Acute Phosphodiesterase 5 Inhibition Mimics Hemodynamic Effects of B-Type Natriuretic Peptide and Potentiates B-Type Natriuretic Peptide Effects in Failing But Not Normal Canine Heart

Correlates of Plasma NT-proBNP/Cyclic GMP Ratio in Heart Failure With Preserved Ejection Fraction: An Analysis of the RELAX Trial

BACKGROUND

Phosphodiesterases degrade cyclic GMP (cGMP), the second messenger that mediates the cardioprotective effects of natriuretic peptides. High natriuretic peptide/cGMP ratio may reflect, in part, phosphodiesterase activity. Correlates of natriuretic peptide/cGMP in patients with heart failure with preserved ejection fraction are not well understood. Among patients with heart failure with preserved ejection fraction in the RELAX (Phosphodiesterase-5 Inhibition to Improve Clinical Status and Exercise Capacity in Heart Failure With Preserved Ejection Fraction) trial, we examined (1) cross-sectional correlates of circulating NT-proBNP (N-terminal pro-B-type natriuretic peptide)/cGMP ratio, (2) whether selective phosphodiesterase-5 inhibition by sildenafil changed the ratio, and (3) whether the effect of sildenafil on 24-week outcomes varied by baseline ratio.

METHODS AND RESULTS

In 212 subjects, NT-proBNP/cGMP ratio was calculated at randomization and 24 weeks. Correlates of the ratio and its change were examined in multivariable proportional odds models. Whether baseline ratio modified the sildenafil effect on outcomes was examined by interaction terms. Higher NT-proBNP/cGMP ratio was associated with greater left ventricular mass and troponin, the presence of atrial fibrillation, and lower estimated glomerular filtration rate and peak oxygen consumption. Compared with placebo, sildenafil did not alter the ratio from baseline to 24 weeks (P=0.17). The effect of sildenafil on 24-week change in peak oxygen consumption, left ventricular mass, or clinical composite outcome was not modified by baseline NT-proBNP/cGMP ratio (P-interaction >0.30 for all).

CONCLUSIONS

Among patients with heart failure with preserved ejection fraction, higher NT-proBNP/cGMP ratio associated with an adverse cardiorenal phenotype, which was not improved by selective phosphodiesterase-5 inhibition. Other phosphodiesterases may be greater contributors than phosphodiesterase-5 to the adverse phenotype associated with a high natriuretic peptide/cGMP ratio in HFpEF.

REGISTRATION INFORMATION

clinicaltrials.gov. Identifier: NCT00763867.

The impact of phosphodiesterase-5 inhibition or angiotensin-converting enzyme inhibition on right and left ventricular remodeling in heart failure due to chronic volume overload

While phosphodiesterase-5 inhibition (PED5i) may prevent hypertrophy and failure in pressure-overloaded heart in an experimental model, the impact of PDE5i on volume-overload (VO)-induced hypertrophy is unknown. It is also unclear whether the hypertrophied right ventricle (RV) and left ventricle (LV) differ in their responsiveness to long-term PDE5i and if this therapy affects renal function. The goal of this study was to elucidate the effect of PDE5i treatment in VO due to aorto-caval fistula (ACF) and to compare PDE5i treatment with standard heart failure (HF) therapy with angiotensin-converting enzyme inhibitor (ACEi). ACF/sham procedure was performed on male HanSD rats aged 8 weeks. ACF animals were randomized for PDE5i sildenafil, ACEi trandolapril, or placebo treatments. After 20 weeks, RV and LV function (echocardiography, pressure-volume analysis), myocardial gene expression, and renal function were studied. Separate rat cohorts served for survival analysis. ACF led to biventricular eccentric hypertrophy (LV: +68%, RV: +145%), increased stroke work (LV: 3.6-fold, RV: 6.7-fold), and reduced load-independent systolic function (PRSW, LV: -54%, RV: -51%). Both ACF ventricles exhibited upregulation of the genes of myocardial stress and glucose metabolism. ACEi but not PDE5i attenuated pulmonary congestion, LV remodeling, albuminuria, and improved survival (median survival in ACF/ACEi was 41 weeks vs. 35 weeks in ACF/placebo, p = .02). PDE5i increased cyclic guanosine monophosphate levels in the lungs, but not in the RV, LV, or kidney. PDE5i did not improve survival rate and cardiac and renal function in ACF rats, in contrast to ACEi. VO-induced HF is not responsive to PDE5i therapy.

Combined Inhibition of Phosphodiesterase-5 and -9 in Experimental Heart Failure

BACKGROUND

Intracellular second messenger cyclic guanosine monophosphate (cGMP) mediates bioactivity of the natriuretic peptides and nitric oxide, and is key to circulatory homeostasis and protection against cardiovascular disease. Inhibition of cGMP-degrading phosphodiesterases (PDEs) PDE5 and PDE9 are emerging as pharmacological targets in heart failure (HF).

OBJECTIVES

The present study investigated dual enhancement of cGMP in experimental HF by combining inhibition of PDE-5 (P5-I) and PDE-9 (P9-I).

METHODS

Eight sheep with pacing-induced HF received on separate days intravenous P5-I (sildenafil), P9-I (PF-04749982), P5-I+P9-I, and vehicle control, in counterbalanced order.

RESULTS

Compared with control, separate P5-I and P9-I significantly increased circulating cGMP concentrations in association with reductions in mean arterial pressure (MAP), left atrial pressure (LAP), and pulmonary arterial pressure (PAP), with effects of P5-I on cGMP, MAP, and PAP greater than those of P9-I. Only P5-I decreased pulmonary vascular resistance. Combination P5-I+P9-I further reduced MAP, LAP, and PAP relative to inhibition of either phosphodiesterase alone. P9-I and, especially, P5-I elevated urinary cGMP levels relative to control. However, whereas inhibition of either enzyme increased urine creatinine excretion and clearance, only P9-I induced a significant diuresis and natriuresis. Combined P5-I+P9-I further elevated urine cGMP with concomitant increases in urine volume, sodium and creatinine excretion, and clearance similar to P9-I alone, despite the greater MAP reductions induced by combination treatment.

