Recognition and management of pulmonary hypertension

Riociguat versus sildenafil on hypoxic pulmonary vasoconstriction and ventilation/perfusion matching

INTRODUCTION

Current treatment with vasodilators for pulmonary hypertension associated with respiratory diseases is limited by their inhibitory effect on hypoxic pulmonary vasoconstriction (HPV) and uncoupling effects on ventilation-perfusion (V'/Q'). Hypoxia is also a well-known modulator of the nitric oxide (NO) pathway, and may therefore differentially affect the responses to phosphodiesterase 5 (PDE5) inhibitors and soluble guanylyl cyclase (sGC) stimulators. So far, the effects of the sGC stimulator riociguat on HPV have been poorly characterized.

MATERIALS AND METHODS

Contraction was recorded in pulmonary arteries (PA) in a wire myograph. Anesthetized rats were catheterized to record PA pressure. Ventilation and perfusion were analyzed by micro-CT-SPECT images in rats with pulmonary fibrosis induced by bleomycin.

RESULTS

The PDE5 inhibitor sildenafil and the sGC stimulator riociguat similarly inhibited HPV in vitro and in vivo. Riociguat was more effective as vasodilator in isolated rat and human PA than sildenafil. Riociguat was ≈3-fold more potent under hypoxic conditions and it markedly inhibited HPV in vivo at a dose that barely affected the thromboxane A2 (TXA2) mimetic U46619-induced pressor responses. Pulmonary fibrosis was associated with V'/Q' uncoupling and riociguat did not affect the V'/Q' ratio.

CONCLUSION

PDE5 inhibitors and sGC stimulators show a different vasodilator profile. Riociguat was highly effective and potentiated by hypoxia in rat and human PA. In vivo, riociguat preferentially inhibited hypoxic than non-hypoxic vasoconstriction. However, it did not worsen V'/Q' coupling in a rat model of pulmonary fibrosis.

Sildenafil for the treatment of pulmonary hypertension in pediatric patients

Sildenafil is a phosphodiesterase 5 inhibitor widely used for the treatment of pulmonary hypertension in children. Despite limited available safety and efficacy evidence, use of sildenafil continues to increase. To date, sildenafil use for pediatric pulmonary hypertension has been characterized for 193 children through 16 studies and 28 case series and reports. The primary efficacy data suggest that sildenafil is beneficial for facilitating the weaning of inhaled nitric oxide in children after cardiac surgery. Compiled safety data suggest that sildenafil is well tolerated among children with idiopathic pulmonary arterial hypertension and pulmonary arterial hypertension associated with congenital heart disease. This review summarizes the available data describing the use, safety, and efficacy of sildenafil for children with pulmonary hypertension.

Can we improve outcome of congenital diaphragmatic hernia?

This review gives an overview of the disease spectrum of congenital diaphragmatic hernia (CDH). Etiological factors, prenatal predictors of survival, new treatment strategies and long-term morbidity are described. Early recognition of problems and improvement of treatment strategies in CDH patients may increase survival and prevent secondary morbidity. Multidisciplinary healthcare is necessary to improve healthcare for CDH patients. Absence of international therapy guidelines, lack of evidence of many therapeutic modalities and the relative low number of CDH patients calls for cooperation between centers with an expertise in the treatment of CDH patients. The international CDH Euro-Consortium is an example of such a collaborative network, which enhances exchange of knowledge, future research and development of treatment protocols.

RhoA/Rho-kinase signaling: a therapeutic target in pulmonary hypertension

Pulmonary arterial hypertension (PAH) is a devastating disease characterized by progressive elevation of pulmonary arterial pressure and vascular resistance due to pulmonary vasoconstriction and vessel remodeling as well as inflammation. Rho-kinases (ROCKs) are one of the best-described effectors of the small G-protein RhoA, and ROCKs are involved in a variety of cellular functions including muscle cell contraction, proliferation and vascular inflammation through inhibition of myosin light chain phosphatase and activation of downstream mediators. A plethora of evidence in animal models suggests that heightened RhoA/ROCK signaling is important in the pathogenesis of pulmonary hypertension by causing enhanced constriction and remodeling of the pulmonary vasculature. Both animal and clinical studies suggest that ROCK inhibitors are effective for treatment of severe PAH with minimal risk, which supports the premise that ROCKs are important therapeutic targets in pulmonary hypertension and that ROCK inhibitors are a promising new class of drugs for this devastating disease.

