Sympathetic responses to atrial natriuretic peptide in patients with congestive heart failure

Acute effects of angiotensin-converting enzyme inhibition versus angiotensin II receptor blockade on cardiac sympathetic activity in patients with heart failure

The beneficial effects of angiotensin-converting enzyme (ACE) inhibitors and angiotensin II (ANG II) receptor antagonists in patients with heart failure secondary to reduced ejection fraction (HFrEF) are felt to result from prevention of the adverse effects of ANG II on systemic afterload and renal homeostasis. However, ANG II can activate the sympathetic nervous system, and part of the beneficial effects of ACE inhibitors and ANG II antagonists may result from their ability to inhibit such activation. We examined the acute effects of the ACE inhibitor captopril (25 mg, n = 9) and the ANG II receptor antagonist losartan (50 mg, n = 10) on hemodynamics as well as total body and cardiac norepinephrine spillover in patients with chronic HFrEF. Hemodynamic and neurochemical measurements were made at baseline and at 1, 2, and 4 h after oral dosing. Administration of both drugs caused significant reductions in systemic arterial, cardiac filling, and pulmonary artery pressures (P < 0.05 vs. baseline). There was no significant difference in the magnitude of those hemodynamic effects. Plasma concentrations of ANG II were significantly decreased by captopril and increased by losartan (P < 0.05 vs. baseline for both). Total body sympathetic activity increased in response to both captopril and losartan (P < 0.05 vs. baseline for both); however, there was no change in cardiac sympathetic activity in response to either drug. The results of the present study do not support the hypothesis that the acute inhibition of the renin-angiotensin system has sympathoinhibitory effects in patients with chronic HFrEF.

Exercise training attenuates the pressor response evoked by peripheral chemoreflex in rats with heart failure

The effects of exercise training (ExT) on the pressor response elicited by potassium cyanide (KCN) in the rat model of ischemia-induced heart failure (HF) are unknown. We evaluated the effects of ExT on chemoreflex sensitivity and its interaction with baroreflex in rats with HF. Wistar rats were divided into four groups: trained HF (Tr-HF), sedentary HF (Sed-HF), trained sham (Tr-Sham), and sedentary sham (Sed-Sham). Trained animals underwent to a treadmill running protocol for 8 weeks (60 m/day, 5 days/week, 16 m/min). After ExT, arterial pressure (AP), baroreflex sensitivity (BRS), peripheral chemoreflex (KCN: 100 μg/kg body mass), and cardiac function were evaluated. The results demonstrate that ExT induces an improvement in BRS and attenuates the pressor response to KCN relative to the Sed-HF group (P < 0.05). The improvement in BRS was associated with a reduction in the pressor response following ExT in HF rats (P < 0.05). Moreover, ExT induced a reduction in left ventricular end-diastolic pressure and pulmonary congestion compared with the Sed-HF group (P < 0.05). The pressor response to KCN in the hypotensive state is decreased in sedentary HF rats. These results suggest that ExT improves cardiac function and BRS and attenuates the pressor response evoked by KCN in HF rats.

Low-dose B-type natriuretic peptide raises cardiac sympathetic nerve activity in sheep