CONCLUSIONS

Combined P5-I+P9-I amalgamated the superior renal effects of P9-I and pulmonary effects of P5-1, while concurrently further reducing cardiac preload and afterload. These findings support combination P5-I+P9-I as a therapeutic strategy in HF.

Pharmacologic blockade of the natriuretic peptide clearance receptor promotes weight loss and enhances insulin sensitivity in type 2 diabetes

While natriuretic peptides (NPs) are primarily known for their renal and cardiovascular actions, NPs stimulate lipolysis in adipocytes and induce a thermogenic program in white adipose tissue (WAT) that resembles brown fat. The biologic effects of NPs are negatively regulated by the NP clearance receptor (NPRC), which binds and degrades NPs. Knockout (KO) of NPRC protects against diet induced obesity and improves insulin sensitivity in obese mice. To determine if pharmacologic blockade of NPRC enhanced the beneficial metabolic actions of NPs in type 2 diabetes, we blocked NP clearance in a mouse model of type 2 diabetes using the specific NPRC ligand ANP(4-23). We found that treatment with ANP(4-23) caused a significant decrease in body weight by increasing energy expenditure and reducing fat mass without a change in lean body mass. The decrease in fat mass was associated with a significant improvement in insulin sensitivity and reduced serum insulin levels. These beneficial effects were accompanied by a decrease in infiltrating macrophages in adipose tissue, and reduced expression of inflammatory markers in both serum and WAT. These data suggest that inhibiting NP clearance may be an effective pharmacologic approach to promote weight loss and enhance insulin sensitivity in type 2 diabetes. Optimizing the therapeutic approach may lead to useful therapies for obesity and type 2 diabetes.

Neprilysin Inhibitors in Heart Failure: The Science, Mechanism of Action, Clinical Studies, and Unanswered Questions

This article provides a contemporary review and a new perspective on the role of neprilysin inhibition in heart failure (HF) in the context of recent clinical trials and addresses potential mechanisms and unanswered questions in certain HF patient populations. Neprilysin is an endopeptidase that cleaves a variety of peptides such as natriuretic peptides, bradykinin, adrenomedullin, substance P, angiotensin I and II, and endothelin. It has a broad role in cardiovascular, renal, pulmonary, gastrointestinal, endocrine, and neurologic functions. The combined angiotensin receptor and neprilysin inhibitor (ARNi) has been developed with an intent to increase vasodilatory natriuretic peptides and prevent counterregulatory activation of the angiotensin system. ARNi therapy is very effective in reducing the risks of death and hospitalization for HF in patients with HF and New York Heart Association functional class II to III symptoms, but studies failed to show any benefits with ARNi when compared with angiotensin-converting enzyme inhibitors or angiotensin receptor blocker in patients with advanced HF with reduced ejection fraction or in patients following myocardial infarction with left ventricular dysfunction but without HF. These raise the questions about whether the enzymatic breakdown of natriuretic peptides may not be a very effective solution in advanced HF patients when there is downstream blunting of the response to natriuretic peptides or among post-myocardial infarction patients in the absence of HF when there may not be a need for increased natriuretic peptide availability. Furthermore, there is a need for additional studies to determine the long-term effects of ARNi on albuminuria, obesity, glycemic control and lipid profile, blood pressure, and cognitive function in patients with HF.

A new biomarker of cardiac resynchronization therapy response: cGMP to mature BNP ratio

BACKGROUND

Biomarkers that can predict cardiac resynchronization therapy (CRT) response have not yet been identified. The purpose of this study was to assess whether individual measurements of four brain/B-type natriuretic peptide (BNP) forms, coupled with cyclic guanosine monophosphate (cGMP) might contribute to the prediction of echocardiographic CRT responders.

METHODS

A BNP precursor (proBNP) and total BNP (= proBNP + mature BNP) were measured with newly developed kits, while an N-terminal fragment of proBNP (NT-proBNP) and cGMP were measured with commercial kits on the day before CRT implantation. Estimated mature BNP (emBNP = total BNP-proBNP), and the ratio of cGMP to each BNP form, as well as the concentrations of three other BNP forms, were prospectively investigated for their capability in predicting a response to CRT. A CRT responder was defined as an improvement in left ventricular ejection fraction >10% and/or a reduction in left ventricular end-systolic volume >15% at 6-month follow-up.

RESULTS

Out of 77 patients, 46 (60%) were categorized as CRT responders. Among the measurement parameters, only the highest quartile of the cGMP to emBNP ratio was an independent predictor of CRT responders (odds ratio 4.87, 95% confidence interval 1.25-18.89, p = 0.02). The cGMP to emBNP ratio was associated with the cumulative events of heart failure hospitalization within one year following CRT implantation (log-rank p = 0.029).

CONCLUSIONS

The cGMP to emBNP ratio could be utilized as a predictive biomarker of CRT responders. (Clinical Study on Responder Prediction in Cardiac Resynchronization Therapy Using Individual Molecular Measurement of Natriuretic Peptide: UMIN R000038927).

Effects of phosphodiesterase V inhibition alone and in combination with BNP on cardiovascular and renal response to volume load in human preclinical diastolic dysfunction

Preclinical diastolic dysfunction (PDD) results in impaired cardiorenal response to volume load (VL) which may contribute to the progression to clinical heart failure with preserved ejection fraction (HFpEF). The objective was to evaluate if phosphodiesterase V inhibition (PDEVI) alone or combination PDEVI plus B-type natriuretic peptide (BNP) administration will correct the impaired cardiorenal response to VL in PDD. A randomized double-blinded placebo-controlled cross-over study was conducted in 20 subjects with PDD, defined as left ventricular ejection fraction (LVEF) >50% with moderate or severe diastolic dysfunction by Doppler echocardiography and without HF diagnosis or symptoms. Effects of PDEVI with oral tadalafil alone and tadalafil plus subcutaneous (SC) BNP, administered prior to acute volume loading, were assessed. Tadalafil alone did not result in improvement in cardiac response to VL, as measured by LVEF, LV end diastolic volume, left atrial volume (LAV), or right ventricular systolic pressure (RVSP). Tadalafil plus SC BNP resulted in improved cardiac response to VL, with increased LVEF (4.1 vs. 1.8%, p = 0.08) and heart rate (4.3 vs. 1.6 bpm, p = 0.08), and reductions in both LAV (-4.3 ± 10.4 vs. 2.8 ± 6.6 ml, p = 0.03) and RVSP (-4.0 ± 3.0 vs. 2.1 ± 6.0 mmHg, p < 0.01) versus tadalafil alone. Plasma and urinary cyclic guanosine monophosphate (cGMP) excretion levels were higher (11.3 ± 12.3 vs. 1.7 ± 3.8 pmol/ml, 1851.0 ± 1386.4 vs. 173.4 ± 517.9 pmol/min, p < 0.01) with tadalafil plus SC BNP versus tadalafil alone. There was no improvement in renal response as measured by GFR, renal plasma flow, sodium excretion, and urine flow with tadalafil plus SC BNP compared to tadalafil alone. In subjects with PDD, tadalafil alone resulted in no improvement in cardiac adaptation, while tadalafil and SC BNP resulted in enhanced cardiac adaptation to VL. TRIAL REGISTRATION: ClinicalTrials.gov NCT01544998.

