Effect of endogenous natriuretic peptide system on ventricular and coronary function in failing heart

Atrial Natriuretic Peptide31-67: A Novel Therapeutic Factor for Cardiovascular Diseases

The characterization of the cardiac hormone atrial natriuretic peptide (ANP_99–126), synthesized and secreted predominantly by atrial myocytes under stimulation by mechanical stretch, has established the heart as an endocrine organ with potent natriuretic, diuretic, and vasodilating actions. Three additional distinct polypeptides resulting from proteolytic cleavage of proANP have been identified in the circulation in humans. The mid-sequence proANP fragment 31–67 (also known as proANP_31–67) has unique potent and prolonged diuretic and natriuretic properties. In this review, we report the main effects of this circulating hormone in different tissues and organs, and its mechanisms of actions. We further highlight recent evidence on the cardiorenal protective actions of chronic supplementation of synthetic proANP_31–67 in preclinical models of cardiorenal disease. Finally, we evaluate the use of proANP_31–67 as a new therapeutic strategy to repair end-organ damage secondary to hypertension, diabetes mellitus, renal diseases, obesity, heart failure, and other morbidities that can lead to impaired cardiac function and structure.

Cardiac-Specific Overexpression of Catalytically Inactive Corin Reduces Edema, Contractile Dysfunction, and Death in Mice with Dilated Cardiomyopathy

Humans with dilated cardiomyopathy (DCM) and heart failure (HF) develop low levels of corin, a multi-domain, cardiac-selective serine protease involved in natriuretic peptide cleavage and sodium and water regulation. However, experimental restoration of corin levels markedly attenuates HF progression. To determine whether the beneficial effects of corin in HF require catalytic activity, we engineered cardiac overexpression of an enzymatically inactive corin transgene (corin-Tg(i)). On a wild-type (WT) background, corin-Tg(i) had no evident phenotypic effects. However, in a well-established genetic model of DCM, corin-Tg(i)/DCM mice had increased survival (p < 0.01 to 0.001) vs. littermate corin-WT/DCM controls. Pleural effusion (p < 0.01), lung edema (p < 0.05), systemic extracellular free water (p < 0.01), and heart weight were decreased (p < 0.01) in corin-Tg(i)/DCM vs. corin-WT/DCM mice. Cardiac ejection fraction and fractional shortening improved (p < 0.01), while ventricular dilation decreased (p < 0.0001) in corin-Tg(i)/DCM mice. Plasma atrial natriuretic peptide, cyclic guanosine monophosphate, and neprilysin were significantly decreased. Cardiac phosphorylated glycogen synthase kinase-3β (pSer9-GSK3β) levels were increased in corin(i)-Tg/DCM mice (p < 0.01). In summary, catalytically inactive corin-Tg(i) decreased fluid retention, improved contractile function, decreased HF biomarkers, and diminished cardiac GSK3β activity. Thus, the protective effects of cardiac corin on HF progression and survival in experimental DCM do not require the serine protease activity of the molecule.

Cardiorenal and endocrine effects of synthetic canine BNP1-32 in dogs with compensated congestive heart failure caused by myxomatous mitral valve disease

Background

The effects of synthetic brain natriuretic peptide (BNP1‐32) on cardiorenal and renin angiotensin aldosterone system in dogs with naturally occurring congestive heart failure (CHF) are unknown.

Objectives

To evaluate the cardiorenal and endocrine effects of SC administered synthetic canine BNP1‐32, with or without furosemide, in dogs with CHF caused by myxomatous mitral valve disease (MMVD).

Animals

Seven client‐owned male dogs with compensated American College of Veterinary Internal Medicine stage C CHF caused by MMVD on chronic treatment with furosemide, benazepril, and pimobendan.

Methods

A single‐dose, crossover, pilot study. Each dog received a dose of BNP1‐32 (5 μg/kg), furosemide (2 mg/kg), and both BNP1‐32/furosemide (5 μg/kg and 2 mg/kg, respectively) SC with a 2‐week washout period among each treatment. Between‐ and within‐treatment effects were evaluated using linear mixed modeling with restricted maximum likelihood estimation and evaluation of least square differences.

Results

Rapid absorption of BNP1‐32 and a corresponding rise in urinary cyclic guanosine monophosphate excretion was observed at 1‐2 hours after any treatment containing BNP1‐32 (P < .05). However, BNP1‐32 did not influence measured cardiorenal variables. Plasma aldosterone concentrations were below quantifiable levels in majority of the samples.

Conclusions and Clinical Importance

No beneficial cardiorenal effects were detected. It is possible that dogs with chronic CHF have a reduction in natriuretic peptide responsiveness.

