Effects of chronic clonidine administration on sympathetic nerve traffic and baroreflex function in heart failure

Chronic Cannabigerol as an Effective Therapeutic for Cisplatin-Induced Neuropathic Pain

Cannabigerol (CBG), derived from the cannabis plant, acts as an acute analgesic in a model of cisplatin-induced peripheral neuropathy (CIPN) in mice. There are no curative, long-lasting treatments for CIPN available to humans. We investigated the ability of chronic CBG to alleviate mechanical hypersensitivity due to CIPN in mice by measuring responses to 7 and 14 days of daily CBG. We found that CBG treatment (i.p.) for 7 and 14 consecutive days significantly reduced mechanical hypersensitivity in male and female mice with CIPN and reduced pain sensitivity up to 60-70% of baseline levels (p < 0.001 for all), 24 h after the last injection. Additionally, we found that daily treatment with CBG did not evoke tolerance and did not incur significant weight change or adverse events. The efficacy of CBG was independent of the estrous cycle phase. Therefore, chronic CBG administration can provide at least 24 h of antinociceptive effect in mice. These findings support the study of CBG as a long-lasting neuropathic pain therapy, which acts without tolerance in both males and females.

CENTRAL AND PERIPHERAL SYMPATHETIC ACTIVATION IN HEART FAILURE

The sympathetic nervous system overdrive occurring in heart failure has been reported since more than half a century. Refinements in the methodological approaches to assess human sympathetic neural function have allowed during recent years to better define various aspects related to the neuroadrenergic alteration. These include 1) the different participation of the individual regional sympathetic cardiovascular districts at the process, 2) the role of the central nervous system in determining the neuroadrenergic overdrive, 3) the involvement of baroreflex, cardiopulmonary reflex and chemoreflex mechanisms in the phoenomenon, which is also closely linked to inflammation and the immune reaction, 4) the relationships with the severity of the disease, its ischaemic or idiopathic nature and the preserved or reduced left ventricular ejection fraction and 5) the adverse functional and structural impact of the sympathetic activation on cardiovascular organs, such as the brain, the heart and the kidneys. Information have been also gained on the active role exerted by the sympathetic activation on the disease outcome and its potential relevance as target of the therapeutic interventions based on non-pharmacological, pharmacological and invasive approaches, including the renal denervation, the splanchnic sympathetic nerve ablation and the carotid baroreflex stimulation. The still undefined aspects of the neurogenic alterations and the unmet goals of the therapeutic approach having the sympathetic activation as a target of the intervention will be finally mentioned.

Sympathetic neural overdrive in congestive heart failure and its correlates: systematic reviews and meta-analysis

BACKGROUND AND OBJECTIVES

Sympathetic neural activation occurs in congestive heart failure (CHF). However, the small sample size of the microneurographic studies, heterogeneity of the patients examined, presence of comorbidities as well as confounders (including treatment) represented major weaknesses not allowing to identify the major features of the phoenomenon, particularly in mild CHF. This meta-analysis evaluated 2530 heart failure (CHF) patients recruited in 106 microneurographic studies. It was based on muscle sympathetic nerve activity (MSNA) quantification in CHF of different clinical severity, but data from less widely addressed conditions, such as ischemic vs. idiopathic, were also considered.

METHODS

Assessment was extended to the relationships of MSNA with venous plasma norepinephrine, heart rate (HR) and echocardiographic parameters of cardiac morphology [left ventricular (LV) end-diastolic diameter] and function (LV ejection fraction) as well.

RESULTS

MSNA was significantly greater (1.9 times, P < 0.001) in CHF patients as compared with healthy controls, a progressive significant increase being observed from New York Heart Association classes I-IV in unadjusted and adjusted analyses. MSNA was significantly greater in both untreated and treated CHF (P < 0.001 for both), related to left ventricular (LV) end-diastolic diameter and to a lesser extent to LV ejection fraction (r = 0.24 and -0.05, P < 0.001 and <0.01, respectively), and closely associated with HR (r = 0.66, P < 0.001) and plasma norepinephrine (r = 0.68, P < 0.001).

