Interaction between cardiac sympathetic drive and heart rate in heart failure: modulation by adrenergic receptor genotype

Sympatho-adrenergic mechanisms in heart failure: new insights into pathophysiology

The sympathetic nervous system is activated in the setting of heart failure (HF) to compensate for hemodynamic instability. However, acute sympathetic surge or sustained high neuronal firing rates activates β-adrenergic receptor (βAR) signaling contributing to myocardial remodeling, dysfunction and electrical instability. Thus, sympatho-βAR activation is regarded as a hallmark of HF and forms pathophysiological basis for β-blocking therapy. Building upon earlier research findings, studies conducted in the recent decades have significantly advanced our understanding on the sympatho-adrenergic mechanism in HF, which forms the focus of this article. This review notes recent research progress regarding the roles of cardiac β2AR or α1AR in the failing heart, significance of β1AR-autoantibodies, and βAR signaling through G-protein independent signaling pathways. Sympatho-βAR regulation of immune cells or fibroblasts is specifically discussed. On the neuronal aspects, knowledge is assembled on the remodeling of sympathetic nerves of the failing heart, regulation by presynaptic α2AR of NE release, and findings on device-based neuromodulation of the sympathetic nervous system. The review ends with highlighting areas where significant knowledge gaps exist but hold promise for new breakthroughs.

Clinical Relevance of the Sympathetic-Vascular Interactions in Health and Disease

The sympathetic nervous system is known to play a pivotal role in the short- and long-term regulation of different cardiovascular functions. In recent decades, increasing evidence has demonstrated that sympathetic neural influences are involved not only in the vasomotor modulation of small resistance arteries but also in the control of large arteries. Sympathetic activity and vascular function, which are key factors in the pathophysiology and prognosis of cardiovascular disease, are linked by a close relationship. Evidence from experimental studies indicates that the sympathetic nervous system is critically influenced, at the central and also at the peripheral level, by the most relevant factors regulating vascular function, namely nitric oxide, reactive oxygen species and endothelin. Additionally, there is evidence of a reciprocal influence between endothelial function and sympathetic mechanisms. This paper will provide an overview of the relationships between endothelial function and the sympathetic nervous system characterizing physiological states. It will also briefly mention the alterations described in cardiovascular disease, with particular emphasis on essential hypertension and congestive heart failure, i.e., the two pathological states in which endothelial dysfunction and neuroadrenergic activation appear to be relevant factors for determining cardiovascular prognosis.

The Baker Biobank: Understanding Cardiovascular Outcomes

BACKGROUND

Cardiovascular diseases (CVDs) and diabetes are two of the most important public health problems. Outcomes for patients with these disorders vary considerably, likely due to the added influence of a range of interacting clinical, metabolic, environmental, lifestyle, genetic and psychosocial risk factors associated with these diseases. The Baker Biobank study was designed to characterise these factors to inform better risk prediction, earlier diagnosis and better treatment of CVDs and diabetes.

METHODS

This paper describes the detailed methods for the establishment of the Baker Biobank. The study collected extensive phenotypic detail about the participants recruited from Victoria, Australia. Data and samples were collected at the Departments of Cardiology and Respiratory Medicine at the Alfred Hospital and Healthy Hearts Program at the Baker Institute.

RESULTS

A total of 6,530 adults with age 18-69 years were recruited into the Biobank. The majority of these participants (63%) were male. The mean (standard deviation [SD]) age of the Biobank Cohort at the time of data collection was 57(15) years. The study collected data on socio-demographic characteristics, behavioural and lifestyle factors, anthropometric measurements, medical and medication history, and blood levels of various biomarkers. The study also collected and stored Guthrie cards, serum, plasma, buffy coat, whole blood collected in Tempus tubes (for RNA extraction). For some samples extracted DNA and RNA is stored. The Biobank data is also linked to echocardiogram, hospital admission, pathology and mortality datasets. The Baker Biobank data and samples are available for health researchers with approval of Biobank Steering Group and Human Research Ethics Committee.

CONCLUSION

The Baker Biobank provides valuable data and samples into the study of the interplay among cardiovascular diseases risk factors and their impact on morbidity and mortality in Australia.