Angiotensin Receptor-Neprilysin Inhibitors and the Natriuretic Peptide Axis

PURPOSE OF THE REVIEW

The purpose of this review is to describe the effects of angiotensin receptor neprilysin inhibitor (ARNI) therapy on the natriuretic peptide axis (NPA), with a particular focus on B-type natriuretic peptide (BNP), atrial natriuretic peptide (ANP), and C-type natriuretic peptide (CNP) to better understand the biology behind the improved outcomes in patients with heart failure with reduced ejection fraction (HFrEF).

RECENT FINDINGS

BNP, ANP, and CNP are the three main natriuretic peptides (NP); they share a common structure and ultimately mediate their actions by activating cyclic guanosine monophosphate (cGMP). ARNI therapy results in a decrease of N-terminal pro-BNP (NT-proBNP) and increase of BNP levels respectively. It is been questioned whether these changes may result from unique laboratory assays characteristics rather than actual biological implications. It appears to be that the prognostic accuracy of BNP for cardiovascular outcomes remains independent and comparable to that of NT-proBNP while on ARNI therapy. ANP levels also increase with ARNI therapy, but no consistent change has been described for CNP levels. There is evidence that the changes in BNP and NT-proBNP correlate with improvement in echocardiographic parameters of volume and function. The dual effect of neprilysin inhibition and angiotensin receptor blockade has substantial implications on the natriuretic peptide axis (NPA). The changes seen in BNP and NT-proBNP specifically have shown to correlate with improvement in echocardiographic parameters. Further results exploring the biologic effects of ARNI therapy on other NPs are still pending and likely will provide further insights in the mechanisms behind the improvement in cardiac function and clinical outcomes.

Metabonomics Analysis of Myocardial Metabolic Dysfunction in Patients with Cardiac Natriuretic Peptide Resistance

Brain natriuretic peptide (BNP) is an important biological marker and regulator of cardiac function. BNP resistance is characterized by high concentrations of less functionally effective BNP and common in heart failure (HF) patients. However, the roles and consequences of BNP resistance remain poorly understood. Investigate the effects of cardiac BNP resistance and identify potential metabolic biomarkers for screening and diagnosis. Thirty patients and thirty healthy subjects were enrolled in this study. Cardiac functions were evaluated by echocardiography. The plasma levels of cyclic guanosine monophosphate (cGMP) and BNP were measured by enzyme-linked immunosorbent assay (ELISA) and the cGMP/BNP ratio is calculated to determine cardiac natriuretic peptide resistance. Liquid chromatograph tandem mass spectrometry (LC-MS) based untargeted metabolomics analysis was applied to screen metabolic changes. The cGMP/BNP ratio was markedly lower in HF patients than controls. The cGMP/BNP ratio and ejection fraction (EF) were strongly correlated (R² = 0.676, P < 0.05). Importantly, metabolic profiles were substantially different between HF patients and healthy controls. Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis demonstrated that the differentially expressed metabolites are involved in signaling pathways that regulate cardiac functions. In HF patients, BNP resistance develops in association with a reduction in heart function and metabolic remodeling. It suggests possible functional roles of BNP resistance in the regulation of cardiac metabolism.

Cardiac Versus Renal Response to Volume Expansion in Preclinical Systolic Dysfunction With PDEV Inhibition and BNP

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In preclinical systolic dysfunction, defined as left ventricular systolic dysfunction with no heart failure signs or symptoms, impairment in cardiorenal response to volume expansion may lead to symptomatic heart failure. Rescue of this impaired process in preclinical disease may prevent development of symptomatic heart failure.

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In preclinical systolic dysfunction, inhibition of phosphodiesterase-V in combination with exogenous B-type natriuretic peptide administration results in improved cardiac function but worsened renal function in response to acute volume expansion.

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Future studies are needed to further define the physiological effects and long-term outcomes of phosphodiesterase-V inhibition and exogenous BNP administration. Understanding the cardiorenal effects and outcomes of combination phosphodiesterase-V with exogenous B-type natriuretic peptide may affect the clinical management of patients with preclinical systolic dysfunction and renal dysfunction.

Impaired cardiorenal response to acute saline volume expansion in preclinical systolic dysfunction (PSD) may lead to symptomatic heart failure. The objective was to determine if combination phosphodiesterase-V inhibition and exogenous B-type natriuretic peptide (BNP) administration may enhance cardiorenal response. A randomized double-blinded, placebo-controlled study was conducted in 21 subjects with PSD and renal dysfunction. Pre-treatment with tadalafil and subcutaneous BNP resulted in improved cardiac function, as evidenced by improvement in ejection fraction, left atrial volume index, and left ventricular end-diastolic volume. However, there was reduced renal response with reduction in renal plasma flow, glomerular filtration rate, and urine flow. (Tadalafil and Nesiritide as Therapy in Pre-clinical Heart Failure; NCT01544998)

Associations Between the Cyclic Guanosine Monophosphate Pathway and Cardiovascular Risk Factors: MESA

Background

cGMP mediates numerous cardioprotective functions and is a potential therapeutic target for cardiovascular disease. Preclinical studies suggest that plasma cGMP is reflective of natriuretic peptide stimulation. Epidemiologic associations between cGMP and natriuretic peptide, as well as cardiovascular disease risk factors, are unknown.

