Pulmonary vascular effects of sildenafil on the development of chronic pulmonary hypertension in the ovine fetus

Case Report: Persistent Pulmonary Hypertension of the Newborn and Narrowing of the Ductus Arteriosus After Topical Use of Non-Steroidal Anti-Inflammatory During Pregnancy

Background: The use of non-steroidal anti-inflammatory drugs (NSAIDs) during the third trimester of pregnancy can cause premature constriction of the ductus arteriosus. This report describes a case of in utero narrowing of the ductus arteriosus (DA) diagnosed postnatally in a baby with Persistent Pulmonary Hypertension of the Newborn (PPHN), after maternal use of Diclofenac-Epolamine 140 mg patch during the second and third trimester.

Case Presentation: A fetal ultrasounds revealed an enlarged hypertrophic right ventricle at 32 weeks of gestation. Detailed questioning of the mother highlighted that topical Diclofenac (FLECTOR^®) had been used at 26 and at 31 weeks of gestation. An echocardiography performed 8 h postnatally showed supra-systemic pulmonary hypertension, a restrictive ductus arteriosus and a dilated right ventricle. The newborn was treated by inhaled nitric oxide and oral Sildenafil and was discharged from hospital on day 24. He had a complete normalization of his pulmonary vascular resistance on day 48.

Conclusion: This case illustrates the potential fetal and neonatal complications associated with maternal topical Diclofenac medication during pregnancy resulting in antenatal closure of the DA.

Pharmacokinetics and pharmacodynamics of sildenafil in fetal lambs on extracorporeal support

BACKGROUND

Maternal transplacental administration of sildenafil is being considered for a variety of fetal conditions. Clinical translation also requires evaluation of fetal safety in a higher species, such as the fetal lamb. Experiments with the pregnant ewe are curtailed by minimal transplacental transfer as well as limited access to the fetus. The EXTra-uterine Environment for Neonatal Development (EXTEND) model renders the isolated fetal lamb readily accessible and allows for direct fetal administration of sildenafil.

METHODS

Five fetal lambs were placed on extracorporeal support in the EXTEND device and received continuous intravenous (IV) sildenafil (0.3-0.5-0.7 mg/kg/24hr) for a duration of one to seven days. Plasma sildenafil concentrations were sampled at regular intervals to establish the pharmacokinetic profile using population pharmacokinetic modeling. Serial Doppler ultrasound examination, continuous non-invasive hemodynamic monitoring and blood gas analysis were done to evaluate the pharmacodynamic effects and fetal response.

FINDINGS

The target concentration range (47-500 ng/mL) was attained with all doses. Sildenafil induced an immediate and temporary reduction of pulmonary vascular resistance, mean arterial pressure and circuit flow, without change in fetal lactate levels and acid-base status. The duration of the systemic effects increased with the dose.

INTERPRETATION

Immediate temporary pulmonary vascular and systemic hemodynamic changes induced by sildenafil were biochemically well tolerated by fetal lambs on extracorporeal support, with the 0.5 mg/kg/24 h dose balancing rapid attainment of target concentrations with short-lived systemic effects.

RESEARCH IN CONTEXT

None.

SEARCH STRATEGY BEFORE UNDERTAKING THE STUDY

A literature review was conducted searching online databases (Medline, Embase and Cochrane), using search terms: fetal OR prenatal OR antenatal AND sildenafil, without time-limit and excluding human studies. Where relevant, investigators were contacted in order to avoid duplication of work.

EVIDENCE BEFORE THIS STUDY

Prenatal therapy with sildenafil, a phosphodiesterase-5 inhibitor with vasodilatory and anti-remodeling effects on vascular smooth muscle cells, has been considered for a variety of fetal conditions. One multicenter clinical trial investigating the benefit of sildenafil in severe intrauterine growth restriction (the STRIDER-trial) was halted early due to excess mortality in the sildenafil-exposed arm at one treatment site. Such findings demonstrate the importance of extensive preclinical safety assessment in relevant animal models. Transplacentally administered sildenafil leads to decreased pulmonary arterial muscularization, preventing or reducing the occurrence of pulmonary hypertension in rat and rabbit fetuses with diaphragmatic hernia (DH). Validation of these results in a higher and relevant animal model, e.g. fetal lambs, is the next step to advance clinical translation. We recently demonstrated that, in contrast to humans, transplacental transfer of sildenafil in sheep is minimal, precluding the in vivo study of fetal effects at target concentrations using the conventional pregnant ewe model.

