortic regurgitation in seven rabbits. Chronic heart failure was induced by adriamycin treatment in another seven rabbits.

RESULTS

Cardiac output was lower in rabbits with aortic regurgitation than in seven sham-operated rabbits. Left ventricular end-diastolic pressure was higher in rabbits with aortic regurgitation, but no significant difference in right ventricular end-diastolic pressure was observed. Beta-adrenoceptor density and norepinephrine concentration in the left ventricular myocardium were lower in rabbits with aortic regurgitation; no such differences were observed for the right ventricular myocardium. Cardiac output was lower in adriamycin-treated rabbits than in seven control rabbits. Both left and right ventricular end-diastolic pressures were higher in experimental rabbits than in control rabbits. Myocardial beta-adrenoceptor density and norepinephrine content were reduced in both ventricles.

CONCLUSIONS

In chronic heart failure induced by adriamycin, sympathoneuronal activity was altered in both ventricles, whereas in acute left ventricular failure induced by aortic regurgitation, sympathoneuronal activity was affected only in the left ventricle despite a similar increase in plasma norepinephrine concentration in both animal models. Local abnormalities in sympathoneuronal regulation in failing myocardium therefore appear to be responsible for these phenomena.

Pronounced increase in defibrillation threshold associated with pacing-induced cardiomyopathy in the dog

Progressive changes in myopathology after implantation of an automatic defibrillator could compromise device efficacy. The influence of heart failure development on the defibrillation threshold was evaluated by means of a rapid ventricular pacing model of heart failure in dogs. After transvenous pacemaker lead implantation, adult mongrel dogs were randomly assigned to either the control (n = 7) or rapidly paced group (240 beats/min, n = 6). Seventeen days after implantation, triplicate determinations of the defibrillation threshold were made with three epicardial electrodes. The average defibrillation threshold was four times higher in the rapidly paced group, 13.3 +/- 2.0 joules (mean +/- SEM), than in the control group, 3.3 +/- 0.7 joules (p < 0.01), and was significantly correlated with ventricular weight (r = 0.70, p < 0.01). Both defibrillation threshold energy per gram of ventricle and ventricular weight corrected for body weight were significantly higher in rapidly paced dogs compared with control dogs. It was concluded that myocardial hypertrophy and heart failure may profoundly increase defibrillation energy requirements.

Cardiac noradrenergic nerve terminal abnormalities in dogs with experimental congestive heart failure

BACKGROUND

We have shown previously that norepinephrine (NE) uptake activity is reduced in the failing right ventricle of animals with right heart failure (RHF) produced by tricuspid avulsion and progressive pulmonary constriction. However, it is unknown whether this defect in neuronal NE uptake is related to reduction of noradrenergic nerve terminals or whether these changes also occur in animals with left heart failure (LHF). It is also unknown whether increased NE release in heart failure contributes to the noradrenergic nerve abnormalities.

METHODS AND RESULTS

We measured myocardial NE content. NE uptake function, and noradrenergic nerve profiles in dogs with either RHF or LHF induced by rapid ventricular pacing. NE uptake activity was measured using [3H]NE, and noradrenergic nerve profiles were visualized by glyoxylic acid (SPG)-induced histofluorescence and tyrosine hydroxylase immunocytochemical staining. To study the effects of excess NE, we exposed normal dogs to 8 weeks of chronic NE infusion using subcutaneous osmotic minipumps. RHF and LHF animals exhibited reduced myocardial contractile function and congestive heart failure, as evidence by reduced cardiac output and elevated right atrial pressure. However, unlike that in LHF, left atrial pressure was not increased in RHF. The animals also showed an increase in plasma NE and a decrease in cardiac NE. In addition, SPG-induced histofluorescence correlated significantly with NE uptake activity (r = .712, P < .001) and tyrosine hydroxylase immunoreactive profiles (r = .569, P < .001) in the right ventricles of RHF dogs and in both ventricles of LHF dogs. The numbers of catecholaminergic profiles and tyrosine hydroxylase profiles significantly correlated with cardiac filling pressures. Chronic infusion of NE decreased heart rate in normal dogs but had no effect on either mean aortic pressure or left atrial pressure; like heart failure, it resulted in significant decreases in myocardial NE uptake activity and numbers of SPG-induced catecholaminergic histofluorescence and immunoreactive tyrosine hydroxylase profiles.

