Effects of dipyridamole and inhaled nitric oxide in pediatric patients with pulmonary hypertension

Advances in the research of sulfur dioxide and pulmonary hypertension

Pulmonary hypertension (PH) is a fatal disease caused by progressive pulmonary vascular remodeling (PVR). Currently, the mechanisms underlying the occurrence and progression of PVR remain unclear, and effective therapeutic approaches to reverse PVR and PH are lacking. Since the beginning of the 21st century, the endogenous sulfur dioxide (SO2)/aspartate transaminase system has emerged as a novel research focus in the fields of PH and PVR. As a gaseous signaling molecule, SO2 metabolism is tightly regulated in the pulmonary vasculature and is associated with the development of PH as it is involved in the regulation of pathological and physiological activities, such as pulmonary vascular cellular inflammation, proliferation and collagen metabolism, to exert a protective effect against PH. In this review, we present an overview of the studies conducted to date that have provided a theoretical basis for the development of SO2-related drug to inhibit or reverse PVR and effectively treat PH-related diseases.

Phosphodiesterase Inhibitors in Acute Lung Injury: What Are the Perspectives?

Despite progress in understanding the pathophysiology of acute lung damage, currently approved treatment possibilities are limited to lung-protective ventilation, prone positioning, and supportive interventions. Various pharmacological approaches have also been tested, with neuromuscular blockers and corticosteroids considered as the most promising. However, inhibitors of phosphodiesterases (PDEs) also exert a broad spectrum of favorable effects potentially beneficial in acute lung damage. This article reviews pharmacological action and therapeutical potential of nonselective and selective PDE inhibitors and summarizes the results from available studies focused on the use of PDE inhibitors in animal models and clinical studies, including their adverse effects. The data suggest that xanthines as representatives of nonselective PDE inhibitors may reduce acute lung damage, and decrease mortality and length of hospital stay. Various (selective) PDE3, PDE4, and PDE5 inhibitors have also demonstrated stabilization of the pulmonary epithelial-endothelial barrier and reduction the sepsis- and inflammation-increased microvascular permeability, and suppression of the production of inflammatory mediators, which finally resulted in improved oxygenation and ventilatory parameters. However, the current lack of sufficient clinical evidence limits their recommendation for a broader use. A separate chapter focuses on involvement of cyclic adenosine monophosphate (cAMP) and PDE-related changes in its metabolism in association with coronavirus disease 2019 (COVID-19). The chapter illuminates perspectives of the use of PDE inhibitors as an add-on treatment based on actual experimental and clinical trials with preliminary data suggesting their potential benefit.

Established and emerging therapeutic uses of PDE type 5 inhibitors in cardiovascular disease

PDE type 5 inhibitors (PDE5Is), such as sildenafil, tadalafil and vardenafil, are a class of drugs used to prolong the physiological effects of NO/cGMP signalling in tissues through the inhibition of cGMP degradation. Although these agents were originally developed for the treatment of hypertension and angina, unanticipated side effects led to advances in the treatment of erectile dysfunction and, later, pulmonary arterial hypertension. In the last decade, accumulating evidence suggests that PDE5Is may confer a wider range of clinical benefits than was previously recognised. This has led to a broader interest in the cardiovascular therapeutic potential of PDE5Is, in conditions such as hypertension, myocardial infarction, stroke, peripheral arterial disease, chronic kidney disease and diabetes mellitus. Here, we review the pharmacological properties and established licensed uses of this class of drug, along with emerging therapeutic developments and possible future indications.

Recent Advances in Neonatal Pharmacotherapy

Objective:

To provide commentary and reviews and brief discussions in controversial or innovative recent advances in neonatal pharmacotherapy. To discuss cutting edge drug delivery systems that may become useful in neonatal drug delivery in the future.

Data Sources:

Articles were identified through searches of MEDLINE (1990–October 2005), key articles in the authors' files, and in some cases, through data generated and/or published by the author of a particular topic.

Data Selection:

Article selection and relevance to the topics under discussion was determined by individual authors.

Data Synthesis:

Therapeutic strategies addressed in this review include the use of hematopoietic growth factors including a simulated amniotic fluid preparation containing these growth factors for neonates with selected gastrointestinal problems, erythropoietin for neuroprotection following perinatal asphyxia, drug therapy advances in treatment of patent ductus arteriosus (PDA), evaluation of advances in transdermal drug delivery, and its potential application to neonates and advances in the treatment of persistent pulmonary hypertension (PPHN) of the newborn.

Conclusions:

Despite being over 30 years old, the practice of neonatology is as much of an art as a science. Advances in the basic science research have improved our understanding of use of pharmacologic agents in the premature and full-term neonate including drug disposition pathways. Expanding our knowledge on issues such as physiology of hematopoietic factors, the pharmacologic responses of conditions such as PDA and PPHN, and newer technologies for drug administration, as well as other pharmacologic reponses in the neonate are vital in the development of safe and efficacious treatments for neonates. Many questions remain unanswered, and every clinician must make an effort to contribute to the knowledge and understanding of pharmacotherapy in this patient population.

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.

Attenuated vasodilatation in lambs with endogenous and exogenous activation of cGMP signaling: role of protein kinase G nitration

Pulmonary vasodilation is mediated through the activation of protein kinase G (PKG) via a signaling pathway involving nitric oxide (NO), natriuretic peptides (NP), and cyclic guanosine monophosphate (cGMP). In pulmonary hypertension secondary to congenital heart disease, this pathway is endogenously activated by an early vascular upregulation of NO and increased myocardial B-type NP expression and release. In the treatment of pulmonary hypertension, this pathway is exogenously activated using inhaled NO or other pharmacological agents. Despite this activation of cGMP, vascular dysfunction is present, suggesting that NO-cGMP independent mechanisms are involved and were the focus of this study. Exposure of pulmonary artery endothelial or smooth muscle cells to the NO donor, Spermine NONOate (SpNONOate), increased peroxynitrite (ONOO(-) ) generation and PKG-1α nitration, while PKG-1α activity was decreased. These changes were prevented by superoxide dismutase (SOD) or manganese(III)tetrakis(1-methyl-4-pyridyl)porphyrin (MnTMPyP) and mimicked by the ONOO(-) donor, 3-morpholinosydnonimine N-ethylcarbamide (SIN-1). Peripheral lung extracts from 4-week old lambs with increased pulmonary blood flow and pulmonary hypertension (Shunt lambs with endogenous activation of cGMP) or juvenile lambs treated with inhaled NO for 24 h (with exogenous activation of cGMP) revealed increased ONOO(-) levels, elevated PKG-1α nitration, and decreased kinase activity without changes in PKG-1α protein levels. However, in Shunt lambs treated with L-arginine or lambs administered polyethylene glycol conjugated-SOD (PEG-SOD) during inhaled NO exposure, ONOO(-) and PKG-1α nitration were diminished and kinase activity was preserved. Together our data reveal that vascular dysfunction can occur, despite elevated levels of cGMP, due to PKG-1α nitration and subsequent attenuation of activity.