Methods and Results

We measured plasma cGMP in 542 men and 496 women free of cardiovascular disease and heart failure in MESA (Multi‐Ethnic Study of Atherosclerosis). Cross‐sectional associations of N‐terminal pro‐B type natriuretic peptide, sex hormones, and cardiovascular disease/heart failure risk factors with log(cGMP) were analyzed using multivariable linear regression models. Mean (SD) cGMP was 4.7 (2.6) pmol/mL, with no difference between the sexes. After adjusting for cardiovascular risk factors, N‐terminal pro‐B type natriuretic peptide was significantly positively associated with cGMP (P<0.05). Higher blood pressure and lower estimated glomerular filtration rate were associated with higher cGMP (P<0.05). Triglyceride levels, total/high‐density lipoprotein cholesterol ratio, presence of diabetes mellitus, and the homeostatic model assessment of insulin resistance were inversely associated with cGMP (P<0.05). Among women, free testosterone and dehydroepiandrosterone were inversely associated with cGMP, while sex hormone binding globulin was positively associated (P<0.05).

Conclusions

In a community‐cohort, plasma cGMP was associated with natriuretic peptide signaling. Higher blood pressure and greater renal dysfunction were positively associated with cGMP, while adverse metabolic risk factors were inversely associated. Increased androgenicity in postmenopausal women was inversely associated with cGMP. These novel associations further our understanding of the role of cGMP in a general population.

B-type natriuretic peptide and its role in altering Ca2+-regulatory proteins in heart failure-mechanistic insights

Heart failure (HF) is a worldwide disease with high levels of morbidity and mortality. The pathogenesis of HF is complicated and involves imbalances in hormone and electrolyte. B-type natriuretic peptide (BNP) has served as a biomarker of HF severity, and in recent years, it has been used to treat the disease, thanks to its cardio-protective effects, such as diuresis, natriuresis, and vasodilatation. In stage C/D HF, symptoms are severe despite elevated BNP. Disturbances in Ca²⁺ homeostasis are often a dominating feature of the disease, causing Ca²⁺-regulatory protein dysfunction, including reduced expression and activity of sarcoplasmic reticulum Ca²⁺-ATPase2a (SERCA2a), impaired ryanodine receptors (RYRs) function, intensive Na⁺-Ca²⁺ exchanger (NCX), and downregulation of S100A1. The relationship between natriuretic peptides (NPs) and Ca²⁺-regulatory proteins has been widely studied and represents important mechanisms in the etiology of HF. In this review, we present evidence that BNP may regulate Ca²⁺-regulatory proteins, in particular, suppressing SERCA2a and S100A1 expression. However, relationships between BNP and other Ca²⁺-regulatory proteins remain vague.

Skeletal muscle alterations in tachycardia-induced heart failure are linked to deficient natriuretic peptide signalling and are attenuated by RAS-/NEP-inhibition

Background

Heart failure induced cachexia is highly prevalent. Insights into disease progression are lacking.

Methods

Early state of left ventricular dysfunction (ELVD) and symptomatic systolic heart failure (HF) were both induced in rabbits by tachypacing. Tissue of limb muscle (LM) was subjected to histologic assessment. For unbiased characterisation of early and late myopathy, a proteomic approach followed by computational pathway-analyses was performed and combined with pathway-focused gene expression analyses. Specimen of thoracic diaphragm (TD) served as control for inactivity-induced skeletal muscle alterations. In a subsequent study, inhibition of the renin-angiotensin-system and neprilysin (RAS-/NEP) was compared to placebo.

Results

HF was accompanied by loss of protein content (8.7±0.4% vs. 7.0±0.5%, mean±SEM, control vs. HF, p<0.01) and a slow-to-fast fibre type switch, establishing hallmarks of cachexia. In ELVD, the enzymatic set-up of LM and TD shifted to a catabolic state. A disturbed malate-aspartate shuttle went well with increased enzymes of glycolysis, forming the enzymatic basis for enforced anoxic energy regeneration. The histological findings and the pathway analysis of metabolic results drew the picture of suppressed PGC-1α signalling, linked to the natriuretic peptide system. In HF, natriuretic peptide signalling was desensitised, as confirmed by an increase in the ratio of serum BNP to tissue cGMP (57.0±18.6pg/ml/nM/ml vs. 165.8±16.76pg/ml/nM/ml, p<0.05) and a reduced expression of natriuretic peptide receptor-A. In HF, combined RAS-/NEP-inhibition prevented from loss in protein content (8.7±0.3% vs. 6.0±0.6% vs. 8.3±0.9%, Baseline vs. HF-Placebo vs. HF-RAS/NEP, p<0.05 Baseline vs. HF-Placebo, p = 0.7 Baseline vs. HF-RAS/NEP).

Conclusions

Tachypacing-induced heart failure entails a generalised myopathy, preceding systolic dysfunction. The characterisation of “pre-cachectic” state and its progression is feasible. Early enzymatic alterations of LM depict a catabolic state, rendering LM prone to futile substrate metabolism. A combined RAS-/NEP-inhibition ameliorates cardiac-induced myopathy independent of systolic function, which could be linked to stabilised natriuretic peptide/cGMP/PGC-1α signalling.

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.

Targeting phosphodiesterase 5 as a therapeutic option against myocardial ischaemia/reperfusion injury and for treating heart failure

Phosphodiesterase type 5 (PDE5) selectively hydrolyses the second messenger cGMP into 5'-GMP, thereby regulating its intracellular concentrations. Dysregulation of the cGMP-dependent pathway plays a significant role in various cardiovascular diseases. Therefore, its modulation by drugs, such as PDE5 inhibitors, may represent an effective therapeutic approach. There are currently four PDE5 inhibitors available for the treatment of erectile dysfunction: sildenafil, vardenafil, tadalafil and avanafil. Sildenafil and tadalafil have also received Food and Drug Administration approval for the treatment of pulmonary arterial hypertension. This review summarizes the pharmacological aspects and clinical potential of PDE5 inhibition for the treatment of myocardial ischaemia/reperfusion injury and heart failure.

LINKED ARTICLES

This article is part of a themed section on Inventing New Therapies Without Reinventing the Wheel: The Power of Drug Repurposing. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v175.2/issuetoc.

