Dual natriuretic peptide system in experimental heart failure

How arrhythmias weaken the ventricle: an often underestimated vicious cycle

Arrhythmia-induced cardiomyopathy (AIC) is classified as a form of dilated cardiomyopathy in which left ventricular systolic dysfunction (LVSD) is triggered by tachycardic or arrhythmic heart rates. On the one hand AIC can develop in patients without cardiac disease and on the other hand it can appear in patients with pre-existing LVSD, leading to a further reduction in left ventricular (LV) ejection fraction. A special aspect of AIC is the potential termination or partial reversibility of LVSD; thus, AIC is curatively treatable by the elimination of the underlying arrhythmia. Since arrhythmias are often seen merely as a consequence than as an underlying cause of LVSD, and due to the fact that the diagnosis of AIC can be made only after recovery of LV function, the prevalence of AIC is probably underestimated in clinical practice. Pathophysiologically, animal models have shown that continuous tachycardic pacing induces consecutive changes such as the occurrence of LVSD, increased filling pressures, LV dilatation, and decreased cardiac output. After termination of tachycardia, reversibility of the described pathologies can usually be observed. Studies in human ventricular myocardium have recently demonstrated that various cellular structural and functional mechanisms are activated even by normofrequent atrial fibrillation, which may help to explain the clinical AIC phenotype.

Emerging concepts in heart failure management and treatment: focus on tachycardia-induced cardiomyopathy

Tachycardia-induced cardiomyopathy is an entity characterized by reversible dysfunction of the left ventricle, which can be induced by different types of arrhythmia such as atrial fibrillation, atrial flutter, incessant supraventricular tachycardia and ventricular arrhythmia (more frequent causes). Correct identification of the causative arrhythmia and normalization of the heart rate (e.g through medical treatment, electrical cardioversion, ablation) can lead to recovery of left ventricular function. Tachycardia-induced cardiomyopathy should be suspected in patients with tachycardia and left ventricular dysfunction (heart failure setting), especially when there is no history of previous heart disease. Its usual phenotype is that of non-ischaemic/non-valvular dilated cardiomyopathy and it can occur in both children (main cause: permanent junctional reciprocating tachycardia) and adults (main cause: atrial fibrillation). With proper treatment, most cases recover within a few months, though there is a risk of relapse, especially when the causal arrhythmia reappears or its control is lost. This is a narrative review that comprehensively addresses the pathophysiology, clinical manifestations, and therapeutic management of tachycardia-induced cardiomyopathy. This article is part of the Emerging concepts in heart failure management and treatment Special Issue: https://www.drugsincontext.com/special_issues/emerging-concepts-in-heart-failure-management-and-treatment.

Mid-regional pro-adrenomedullin for diagnosing evolution after cardiac surgery in newborns: the PRONEW study

Newborns are the most vulnerable patients after cardiac surgery. Although mortality risk scores before surgery may help predict the risk of poor outcome, new tools are required, and biomarkers could add objective data to these tools. The aim of this study was to assess the ability of mid-regional pro-adrenomedullin (pro-ADM) and pro-atrial natriuretic peptide (pro-ANP) to predict poor outcome after cardiac surgery. This is a pilot diagnostic accuracy study that includes newborns and infants under 2 months admitted to an intensive care unit after cardiac surgery. Pro-ADM and pro-ANP were determined immediately upon admission. Poor outcome was defined as mortality, cardiac arrest, requiring extracorporeal support, requiring renal replacement therapy, or neurological injury. Forty-four patients were included. Twenty-six (59%) had a STAT category of ≥ 4. Ten patients (22.7%) presented a poor outcome, four of whom (9.1%) died. Pro-ADM was higher in patients with poor outcome (p = 0.024) and death (p = 0.012). Pro-ADM showed the best area under curve (AUC) for predicting poor outcome (0.735) and mortality alone (0.869). A pro-ADM of 2 nmol/L had a Sn of 75% and a Sp of 85% for predicting mortality. Pro-ADM > 2 nmol/L was independently associated with poor outcome (OR 5.8) and mortality (OR 14.1). Although higher pro-ANP values were associated with poor outcomes, no cut-off point were found. The combination of STAT ≥ 4 and the biomarkers did not enhance predictive power for poor outcome or mortality.Conclusion: Pro-ADM and pro-ANP determined immediately after surgery could be helpful for stratifying risk of poor outcome and mortality in newborns. What is Known: • Some congenital heart diseases must be corrected/palliated during the first days of life. A useful tool to predict the risk of severe complications has not been proposed. • Most unstable newborns would have higher values of biomarkers such as pro-ADM and pro-ANP related to shock and compensatory actions. What is New: • Pro-ADM and pro-ANP seem to be good biomarkers to predict poor outcome after cardiac surgery. A pro-ADM < 2 nmol/L would imply a low likelihood of a poor outcome. • Deepening the analysis of biomarkers can help in making decisions to prevent/treat complications.