Arterial pulmonary hypertension in noncardiac intensive care unit

Pulmonary artery pressure elevation complicates the course of many complex disorders treated in a noncardiac intensive care unit. Acute pulmonary hypertension, however, remains underdiagnosed and its treatment frequently begins only after serious complications have developed. Significant pathophysiologic differences between acute and chronic pulmonary hypertension make current classification and treatment recommendations for chronic pulmonary hypertension barely applicable to acute pulmonary hypertension. In order to clarify the terminology of acute pulmonary hypertension and distinguish it from chronic pulmonary hypertension, we provide a classification of acute pulmonary hypertension according to underlying pathophysiologic mechanisms, clinical features, natural history, and response to treatment. Based on available data, therapy of acute arterial pulmonary hypertension should generally be aimed at acutely relieving right ventricular (RV) pressure overload and preventing RV dysfunction. Cases of severe acute pulmonary hypertension complicated by RV failure and systemic arterial hypotension are real clinical challenges requiring tight hemodynamic monitoring and aggressive treatment including combinations of pulmonary vasodilators, inotropic agents and systemic arterial vasoconstrictors. The choice of vasopressor and inotropes in patients with acute pulmonary hypertension should take into consideration their effects on vascular resistance and cardiac output when used alone or in combinations with other agents, and must be individualized based on patient response.

Postnatal management and long-term outcome for survivors with congenital diaphragmatic hernia

Significant advances in the postnatal management of patients with congenital diaphragmatic hernia (CDH) have resulted in a remarkable improvement in survival rates over the past two decades. The success of current postnatal management of CDH patients has rendered fetal intervention to be limited to the most severe cases, and the role for prenatal treatment of CDH patients remains unclear. The adoption of lung-preserving strategies including high-frequency oscillatory ventilation (HFOV) and extracorporeal membrane oxygenation (ECMO) have improved CDH outcomes especially in those patients with significant ventilatory or circulatory compromise. Survival rates of up to 90% are being reported in some high-volume centers. However, the increased survival in CDH patients has been accompanied by an increase in neurological, nutritional and musculoskeletal morbidity among the long-term survivors. This has resulted in the need to provide resources for the long-term follow-up and support of this patient population. In this article, the postnatal management strategies and primary and secondary outcomes of high-volume international pediatric surgical centers will be reviewed. Finally, the role of a multidisciplinary management team for the follow-up of long-term CDH survivors will be discussed.

Long-term inhaled nitric oxide plus phosphodiesterase 5 inhibitors for severe pulmonary hypertension

BACKGROUND

Inhaled nitric oxide (iNO) is a potent pulmonary vasodilator, but therapeutic experience in patients with severe pulmonary hypertension is scarce.

METHODS

Eleven patients with severe pulmonary hypertension, 6 due to pulmonary arterial hypertension and 4 due to chronic thromboembolic disease, were selected for iNO therapy. A phosphodiesterase type 5 inhibitor (PDE5i) was added in cases of clinical worsening. In this study we evaluate the clinical effectiveness and safety of long-term treatment with iNO either alone or combined with a PDE5i.

RESULTS

After 1 month of iNO administration, improvements were observed in World Health Organization functional class, Borg scale (p = 0.003), brain natriuretic peptide levels (p = 0.002) and 6-minute walk test (p = 0.003). After 6 months of treatment, 7 patients had clinical deterioration that was reversed upon adding a PDE5i. One of these patients died in Month 8 and another underwent pulmonary transplantation in Month 9. The clinical condition of the remaining 9 patients was unchanged after 1 year. A second right catheterization showed improvement in mean pulmonary arterial pressure (66 +/- 15 mm Hg to 56 +/- 18 mm Hg; p = 0.01), pulmonary vascular resistance (1,234 +/- 380 dyn/s/cm(5) to 911 +/- 410 dyn/s/cm(5); p = 0.008) and cardiac index (2.0 +/- 0.4 liters/min/m(2) to 2.5 +/- 0.4 liters/min/m(2); p = 0.04). There was no significant increase in methemoglobin, no worsening of pulmonary function and no sudden withdrawal syndrome.

CONCLUSIONS

We suggest that iNO therapy alone or in combination with a PDE5i could be a therapeutic alternative for severe pulmonary hypertension.

Vardenafil, but not sildenafil or tadalafil, has calcium-channel blocking activity in rabbit isolated pulmonary artery and human washed platelets

BACKGROUND AND PURPOSE

Phosphodiesterase type-5 (PDE5) inhibitors constitute a novel and important therapeutic option for the treatment of pulmonary hypertension. The effects of the PDE5 inhibitors sildenafil, tadalafil and vardenafil on rabbit isolated pulmonary artery ring preparations and on intracellular Ca2+ concentration of thrombin-stimulated human platelets were investigated.

EXPERIMENTAL APPROACH

Rabbit pulmonary artery rings were mounted in 10 mL organ bath containing Krebs solution. Tissues were connected to force-displacement transducers, and changes in isometric force were recorded. Ca2+ flux in human washed platelets was measured.

KEY RESULTS

Sildenafil, tadalafil and vardenafil (0.0001-10 microM) concentration-dependently relaxed endothelium-intact and endothelium-denuded pulmonary artery rings. Endothelium denudation caused rightward shifts in the concentration-response curves to sildenafil, tadalafil and vardenafil (9-, 12- and 123-fold, respectively). Incubation with N(omega)-nitro-L-arginine methyl ester (100 microM) or ODQ (1H-[1,2,4] oxadiazolo [4,3,-a]quinoxalin-1-one) (10 microM) caused similar reductions of PDE5-induced vasorelaxations in intact rings. Sildenafil and tadalafil did not affect the phenylephrine-induced contractions, whereas vardenafil reduced the maximal responses, and shifted the phenylephrine-induced contraction curves to the right in endothelium-denuded rings (5- and 19-fold for 1 and 10 microM, respectively). Vardenafil (but neither sildenafil nor tadalafil) caused a marked rightward shift and a decrease of maximal contractile response to CaCl2. Vardenafil, but neither sildenafil nor tadalafil, significantly reduced the Ca2+ mobilization and Ca2+ influx in thrombin-stimulated washed platelets.

CONCLUSIONS AND IMPLICATIONS

Our results indicate that vardenafil, in contrast to sildenafil or tadalafil, also blocked Ca2+ fluxes, thus enhancing its vasorelaxation of the pulmonary artery.

Effect of prepro-calcitonin gene-related peptide-expressing endothelial progenitor cells on pulmonary hypertension

BACKGROUND

Calcitonin gene-related peptide (CGRP) is a potent smooth muscle cell proliferation inhibitor and vasodilator. It is now believed that CGRP plays an important role in maintaining a low pulmonary vascular resistance. We evaluated the therapeutic effect of intravenously administered CGRP-expressing endothelial progenitor cells (EPCs) on left-to-right shunt-induced pulmonary hypertension in rats.

METHODS

Endothelial progenitor cells were obtained from cultured human peripheral blood mononuclear cells. The genetic sequence for CGRP was subcloned into cultured EPCs by human expression plasmid. Pulmonary hypertension was established in immunodeficient rats with an abdominal aorta to inferior vena cava shunt operation. The transfected EPCs were injected through the left jugular vein at 10 weeks after the shunt operation. Mean pulmonary artery pressure and total pulmonary vascular resistance were detected with right cardiac catheterization at 4 weeks. The distribution of EPCs in the lung tissue was examined with immunofluorescence technique. Histopathologic changes in the structure of the pulmonary arteries was observed with electron microscopy and subjected to computerized image analysis.