A perspective on sympathetic renal denervation in chronic congestive heart failure

Medical therapy has indisputably been the mainstay of management for chronic congestive heart failure. However, a significant percentage of patients continue to experience worsening heart failure (HF) symptoms despite treatment with multiple therapeutic agents. Recently, catheter-based interventional strategies that interrupt the renal sympathetic nervous system have shown promising results in providing better symptom control in patients with HF. In this article, we will review the pathophysiology of HF for better understanding of the interplay between the cardiovascular system and the kidney. Subsequently, we will briefly discuss pivotal renal denervation (RDN) therapy trials in patients with resistant hypertension and then present the available evidence on the role of RDN in HF therapy.

Plasma brain-type natriuretic Peptide level following seizure and syncope: pilot study

Background and Purpose:

To explore the clinical feasibility of plasma brain-type natriuretic peptide (proBNP) level to differentiate the two major causes of transient unconsciousness, seizure and vasovagal syncope (VVS) in adult patients.

Methods:

ProBNP levels were evaluated within 24 hours following attack in patients who had experienced a transient episode of unconsciousness. For confirmatory diagnosis, clinical history was reviewed thoroughly and several work-ups including electroencephalography and cerebral imaging and tilt-table test, were performed in cases of putative VVS, as a part of routine clinical approaches.

Results:

According to various relevant evaluations, 15 patients were diagnosed as seizure (age, 40.3±13.8 years) and 12 patients were VVS (age, 38.1±17.1 years). Plasma concentrations of pro-BNP were not different between two groups (p=0.714). Median level was 34.3 pg/mL (interquartile range: 12.9–91.1) in post-seizure group and 32.3 pg/mL (interquartile range 8.9–77.4) in post-VVS group. Additionally, it was not correlated with the sampling times within 24 hours after the episodes.

Conclusions:

The plasma level of pro-BNP has a limited clinical value in differentiating seizure and vasovagal syncope in adults. However, the more validated results with a large population should be sought in the future studies to confirm its value.

Heart failure with preserved ejection fraction

As part of this series devoted to heart failure (HF), we review the epidemiology, diagnosis, pathophysiology, and treatment of HF with preserved ejection fraction (HFpEF). Gaps in knowledge and needed future research are discussed.

A functional genetic variant (N521D) in natriuretic peptide receptor 3 is associated with diastolic dysfunction: the prevalence of asymptomatic ventricular dysfunction study

Objectives

To evaluate the impact of a functional genetic variant in the natriuretic peptide clearance receptor, NPR3, on circulating natriuretic peptides (NPs) and myocardial structure and function in the general community.

Background

NPR3 plays an important role in the clearance of NPs and through direct signaling mechanisms modulates smooth muscle cell function and cardiac fibroblast proliferation. A NPR3 nonsynonymous single nucleotide polymorphism (SNP) rs2270915, resulting in a N521D substitution in the intracellular catalytic domain that interacts with Gi could affect receptor function. Whether this SNP is associated with alterations in NPs levels and altered cardiac structure and function is unknown.

Methods

DNA samples of 1931 randomly selected residents of Olmsted County, Minnesota were genotyped. Plasma NT-proANP_1-98, ANP_1-28, proBNP_1-108, NT-proBNP_1-76, BNP_1-32 and BNP_3-32 levels were measured. All subjects underwent comprehensive echocardiography.

Results

Genotype frequencies for rs2270915 were as follows: (A/A 60%, A/G 36%, G/G 4%). All analyses performed were for homozygotes G/G versus wild type A/A plus the heterozygotes A/G. Diastolic dysfunction was significantly more common (p = 0.007) in the homozygotes G/G (43%) than the A/A+A/G (28%) group. Multivariate regression adjusted for age, sex, body mass index and hypertension demonstrated rs2270915 to be independently associated with diastolic dysfunction (odds ratio 1.94, p = 0.03). There was no significant difference in NPs levels between the 2 groups suggesting that the clearance function of the receptor was not affected.

Conclusions

A nonsynonymous NPR3 SNP is independently associated with diastolic dysfunction and this association does not appear to be related to alterations in circulating levels of natriuretic peptides.

Novel natriuretic peptides: new compounds and new approaches

The natriuretic peptides (NPs) are a group of structurally similar yet genetically distinct peptides that have diverse actions in cardiovascular, renal, and endocrine homeostasis. Since the discovery of atrial natriuretic peptide in 1981, the diagnostic, prognostic, and therapeutic significance of NPs have been studied extensively in relation to heart failure. Indeed, it now is understood that a hallmark of heart failure is the activation of the cardiac endocrine system, in particular the natriuretic peptide family including atrial natriuretic peptide and B-type natriuretic peptide. Currently, the only approved therapeutic application for NPs is the intravenous treatment of acute decompensated heart failure. However, in recent years there has been considerable research aimed at creating novel NPs and administering them via novel routes. This review focuses on the novel NPs that have been created and on novel approaches for their administration.