CONCLUSIONS

Myocardial NE uptake activity was reduced only in the failing ventricles with elevated filling pressure in RHF and LHF. These changes probably were caused by loss of noradrenergic nerve terminals in the failing ventricles, as evidenced by the reductions of catecholaminergic histofluorescence and tyrosine hydroxylase immunostained profiles. Furthermore, since similar reductions of myocardial NE uptake and noradrenergic nerve profiles could be produced by chronic NE infusion in normal dogs, elevated NE levels may play a role in the development of cardiac noradrenergic nerve abnormalities in congestive heart failure.

Myocardial beta-adrenergic receptor function during the development of pacing-induced heart failure

The development of pacing-induced heart failure was studied in chronically instrumented, conscious dogs paced at a rate of 240 beats/min for 1 d (n = 6), 1 wk (n = 6), and 3-4 wk (n = 7). Left ventricular (LV) dP/dt was decreased (P < 0.0125) at 1 d, LV end-diastolic pressure and heart rate were increased (P < 0.0125) at 1 wk, but clinical signs of heart failure were only observed after 3-4 wk of pacing. Plasma norepinephrine rose (P < 0.0125) after 1 d of pacing, whereas LV norepinephrine was reduced (P < 0.0125) only after 3-4 wk of pacing. Both the fraction of beta-adrenergic receptors binding agonist with high affinity and adenylyl cyclase activity decreased (P < 0.0125) after 1 d of pacing. Total beta-adrenergic receptor density was not changed at any time point, but beta 1-adrenergic receptor density was decreased (P < 0.0125) after 1 wk. The functional activity of the guanine nucleotide binding protein, Gs, was not reduced, but the Gi alpha 2 isoform of the alpha subunit of the GTP-inhibitory protein rose after 3-4 wk of pacing. Thus, myocardial beta-adrenergic signal transduction undergoes change shortly (1d) after the initiation of pacing, before heart failure develops. The mechanism of beta-adrenergic receptor dysfunction in pacing-induced heart failure is characterized initially by elevated plasma levels of catecholamines, uncoupling of beta-adrenergic receptors, and a defect in the adenylyl cyclase catalytic unit. Selective down-regulation of beta 1-adrenergic receptors, increases in Gi alpha 2, and decreases in myocardial catecholamine levels occur as later events.

Changes in adrenergic receptors during the development of heart failure

Moderate and severe stages of congestive heart failure due to the loss of myocardium upon coronary occlusion in rats was associated with an increase in alpha-adrenergic receptors and a decrease in beta-adrenergic receptors in the viable left ventricle. However, at early stages of heart failure the number of beta-adrenergic receptors was decreased without any changes in the number of alpha-adrenergic receptors. The affinities of these receptors to alpha receptor antagonist (3H-prazosin) and beta receptor antagonist (3H-dihydroalprenolol) were not altered in the failing hearts. On the other hand, the pattern of changes in both alpha- and beta-adrenergic receptors in heart membranes treated with oxygen free radical generating system was different from that seen in the failing hearts. In particular, the affinities for these receptors were decreased whereas the number of beta-receptors was increased and the number of alpha-receptors was decreased or unchanged. These results indicate that alterations in the adrenergic receptors in heart failure are not due to the formation of oxygen free radicals.