How valid are animal models to evaluate treatments for pulmonary hypertension?

Various animal models of pulmonary hypertension (PH) exist, among which injection of monocrotaline (MCT) and exposure to hypoxia are used most frequently. These animal models have not only been used to characterize the pathophysiology of PH and its sequelae such as right ventricular hypertrophy and failure, but also to test novel therapeutic strategies. This manuscript summarizes the available treatment studies in animal models of PH, and compares the findings to those obtained in patients with PH. The analysis shows that all approaches which have proven successful in patients, most notably prostacyclin and its analogs and endothelin receptor antagonists, are also effective in various animal models. However, the opposite it not always true. Therefore, promising results in animals have to be interpreted carefully until confirmed in clinical studies.

Short-term effects of levosimendan and prostaglandin E1 on hemodynamic parameters and B-type natriuretic peptide levels in patients with decompensated chronic heart failure

BACKGROUND

Both levosimendan and prostaglandin E1 (PGE1) have beneficial effects on hemodynamic parameters and outcome compared to dobutamine in decompensated chronic heart failure (CHF).

AIMS

We compared short-term effects of levosimendan versus PGE1 on hemodynamic parameters and B-type natriuretic peptide levels (BNP) in patients with decompensated CHF.

METHODS AND RESULTS

73 patients (cardiac index < 2.5 L/min/m2, pulmonary capillary wedge pressure (PCP) >15 mmHg) with decompensated CHF were randomised to treatment with either a 24 h-infusion of levosimendan (n=38) or a chronic infusion of PGE1 (n = 35). Hemodynamic parameters and BNP were measured at baseline, 24 and 48 h, BNP levels were also measured after 1 week. Baseline characteristics including concomitant medication were similar in both groups. Levosimendan and PGE1 increased cardiac output (CO) after 24 and 48 h. Levosimendan increased CO twice as much as PGE1 (24 h: Levosimendan +1.1 +/- 0.1 L/min, PGE1 +0.6 +/- 0.1 L/min, p < 0.001). Both drugs produced a comparable reduction in PCP and pulmonary artery pressure after 24 and 48 h. Levosimendan decreased BNP by 28% after 24 h and 22% after 48 h, but effects disappeared after 1 week. In contrast, PGE1 decreased BNP by 15% after 48 h (no change at 24 h), but a decrease of 20% was sustained at 1 week.

CONCLUSIONS

The differential beneficial effects of levosimendan (greater increase in CO) and PGE1 (sustained decrease in BNP) may have a potential impact on clinical outcome.

[The methods for screening pulmonary hypertension related to systemic sclerosis in France. Descriptive survey of the French Research Group on Sclerosis]

CONTEXT AND OBJECTIVES

Pulmonary hypertension (PHT) represents one of the severest complications and is life-threatening for patients suffering from systemic sclerosis (SSc). In France, the modalities for screening and treating PHT related to SSc are not well codified and no consensus has been reached. We conducted a survey among physicians inscribed on the list of the French Research Group on Sclerosis (GRFS - Groupe de Recherche Francais sur la Sclerodermie) to gather information on the status of the management of PHT related to SSc.

METHODS

In 2002, we sent a questionnaire to 160 physicians, members of the GRFS, to assess the epidemiology and clinical profile of SSc patients as well as the modalities of screening and management of PHT in these patients.

RESULTS

Eighty-eight physicians in 71 centres replied to the questionnaire. Each centre followed-up a mean of 33 SSc patients, with a global distribution of 53% limited and 47% diffused SSc. These physicians saw a mean of 5 new cases of SSc per year. The patients had been referred by town practitioners (53%) or from the hospital (47%). The mean number of SSc patients with PHT was of 5.1 per physician (1.5 new SSc + PHT patients per year). Almost all the centres (65/67) who replied systematically screened for PHT in SSc patients using Doppler echocardiography a mean of every 1.3 years. For the management of the patients exhibiting PHT, the majority (41/63) of centres collaborated with a specialized unit. Around one third of the centres treated these patients with calcium channel inhibitors (82%) and/or prostacyclin (90%). All the patients were followed-up by Doppler echocardiography. The majority of the physicians (72%) were interested in a research protocol on the subject and each could have included 4 patients, i.e., a total of 160.