The reported effects of atrial natriuretic peptide (ANP) on sympathetic nerve activity (SNA) are variable, dependent on concomitant hemodynamic actions, and likely to be regionally differentiated. There are few reports of the effect of B-type natriuretic peptide (BNP) on SNA and none have measured cardiac SNA (CSNA) by direct microneurography. We measured the effects of low-dose ANP and BNP (2.4 pmol·kg−1·min−1 infused for 120 min) on CSNA and hemodynamics in conscious sheep ( n = 8). While there was a trend for mean arterial pressure and cardiac output to fall with both ANP and BNP, changes were not significant compared with vehicle control. However, BNP did significantly reduce systolic arterial (97 ± 4.2 vs. 107 ± 6.8 mmHg during control; P = 0.043) and pulse pressures (0.047) and increase heart rate (110 ± 6.7 vs. 96 ± 7.3 beats/min; P = 0.044). Trends for these hemodynamic parameters to change with ANP did not achieve statistical significance. ANP also had no significant effect on any CSNA parameters measured. In contrast, BNP induced a rise in both CSNA burst frequency (∼20 bursts/min higher than control, P = 0.011) and burst area (∼40% higher than control, P = 0.013). BNP-induced rises in burst incidence (bursts/100 beats), and burst area per 100 beats, however, were not significant. In conclusion, BNP infused at low doses that only had subtle effects on hemodynamics increased CSNA burst frequency and burst are per minute. This increase in CSNA may in large part be secondary to an increase in heart rate as CSNA burst incidence and burst area per 100 beats were not significantly increased. This study provides no evidence for inhibition of CSNA by natriuretic peptides.

Β-adrenergic blockade combined with subcutaneous B-type natriuretic peptide: a promising approach to reduce ventricular arrhythmia in heart failure?

AIMS

Clinical studies failed to prove convincingly efficiency of intravenous infusion of neseritide during heart failure and evidence suggested a pro-adrenergic action of B-type natriuretic peptide (BNP). However, subcutaneous BNP therapy was recently proposed in heart failure, thus raising new perspectives over what was considered as a promising treatment. We tested the efficiency of a combination of oral β1-adrenergic receptor blocker metoprolol and subcutaneous BNP infusion in decompensated heart failure.

METHODS AND RESULTS

The effects of metoprolol or/and BNP were studied on cardiac remodelling, excitation-contraction coupling and arrhythmias in an experimental mouse model of ischaemic heart failure following postmyocardial infarction. We determined the cellular and molecular mechanisms involved in anti-remodelling and antiarrhythmic actions. As major findings, the combination was more effective than metoprolol alone in reversing cardiac remodelling and preventing ventricular arrhythmia. The association of the two molecules improved cardiac function, reduced hypertrophy and fibrosis, and corrected the heart rate, sympatho-vagal balance (low frequencies/high frequencies) and ECG parameters (P to R wave interval (PR), QRS duration, QTc intervals). It also improved altered Ca(2+) cycling by normalising Ca(2+)-handling protein levels (S100A1, SERCA2a, RyR2), and prevented pro-arrhythmogenic Ca(2+) waves derived from abnormal Ca(2+) sparks in ventricular cardiomyocytes. Altogether these effects accounted for decreased occurrence of ventricular arrhythmias.

CONCLUSIONS

Association of subcutaneous BNP and oral metoprolol appeared to be more effective than metoprolol alone. Breaking the deleterious loop linking BNP and sympathetic overdrive in heart failure could unmask the efficiency of BNP against deleterious damages in heart failure and bring a new potential approach against lethal arrhythmia during heart failure.

The role of atrial natriuretic peptide in modulating cardiac electrophysiology

Since the discovery of atrial natriuretic peptide (ANP) in 1981, significant progress has been made in understanding the mechanism of its release and its role in salt and water balance in the body. It has also become clear that ANP plays a key role in cardiac electrophysiology, modulating the autonomic nervous system and regulating the function of cardiac ion channels. The clinical importance of this role was established when mutations in NPPA, the gene encoding ANP, were identified as a cause of familial atrial fibrillation. This review examines our current understanding of the electrophysiological effects of ANP, and their physiological relationship to clinical studies linking ANP and atrial fibrillation.

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.

Effect of nesiritide (human b-type natriuretic peptide) and dobutamine on heart rate variability in decompensated heart failure

BACKGROUND

Previous studies have suggested that natriuretic peptides may have direct sympathoinhibitory effects. Nesiritide (recombinant human B-type natriuretic peptide) has been recently approved for treatment of decompensated congestive heart failure (CHF). We sought to assess the effects of nesiritide compared with dobutamine on time-domain indices of heart rate variability (HRV) in patients with decompensated CHF.