Pulmonary vasodilation by phosphodiesterase 5 inhibition is enhanced and nitric oxide independent in early pulmonary hypertension after myocardial infarction

Myocardial infarction (MI) may result in pulmonary hypertension (PH). Inhibition of phosphodiesterase 5 (PDE5), the enzyme responsible for the breakdown of cGMP in vascular smooth muscle, has become part of the contemporary therapeutic armamentarium for pulmonary arterial hypertension and may also be beneficial for PH secondary to MI. Nitric oxide (NO) is an important activator of cGMP synthesis and can be enhanced in early PH and decreased in severe PH. In the present study, we investigated if PDE5 inhibition ameliorates pulmonary hemodynamics in swine with PH secondary to MI and whether NO is essential. The PDE5 inhibitor EMD360527 was administered in awake, chronically instrumented swine with or without MI. At rest, PDE5 inhibition produced pulmonary vasodilation as evidenced by a decrease in pulmonary vascular resistance, which was more pronounced in MI ( n = 5) compared with normal swine ( n = 10, P ≤ 0.01) and was accompanied by an increase in stroke volume in MI swine. Both pulmonary vasodilation and increased stroke volume were maintained during exercise, suggesting that this therapy may improve exercise capacity in patients with PH secondary to MI. Interestingly, prior inhibition of NO significantly enhanced ( P ≤ 0.01) pulmonary vasodilation by PDE5 inhibition in both normal ( n = 8) and MI swine ( n = 5, P ≤ 0.05 vs. normal). This suggests that the increased vasodilator responses to PDE5 inhibition after MI were not due to an increase in NO-induced cGMP production. These observations indicate that PDE5 inhibition represents an interesting pharmacotherapeutic approach in early PH after a recent MI to prevent overt PH. NEW & NOTEWORTHY This research article is the first to describe that pulmonary vasodilation to phosphodiesterase 5 inhibition is enhanced and nitric oxide independent in resting and exercising swine with pulmonary hypertension as a result of myocardial infarction. This suggests that phosphodiesterase 5 inhibition can normalize pulmonary hemodynamics in postcapillary pulmonary hypertension after a recent myocardial infarction and may improve exercise capacity.

A comprehensive review on the potential therapeutic benefits of phosphodiesterase inhibitors on cardiovascular diseases

Phosphodiesterases are a group of enzymes that hydrolyze cyclic nucleotides, which assume a key role in directing intracellular levels of the second messengers' cAMP and cGMP, and consequently cell function. The disclosure of 11 isoenzyme families and our expanded knowledge of their functions at the cell and molecular level stimulate the improvement of isoenzyme selective inhibitors for the treatment of various diseases, particularly cardiovascular diseases. Hence, future and new mechanistic investigations and carefully designed clinical trials could help reap additional benefits of natural/synthetic PDE inhibitors for cardiovascular disease in patients. This review has concentrated on the potential therapeutic benefits of phosphodiesterase inhibitors on cardiovascular diseases.

Chronic heart failure as a state of reduced effectiveness of the natriuretic peptide system: implications for therapy

Natriuretic peptides (NPs) promote diuresis, natriuresis and vasodilation in early chronic heart failure (CHF), countering renin-angiotensin-aldosterone system (RAAS) and sympathetic nervous system (SNS) overstimulation. Despite dramatic increases in circulating NP concentrations as CHF progresses, their effects become blunted. Increases in diuresis, natriuresis, and vasodilation after administration of exogenous atrial (ANP) or brain (BNP) natriuretic peptides are attenuated in patients with advanced CHF compared with controls. Several major factors may account for the reduced effectiveness of the natriuretic peptide system (NPS) in CHF. First, there is reduced availability of active forms of NPs, namely BNP. Second, target organ responsiveness becomes diminished. Third, the counter-regulatory hormones of the RAAS and SNS, and endothelin-1 become over-activated. Therefore, pharmacological approaches to enhance the functional effectiveness of the NPS in CHF have been explored in recent years. In terms of clinical outcomes, studies of synthetic BNP, or of neprilysin inhibitors alone or associated with an angiotensin converting enzyme inhibitor, have been controversial for several reasons. Recently, however, encouraging results have been obtained with the angiotensin receptor neprilysin inhibitor sacubitril/valsartan. The available data show that treatment with sacubitril/valsartan is associated with increased levels of NPs and their intracellular mediator cyclic guanosine monophosphate, suggesting improved functional effectiveness of the NPS, in addition to beneficial effects on mortality and morbidity outcomes. Therefore, combined targeting of the NPS and RAAS with sacubitril/valsartan emerges as the current optimal approach for redressing the neurohormonal imbalance in CHF.

Evolving Concepts of Pulmonary Hypertension Secondary to Left Heart Disease

Pulmonary hypertension associated with left heart disease is the most common form of pulmonary hypertension. Although its pathophysiology remains incompletely understood, it is now well recognized that the presence of pulmonary hypertension is associated with a worse prognosis. Right ventricular failure has independent and additive prognostic value over pulmonary hypertension for adverse outcomes in left heart disease. Recently, several new terminologies have been introduced to better define and characterize the nature and severity of pulmonary hypertension. Several new treatment options including the use of pulmonary arterial hypertension specific therapies are being considered, but there is lack of evidence. Here, we review the recent advances in this field and summarize the diagnostic and therapeutic modalities of use in the management of pulmonary hypertension associated with left heart disease.