CONCLUSION

Pulmonary hypertension, a severe complication of SSc is screened for by the physicians of the GRFS using echocardiography with a frequency similar to Who guidelines (1.3 versus once/year).

Chest pain in adult congenital heart disease: where does it come from?

Chest pain is common in adolescents and in young adults and usually not associated with a severe underlying cardiovascular disorder. However, in adults with congenital heart disease, residua or sequellae of previous interventions may provoke potential complications. Moreover, chest pain may be the first sign of a life-threatening condition. Basic knowledge is mandatory and will lead to the correct diagnosis and treatment. Data in literature, which focus on this issue, are scarce and motivated to summarize the experience of daily practice from the eye point of the clinician.

Acute myocardial infarction caused by delayed heparin-induced thrombocytopenia and acute immunoreaction due to re-exposure to heparin in a systemic lupus erythematosus patient with HIT antibodies

A patient with systemic lupus erythematosus and anticardiolipin antibodies and antibodies to platelet factor 4/heparin complexes suffered an acute myocardial infarction caused by delayed heparin-induced thrombocytopenia after heparin administration given to treat pulmonary hypertension. Furthermore, additional heparin administration for emergency coronary angiography appeared to have led to an acute immunoreaction, which might have resulted in acute coronary occlusion during coronary angiography and to a decreased platelet count. The present findings suggest that one must suspect delayed-type HIT in rare cases of induction of thrombosis after the cessation of heparin treatment, and avoid re-exposure to heparin in such cases.

S-nitrosocaptopril: acute in-vivo pulmonary vasodepressor effects in pulmonary hypertensive rats

The effects of S-nitrosocaptopril (SNOcap), administered either intravenously or by oral gavage, on pulmonary artery pressure (PAP) were examined in anaesthetised normotensive rats and rats with hypoxic pulmonary hypertension (10% oxygen for 1 week). Mean PAP (MPAP) values in hypoxic and normoxic rats were (mmHg) 26 +/- 1.7 and 15 +/- 1.1, respectively. When given intravenously, 1 mg kg(-1) SNOcap reduced MPAP by 28 and 32% in hypoxic and normoxic rats, respectively. The effects of 2 mg kg(-1) were no greater than those of 1 mg kg(-1). Pulmonary vasodepressor responses reached equilibrium in 1.7 +/- 0.18 min following intravenous administration. When given orally 30 min before the measurement of PAP, 30 mg kg(-1), but not 10 mg kg(-1), significantly reduced MPAP in hypoxic rats to 17 +/- 1.5 mmHg. These in-vivo data are consistent with previous in-vitro data showing that SNOcap has direct pulmonary vasorelaxant properties in both large and small pulmonary arteries and also show that SNOcap causes pulmonary vasodepression in the setting of pulmonary hypertension. Since SNOcap also inhibits pulmonary vascular angiotensin converting enzyme (ACE) in pulmonary blood vessels (previous study), it would be an interesting drug with which to assess the benefits of direct pulmonary vasodilatation combined with ACE inhibition (which attenuates pulmonary vascular remodelling) in a long-term study in pulmonary hypertension.

S-nitrosocaptopril: in vitro characterization of pulmonary vascular effects in rats

(1) On rat isolated pulmonary arteries, vasorelaxation by S-nitrosocaptopril (SNOcap) was compared with S-nitrosoglutathione (GSNO) and nitroprusside, and inhibition by SNOcap of contractions to angiotensin I was compared with the angiotensin converting enzyme (ACE) inhibitor, captopril. (2) SNOcap was equipotent as a vasorelaxant on main (i.d. 2-3 mm) and intralobar (i.d. 600 micro m) pulmonary arteries (pIC(50) values: 5.00 and 4.85, respectively). Vasorelaxant responses reached equilibrium rapidly (2-3 min). (3) Pulmonary vasorelaxant responses to SNOcap, like GSNO, were (i) partially inhibited by the soluble guanylate cyclase inhibitor, ODQ (1H-(1,2,4) oxadiazolo(4,3-a)-quinoxalin-1-one; 3 micro M) whereas responses to nitroprusside were abolished and (ii) potentiated by hydroxocobalamin (HCOB; NO. free radical scavenger; 100 micro M) whereas responses to nitroprusside were inhibited. (4) The relative potencies for pulmonary vasorelaxation compared with inhibition of platelet aggregation were: SNOcap 7 : 1; GSNO 25 : 1; nitroprusside >2000 : 1. (5) SNOcap, like captopril, concentration-dependently and time-dependently increased the EC(50) for angiotensin I but not angiotensin II. The dependence on incubation time was independent of the presence of tissue but differed for SNOcap and captopril. This difference reflected the slow dissociation of SNOcap and instability of captopril, and precluded a valid comparison of the potency of the two drugs. After prolonged incubation (>/=5.6 h) SNOcap was more effective than captopril. (6) Thus, in pulmonary arteries SNOcap (i) possesses NO donor properties characteristic of S-nitrosothiols but different from nitroprusside and (ii) inhibits ACE at least as effectively as captopril. These properties suggest that SNOcap could be valuable in the treatment of pulmonary hypertension.

