Myocardial beta-adrenoceptor changes in heart failure: concomitant reduction in beta 1- and beta 2-adrenoceptor function related to the degree of heart failure in patients with mitral valve disease

Cardiac myosin binding protein-C phosphorylation as a function of multiple protein kinase and phosphatase activities

Phosphorylation of cardiac myosin binding protein-C (cMyBP-C) is a determinant of cardiac myofilament function. Although cMyBP-C phosphorylation by various protein kinases has been extensively studied, the influence of protein phosphatases on cMyBP-C's multiple phosphorylation sites has remained largely obscure. Here we provide a detailed biochemical characterization of cMyBP-C dephosphorylation by protein phosphatases 1 and 2 A (PP1 and PP2A), and develop an integrated kinetic model for cMyBP-C phosphorylation using data for both PP1, PP2A and various protein kinases known to phosphorylate cMyBP-C. We find strong site-specificity and a hierarchical mechanism for both phosphatases, proceeding in the opposite direction of sequential phosphorylation by potein kinase A. The model is consistent with published data from human patients and predicts complex non-linear cMyBP-C phosphorylation patterns that are validated experimentally. Our results suggest non-redundant roles for PP1 and PP2A under both physiological and heart failure conditions, and emphasize the importance of phosphatases for cMyBP-C regulation.

GRK2 in cardiovascular disease and its potential as a therapeutic target

Cardiovascular diseases (CVDs) represent the leading cause of death globally. Despite major advances in the field of pharmacological CVD treatments, particularly in the field of heart failure (HF) research, case numbers and overall mortality remain high and have trended upwards over the last few years. Thus, identifying novel molecular targets for developing HF therapeutics remains a key research focus. G protein-coupled receptors (GPCRs) are critical myocardial signal transducers which regulate cardiac contractility, growth, adaptation and metabolism. Additionally, GPCR dysregulation underlies multiple models of cardiac pathology, and most pharmacological therapeutics currently used in HF target these receptors. Currently-approved treatments have improved patient outcomes, but therapies to stop or reverse HF are lacking. A recent focus on GPCR intracellular-regulating proteins such as GPCR kinases (GRKs) has uncovered GRK2 as a promising target for combating HF. Current literature strongly establishes increased levels and activity of GRK2 in multiple models of CVD. Additionally, the GRK2 interactome includes numerous proteins which interact with differential domains of GRK2 to modulate both beneficial and deleterious signaling pathways in the heart, indicating that these domains can be targeted with a high level of specificity unique to various cardiac pathologies. These data support the premise that GRK2 should be at the forefront of a novel investigative drug search. This perspective reviews cardiac GPCRs, describes the structure and functions of GRK2 in cardiac function and maladaptive pathology, and summarizes the ongoing and future research for targeting this critical kinase across cellular, animal and human models of cardiac dysfunction and HF.

β-Adrenergic Receptor Desensitization/Down-Regulation in Heart Failure: A Friend or Foe?

Cardiac sympathetic activation, mediated by β-adrenergic receptors (β-ARs), normally increases cardiac contraction and relaxation. Accomplishing this task requires a physiological, concerted Ca²⁺ signaling, being able to increase Ca²⁺ release from sarcoplasmic reticulum (SR) in systole and speed up Ca²⁺ re-uptake in diastole. In heart failure (HF) myocardial β-ARs undergo desensitization/down-regulation due to sustained sympathetic adrenergic activation. β-AR desensitization/down-regulation diminishes adrenergic signaling and cardiac contractile reserve, and is conventionally considered to be detrimental in HF progression. Abnormal Ca²⁺ handling, manifested as cardiac ryanodine receptor (RyR2) dysfunction and diastolic Ca²⁺ leak (due to sustained adrenergic activation) also occur in HF. RyR2 dysfunction and Ca²⁺ leak deplete SR Ca²⁺ store, diminish Ca²⁺ release in systole and elevate Ca²⁺ levels in diastole, impairing both systolic and diastolic ventricular function. Moreover, elevated Ca²⁺ levels in diastole promote triggered activity and arrhythmogenesis. In the presence of RyR2 dysfunction and Ca²⁺ leak, further activation of the β-AR signaling in HF would worsen the existing abnormal Ca²⁺ handling, exacerbating not only cardiac dysfunction, but also ventricular arrhythmogenesis and sudden cardiac death. Thus, we conclude that β-AR desensitization/down-regulation may be a self-preserving, adaptive process (acting like an intrinsic β-AR blocker) protecting the failing heart from developing lethal ventricular arrhythmias under conditions of elevated sympathetic drive and catecholamine levels in HF, rather than a conventionally considered detrimental process. This also implies that medications simply enhancing β-AR signaling (like β-AR agonists) may not be so beneficial unless they can also correct dysfunctional Ca²⁺ handling in HF.

In Vivo Stimulation of α- and β-Adrenoceptors in Mice Differentially Alters Small RNA Content of Circulating Extracellular Vesicles

When myocardial function is compromised as in heart failure (HF), there is activation of the sympathetic nervous system with elevated circulating catecholamine levels. These catecholamines activate cardiac and extra-cardiac adrenergic receptors (ARs). Interest in secreted extracellular vesicles (EVs) from the heart is growing and in HF, it is not known whether excessive activation of α- or β-adrenergic receptors (ARs) could induce specific changes in EV content. In this study, we have evaluated, by next generation sequencing, the small RNA content, including micro-RNAs (miRs), of circulating EVs of mice exposed to chronic selective α- or β- AR stimulation. EVs from mouse blood were purified by differential ultracentrifugation resulting in EVs with an average size of 116.6 ± 4.8 nm that by immunoblotting included protein markers of EVs. We identified the presence of miRs in blood EVs using miR-21-5p and -16-5p real-time PCR as known constituents of blood exosomes that make up a portion of EVs. We next performed next generation sequencing (NGS) of small non-coding RNAs found in blood EVs from mice following 7 days of chronic treatment with isoproterenol (ISO) or phenylephrine (PE) to stimulate α- or β-ARs, respectively. PE increased the percent of genomic repeat region reads and decreased the percent of miR reads. In miR expression analysis, PE and ISO displayed specific patterns of miR expression that suggests differential pathway regulation. The top 20 KEGG pathways predicted by differential expressed miRs show that PE and ISO share 11 of 20 pathways analyzed and reveal also key differences including three synapse relative pathways induced by ISO relative to PE treatment. Both α-and β-AR agonists can alter small RNA content of circulating blood EVs/exosomes including differential expression and loading of miRs that indicate regulation of distinct pathways. This study provides novel insight into chronic sympathetic nervous system activation in HF where excessive catecholamines may not only participate in pathological remodeling of the heart but alter other organs due to secretion of EVs with altered miR content.