RESULTS

The lungs of rats transplanted with CGRP-expressing EPCs demonstrated a decrease in both mean pulmonary artery pressure (17.64 +/- 0.79 versus 22.08 +/- 0.95 mm Hg; p = 0.018) and total pulmonary vascular resistance (1.26 +/- 0.07 versus 2.45 +/- 0.18 mm Hg x min/mL; p = 0.037) at 4 weeks. Immunofluorescence revealed that intravenously administered cells were incorporated into the pulmonary vasculature. Pulmonary vascular remodeling was remarkably attenuated with the administration of CGRP-expressing EPCs.

CONCLUSIONS

The transplantation of CGRP-expressing EPCs may effectively attenuate established pulmonary hypertension and exert reversal effects on pulmonary vascular remodeling. Our findings suggest that the therapy based on the combination of both CGRP transfection and EPCs may be a potentially useful strategy for the treatment of pulmonary hypertensive disorders.

The nitric oxide/cGMP signaling pathway in pulmonary hypertension

This article briefly reviews the background of endothelium-dependent vasorelaxation, describes the nitric oxide/cGMP/protein kinase pathway and its role in modulating pulmonary vascular tone and remodeling, and describes three approaches that target the nitric oxide/cGMP pathway in the treatment of patients with pulmonary arterial hypertension.

Pulmonary hypertension in congenital diaphragmatic hernia

Clinically significant pulmonary hypertension (PHTN) is a common finding in newborn infants with congenital diaphragmatic hernia (CDH) resulting in right to left shunting at pre- and postductal level, hypoxemia, and acute right heart failure in those most severely affected. Even in those without clinical manifestations of ductal shunting, cardiac echo studies would suggest that increased pulmonary vascular resistance and right ventricular pressures are almost a universal finding in this disease, and in some instances, may persist well into the postnatal period. The lung is small and structurally abnormal, and the pulmonary vascular bed is not only reduced in size, but responds abnormally to vasodilators. During the last 20 years, "gentle" ventilation, delayed surgery, and improved peri-operative care have made the greatest impact in decreasing mortality in this condition. Use of PGE1 should be considered early if there is hemodynamically significant PHTN, right ventricular dysfunction, and the patent ductus arteriosus (PDA) is becoming restrictive. In individual patients, inhaled nitric oxide (iNO) might be helpful, but the response to iNO should be confirmed using echocardiography. In patients who survive operation and leave the hospital, there are chronic causes of morbidity that need to be looked for and managed in a multi-disciplinary follow-up clinic.

Hypoxic respiratory failure in the late preterm infant

Hypoxic respiratory failure in late preterm infants has received increased attention in the last decade, and while the incidence is low, it accounts for a significant number of admissions to neonatal ICUs because of the large number of late preterm births in the United States and worldwide. Causes of respiratory distress include transient tachypnea of the newborn, surfactant deficiency, pneumonia, and pulmonary hypertension. The physiologic mechanisms underlying delayed transition caused by surfactant deficiency and poor fetal lung fluid absorption have been reviewed recently elsewhere. This article focuses on the less-explored problem of severe hypoxic respiratory failure in the late preterm infant and discusses potential strategies for management.

Sildenafil: from angina to erectile dysfunction to pulmonary hypertension and beyond

In less than 20 years, the first selective type 5 phosphodiesterase inhibitor, sildenafil, has evolved from a potential anti-angina drug to an on-demand oral treatment for erectile dysfunction (Viagra), and more recently to a new orally active treatment for pulmonary hypertension (Revatio). Here we describe the key milestones in the development of sildenafil for these diverse medical conditions, discuss the advances in science and clinical medicine that have accompanied this journey and consider possible future indications for this versatile drug.

Combination pharmacotherapy for severe neonatal pulmonary hypertension

Pulmonary hypertension can complicate the early clinical course in newborn infants with congenital diaphragmatic hernia. We report the successful use of combination therapy with enteral sildenafil and intravenous prostaglandin E1 in a preterm infant with severe pulmonary hypertension and right heart failure early after congenital diaphragmatic hernia repair.

Effects of Phosphodiesterase 5 Inhibitor on Pulmonary Vascular Reactivity in the Fetal Lamb

BACKGROUND

Nitric oxide released by pulmonary vascular endothelium is a potent vasodilator related to increased cyclic guanosine monophosphate (cGMP) content. Hydrolysis of cGMP is achieved predominately by cGMP-specific phosphodiesterases. Sildenafil is a selective phosphodiesterase-5 (PDE5) inhibitor. The purpose of the study is to assess the effects of sildenafil on pulmonary vascular circulation during the perinatal period.

METHODS

Thirty-two pregnant ewes were operated on at the end of gestation, and fetal lambs were prepared with catheters placed into the aorta, vena cava, pulmonary artery, and left atrium. An ultrasonic flow transducer and an inflatable vascular occluder were placed respectively around the left pulmonary artery and the ductus arteriosus. Fetal lambs were randomly divided into two groups: (1) sildenafil group, infused continuously with sildenafil for 24 hours at a rate of 1 mg/h; or (2) control group, infused with saline for 24 hours. After 24 hours of infusion, we compared basal pulmonary vascular resistance and the pulmonary vascular responses to increase in fetal PaO2 and to acute ductus arteriosus compression causing "shear stress."

RESULTS

Sildenafil infusion did not change mean aortic and pulmonary artery pressures, increased mean left pulmonary blood flow by 160%, and decreased pulmonary vascular resistance by 60% (p < 0.05). However, both mean flow (Q) and pulmonary vascular resistance returned to baseline values after 2 hours of sildenafil infusion. Despite similar baseline values, pulmonary vascular resistance during maternal O2 inhalation was lower in the sildenafil group than in the control group (0.21 +/- 0.03 versus 0.33 +/- 0.03 mm Hg.mL(-1).min(-1), respectively; p < 0.01). Furthermore, drop in pulmonary vascular resistance during acute ductus arteriosus compression was greater in the sildenafil group (from 0.56 +/- 0.06 to 0.26 +/- 0.04 mm Hg.mL(-1).min(-1)) than in the control group (from 0.55 +/- 0.05 to 0.39 +/- 0.03 mm Hg.mL(-1).min(-1); p < 0.01).

CONCLUSIONS

Although sildenafil induces a transient pulmonary vasodilation, it mediates a sustained change in vascular reactivity, especially to birth-related stimuli in the ovine fetal lung. These data suggest that PDE5 is involved in the regulation of pulmonary vascular reactivity during the perinatal period and may potentiate birth-related pulmonary vasodilator stimuli.

Long-term inhaled nitric oxide plus dipyridamole for pulmonary arterial hypertension

Inhaled nitric oxide (iNO) has been shown to be a potent and selective vasodilator in pulmonary arterial hypertension (PAH). However, the clinical experience in prolonged treatment is limited. We assess the safety and effectiveness of long-term administration of iNO in severe PAH. Two female patients were admitted to our hospital because of severe dyspnea (World Health Organization functional class IV) and hypoxemia. They were diagnosed with PAH (primary and secondary to congenital heart disease) and treated with iNO for 2 years. The delivery system consisted of an NO tank of 800 ppm, a modified gas-pulsing device, and nasal cannulas. On iNO treatment the patients showed remarkable improvement of symptoms, oxygenation and 6-min walk distance. After 16 months the patients began to experience a progressive rebound of symptoms. A phosphodiesterase type 5 inhibitor (dipyridamole) was added to iNO. This intervention proved useful in improving clinical deterioration and hemodynamics. This is the first study reporting 2-year iNO therapy in 2 patients with primary and secondary pulmonary hypertension. The combination of dipyridamole with iNO augments the pulmonary vasodilatation and may be useful in managing PAH.