Secretion of glycosylated pro-B-type natriuretic peptide from normal cardiomyocytes

BACKGROUND

B-type natriuretic peptide (BNP), a key cardiac hormone in cardiorenal homeostasis, is produced as a 108 amino acid prohormone, proBNP1-108, which is converted to a biologically active peptide BNP1-32 and an inactive N-terminal (NT)-proBNP1-76. The widely accepted model is that the normal heart releases a proteolytically processed BNP1-32 and NT-proBNP, whereas the diseased heart secretes high amounts of unprocessed/glycosylated proBNP1-108 or inappropriately processed BNPs. In contrast, circulating proBNP1-108 has recently been identified in healthy individuals, indicating that the normal heart also secretes unprocessed proBNP1-108. However, the mechanism of proBNP1-108 secretion from the normal heart remains elusive. Our goal was to determine the molecular mechanisms underlying proBNP1-108 intracellular trafficking and secretion from the normal heart.

METHODS

We expressed preproBNP in cardiomyocytes, and determined the subcellular localization and dominant intracellular and extracellular forms of BNP.

RESULTS

Intracellular immunoreactive BNPs were first accumulated in the Golgi apparatus, and then distributed throughout the cytoplasm as secretory vesicles. The predominant intracellular form of BNP was nonglycosylated proBNP1-108, rather than BNP1-32. Glycosylated proBNP1-108, but not nonglycosylated proBNP1-108, was detected as the major extracellular form in the culture supernatants of preproBNP-expressing cell lines and primary human cardiomyocytes. Ablation of O-glycosylation of proBNP1-108 at T71 residue, near the convertase recognition site, reduced the extracellular proBNP1-108 and increased extracellular BNP1-32.

CONCLUSIONS

Intracellular proBNP trafficking occurs through a conventional Golgi-endoplasmic reticulum pathway. Glycosylation of proBNP1-108 controls the stability and processing of extracellular proBNP1-108. Our data establish a new BNP secretion model in which the normal cardiac cells secrete glycosylated proBNP1-108.

Decompensated heart failure is associated with reduced corin levels and decreased cleavage of pro-atrial natriuretic peptide

BACKGROUND

By promoting salt and water excretion, the corin and the atrial natriuretic peptide (ANP) system should help to maintain fluid balance in heart failure. Yet, the development of fluid retention despite high levels of ANP-related peptides suggests that this compensatory system is limited.

METHODS AND RESULTS

Levels of circulating corin (the pro-ANP-converting enzyme) and pro-ANP were measured in hospitalized patients with heart failure, using novel immunoassays. Patients (n=14) had severe heart failure (New York Heart Association class III-IV) with a median ejection fraction of 18% and median brain natriuretic peptide levels of 1940 pg/mL. In heart failure, median plasma corin levels were 7.6-fold lower than measured in plasma from 16 normal control subjects (180 versus 1368 pg/mL, P<0.01). In contrast, in patients with heart failure, levels of plasma N-terminal ANP peptides (N-ANP and pro-ANP) levels were markedly elevated (42.0 versus 7.5 ng/mL, P<0.01). Levels of uncleaved pro-ANP, measured by novel immunoassays, were significantly higher in patients with heart failure (P<0.01), suggesting that corin cleavage of pro-ANP was impaired. Median plasma levels of cyclic guanosine monophosphate were elevated in patients with heart failure (150.0 versus 7.6 pmol/mL, P<0.01), and plasma cyclic guanosine monophosphate levels positively correlated with the fractional amount of cleaved pro-ANP (r(s)=0.59, P<0.03) but not with levels of uncleaved pro-ANP, implying that the cellular response to ANP remained intact.

CONCLUSIONS

Taken together, these data suggest that there may be patients for whom low corin levels and impaired pro-ANP cleavage contribute to acute decompensation.

Long-term effects of B-type natriuretic peptide infusion after acute myocardial infarction in a rat model

INTRODUCTION

The effects of exogenous B-type natriuretic peptide (BNP) on postmyocardial infarction (MI) are not known. We tested the hypothesis that in vivo infusion of BNP would improve cardiac function and affect left ventricular (LV) remodeling in an experimental model of MI.