Beta-adrenergic neuroeffector abnormalities in the failing human heart are produced by local rather than systemic mechanisms

In order to investigate the general cause of beta-adrenergic receptor neuroeffector abnormalities in the failing human heart, we measured ventricular myocardial adrenergic receptors, adrenergic neurotransmitters, and beta-adrenergic receptor-effector responses in nonfailing and failing hearts taken from nonfailing organ donors, subjects with endstage biventricular failure due to idiopathic dilated cardiomyopathy (IDC), and subjects with primary pulmonary hypertension (PPH) who exhibited isolated right ventricular failure. Relative to nonfailing PPH left ventricles, failing PPH right ventricles exhibited (a) markedly decreased beta 1-adrenergic receptor density, (b) marked depletion of tissue norepinephrine and neuropeptide Y, (c) decreased adenylate cyclase stimulation in response to the beta agonists isoproterenol and zinterol, and (d) decreased adenylate cyclase stimulation in response to Gpp(NH)p and forskolin. These abnormalities were directionally similar to, but generally more pronounced than, corresponding findings in failing IDC right ventricles, whereas values for these parameters in nonfailing left ventricles of PPH subjects were similar to values in the nonfailing left ventricles of organ donors. Additionally, relative to paired nonfailing PPH left ventricles and nonfailing right ventricles from organ donors, failing right ventricles from PPH subjects exhibited decreased adenylate cyclase stimulation by MnCl2. These data indicate that: (a) Adrenergic neuroeffector abnormalities present in the failing human heart are due to local mechanisms; systemic processes do not produce beta-adrenergic neuroeffector abnormalities. (b) Pressure-overloaded failing right ventricles of PPH subjects exhibit decreased activity of the catalytic subunit of adenylate cyclase, an abnormality not previously described in the failing human heart.

Beta-adrenergic receptor-G protein-adenylate cyclase complex in experimental canine congestive heart failure produced by rapid ventricular pacing

Changes in the beta-adrenergic receptor-G protein-adenylate cyclase complex were investigated in an experimental canine model of low-output heart failure produced by chronic rapid ventricular pacing. The contractile response occurring after exposure to the beta-adrenergic agonist dobutamine, measured as peak left ventricular + dP/dt, was decreased after 3 weeks of pacing. To further characterize the diminished functional responsiveness to beta-adrenergic receptor stimulation, beta-adrenergic receptor-adenylate cyclase coupling was investigated using membranes prepared from both control and paced animals. The density of beta-adrenergic receptors was decreased by 40% with a selective downregulation of the beta 1-subtype. The affinity of the receptor for the antagonist radioligand [125I]iodocyanopindolol remained unchanged. A defect in coupling was suggested by a decreased ability of isoproterenol, fluoride, and forskolin to stimulate adenylate cyclase in membranes prepared from failing hearts. Determination of the levels of Gi alpha (the alpha-subunit of Gi) by immunoblotting and pertussis toxin labeling revealed modest increases of approximately 30%. Furthermore, Mn2+ and purified Gs failed to stimulate adenylate cyclase in membranes prepared from failing hearts, indicating an impairment in the catalytic moiety of adenylate cyclase itself or in the ability of adenylate cyclase to couple to Gs. In contrast, complementation assay did not reveal differences in the functional activity of Gs alpha (the alpha-subunit of Gs). Taken together, these data demonstrate a selective decrease in the beta 1-subtype of adrenergic receptors and an increase in a 40-kd G1-like protein in the failing heart. Similar changes have been described in human idiopathic dilated cardiomyopathy. In addition to these changes, we identified a possible defect at the level of the catalytic subunit of adenylate cyclase.

Both cell surface and internalized beta-adrenoceptors are reduced in the failing myocardium

To study myocardial beta-adrenoceptor internalization in heart failure, we measured beta-adrenoceptor density in the particulate, light vesicle and supernatant fractions of ventricular tissue of dogs with experimental right ventricular failure and sham-operated dogs. Tissue was fractionated by centrifugation, and beta-adrenoceptors were measured by [125I]iodocyanopindolol binding. Compared to sham-operated controls, beta-adrenoceptors were reduced in all fractions of right ventricular tissue from heart failure animals. Thus, the decreased surface (particulate fraction) receptors observed cannot be explained by internalization alone, and must be associated with altered receptor synthesis or degradation.