Bisoprolol-based 18F-PET tracer: Synthesis and preliminary in vivo validation of β1-blocker selectivity for β1-adrenergic receptors in the heart

The selectivity of a drug toward various isoforms of the target protein family is important in terms of toxicology. Typically, drug or candidate selectivity is assessed by in vitro assays, but in vivo investigations are currently lacking. Positron emission tomography (PET) allows the non-invasive determination of the in vivo distribution of a radiolabeled drug, which can provide in vivo data regarding drug selectivity. Since the discovery of propranolol, a non-selective β-blocker inhibiting both β₁- and β₂-adrenoreceptors (β-ARs), various selective β₁-blockers, including bisoprolol, have been developed to overcome disadvantages associated with β₂-AR inhibition. As a proof of concept, we performed an in vivo PET study to understand the selectivity and efficacy of bisoprolol as a selective β-blocker toward β₁-AR, as the heart and peripheral smooth muscles demonstrate distinct populations of β₁- and β₂-ARs. Biodistribution of ¹⁸F-labeled bisoprolol (1, [¹⁸F]bisoprolol) showed the retention of its uptake in the heart compared with other β-AR-rich organs at late time points post-injection. The competitive blocking assay using unlabeled bisoprolol exhibited no inhibition of [¹⁸F]bisoprolol uptake in any organ but exhibited significantly rapid loss of radioactivity between two different time points in β₁-AR-rich organs such as the heart and brain. Furthermore, the organ-to-blood ratio revealed the slow excretion and better accumulation of [¹⁸F]bisoprolol inside the heart. Collectively, the ex vivo biodistribution and blocking study presented insightful evidence to better comprehend the in vivo distribution pattern of bisoprolol as a selective inhibitor targeting β₁-ARs in the heart and provided the possibility of PET as an in vivo technique for evaluating drug selectivity.

No impact of sex and age on beta-adrenoceptor-mediated inotropy in human right atrial trabeculae

AIM

There is an increasing awareness of the impact of age and sex on cardiovascular diseases (CVDs). Differences in physiology are suspected. Beta-adrenoceptors (beta-ARs) are an important drug target in CVD and potential differences might have significant impact on the treatment of many patients. To investigate whether age and sex affects beta-AR function, we analysed a large data set on beta-AR-induced inotropy in human atrial trabeculae.

METHODS

We performed multivariable analysis of individual atrial contractility data from trabeculae obtained during heart surgery of patients in sinus rhythm (535 trabeculae from 165 patients). Noradrenaline or adrenaline were used in the presence of the beta₂ -selective antagonist (ICI 118 551, 50 nmol/L) or the beta₁ -selective antagonist (CGP 20712A, 300 nmol/L) to stimulate beta₁ -AR or beta₂ -AR respectively. Agonist concentration required to achieve half-maximum inotropic effects (EC₅₀ ) was taken as a measure of beta-AR sensitivity.

RESULTS

Impact of clinical variables was modelled using multivariable mixed model regression. As previously reported, chronic treatment with beta-blockers sensitized beta-AR. However, there was no significant interaction between basal force, maximum force and beta-AR sensitivity when age and sex were modelled continuously. In addition, there was no statistically significant effect of body mass index or diabetes on atrial contractility.

CONCLUSION

Our large, multivariable analysis shows that neither age nor sex affects beta-AR-mediated inotropy or catecholamine sensitivity in human atrial trabeculae. These findings may have important clinical implications because beta-ARs, as a common drug target in CVD and heart failure, do not behave differently in women and men across age decades.

G protein-coupled receptor kinases as therapeutic targets in the heart

G protein-coupled receptors (GPCRs) are critical cellular sensors that mediate numerous physiological processes. In the heart, multiple GPCRs are expressed on various cell types, where they coordinate to regulate cardiac function by modulating critical processes such as contractility and blood flow. Under pathological settings, these receptors undergo aberrant changes in expression levels, localization and capacity to couple to downstream signalling pathways. Conventional therapies for heart failure work by targeting GPCRs, such as β-adrenergic receptor and angiotensin II receptor antagonists. Although these treatments have improved patient survival, heart failure remains one of the leading causes of mortality worldwide. GPCR kinases (GRKs) are responsible for GPCR phosphorylation and, therefore, desensitization and downregulation of GPCRs. In this Review, we discuss the GPCR signalling pathways and the GRKs involved in the pathophysiology of heart disease. Given that increased expression and activity of GRK2 and GRK5 contribute to the loss of contractile reserve in the stressed and failing heart, inhibition of overactive GRKs has been proposed as a novel therapeutic approach to treat heart failure.

Heart rate variability is impaired in adults after closure of ventricular septal defect in childhood: A novel finding associated with right bundle branch block

BACKGROUND

Ventricular septal defects (VSDs) generally have benign long-term prognoses, but recent studies have indicated increased pulmonary vascular resistance. A potential tool for monitoring pulmonary artery pressure is heart rate variability, and therefore, the aim of this study was to assess heart rate variability in adults with a surgically repaired or unrepaired VSD.

METHODS

In a long-term, follow-up study, three groups were included; VSD-patients operated in early childhood, patients with an open VSD, and controls. For each patient, 24-hour Holter monitoring was performed and heart rate variability was assessed.

RESULTS

In total, 30 participants with a surgically closed VSD, 30 participants with an unrepaired VSD, and 36 controls were included. In the closed VSD group, there was a higher proportion of participants, who had low sNN50 (p = 0.005) and low sNN6% (p = 0.017) than in the other two groups. Similar differences were found when sNN50 was divided into increases and decreases (p = 0.007 and p = 0.005, respectively) as well as sNN6% (p = 0.014 and p = 0.014, respectively). Lastly, there was a higher proportion of patients in the closed VSD group with low rMSSD than in the other two groups (p = 0.005). For the closed VSD group, the proportion of participants with low total sNN50 (p = 0.046) and low total sNN6% (p = 0.046) were higher among participants with a complete right bundle branch block (RBBB) than among participants with no or an incomplete RBBB.

CONCLUSIONS

Adults who had surgical VSD closure in early childhood had impaired heart rate variability and, particularly, participants with complete RBBB had lower heart rate variability.

β2‑adrenergic receptor functionality and genotype in two different models of chronic inflammatory disease: Liver cirrhosis and osteoarthritis

The present study was designed to investigate the functional status of β2 adrenoceptors (β2AR) in two models of chronic inflammatory disease: liver cirrhosis (LC) and osteoarthritis (OA). The β2AR gene contains three single nucleotide polymorphisms at amino acid positions 16, 27 and 164. The aim of the present study was to investigate the potential influence of lymphocyte β2AR receptor functionality and genotype in LC and OA patients. Blood samples from cirrhotic patients (n=52, hepatic venous pressure gradient 13±4 mmHg, CHILD 7±2 and MELD 11±4 scores), OA patients (n=30, 84% Kellgren‑Lawrence severity 4 grade, 14% knee replacement joint) and healthy volunteers as control group (n=26) were analyzed. Peripheral blood mononuclear cells (PBMC) were isolated from whole blood and basal and isoproterenol induced adenylate cyclase activity (isoproterenol stimulus from 10‑9 to 10‑4 mM), and β2AR allelic variants (rs1042713, rs1042714, rs1800888) were determined. β2AR functionality was decreased in the two different models of chronic inflammatory disease studied, OA (50% vs. control) and LC (85% vs. control). In these patients, the strength of the β2AR response to adrenergic stimulation was very limited. Adrenergic modulation of PBMC function through the β2AR stimulus is decreased in chronic inflammatory processes including LC and OA, suggesting that the adrenergic system may be important in the development of these processes.