METHODS

MI was induced by coronary ligation in rats and confirmed by echocardiography. 19 rats were randomized to 1 of 3 groups: sham (n = 7), MI + saline (n = 5), MI + BNP (400 ng.kg(-1).minute(-1)) (n = 7). Infusions were delivered for 7 days via venous catheters tunneled to an infusion pump. Rats were followed for 8 weeks. Echocardiography, hemodynamics, histology, and in vivo and ex vivo pressure-volume relationships were examined.

RESULTS

LV systolic pressure, LV dP/dtmax, and infarct size improved with BNP treatment versus control MI group (132 +/- 4 vs.110 +/- 2 mm Hg, 8097 +/- 317 vs. 5816 +/- 378 mm Hg/s, 19.3% +/- 1.6% vs. 23.3% +/- 1.9%, respectively; all P < 0.05). Ex vivo end-diastolic pressure-volume relationship demonstrated reduced diastolic dysfunction after BNP therapy (P < 0.05 vs. control MI). Serum BNP levels confirmed delivery of BNP.

CONCLUSIONS

We demonstrate beneficial effects on LV function and decreased LV remodeling with BNP infusion in an experimental model of acute MI.

Therapeutic strategies for diastolic dysfunction: a clinical perspective

Diastolic dysfunction, which is increasingly viewed as being influential in precipitating heart failure and determining prognosis, is often unrecognized and has therapeutic implications distinct from those that occur with systolic dysfunction. In this review, several therapeutic modalities including pharmacologic, nonpharmacologic, and surgical approaches for primary diastolic dysfunction and heart failure will be discussed.

Insights into natriuretic peptides in heart failure: an update

Natriuretic peptides (NPs) secreted by the heart in response to volume overload are pleiotropic molecules with vasodilating, diuretic, natriuretic, antiproliferative, and antifibrotic actions. Functioning of the NP system is altered in congestive heart failure (CHF), suggesting that support of the NP system might be beneficial in treatment of acute and chronic CHF. Several approaches alone or in combination with other pharmacologic therapies have been shown to enhance function of the NP system: direct administration of native and designer NPs, inhibition of degradation of NPs and their second messenger (cyclic guanosine monophosphate ), and stimulation of cGMP generation. Despite increasing numbers of studies using NPs in therapy of acute and chronic CHF, several controversies regarding safety, efficacy, and dosing of NPs need to be addressed. Moreover, further research is warranted to identify the stages and etiologies of CHF that may profit from NP therapy.

Amino-terminal pro-B-type natriuretic peptide and B-type natriuretic peptide: biomarkers for mortality in a large community-based cohort free of heart failure

Recent studies report that, in the absence of heart failure and renal failure, plasma B-type natriuretic peptide (BNP) has prognostic value for mortality. We sought to confirm and extend these previous studies to assess BNP, measured by 3 distinct assays, as a biomarker for mortality in a strategy to enhance efforts at primary prevention and to better understand the clinical phenotype of such subjects at risk. We used a community-based cohort of 2042 subjects from Olmsted County, Minn, and individuals with heart or renal failure were excluded. BNP was assessed using 3 assays including Biosite and Shionogi for mature, biologically active BNP and the Roche assay for apparently nonbiologically active amino-terminal pro-BNP (NT-proBNP). Thorough echocardiographic and clinical data were recorded for all of the participants. Median follow-up for mortality was 5.6 years. BNP by all 3 of the assays was predictive of mortality. NT-proBNP and Biosite assays remained significant even after adjustment for traditional clinical risk factors and echocardiographic abnormalities including left ventricular hypertrophy and diastolic dysfunction. Echocardiography documented widespread structural changes in those with increasing BNP levels yet below levels observed in heart failure. We report in a large, well-characterized community-based cohort, free of heart failure, the first study to compare 3 distinct BNP assays as biomarkers for mortality in the same cohort. Our findings confirm the potential use of NT-proBNP and BNP biomarkers for future events and underscore that these peptides may also serve as biomarkers for underlying cardiac remodeling secondary to diverse cardiovascular disease entities.

Brain natriuretic peptide as a hormonal marker of ventricular diastolic dysfunction in children with Kawasaki disease

Although an increased level of serum brain natriuretic peptide (BNP) has been reported in children in the acute phase of Kawasaki disease (KD), no precise relation was documented between the serum BNP level and left ventricular (LV) systolic function. We hypothesized that the increased BNP levels may be explained by diastolic abnormalities in those with KD. We prospectively studied 25 patients in the acute phase of KD. Patients with abnormal systolic function were excluded. Pediatric cardiologists making the assessment of LV diastolic function were blinded to the BNP levels. Doppler interrogation was applied to measure LV inflow velocities, which were transformed to z scores using control measurements obtained from 83 healthy subjects. In the patients, the BNP levels ranged from 2.0 to 450.0 pg/ml, with a mean of 54.0 +/- 102.8 pg/ml. Six patients with abnormal velocities (> 2 SD in z score) showed significantly higher levels of BNP (152 +/- 173 pg/ml) than those in the remaining patients (p < 0.01). The BNP levels correlated positively with diastolic atrial velocity in z score (r = 0.51, p < 0.05), and negatively with diastolic early velocity to atrial velocity ratio in z score (r = -0.75, p < 0.01). This study suggests that LV diastolic dysfunction may occur in some children in the acute phase of KD, causing an increased level of BNP.