ADDED VALUE OF THIS STUDY

We therefore used the extracorporeal support model for fetal lambs, referred to as the EXTra-uterine Environment for Neonatal Development (EXTEND) system, bypassing placental and maternal metabolism, to investigate at what dose the target concentrations are reached, and what the fetal hemodynamic impact and response are. Fetal hemodynamic and metabolic tolerance to sildenafil are a crucial missing element on the road to clinical translation. This is therefore the first study investigating the pharmacokinetics, hemodynamic and biochemical effects of clinical-range concentrations of sildenafil in fetal lambs, free from placental and maternal interference.

IMPLICATIONS OF ALL THE AVAILABLE EVIDENCE

We demonstrated self-limiting pulmonary vasodilation, a decrease of both systemic arterial pressures and circuit flows, induced by clinical range concentrations of sildenafil, without the development of fetal acidosis. This paves the way for further investigation of prenatal sildenafil in fetal lambs on extracorporeal support. A dose of 0.5 mg/kg/24 h offered the best trade-off between rapid achievement of target concentrations and shortest duration of systemic effects. This is also the first study using the EXTEND as a model for pharmacotherapy during pregnancy.

Decreased Cyclic GMP-protein Kinase G signaling impairs Angiogenesis in a Lamb Model of Persistent Pulmonary Hypertension of Newborn

Impaired angiogenesis function of pulmonary artery endothelial cells (PAEC) contributes to persistent pulmonary hypertension of the newborn (PPHN). Decreased nitric oxide (NO) levels in PPHN lead to impaired mitochondrial biogenesis and angiogenesis in the lung; the mechanisms remain unclear. We hypothesized that decreased cGMP-Protein kinase G (PKG) signaling downstream of NO leads to decreased mitochondrial biogenesis and angiogenesis in PPHN. PPHN was induced by ductus arteriosus constriction from 128-136d gestation in fetal lambs. Controls were gestation matched lambs without ductal constriction. PAEC isolated from PPHN lambs were treated with soluble guanylyl cyclase activator, cinaciguat, PKG activator, 8-Br-cGMP or phosphodiesterase-V inhibitor, sildenafil. Lysates were immunoblotted for mitochondrial transcription factors and electron transport chain (ETC) complex proteins I-V. In vitro angiogenesis of PAEC was evaluated by tube formation and scratch recovery assays. cGMP levels were measured by enzyme immunoassay. Fetal lambs with ductal constriction were given sildenafil or control saline by continuous infusion in utero and lung histology, capillary counts, vessel density and right ventricular pressure were assessed at birth. PPHN PAEC showed decreased mitochondrial transcription factors, ETC proteins, and in vitro tube formation and cell migration; these were restored by cinaciguat, 8-Br-cGMP and sildenafil. Cinaciguat and sildenafil increased cGMP levels in PPHN PAEC. Radial alveolar and capillary counts and vessel density were lower and RV pressure and Fulton index higher in PPHN lungs; these were improved by in utero sildenafil infusion. cGMP-PKG signaling is a potential therapeutic target to restore decreased mitochondrial biogenesis and angiogenesis in PPHN.

Sildenafil for Antenatal Treatment of Congenital Diaphragmatic Hernia: From Bench to Bedside

BACKGROUND

Persistent pulmonary hypertension (PPH) is one of the main causes of mortality and morbidity in infants affected by congenital diaphragmatic hernia (CDH). Since the structural changes that lead to PPH take place already in utero, a treatment starting in the prenatal phase may prevent the occurrence of this complication.

OBJECTIVE

To summarize the development process of antenatal sildenafil for CDH.

METHODS

The pharmacokinetics and efficacy of sildenafil have been assessed in the rat and the rabbit model. The transfer of the drug through the human placenta has been measured with the ex-vivo placenta perfusion model. Results from this experiment are being incorporated in a pregnancy-physiologically based pharmacokinetic (p- PBPK) model. A phase I-IIb placental transfer and safety study is ongoing.