Prenatal Testosterone Exposure Decreases Aldosterone Production but Maintains Normal Plasma Volume and Increases Blood Pressure in Adult Female Rats

Plasma testosterone levels are elevated in pregnant women with preeclampsia and polycystic ovaries; their offspring are at increased risk for hypertension during adult life. We tested the hypothesis that prenatal testosterone exposure induces dysregulation of the renin-angiotensin-aldosterone system, which is known to play an important role in water and electrolyte balance and blood pressure regulation. Female rats (6 mo old) prenatally exposed to testosterone were examined for adrenal expression of steroidogenic genes, telemetric blood pressure, blood volume and Na⁺ and K⁺ levels, plasma aldosterone, angiotensin II and vasopressin levels, and vascular responses to angiotensin II and arg⁸-vasopressin. The levels of Cyp11b2 (aldosterone synthase), but not the other adrenal steroidogenic genes, were decreased in testosterone females. Accordingly, plasma aldosterone levels were lower in testosterone females. Plasma volume and serum and urine Na⁺ and K⁺ levels were not significantly different between control and testosterone females; however, prenatal testosterone exposure significantly increased plasma vasopressin and angiotensin II levels and arterial pressure in adult females. In testosterone females, mesenteric artery contractile responses to angiotensin II were significantly greater, while contractile responses to vasopressin were unaffected. Angiotensin II type-1 receptor expression was increased, while angiotensin II type-2 receptor was decreased in testosterone arteries. These results suggest that prenatal testosterone exposure downregulates adrenal Cyp11b2 expression, leading to decreased plasma aldosterone levels. Elevated angiotensin II and vasopressin levels along with enhanced vascular responsiveness to angiotensin II may serve as an underlying mechanism to maintain plasma volume and Na⁺ and K⁺ levels and mediate hypertension in adult testosterone females.

Adrenergic receptor genotype influences heart failure severity and β-blocker response in children with dilated cardiomyopathy

BACKGROUND

Adrenergic receptor (ADR) genotypes are associated with heart failure (HF) and β-blocker response in adults. We assessed the influence of ADR genotypes in children with dilated cardiomyopathy (DCM).

METHODS

Ninety-one children with advanced DCM and 44 with stable DCM were genotyped for three ADR genotypes associated with HF risk in adults: α2cdel322-325, β1Arg389, and β2Arg16. Data were analyzed by genotype and β-blocker use. Mean age at enrollment was 8.5 y.

RESULTS

One-year event-free survival was 51% in advanced and 80% in stable DCM. High-risk genotypes were associated with higher left ventricular (LV) filling pressures, higher systemic and pulmonary vascular resistance, greater decline in LV ejection fraction (P < 0.05), and a higher frequency of mechanical circulatory support while awaiting transplant (P = 0.05). While β-blockers did not reduce HF severity in the overall cohort, in the subset with multiple high-risk genotypes, those receiving β-blockers showed better preservation of cardiac function and hemodynamics compared with those not receiving β-blockers (interaction P < 0.05).

CONCLUSION

Our study identifies genetic risk markers that may help in the identification of patients at risk for developing decompensated HF and who may benefit from early institution of β-blocker therapy before progression to decompensated HF.

Increase in paced heart rate reduces muscle sympathetic nerve activity in heart failure patients treated with cardiac resynchronization therapy

AIMS

To test the hypothesis that acute increased biventricularly (BiV) paced heart rate (pHR) results in decreased muscle sympathetic nerve activity (MSNA), and that dyssynchronous pacing (AAI) attenuates this effect, in heart failure patients receiving cardiac resynchronization therapy (CRT).

METHODS AND RESULTS

Fourteen CRT patients (NYHA II-III, 12 males, mean EF 28 ± 14%) were recruited. Three different pHRs (50-90 b.p.m.) were randomly programmed in BiV- and AAI-pacing modes. Muscle sympathetic nerve activity (total sympathetic nerve activity/min (units) and number of bursts/100 RR) were recorded from the peroneal nerve using a microelectrode. In addition, cardiac output (CO) and mean blood pressure (mBP) were measured. With BiV pacing, the total MSNA/min was lower at 70 b.p.m. (-7 ± 21%, P = 0.18) and 90 b.p.m. (-29 ± 18%, P = 0.01) compared with at 50 b.p.m. (280 ± 180 U). Similarly, bursts/100RR decreased with increased BiV pHR. Cardiac output (3.7 L/min at 50 b.p.m., +12 ± 12% at 70 b.p.m., and +18 ± 19% at 90 b.p.m.) and mBP (78 ± 11 mmHg at 50 b.p.m., +6 ± 6% at 70 b.p.m. and +11 ± 8% at 90 b.p.m.) increased significantly at elevated pHRs in BiV-pacing mode. The effect on MSNA, CO, and mBP was less pronounced in AAImode but we found no significant differences between the pacing modes.

CONCLUSION

Increased pHR acutely reduces MSNA and improves haemodynamics in HF patients treated with CRT with no evident differences between BiV- and AAI-pacing modes. Further studies are warranted to guide the programming of basic pHR in CRT patients.