Natriuretic Peptides in the Perioperative Management of Cardiac Surgery Patients

Both heart failure (HF) and cardiac surgery with cardiopulmonary bypass result in a release of neurohormones, with a variety of physiologic effects. Administration of exogenous B-type natriuretic peptide (BNP) has beneficial hemodynamic effects and reduces the level of several neurohormones in HF patients. BNP is currently being investigated in the perioperative management of cardiac surgery patients and may be especially beneficial for patients with ventricular dysfunction, pulmonary hypertension, or renal dysfunction. Using a neurohormonal approach to supportive therapy may enhance future strategies for patients undergoing cardiac surgery, especially those at greatest risk for complications.

Cardiac-specific attenuation of natriuretic peptide A receptor activity accentuates adverse cardiac remodeling and mortality in response to pressure overload

Atrial (ANP) and brain (BNP) natriuretic peptides are hormones of myocardial cell origin. These hormones bind to the natriuretic peptide A receptor (NPRA) throughout the body, stimulating cGMP production and playing a key role in blood pressure control. Because NPRA receptors are present on cardiomyocytes, we hypothesized that natriuretic peptides may have direct autocrine or paracrine effects on cardiomyocytes or adjacent cardiac cells. Because both natriuretic peptides and NPRA gene expression are upregulated in states of pressure overload, we speculated that the effects of the natriuretic peptides on cardiac structure and function would be most apparent after pressure overload. To attenuate cardiomyocyte NPRA activity, transgenic mice with cardiac specific expression of a dominant-negative (DN-NPRA) mutation (HCAT D 893A) in the NPRA receptor were created. Cardiac structure and function were assessed (avertin anesthesia) in the absence and presence of pressure overload produced by suprarenal aortic banding. In the absence of pressure overload, basal and BNP-stimulated guanylyl cyclase activity assessed in cardiac membrane fractions was reduced. However, systolic blood pressure, myocardial cGMP, log plasma ANP levels, and ventricular structure and function were similar in wild-type (WT-NPRA) and DN-NPRA mice. In the presence of pressure overload, myocardial cGMP levels were reduced, and ventricular hypertrophy, fibrosis, filling pressures, and mortality were increased in DN-NPRA compared with WT-NPRA mice. In addition to their hormonal effects, endogenous natriuretic peptides exert physiologically relevant autocrine and paracrine effects via cardiomyocyte NPRA receptors to modulate cardiac hypertrophy and fibrosis in response to pressure overload.

Ventricular structure and function in aged dogs with renal hypertension: a model of experimental diastolic heart failure

BACKGROUND

Heart failure (HF) with normal ejection fraction (diastolic HF [DHF]) usually occurs in elderly patients with hypertension. The presence and significance of altered systolic and diastolic ventricular function in DHF is increasingly controversial. Our objective was to develop a clinically relevant large-animal model to better understand the pathophysiology of DHF.

METHODS AND RESULTS

Ventricular structure and function were characterized in young control (YC group; n=6), old control (OC group; n=7), and old dogs made hypertensive by renal wrapping (experimental DHF [ExDHF] group; n=8). The ExDHF group was associated with normal left ventricular (LV) volume, increased LV mass, and myocardial fibrosis. LV relaxation was impaired in ExDHF (tau=53+/-6 ms) compared with OC (tau=35+/-3 ms; P<0.05) and YC (tau=33+/-6 ms; P<0.05) dogs. The percent diastole at which relaxation is complete was increased in ExDHF (116+/-30%) compared with OC (69+/-8%; P<0.05) and YC (35+/-5%; P<0.05) dogs. The coefficient of LV diastolic stiffness was similar in OC, YC, and ExDHF dogs. Diastolic pressures increased dramatically in response to increases in blood pressure. End-systolic LV stiffness was enhanced in ExDHF dogs and after load enhancement of myocardial performance was maintained. Arterial stiffness was increased in ExDHF dogs.

CONCLUSIONS

Aged dogs with chronic hypertension exhibit LV hypertrophy and fibrosis with impaired LV relaxation but no increase in the coefficient of LV diastolic stiffness. LV systolic and arterial stiffness are increased, which may exacerbate load-dependent impairment of relaxation and contribute to increased filling pressures with hypertensive episodes. This model mimics many of the structural and functional characteristics described in the limited studies of human DHF and provides insight into the pathogenesis of DHF.