Intraventricular flow patterns during right ventricular apical pacing

Objectives

To assess differences in blood flow momentum (BFM) and kinetic energy (KE) dissipation in a model of cardiac dyssynchrony induced by electrical right ventricular apical (RVA) stimulation compared with spontaneous sinus rhythm.

Methods

We cross-sectionally enrolled 12 consecutive patients (mean age 74±8 years, 60% male, mean left ventricular ejection fraction 58%±6 %), within 48 hours from pacemaker (PMK) implantation. Inclusion criteria were: age>18 years, no PMK-dependency, sinus rhythm with a spontaneous narrow QRS at the ECG, preserved ejection fraction (>50%) and a low percentage of PMK-stimulation (<20%). All the participants underwent a complete echocardiographic evaluation, including left ventricular strain analysis and particle image velocimetry.

Results

Compared with sinus rhythm, BFM shifted from 27±3.3 to 34±7.6° (p=0.016), while RVA-pacing was characterised by a 35% of increment in KE dissipation, during diastole (p=0.043) and 32% during systole (p=0.016). In the same conditions, left ventricle global longitudinal strain (LV GLS) significantly decreased from 17±3.3 to 11%±2.8% (p=0.004) during RVA-stimulation. At the multivariable analysis, BFM and diastolic KE dissipation were significantly associated with LV GLS deterioration (Beta Coeff.=0.54, 95% CI 0.07 to 1.00, p=0.034 and Beta Coeff.=0.29, 95% CI 0.02 to 0.57, p=0.049, respectively).

Conclusions

In RVA-stimulation, BFM impairment and KE dissipation were found to be significantly associated with LV GLS deterioration, when controlling for potential confounders. Such changes may favour the onset of cardiac remodelling and sustain heart failure.

Invasive therapies for patients with concomitant heart failure and atrial fibrillation

Atrial fibrillation (AF) and heart failure (HF) are two clinical entities that can present either separately or concurrently. One entity can lead to the other and vice versa as AF can not only be the underlying etiology of HF but also exacerbate HF due to other cardiac diseases. Besides prevention of cerebral and systemic embolism and elimination of AF-related symptoms, restoration of sinus rhythm for AF patients helps to avoid or reduce HF, irrespective of their underlying heart disease. Successful rates of medical therapy for AF are low in persistent AF, and much lower in long-standing AF, while invasive procedures for AF yield promising results. In this review, the authors evaluate the value of invasive therapies for HF patients complicated with non-valvular AF. We examine this clinical problem by interpreting the relationships between these two entities: the mechanism of tachycardia-induced cardiomyopathy (TIC), past opinions about rhythm control and rate control of AF, discrimination of HF-related AF and AF-induced HF, how to identify the AF patients that could benefit from invasive therapies, and how to select invasive therapies for different AF patients and peri-operative treatments.

Localization profiles of natriuretic peptides in hearts of pre-hibernating and hibernating Anatolian ground squirrels (Spermophilus xanthoprymnus)

The Anatolian ground squirrel (Spermophilus xanthoprymnus) is a typical example of true mammalian hibernators. In order to adapt to extreme external and internal environments during hibernation, they lower their body temperatures, heart rates and oxygen consumption; however, pathological events such as ischemia and ventricular fibrillation do not occur in their cardiovascular systems. During the hibernation, maintenance of cardiac function is very important for survival of ground squirrels. Natriuretic peptides (NPs) are key factors in the regulation of cardiovascular hemostasis. Since NPs' role on the protection of heart during hibernation are less clear, the aim of this study was to investigate dynamic changes in NPs content in the cardiac chambers and to reveal the possible role of NPs on establishing cardiac function in ground squirrel during hibernation using immunohistochemistry. The immunohistochemical results indicate that cardiac NP expressions in atrial and ventricular cardiomyocytes were different from each other and were sex-independent. ANP and BNP were expressed in a chamber-dependent manner in female and male squirrel hearts. Furthermore, cardiac NPs expression levels in hibernation period were lower than those at the pre-hibernation period. During prehibernation period, ANP, BNP and CNP were expressed in the white and beige adipocytes of epicardial adipose tissue (EAT); while during hibernation period, the brown adipocytes of EAT were positive for BNP and CNP. These data suggest that the hibernation-dependent reduction in levels of NPs, particularly ANP, in cardiac chambers and EAT may be associated with low heart rate and oxygen consumption during hibernation. However, further studies are needed to better delineate the roles of NPs during the hibernation.