Combined Angiotensin Receptor Antagonism and Neprilysin Inhibition

Heart failure affects ≈5.7 million people in the United States alone. Angiotensin-converting enzyme inhibitors, angiotensin receptor blockers, β-blockers, and aldosterone antagonists have improved mortality in patients with heart failure and reduced ejection fraction, but mortality remains high. In July 2015, the US Food and Drug Administration approved the first of a new class of drugs for the treatment of heart failure: Valsartan/sacubitril (formerly known as LCZ696 and currently marketed by Novartis as Entresto) combines the angiotensin receptor blocker valsartan and the neprilysin inhibitor prodrug sacubitril in a 1:1 ratio in a sodium supramolecular complex. Sacubitril is converted by esterases to LBQ657, which inhibits neprilysin, the enzyme responsible for the degradation of the natriuretic peptides and many other vasoactive peptides. Thus, this combined angiotensin receptor antagonist and neprilysin inhibitor addresses 2 of the pathophysiological mechanisms of heart failure: activation of the renin-angiotensin-aldosterone system and decreased sensitivity to natriuretic peptides. In the Prospective Comparison of ARNI With ACEI to Determine Impact on Global Mortality and Morbidity in Heart Failure (PARADIGM-HF) trial, valsartan/sacubitril significantly reduced mortality and hospitalization for heart failure, as well as blood pressure, compared with enalapril in patients with heart failure, reduced ejection fraction, and an elevated circulating level of brain natriuretic peptide or N-terminal pro-brain natriuretic peptide. Ongoing clinical trials are evaluating the role of valsartan/sacubitril in the treatment of heart failure with preserved ejection fraction and hypertension. We review here the mechanisms of action of valsartan/sacubitril, the pharmacological properties of the drug, and its efficacy and safety in the treatment of heart failure and hypertension.

Natriuretic Peptide Resistance of Mesenteric Arteries in Spontaneous Hypertensive Rat Is Alleviated by Exercise

Proximal resistance vessels, such as the mesenteric arteries, contribute substantially to the peripheral resistance. The reactivity of resistance vessels to vasoactive substance like natriuretic peptides plays an important role in the regulation of blood pressure. In current study, we investigated the reactivity of mesenteric arteries to atrial natriuretic peptide (ANP), a well known vasodilating factor, in spontaneously hypertensive rats (SHR), as well as the effects of exercise training on it. As a result, ANP-induced vasorelaxation was attenuated in SHR with significantly increased phosphodiesterase type 5 (PDE5), and decreased cGMP/ANP ratio, compared with WKY rats as control. Intriguingly, the decreased reactivity to ANP in SHR was markedly reversed by exercise training. In addition, ANP resistance of in vitro mesenteric arteries was diminished by sildenafil a potent selective inhibitor of PDE5. In conclusion, ANP resistance occurs in resistance vessels of SHR, suggesting predisposition to hypertension, which can be reversed by exercise.

Angiotensin receptor neprilysin inhibition in heart failure: mechanistic action and clinical impact

Heart failure (HF) is an increasingly common syndrome associated with high mortality and economic burden, and there has been a paucity over the past decade of new pharmacotherapies that improve outcomes. However, recent data from a large randomized controlled trial compared the novel agent LCZ696, a dual-acting angiotensin receptor blocker and neprilysin inhibitor (ARNi), with the well established angiotensin-converting enzyme (ACE) inhibitor enalapril and found significant reduction in mortality among the chronic reduced ejection fraction HF population. Preclinical and clinical data suggest that neprilysin inhibition provides beneficial outcomes in HF patients by preventing the degradation of natriuretic peptides and thereby promoting natriuresis and vasodilatation and counteracting the negative cardiorenal effects of the up-regulated renin-angiotensin-aldosterone system. Agents such as omapatrilat combined neprilysin and ACE inhibition but had increased rates of angioedema. Goals of an improved safety profile provided the rationale for the development of the ARNi LCZ696. Along with significant reductions in mortality and hospitalizations, clinical trials suggest that LCZ696 may improve surrogate markers of HF severity. In this paper, we review the preclinical and clinical data that led to the development of LCZ696, the understanding of the underlying mechanistic action, and the robust clinical impact that LCZ696 may have in the near future.

Mechanisms of renal hyporesponsiveness to BNP in heart failure

The B-type natriuretic peptide (BNP), a member of the family of vasoactive peptides, is a potent natriuretic, diuretic, and vasodilatory peptide that contributes to blood pressure and volume homeostasis. These attributes make BNP an ideal drug that could aid in diuresing a fluid-overloaded patient who had poor or worsening renal function. Despite the potential benefits of BNP, accumulating evidence suggests that simply increasing the amount of circulating BNP does not necessarily increase natriuresis in patients with heart failure (HF). Moreover, despite high BNP levels, natriuresis falls when HF progresses from a compensated to a decompensated state, suggesting the emergence of renal resistance to BNP. Although likely multifactorial, several mechanisms have been proposed to explain renal hyporesponsiveness in HF, including, but not limited to, decreased renal BNP availability, down-regulation of natriuretic peptide receptors, and altered BNP intracellular signal transduction pathways. Thus, a better understanding of renal hyporesponsiveness in HF is required to devise strategies to develop novel agents and technologies that directly restore renal BNP efficiency. It is hoped that development of these new therapeutic approaches will serve to limit sodium retention in patients with HF, which may ultimately delay the progression to overt HF.

Obesity and natriuretic peptides, BNP and NT-proBNP: mechanisms and diagnostic implications for heart failure

Many advances have been made in the diagnosis and management of heart failure (HF) in recent years. Cardiac biomarkers are an essential tool for clinicians: point of care B-type natriuretic peptide (BNP) and its N-terminal counterpart (NT-proBNP) levels help distinguish cardiac from non-cardiac causes of dyspnea and are also useful in the prognosis and monitoring of the efficacy of therapy. One of the major limitations of HF biomarkers is in obese patients where the relationship between BNP and NT-proBNP levels and myocardial stiffness is complex. Recent data suggest an inverse relationship between BNP and NT-proBNP levels and body mass index. Given the ever-increasing prevalence of obesity world-wide, it is important to understand the benefits and limitations of HF biomarkers in this population. This review will explore the biology, physiology, and pathophysiology of these peptides and the cardiac endocrine paradox in HF. We also examine the clinical evidence, mechanisms, and plausible biological explanations for the discord between BNP levels and HF in obese patients.