CONCLUSION

CHF is characterized by sympathetic overactivity which mirrors the degree of LV dysfunction independently of the stage of CHF, its cause and presence of confounders or pharmacological treatment. plasma norepinephrine and HR represent potentially valuable surrogate markers of sympathetic activation in the clinical setting.

Chronic baroreflex activation effects on sympathetic nerve traffic, baroreflex function, and cardiac haemodynamics in heart failure: a proof-of-concept study

Aims

Heart failure (HF) pathophysiology is believed to be mediated by autonomic dysfunction, including chronic sympathoexcitation and diminished baroreflex sensitivity, which correlate with mortality risk. Baroreflex activation therapy (BAT) is a device-based treatment providing chronic baroreflex activation through electrical stimulation of the carotid sinus. BAT chronically reduces sympathetic activity in resistant hypertension. The purpose of this investigation is to determine BAT effects in clinical HF.

Methods and results

In a single-centre, open-label evaluation, patients with NYHA class III HF, EF <40%, optimized medical therapy, and ineligible for cardiac resynchronization received BAT for 6 months. Efficacy was assessed with serial measurement of muscle sympathetic nerve activity (MSNA) and clinical measures of quality of life and functional capacity. Eleven patients participated in the trial. MSNA was reduced over 6 months from 45.1 ± 7.7 to 31.3 ± 8.3 bursts/min and from 67.6 ± 12.7 to 45.1 ± 11.6 bursts/100 heartbeats, decreases of 31% and 33%, respectively (P < 0.01). Concomitant improvements occurred in baroreflex sensitivity, EF, NYHA class, quality of life and 6 min hall walk (6MHW) distance (P ≤ 0.05 each). On an observational basis, hospitalization and emergency department visits for worsening HF were markedly reduced. One complication, perioperative anaemia requiring transfusion, occurred during the study.

Conclusion

BAT was safe and provided chronic improvement in MSNA and clinical variables. Based on present understanding of HF pathophysiology, these results suggest that BAT may improve outcome in HF by modulating autonomic balance. Prospective, randomized trials to test the hypothesis are warranted.

Intact skeletal muscle mitochondrial enzyme activity but diminished exercise capacity in advanced heart failure patients on optimal medical and device therapy

BACKGROUND

A skeletal myopathy, perhaps attributable to neuro-endocrine excitation or disuse, has been described in heart failure (HF) patients, and is thought to contribute to their exercise limitation. Our purpose was to assess biochemical and morphometric characteristics of skeletal muscles of HF patients on optimal HF therapy. A secondary purpose was to explore the effects of clonidine, which interrupts the neuro-endocrine excitation, on these same muscle characteristics.

METHODS AND RESULTS

Eleven HF patients (50.8 ± 3.4 years, peak VO2 11.6 ± 2.5 ml/kg/min) underwent two vastus lateralis biopsies (pre/post clonidine). Baseline values were compared to biopsies in 11 age-matched, healthy controls. Scatter plots of individual values for each mitochondrial enzyme revealed almost complete overlap between HF and control groups; mean values, although tending to be greater in controls versus HF patients, were not significantly different. The proportion of type 1 fibers was diminished in 10 of 11 patients. There was no difference in any of the variables after 3 months clonidine versus placebo.

CONCLUSION

In HF patients treated with optimal medical and device therapy, characteristic abnormalities of mitochondrial enzyme activity are not found, but muscle fiber type shifts are present. The remaining severe impairment in exercise capacity cannot be attributed to mitochondrial abnormalities.

Effects of moxonidine on sympathetic nerve activity in patients with end-stage renal disease

OBJECTIVE

End-stage renal disease (ESRD) is characterized by markedly increased sympathetic outflow that contributes to increased cardiovascular mortality in these patients. The central sympatholytic drug moxonidine (MOX) has been shown to reduce muscle sympathetic nerve activity (MSNA) in initial stages of chronic kidney disease; however, the effects in ESRD are not known. The aim of this study was to test the hypothesis that low-dose MOX causes sustained decreases in sympathetic outflow in ESRD patients.