Effects of continuous intermedin infusion on blood pressure and hemodynamic function in spontaneously hypertensive rats

OBJECTIVE

To examine the effects of exogenously administered intermedin (IMD, adrenomedullin-2) on arterial blood pressure, cardiac function and the cardiovascular IMD receptor system in spontaneously hypertensive rats (SHRs) as well as to investigate the associated mechanisms.

METHODS

Thirteen week-old male rats were divided in Wistar Kyoto (WKY) group (n = 12), SHR group (n = 12), IMD group (SHRs infused with IMD 1-47 500 ng/kg per hour, n = 12), and ADM group (SHRs infused with adrenomedullin 500 ng/kg per hour, n = 12).

RESULTS

A two-week continuous administration of low dose IMD 1-47 via mini-osmotic pumps markedly reduced blood pressure, the maximal rates of increase and decrease of left-ventricle pressure development (LV ± dp/dt(max)), left ventricular systolic pressure and heart rate in SHRs. Furthermore, IMD also inhibited protein over-expression of cardiovascular IMD receptors, myocardial Receptor Activity-Modifying Proteins (RAMP1 and RAMP2), aortic RAMP1, RAMP2, RAMP3, and calcitonin receptor-like receptor (CRLR); suppressed up-regulation of aortic RAMP1, RAMP2, RAMP3 and CRLR gene expression; and markedly elevated the mRNA abundance of myocardial atrial natriuretic peptide (ANP) and myocardial brain natriuretic peptide (BNP). Additionally, IMD 1-47 administration in SHRs increased aortic cAMP concentration and reduced myocardial cAMP concentration.

CONCLUSION

These findings support the speculation that IMD, as a cardiovascular active peptide, is involved in blood pressure reduction and cardiac function amelioration during hypertension. The mechanism underlying this effect may involve IMD binding of a receptor complex formed by RAMPs and CRLR, and consequential regulation of cAMP levels and other cardiovascular active factors, such as ANP and BNP.

Abnormal baroreflex function is dissociated from central angiotensin II receptor expression in chronic heart failure

Neurohumoral disturbances characterize chronic heart failure (CHF) and are reflected, in part, as impairment of baroreflex sensitivity (BRS) and sympathetic function. However, the mechanisms that trigger these neurohumoral abnormalities in CHF are not clear. We hypothesized that the BRS is blunted early in CHF and that the humoral effects occur later and contribute to progressive loss of cardiovascular control in CHF. We assessed the BRS (beats/min per mmHg) and recorded renal sympathetic nerve activity (RSNA) in four groups of conscious rabbits at varying time intervals: control, 1-week CHF, 2-week CHF, and 3-week CHF. Chronic heart failure was induced by ventricular pacing at 360 beats/min and was assessed by echocardiography. Arterial blood pressure and heart rate were recorded by an implanted telemetric device and RSNA through an implanted electrode. A significant fall in the ejection fraction, fractional shortening, and an increase in left ventricular end-systolic diameter and left ventricular end-diastolic diameter were observed in all CHF groups. The BRS was significantly reduced in all the CHF groups with no significant change in the basal RSNA (% of maximum) after 1 week of pacing; a small but insignificant rise in RSNA was seen at 2 weeks, and a significant rise in RSNA was observed at 3 weeks. Angiotensin II type 1 (AT-1) receptor protein (Western Blot) and mRNA (reverse transcriptase-polymerase chain reaction) expression in the rostral ventrolateral medulla exhibited a progressive increase with the duration of CHF, reaching significance after 3 weeks, the same time point in which RSNA was significantly elevated. These data are the first to examine early changes in central AT-1 receptors in CHF and suggest that the fall in BRS and hemodynamic changes occur early in the development of CHF followed by sympathoexcitation and overexpression of AT-1 receptors with the progression of CHF, causing further impairment of cardiovascular control.

The α(2C)-Del322-325 adrenoceptor polymorphism and the occurrence of left ventricular hypertrophy in hypertensives

OBJECTIVES

Sympathetic activation has a role in the development of left ventricular hypertrophy (LVH). The presynaptic α(2C)-adrenoceptor inhibits the release of norepinephrine from sympathetic nerve terminals in the heart. A deletion polymorphism in the α(2C)-adrenoceptor (α(2C)Del322-325) generates a hypofunctional α(2C)-adrenoceptor, which may result in chronic adrenergic signalling. This study aimed to investigate whether the α(2C)Del322-325 polymorphism was associated with an increased prevalence of LVH in patients with systemic hypertension.

METHODS

Left ventricular mass was measured in 205 patients with systemic hypertension and 60 normal volunteers using a 1.5-T Philips MRI system. Genotyping was performed using a restriction fragment length polymorphism assay.