A combination of oral endothelin-A receptor antagonist and oral prostacyclin analogue is superior to each drug alone in ameliorating pulmonary hypertension in rats

OBJECTIVES

We sought to investigate whether the combination of an oral endothelin (ET)A receptor antagonist and an oral prostacyclin (PGI(2)) analogue is superior to the single use of each drug alone for treating pulmonary hypertension (PH).

BACKGROUND

Treatment with intravenous PGI(2) or an ET(A) receptor antagonist was effective for PH; however, the effect of both agents is unclear.

METHODS

We administered the oral ET(A) receptor antagonist TA-0201 and/or the oral PGI(2) analogue beraprost sodium (BPS) to rats with monocrotaline-induced PH for 19 days. The groups were: normal rats with vehicle treatment (Control group), PH rats with vehicle treatment (PH group), PH rats with TA-0201 treatment (PH + TA group), PH rats with BPS treatment (PH + BPS group) and PH rats with TA-0201 and BPS treatment (PH + TA + BPS group).

RESULTS

Right ventricular (RV) systolic pressure and the ratio of RV systolic pressure to systemic systolic blood pressure (Pp/Ps) were markedly higher in the PH group than in the Control group. The increased RV systolic pressure and Pp/Ps were significantly and comparably depressed in the PH + TA and PH + BPS groups; it was more greatly depressed in the PH + TA + BPS group than in the groups with each drug alone. The indexes of RV hypertrophy showed the same tendency as the increase in RV systolic pressure among the five groups. The expression of beta-myosin heavy chain messenger ribonucleic acid in the RV was markedly augmented in the PH group; the enhancement was inhibited in the PH + TA + BPS group to the greatest degree. Medial wall thickness of the pulmonary artery was markedly increased in the PH group; the increase was depressed in the PH + TA + BPS group. Combined treatment also ameliorated PH, even if it started after the onset of PH.

CONCLUSIONS

The combination of an oral ETA receptor antagonist and an oral PGI(2) analogue is superior to the single use of each drug alone in inhibiting the progression of PH.

Bosentan: a dual endothelin receptor antagonist

The peptide endothelin plays a significant role in a wide array of pathological conditions, including primary pulmonary hypertension and pulmonary arterial hypertension associated with collagen vascular disease. These are life-threatening conditions that can severely compromise the function of the lungs and heart. Inhibiting the actions of endothelin by blockade of its receptors provides a new and effective approach to therapy for patients with these conditions. Bosentan (Tracleer ) is the first orally-active dual endothelin receptor antagonist and has recently been approved in the US, Canada, Switzerland and the EU for the treatment of pulmonary arterial hypertension. Bosentan significantly improves exercise capacity, symptoms and functional status in patients with this disease and also slows clinical deterioration, which may be indicative of a delay of disease progression. Results from large-scale studies of bosentan in patients with pulmonary arterial hypertension and chronic heart failure have established its long-term safety and tolerability profiles. The introduction of the dual endothelin receptor antagonist bosentan has provided an essential treatment for pulmonary arterial hypertension and ongoing trials are evaluating its potential role in the management of other endothelin-mediated disease states.