What About Tachycardia-induced Cardiomyopathy?

Long-standing tachycardia is a well-recognised cause of heart failure and left ventricular dysfunction, and has led to the nomenclature, tachycardia-induced cardiomyopathy (TIC). TIC is generally a reversible cardiomyopathy if the causative tachycardia can be treated effectively, either with medications, surgery or catheter ablation. The diagnosis is usually made after demonstrating recovery of left ventricular function with normalisation of heart rate in the absence of other identifiable aetiologies. One hundred years after the first reported case of TIC, our understanding of the pathophysiology of TIC in humans remains limited despite extensive work in animal models of TIC. In this review we will discuss the proposed mechanisms of TIC, the causative tachyarrhythmias and their treatment, outcomes for patients diagnosed with TIC, and future directions for research and clinical care.

Arrhythmia-Induced Cardiomyopathies: Mechanisms, Recognition, and Management

Arrhythmia-induced cardiomyopathy (AIC) is a potentially reversible condition in which left ventricular dysfunction is induced or mediated by atrial or ventricular arrhythmias. Cellular and extracellular changes in response to the culprit arrhythmia have been identified, but specific pathophysiological mechanisms remain unclear. Early recognition of AIC and prompt treatment of the culprit arrhythmia using pharmacological or ablative techniques result in symptom resolution and recovery of ventricular function. Although cardiomyopathy in response to an arrhythmia may take months to years to develop, recurrent arrhythmia can result in rapid decline in ventricular function with development of heart failure, suggesting residual ultrastructural abnormalities. Reports of sudden death in patients with normalized left ventricular ejection fraction cast doubt on the complete reversibility of this condition. Several aspects of AIC, including specific pathophysiological mechanisms, predisposing factors, optimal therapeutic strategies to prevent ultrastructural changes, and long-term risk of sudden death remain unresolved and need further research.

Neurohormones and inflammatory mediators in patients with heart failure undergoing cardiac resynchronization therapy: time courses and prediction of response

Despite interest in neurohormonal activation as a determinant of prognosis in chronic heart failure (CHF) and as a target for pharmacological treatments, data are lacking on the time-related effects of electrical cardiac resynchronization therapy (CRT) on a broad spectrum of neurohormones and cytokines. The aim of this study was to assess time-courses and extents of changes within the neurohormonal profile of CHF patients treated with CRT. We performed a prospective follow-up study in 32 patients with NYHA class III-IV CHF to investigate the effects of CRT on a broad panel of neurohormones proposed for characterization of CHF patients. Levels of atrial and brain natriuretic peptides (ANP, BNP), epinephrine, norepinephrine, aldosterone, plasma renin activity, IL-6, TNF, soluble receptors sTNFR1 and 2, and chromogranin A were assessed before implantation and after 3 months of CRT; when feasible, measurements were also performed at 1 week, 1 month and 12 months (clinical evaluation, echocardiography and ECG were also performed at each time-point). The results showed that at 3 months improvement in NYHA class and echographically assessed left ventricular (LV) reverse structural remodeling were accompanied by significant reductions versus baseline in ANP and BNP, but not in other neurohormones. Moreover a baseline ANP concentration < or = 150 pg/ml was a good predictor of response to CRT in terms of NYHA class reduction and reverse LV remodeling. In conclusion 3 months of CRT significantly reduce natriuretic peptides concentrations, while values of other neurohormones and inflammatory cytokines are relatively unvaried. A baseline ANP concentration < or = 150 pg/ml might be a clinically useful predictor of medium-term response to CRT.