RESULTS

No significant difference was observed between the distribution of the α(2C)Del322-325 genotypes in hypertensive patients with LVH compared with those without LVH. Adjusting for confounding variables the odds ratio (OR) of being ins/del for the α(2C)Del322-325 and having LVH was 0.49 (95% CI 0.14-1.69, p = 0.256).

CONCLUSIONS

These observations suggest that there is little evidence for an association between α(2C)Del322-325 polymorphism and an increased prevalence of LVH in patients with systemic hypertension.

Bucindolol: a pharmacogenomic perspective on its use in chronic heart failure

Bucindolol is a non-selective β-adrenergic receptor blocker with α-1 blocker properties and mild intrinsic sympatholytic activity. The Beta-Blocker Evaluation of Survival Trial (BEST), which is the largest clinical trial of bucindolol in patients with heart failure, was terminated prematurely and failed to show an overall mortality benefit. However, benefits on cardiac mortality and re-hospitalization rates were observed in the BEST trial. Bucindolol has not shown benefits in African Americans, those with significantly low ejection fraction and those in NYHA class IV heart failure. These observations could be due to the exaggerated sympatholytic response to bucindolol in these sub-groups that may be mediated by genetic polymorphisms or changes in gene regulation due to advanced heart failure. This paper provides a timely clinical update on the use of bucindolol in chronic heart failure.

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

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

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

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

Pharmacogenetic profiling in the treatment of heart disease

Pharmacogenetics is the study of gene-drug interactions. In the post-Human Genome era, and with the realization that personal genotypes differ by millions of bases (gene polymorphisms), the application of genetics to explain interindividual differences in clinical drug response seems to offer great promise. Here, recent basic and translational developments in pharmacogenetic profiling of beta-blocker response in heart failure are reviewed in the context of the possible consequences of such advances on drug development and clinical therapeutics.

Clinical and genetic modifiers of long-term survival in heart failure

OBJECTIVES

This study sought to identify genetic modifiers of beta-blocker response and long-term survival in heart failure (HF).

BACKGROUND

Differences in beta-blocker treatment effect between Caucasians and African Americans with HF have been reported.

METHODS

This was a prospective cohort study of 2,460 patients (711 African American, 1,749 Caucasian) enrolled between 1999 and 2007; 2,039 patients (81.7%) were treated with a beta-blocker. Each was genotyped for beta1-adrenergic receptor (ADRB1) Arg389>Gly and G-protein receptor kinase 5 (GRK5) Gln41>Leu polymorphisms, which are more prevalent among African Americans than Caucasians. The primary end point was survival time from HF onset.

RESULTS

There were 765 deaths during follow-up (median 46 months). beta-blocker treatment increased survival in Caucasians (log-rank p = 0.00038) but not African Americans (log-rank p = 0.327). Among patients not taking beta-blockers, ADRB1 Gly389 was associated with decreased survival in Caucasians (hazard ratio [HR]: 1.98, 95% confidence interval [CI]: 1.1 to 3.7, p = 0.03) whereas GRK5 Leu41 was associated with improved survival in African Americans (HR: 0.325, CI: 0.133 to 0.796, p = 0.01). African Americans with ADRB1 Gly389Gly GRK5 Gln41Gln derived a similar survival benefit from beta-blocker therapy (HR: 0.385, 95% CI: 0.182 to 0.813, p = 0.012) as Caucasians with the same genotype (HR: 0.529, 95% CI: 0.326 to 0.858, p = 0.0098).

CONCLUSIONS

These data show that differences caused by beta-adrenergic receptor signaling pathway gene polymorphisms, rather than race, are the major factors contributing to apparent differences in the beta-blocker treatment effect between Caucasians and African Americans; proper evaluation of treatment response should account for genetic variance.

Sympathetic nervous system activation in human heart failure: clinical implications of an updated model