β-adrenergic receptor responsiveness in aging heart and clinical implications

Elderly healthy individuals have a reduced exercise tolerance and a decreased left ventricle inotropic reserve related to increased vascular afterload, arterial-ventricular load mismatching, physical deconditioning and impaired autonomic regulation (the so called "β-adrenergic desensitization"). Adrenergic responsiveness is altered with aging and the age-related changes are limited to the β-adrenergic receptor density reduction and to the β-adrenoceptor-G-protein(s)-adenylyl cyclase system abnormalities, while the type and level of abnormalities change with species and tissues. Epidemiological studies have shown an high incidence and prevalence of heart failure in the elderly and a great body of evidence correlate the changes of β-adrenergic system with heart failure pathogenesis. In particular it is well known that: (a) levels of cathecolamines are directly correlated with mortality and functional status in heart failure, (b) β1-adrenergic receptor subtype is down-regulated in heart failure, (c) heart failure-dependent cardiac adrenergic responsiveness reduction is related to changes in G proteins activity. In this review we focus on the cardiovascular β-adrenergic changes involvement in the aging process and on similarities and differences between aging heart and heart failure.

Regulation of cyclic adenosine monophosphate release by selective β2-adrenergic receptor stimulation in human terminal failing myocardium before and after ventricular assist device support

BACKGROUND

Response to catecholamines is blunted in terminal heart failure due to β-receptor downregulation and uncoupling from adenylyl cyclase (AC). Improved myocardial responsiveness to catecholamines after ventricular assist device (VAD) support is associated with upregulation of β1-adrenergic receptors (β1-ARs). Little is known about the regulation of AC and β2-AR coupling after VAD; moreover β2-AR stimulation during VAD was claimed to induce myocardial recovery.

METHODS

We analyzed in VAD-supported human myocardium the regulation of AC activity upon β1-AR and selective β2-AR stimulation in 8 non-failing hearts (NF) and 17 paired samples of VAD patients. AC messenger RNA was measured by TaqMan. AC was stimulated via β2-AR using clenbuterol (β2-AR agonist) and bisoprolol (β1-AR blocker). Organ bath experiments were done with trabeculae from both ventricles. Samples were stratified according to chronic or acute heart failure history.

RESULTS

Isoprenaline-induced AC activity was downregulated (p < 0.001) pre-VAD and increased significantly (p < 0.05) after unloading (mean ± standard deviation pmole/mg/min) in NF (47.9 ± 14.9), pre-VAD (24.35 ± 13.3), and post-VAD (50.04 ± 50.25). Forskolin stimulation revealed significant (p < 0.05) upregulation of AC activity during VAD, especially in acutely failing hearts (NF, 192.1 ± 68.7; pre-VAD, 191.1 ± 60.4; post-VAD, 281.5 ± 133). However, forskolin stimulation relative to isoprenaline-induced inotropy remained reduced before and after VAD compared with NF. The selective stimulation of β2-AR did not reveal influence of VAD support on β2-AR-AC coupling. Stimulation of ventricular trabeculae by > 100 μmole/liter clenbuterol revealed negative inotropic responses.

CONCLUSIONS

VAD does not influence β2-AR coupling to AC stimulation. Elevated response to catecholamines after VAD support is influenced by β1-AR upregulation and modulation of AC activity. Restoration of β-adrenergic responsiveness was restricted to acutely failing hearts.

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.

Preclinical evaluation of an 18F-labelled beta1-adrenoceptor selective radioligand based on ICI 89,406

PURPOSE

Radioligand binding studies indicate a down-regulation of myocardial beta(1)-adrenoceptors (beta(1)-AR) in cardiac disease which may or may not be associated with a decrease in beta(2)-ARs. We have chosen ICI 89,406, a beta(1)-selective AR antagonist, as the lead structure to develop new beta(1)-AR radioligands for PET and have synthesised a fluoro-ethoxy derivative (F-ICI).

METHODS

(S)-N-[2-[3-(2-Cyano-phenoxy)-2-hydroxy-propylamino]-ethyl]-N'-[4-(2-[(18)F]fluoro-ethoxy)-phenyl]-urea ((S)-[(18)F]F-ICI) was synthesised. Myocardial uptake of radioactivity after intravenous injection of (S)-[(18)F]F-ICI into adult CD(1) mice or Wistar rats was assessed with positron emission tomography (PET) and postmortem dissection. Metabolism was assessed by high-performance liquid chromatography analysis of plasma and urine.

RESULTS

The heart was visualised with PET after injection of (S)-[(18)F]F-ICI but neither unlabelled F-ICI nor propranolol (non-selective beta-AR antagonist) injected 15 min after (S)-[(18)F]F-ICI affected myocardial radioactivity. Ex vivo dissection demonstrated that predosing with propranolol or CGP 20712 (beta(1)-selective AR-antagonist) did not affect myocardial radioactivity. Radiometabolites rapidly appeared in plasma and both (S)-[(18)F]F-ICI and radiometabolites accumulated in urine.

CONCLUSIONS

Myocardial uptake of (S)-[(18)F]F-ICI after intravenous injection was mainly at sites unrelated to beta(1)-ARs. (S)-[(18)F]F-ICI is not a suitable beta(1)-selective-AR radioligand for PET.

Location and density of alpha- and beta-adrenoreceptor sub-types in myocardium after mechanical left ventricular unloading

BACKGROUND

We hypothesized that not all subtypes of alpha- and beta-adrenoreceptors undergo similar upregulation and redistribution in human myocardium after mechanical unloading with an assist device.

METHODS

We obtained core biopsy samples of the left ventricle in 19 patients before and after removal of a Jarvik or Thoratec left ventricular assist device (LVAD) to study the effect of mechanical unloading on the distribution of alpha- and beta-adrenoreceptors. Fresh, embedded tissue sections were incubated with receptor blockers and antibodies before the fluorescent labeling of receptors. Images were obtained by fluorescence deconvolution microscopy, and composite tissue renditions were made from the stacked images. Multiple adrenoreceptor subtypes were studied.

RESULTS

We saw a reversal of myocyte hypertrophy in all patients, but the upregulation of receptors was not seen in all post-LVAD tissue samples. Furthermore, we noted receptor relocalization from an initial punctate/clumped pattern to a normal homogeneous distribution in many patients. Significant differences were seen in the distribution of beta(2)- and alpha(1)-receptors and in alpha(1A) subtypes.

CONCLUSIONS

In this study we show not only the expected reversal of myocyte hypertrophy and the increase in adrenoreceptors after ventricular unloading, but also the relocalization of specific receptor subtypes.

Are [O-methyl-11C]derivatives of ICI 89,406 beta1-adrenoceptor selective radioligands suitable for PET?

PURPOSE

Radioligand binding studies show that beta(1)-adrenoceptor (beta(1)-AR) density may be reduced in heart disease without down regulation of beta(2)-ARs. Radioligands are available for measuring total beta-AR density non-invasively with clinical positron emission tomography (PET) but none are selective for beta(1)- or beta(2)-ARs. The aim was to evaluate ICI 89,406, a beta(1)-AR-selective antagonist amenable to labelling with positron emitters, for PET.

METHODS

The S-enantiomer of an [O-methyl-(11)C] derivative of ICI 89,406 ((S)-[(11)C]ICI-OMe) was synthesised. Tissue radioactivity after i.v. injection of (S)-[(11)C]ICI-OMe (< 2 nmol x kg(-1)) into adult Wistar rats was assessed by small animal PET and post mortem dissection. Metabolism was assessed by HPLC of extracts prepared from plasma and tissues and by measuring [(11)C]CO(2) in exhaled air.