Induction of cardiac hypertrophy by a controlled reproducible sutureless aortocaval shunt in the mouse

Much of the understanding about the pathophysiological responses to chronic cardiac overload has been gained by the use of rat and dog models of aortocaval fistula (ACF). The use of a similar model in genetically manipulated mice may further elucidate the molecular mechanisms in these responses. The only reports about ACF in mice to date have applied a needle puncture to create the ACF, which may result in an uncontrolled and irreproducible size of the shunt, and require several weeks to induce the characteristic cardiac changes. In order to obtain a more consistent approach to characterize this mode of cardiac hyperfunction, we present a surgical murine model of ACF that results in rapid progression of the typical systemic and cardiac changes. A sutureless side-to-side infrarenal surgical anastomosis of 0.6-0.8 mm in diameter was created between the abdominal aorta and inferior vena cava in ICR (Institute of Cancer Research) mice. Six to 7 days later, significant cardiac hypertrophy developed. The heart/body weight ratio increased from 0.45 +/- 0.02% in control mice to 0.77 +/- 0.03% in mice with ACF (p < .003). The dry heart weight ratio increased from 0.099 +/- 0.0033% to 0.13 +/- 0.008% (p < .006). The ACF dramatically induced the atrial and ventricular expression of atrial natriuretic factor mRNA, and increased the total cardiac content of endothelin-1 (162.5 +/- 50.6 vs. 83.9 +/- 9.0 pg). Mean arterial pressure in anesthetized mice with ACF decreased from 69.8 +/- 4.9 to 54.8 +/- 5.5 mm Hg (p < .025). Urinary sodium excretion returned to preoperative levels several days following surgery. These results demonstrate that cardiac hypertrophy could be rapidly and reproducibly achieved in mice by the placement of a surgical ACF. This model, when applied in genetically manipulated mice, may be a valuable tool for functional genomic studies about the pathogenesis of cardiac hypertrophy and heart failure.

Assessment of plasma brain natriuretic peptide concentration in Boxers with arrhythmogenic right ventricular cardiomyopathy

OBJECTIVE

To determine whether Boxers with a clinical diagnosis of arrhythmogenic right ventricular cardiomyopathy (ARVC) have increased plasma concentrations of brain natriuretic peptide (BNP), compared with concentrations in clinically normal dogs.

ANIMALS

13 Boxers with ARVC, 9 clinically normal Boxers, 10 clinically normal non-Boxer dogs, and 5 hound dogs with systolic dysfunction.

PROCEDURE

All Boxers were evaluated via 24-hour ambulatory electrocardiography and echocardiography; the number of ventricular premature contractions (VPCs) per 24 hours was assessed. Hound dogs with cardiac pacing-induced systolic dysfunction (positive control dogs) and clinically normal non-Boxer dogs (negative control dogs) were evaluated echocardiographically. Three milliliters of blood was collected from each dog for measurement of plasma BNP concentration by use of a radioimmunoassay.

RESULTS

Mean +/- SD plasma BNP concentration for the ARVC-affected Boxers, clinically normal Boxers, negative control dogs, and positive control dogs was 11.0 +/- 4.6 pg/mL, 7.9 +/- 3.2 pg/mL, 11.5 +/- 4.9 pg/mL, and 100.8 +/- 56.8 pg/mL, respectively. Compared with findings in the positive control group, plasma BNP concentration in each of the other 3 groups was significantly different. There was no significant difference in BNP concentration between the 2 groups of Boxers. A significant correlation between plasma BNP concentration and number of VPCs per 24 hours in the ARVC-affected Boxers was not identified.

CONCLUSIONS AND CLINICAL RELEVANCE

A significant difference in BNP concentration between Boxers with ARVC and clinically normal Boxers was not identified. Results suggest that BNP concentration may not be an indicator of ARVC in Boxers.

Brain natriuretic peptide concentration in dogs with heart disease and congestive heart failure

Plasma brain natriuretic peptide concentration ([BNP]) is high in humans with cardiac disease and is further increased with congestive heart failure (CHF). The hypotheses of this study were that dogs with moderate to severe mitral regurgitation due to myxomatous mitral valve disease (MVD) would have increased plasma [BNP] compared to normal dogs, that plasma [BNP] would be higher in dogs with CHP, and that plasma [BNP] would predict premature death from cardiovascular disease. The study population consisted of 34 dogs: 9 normal dogs and 25 dogs with MVD. Patients were divided into 4 groups: group 1-10 dogs with moderate to severe MVD and no radiographic evidence of CHF; group II--6 dogs with severe MVD and mild CHF; group III--7 dogs with severe MVD and moderate CHF; and group IV--2 dogs with severe MVD and severe CHF. Diagnostic tests included thoracic radiographs, an echocardiogram, a serum chemistry profile, and the measurement of plasma [BNP] by a canine-specific radioimmunoassay. There was a significant positive correlation between the plasma [BNP] and heart disease/failure groups (P = .0036). Plasma [BNP] increased with progressively increasing severity of MVD and CHE Group I dogs had higher plasma [BNP] than did control dogs (P < .0001), and plasma [BNP] was higher in dogs with CHF (groups II-IV versus group I; P = .012). Plasma [BNP] was also weakly positively correlated with left atrial size (r = 0.43, P = .04). For every 10-pg/mL increase in plasma [BNP], the mortality rate over 4 months' time increased approximately 44%.