Angiotensin II type 1 receptor blockade prevents diastolic heart failure through modulation of Ca(2+) regulatory proteins and extracellular matrix

BACKGROUND

Angiotensin II type 1 receptor (AT(1)R) blockade attenuates left ventricular relaxation abnormality and myocardial stiffening in a model of hypertensive diastolic heart failure, but the mechanisms remain unclear.

OBJECTIVE

To test the hypothesis that such benefits are provided by modulation of the quantitative or qualitative changes, or both, in Ca2+ regulatory proteins and extracellular matrix.

DESIGN AND METHODS

Dahl salt-sensitive rats fed a diet containing 8% sodium chloride from 7 weeks of age present pulmonary congestion as a result of diastolic dysfunction with preserved systolic function, around 20 weeks of age. In this study, animals of this model were divided into groups that received (n = 7) or did not receive (n = 6) a subdepressor dose of an AT(1)R antagonist (candesartan cilexetil) from 8 weeks of age.

RESULTS

Long-term AT(1)R blockade prevented the development of diastolic heart failure through attenuation of left ventricular relaxation abnormality and myocardial stiffening without a reduction in blood pressure. Left ventricular relaxation abnormality was not associated with any change in the ratio of abundance of phospholamban to that of sarcoplasmic reticulum Ca2+-ATPase 2a protein, but was accompanied by a decrease in Ser16-phosphorylated phospholamban. The AT(1)R blockade inhibited this decrease. Attenuation in myocardial stiffening was associated with reduced tissue collagen content, attenuated collagen cross-linking, and suppressed gene expression of collagen type I rather than type III.

CONCLUSIONS

AT(1)R blockade prevented abnormal relaxation at least partly through functional alterations in Ca2+-handling proteins in a hypertensive model of diastolic heart failure. It attenuated myocardial stiffening through preventing a shift in the phenotype of collagen synthesized and the accumulation of cross-linked collagen. These beneficial effects of AT(1)R blockade in diastolic heart failure are achieved without a reduction in blood pressure.

B-type natriuretic peptide limits infarct size in rat isolated hearts via KATP channel opening

B-type natriuretic peptide (BNP) has been reported to be released from the myocardium during ischemia. We hypothesized that BNP mediates cardioprotection during ischemia-reperfusion and examined whether exogenous BNP limits myocardial infarction and the potential role of ATP-sensitive potassium (K(ATP)) channel opening. Langendorff-perfused rat hearts underwent 35 min of left coronary artery occlusion and 120 min of reperfusion. The control infarct-to-risk ratio was 44.8 +/- 4.4% (means +/- SE). BNP perfused 10 min before ischemia limited infarct size in a concentration-dependent manner, with maximal protection observed at 10(-8) M (infarct-to-risk ratio: 20.1 +/- 5.2%, P < 0.01 vs. control), associated with a 2.5-fold elevation of myocardial cGMP above the control value. To examine the role of K(ATP) channel opening, glibenclamide (10(-6) M), 5-hydroxydecanoate (5-HD; 10(-4) M), or HMR-1098 (10(-5) M) was coperfused with BNP (10(-8) M). Protection afforded by BNP was abolished by glibenclamide or 5-HD but not by HMR-1098, suggesting the involvement of putative mitochondrial but not sarcolemmal K(ATP) channel opening. We conclude that natriuretic peptide/cGMP/K(ATP) channel signaling may constitute an important injury-limiting mechanism in myocardium.

Effect of PDE5 inhibition on coronary hemodynamics in pacing-induced heart failure

Inhibition of phosphodiesterase type 5 (PDE5) can relax systemic and coronary vessels by causing accumulation of cGMP. Both the endothelial dysfunction with decreased nitric oxide production and increased natriuretic peptide levels in congestive heart failure (CHF) have the potential to alter cGMP production, thereby influencing the response to PDE5 inhibition. Consequently, this study examined the effects of PDE5 inhibition with sildenafil in dogs with CHF produced by rapid ventricular pacing. CHF resulted in decreases of left ventricular (LV) systolic pressure, coronary blood flow, and the maximal first time derivative of LV pressure (LV dP/dt(max)) at rest and during treadmill exercise compared with normal, whereas resting LV end-diastolic pressure increased from 10 +/- 1.4 to 23 +/- 1.4 mmHg. Sildenafil (2 and 10 mg/kg per os) caused a 5- to 6-mmHg decrease of aortic pressure (P < 0.05), with no change of heart rate, LV systolic pressure, or LV dP/dt(max). Sildenafil caused no change in coronary flow or myocardial oxygen consumption in animals with CHF at rest or during exercise. In contrast to findings in normal animals, sildenafil did not augment endothelium-dependent coronary vasodilation in response to acetylcholine in animals with CHF. Furthermore, Western blotting showed decreased PDE5 protein expression in myocardium from failing hearts. These findings demonstrate that PDE5 contributes little to regulation of coronary hemodynamics in CHF.