RESULTS

The heart was visualised by PET after injection of (S)-[(11)C]ICI-OMe but neither unlabelled (S)-ICI-OMe nor propranolol (non-selective beta-AR antagonist) injected 15 min after (S)-[(11)C]ICI-OMe affected myocardial radioactivity. Ex vivo dissection showed that injecting unlabelled (S)-ICI-OMe, propranolol or CGP 20712A (beta(1)-selective AR antagonist) at high dose (> 2 mumol x kg(-1)) before (S)-[(11)C]ICI-OMe had a small effect on myocardial radioactivity. HPLC demonstrated that radioactivity in myocardium was due to unmetabolised (S)-[(11)C]ICI-OMe although (11)C-labelled metabolites rapidly appeared in plasma and liver and [(11)C]CO(2) was detected in exhaled air.

CONCLUSION

Myocardial uptake of (S)-[(11)C]ICI-OMe after i.v. injection was low, possibly due to rapid metabolism in other tissues. Injection of unlabelled ligand or beta-AR antagonists had little effect indicating that binding was mainly to non-specific myocardial sites, thus precluding the use of (S)-[(11)C]ICI-OMe to assess beta(1)-ARs with PET.

Selective upregulation of β1-adrenergic receptors and dephosphorylation of troponin I in end-stage heart failure patients supported by ventricular assist devices

In terminal failing hearts, adrenergic receptors are downregulated and intracellular adrenergic signal transduction is inhibited. Mechanical circulatory support by ventricular assist devices (VAD) is used to bridge patients to heart transplantation. Mechanical unloading by VAD may induce reverse remodeling in heart transplantation (HTx) candidates. However, little is known on beta-adrenergic receptor subtype regulation and adrenergic signal transduction under VAD-support. We investigated paired myocardial samples from 16 VAD-supported patients and 9 non-failing donor hearts. We analyzed beta-adrenergic receptor subtype regulation by real-time PCR and radioligand binding and cardiac troponin I phosphorylation (by phospho-cTnI-specific antibodies). We found that the beta1-adrenergic receptor (beta1AR) is downregulated at VAD-implantation on mRNA and protein levels whereas the beta2-adrenergic receptor (beta2AR) was not. After VAD-support, beta1AR protein but not its mRNA was upregulated, whereas the degree of cTnI-phosphorylation was reduced. Upregulation of beta1AR was enhanced by beta blocking medication during VAD-support. However, in 9 out of 15 patients, beta1AR-density remained below the 0.25 percentile of donor hearts. VAD-support is associated with partial normalization of the betaAR-signal transduction pathways. This beneficial effect is related to a posttranscriptional increase in beta1AR-density.

Functional mitral regurgitation predicts 1-year mortality in elderly patients with systolic chronic heart failure

BACKGROUND AND AIM

Mitral regurgitation (MR) has been demonstrated to be a powerful predictor of adverse outcome in middle-aged patients with chronic heart failure (CHF). In this study, we sought to define the prognostic impact of functional mitral regurgitation in a population of elderly patients with systolic CHF.

METHODS

One hundred seventy-five outpatients aged >70 years with validated CHF and left ventricular ejection fraction <40% underwent clinical and echocardiographic evaluations at baseline. Mitral regurgitation was diagnosed by Color Doppler and quantified in 5 categorical values using a 0-4+ grading system. Outcome measures included 1-year mortality and hospitalization for worsening CHF.

RESULTS

The distribution of patients according to the 5 different degrees of MR detected at baseline was: absent=11%, 1+=31%, 2+=38%, 3+=16%, 4+=4%. The relationship between MR and mortality was direct and approximately linear (r=0.39, p=0.00001). The prevalence of death in the 5 subgroups was 0%, 7%, 15%, 45%, 57%, respectively. Multivariate logistic regression analysis showed that MR was the strongest predictor of death (OR 4.47, 95% CI 1.50-13.0), independently of the presence of diabetes mellitus, older age and larger left ventricular end-diastolic volume. No association was found between MR and hospitalization for worsening CHF (r=0.08, p=0.41).

CONCLUSIONS

This study establishes the direct and independent relationship between MR severity and one-year mortality among elders with systolic CHF. Conversely, MR does not provide useful information regarding the risk of subsequent hospitalization for worsening CHF.

Alterations in adrenergic receptor signaling in heart failure

In the failing heart, several changes occur in cardiac adrenergic receptor-signal transduction pathways. The most striking of these changes occur in beta-ARs, and of the changes in beta-adrenergic receptors, beta1-receptor down-regulation is the most prominent. Other changes include uncoupling of beta2-adrenergic receptors and increased activity of the inhibitory G-protein, Gi. Most of these changes appear to be related to increased activity of the adrenergic nervous system, i.e. increased exposure to norepinephrine. Antagonists of the adrenergic nervous system improve left ventricular function and outcome in patients with heart failure. This fact supports the notion that activation of these neurohormonal systems exerts a net long-term detrimental effect on the natural history of chronic heart failure and that myocardial adrenergic desensitization phenomena are at least partially adaptive in the setting of left ventricular dysfunction.

Renal, but not systemic, hemodynamic effects of dopamine are influenced by the severity of congestive heart failure

OBJECTIVE

To determine whether the short-term systemic and renal hemodynamic response to dopamine is influenced by clinical severity of congestive heart failure.

DESIGN

Effects of increasing doses of dopamine were assessed in patients consecutively admitted for acutely decompensated congestive heart failure.

SETTING

Intensive care unit.

PATIENTS

We enrolled 16 congestive heart failure patients stratified by clinical severity (New York Heart Association [NYHA] class III, n = 8; NYHA class IV, n = 8) and two additional NYHA class III patients as controls.

INTERVENTIONS

Measurements were carried out throughout five 20-min experimental periods: baseline, dopamine infusion at 2, 4, and 6 microg x kg(-1) x min(-1), and recovery. Controls received a similar amount of saline.

MEASUREMENTS AND MAIN RESULTS

Systemic and renal hemodynamics were determined respectively by right cardiac catheterization and radioisotopes (iodine 131-labeled hippuran and iodine 125-labeled iothalamate clearance). The peak increase in heart rate and cardiac index occurred at a dopamine dose of 4-6 microg x kg(-1) x min(-1). The dose-response relation was similar in NYHA classes III and IV. Improvement in effective renal plasma flow and glomerular filtration rate, peaking at 4 microg x kg(-1) x min(-1), was more rapid and marked in NYHA class III than class IV patients, in whom the renal fraction of cardiac output failed to increase. The systemic and renal effects of dopamine were independent of age. No change occurred in controls.

CONCLUSIONS

The dose of dopamine producing an optimal improvement of systemic and renal hemodynamics in congestive heart failure is higher than usually reported. A greater clinical severity of congestive heart failure impairs the renal effects of dopamine, probably through a selective loss in renal vasodilating capacity.

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.

Effects of therapeutic beta blockade on myocardial function and cardiac remodelling in congenital cardiac disease

BACKGROUND

Cardiac remodelling is now recognised as an important aspect of cardiovascular disease progression and is, therefore, emerging as a therapeutic target in cardiac failure due to different etiologies. Little is known about the influence of different therapies for cardiac failure on the remodelling seen in infants with congenital cardiac disease.

METHODS

During follow-up of a prospective and randomized trial, we investigated therapeutic effects on neurohormonal activation, ventricular function, and myocardial gene expression. We compared the data from 8 infants with severe congestive heart failure due to left-to-right shunts, who received digoxin and diuretics alone, to 9 infants who received additional treatment with propranolol.