Combined Administration of Intravenous Dipyridamole and Inhaled Nitric Oxide to Assess Reversibility of Pulmonary Arterial Hypertension in Potential Cardiac Transplant Recipients

BACKGROUND

Irreversible, severe pulmonary hypertension (PH) can produce right heart failure and early mortality after cardiac transplantation. We hypothesized that dipyridamole, an inhibitor of Type 5 phosphodiesterase, would augment the ability of inhaled nitric oxide (NO) to identify reversibility of PH.

METHODS

In 9 patients with congestive heart failure (CHF) and severe PH who were breathing 100% oxygen during right heart catheterization, we administered inhaled NO (80 ppm) alone and in combination with intravenous dipyridamole (0.2-mg/kg bolus, with an infusion of 0.0375 mg/kg/min).

RESULTS

Compared with breathing oxygen alone, NO inhalation decreased pulmonary artery pressure and pulmonary vascular resistance (PVR) (by 10 +/- 4% and 26 +/- 12% [mean +/- SEM], respectively; both p < 0.05). The combination of NO and dipyridamole reduced PVR (43 +/- 7%; p < 0.05) to a greater extent than did administration of NO alone, and increased the duration of pulmonary vasodilation produced by NO inhalation. Combined administration of inhaled NO and intravenous dipyridamole increased cardiac index (by 23 +/- 10%) and reduced SVR (by 19 +/- 6%, both p < 0.05) without changing systemic arterial pressure. NO inhalation reduced PVR to <200 dyne x s/cm5 in 3 of 7 patients who had a PVR of >200 dyne x s/cm5 when breathing oxygen alone, whereas the combination of NO and dipyridamole decreased PVR to <200 dyne.s/cm(5) in 2 additional patients.

CONCLUSIONS

Intravenous dipyridamole augments and prolongs the pulmonary vasodilator effects of inhaled NO in CHF patients with severe PH and, when administered in combination with NO inhalation, can identify PH reversibility in potential cardiac transplant recipients in whom a pulmonary vasodilator response to inhalation of NO alone is not observed.

The acute hemodynamic effect of IV nitroglycerin and dipyridamole in patients with pulmonary arterial hypertension: comparison with IV epoprostenol

Nitroglycerin and dipyridamole are two commonly available and well tolerated vasoactive medications. Their acute hemodynamic effects in patients with pulmonary arterial hypertension are not well defined in the current literature. The authors retrospectively analyzed the acute hemodynamic effects of IV nitroglycerin, dipyridamole, and epoprostenol in 59 patients with pulmonary arterial hypertension as determined by changes from baseline in systemic and pulmonary hemodynamic parameters. Statistical analysis was performed using the independent sample t test. A p value <0.05 was considered significant. Nitroglycerin is predominantly a vasodilator of the pulmonary vasculature with moderate systemic vasodilator effect, while dipyridamole is primarily a positive inotropic agent. Epoprostenol is a potent vasodilator of both pulmonary and systemic vessels and a strong positive inotropic agent. Nitroglycerin and dipyridamole may be useful in the acute management of pulmonary arterial hypertension.

Hemodynamic effects of inhaled nitric oxide and phosphodiesterase inhibitor (dipyridamole) on secondary pulmonary hypertension following heart valve surgery in adults

BACKGROUND

Inhaled nitric oxide (iNO) is proposed in the management of pulmonary hypertension (PH) in patients undergoing cardiac surgery. Secondary PH related to a long-standing heart valve disease however may be refractory to iNO. Aim of this prospective study was to determine whether the combination of iNO plus dipyridamole (DP), a cyclic guanosine monophosphate-specific phosphodiesterase inhibitor (PDE5), may enhance and/or prolong the response to iNO in adult patients with secondary valve-related PH undergoing cardiac surgery, and attenuate rebound events related to its discontinuation.

METHODS

Responses in 27 patients, 11 male, mean age 72+/-11 years, with PH due to mitral and/or aortic valve disease, were studied in the Intensive Care Unit after cardiac surgery, during sedation and stable hemodynamic conditions. The effect of isolated iNO administration (40 ppm), iNO combined with DP (0.2 mg/kg i.v.), and DP alone (1 mg/kg/24 h) on pulmonary vascular resistance, mean pulmonary artery pressure, cardiac index, mixed venous O2Sat%, and mean arterial pressure were determined.

RESULTS

All patients showed at least a 10% decrease in pulmonary vascular resistance vs. baseline after administration of iNO [responders]. Inhaled NO and the combination of iNO/DP produced a reduction of pulmonary vascular resistance and mean pulmonary artery pressure (p<0.05). Cardiac index improved with a significant difference between iNO and the association iNO/DP versus baseline (p<0.05). This significant hemodynamic improvement versus baseline was maintained during isolated DP administration (p<0.05), but not during isolated iNO discontinuation. Mixed venous oxygen saturation showed an overall improvement of 17% (p<0.05).

CONCLUSIONS

Inhaled NO and DP infusion might represent a valuable association in the management of PH secondary to a heart valve disease in patients undergoing cardiac surgery. Their beneficial hemodynamic effects might be particularly valuable in the management of patients with associated right ventricular dysfunction.

The effect of Sildenafil on human platelet secretory function is controlled by a complex interplay between phosphodiesterases 2, 3 and 5

Human platelets contain the cyclic nucleotide-hydrolyzing phosphodiesterases (PDEs) 2, 3 and 5. The cGMP-PDE5 inhibitors Sildenafil and Zaprinast have been demonstrated to potentiate the anti-platelet aggregatory effect of NO donors like sodium nitroprusside (SNP) in vitro but the mechanisms of Sildenafil's action on the secretory function of human platelets have not been analysed in detail. In the present paper, we show (1) that both compounds potentiate the SNP-induced increase in cGMP in human platelets concentration-dependently. (2) However, whereas Sildenafil plus SNP treatment only partially inhibits thrombin-induced release of serotonin, the less selective Zaprinast plus SNP cause a complete inhibition. (3) The inhibition mediated by Sildenafil plus SNP is limited to low compound concentrations at which cAMP levels are increased, probably due to cGMP-mediated inhibition of PDE3. (4) High concentrations of Sildenafil (plus SNP) neither affect cAMP levels, likely due to the activation of PDE2, nor inhibits the release of serotonin. Thus, increases in both cyclic nucleotides seem to control platelet function. (5) Accordingly, treatment with increasing concentrations of Sildenafil plus SNP and a selective PDE2 inhibitor, which by its own has no effect, induced a concentration-dependent increase in cAMP and complete inhibition of platelet activation. In summary, our data indicate that Sildenafil inhibits secretory function of human platelets at least in part due to the cGMP-mediated effects on intracellular cAMP and that entire inhibition of serotonin release from thrombin-activated platelets is controlled by both cyclic nucleotides.

Effects of a new phosphodiesterase enzyme type V inhibitor (UK 343-664) versus milrinone in a porcine model of acute pulmonary hypertension

BACKGROUND

Perioperative pulmonary hypertension remains a clinical challenge. The phosphodiesterase enzyme type III inhibitor milrinone produces pulmonary vasodilation but lacks selectivity. Sildenafil, a phosphodiesterase enzyme type V inhibitor, can also induce relaxation of the pulmonary vasculature; however, only the oral formulation is presently available. This study evaluated the effects of a new intravenous sildenafil analogue--UK 343-664--compared with milrinone during acute pulmonary hypertension in a porcine model of thromboxane-induced pulmonary hypertension.