RESULTS

Sildenafil administration to pregnant rats and rabbits led to therapeutic foetal drug levels without maternal and foetal toxicity, although it was associated with impaired vascular development in foetuses with nonhypoplastic lungs. Peak concentrations and 24-hour exposure were higher in pregnant rabbits compared to nonpregnant ones. In rat and rabbit foetuses with CDH, sildenafil rescued the lung vascular anomalies and partially improved parenchymal development. Sildenafil crossed the human placenta at a high rate ex-vivo, independently from the initial maternal concentration.

CONCLUSION

There is preclinical evidence that maternally administered sildenafil prevents the vascular changes that lead to PPH in CDH newborns. The phase I/IIb clinical study together with the p-PBPK model will define the maternal dose needed for a therapeutic effect in the foetus. Foetal safety will be investigated both in the clinical study and in the sheep. The final step will be a multicentre, randomized, placebo-controlled trial.

Effects of Eicosapentaenoic Acid (EPA) and Docosahexaenoic Acid (DHA) on Fetal Pulmonary Circulation: An Experimental Study in Fetal Lambs

Background: Persistent pulmonary hypertension of the newborn (PPHN) causes significant morbidity and mortality in neonates. n-3 Poly-unsaturated fatty acids have vasodilatory properties in the perinatal lung. We studied the circulatory effects of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) in fetal sheep and in fetal pulmonary arterial rings. Methods: At 128 days of gestation, catheters were placed surgically in fetal systemic and pulmonary circulation, and a Doppler probe around the left pulmonary artery (LPA). Pulmonary arterial pressure and LPA flow were measured while infusing EPA or DHA for 120 min to the fetus, to compute pulmonary vascular resistance (PVR). The dose effects of EPA or DHA were studied in vascular rings pre-constricted with serotonin. Rings treated with EPA were separated into three groups: E+ (intact endothelium), E− (endothelium stripped) and LNA E+ (pretreatment of E+ rings with l-nitro-arginine). Results: EPA, but not DHA, induced a significant and prolonged 25% drop in PVR (n = 8, p < 0.001). Incubation of vascular rings with EPA (100 µM) caused a maximum relaxation of 60% in the E+ (n = 6), whereas vessel tone did not change in the E− (n = 6, p < 0.001). The vascular effects of EPA were significantly decreased in LNA E+ (n = 6). Incubation with DHA resulted in only a mild relaxation at the highest concentration of DHA (300 µM) compared to E+. Conclusions: EPA induces a sustained pulmonary vasodilatation in fetal lambs. This effect is endothelium- and dose-dependent and involves nitric oxide (NO) production. We speculate that EPA supplementation may improve pulmonary circulation in clinical conditions with PPHN.

The role of phosphodiesterase inhibitors in the management of pulmonary vascular diseases

Phosphodiesterase inhibitors (PDE) can be used as therapeutic agents for various diseases such as dementia, depression, schizophrenia and erectile dysfunction in men, as well as congestive heart failure, chronic obstructive pulmonary disease, rheumatoid arthritis, other inflammatory diseases, diabetes and various other conditions. In this review we will concentrate on one type of PDE, mainly PDE5 and its role in pulmonary vascular diseases.

Pathophysiology of persistent pulmonary hypertension of the newborn: impact of the perinatal environment

The main cause of pulmonary hypertension in newborn babies results from the failure of the pulmonary circulation to dilate at birth, termed 'persistent pulmonary hypertension of the newborn' (PPHN). This syndrome is characterized by sustained elevation of pulmonary vascular resistance, causing extrapulmonary right-to-left shunting of blood across the ductus arteriosus and foramen ovale and severe hypoxaemia. It can also lead to life-threatening circulatory failure. There are many controversial and unresolved issues regarding the pathophysiology of PPHN, and these are discussed. PPHN is generally associated with factors such as congenital diaphragmatic hernia, birth asphyxia, sepsis, meconium aspiration and respiratory distress syndrome. However, the perinatal environment-exposure to nicotine and certain medications, maternal obesity and diabetes, epigenetics, painful stimuli and birth by Caesarean section-may also affect the maladaptation of the lung circulation at birth. In infants with PPHN, it is important to optimize circulatory function. Suggested management strategies for PPHN include: avoidance of environmental factors that worsen PPHN (e.g. noxious stimuli, lung overdistension); adequate lung recruitment and alveolar ventilation; inhaled nitric oxide (or sildenafil, if inhaled nitric oxide is not available); haemodynamic assessment; appropriate fluid and cardiovascular resuscitation and inotropic and vasoactive agents.