RESULTS

In these infants, beta-adrenergic blockade significantly reduced highly elevated levels of renin, from 284 +/- 319 microU/ml compared to 1061 +/- 769 microU/ml. Systolic ventricular function was normal in both groups, but diastolic ventricular function was improved in those receiving propranolol, indicated by significantly lower left atrial pressures, lower end-diastolic pressures, and less pronounced ventricular hypertrophy, the latter estimated by lower ratios of myocardial wall to ventricular cavity areas on average of 42%. Further hemodynamic parameters showed no significant differences between the groups, except for the lower heart rate in infants treated with propranolol. In those treated with digoxin and diuretics, there was a significant downregulation of beta2-receptor and angiotensin-2 receptor genes, and up-regulation of endothelin A receptor and connective tissue growth factor genes, that were partially prevented by additional treatment with propranolol.

CONCLUSIONS

Beta-blockade is a new therapeutic approach for congestive heart failure in infants with congenital cardiac disease, producing with significant benefits on neurohormonal activation, diastolic ventricular function, and cardiac remodelling.

Characterization of lymphocyte beta 2-adrenoceptor signalling in patients with left ventricular volume overload disease

1. Studies using animal experimental models have suggested that the beta2-adrenoceptor is uncoupled in association with alterations in the expression of G-protein-coupled receptor kinases (GRK) 2/3 in heart failure. However, the functional expression of the components of this pathway in human disease has not been fully elucidated yet. In the present study, we evaluated the possibility that the regulation of beta2-adrenoceptor signalling components in patients with left ventricular volume overload (VOL) depends on the severity of the overload. 2. We characterized the lymphocyte GRK 2-6, beta-arrestins 1 and 2, beta2-adrenoceptor expression at the mRNA and protein levels, as well as the activity of adenylyl cyclase, protein kinases (PK) A and PKC in patients with VOL using healthy blood donors as controls. 3. In the patient group, GRK2 mRNA was increased by 61% (P < 0.001), GRK3 was increased by 54% (P < 0.005), GRK5 was increased fivefold (P < 0.001) and the beta-arrestin 2 mRNA was increased by 40% (P < 0.05). These increases were paralleled with a sixfold increase in GRK2, a twofold increase in GRK3 and a 1.3-fold increase in GRK5 protein levels. These changes were associated with a significant decrease in beta2-adrenoceptor mRNA, the basal, catalytic and receptor-mediated activity of adenylyl cyclase and sensitization of the forskolin-stimulated activity towards augmented inhibition by guanylimidodiphosphate. In general, the increase in GRK2 and 5 mRNA exhibited a positive correlation with the gravity of the haemodynamic load, as determined by changes in left ventricular fractional shortening. 4. The results suggest that VOL induces an increase in the expression of lymphocyte beta2-adrenoceptor-specific GRK and beta-arrestin 2 in association with an attenuation in beta2-adrenoceptor levels. It can be speculated that the cardiac circulatory system adapts itself to altered haemodynamic functional demands partly by altering beta2-adrenoceptor signalling.

Beta-receptor downregulation in congenital heart disease: a risk factor for complications after surgical repair?

BACKGROUND

Neurohormonal activation in children with heart failure due to congenital heart disease leads to downregulation of myocardial beta-receptors that may influence the postoperative course after cardiothoracic surgery.

METHODS

Myocardial biopsies of 26 children (aged 14+/-4 months) were obtained from the right atrium during cardiac surgery. Patients were allocated to either of two groups based on the duration of their intensive care unit stay: group 1 comprised those who stayed less than 7 days (n = 17), whereas group 2 comprised those who stayed more than 7 days, plus 3 infants who died during the early postoperative course (n = 9). For beta1- and beta2-mRNA quantitation, real-time polymerase chain reaction with fluorescence-labeled products was used.

RESULTS

Values for myocardial beta1-receptor gene expression were twice as high in group 1 children compared with group 2 (beta1-receptor 0.12+/-0.07 versus 0.06+/-0.03, p = 0.0016; beta2-receptor 0.12+/-0.07 versus 0.06+/-0.03, p = 0.0071). Beta-receptor gene expression in 16 children who received standard treatment for heart failure averaged lower than in the 10 children who received additional propranolol.

CONCLUSIONS

Beta-receptor downregulation due to congestive heart failure has an impact on the postoperative course in children with congenital disease and depends on heart failure therapy.

Myocardial-directed overexpression of the human beta(1)-adrenergic receptor in transgenic mice

The beta(1)-adrenergic receptor (AR) is the dominant subtype in non-failing and failing myocardium. beta(1)-AR signaling, by the endogenous neurotransmitter norepinephrine, is central to the regulation of myocardial contractility. In heart failure, the beta(1)-AR undergoes subtype-selective downregulation which may protect against the increased cardiac adrenergic drive associated with this pathophysiological state. To examine the hypothesis that chronically increased beta(1)-AR mediated signaling has adverse myocardial effects, transgenic mice overexpressing the human beta(1)-AR in a cardiac-selective context were produced, utilizing an alpha-myosin heavy chain (MHC) promoter. In these mice, beta(1)-AR protein abundance was approximately 24-46-fold (1-2 pmol/mg protein) that of wild-type mice. Histopathological examination of young (4 months old) and old (approximately 9 months old) transgenic mouse hearts consistently demonstrated large areas of interstitial replacement fibrosis, marked myocyte hypertrophy and myofibrilar disarray. In addition, increased expression of the pre-apoptotic marker, Bax, was observed coincident with regions of fibrosis accompanied by an increased apoptotic index, as measured by TUNEL assay. Older non-transgenic mice exhibited a slight tendency towards a decreased fractional shortening, whereas older beta(1)-AR transgenic mice had a marked reduction in fractional shortening (%FS approximately 30) as determined by echocardiography. Additionally, older beta(1)-AR transgenic mice had an increased left ventricular chamber size. In summary, cardiac-directed overexpression of the human beta(1)-AR in transgenic mice leads to a significant histopathological phenotype with no apparent functional consequence in younger mice and a variable degree of cardiac dysfunction in older animals. This model system may ultimately prove useful for investigating the biological basis of adrenergically-mediated myocardial damage in humans.