Disturbances in cardiovascular neural regulation, influencing both disease course and survival, progress as heart failure worsens. Heart failure due to left ventricular systolic dysfunction has long been considered a state of generalized sympathetic activation, itself a reflex response to alterations in cardiac and peripheral hemodynamics that is initially appropriate, but ultimately pathological. Because arterial baroreceptor reflex vagal control of heart rate is impaired early in heart failure, a parallel reduction in its reflex buffering of sympathetic outflow has been assumed. However, it is now recognized that: 1) the time course and magnitude of sympathetic activation are target organ-specific, not generalized, and independent of ventricular systolic function; and 2) human heart failure is characterized by rapidly responsive arterial baroreflex regulation of muscle sympathetic nerve activity (MSNA), attenuated cardiopulmonary reflex modulation of MSNA, a cardiac sympathoexcitatory reflex related to increased cardiopulmonary filling pressure, and by individual variation in nonbaroreflex-mediated sympathoexcitatory mechanisms, including coexisting sleep apnea, myocardial ischemia, obesity, and reflexes from exercising muscle. Thus, sympathetic activation in the setting of impaired systolic function reflects the net balance and interaction between appropriate reflex compensatory responses to impaired systolic function and excitatory stimuli that elicit adrenergic responses in excess of homeostatic requirements. Recent observations have been incorporated into an updated model of cardiovascular neural regulation in chronic heart failure due to ventricular systolic dysfunction, with implications for the clinical evaluation of patients, application of current treatment, and development of new therapies.

cAMP signal transduction in the heart: understanding spatial control for the development of novel therapeutic strategies

3'-5'-Cyclic adenosine monophosphate (cAMP) is a pleiotropic intracellular second messenger generated in response to activation of G(s) protein-coupled receptors. In the heart, cAMP mediates the catecholaminergic control on heart rate and contractility but, at the same time, it is responsible for the functional response to a wide variety of other hormones and neurotransmitters, raising the question of how the myocyte can decode the cAMP signal and generate the appropriate functional output to each individual extracellular stimulus. A growing body of evidence points to the spatial organization of the components of the cAMP signalling pathway in distinct, spatially segregated signalling domains as the key feature underpinning specificity of response and data is emerging, indicating that alteration of spatial control of the cAMP signal cascade associates with heart pathology. Most of the details of the molecular organization and regulation of individual cAMP signalling compartments are still to be elucidated but future research should provide the knowledge necessary to develop and test new therapeutic strategies that, by acting on a limited subset of downstream targets, would improve efficacy and minimize off-target effects.

Upregulated expression of intermedin and its receptor in the myocardium and aorta in spontaneously hypertensive rats

Intermedin (IMD), also called adrenomedullin 2 (ADM2), is a 47-amino acid peptide belonging to the calcitonin/calcitonin gene-related peptide (CGRP) family. IMD has similar or more potent vasodilatory and hypotensive actions compared with adrenomedullin (ADM) and CGRP. This study was designed to explore the role of IMD and its receptor in the pathogenesis of spontaneous hypertension and cardiac hypertrophy. Radioimmunoassay was employed to determine plasma immunoreactive IMD concentration and tissue immunoreactive IMD levels in the myocardium and aorta as well as cAMP concentration in the cardiovascular tissues in 13-week-old Wistar Kyoto (WKY) rats and spontaneously hypertensive rats (SHRs). The mRNA expression of IMD, its receptor, calcitonin receptor-like receptor (CRLR) and receptor activity-modifying proteins (RAMP)) were determined by semi-quantitative RT-PCR. Protein levels of CRLR and RAMPs were assayed by Western blotting. Our results showed that immunoreactive IMD concentration was enhanced in the SHR myocardium, aortas and plasma. Both the mRNA and protein levels of IMD, as well as those of CRLR and RAMP 1-3 were upregulated in SHRs. IMD affected cAMP generation in the myocardium and aorta, which were not attenuated by prior addition of either CGRP(8-37) or ADM(22-52) alone. These results indicate that the elevation of IMD and its receptor in the cardiovascular tissue may play an important role in the pathogenesis of spontaneous hypertension.

Central Sympatholysis as a Novel Countermeasure for Cocaine-Induced Sympathetic Activation and Vasoconstriction in Humans

OBJECTIVES

The aim of this study was to determine whether cocaine's sympathomimetic actions can be reversed by a potent centrally acting alpha2 adrenergic receptor (AR) agonist (dexmedetomidine).

BACKGROUND

We recently showed that cocaine stimulates the human cardiovascular system primarily by acting in the brain to increase sympathetic nerve activity (SNA), the neural stimulus to norepinephrine release. Thus, SNA constitutes a putative new drug target to block cocaine's adverse cardiovascular effects at their origin.

METHODS

In 22 healthy cocaine-naïve humans, we measured skin SNA (microneurography) and skin blood flow (laser Doppler velocimetry) as well as heart rate and blood pressure before and after intranasal cocaine (2 mg/kg) alone and in combination with dexmedetomidine or saline.

RESULTS

During intranasal cocaine alone, SNA increased by 2-fold and skin vascular resistance increased from 13.2 +/- 2.3 to 20.1 +/- 2.2 resistance units while mean arterial pressure increased by 14 +/- 3 mm Hg and heart rate by 18 +/- 3 beats/min (p < 0.01). Dexmedetomidine abolished these increases, whereas intravenous saline was without effect. Dexmedetomidine was effective in blocking these sympathomimetic actions of cocaine even in all 7 subjects who were homozygous for the Del322-325 polymorphism in the alpha2C AR, a loss-of-function mutation that is highly enriched in blacks.