Actions of a novel synthetic natriuretic peptide on hemodynamics and ventricular function in the dog

Dendroaspis natriuretic peptide (DNP) is a recently discovered peptide with structural similarity to known natriuretic peptides. DNP has been shown to possess potent renal actions. Our objectives were to define the acute hemodynamic actions of DNP in normal anesthetized dogs and the acute effects of DNP on left ventricular (LV) function in conscious chronically instrumented dogs. In anesthetized dogs, DNP, but not placebo, decreased mean arterial pressure (141 +/- 6 to 109 +/- 7 mmHg, P < 0.05) and pulmonary capillary wedge pressure (5.8 +/- 0.3 to 3.4 +/- 0.2 mmHg, P < 0.05). Cardiac output decreased and systemic vascular resistance increased with DNP and placebo. DNP-like immunoreactivity and guanosine 3',5'-cyclic monophosphate concentration increased without changes in other natriuretic peptides. In conscious dogs, DNP decreased LV end-systolic pressure (120 +/- 7 to 102 +/- 6 mmHg, P < 0.05) and volume (32 +/- 6 to 28 +/- 6 ml, P < 0.05) and LV end-diastolic volume (38 +/- 5 to 31 +/- 4 ml, P < 0.05) but not arterial elastance. LV end-systolic elastance increased (6.1 +/- 0.7 to 7.4 +/- 0.6 mmHg/ml, P < 0.05), and Tau decreased (31 +/- 2 to 27 +/- 1 ms, P < 0.05). The effects on hemodynamics, LV function, and second messenger generation suggest synthetic DNP may have a role as a cardiac unloading and lusitropic peptide.

Differential effects of natriuretic peptides and NO on LV function in heart failure and normal dogs

beta-Adrenergic hyporesponsiveness in congestive heart failure (CHF) is mediated, in part, by nitric oxide (NO). NO and brain natriuretic peptide (BNP) share cGMP as a second messenger. Left ventricular (LV) function and inotropic response to intravenous dobutamine (Dob) were assessed during sequential intracoronary infusion of saline, HS-142-1 (a BNP receptor antagonist), and HS-142-1 + N(G)-monomethyl-L-arginine (L-NMMA) in anesthetized dogs with CHF due to rapid pacing and in normal dogs during intracoronary infusion of saline, exogenous BNP, and sodium nitroprusside (SNP). In CHF dogs, intracoronary HS-142-1 did not alter the inotropic response to Dob [percent change in first derivative of LV pressure (% Delta dP/dt) 47 +/- 4% saline vs. 54 +/- 7% HS-142-1, P = not significant]. Addition of intracoronary L-NMMA to HS-142-1 enhanced the response to Dob (% Delta dP/dt 73 +/- 8% L-NMMA + HS-142-1, P < 0.05 vs. H142-1). In normal dogs, intracoronary SNP blunted the inotropic response to Dob (% Delta dP/dt 93 +/- 6% saline vs. 71 +/- 5% SNP, P < 0.05), whereas intracoronary BNP had no effect. In CHF dogs, the time constant of LV pressure decay during isovolumic relaxation increased with intracoronary HS-142-1 (48 +/- 4 ms saline vs. 58 +/- 5 ms HS-142-1, P < 0.05) and further increased with intracoronary L-NMMA (56 +/- 6 ms HS-142-1 vs. 66 +/- 7 ms L-NMMA + HS-142-1, P < 0.05). Endogenous BNP and NO preserve diastolic function in CHF, whereas NO but not BNP inhibits beta-adrenergic responsiveness.