Down regulation of myocardial beta1-adrenoceptor signal transduction system in pacing-induced failure in dogs with aortic stenosis-induced left ventricular hypertrophy

We recently demonstrated that rapid ventricular pacing caused cardiac failure (Failure) in dogs with aortic stenosis-induced left ventricular hypertrophy (Hypertrophy) and isoproterenol caused no significant increases in function, O2 consumption and intracellular cyclic AMP level in the failing hypertrophied hearts. We tested the hypothesis that alterations in the beta1-adrenoceptor-signal transduction pathway would correlate with the reduced functional and metabolic responses to beta-adrenergic stimulation during the transition from the compensated hypertrophy to failure. Pressure overload-induced left ventricular hypertrophy was created using aortic valve plication in 10 dogs over a 6-month period. Five months after aortic valve plication, congestive heart failure was induced in 5 dogs by rapid ventricular pacing at 240 bpm for 4 weeks. The density of myocardial beta1-adrenoceptors (fmoles/mg membrane protein; fmoles/g wet tissue) was significantly reduced in the Failure dogs (176+/-19; 755+/-136) when compared to those of the Control (344+/-51; 1,551+/-203) and the Hypertrophy (298+/-33; 1,721+/-162) dogs. The receptor affinities were not significantly different among all groups. There was a small but significant decrease in the percentage of beta1-adrenoceptors of the failing hypertrophied hearts (62+/-3%) when compared to that of the hypertrophied hearts (77+/-5%). The basal myocardial adenylyl cyclase activity (pmoles/mg protein/min) was significantly lower in the Failure dogs (45+/-4) than in the Control (116+/-14) and Hypertrophy (86+/-6) dogs. The forskolin (0.1 mM)-stimulated adenylyl cyclase activity was also significantly lower in the Failure dogs (158+/-17) than in the Control dogs (296+/-35) and slightly lower than in the Hypertrophy dogs (215+/-10). There were no significant differences in low Km cyclic AMP-phosphodiesterase activities among all groups. We conclude that down regulation of beta1-adrenoceptors and reduced adenylyl cyclase activities contribute to the decreases in myocardial functions and beta-adrenergic responses in the failing hypertrophied hearts induced by rapid ventricular pacing.

Mechanism of preserved positive lusitropy by cAMP-dependent drugs in heart failure

In tachycardia-induced heart failure (HF), positive lusitropic effects of milrinone or dobutamine were assessed by evaluating the time constant of left ventricular (LV) pressure decay (tau) and Ca(2+)-ATPase activity of the sarcoplasmic reticulum (SR). The peak value of the positive first derivative of LV pressure (+dP/dt) was less increased, either by dobutamine (2-10 microg x kg(-1) x min(-1)) or by milrinone (4-20 microg/kg), in HF than in control (P < 0.05), whereas tau was shortened to an extent similar to that in control with dobutamine [P = not significant (NS)] and to an even greater extent with milrinone (P < 0.05). Ca(2+)-ATPase activity increased similarly in HF and control with dobutamine (1 microM; +11% in HF vs. +12% in control, P = NS), whereas it increased more with milrinone (1 microM; +19% in HF vs. +11% in control, P < 0.05). Ca(2+)-ATPase activity-cAMP relationships were shifted to the left by milrinone or dobutamine in HF compared with control. Thus, in HF, the sensitivity of Ca(2+)-ATPase activity to cAMP was increased on addition of cAMP-dependent inotropic agents, contributing to the preservation of positive lusitropy.

Recent advances in cardiac beta(2)-adrenergic signal transduction

Recent studies have added complexities to the conceptual framework of cardiac beta-adrenergic receptor (beta-AR) signal transduction. Whereas the classical linear G(s)-adenylyl cyclase-cAMP-protein kinase A (PKA) signaling cascade has been corroborated for beta(1)-AR stimulation, the beta(2)-AR signaling pathway bifurcates at the very first postreceptor step, the G protein level. In addition to G(s), beta(2)-AR couples to pertussis toxin-sensitive G(i) proteins, G(i2) and G(i3). The coupling of beta(2)-AR to G(i) proteins mediates, to a large extent, the differential actions of the beta-AR subtypes on cardiac Ca(2+) handling, contractility, cAMP accumulation, and PKA-mediated protein phosphorylation. The extent of G(i) coupling in ventricular myocytes appears to be the basis of the substantial species-to-species diversity in beta(2)-AR-mediated cardiac responses. There is an apparent dissociation of beta(2)-AR-induced augmentations of the intracellular Ca(2+) (Ca(i)) transient and contractility from cAMP production and PKA-dependent cytoplasmic protein phosphorylation. This can be largely explained by G(i)-dependent functional compartmentalization of the beta(2)-AR-directed cAMP/PKA signaling to the sarcolemmal microdomain. This compartmentalization allows the common second messenger, cAMP, to perform selective functions during beta-AR subtype stimulation. Emerging evidence also points to distinctly different roles of these beta-AR subtypes in modulating noncontractile cellular processes. These recent findings not only reveal the diversity and specificity of beta-AR and G protein interactions but also provide new insights for understanding the differential regulation and functionality of beta-AR subtypes in healthy and diseased hearts.

Age and the cardiovascular system

Congestive heart failure is a common cause of morbidity and mortality in the elderly population. Important changes occur in the structure and function of the cardiovascular system with advancing age. An understanding of these changes is vital for optimum management of these patients.

Progressive hypertrophy and heart failure in beta1-adrenergic receptor transgenic mice

Stimulation of cardiac beta1-adrenergic receptors is the main mechanism that increases heart rate and contractility. Consequently, several pharmacological and gene transfer strategies for the prevention of heart failure aim at improving the function of the cardiac beta-adrenergic receptor system, whereas current clinical treatment favors a reduction of cardiac stimulation. To address this controversy, we have generated mice with heart-specific overexpression of beta1-adrenergic receptors. Their cardiac function was investigated in organ bath experiments as well as in vivo by cardiac catheterization and by time-resolved NMR imaging. The transgenic mice had increased cardiac contractility at a young age but also developed marked myocyte hypertrophy (3.5-fold increase in myocyte area). This increase was followed by progressive heart failure with functional and histological deficits typical for humans with heart failure. Contractility was reduced by approximately 50% in 35-week-old mice, and ejection fraction was reduced down to a minimum of approximately 20%. We conclude that overexpression of beta1-adrenergic receptors in the heart may lead to a short-lived improvement of cardiac function, but that increased beta1-adrenergic receptor signalling is ultimately detrimental.

Myocardial dysfunction in donor hearts. A possible etiology

BACKGROUND

Potential cardiac donors show various degrees of myocardial dysfunction, and the most severely affected hearts are unsuitable for transplantation. The cause of this acute heart failure is poorly understood. We investigated whether alterations in calcium-handling proteins, beta-adrenoceptor density, or the inhibitory G protein Gialpha could account for this phenomenon in unused donor hearts (n=4 to 8). We compared these with end-stage failing hearts (n=14 to 16) and nonfailing hearts (n=3 to 12).

METHODS AND RESULTS

Myocardial samples were obtained from unused donor hearts displaying ejection fractions <30%. Both trabeculae and isolated myocytes responded as poorly as those from the group of failing hearts to increasing stimulation frequency with regard to inotropic function in vitro. Immunodetectable abundance of sarcoplasmic reticulum calcium-ATPase and sodium calcium exchanger were greater (177%; P<0.01) and smaller (29%; P<0.01), respectively, in the unused donor hearts relative to the failing group, which suggests that alterations of these proteins are not a common cause of contractile dysfunction in the 2 groups. Myocytes from the unused donor group were desensitized to isoprenaline to a similar degree as those from the failing heart group. However, beta-adrenoceptor density was reduced in the failing (P<0.001) but not in the unused donor heart group (P=0.37) relative to the nonfailing heart group (n=5). Gialpha activity was increased in samples from unused donor and failing hearts relative to nonfailing hearts (P<0.05).

CONCLUSIONS

Increased activity of the inhibitory G protein Gialpha is a significant contributory factor for impaired contractility in these acutely failing donor hearts.

Cardiac sympathetic innervation in patients with idiopathic right ventricular outflow tract tachycardia

OBJECTIVES

This study investigated the neuronal reuptake of norepinephrine (uptake-1) and the beta-adrenoceptor density in patients with idiopathic right ventricular outflow tract tachycardia (RVO-VT).