DESIGN AND METHODS

Twenty-three ESRD patients (mean age 46.4 +/- 16 years, 14 men, seven women, no diabetic patients) were randomized to a daily treatment of 0.3 mg MOX or placebo (PLA) in addition to pre-existing antihypertensive therapy. At baseline and after 1 and 6 months of treatment, heart rate (HR, ECG), blood pressure (mean arterial pressure, automatic sphygmanometer), calf blood flow (CBF, venous occlusion plethysmography), muscle sympathetic nerve activity (MSNA) (microneurography at the peroneal nerve) were measured. Data are mean +/- SEM.

RESULTS

MOX acutely decreased MSNA within 2 h after oral intake (from 45 +/- 3.7 to 35 +/- 3.9 bursts/min, P < 0.05). This decrease was sustained over 6 months (MSNA 45 +/- 3.7, 35 +/- 4.6, 33 +/- 4.5 bursts/min at 0, 1 and 6 months, P < 0.05). PLA had no effect. Neither MOX nor PLA resulted in any significant acute or long-term changes in HR, MAP or CBF.

CONCLUSIONS

In ESRD patients, low-dose MOX produced sustained and substantial reductions in sympathetic outflow without hemodynamically compromising them. We suggest that the inhibition of central sympathetic outflow may improve cardiovascular prognosis in ESRD.

The effects of clonidine on arterial baroreflex sensitivity and cardiopulmonary baroreflex control of sympathetic nerve activity in patients with left ventricular dysfunction

BACKGROUND

  Clonidine is a potent sympatholytic drug with central neural effects. The aim of this study was to evaluate the effects of clonidine on arterial baroreflex sensitivity (BRS) and cardiopulmonary (CP) baroreflex control of muscle sympathetic nerve activity (MSNA) in patients with left ventricular (LV) dysfunction.

METHOD

  Twenty patients were randomly assigned to either clonidine or placebo groups (10 in each group). BRS (by phenylephrine method) and CP baroreflex (by lower body negative pressure) effects on sympathetic nerve activity (circulating norepinephrine and MSNA recordings) were measured before and after a 4-week treatment period.

RESULTS

  Clonidine lowered blood pressure and heart rate. Clonidine was accompanied not only by a decrease in plasma noradrenaline (from 444±196 to 260±144 pg ml(-1) ) but also by a reduction in directly measured MSNA (from 47±16 to 36±16 bursts min(-1) ). BRS increased significantly from 3·01±1·19 to 6·86±2·84 ms mmHg(-1) after clonidine. When expressed as per cent change in MSNA during CP baroreceptor stimulation, CP baroreflex control of MSNA was significantly increased from 9·26±8·93% to 28·83±11·96% after clonidine. However, there were no significant changes in the measured variables in the control group.

CONCLUSION

  Clonidine enhanced BRS and CP baroreflex control of MSNA while reducing baseline sympathetic activity in patients with LV dysfunction.

Is kidney ischemia the central mechanism in parallel activation of the renin and sympathetic system?

In chronic kidney disease simultaneous activation of the renin-angiotensin and sympathetic systems occurs. Kidney ischemia seems to play a key role in the pathogenesis. This review firstly summarizes experimental and clinical evidence in chronic kidney disease supporting this idea and addresses the possibility that this mechanism is also relevant in some other disease conditions.