Heart failure with preserved ejection fraction: mechanisms, clinical features, and therapies

The clinical syndrome comprising heart failure (HF) symptoms but with a left ventricular ejection fraction (EF) that is not diminished, eg, HF with preserved EF, is increasingly the predominant form of HF in the developed world, and soon to reach epidemic proportions. It remains among the most challenging of clinical syndromes for the practicing clinician and scientist alike, with a multitude of proposed mechanisms involving the heart and other organs and complex interplay with common comorbidities. Importantly, its morbidity and mortality are on par with HF with reduced EF, and as the list of failed treatments continues to grow, HF with preserved EF clearly represents a major unmet medical need. The field is greatly in need of a more unified approach to its definition and view of the syndrome that engages integrative and reserve pathophysiology beyond that related to the heart alone. We need to reflect on prior treatment failures and the message this is providing, and redirect our approaches likely with a paradigm shift in how the disease is viewed. Success will require interactions between clinicians, translational researchers, and basic physiologists. Here, we review recent translational and clinical research into HF with preserved EF and give perspectives on its evolving demographics and epidemiology, the role of multiorgan deficiencies, potential mechanisms that involve the heart and other organs, clinical trials, and future directions.

Natriuretic peptides: molecular biology, pathophysiology and clinical implications for the cardiologist

Natriuretic peptides (NPs) counter the effects of volume overload or adrenergic activation of the cardiovascular system. They are able to induce arterial vasodilatations, natriuresis and diuresis, and they reduce the activities of the renin-angiotensin-aldosterone system and the sympathetic nervous system. However, in addition to wall stress, other factors have been associated with elevated natriuretic peptide levels. Since 2000, because of their characteristics, NPs have become quantitative plasma biomarkers of heart failure. Nowadays, NPs play an important role not only in the diagnosis of heart failure, but also for a prognostic purpose and a guide to medical therapy. Finally, a new drug that modulates the NP system or recombinant analogs of NPs are now available in patients with heart failure.

Acute effects of sildenafil and dobutamine in the hypertrophic and failing right heart in vivo

Abstract The purpose of this study was to investigate whether acute intravenous administration of the phosphodiesterase type 5 (PDE-5) inhibitor sildenafil in a single clinically relevant dose improves the in vivo function of the hypertrophic and failing right ventricle (RV). Wistar rats ([Formula: see text]) were subjected to pulmonary trunk banding (PTB) causing RV hypertrophy and failure. Four weeks after surgery, they were randomized to receive an intravenous bolus dose of sildenafil (1 mg/kg; [Formula: see text]), vehicle ([Formula: see text]), or dobutamine (10 μg/kg; [Formula: see text]). Invasive RV pressures were recorded continuously, and transthoracic echocardiography was performed 1, 5, 15, 25, 35, 50, 70, and 90 minutes after injecting the bolus. Cardiac function was compared to baseline measurements to evaluate the in vivo effects of each specific treatment. The PTB procedure caused significant hypertrophy, cardiac fibrosis, and reduction in RV function evaluated by echocardiography (TAPSE) and invasive pressure measurements. Sildenafil did not improve the function of the hypertrophic failing right heart in vivo, measured by TAPSE, RV systolic pressure (RVsP), and dp/dtmax. Dobutamine improved RV function 1 minute after injection measured by TAPSE ([Formula: see text] vs. [Formula: see text] cm; [Formula: see text]), RVsP ([Formula: see text] vs. [Formula: see text] mmHg; [Formula: see text]), and dp/dtmax ([Formula: see text] vs. [Formula: see text] mmHg/s; [Formula: see text]). Acute administration of the PDE-5 inhibitor sildenafil in a single clinically relevant dose did not modulate the in vivo function of the hypertrophic failing right heart of the rat measured by echocardiography and invasive hemodynamics. In the same model, dobutamine acutely improved RV function.

Pathological cardiac hypertrophy alters intracellular targeting of phosphodiesterase type 5 from nitric oxide synthase-3 to natriuretic peptide signaling

BACKGROUND

In the normal heart, phosphodiesterase type 5 (PDE5) hydrolyzes cGMP coupled to nitric oxide- (specifically from nitric oxide synthase 3) but not natriuretic peptide (NP)-stimulated guanylyl cyclase. PDE5 is upregulated in hypertrophied and failing hearts and is thought to contribute to their pathophysiology. Because nitric oxide signaling declines whereas NP-derived cGMP rises in such diseases, we hypothesized that PDE5 substrate selectivity is retargeted to blunt NP-derived signaling.

METHODS AND RESULTS

Mice with cardiac myocyte inducible PDE5 overexpression (P5(+)) were crossed to those lacking nitric oxide synthase 3 (N3(-)), and each model, the double cross, and controls were subjected to transaortic constriction. P5(+) mice developed worse dysfunction and hypertrophy and enhanced NP stimulation, whereas N3(-) mice were protected. However, P5(+)/N3(-) mice behaved similarly to P5(+) mice despite the lack of nitric oxide synthase 3-coupled cGMP generation, with protein kinase G activity suppressed in both models. PDE5 inhibition did not alter atrial natriuretic peptide-stimulated cGMP in the resting heart but augmented it in the transaortic constriction heart. This functional retargeting was associated with PDE5 translocation from sarcomeres to a dispersed distribution. P5(+) hearts exhibited higher oxidative stress, whereas P5(+)/N3(-) hearts had low levels (likely owing to the absence of nitric oxide synthase 3 uncoupling). This highlights the importance of myocyte protein kinase G activity as a protection for pathological remodeling.

CONCLUSIONS

These data provide the first evidence for functional retargeting of PDE5 from one compartment to another, revealing a role for natriuretic peptide-derived cGMP hydrolysis by this esterase in diseased heart myocardium. Retargeting likely affects the pathophysiological consequence and the therapeutic impact of PDE5 modulation in heart disease.

Phosphodiesterase 5 inhibition protects against increased intra-abdominal pressure-induced renal dysfunction in experimental congestive heart failure

AIMS

Congestive heart failure (CHF) is associated with impaired renal function. Previously, we have demonstrated that rats with decompensated CHF exhibited exaggerated sensitivity to the adverse renal effects of increased increased intra-abdominal pressure (IAP) as compared with normal controls. This study tested whether phosphodiesterase 5 (PDE5) inhibition protects against the adverse renal effects of increased IAP in rats with CHF.