BACKGROUND

Clinical findings, such as the inducibility of ventricular tachycardia by stress or catecholamine infusion, and the therapeutic efficacy of antiarrhythmic drugs with antiadrenergic properties suggest abnormalities of cardiac sympathetic innervation in patients with idiopathic RVO-VT.

METHODS

Eight patients with idiopathic RVO-VT and a total of 29 age-matched control subjects were investigated by positron emission tomography using [11C]hydroxyephedrine (HED) (volume of distribution of [11C]HED) to assess presynaptic norepinephrine reuptake; [11C]CGP 12177 (maximal binding capacity of [11C]CGP 12177) to measure postsynaptic beta-adrenoceptor density; and oxygen-15-labeled water for quantification of myocardial blood flow (MBF).

RESULTS

Both myocardial catecholamine reuptake and beta-adrenoceptor density were significantly reduced in patients with idiopathic RVO-VT. The volume of distribution of [11C]HED in patients with RVO-VT was (mean +/- SD) 41.0 +/- 13.5 versus 71.0 +/- 18.8 ml/g in control subjects (p < 0.002). The maximal binding capacity of the beta-adrenoceptor antagonist [11C] CGP 12177 was 6.8 +/- 1.2 pmol/g in patients with RVO-VT versus 10.2 +/- 2.9 pmol/g in control subjects (p < 0.004). There were no significant differences in MBF at rest (0.98 +/- 0.14 vs. 0.97 +/- 0.24 ml/min per g, p = NS) between patients with RVO-VT and control subjects.

CONCLUSIONS

The findings of the present study suggest that myocardial beta-adrenoceptor downregulation in patients with RVO-VT occurs subsequently to increased local synaptic catecholamine levels caused by impaired catecholamine reuptake.

Myocyte recovery after mechanical circulatory support in humans with end-stage heart failure

BACKGROUND

The failing myocardium is characterized by decreased force production, slowed relaxation, and depressed responses to beta-adrenergic stimulation. In some heart failure patients, heart function is so poor that a left ventricular assist device (LVAD) is inserted as a bridge to transplantation. In the present research, we investigated whether circulatory support with an LVAD influenced the functional properties of myocytes from the failing heart.

METHODS AND RESULTS

Myocytes were isolated from human explanted failing hearts (HF-myocytes) and failing hearts with antecedent LVAD support (HF-LVAD-myocytes). Studies of myocyte function indicated that the magnitude of contraction was greater (9.6+/-0.7% versus 6.9+/-0.5% shortening), the time to peak contraction was significantly abbreviated (0.37+/-0.01 versus 0.75+/-0.04 seconds), and the time to 50% relaxation was reduced (0.55+/-0.02 versus 1.45+/-0.11 seconds) in the HF-LVAD-myocytes compared with the HF-myocytes (P<0.05). The HF-LVAD-myocytes had larger contractions than the HF-myocytes at all frequencies of stimulation tested. The negative force-frequency relationship of the HF-myocytes was improved in HF-LVAD-myocytes but was not reversed. Responses to beta-adrenergic stimulation (by isoproterenol) were greater in HF-LVAD-myocytes versus HF-myocytes.

CONCLUSIONS

The results of the study strongly support the idea that circulatory support with an LVAD improves myocyte contractile properties and increases beta-adrenergic responsiveness.

Diminished responsiveness of Gs-coupled receptors in severely failing human hearts: no difference in dilated versus ischemic cardiomyopathy

In end-stage heart failure, cardiac beta-adrenoceptors are decreased and cardiac Gi protein is increased. We assessed beta-adrenoceptors, G proteins, and effects of several beta-adrenoceptor agonists, histamine, and 5-HT on adenylyl cyclase activity in right and left atria and left ventricles and on left ventricular contractility in six potential heart transplant donors (nonfailing hearts; NFHs) and in nine patients with end-stage dilated cardiomyopathy (DCM) and 11 patients with end-stage ischemic cardiomyopathy (ICM) to establish whether the functional responsiveness of all cardiac Gs-coupled receptors is reduced. Beta-adrenoceptors were reduced in all three tissues; in DCM, beta1-adrenoceptors were more markedly downregulated; in ICM, both beta1- and beta2-adrenoceptors were diminished. In all three tissues, isoprenaline-, terbutaline-, histamine- and 5-HT-induced adenylyl cyclase activation was reduced similarly in DCM and ICM. Moreover, in DCM and ICM, guanosine triphosphate (GTP)- (involving Gs and Gi) activated adenylyl cyclase was significantly diminished, whereas NaF-activated (involving only Gs) and Mn2+-activated (acting at the catalytic unit of the enzyme) adenylyl cyclase was unaltered. Left ventricular positive inotropic responses to beta1- (noradrenaline, dopamine, and dobutamine), beta2- (terbutaline), and beta1- and beta2-adrenoceptors (isoprenaline, adrenaline, and epinine), as well as H2-receptor (histamine) stimulation were significantly reduced. The extent of reduction was not different for each agonist in ICM and DCM. We conclude that in DCM and ICM, functional responsiveness of all cardiac Gs-coupled receptors is similarly reduced.

Alterations in beta-adrenoceptor mechanisms in the aging heart. Relationship with heart failure

In chronic heart failure substantial and characteristic changes occur in the function of the adrenergic nervous system. Studies in isolated left ventricular muscle and in single cardiomyocytes from experimental models of aging and, recently, from humans show an age-related reduced contractile response to beta-adrenoceptor stimulation. "beta-adrenoceptor desensitization" is thought to be a general and common mechanism to explain the age- and heart failure-related decrease in beta-adrenoceptor response. The aim of this review is to compare alterations in beta-adrenoceptor mechanisms in physiological cardiovascular aging and chronic heart failure. From an analysis of the overall data on the role of aging in beta-adrenoceptor regulation in human and animal hearts, it is possible to conclude that the reduced response to beta-agonists is common to all species and all cardiac tissues. Moreover, the age-related changes are limited to beta-adrenoceptor-G-protein (s)-adenylyl cyclase system abnormalities, while the type and level of abnormalities change with species and tissues. The modifications shown in the aging heart are not very different from some observed in heart failure. In particular, both in aged and failing hearts we may see that the decrease in beta-adrenoceptor responsiveness is related to changes in G-protein function.

Changes in gene expression in the intact human heart. Downregulation of alpha-myosin heavy chain in hypertrophied, failing ventricular myocardium

Using quantitative RT-PCR in RNA from right ventricular (RV) endomyocardial biopsies from intact nonfailing hearts, and subjects with moderate RV failure from primary pulmonary hypertension (PPH) or idiopathic dilated cardiomyopathy (IDC), we measured expression of genes involved in regulation of contractility or hypertrophy. Gene expression was also assessed in LV (left ventricular) and RV free wall and RV endomyocardium of hearts from end-stage IDC subjects undergoing heart transplantation or from nonfailing donors. In intact failing hearts, downregulation of beta1-receptor mRNA and protein, upregulation of atrial natriuretic peptide mRNA expression, and increased myocyte diameter indicated similar degrees of failure and hypertrophy in the IDC and PPH phenotypes. The only molecular phenotypic difference between PPH and IDC RVs was upregulation of beta2-receptor gene expression in PPH but not IDC. The major new findings were that (a) both nonfailing intact and explanted human ventricular myocardium expressed substantial amounts of alpha-myosin heavy chain mRNA (alpha-MHC, 23-34% of total), and (b) in heart failure alpha-MHC was downregulated (by 67-84%) and beta-MHC gene expression was upregulated. We conclude that at the mRNA level nonfailing human heart expresses substantial alpha-MHC. In myocardial failure this alteration in gene expression of MHC isoforms, if translated into protein expression, would decrease myosin ATPase enzyme velocity and slow speed of contraction.