Central sympathetic overactivity: maladies and mechanisms

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

Long-term consequences of drugs on the paediatric cardiovascular system

Many pharmacological and toxicological actions of drugs in children cannot be fully predicted from adult clinical experience or from standard non-clinical toxicology studies. Numerous drugs have direct or indirect pharmacological effects on the heart and are prescribed for children of all ages. Toxicity or secondary effects may be immediate or delayed for years after drug exposure has ceased. Originally, the aim of this review was to compile information on the effect of specific drugs on the post-natal development of the cardiovascular system and to examine long-term follow-up of the use of cardio-active drugs in children. The limited database of published information caused the original question to evolve into an examination of the medical literature for three areas of information: (i) whether vulnerable developmental windows have been identified that reflect the substantial functional development that the cardiovascular system undergoes after birth; (ii) what is known about pharmacological perturbation of development; and (iii) what the likelihood is of drug exposure during childhood. We examined different scenarios for exposure including random, isolated exposure, conditions historically associated with adults, primary or secondary cardiac disease, psychiatric and neurological conditions, asthma, cancer and HIV. Except for random, isolated drug exposures, each category of possible exposure contained numerous drugs known to have either primary or secondary effects on the cardiovascular system or to influence factors associated with atherosclerosis. It is likely that a significant number of children will be prescribed drugs having either direct or indirect effects upon the immature cardiovascular system. A confounding factor is the simultaneous use of over-the-counter medications and herbal or nutraceutical preparations that a patient, parent or guardian does not mention to a prescribing physician. Metabolism is also important in assessing drug effects in children. Differences in body water : body fat ratio, age-related gastrointestinal absorption, distribution, excretion, renal function and drug metabolizing capabilities make it possible for children to have a different metabolite profile for a drug compared with adults. There is little examination of drug effects on the interdependent processes of cardiac maturation and less examination of metabolite effects. It is difficult to identify delayed toxicities in children as these adverse events may take years to manifest with many patients lost to follow-up. Clearly this is an area of study where intermediate endpoints and surrogate markers would be of great benefit. Pharmacogenomics may be useful in providing markers of increased risk or susceptibility. A perspective must be kept in balancing the possibility of a problem with the very real benefits that many children experience from the use of these pharmaceuticals.

Clonidine Lowers Blood Pressure by Reducing Vascular Resistance and Cardiac Output in Young, Healthy Males

PURPOSE

Clonidine is a classical sympatholytic drug that is widely used for the treatment of hypertension. Experimental and clinical studies suggest that Clonidine may activate baroreflex. The aim of this study was to determine the hemodynamic response to Clonidine under physiological conditions and to test the hypothesis that Clonidine would reduce cardiac output and blood pressure resulting in an increase in total peripheral resistance.

METHODS

Clonidine's hemodynamic effect was evaluated in 28 young, healthy subjects after a single i.v. dose of 1 microg x kg(- 1). Impedance cardiography, systolic time intervals and pulse wave analysis were used to characterize myocardial and vascular function.

RESULTS

Clonidine lowered blood pressure, heart rate, left ventricular ejection time, and pulse wave velocity and increased pre-ejection period. Stroke volume and cardiac output decreased gradually over the investigation time of 240 min. Central systolic blood pressure (SBP) was lowered to a larger extent than peripheral SBP. Total peripheral resistance was characterized by an immediate fall of short duration followed by a continuous rise above baseline after 120 min. Placebo did not have any significant effect on hemodynamic parameters.

CONCLUSIONS

Clonidine's blood pressure lowering effect is mediated by both an immediate decrease in vascular resistance and a prolonged decrease in cardiac output, and Clonidine lowers central SBP more than peripheral SBP.

The I1-imidazoline agonist moxonidine decreases sympathetic tone under physical and mental stress

AIMS

Moxonidine is an I1-imidazoline receptor agonist that reduces blood pressure by inhibition of central sympathetic activity. The effects of the drug under physical and mental stress have not been studied in detail.

METHODS

We investigated the effects of 0.4 mg moxonidine orally on sympathetic activity, blood pressure and heart rate in a double-blind, placebo-controlled crossover study in 12 healthy volunteers. The subjects underwent physical exercise test using bicycle ergometry and a mental stress test using an adaptive reaction test device. Potential association of parameters with the GNB3 C825T polymorphism was also assessed.