Natriuretic peptide system in fetal heart and circulation

Atrial natriuretic peptide, brain natriuretic peptide and C-type natriuretic peptide belong to a family of hormones that have diuretic, natriuretic and vasodepressor activity and play a part in pressure and volume homeostasis in adults. As little is known about the natriuretic peptides during cardiac maturation, this review summarizes current knowledge about the early expression of components of the natriuretic peptide system in the heart during embryonic and fetal development. The data indicate a functional importance of the fetal natriuretic peptide system, especially under pathophysiological conditions. Thus, in the fetus, the system fulfils important beneficial compensatory roles in cardiovascular disease, rather than in day-to-day pressure and volume homeostasis. In comparison with data on the relevance of natriuretic peptides in adults, those summarized here indicate a functional maturation of the natriuretic peptide system during ontogeny in mammals.

Evaluation of atrial natriuretic peptide and brain natriuretic peptide in atrial granules of rats with experimental congestive heart failure

The natriuretic peptides are believed to play an important role in the pathophysiology of congestive heart failure (CHF). We utilized a quantitative cytomorphometric method, using double immunocytochemical labeling, to assess the characteristics of atrial natriuretic peptide (ANP) and brain natriuretic peptide (BNP) in atrial granules in an experimental model of rats with CHF induced by aortocaval fistula. Rats with CHF were further divided into decompensated (sodium-retaining) and compensated (sodium-excreting) subgroups and compared with a sham-operated control group. A total of 947 granules in myocytes in the right atrium were analyzed, using electron microscopy and a computerized analysis system. Decompensated CHF was associated with alterations in the modal nature of granule content packing, as depicted by moving bin analysis, and in the granule density of both peptides. In control rats, the mean density of gold particles attached to both peptides was 347.0 +/- 103.6 and 306.3 +/- 89.9 gold particles/microm2 for ANP and BNP, respectively. Similar mean density was revealed in the compensated rats (390.6 +/- 81.0 and 351.3 +/- 62.1 gold particles/microm2 for ANP and BNP, respectively). However, in rats with decompensated CHF, a significant decrease in the mean density of gold particles was observed (141.6 +/- 67.3 and 158.0 +/- 71.2 gold particles/microm2 for ANP and BNP, respectively; p<0.05 compared with compensated rats, for both ANP and BNP). The ANP:BNP ratio did not differ between groups. These findings indicate that the development of decompensated CHF in rats with aortocaval fistula is associated with a marked decrease in the density of both peptides in atrial granules, as well as in alterations in the quantal nature of granule formation. The data further suggest that both peptides, ANP and BNP, may be regulated in the atrium by a common secretory mechanism in CHF.

Nesiritide (hBNP): a new class of therapeutic peptide for the treatment of decompensated congestive heart failure

Natriuretic peptides are a family of endogenous peptide hormones with vasodilating, natriuretic, diuretic, and lusitropic properties. Administration of pharmacologic doses of exogenous natriuretic peptides may provide therapeutic benefit in patients with chronic heart failure. In controlled clinical trials, short-term administration of nesiritide (human brain natriuretic peptide) to patients with heart failure is associated with improved resting hemodynamics, modest increases in sodium excretion, evidence of suppression of neurohormonal activation, and improvements in symptoms of heart failure. Additional trials to determine the clinical efficacy and safety of nesiritide are warranted. (c)2001 by CHF, Inc.

Cardiac natriuretic peptides and continuously monitored atrial pressures during chronic rapid pacing in pigs