Reversal of fetal ductal constriction after maternal restriction of polyphenol-rich foods: an open clinical trial

OBJECTIVE

To test the hypothesis that maternal restriction of polyphenol-rich foods (PRF), which, like non-steroidal anti-inflammatory drugs (NSAID), inhibit prostaglandin synthesis in the third trimester, reverse fetal ductal constriction (DC).

STUDY DESIGN

An open clinical trial of 51 third trimester fetuses with DC with no history of NSAID intake was designed. All mothers were submitted to a food frequency questionnaire and were oriented to withdrawl PRF, being reassessed after 3 weeks. Doppler parameters were assessed before and after discontinuation of these substances. A control group of 26 third trimester normal fetuses, with no ductus arteriosus (DA) constriction, in which no dietary intervention was offered, was reviewed after 3 weeks. Student's t-test and Wilcoxon's test were used.

RESULT

Mean gestational age was 32±3 weeks (28 to 37 weeks). After discontinuation of PRF (≥3 weeks), 48/51 fetuses (96%) showed complete reversal of DC, with decrease in mean ductal systolic velocity (1.74±0.20 m s(-1) to 1.31±0.34 m s(-1), P<0.001), mean diastolic velocity (0.33±0.09 m s(-1) to 0.21±0.07 m s(-1), P<0.001) and mean right to left ventricular dimension ratio (1.37±0.26 to 1.12±0.17, P<0.001) and increase in mean ductal pulsatility index (PI) (1.98±0.36 to 2.46±0.23, P<0.001). Median daily maternal consumption of PRF was 286 mg per day and decreased after orientation to 0 mg per day, P<0.001. In the control group, with GA of 32±4 w (29-37 w), there was no significant differences in median daily maternal consumption of PRF, mean ductal systolic velocitiy, diastolic velocity, PI and right ventricular to left ventricular diameter ratio (RV/LV) ratio.

CONCLUSION

Reduction of maternal PRF intake during pregnancy, especially in the third trimester, is followed by complete reversal of DC (wide open DA), which may influence maternal dietary habits in late pregnancy.

Antenatal sildenafil treatment attenuates pulmonary hypertension in experimental congenital diaphragmatic hernia

BACKGROUND

Lung hypoplasia and persistent pulmonary hypertension of the newborn limit survival in congenital diaphragmatic hernia (CDH). Unlike other diseases resulting in persistent pulmonary hypertension of the newborn, infants with CDH are refractory to inhaled nitric oxide (NO). Nitric oxide mediates pulmonary vasodilatation at birth in part via cyclic GMP production. Phosphodiesterase type 5 (PDE5) limits the effects of NO by inactivation of cyclic GMP. Because of the limited success in postnatal management of CDH, we hypothesized that antenatal PDE5 inhibition would attenuate pulmonary artery remodeling in experimental nitrofen-induced CDH.

METHODS AND RESULTS

Nitrofen administered at embryonic day 9.5 to pregnant rats resulted in a 60% incidence of CDH in the offspring and recapitulated features seen in human CDH, including structural abnormalities (lung hypoplasia, decreased pulmonary vascular density, pulmonary artery remodeling, right ventricular hypertrophy), and functional abnormalities (decreased pulmonary artery relaxation in response to the NO donor 2-(N,N-diethylamino)-diazenolate-2-oxide). Antenatal sildenafil administered to the pregnant rat from embryonic day 11.5 to embryonic day 20.5 crossed the placenta, increased fetal lung cyclic GMP and decreased active PDE5 expression. Antenatal sildenafil improved lung structure, increased pulmonary vessel density, reduced right ventricular hypertrophy, and improved postnatal NO donor 2-(N,N-diethylamino)-diazenolate-2-oxide-induced pulmonary artery relaxation. This was associated with increased lung endothelial NO synthase and vascular endothelial growth factor protein expression. Antenatal sildenafil had no adverse effect on retinal structure/function and brain development.

CONCLUSIONS

Antenatal sildenafil improves pathological features of persistent pulmonary hypertension of the newborn in experimental CDH and does not alter the development of other PDE5-expressing organs. Given the high mortality/morbidity of CDH, the potential benefit of prenatal PDE5 inhibition in improving the outcome for infants with CDH warrants further studies.