METHODS

After acute pulmonary hypertension, 24 adult swine were randomized to 3 groups. Group 1 (n = 9) received an intravenous dose of 500 microg of UK 343-664, group 2 (n = 8) received milrinone 50 mg/kg, and group 3 (n = 7) received 10 mL of normal saline solution. All agents were administered for more than 5 minutes. Data were recorded continuously for 30 minutes.

RESULTS

Both milrinone and UK 343-664 partially reversed thromboxane-induced pulmonary hypertension, with a notable decrease in mean pulmonary artery pressure and pulmonary vascular resistance and a concomitant increase in cardiac output. In addition, milrinone improved right ventricular contractility but produced marked systemic vasodilatation. In contrast, the administration of UK 343-664 was associated with pulmonary vasodilatation, without appreciable changes in systemic arterial pressure or vascular resistance.

CONCLUSIONS

Milrinone and UK 343-664 were equally effective as pulmonary vasodilators; however, only UK 343-664 exhibited a high degree of pulmonary selectivity. Potential uses for this new phosphodiesterase enzyme type V inhibitor warrant further study.

Inhaled nitric oxide therapy in adults: European expert recommendations

BACKGROUND

Inhaled nitric oxide (iNO) has been used for treatment of acute respiratory failure and pulmonary hypertension since 1991 in adult patients in the perioperative setting and in critical care.

METHODS

This contribution assesses evidence for the use of iNO in this population as presented to a expert group jointly organised by the European Society of Intensive Care Medicine and the European Association of Cardiothoracic Anaesthesiologists.

CONCLUSIONS

Expert recommendations on the use of iNO in adults were agreed on following presentation of the evidence at the expert meeting held in June 2004.

Oral Sildenafil Reduces Pulmonary Hypertension After Cardiac Surgery

BACKGROUND

Treatment of postoperative pulmonary hypertension with intravenous (IV) pulmonary vasodilators is hampered by the lack of selectivity. Inhaled nitric oxide produces selective pulmonary vasodilation; however, it requires a special device, and weaning can cause rebound. Oral sildenafil is a phosphodiesterase type V inhibitor. Sildenafil can produce sustained pulmonary vasodilatation in patients with hypoxic or primary pulmonary hypertension; however, experience with postoperative pulmonary hypertension is limited. We report our initial experience with eight patients who received oral sildenafil as adjunctive therapy for postoperative pulmonary hypertension

METHODS

We reviewed the charts of eight adult patients with postoperative pulmonary hypertension who received oral sildenafil (25 to 50 mg) to facilitate weaning of IV (milrinone, nitroglycerine, and sodium nitroprusside) and inhaled (nitric oxide) pulmonary vasodilators. Hemodynamic data were recorded before and 30 and 60 minutes after the initial dose of sildenafil.

RESULTS

After the initial dose of sildenafil, mean pulmonary artery pressure was reduced by 20% and 22% at 30 and 60 minutes, respectively (p < 0.05). Pulmonary vascular resistance index decreased by 49% and 44% at 30 and 60 minutes, respectively (p < 0.05). Sildenafil had no clinically significant effects on cardiac index, mean arterial pressure, or systemic vascular resistance. Subsequent doses of sildenafil were administered at regular intervals, allowing successful weaning of concomitant pulmonary vasodilators.

CONCLUSIONS

Oral sildenafil is an effective agent for treatment of postoperative pulmonary hypertension and can be used to facilitate weaning of inhaled and IV pulmonary vasodilators.

Pulmonary Vascular Effects of Inhaled Nitric Oxide and Oxygen Tension in Bronchopulmonary Dysplasia

Pulmonary hypertension contributes significantly to morbidity and mortality in bronchopulmonary dysplasia (BPD), but little is known about the relative contribution of arterial tone, structural remodeling, and vessel density to pulmonary hypertension, especially in older patients. To determine the role of high pulmonary vascular tone in pulmonary hypertension, we studied the acute effects of oxygen tension, inhaled nitric oxide (iNO), and calcium channel blockers (CCB) in 10 patients with BPD who underwent cardiac catheterization for evaluation of pulmonary hypertension. During normoxic conditions, mean pulmonary arterial pressure (PAP) and pulmonary to systemic vascular resistance ratio (PVR/SVR) were 34 +/- 3 mm Hg and 0.42 +/- 0.07, respectively. In response to hypoxia, PAP and PVR/SVR increased by 50 +/- 8% and 82 +/- 14%, respectively (p < 0.01). Hyperoxia decreased PVR/SVR by 28 +/- 9% (p = 0.05). The addition of iNO treatment (20-40 ppm) to hyperoxia decreased PAP and PVR/SVR by 29 +/- 5% (p < 0.01) and 45 +/- 6% (p < 0.05) from baseline values, respectively, achieving near normal values. CCB did not alter PAP or PVR/SVR from baseline values. We conclude that hyperoxia plus iNO causes marked pulmonary vasodilatation in older patients with BPD, suggesting that heightened pulmonary vascular tone contributes to pulmonary vascular disease in BPD.

Medical therapy for pulmonary arterial hypertension: ACCP evidence-based clinical practice guidelines

Pulmonary arterial hypertension (PAH) is often difficult to diagnose and challenging to treat. Untreated, it is characterized by a progressive increase in pulmonary vascular resistance leading to right ventricular failure and death. The past decade has seen remarkable improvements in therapy, driven largely by the conduct of randomized controlled trials. Still, the selection of most appropriate therapy is complex, and requires familiarity with the disease process, evidence from treatment trials, complicated drug delivery systems, dosing regimens, side effects, and complications. This chapter will provide evidence-based treatment recommendations for physicians involved in the care of these complex patients. Due to the complexity of the diagnostic evaluation required, and the treatment options available, it is strongly recommended that consideration be given to referral of patients with PAH to a specialized center.

DA-8159, a new PDE5 inhibitor, attenuates the development of compensatory right ventricular hypertrophy in a rat model of pulmonary hypertension

This study evaluated the effect of DA-8159, a new phosphodiesterase 5 inhibitor, on the compensatory development of right ventricular hypertrophy in monocrotaline (MCT)-induced pulmonary hypertension (PH). Rats treated with subcutaneous MCT were divided into three groups, which received DA-8159 1 mg/kg, DA-8159 5 mg/kg or saline-vehicle orally, twice daily for 21 days. The vehicle group demonstrated increased right ventricular weight, pulmonary artery medial wall thickening, myocardial fibrosis, increased plasma cyclic guanosine monophosphate (cGMP) concentration and reduced body weight gains. DA-8159, however, markedly attenuated the compensatory development of right ventricular hypertrophy and pulmonary artery medial wall thickening, amplified the increase in plasma cGMP levels and increased lung cGMP concentrations. In addition, DA-8159 prevented myocardial fibrosis induced by MCT. These results demonstrate that DA-8159 attenuates the compensatory development of right ventricular hypertrophy in a rate model of PH. DA-8159 might, therefore, be a useful treatment option for PH, but its efficacy in humans needs evaluating.

Effects of sildenafil analogue UK 343-664 on a porcine model of acute pulmonary hypertension

BACKGROUND

Sildenafil (Pfizer Pharmaceuticals, Sandwich, Kent, UK) has been associated with pulmonary vasorelaxation. A more potent Sildenafil analogue (UK 343-664 [Pfizer Pharmaceuticals]) has been developed, but its effects in vivo have not been studied. This study evaluated the effects of UK 343-664 (Pfizer) during acute pulmonary hypertension.