Change of complex and periodic heart rate dynamics with change of pulmonary artery pressure in infants with left-to-right shunt lesion

We studied how complex and periodic heart rate dynamic changed as pulmonary artery pressure elevated in 32 infants with ventricular septal defect. In addition, we tested the possibility that the dynamical change could be used to predict the pulmonary artery pressure noninvasively. During cardiac catheterization, mean pulmonary artery pressure was measured and, at the same time, 5-min segments of continuous electrocardiographic recording was stored into computer files. High- (>0.15 hertz) and low- (0.03-0.15 hertz) frequency components of heart rate variability were computed using spectral analysis. The overall complexity of heart rate time series was quantified by its approximate entropy. Pulmonary hypertensive infants (mean pulmonary artery pressure >20 mm Hg, n=17) have significantly lower low- (p<0.05) and high- (p<0.05) frequency power and lower approximate entropy (p<0.0001) than pulmonary normotensive infants (mean pulmonary artery pressure < or =20 mm Hg, n=15). The mean pulmonary artery pressure is significantly correlated not with the spectral powers but with the approximate entropy (r=-0.71, p=0.0001). It can be concluded that, in infants, pulmonary hypertension induced by left- to-right shunt lesions suppresses both periodic and complex heart rate oscillation and that mean pulmonary artery pressure can be predicted by calculating the approximate entropy of heart rate variability.

Cardiopulmonary effects of enoximone or dobutamine and nitroglycerin on mitral valve regurgitation and pulmonary venous hypertension

OBJECTIVE

To compare the cardiovascular and pulmonary effects of the phosphodiesterase III inhibitor enoximone (EN) or a combination of dobutamine (DOB) and nitroglycerin (NTG) before and after mitral valve repair or replacement.

DESIGN

Prospective, randomized, controlled clinical study.

SETTING

University hospital.

PARTICIPANTS

Twenty patients with mitral regurgitation and pulmonary venous hypertension scheduled for elective mitral valve surgery.

INTERVENTIONS

Patients fulfilling the inclusion criteria of the study were randomly allocated into a group treated with EN (group 1, n = 10) or DOB and NTG (group 2, n = 10). A cardiopulmonary status was obtained after induction of anesthesia and mechanical ventilation during stable hemodynamic conditions (control). Then the patients received either EN (bolus dose 1.0 mg/kg followed by a continuous infusion of 10 micrograms/kg/min) or DOB (8.0 micrograms/kg/min) and NTG (1.0 microgram/kg/min) according to the randomization. After a period of 20 minutes, all parameters were measured again. The study drugs were stopped, and cardiac surgery was performed. Infusions of EN (without additional loading dose) or DOB and NTG were started again in the above-described doses 10 minutes before separation from cardiopulmonary bypass (CPB). Respiratory and hemodynamic measurements were made 20 minutes after weaning from CPB and 60 minutes after admission of the patient to the intensive care unit.

MEASUREMENTS AND MAIN RESULTS

Both groups were comparable regarding preoperative and control data. Before mitral valve surgery, cardiac output (CO) and heart rate (HR) increased by 46% (p < 0.05) and 31% (p < 0.01) during infusion of EN with minor changes of mean systemic arterial pressure (PSA) and gas exchange. Mean pulmonary arterial pressure (PPA) decreased from 32 +/- 11 mmHg to 23 +/- 11 mmHg (p < 0.05). Similar alterations were observed in group 2 (delta CO + 26%, p < 0.05, delta HR + 39%, p < 0.01); however, PPA and calculated pulmonary vascular resistance remained unchanged. After separation from CPB, EN and DOB-NTG achieved comparable effects on CO, HR, and PSA, but PPA was significantly lower in group 1. In addition, venous admixture and alveolo-arterial oxygen tension gradient were lower in EN-treated patients.

CONCLUSION

Enoximone or DOB and NTG have comparable effects on CO, PSA, and HR in mitral regurgitation and pulmonary hypertension, but EN is more effective in reducing PPA without deterioration of gas exchange.

Modulation of pacemaker activity in sheep cardiac Purkinje fibers by stimulation of beta-adrenoceptor subtypes

The electrophysiological effects mediated by beta 1- and beta 2-adrenoceptors in spontaneously active sheep cardiac Purkinje fibers were investigated using the non-selective agonist (-)-isoproterenol (IPN) and the selective agonists (-)-noradrenaline (beta 1) and procaterol (beta 2) in the absence and presence of the selective antagonists bisoprolol (beta 1) and ICI 118,551 (beta 2). IPN (0.01 mumol/l) increased the spontaneous rate by 54% and the slope of diastolic depolarization by 68% of the respective control values. Further, IPN increased the action potential duration at -20 mV (APD -20 mV) from 96 to 154 ms, reduced the APD-70 mV by 17% and the duration of the diastole by 39% and slightly hyperpolarized the maximum diastolic potential. These effects were partially inhibited by ICI 118,551 (0.03 mumol/l), diminished by bisoprolol (0.1 mumol/l) and almost completely blocked by the combination of both antagonists. Concentration response curves of IPN were influenced by the selective antagonists as follows: ICI 118,551 (0.03 mumol/l) shifted the curves to the right by 0.2-0.4 log units and increased the slope factor. Bisoprolol (0.1 mumol/l) induced a greater shift to the right by 1.1-1.5 log units. Combination of bisoprolol with ICI 118,551 shifted the curves to the right by 1.5-1.7 log units. Noradrenaline (0.3 mumol/l) elicited similar actions as IPN. Bisoprolol (0.1 mumol/l) shifted the concentration response curves of noradrenaline to the right by 1.1-1.9 log units. Actions of procaterol (0.1 mumol/l) were weak, attained only 15-35% of the maximal effects of IPN and could be blocked by ICI 118,551 (0.03 mumol/l). These results show that the increase of pacemaker activity induced by catecholamines in sheep cardiac Purkinje fibers is predominantly mediated by stimulation of beta 1-receptors. However, contribution of beta 2-receptor mediated effects could be demonstrated.

Myocardial contractile reserve as prognostic determinant in patients with idiopathic dilated cardiomyopathy without overt heart failure

To assess the prognostic significance of myocardial contractile reserve in patients with idiopathic dilated cardiomyopathy (DCM) without overt heart failure (New York Heart Association functional class I or II), seventy-one patients underwent exercise radionuclide angiography in addition to clinical, radiographic, hemodynamic, and echocardiographic evaluations. Myocardial contractile reserve was assessed as left ventricular ejection fraction (LVEF) during peak exercise minus LVEF at rest (delta LVEF). During an average of 49 months, 18 patients died of the disease. Cox's proportional-hazards regression analysis showed that the delta LVEF was the most powerful and independent discriminator for survival (p = 0.0002). Ejection time (p = 0.0029) and cardiothoracic ratio (p = 0.017) were the second and third most predictive variables, respectively. Evaluation of the delta LVEF, which reflects residual myocardial contractile reserve, can provide important information about the prognosis of patients with DCM and mild symptoms.