Sildenafil citrate treatment enhances amino acid availability in the conceptus and fetal growth in an ovine model of intrauterine growth restriction

Adequate placental blood flow is essential for the optimal delivery of nutrients from mother to fetus for conceptus growth. Restricted fetal development results from pathophysiological and environmental factors that alter utero-placental blood flow, placental function, and, therefore, nutrient availability in the fetus. To test this hypothesis, 0, 75, or 150 mg/d sildenafil citrate (Viagra) was administered subcutaneously from d 28 to 115 of gestation to either nutrient-restricted [50% of NRC requirements) or adequately-fed ewes (100% of NRC requirements). On d 115, maternal, fetal, and placental tissues and fluids were collected. Concentrations of total amino acids and polyamines in uterine venous and arterial sera, amniotic and allantoic fluids, and fetal umbilical venous serum were lower (P < 0.05) in nutrient-restricted ewes than in adequately fed ewes, as were the ratios of total amino acids in fetal umbilical venous serum to uterine arterial serum. Sildenafil citrate dose-dependently increased (P < 0.05) total amino acids and polyamines in amniotic fluid, allantoic fluid, and fetal serum without affecting values in maternal serum. Fetal weight was lower (P < 0.05) in nutrient-restricted ewes on d 115. Sildenafil citrate treatment dose-dependently increased (P < 0.05) fetal weight in both nutrient-restricted and adequately fed ewes. This study supports the hypothesis that long-term sildenafil citrate treatment enhances fetal growth, at least in part, by increasing the availability of amino acids in the conceptus. These findings may lead to the clinical use of sildenafil citrate in human pregnancies suspected to be at risk for intrauterine fetal growth retardation.

Maternal consumption of polyphenol-rich foods in late pregnancy and fetal ductus arteriosus flow dynamics

OBJECTIVE

To test the hypothesis that maternal consumption of polyphenol-rich foods during third trimester interferes with fetal ductal dynamics by inhibition of prostaglandin synthesis.

STUDY DESIGN

In a prospective analysis, Doppler ductal velocities and right-to-left ventricular dimensions ratio of 102 fetuses exposed to polyphenol-rich foods (daily estimated maternal consumption >75th percentile, or 1089 mg) were compared with 41 unexposed fetuses (flavonoid ingestion <25th percentile, or 127 mg).

RESULT

In the exposed fetuses, ductal velocities were higher (systolic: 0.96+/-0.23 m/s; diastolic: 0.17+/-0.05 m/s) and right-to-left ventricular ratio was higher (1.23+/-0.23) than in unexposed fetuses (systolic: 0.61+/-0.18 m/s, P<0.001; diastolic: 0.11+/-0.04 m/s, P=0.011; right-to-left ventricular ratio: 0.94+/-0.14, P<0.001).

CONCLUSION

As maternal polyphenol-rich foods intake in late gestation may trigger alterations in fetal ductal dynamics, changes in perinatal dietary orientation are warranted.

Inhibition of cGMP phosphodiesterase 5 suppresses matrix metalloproteinase-2 production in pulmonary artery smooth muscles cells

1. It has been shown that the beneficial effects of phosphodiesterase (PDE) 5 inhibition on pulmonary hypertension (PH) are associated with the induction of vascular relaxation and suppression of the proliferation of pulmonary artery smooth muscle cells (PASMC). In the present study, we investigated whether PDE5 inhibition affects the production and/or secretion of matrix metalloproteinases (MMPs) in PASMC, resulting in extracellular matrix remodelling in the pulmonary vasculature and, thus, the development of PH. 2. Primary cultured PASMC were stimulated with endothelin (ET)-1 and MMP-2 production and RhoA activation were then determinded using gelatin zymography and a GTP-bound RhoA assay, respectively. The effects of the selective PDE5 inhibitor sildenafil and subsequent protein kinase G-specific inhibitor Rp-8Br-cGMPs on MMP-2 production and RhoA activation were further exmamined. 3. Endothelin-1 (1-1000 nmol/L) concentration-dependently stimulated MMP-2 production and/or secretion in primary cultured PASMC, with 100 nmol/L ET-1 causing a 2.41-fold increase in MMP-2 production compared with control (P < 0.01). This increase in MMP-2 production was accompanied by RhoA activation, which was abolished by preincubation of cells with 10 micromol/L Y27632, an inhibitor of Rho-associated kinase (ROCK). Furthermore, 10 micromol/L Y27632 abolished the ET-1-induced production of MMP-2. 4. The selective PDE5 inhibitor sildenafil (0.1-1 micromol/L) concentration-dependently reduced the increased MMP-2 production induced by 100 nmol/L ET-1. Specifically, in the presence of 1 micromol/L sildenafil, the 100 nmol/L ET-1-induced increase in MMP-2 production was only increased 1.3-fold over that of the control (P < 0.01 vs 100 nmol/L ET-1-stimulated cells). 5. Suppression of RhoA activation was found to mediate the inhibitory effect of sildenafil on ET-1-induced increases in MMP-2 production. Furthermore, the protein kinase G-specific inhibitor Rp-8Br-cGMPs reversed the inhibitory effects of sildenafil on RhoA activation and MMP-2 production. 6. The results of the present study indicate that PDE5 inhibition suppresses RhoA/ROCK-mediated MMP-2 production by PASMC, which may contribute to the regulation of pulmonary vascular remodelling. Thus, PDE5 inhibition may benefit patients with PH through multiple mechanisms of action.