METHODS

Fourteen adult swine were anesthetized with 1 minimum alveolar concentration isoflurane and were mechanically ventilated with an FIO(2) of 50%. End tidal CO(2) was maintained between 32 and 36 mm Hg. Micromanometer tipped catheters were placed in the ascending aorta, pulmonary artery, and right ventricle. Pulmonary flow was measured with a perivascular probe using transit time ultrasound.

RESULTS

Pulmonary hypertension was induced with a continuous infusion of the thromboxane analogue U46619. Animals were randomized into two groups. Group 1 (n = 9) received 500 microg of UK 343-664 (Pfizer) intravenously for more than 2 minutes. Group 2 (n = 5) served as the control group. Data were recorded continuously for 60 minutes. Statistical analyses were performed with the analysis of variance and t tests. A p less than 0.05 was considered significant.Pulmonary hypertension was achieved in all animals. The administration of UK 343-664 (Pfizer) was associated with a significant decrease in pulmonary artery pressure (30.3%; p < 0.05) and pulmonary vascular resistance (42%; p < 0.05) with mild systemic vasodilatation. These effects were partially maintained at 30 minutes (a 17.3% and 39% decrease, respectively; p < 0.05).

CONCLUSIONS

The administration of UK 343-664 (Pfizer) was associated with predominant pulmonary vasodilatation without systemic hypotension. This may represent a significant advance in the treatment of acute pulmonary hypertension. Potential clinical implications for this new phosphodiesterase enzyme type V (PDEV) inhibitor merit further study.

Is there a place for inhaled nitric oxide in the therapy of acute pulmonary embolism?

Acute pulmonary embolism (PE) is a serious complication resulting from the migration of emboli to the lungs. Although deep venous thrombi are the most common source of emboli to the lungs, other important sources include air, amniotic fluid, fat and bone marrow. Regardless of the specific source of the emboli, very little progress has been made in the pharmacological management of this high mortality condition. Because the prognosis is linked to the degree of elevation of pulmonary vascular resistance, any therapeutic intervention to improve the hemodynamics would probably increase the low survival rate of this critical condition. Inhaled nitric oxide (iNO) has been widely tested and used in cases of pulmonary hypertension of different causes. In the last few years some authors have described beneficial effects of iNO in animal models of acute PE and in anecdotal cases of massive PE. The primary cause of death in massive PE that is caused by deep venous thrombi, gas or amniotic fluid, is acute right heart failure and circulatory shock. Increased pulmonary vascular resistance following acute PE is the cumulative result of mechanical obstruction of pulmonary vessels and pulmonary arteriolar constriction (attributable to a neurogenic reflex and to the release of vasoconstrictors). As such, the vasodilator effects of iNO could actively oppose the pulmonary hypertension following PE. This hypothesis is consistently supported by experimental studies in different animal models of PE, which demonstrated that iNO decreased (by 10 to 20%) the pulmonary artery pressure without improving pulmonary gas exchange. Although maximal vasodilatory effects are probably achieved by less than 5 parts per million iNO, which is a relatively low concentration, no dose-response study has been published so far. In addition to the animal studies, a few anecdotal reports in the literature suggest that iNO may improve the hemodynamics during acute PE. However, no prospective, controlled, randomized clinical trial addressing this issue has been conducted to date. Future investigations addressing the effects of iNO combined with other drugs such as vasoconstrictors and inhibitors of phosphodiesterase III or V, may increase the responsiveness to iNO in acute PE.

Intermittent nitric oxide combined with intravenous dipyridamole in a piglet model of acute pulmonary hypertension

Continuous administration of inhaled nitric oxide is now widely used as a potent and selective pulmonary vasodilator. We have evaluated the effects of IV dipyridamole, a cyclic guanosine monophosphate (cGMP) phosphodiesterase inhibitor, on the magnitude and duration of action of inhaled nitric oxide (NO)-mediated pulmonary vasodilation. We hypothesized that inhibition of cGMP degradation could augment and prolong the pulmonary vasodilating effects of NO and allow for intermittent NO inhalation. In eight anesthetized and mechanically ventilated piglets, IV U-46619, a thromboxane A(2) analog, was used to induce pulmonary hypertension. The effects of 2, 5, and 10 ppm of NO, delivered during 4 min for each concentration and followed by a 10-min NO-free interval after each NO concentration, were evaluated without and with dipyridamole. Pulmonary vascular resistance decreased from 825 +/- 49 dynes. s. cm(-5) (U-46619) to 533 +/- 48 dynes. s. cm(-5) (10 ppm NO) (P < 0.05 versus U-46619) and 396 +/- 42 dynes. s. cm(-5) (dipyridamole 10 microg kg-1x min-1 and 10 ppm NO) (P <0.05 versus NO), and cardiac output increased from 1.93 +/- 0.09 L/min to 2.03 +/- 0.13 L/min and 2.60 +/- 0.30 L/min (P < 0.05 versus NO). Mean arterial blood pressure decreased from 90 +/- 5 mm Hg (10 ppm NO) to 75 +/- 3 mm Hg (dipyridamole plus 10 ppm NO) (P < 0.01). The pulmonary vasodilation obtained with NO alone could be prolonged from 12 to 42 min when inhaled NO was combined with IV dipyridamole, accounting for a time-weighted reduction in NO exposure by 72%. We conclude that dipyridamole augments the effects of NO on right ventricular afterload, allows for intermittent NO inhalation, and can significantly reduce exposure to NO.

IMPLICATIONS

IV dipyridamole prolongs the action of inhaled nitric oxide (NO) in a piglet model of acute pulmonary hypertension. Intermittent NO inhalation combined with IV dipyridamole decreases pulmonary artery pressure for a prolonged period of time and reduces exposure to NO.

DA-8159, a potent cGMP phosphodiesterase inhibitor, attenuates monocrotaline-induced pulmonary hypertension in rats

In this study, we evaluated the effects of oral administration of DA-8159, a selective phosphodiesterase-5 inhibitor, on the development of pulmonary hypertension (PH) induced by monocrotaline (MCT). Rats were administered either MCT (60 mg/kg) or saline. MCT-treated rats were divided into three groups and received orally administered vehicle, or 1 mg/kg or 5 mg/kg of DA-8159, twice a day for twenty-one days. The MCT group demonstrated increased right ventricular weights, medial wall thickening in the pulmonary arteries, myocardial fibrosis and the level of plasma cyclic guanosine monophosphate (cGMP), along with decreased body weight gains. However, DA-8159 markedly and dose-dependently reduced the development of right ventricular hypertrophy and medial wall thickening. DA-8159 also amplified the increase in plasma cGMP level and significantly increased the level of lung cGMP, compared with the MCT group. Although the body weight gain was still lower from the saline-treated control group, DA-8159 demonstrated a significant increase in body weight gains, in both 1 mg/kg and 5 mg/kg groups, when compared with the MCT group. In myocardial morphology, MCT-induced myocardial fibrosis was markedly prevented by DA-8159. These results suggest that DA-8159 may be a useful oral treatment option for PH.