CONCLUSIONS

The data advance the novel hypothesis that central sympatholysis with dexmedetomidine constitutes a highly effective countermeasure for cocaine's sympathomimetic actions on the human cardiovascular system, even in individuals carrying the alpha2CDel322-325 polymorphism. (Study to Improve Scientific Understanding of the Cardiovascular Actions of Cocaine; http://clinicaltrials.gov/ct/show/NCT00338546?order=1; NCT00338546).

Hypertension caused by prenatal testosterone excess in female sheep

Polycystic ovary syndrome (PCOS), a leading cause of infertility, affects approximately 10% of women of reproductive age. The etiology and pathophysiology of PCOS are poorly understood. PCOS is multifaceted and includes reproductive abnormalities and components of the metabolic syndrome such as insulin resistance, obesity, dyslipidemia, and hypertension. Exposure to excess testosterone (T) during the prenatal period may predispose individuals to PCOS phenotype. The goal of this study was to determine whether hypertension and dyslipidemia occur in a well-characterized model of PCOS produced by prenatal treatment of sheep with T. Radiotelemetry was used to measure blood pressure over a 24-h period in conscious, undisturbed animals. To normalize circulating estradiol levels across treatment, control (n = 4) and prenatal T-treated (100 mg T propionate im twice weekly from days 30 to 90 of fetal life, n = 4) 2-yr-old females were ovariectomized, instrumented with a radiotelemetry transmitter, and clamped with early follicular phase levels of estrogen using an implant. Six days later, a 24-h recording period commenced. Prenatal T-treated sheep were hypertensive compared with control sheep, and heart rate tended to be higher. T-treated sheep had hyperglycemia, insulin resistance, hypernatremia, and hyperchloremia, and both total and LDL cholesterol tended to be higher. Plasma aldosterone and epinephrine were significantly lower in T-treated sheep, whereas norepinephrine was unchanged. This first-ever use of radiotelemetric blood pressure recordings in sheep demonstrates that mild hypertension, a risk factor reported in some women with PCOS, is also a feature of the sheep model of PCOS produced by prenatal T treatment.

Presynaptic α-2C Adrenoceptor-mediated Control of Noradrenaline Release in Humans: Genotype- or Age-Dependent?

In vitro alpha-2CDel322-325 adrenoceptor (AR) polymorphism exhibits reduced functional responsiveness. We studied whether this is true also in vivo in humans. We assessed in nine young wild-type (WT) alpha-2C AR subjects (aged 23 years), 10 elder WT alpha-2C AR subjects (aged 63 years), and nine alpha-2CDel AR subjects (aged 28 years) clonidine (1 microg/kg intravenous (i.v.) bolus)-evoked plasma noradrenaline (pNA), heart rate (HR), and blood pressure (BP) changes. Clonidine-evoked pNA decreases were comparable in young WT alpha-2C and in alpha-2CDel AR subjects, but significantly lower (P=0.033) in elder subjects. Similarly, clonidine-evoked HR decreases were significantly larger in young WT alpha-2C and in alpha-2CDel AR subjects than in elder subjects, whereas clonidine-evoked BP decreases were larger in elder subjects. In conclusion, alpha-2CDel AR appears to play only a minor role in presynaptic regulation of NA release and/or to be not hypofunctional in vivo in humans, but functional responsiveness of presynaptic alpha-2 AR declines with ageing.

Chronic low-dose angiotensin II infusion increases venomotor tone by neurogenic mechanisms

The purpose of this study was to identify changes in venomotor tone in the chronic low-dose angiotensin II (Ang II) model of hypertension and to establish the contribution of sympathetic nerve activation to these venomotor tone changes. Male Sprague-Dawley rats were acclimatized to a 0.4% or 2.0% NaCl diet for 7 days and then catheterized to allow chronic and repeated measures of arterial pressure, central venous pressure, and mean circulatory filling pressure (MCFP), an index of venous smooth muscle tone, in conscious undisturbed rats. After 4 days of recovery and a 3-day control period, an Ang II or physiological saline-filled osmotic minipump was implanted subcutaneously to deliver Ang II (150 ng/kg per minute) or vehicle control for 14 days. MCFP was measured in duplicate before and after acute ganglionic blockade with hexamethonium (30 mg/kg i.v.) on control day 2 and Ang II infusion on days 1, 3, 7, and 14. Blood volume was also measured on these days and was unchanged for the duration of the study in all of the groups. Arterial pressure was increased for the duration of Ang II infusion in rats on both 0.4% and 2% NaCl diets, but the increase was significantly greater in the 2% NaCl group and completely abolished by hexamethonium. MCFP was significantly increased for the entire Ang II infusion period only in rats fed 2% NaCl, and this increase was completely abolished by hexamethonium. We conclude that the combination of chronic low-dose Ang II infusion and high dietary salt intake engages the sympathetic nervous system to increase venomotor tone.