METHODS AND RESULTS

Following baseline periods, rats with compensated and decompensated CHF induced by the placement of an aorto-caval fistula (ACF), rats with myocardial infarction (MI) induced by left anterior descending (LAD) artery ligation, and sham controls were subjected to consecutive IAPs: 7, 10, or 14 mmHg. Urine flow (V), Na(+) excretion (U(Na)V), glomerular filtration rate (GFR), and renal plasma flow (RPF) were determined. The effects of pre-treatment with tadalafil on the adverse renal effects of IAP were examined in rats with decompensated CHF and MI. Elevation of IAP to 10 and 14 mmHg produced linear reductions in these parameters. Basal renal function and haemodynamics were lower in CHF rats. Decompensated CHF rats and MI rats that were subjected to 10 and 14 mmHg exhibited exaggerated declines in V, U(Na)V, GFR, and RPF. In contrast, no adverse renal effects were observed in rats with compensated CHF subjected to IAP. Pre-treatment of decompensated CHF rats and MI rats with tadalafil ameliorated the adverse renal effects of high IAP.

CONCLUSION

Decompensated CHF and MI rats are vulnerable to the adverse renal effects of IAP. Tadalafil abolishes IAP-induced renal dysfunction, supporting a therapeutic role for PDE5 inhibition in CHF associated with ascites.

Pathophysiology and therapy of cardiac dysfunction in Duchenne muscular dystrophy

Cardiac dysfunction is a frequent manifestation of Duchenne muscular dystrophy (DMD) and a common cause of death for individuals with this condition. Early diastolic dysfunction and focal fibrosis proceed to dilated cardiomyopathy (DCM), complicated by heart failure and arrhythmia in most patients. Improvements in the management of respiratory insufficiency in DMD have improved lifespan and overall prognosis, but heart failure and sudden death continue to impact survival and quality of life for people with DMD. Since the specific mechanisms resulting in heart failure for people with DMD are poorly understood, current treatments are not targeted, but rely on approaches that are considered standard for DCM. These approaches include angiotensin-converting enzyme (ACE) inhibitors and β-adrenoceptor antagonists. Data from one trial in DMD support the use of ACE inhibitors before the onset of left ventricular dysfunction. Angiotensin receptor blockers have shown similar efficacy to ACE inhibitors in numerous studies of dilated cardiomyopathy, and are a good choice for patients who cannot tolerate ACE inhibition. The pathogenesis of DMD-associated cardiomyopathy may be similar to other genetic disorders of the cytoskeletal complex of ventricular myocytes, though unique features offer targeted opportunities to impact treatment. Novel areas of investigation are focused on the regulatory role of dystrophin in relation to neuronal nitric oxide synthase (nNOS) and transient receptor potential canonical channels (TRPC). Inhibition of phosphodiesterase-5 (PDE5) addresses several aspects of regulatory dysfunction induced by dystrophin deficiency, and studies with PDE5-inhibitors have shown benefits in murine models of DMD. PDE5-inhibitors are currently under investigation in at least one study in humans. This article focuses on mechanisms of cardiac dysfunction, as well as potential targets for pharmacologic manipulation to prevent or improve cardiomyopathy in DMD.

Thirty years of the heart as an endocrine organ: physiological role and clinical utility of cardiac natriuretic hormones

Thirty years ago, De Bold et al. ( 20 ) reported that atrial extracts contain some biologically active peptides, which promote a rapid and massive diuresis and natriuresis when injected in rats. It is now clear that the heart also exerts an endocrine function and in this way plays a key role in the regulation of cardiovascular and renal systems. The aim of this review is to discuss some recent insights and still-debated findings regarding the cardiac natriuretic hormones (CNHs) produced and secreted by cardiomyocytes (i.e., atrial natriuretic peptide and B-type natriuretic peptide). The functional status of the CNH system depends not only on the production/secretion of CNHs by cardiomyocytes but also on both the peripheral activation of circulating inactive precursor of natriuretic hormones and the transduction of the hormone signal by specific receptors. In this review, we will discuss the data supporting the hypothesis that the production and secretion of CNHs is the result of a complex integration among mechanical, chemical, hemodynamic, humoral, ischemic, and inflammatory inputs. The cross talk among endocrine function, adipose tissue, and sex steroid hormones will be discussed more in detail, considering the clinically relevant relationships linking together cardiovascular risk, sex, and body fat development and distribution. Finally, we will review the pathophysiological role and the clinical relevance of both peripheral maturation of the precursor of B-type natriuretic peptides and hormone signal transduction .

Systems biology and heart failure: concepts, methods, and potential research applications

Dramatic advances in molecular biology dominated twentieth century biomedical science and delineated the function of individual genes and molecules in exquisite detail. However, biological processes cannot be fully understood based on the properties of individual genes and molecules alone, since these elements act in concert to enable the specific functions that make for living cells and organisms. The discipline of systems biology provides a novel conceptual framework for understanding biological phenomenon. Systems biology synthesizes information concerning the interactions of genes and molecules and allows characterization of the supramolecular networks and functional modules that represent the most essential aspects of cell organization and physiology.

Sildenafil Is More Selective Pulmonary Vasodilator Than Prostaglandin E1 in Patients With Pulmonary Hypertension Due to Heart Failure

In some patients, heart failure (HF) is associated with increased pulmonary vascular resistance (PVR). The magnitude and the reversibility of PVR elevation affect the HF management. Sildenafil has been recently recognized as potent PVR-lowering drug in HF. The aim of the study was to compare hemodynamic effects and pulmonary selectivity of sildenafil to prostaglandin E1 (PGE1). Right-heart catheterization was performed in 13 euvolemic advanced HF patients with elevated PVR (6.3±2 Wood´s units). Hemodynamic parameters were measured at the baseline, during i.v. infusion of PGE1 (alprostadil 200 ng∙kg-1∙min-1) and after 40 mg oral dose of sildenafil. Both drugs similarly reduced systemic vascular resistance (SVR), but sildenafil had higher effect on PVR (–28 % vs. –49 %, p=0.05) and transpulmonary pressure gradient than PGE1. The PVR/SVR ratio – an index of pulmonary selectivity, did not change after PGE1 (p=0.7) but it decreased by –32 % (p=0.004) after sildenafil. Both drugs similarly reduced pulmonary artery mean and wedge pressures and increased cardiac index (+27 % and +28 %). Sildenafil led more often to transplant-acceptable PVR while causing smaller drop of mean systemic pressure than PGE1. In conclusion, vasodilatatory effects of sildenafil in patients with heart failure are more pronounced in pulmonary than in systemic circulation.