Effect of sildenafil on cyclic nucleotide phosphodiesterase activity, vascular tone and calcium signaling in rat pulmonary artery

(1) Sildenafil (viagra) is a potent PDE5 inhibitor and thus a relaxant drug in corpus carvernosum smooth muscle. In the present work, we evidenced the presence of PDE5 isozyme and investigated the effect of sildenafil on the specific cyclic nucleotide phosphodiesterase (PDE) activity, smooth muscle tone and calcium signaling in the rat main pulmonary artery (MPA). (2) The PDE activity was measured in cytosolic and microsomal fractions. Total cAMP and cGMP-PDE activities were mainly present in the cytosolic fraction. Sildenafil (0.1 micro M) reduced by 72% cGMP-PDE activity, whereas zaprinast (10 micro M), a relatively selective PDE5 inhibitor, reduced this activity by 63%. Sildenafil (0.1 micro M) also inhibited significantly (22%) the cAMP-PDE activity. (3) Western blot analysis revealed the expression of PDE5 mainly in the cytosolic fraction of MPA. Sildenafil concentration-dependently inhibited (IC(50)=3.4 nM) the activity of MPA PDE5 partially purified by HPLC. (4) Sildenafil (0.1 nM-50 micro M) concentration-dependently relaxed MPA rings precontracted with phenylephrine (0.5 micro M). The potency of sildenafil (IC(50)=11 nM) was similar to that of a nitric oxide donor, sodium nitroprusside, but higher than that of zaprinast (IC(50)=600 nM). The vasorelaxant effect of sildenafil was not altered by endothelium removal or in the presence of KT 5823 (1 micro M) and H89 (1 micro M), potent inhibitors of PKG and PKA, respectively. (5) In isolated MPA myocytes, which had been loaded with the calcium fluorophore indo-1, sildenafil (10-100 nM) antagonized ATP- and endothelin-1-induced calcium oscillations but had no effect on the transient caffeine-induced [Ca(2+)](i) response. (6) This study demonstrates the presence of a functional and highly sildenafil-sensitive PDE5 isozyme in rat MPA. Inhibition of this isozyme mainly accounts for the potent pulmonary vasodilator action of sildenafil, which involves alteration in the inositol triphosphate-mediated calcium signaling pathway.

Selective pulmonary vasodilation in acute respiratory distress syndrome

Acute respiratory distress syndrome (ARDS) is characterized by a marked maldistribution of pulmonary perfusion in favor of nonventilated, atelectatic areas of the lungs, and it is the main cause of pulmonary right-to-left shunting and hypoxemia. Therapeutic interventions to selectively influence pulmonary perfusion in ARDS became feasible with the introduction of inhaled nitric oxide, which provided a means not only to reduce pulmonary hypertension, but also to improve matching of ventilation to perfusion and, thus, hypoxemia. Clinical studies in ARDS subsequently demonstrated that the combination of inhaled nitric oxide with other interventions, such as positive end-expiratory pressure and prone positioning, yielded beneficial and additive effects on arterial oxygenation. Although the available randomized, controlled trials of this novel concept have so far failed to show an improved outcome in ARDS, inhaled nitric oxide is a clinically valuable option for the treatment of severe refractory hypoxemia in ARDS, and largely promoted the concept of selective pulmonary vasodilation in intensive care practice. Currently, aerosolization of various vasodilators, in particular prostaglandins, is under evaluation in models of acute lung injury and human ARDS. Ongoing research aims to augment the effectiveness of vasodilators with specific inhibitors of phosphodiesterases or by combination with intravenous vasoconstrictors. Consequently, several alternative ways to selectively modulate pulmonary vascular tone in patients with ARDS may be available in the near future. Cost-benefit analysis of these therapeutic options will largely determine their future perspective.

Increased expression of the cGMP-inhibited cAMP-specific (PDE3) and cGMP binding cGMP-specific (PDE5) phosphodiesterases in models of pulmonary hypertension

1. Chronic hypoxic treatment of rats (to induce pulmonary hypertension, PHT) for 14 days increased cGMP-inhibited cAMP specific phosphodiesterase (PDE3) and cGMP binding cGMP specific phosphodiesterase (PDE5) activities in pulmonary arteries. The objective of this study was to establish the molecular basis for these changes in both animal and cell models of PHT. In this regard, RT-PCR and quantitative Western blotting analysis was applied to rat pulmonary artery homogenates and human pulmonary "artery" smooth muscle cell (HPASMC) lysates. 2. PDE3A/B gene transcript levels were increased in the main, first, intrapulmonary and resistance pulmonary arteries by chronic hypoxia. mRNA transcript and protein levels of PDE5A2 in the main and first branch pulmonary arteries were also increased by chronic hypoxia, with no effect on PDE5A1/A2 in the intra-pulmonary and resistance vessels. 3. The expression of PDE3A was increased in HPASMCs maintained under chronic hypoxic conditions for 14 days. This may be mediated via a protein kinase A-dependent mechanism, as treatment of cells with Br-cAMP (100 microM) mimicked chronic hypoxia in increasing PDE3A expression, while the PKA inhibitor, H8 peptide (50 microM) abolished the hypoxic-dependent increase in PDE3A transcript. 4. We also found that the treatment of HPASMCs with the inhibitor of kappaB degradation Tosyl-Leucyl-Chloro-Ketone (TLCK, 50 microM) reduced PDE5 transcript levels, suggesting a role for this transcription factor in the regulation of PDE5 gene expression. 5. Our results show that increased expression of PDE3 and PDE5 might explain some changes in vascular reactivity of pulmonary vessels from rats with PHT. We also report that NF-kappaB might regulate basal PDE5 expression.

Intravenous dipyridamole enhances the effects of inhaled nitric oxide and prevents rebound pulmonary hypertension in piglets

Inhaled nitric oxide (NO) is increasingly used in the treatment of pulmonary hypertension, despite its potential toxicity and the risk of life-threatening rebound pulmonary hypertension upon its discontinuation. We investigated whether i.v. dipyridamole, a cGMP phosphodiesterase inhibitor, increased the effects of inhaled NO and prevented rebound pulmonary hypertension. In 14 anesthetized and mechanically ventilated piglets, pulmonary hypertension was induced with U-46619, a thromboxane A(2) analogue. Response to NO and rebound pulmonary hypertension were evaluated without and with i.v. dipyridamole. Low-dose dipyridamole (10 micro g/kg/min) increased cardiac output and augmented the effects of inhaled NO on pulmonary vascular resistance, with marginal additive effect on mean pulmonary artery pressure. Pulmonary vascular resistance decreased from 904 to 511 (20 parts per million NO) (p < 0.0005) and 358 dyne s cm(-5) (20 parts per million NO + dipyridamole) (p < 0.001 versus NO alone), and mean pulmonary artery pressure decreased from 29.0 to 20.5 (p < 0.0001) and 19.3 mm Hg (NS versus NO), respectively. Mean arterial pressure decreased from 85 to 74 mm Hg (dipyridamole + NO) (p < 0.01). High-dose dipyridamole (100 micro g/kg/min) with inhaled NO reduced pulmonary vascular resistance to 334 dyne s cm(-5) but also decreased mean arterial pressure to 57 mm Hg. Eight piglets developed rebound pulmonary hypertension. Two died of acute right ventricular failure and, in five, rebound pulmonary hypertension was prevented by low-dose dipyridamole. In conclusion, low-dose i.v. dipyridamole augments the effects of inhaled NO on right ventricular afterload with moderate changes in systemic hemodynamics, and can prevent rebound pulmonary hypertension.