Role of phosphodiesterase 5 in synaptic plasticity and memory

Phosphodiesterases (PDEs) are enzymes that break down the phosphodiesteric bond of the cyclic nucleotides, cAMP and cGMP, second messengers that regulate many biological processes. PDEs participate in the regulation of signal transduction by means of a fine regulation of cyclic nucleotides so that the response to cell stimuli is both specific and activates the correct third messengers. Several PDE inhibitors have been developed and used as therapeutic agents because they increase cyclic nucleotide levels by blocking the PDE function. In particular, sildenafil, an inhibitor of PDE5, has been mainly used in the treatment of erectile dysfunction but is now also utilized against pulmonary hypertension. This review examines the physiological role of PDE5 in synaptic plasticity and memory and the use of PDE5 inhibitors as possible therapeutic agents against disorders of the central nervous system (CNS).

Effects of sildenafil on the fetal growth of guinea pigs and their ability to survive induced intrapartum asphyxia

OBJECTIVE

Our goal was to determine whether sildenafil increased fetal weight and favored fetal tolerance to induced asphyxia at birth in guinea pigs.

STUDY DESIGN

Twenty guinea pigs were randomly allocated to placebo (n = 10) or sildenafil 50 microg/kg (n = 5) or 500 microg/kg (n = 5), starting from day 35 of gestation to delivery. Fetuses were delivered by cesarean section. Fetal asphyxia was induced by clamping the umbilical cord at birth for 5 minutes.

RESULTS

Sildenafil protected the pups against induced asphyxia at birth in a dose-dependent manner (eg, partial pressure (tension) of carbon dioxide levels were 75.9 +/- 19.3, 66.9 +/- 18.8, and 54.8 +/- 13.0 in the control and low- and high-dose sildenafil groups, respectively). The high-dose sildenafil group of piglets gained 1.5 times more body weight.

CONCLUSION

In guinea pigs, low doses of sildenafil administered from day 35 to the end of gestation favored fetal tolerability to induced intrapartum asphyxia. High doses of sildenafil increased fetal weight.

Inhibitors of cyclic nucleotide phosphodiesterase 3 and 5 as therapeutic agents in heart failure

Cyclic nucleotide phosphodiesterases (PDE) 3 and 5 regulate cAMP and cGMP signalling in cardiac and smooth muscle myocytes. Important advances in the understanding of the roles of these enzymes have recently been made. PDE3 inhibitors have inotropic and vasodilatory properties, and although they acutely improve haemodynamics in patients with heart failure, they do not improve long-term morbidity and mortality. Although combination therapy with beta-adrenergic receptor antagonists or selective inhibition of specific PDE3 isoforms might result in a more favourable long-term outcome, more clinical data are needed to test this proposition. The role of PDE5 inhibitors in the treatment of cardiac disease is evolving. PDE5 inhibitors cause pulmonary and systemic vasodilation. How these drugs will compare with other vasodilators in terms of long-term outcomes in patients with heart failure is unknown. Recent studies also suggest that PDE5 inhibitors may have antihypertropic effects, exerted through increased myocardial cGMP signalling, that could be of additional benefit in patients with heart failure.