METHODS

The study population consisted of 185 patients, who were randomized to intravenous nesiritide at a low (0.015 microg/kg/min, n = 56) or high (0.03 microg/kg/min, n = 58) dose, or to dobutamine (> or = 5 microg/kg/min, n = 58). Time-domain HRV indices were obtained from 24-hour Holter recordings immediately before and during study drug therapy.

RESULTS

Dobutamine therapy resulted in a decrease in standard deviation of the R-R intervals over a 24-hour period (SDNN), standard deviation of all 5-minute mean R-R intervals (SDANN), and the percentage of R-R intervals with >50 ms variation (pNN50) (all P < .05). Low-dose nesiritide induced an increase in SDNN (P < .05), and high-dose nesiritide resulted in a nonsignificant decrease in all measures of HRV. A significant interaction was noted between baseline HRV and the effect of vasoactive therapy on HRV (P = .028). Therefore, the effect of nesiritide and dobutamine was analyzed in relation to baseline HRV. In the dobutamine group, patients with moderately depressed HRV at baseline displayed a reduction in SDNN (P = .01), SDANN (P = .01), pNN50 (P = .04), and the square root of mean squared differences of successive R-R intervals (RMSSD) (P = .05), whereas no significant changes occurred in patients with severely depressed HRV. In the low-dose nesiritide group, patients with severely depressed HRV displayed an increase in SDNN (P = .001), SDANN (P = .02), and RMSSD (P = .01), with no significant changes in patients with moderately depressed HRV. HRV response to high-dose nesiritide was similar to that of dobutamine.

CONCLUSIONS

Low-dose nesiritide therapy in patients with decompensated CHF improves indices of overall HRV and parasympathetic modulation, particularly if HRV is severely depressed at baseline. Dobutamine and possibly high-dose nesiritide can potentially lead to further deterioration of autonomic dysregulation.

High plasma levels of N-terminal pro-atrial natriuretic peptide associated with low anxiety in severe heart failure

OBJECTIVE

Plasma levels of natriuretic peptides are elevated in congestive heart failure (CHF). These peptides show anxiolytic properties in studies of rodents and patients with panic disorder, but their possible effect on anxiety has never been studied in cardiac patients. We therefore assessed associations of the Atrial Natriuretic Pro-Peptide (pro-ANP) with anxiety in patients with CHF and controls.

METHOD

This was a cross-sectional study of 119 patients (46 with CHF, 76 controls with cardiovascular risk factors) in a tertiary care center. The study included assessment of CHF severity, ejection fraction, pro-ANP (microtiter assay), and psychosocial status (self-rating questionnaires for anxiety, depression, vital exhaustion, and quality of life).

RESULTS

The diagnosis and severity of CHF was significantly related to pro-ANP levels, bad physical quality of life, vital exhaustion, and depression. However, there was no significant effect of disease severity on anxiety. In CHF patients, pro-ANP was negatively correlated with anxiety (rho = -0.30, p =.041). In the whole group, anxiety was independently predicted by vital exhaustion, depression, and younger age (overall adjusted R2 = 0.48). Pro-ANP plasma levels showed an additional, inverse association with anxiety (beta = -0.17, p =.013, adjusted R2 = 0.50). Predicted mean anxiety scores derived from this model showed a good fit with anxiety scores observed in subgroups defined by CHF severity.

CONCLUSION

Pro-ANP plasma levels are independently and inversely related to anxiety. Even in severe CHF with severely compromised quality of life, anxiety tends to decrease with high pro-ANP levels. This might be part of a negative feedback loop limiting psychological distress and its adverse autonomic consequences in severe heart failure.