Pharmacogenetics of the human beta-adrenergic receptors

The beta-adrenergic receptors (ADRBs) are cell surface receptors that play central roles in the sympathetic nervous system. Pharmacological targeting of two of these receptors, ADRB1 and ADRB2, represents a widely used therapeutic approach for common and important diseases including asthma, hypertension and heart failure. Genetic variation in both ADRB1 and ADRB2 has been linked to both in vitro and clinical disease phenotypes. More recently, interest has shifted to studies that explore potential interaction between variation in ADRBs and medications directed at these important receptors. This paper reviews the current state of knowledge and understanding of ADRB genetic variation and explores the likely direction of future studies in this area.

Role of β1- and α2c-adrenergic receptor polymorphisms and their combination in heart failure: A case-control study

BACKGROUND

Adrenergic activation has a central role in the development of HF. The function of the beta1- and the alpha2C-adrenergic receptors is influenced by gene polymorphisms: the beta1Arg389 variant is associated with increased beta1-receptor sensitivity and the alpha2C-receptor Del322-325 variant is associated with decreased alpha2C receptor function and increased norepinephrine release. We hypothesised that these polymorphisms could influence the prevalence of heart failure.

METHODS

The role of the beta1- and alpha2C-adrenergic receptor gene polymorphisms as risk factors for heart failure (HF) was assessed in an Italian white Caucasian population using a case-control study design. Genomic DNA was analysed by polymerase chain reaction-restriction fragment length polymorphism (PCR-RLFP).

RESULTS

We compared 260 Caucasian patients with HF and 230 normal subjects. The beta1Arg389 allele was frequent both in the patients with HF (69%) and in the normal subjects (73%). The alpha2CDel322-325 variant was rare in both groups (9% and 8%, respectively). Patients homozygotes for either the beta1Arg389 or the alpha(2C)Del322-325 alleles had no increased risk of HF (odds ratio [OR], 0.8; 95%CI: 0.5-1.2 and OR, 0.8; 95% CI: 0.4-1.8, respectively). Patients homozygotes for both the beta1Arg389 and the alpha(2C)Del322-325 alleles had no increased risk of HF as well (OR: 0.6; 95% CI: 0.2-2.1).

CONCLUSIONS

Beta1-ARs and alpha2C-ARs polymorphisms are not associated with an increased risk of HF in an Italian white Caucasian population.

New Directions in the Medical Management of Heart Failure

Like the introduction of digitalis more than 200 years ago, novel medical therapies today have the potential to significantly alter the course of heart failure (HF) and save thousands of lives. This review outlines new directions in HF medical management beyond the foundation of neurohormonal blockade. Furthermore, the role of novel risk factors in HF such as chronic renal insufficiency, anemia, and sleep apnea present tantalizing therapeutic targets to extend the morbidity and mortality benefits of current therapies. The course of time will tell which of these risk factors and therapies can hold promise, given the recent litany of negative trials in the HF arena. Advancements in molecular and genetic techniques have allowed us to begin to consider patient specific therapies and lay the groundwork for even further improvements in treatment of symptomatic HF. Finally, advances in telemedicine and device technology will allow the clinician to remotely monitor useful clinical parameters such as heart rate variability and pulmonary filling pressures to make more informed clinical decision-making and improve outcomes.

Mechanisms of disease: beta-adrenergic receptors--alterations in signal transduction and pharmacogenomics in heart failure

Beta-adrenergic signaling is an important regulator of myocardial function. During the progression of heart failure (HF), a reproducible series of biochemical events occurs that affects beta-adrenergic receptor (beta-AR) signaling and cardiac function. Furthermore, there are pathophysiologic alterations in the expression and regulation of proteins that are regulated by beta-ARs during HF. Analyses of these complex signaling pathways have led to a better understanding of HF mechanisms and the use of beta-adrenergic antagonists, which have notably altered HF-related morbidity and mortality. Despite therapeutic advances that have affected beta-AR signaling, HF remains a leading cause of hospitalization and a principal cause of death in industrialized nations. In this review, we summarize current insights into beta-adrenergic signal-transduction pathways, the best-described beta-AR polymorphisms, and therapies that target the beta-AR pathway in HF.