Changes in atrial natriuretic peptide (ANP), N-terminal proatrial natriuretic peptide and brain natriuretic peptide (BNP) were evaluated in relation to continuously monitored atrial pressures in a pacing model of heart failure. Pigs were subjected to rapid atrial pacing (225 beats min-1) for 3 weeks with adjustments of pacing frequencies if the pigs showed overt signs of cardiac decompensation. Atrial pressures were monitored by a telemetry system with the animals unsedated and freely moving. Left atrial pressure responded stronger and more rapidly to the initiation of pacing and to alterations in the rate of pacing than right atrial pressure. Plasma natriuretic peptide levels were measured by radioimmunoassay and all increased during pacing with BNP exhibiting the largest relative increase (2.9-fold increase relative to sham pigs). Multiple regression analysis with dummy variables was used to evaluate the relative changes in natriuretic peptides and atrial pressures and the strongest correlation was found between BNP and left atrial pressure with R 2=0.81. Termination of pacing resulted in rapid normalization of ANP values in spite of persistent elevations in atrial pressures. This may reflect an increased metabolism or an attenuated secretory response of ANP to atrial stretch with established heart failure. In conclusion, 3 weeks of rapid pacing induced significant increases in atrial pressures and natriuretic peptide levels. All the natriuretic peptides correlated with atrial pressures with BNP appearing as a more sensitive marker of cardiac filling pressures than ANP and N-terminal proatrial natriuretic peptide.

Plasma atrial and brain natriuretic peptide levels in dogs with congestive heart failure

Plasma concentrations of atrial natriuretic peptide (ANP) and brain natriuretic peptide (BNP) were measured in 6 dogs with experimental mitral regurgitation (MR) and 19 canine patients with asymptomatic and symptomatic congestive heart failure (CHF). In dogs with experimental MR, ANP and BNP concentrations were significantly correlated with pulmonary capillary wedge pressure (PCWP) (ANP; r=0.852, P=0.0004, BNP; r=0.832, P=0.0008). ANP level was shown to have a predominant effect on PCWP in comparison with BNP using multiple regression analysis. In canine patients with asymptomatic and symptomatic CHF, ANP and BNP concentrations were significantly different among the heart failure classes according to the New York Heart Association functional classification (ANP; P=0.0165, BNP; P=0.0005). In addition, ANP and BNP levels in dogs with decompensated heart failure (n=10) significantly increased in comparison with those in dogs with compensated heart failure (n=9). There was however no correlation between ANP and BNP levels in each heart failure class. In conclusion, plasma ANP and BNP levels may become predictors of PCWP and the severity of heart failure in dogs with MR, although further investigations on ANP and BNP levels in more clinical cases are required.

Bioactivity of natriuretic peptide coinfusions; no evidence for unique effects of BNP in conscious sheep

Few studies have addressed the possibility that brain natriuretic peptide (BNP) possesses a profile of bioactivity that is distinct from that of atrial natriuretic peptide (ANP). Accordingly, we assessed the biologic actions of BNP in the setting of maximal or near-maximal ANP-induced biologic activity. Background ANP infusions (7.5 pmol/kg/min) administered on all study days, increased plasma ANP (approximately 120 pM) and cyclic guanosine monophosphate (GMP) levels (approximately 40 nM), and induced significant decreases in arterial pressure and cardiac output associated with increased heart rate, hematocrit, diuresis, and natriuresis. Increasing the dose twofold after 1 h (experiment 1, n = 5) showed no enhancement of these actions despite a further twofold increase in plasma ANP and cyclic GMP (both p values <0.001). Addition of low-dose BNP (2 pmol/kg/min) after 1 h background infusion (experiment 2, n = 8), increased plasma BNP levels (30 pM, p < 0.001) but caused no significant effects on the hemodynamic, renal, or hormonal indices measured. In conclusion, in the setting of maximal hemodynamic, renal, and endocrine responses to high-dose background infusions of ANP, coinfusion of BNP exhibits no enhancement of, or additional, biologic activity. This study provides no evidence for unique short-term biologic actions of ANP and BNP.

Increased cardiac and pulmonary endothelin-1 mRNA expression in canine pacing-induced heart failure

The canine model of pacing-induced heart failure (HF) simulates human dilated cardiomyopathy and is characterized by severe hemodynamic perturbations. We have previously demonstrated increased plasma endothelin-1 (ET-1) and left ventricular (LV) tissue peptide levels in this model. However, the gene expression of ET-1 has not been studied. Accordingly, we compared preproET-1 mRNA in the lungs and LV in control normal dogs, dogs with severe HF after 3 weeks of rapid pacing (pHF), and pHF dogs chronically treated with an ETA antagonist, LU135252 (pHF-LU). PreproET-1 mRNA expression was determined by ribonuclease protection assay and quantified by densitometry. In paced dogs, mean pulmonary artery pressure (PA) and LV end-diastolic pressure (LVEDP) increased markedly from 16 +/- 4 and 8 +/- 3 mm Hg, respectively, at baseline to 40 +/- 11 and 34 +/- 7 mm Hg, respectively, at 3 weeks (both p < 0.001). Treatment with LU135252 attenuated the increase in PA and LVEDP by 30% and 19%, respectively (p < 0.05 for both). Compared to controls, preproET-1 mRNA expression in the LV and lungs was markedly increased in pHF. This was not changed in the LV but was reduced in the lungs by treatment with the ETA antagonist. Increased pulmonary and LV expression of preproET-1 suggests that ET-1 plays a role in mediating the pulmonary hypertension and LV dysfunction characteristic of this model.