Hormonal, renal, hemodynamic responses to acute neutral endopeptidase inhibition in heart transplant patients

We investigated the hemodynamic, renal, and hormonal responses to neutral endopeptidase (NEP) inhibition during a 6-h, double-blind, randomized, placebo-controlled study in seven chronic, stable heart transplant patients. Baseline characteristics were similar during both experiments, and no significant changes were observed after placebo. NEP inhibition increased circulating endothelin-1 (from 2.01 +/- 0.1 to 2.90 +/- 0.2 pmol/l; P < 0.01), atrial natriuretic peptide (ANP; from 21.5 +/- 2.7 to 29.6 +/- 3.7 pmol/l; P < 0.01), and the ANP second messenger cGMP. Noteworthy, systemic blood pressure did not increase. Renal plasma flow and glomerular filtration rate remained unmodified after NEP inhibition. Filtration fraction (33 +/- 13%), diuresis (196 +/- 62%), and natriuresis (315 +/- 105%) increased significantly in relation to ANP and cGMP. A strong inverse relationship was observed between excreted cGMP and sodium reabsorption (r = -0.71, P < 0.0001). Thus, despite significantly increasing endothelin-1, NEP inhibition did not adversely influence systemic or renal hemodynamics in transplant patients. ANP, possibly through a tubular action, enhances the natriuresis observed after NEP inhibition.

Vasopeptidase inhibitors: a new therapeutic concept in cardiovascular disease?

The cardiovascular system is regulated by hemodynamic and neurohumoral mechanisms. These regulatory systems play a key role in modulating cardiac function, vascular tone, and structure. Although neurohumoral systems are essential in vascular homeostasis, they become maladaptive in disease states such as hypertension, coronary disease, and heart failure. The clinical success of ACE inhibitors has led to efforts to block other humoral systems. Neutral endopeptidase (NEP) is an endothelial cell surface zinc metallopeptidase with similar structure and catalytic site. NEP is the major enzymatic pathway for degradation of natriuretic peptides, a secondary enzymatic pathway for degradation of kinins, and adrenomedullin. The natriuretic peptides can be viewed as endogenous inhibitors of the renin angiotensin system. Inhibition of NEP increases levels of atrial natriuretic peptide (ANP), brain natriuretic peptide (BNP) of myocardial cell origin, and C-type natriuretic peptide (CNP) of endothelial cell origin as well as bradykinin and adrenomedullin. By simultaneously inhibiting the renin-angiotensin-aldosterone system and potentiating the natriuretic peptide and kinin systems, vasopeptidase inhibitors reduce vasoconstriction, enhance vasodilation, improve sodium/water balance, and, in turn, decrease peripheral vascular resistance and blood pressure and improve local blood flow. Within the blood vessel wall, this leads to a reduction of vasoconstrictor and proliferative mediators such as angiotensin II and increased local levels of bradykinin (and, in turn, nitric oxide) and natriuretic peptides. Preliminary clinical experiences with vasopeptidase inhibitors are encouraging. Thus, the combined inhibition of ACE and neutral endopeptidase is a new and promising approach to treat patients with hypertension, atherosclerosis, or heart failure.

Histamine release induced by dendroaspis natriuretic peptide from rat mast cells

Dendroaspis natriuretic peptide (DNP), recently isolated from the venom of the green Mamba snake Dendroaspis angusticeps, is a 38 amino acid peptide containing a 17 amino acid disulfide ring structure similar to that of the natriuretic peptide family. The natriuretic peptide family is known to induce histamine release from human and rat mast cells, but there are no published data concerning the effects of DNP on histamine release from mast cells. The purpose of this study is to investigate whether DNP induces the histamine release from rat peritoneal mast cells (RMPCs) and to determine the mechanism of DNP-induced histamine release from RPMCs. After treatment of RPMC with DNP, mast cell degranulation was observed, and calcium uptake and histamine release were measured. DNP released the histamine, induced the mast cell degranulation, and increased the calcium uptake of RPMCs, in a dose-dependent manner. The results indicate that DNP can increase Ca-uptake and induce histamine release.