Current management of primary pulmonary hypertension

Primary pulmonary hypertension (PPH) is a rare disorder of the lung vasculature characterised by an increase in pulmonary artery pressure. Although the aetiology of this disease remains unknown, knowledge of the pathophysiology of the disease has advanced considerably. Diagnosis of PPH is largely by exclusion. The clinical symptoms associated with PPH are aspecific and similar to those seen in other cardiovascular and pulmonary diseases. Electrocardiography, echocardiography, pulmonary function tests, and a lung perfusion scan are necessary to exclude secondary forms of pulmonary hypertension and also help to confirm the diagnosis of PPH. A definite diagnosis of PPH is established by right-heart catheterisation which gives a precise measure of the blood pressure in the right side of the heart and the pulmonary artery, right ventricular function and cardiac output. Once a diagnosis of PPH is established, treatment involving drug therapy or surgery is commenced on the basis of the New York Heart Association functional class. Conventional treatment consists of lifetime administration of anticoagulants, oxygen, diuretics, and digoxin. Vasodilator therapy with calcium channel antagonists is indicated in patients who are 'vasoreactive' to acute vasodilator challenge as assessed by right-heart catheterisation. Promising results are obtained by continuous intravenous administration of epoprostenol (prostacyclin). Newer therapies for PPH include prostacyclin analogues, endothelin receptor antagonists, nitric oxide, phosphodiesterase-5 inhibitors, elastase inhibitors, and gene therapy. Surgical treatment consists of atrial septostomy, thromboendarterectomy, and lung or heart-lung transplantation.

Pulmonary vascular remodeling: a target for therapeutic intervention in pulmonary hypertension

Pulmonary vascular remodelling is an important pathological feature of pulmonary hypertension, leading to increased pulmonary vascular resistance and reduced compliance. It involves thickening of all three layers of the blood vessel wall (due to hypertrophy and/or hyperplasia of the predominant cell type within each layer), as well as extracellular matrix deposition. Neomuscularisation of non-muscular arteries and formation of plexiform and neointimal lesions also occur. Stimuli responsible for remodelling involve transmural pressure, stretch, shear stress, hypoxia, various mediators [angiotensin II, endothelin (ET)-1, 5-hydroxytryptamine, growth factors, and inflammatory cytokines], increased serine elastase activity, and tenascin-C. In addition, there are reductions in the endothelium-derived antimitogenic substances, nitric oxide, and prostacyclin. Intracellular signalling mechanisms involved in pulmonary vascular remodelling include elevations in intracellular Ca2+ and activation of the phosphatidylinositol pathway, protein kinase C, and mitogen-activated protein kinase. In animal models of pulmonary hypertension, various drugs have been shown to attenuate pulmonary vascular remodelling. These include angiotensin-converting enzyme inhibitors, angiotensin receptor antagonists, ET receptor antagonists, ET-converting enzyme inhibitors, nitric oxide, phosphodiesterase 5 inhibitors, prostacyclin, Ca2+ -channel antagonists, heparin, and serine elastase inhibitors. Inhibition of remodelling is generally accompanied by reductions in pulmonary artery pressure. The efficacy of some of the drugs varies, depending on the animal model of the disease. In view of the complexity of the remodelling process and the diverse aetiology of pulmonary hypertension in humans, it is to be anticipated that successful anti-remodelling therapy in the clinic will require a range of different drug options.

[Pulmonary hypertension screening in systemic scleroderma: a cohort study of 67 patients]

PURPOSE

Pulmonary hypertension is a severe complication of systemic sclerosis and has emerged as a major cause of morbidity and mortality in this condition. Treatment is all the more efficient as pulmonary hypertension is early diagnosed. A good knowledge of the clinical, biological and functional features of pulmonary hypertension in systemic sclerosis is therefore necessary to suspect and to diagnose pulmonary hypertension as early as possible.

METHODS

Sixty seven patients with systemic sclerosis were retrospectively studied. We compared clinical, immunological, functional (spirometry) and morphological (pulmonary fibrosis) features according to the presence (n = 25) and the characteristic of pulmonary hypertension (isolated or secondary) or the absence (n = 42) of pulmonary hypertension, assessed by Doppler echocardiography.