RESULTS

Under resting conditions, moxonidine decreased plasma noradrenaline (NA: -66.1 +/- 12 pg ml(-1); P < 0.01 vs placebo) and adrenaline (A: -18.8 +/- 6 pg ml(-1); P < 0.05 vs placebo). Physical exercise evoked a significant increase in plasma NA and A (NA: 760 +/- 98 pg ml(-1); A: 97 +/- 9 pg ml(-1); P < 0.001 vs baseline), which was significantly reduced after pretreatment with moxonidine (NA: 627 +/- 68 pg ml(-1); P < 0.05 vs placebo; A: 42.8 +/- 4 pg ml(-1); P < 0.01 vs placebo). Maximal physical exercise capacity was not limited by moxonidine (NS). During the mental stress test, increases in NA (placebo: 146 +/- 24 pg ml(-1), moxonidine: 84 +/- 26 pg ml(-1); P < 0.01 vs placebo) and A (placebo: 22.8 +/- 9 pg ml(-1), moxonidine: 8.0 +/- 8 pg ml(-1); P < 0.01 vs placebo) were significantly reduced after pretreatment with moxonidine. Increases in blood pressure during mental stress were significantly lower after pretreatment with moxonidine (P < 0.05 vs placebo). There was no association of the response to moxonidine with GNB3 genotypes (NS).

CONCLUSIONS

Moxonidine decreases total sympathetic tone under basal conditions as well as during physical exercise and mental stress without limiting absolute exercise capacity. Thus, moxonidine appears suitable for the treatment of patients with high SNS activity and hypertension induced by physical or mental stress. As the drug does not reduce exercise capacity, it may be considered as an alternative to beta-adrenoceptor blockers in selected patients.

Effect of Clonidine on Cardiac Norepinephrine Spillover in Isolated Rat Heart

The purpose of this study is to determine the effect of clonidine on cardiac norepinephrine spillover utilizing an isolated rat heart preparation with attached cardiac sympathetic nerves. Following a 20-minute stabilization period, the sympathetic ganglion for each heart preparation was electrically stimulated with 10V and 2 Hz for 30 seconds (S1: 60 pulses). Heart rate, left ventricular developed pressure, and coronary perfusion pressure was allowed to return to baseline and the perfusate was randomly switched to Krebs buffer containing one of two treatments: placebo or clonidine (1 microM). After 10 minutes of treatment, the sympathetic ganglion was again electrically stimulated with 10V and 2 Hz for 30 seconds (S2: 60 pulses). The perfusate exiting the heart before, during, and after each electrical stimulation was collected for the determination of cardiac norepinephrine spillover. Clonidine administration significantly reduced cardiac norepinephrine spillover by approximately 50% (P < 0.05) and was associated with a 36% reduction in heart rate (P < 0.05). These findings provide evidence that clonidine can directly suppress NE spillover from cardiac sympathetic nerve terminals. Thus, suppression of cardiac NE by clonidine may be due to stimulation of presynaptic alpha2-adrenergic receptors or imidazoline subtype I receptors located on cardiac sympathetic nerve terminals. Results from our study demonstrate a reduction in cardiac NE spillover by clonidine and provide additional evidence that it can directly suppress peripheral sympathetic activity in that our results were obtained utilizing an isolated perfused heart preparation with attached cardiac sympathetic nerves devoid of any CNS input.

Presynaptic modulation of evoked NE release contributes to sympathetic activation after pressure overload

Activation of the sympathetic nervous system is well documented in heart failure. Our previous studies demonstrated an increase in evoked norepinephrine (NE) release from left ventricle (LV) slices at 10 days of pressure overload. The purpose of this study was to test the hypothesis that presynaptic modulation of NE release contributes to sympathetic activation after pressure overload. We examined the functional status of the presynaptic α2- and β2-receptors and ANG II subtype 1 (AT1) receptors in LV slices from 10-day aortic constricted (AC) and sham-operated (SO) rats. Evoked 3H overflow from LV slices preloaded with [3H]NE was increased in AC rats. The α2-agonist UK-14,304 decreased evoked 3H overflow with no differences between groups. The β2-agonist salbutamol increased evoked 3H overflow with greater sensitivity in slices from AC rats. The β-antagonist propranolol decreased evoked 3H overflow from LV slices of AC rats but not controls. ANG II increased evoked 3H overflow with greater sensitivity in slices from AC rats. These data support the hypothesis that aberrant presynaptic modulation of catecholamine release contributes to sympathetic activation after pressure overload.