Effects of intravenous brain natriuretic peptide on regional sympathetic activity in patients with chronic heart failure as compared with healthy control subjects

OBJECTIVES

We sought to assess the effects of brain natriuretic peptide (BNP) on systemic and regional sympathetic nervous activity (SNA) in both patients with congestive heart failure (CHF) and healthy control subjects.

BACKGROUND

Although the response of SNA to atrial natriuretic peptide (ANP) has been well documented, the response of SNA to BNP is largely unknown.

METHODS

We assessed cardiac and whole-body SNA using the norepinephrine (NE) tracer dilution method before and after infusion of two doses of BNP (3 and 15 ng/kg body weight per min) in 11 patients with stable CHF (ejection fraction 24 +/- 2%) and 12 age-matched healthy control subjects. In addition, renal SNA and hemodynamic variables were assessed at baseline and after the higher BNP dose.

RESULTS

Low dose BNP did not change blood pressure or whole-body NE spillover, but reduced cardiac NE spillover in both groups by 32 +/- 13 pmol/min (p < 0.05). In both groups, high dose BNP reduced pulmonary capillary pressure by 5 +/- 1 mm Hg (p < 0.001) and mean arterial pressure by 6 +/- 3 mm Hg (p < 0.05), without a concomitant increase in whole-body NE spillover; however, cardiac NE spillover returned to baseline levels. Renal NE spillover remained virtually unchanged in healthy control subjects (501 +/- 120 to 564 +/- 115 pmol/min), but was reduced in patients with CHF (976 +/- 133 to 656 +/- 127 pmol/min, p < 0.01).

CONCLUSIONS

Our results demonstrate a sympathoinhibitory effect of BNP. Cardiac sympathetic inhibition was observed at BNP concentrations within the physiologic range, whereas high dose BNP, when arterial and filling pressures fell and reflex sympathetic stimulation was expected, systemic and cardiac SNA equated to baseline values. There was inhibition of renal SNA in patients with CHF, but not in healthy control subjects. Whether this effect is specific to BNP or related to reduced filling pressure remains to be determined.

Atrial natriuretic peptide augments the variability of sympathetic nerve activity in human heart failure

OBJECTIVES

Activation of the sympathetic nervous system, decreased heart rate variability (HRV), and loss of modulation of muscle sympathetic nerve activity (MSNA) within the low frequency (LF, 0.05-0.15 Hz) range are three adverse features of advanced congestive heart failure (CHF). In healthy men, atrial natriuretic peptide (ANP) infusion attenuates reflex increases in MSNA and reduces LF components of HRV spectral power. Sympathoinhibitory actions have also been documented in CHF, but effects on the variability of MSNA and HRV have not been described.

DESIGN AND METHODS

Heart rate and MSNA were recorded in 10 men (aged 39 +/- 3 years, mean +/- SE) with dilated cardiomyopathy (mean EF 20 +/- 4%) treated with angiotensin converting enzyme (ACE) inhibitors. Subjects received i.v. ANP (50 microg bolus then 50 ng/kg/min) and nitroglycerin (NTG, 8 mg/min) as a hemodynamic control. Signals at baseline, and 13-20 min into each infusion were submitted to spectral analysis.

RESULTS

ANP had no effect on HRV, but increased MSNA LF (from 7.9 +/- 1.5 to 12.1 +/- 2.6 U2; P< 0.02) and total spectral power (from 47.9 +/- 5.4 to 61.9 +/- 6.8 U2; P < 0.05). NTG had no effect on the variability of MSNA or HRV.

CONCLUSIONS

In CHF patients receiving ACE inhibitors, ANP (i) does not suppress HRV and (ii) enhances the modulation of MSNA, particularly within the LF range. This latter action is not observed with NTG. These findings suggest beneficial actions of exogenous ANP on neurogenic circulatory control.