Hemodynamic and renal excretory effects of human brain natriuretic peptide infusion in patients with congestive heart failure. A double-blind, placebo-controlled, randomized crossover trial

BACKGROUND

The pharmacological effects of infusion of human brain natriuretic peptide (hBNP) in patients with severe congestive heart failure have not been characterized previously.

METHODS AND RESULTS

Twenty patients with severe congestive heart failure were randomized in a double-blind, placebo-controlled, crossover trial to receive incremental 90-minute infusions of hBNP (0.003, 0.01, 0.03, and 0.1 microgram/kg per minute) or placebo on 2 consecutive days. At the highest completed dose of the hBNP, mean pulmonary artery pressure decreased from 38.3 +/- 1.6 to 25.9 +/- 1.7 mm Hg; mean pulmonary capillary wedge pressure decreased from 25.1 +/- 1.1 to 13.2 +/- 1.3 mm Hg; mean right atrial pressure decreased from 10.9 +/- 1 to 4.8 +/- 1.0 mm Hg; mean arterial pressure decreased from 85.2 +/- 2.0 to 74.9 +/- 1.7 mm Hg; and cardiac index increased from 2.0 +/- 0.1 to 2.5 +/- 0.1 L/min per square meter (all P < .01 versus placebo). Urine volume and urine sodium excretion increased significantly during hBNP infusion when compared with placebo infusion (90 +/- 38 versus 67 +/- 27 mL/h and 2.6 +/- 2.4 versus 1.4 +/- 1.2 mEq/h, respectively, both P < .05 versus placebo), whereas creatinine clearance and urinary potassium excretion did not change.

CONCLUSIONS

Infusion of incremental doses of hBNP is associated with favorable hemodynamic and natriuretic effects in patients with severe congestive heart failure.

Plasma and cardiac tissue atrial and brain natriuretic peptides in experimental heart failure

OBJECTIVES

This study evaluated the role of changes in heart rate, cardiac filling pressures and cardiac tissue atrial and brain natriuretic peptides in the modulation of their plasma levels in a model of heart failure.

BACKGROUND

Atrial and brain natriuretic peptides constitute a dual natriuretic peptide system that regulates circulatory homeostasis.

METHODS

The effects of 1) acute ventricular pacing, 2) acute volume expansion, and 3) volume expansion after 1 week of continuous pacing on plasma atrial and brain natriuretic peptide levels were compared in eight dogs. Atrial and ventricular tissue levels of the peptides were examined in 5 normal dogs (control group), 21 dogs paced for 1 week (group 1) and 10 dogs paced for 3 weeks (group 2).

RESULTS

Both acute pacing and volume expansion increased plasma atrial natriuretic peptide levels (from 53 +/- 41 to 263 +/- 143 pg/ml [mean +/- SD], p < 0.01, and from 38 +/- 23 to 405 +/- 221 pg/ml, p < 0.001, respectively). After 1 week, there was a marked increase in plasma levels of atrial natriuretic peptide, but the level did not increase further with volume expansion (from 535 +/- 144 to 448 +/- 140 pg/ml, p = 0.72). By contrast, plasma brain natriuretic peptide levels increased only modestly with acute pacing (from 12 +/- 4 to 20 +/- 8 pg/ml, p < 0.05) and after pacing for 1 week (from 13 +/- 4 to 48 +/- 20 pg/ml, p < 0.05) but did not change with acute or repeat volume expansion. In groups 1 and 2, atrial tissue levels of atrial natriuretic peptide (1.9 +/- 1.3 and 2.0 +/- 0.9 ng/mg, respectively) were lower than those in the control group (11.7 +/- 6.8 ng/mg, both p < 0.001), whereas ventricular levels were similar to those in the control group. Atrial tissue brain natriuretic peptide levels in groups 1 and 2 were similar to those in the control group. However, ventricular levels in group 2 (0.018 +/- 0.006 ng/mg) were increased compared with those in the control group (0.013 +/- 0.006 ng/mg, p < 0.05) and in group 1 (0.011 +/- 0.006 ng/mg, p < 0.05).