Characterisation of cyclic nucleotide phosphodiesterase isoforms in the media layer of the main pulmonary artery

Cyclic nucleotides are involved in the control of pulmonary vascular tone. In the present study, we measured the cyclic nucleotide specific phosphodiesterase (PDE) activity in the media of bovine isolated main pulmonary artery (MPA). Total cAMP- and cGMP-PDE activities were measured in microsomal and cytosolic fractions. Both cyclic nucleotides were hydrolysed in these subcellular fractions at consistently higher rate in the cytosolic than in the microsomal fraction. Using different classes of PDE modulator, at least four PDE isoforms (PDE1, 3, 4 and 5) were identified in these fractions. PDE3 (cilostamide-sensitive), PDE4 (rolipram-sensitive) and PDE5 (zaprinast- and DMPPO-sensitive) isoforms appeared as the main isozymes implicated in the cAMP and cGMP hydrolytic activities. Calcium-camodulin stimulated PDE activity (PDE1) was mainly present in the cytosolic fraction. PDE2, although present, had a lower hydrolytic activity since addition of its specific inhibitor, erythro-9-(2-hydroxy-3nonyl)adenine (EHNA), to a combination of inhibitors of PDE3, 4 and 5 produced no further significant reduction in the enzymatic activity. Resolution of PDE activities from the cytosolic fraction using anion exchange chromatography confirmed this finding. Functional experiments performed in endothelium-denuded rings of rat MPA revealed that all specific PDE inhibitors used relaxed precontracted vascular smooth muscle preparations in a concentration-dependent manner. The rank order of potency was cilostamide >zaprinast>rolipram>>EHNA. The present study demonstrates the presence in the smooth muscle cells-containing layer of MPA of PDE1, 3, 4 and 5 isoforms and suggests that PDE3, 4 and 5 are the main enzymes involved in the control of vascular tone.

Cellular pathophysiology and therapy of pulmonary hypertension

The identification of several mutations of the bone morphogenetic protein receptor 2 (BMPR2) gene, a member of the transforming growth factor beta receptor family, gives hope for new insights into the pathophysiology of pulmonary hypertension. Genetic predisposition might dictate the responses of pulmonary artery fibroblasts, smooth muscle cells, and endothelial cells, as well as platelets and leukocytes, or their specific interactions with different extrinsic factors. These cells possess distinct subtypes and interact with each other. Pulmonary hypertension is associated with vasoconstriction, remodeling, and in situ thrombosis of the pulmonary arteries, but the initial events and their relationship to the genetic background are presently unknown. Current therapeutic approaches are based on our knowledge of the physiologic regulation of pulmonary artery tone, pathophysiologic changes, and our clinical experience with different treatment strategies. Beyond diuretics and anticoagulants, prostaglandins are generally accepted therapeutic agents for primary pulmonary hypertension and related diseases, whereas high-dose calcium-channel blockers are reserved for a small subset of patients, those who respond favorably to vasodilators in an acute test. Long-term intravenous prostacyclin infusion has become the most important specific therapy for primary pulmonary hypertension and associated diseases. However, this therapy is hampered by catheter complications and systemic side effects. Alternative application routes of prostacyclin or its stable analogs may avoid these problems. Inhaled application of the prostacyclin analog iloprost results in predominant pulmonary vasodilation with few systemic side effects and may possess clinical efficacy similar to that of intravenous prostacyclin. Inhaled nitric oxide is widely accepted as a screening agent for active responders to vasodilators and has a similar hemodynamic profile as inhaled iloprost, although the percentage of responders is considerably lower. However, there are unsolved toxicologic questions and practical difficulties concerning the safe long-term application of nitric oxide. Combining inhaled vasodilators with phosphodiesterase inhibitors may prolong the duration of the effects and improve the convenience of inhaled therapy for pulmonary hypertension. Therapeutic approaches in the future may aim at the transforming growth factor beta pathway and at the identification of early stages of the disease to prevent further disease progression.

sGC and PDE5 are elevated in lambs with increased pulmonary blood flow and pulmonary hypertension

Utilizing aortopulmonary vascular graft placement, we established a lamb model of pulmonary hypertension that mimics congenital heart disease with increased pulmonary blood flow. We previously demonstrated that endothelial nitric oxide synthase (eNOS) is increased in lambs at age 4 wk. However, these lambs display a selective impairment of endothelium-dependent pulmonary vasodilation that is suggestive of a derangement downstream of NO release. Thus our objective was to characterize potential alterations in the expression and activity of soluble guanylate cyclase (sGC) and phosphodiesterase type 5 (PDE5) induced by increased pulmonary blood flow and pulmonary hypertension. Late-gestational fetal lambs (n = 10) underwent in utero placement of an aortopulmonary vascular graft (shunt). Western blotting analysis on lung tissue from 4-wk-old shunted lambs and age-matched controls showed that protein for both subunits of sGC was increased in shunted lamb lungs compared with age-matched controls. Similarly, cGMP levels were increased in shunted lamb lungs compared with age-matched controls. However, PDE5 expression and activity were also increased in shunted lambs. Thus although cGMP generation was increased, concomitant upregulation of PDE5 expression and activity may have (at least partially) limited and accounted for the impairment of endothelium-dependent pulmonary vasodilation in shunted lambs.

New and experimental therapies for pulmonary hypertension

Advances in the understanding of the molecular and cellular pathogeneses of PPH have led clinicians beyond simple pulmonary vasodilation as the only treatment for PPH and to a realization that what were previously believed to be irreversible vascular lesions may, in fact, be reversible. The development of agents that target the known endothelial and nonendothelial defects in patients with PPH is well underway. Clinicians are witnessing an exciting new era for physicians and patients dealing with this disease.

Diagnosis and treatment of severe pediatric pulmonary hypertension

Advances in the treatment of pulmonary hypertension during the past decade have dramatically improved patient survival. Many of these advances are based on improved understanding of the vascular biology of the normal and hypertensive pulmonary circulations. Pulmonary hypertension is an important determinant of morbidity and mortality in patients with many pediatric diseases, including congenital heart disease. This article describes current diagnostic strategies and treatments for patients with primary and secondary pulmonary hypertension.

Nitric oxide decreases coagulation protein function in rabbits as assessed by thromboelastography

Nitric oxide (NO) is administered via infusion of donors such as nitroglycerin or in inhaled form for treatment of ischemia and pulmonary hypertension, respectively. In rabbits, the NO donor, DETANONOate, decreases whole blood clotting function as assessed by thromboelastographic variables (R, reaction time; alpha, angle; and G, a measure of clot strength). I hypothesized that DETANONOate-derived NO would adversely affect coagulation protein and platelet function. Blood obtained from ear arteries of conscious rabbits (n = 8) anticoagulated with sodium citrate. The blood was then incubated with 0 or 10mM DETANONOate for 30 min. After incubation and recalcification, thromboelastography was performed for 60 min under four conditions: 1) 0mM DETANONOate, 2) 0mM DETANONOate with platelet inhibition with cytochalasin D, 3) 10mM DETANONOate, and 4) 10mM DETANONOate with platelet inhibition. DETANONOate significantly (P < 0.05) increased R and decreased alpha and G in samples with or without platelet inhibition, compared with samples not exposed to DETANONOate. Lastly, the percentage of total G (G(T)) attributable to platelet function (G(P)) was significantly more in the absence of DETANONOate (G(P) = 92.3% +/- 1.6%; mean +/- SD) than after exposure to DETANONOate (G(P) = 90.2% +/- 2.3%). DETANONOate-derived NO significantly decreased coagulation protein function and platelet function. Coagulation protein function may be similarly affected in clinical situations involving the administration of NO or NO donors.