Blood pressure variation in healthy humans: a possible interaction with beta-2 adrenergic receptor genotype and renal epithelial sodium channels

Renal control of Na(+) regulation is a critical component to blood pressure regulation. It has recently been suggested that the beta-2 adrenergic receptor plays a role in blood pressure regulation possibly via renal epithelial sodium channels (ENaC). In the kidneys, gain of function mutations of the ENaC leads to increased salt-sensitivity and hypertension (Liddle's syndrome). In contrast, loss of function mutations of the ENaC leads to pseudohypoaldosteronism and is characterized by hypotension. Polymorphic variation of the beta-2 adrenergic receptor (beta2AR, the Arg16Gly polymorphism) leads to differences in physiologic function, in vivo. Specifically, subjects homozygous for Glycine at amino acid 16 have been shown to have enhanced forearm blood flow in response to isoproterenol and better airway function at baseline and during exercise when compared to subjects homozygous for Arginine at amino acid 16. We hypothesize, therefore, that subjects that are homozygous for Gly at amino acid 16 of the beta2AR have higher baseline blood pressure than Arg16 homozygotes due to beta2AR-mediated increases in ENaC activity in the kidney, caused, at least in part, by greater beta2AR density or enhanced beta2AR function of the Gly16 group.

Influence of heart rate, blood pressure, and beta-blocker dose on outcome and the differences in outcome between carvedilol and metoprolol tartrate in patients with chronic heart failure: results from the COMET trial

AIMS

We studied the influence of heart rate (HR), systolic blood pressure (SBP), and beta-blocker dose on outcome in the 2599 out of 3029 patients in Carvedilol Or Metoprolol European Trial (COMET) who were alive and on study drug at 4 months after randomization (time of first visit on maintenance therapy).

METHODS AND RESULTS

By multivariable analysis, baseline HR, baseline SBP, and their change after 4 months were not independently related to subsequent outcome. In a multivariable analysis including clinical variables, HR above and SBP below the median value achieved at 4 months predicted subsequent increased mortality [relative risk (RR) for HR>68 b.p.m. 1.333; 95% confidence intervals (CI) 1.152-1.542; P<0.0001 and RR for SBP>120 mmHg 0.78; 95% CI 0.671-0.907; P<0.0013]. Achieving target beta-blocker dose was associated with a better outcome (RR 0.779; 95% CI 0.662-0.916; P<0.0025). The superiority of carvedilol as compared to metoprolol tartrate was maintained in a multivariable model (RR 0.767; 95% CI 0.663-0.887; P=0.0004) and there was no interaction with HR, SBP, or beta-blocker dose.

CONCLUSION

Beta-blocker dose, HR, and SBP achieved during beta-blocker therapy have independent prognostic value in heart failure. None of these factors influenced the beneficial effects of carvedilol when compared with metoprolol tartrate at the pre-defined target doses used in COMET.

Arg16/Gly beta2-adrenergic receptor polymorphism alters the cardiac output response to isometric exercise

Normotensive adults homozygous for glycine (Gly) of the Arg16/Gly beta2-adrenergic-receptor polymorphism have 1) greater forearm beta2-receptor mediated vasodilation and 2) a higher heart rate (HR) response to isometric handgrip than arginine (Arg) homozygotes. To test the hypothesis that the higher HR response in Gly16 subjects serves to maintain the pressor response [increased cardiac output (CO)] in the setting of augmented peripheral vasodilation to endogenous catecholamines, we measured continuous HR (ECG), arterial pressure (Finapres), and CO (transthoracic echocardiography) during isometric, 40% submaximal handgrip to fatigue in healthy subjects homozygous for Gly (n = 30; mean age +/- SE: 30 +/- 1.2, 13 women) and Arg (n = 17, age 30 +/- 1.6, 11 women). Resting data were similar between groups. Handgrip produced similar increases in arterial pressure and venous norepinephrine and epinephrine concentrations; however, HR increased more in the Gly group (60.1 +/- 4.3% increase from baseline vs. 45.5 +/- 3.9%, P = 0.03), and this caused CO to be higher (Gly: 7.6 +/- 0.3 l/m vs. Arg: 6.5 +/- 0.3 l/m, P = 0.03), whereas the decrease in systemic vascular resistance in the Gly group did not reach significance (P = 0.09). We conclude that Gly16 homozygotes generate a higher CO to maintain the pressor response to handgrip. The influence of polymorphic variants in the beta2-adrenergic receptor gene on the cardiovascular response to sympathoexcitation may have important implications in the development of hypertension and heart failure.