CONCLUSIONS

Atrial and brain natriuretic peptides respond differently to changes in heart rate and atrial pressures. Reduced atrial tissue atrial natriuretic peptide levels in heart failure may indicate reduced storage after enhanced cardiac release. However, the relatively modest change in cardiac tissue brain natriuretic peptide levels suggests that the elevated plasma levels may be mediated by mechanisms other than increased atrial pressures.

How does intermittent pacing modify the response to rapid ventricular pacing in experimental heart failure?

Rapid ventricular pacing is widely accepted as a useful model to produce heart failure. The heart failure is associated with reduced myocardial energy stores and absence of cardiac hypertrophy. In this study, it was hypothesized that a modification of the protocol to intermittent pacing would permit time for partial recovery of myocardial energetics leading to improved cardiac function and development of hypertrophy. Eight dogs underwent conventional continuous right ventricular pacing to a biologic endpoint of severe heart failure (group 1). Another eight dogs underwent an intermittent pacing protocol over 7 weeks, consisting of 48-hour pacing alternating with 24-hour sinus rhythm (group 2) so as to produce the same total exposure to continuous pacing as in group 1. Six additional normal dogs were used as control animals for tissue metabolic data. Although both paced groups had similar directional changes in hemodynamic, neurohormonal, and echocardiographic variables, the absolute increases in pulmonary capillary wedge and right atrial pressures in group 2 (13 +/- 8 and 3 +/- 4 mmHg, respectively) were less marked than in group 1 (29 +/- 5 and 12 +/- 4 mmHg, respectively; both P = .002). Group 2 also had a more modest rise in plasma atrial natriuretic peptide and norepinephrine concentrations. There was no significant increase, however, in left ventricular mass in either group, and myocardial adenosine 5'-triphosphate levels were reduced to a similar extent compared to the control animals. Intermittent pacing produces a less advanced syndrome of heart failure than continuous pacing. Furthermore, the data suggest that reduced energy stores are not the predominant mechanism for impaired cardiac function, although they may contribute to the failure to hypertrophy in this model.

Atrial natriuretic peptide and its potential role in pharmacotherapy

Atrial natriuretic peptide (ANP) is a 28 amino-acid polypeptide secreted into the blood by atrial myocytes after atrial pressure and distension. Although its role in humans is not clear, it can produce a variety of physiologic effects including vasodilatation, natriuresis, and suppression of the renin-angiotensin-aldosterone axis. These actions are potentially useful in a variety of pathologic states such as hypertension and congestive heart failure, and diverse methods to augment the effects of ANP in these states have been devised. The results are exciting and, despite some problems, may lead to the pharmacologic use of enhancement of ANP actions in several clinical disorders.

Cardiorenal and neurohumoral effects of endogenous atrial natriuretic peptide in dogs with severe congestive heart failure using a specific antagonist for guanylate cyclase-coupled receptors

BACKGROUND

To elucidate the extent of the compensatory role of endogenous atrial natriuretic peptide (ANP) in severe congestive heart failure (CHF), we examined the changes in hemodynamics and neuroendocrine and renal functions after incremental administration of an ANP antagonist, HS-142-1 (HS), in dogs with CHF.

METHODS AND RESULTS

We assessed the effects of HS on the suppression of plasma and urinary cGMP levels as a marker of endogenous ANP activity in dogs without CHF. Bolus injections of 0.3 and 1.0 mg/kg HS reduced plasma cGMP levels to 77% and 60% and urinary cGMP excretion to 78% and 61% of the relevant control levels, respectively. Then the study was performed in dogs with CHF induced by chronic rapid ventricular pacing, and the plasma ANP level was sixfold higher than that in the controls. Hemodynamic, hormonal, and renal variables were determined both before and after subsequent incremental administration (0.3, 1.0, and 3.0 mg/kg every 30 minutes) of HS. HS lowered the plasma and urinary cGMP levels dose dependently to 32% and 37% of the control levels, respectively. Mean arterial, pulmonary capillary wedge, and right atrial pressures and cardiac output did not change significantly. However, plasma renin activity, aldosterone level, and norepinephrine level increased rapidly to 226%, 179%, and 252% of the control values, respectively. Urine flow rate and urinary sodium excretion were significantly inhibited, with no concomitant change in glomerular filtration rate or renal plasma flow.

CONCLUSIONS

These findings suggest that endogenous ANP contributes to the suppression of the activation of the renin-aldosterone system and sympathetic nervous activity and body fluid retention but that the vasodilative action of this peptide is attenuated in advanced CHF.