The role of nitric oxide in the failing heart

Nitric oxide (NO) has effects on contractility, energetics and gene expression of failing myocardium. Initial studies on isolated cardiomyocytes showed NO to reduce systolic shortening but intracoronary infusions of NO-donors or of NO synthase (NOS) inhibitors failed to elicit changes in baseline LV contractility indices such as LVdP/dt(max). Intracoronary infusions of NO-donors or of substance P, which releases NO from the coronary endothelium, however demonstrated NO to induce a downward displacement of the left ventricular (LV) diastolic pressure-volume relation, consistent with increased LV diastolic distensibility. In end-stage failing myocardium, the increased oxygen consumption is related to reduced NO production and in isolated cardiomyocytes, NO blunts the norepinephrine-induced expression of the fetal gene programme thereby preserving myocardial calcium homeostasis.In dilated cardiomyopathy, changed endomyocardial NOS gene expression has been reported. Because of lower endomyocardial NOS gene expression in patients with higher functional class and lower LV stroke work, increased endomyocardial NOS gene expression seems to be beneficial rather than detrimental for the failing heart. A beneficial effect of increased NOS gene expression could result from NO's ability to increase LV diastolic distensibility, to augment LV preload reserve, to reduce myocardial oxygen consumption and to prevent downregulation of calcium ATPase. Upregulated endomyocardial NOS gene expression has also been reported in athlete's heart and could therefore play a role in physiological LV remodeling. Reduced endomyocardial NO content because of decreased NO or increased superoxide production could lower LV diastolic distensibility and contribute to diastolic heart failure. In many conditions such as aging, hypertension, diabetes or posttransplantation, the increased incidence of diastolic heart failure is indeed paralleled by reduced endothelium-dependent vasodilation.

Modulation of mouse cardiac function in vivo by eNOS and ANP

To study the role of endothelial nitric oxide synthase (eNOS) in cardiac function, we compared eNOS expression, contractility, and relaxation in the left ventricles of wild-type and eNOS-deficient mice. eNOS immunostaining is localized to the macro- and microvascular endothelium throughout the myocardium in wild-type mice and is absent in eNOS-/- mice. Whereas blood pressure is elevated in eNOS-/- mice, baseline cardiac contractility (dP/dt(max)) is similar in wild-type and eNOS-/- mice (9,673 +/- 2, 447 and 9,928 +/- 1,566 mmHg/s, respectively). The beta-adrenergic agonist isoproterenol (Iso) at doses of >/=1 ng causes enhanced increases in dP/dt(max) in eNOS-/- mice compared with wild-type controls in vivo (P < 0.01) as well as in Langendorff isolated heart preparations (P < 0.02). beta-Adrenergic receptor binding (B(max)) is not significantly different in the two groups of animals (B(max) = 41.4 +/- 9.4 and 36.1 +/- 5.1 fmol/mg for wild-type and eNOS-/-). Iso-stimulated ventricular relaxation is also enhanced in the eNOS-/- mice, as measured by dP/dt(min) in the isolated heart. However, baseline ventricular relaxation is normal in eNOS-/- mice (tau = 5.2 +/- 1.0 and 5.6 +/- 1.5 ms for wild-type and eNOS-/-, respectively), whereas it is impaired in wild-type mice after NOS inhibition (tau = 8.3 +/- 2.4 ms). cGMP levels in the left ventricle are unaffected by eNOS gene deletion (wild-type: 3.1 +/- 0.8 pmol/mg, eNOS-/-: 3.1 +/- 0.6 pmol/mg), leading us to examine the level of another physiological regulator of cGMP. Atrial natriuretic peptide (ANP) expression is markedly upregulated in the eNOS-/- mice, and exogenous ANP restores ventricular relaxation in wild-type mice treated with NOS inhibitors. These results suggest that eNOS attenuates both inotropic and lusitropic responses to beta-adrenergic stimulation, and it also appears to regulate baseline ventricular relaxation in conjunction with ANP.

Effects of natriuretic peptides on load and myocardial function in normal and heart failure dogs

The effects on myocardial function and loading conditions of clinically relevant doses of the natriuretic peptides (NP) have not been established. The actions of single doses (100 ng x kg(-1) x min(-1) iv over 30 min) of atrial natriuretic peptide (ANP), brain natriuretic peptide (BNP), and C-type natriuretic peptide (CNP) were studied in conscious normal dogs and in dogs with pacing-induced heart failure. All three NP reduced end-diastolic pressure in normal dogs, and ANP and BNP reduced end-diastolic volume. In heart failure ANP and BNP reduced EDP, and ANP reduced EDV. Arterial elastance was unchanged in normal dogs and in dogs with heart failure. ANP increased end-systolic elastance (E(es)) in normal dogs, whereas BNP tended to increase E(es) (P = 0.06). In dogs with heart failure, no inotropic effect was seen. In normal dogs, all NP reduced the time constant of isovolumic relaxation (tau), and ANP and BNP reduced tau in dogs with heart failure. Increases in plasma cGMP in dogs with heart failure were blunted. The NP reduced preload and enhanced systolic and diastolic function in normal dogs. Effects of ANP and BNP on preload and diastolic function were maintained in heart failure. Lack of negative inotropic effects in heart failure supports the validity of the NP as therapeutic agents.