RESULTS

CREST syndrome (calcinosis, Raynaud's phenomenon, oesophageal involvement, sclerodactyly and telangiectasia) was more frequent in patients with isolated pulmonary hypertension than in patients without PH (72.7% vs 28.5%, P < 0.05; odds-ratio [OR] = 6.6) and dyspnea was more severe (P < 0.001; OR = 11.4). The age at time of pulmonary hypertension diagnosis was higher in patients with secondary pulmonary hypertension than in patients with isolated from (median: 62.5 years (range: 32-35) vs 53 years (range: 37-85), P < 0.05). Patients with isolated pulmonary hypertension had anticardiolipin antibodies more frequently than patients without pulmonary hypertension (72.7% vs 35.7%, P < 0.05). Isolated reduction of diffusing capacity was preferentially observed among patients with isolated pulmonary hypertension than among those without pulmonary hypertension. A linear relation between systolic pulmonary artery pressure values and diffusing capacity values (r = 0.72, P < 0.01) was found. Isolated reduction of diffusing capacity was more frequent in patients with isolated pulmonary hypertension than in patients without pulmonary hypertension (63.6% vs 14.3%, P < 0.001; OR = 10.5).

CONCLUSION

The severity of pulmonary hypertension in systemic sclerosis justifies a systematic screening by Doppler echocardiography and diffusing capacity measurement. Our results allow us to better define the characteristics of sclerodermic patients with isolated or secondary pulmonary hypertension. The search for pulmonary hypertension should be repeated with time and clinicians should be particularly vigilant in the case of a patient presenting these characteristics.

Therapeutic potential of endothelin receptor antagonists and nitric oxide donors in pulmonary hypertension

Pulmonary hypertension can occur idiopathically as a primary disorder of the pulmonary circulation or more commonly, it can exist as a haemodynamic manifestation of a wide variety of pulmonary and cardiovascular diseases, including acute lung injury, chronic obstructive lung disease, congenital heart disease, mitral stenosis, chronic left-sided congestive heart failure and connective tissue diseases such as scleroderma. Pulmonary hypertension is associated with changes in vascular tone as well as vascular structure, with the relative contribution of each dependent upon the aetiology of the increased pulmonary vascular resistance. Most currently available treatments utilise anticoagulants as well as vasodilator drugs that only attenuate the vasoconstrictive component of the disease. The latter category includes oral calcium channel blockers, iv. and aerosolised prostacyclin analogues and inhaled nitric oxide but all three classes of vasodilators have disadvantages and limitations. Treatment with vasodilators is often ineffective in patients with longstanding pulmonary hypertension in which structural changes contribute significantly to the pulmonary hypertension, blood flow obstruction and right heart failure. In view of the immense clinical need, new therapies are being developed by pharmaceutical companies to treat pulmonary hypertension. This update will focus on the current development status of endothelin receptor antagonists and nitric oxide donors for the treatment of pulmonary hypertension.

Current perspectives on the use of gene therapy for hypertension

Systemic hypertension is a pathophysiological state that is manifested as high blood pressure and is a major risk factor for stroke, ischemic heart disease, peripheral vascular disease, and progressive renal damage. Pulmonary hypertension occurs in 3 distinct forms: primary pulmonary hypertension, pulmonary hypertension of the newborn, or secondary pulmonary hypertension attributable to a variety of lung and cardiovascular diseases. This review discusses the use of gene therapy in the control of systemic and pulmonary hypertension. Overexpression of vasodilator genes as well as antisense knockdown of vasoconstrictor genes has been successfully used in animal models of both forms of hypertension. Furthermore, the use of viral vectors to deliver these constructs has achieved long-term control of hypertension. The successful establishment of gene therapy techniques in the animal models of hypertension coupled with the anticipated advances in the genetic aspects of this disease would make it highly feasible to attempt gene delivery in the control of human hypertension.

KRN2391: dual action on rat pulmonary artery and no loss of potency in pulmonary hypertension

1. The pulmonary vasorelaxant properties of KRN2391 (N-cyano-N'-(2-nitroxyethyl)-3-pyridinecarboximidamide) were examined in isolated ring preparations of main (MPA) and intralobar (IPA) pulmonary artery from control and pulmonary hypertensive rats (exposure to hypoxia, 10% oxygen, for 1 week). 2. On both MPA and IPA, pulmonary vasorelaxant responses were inhibited by methylene blue (10 micromol/L) or glibenclamide (1 or 10 micromol/L). Thus, KRN2391 has the properties of both a nitric oxide (NO) donor and a K(ATP) channel opener on rat pulmonary arteries. 3. KRN2391 was more potent and gave a greater maximum relaxation on MPA (-log EC(50) 6.47; maximum 92% reversal of induced contraction) than on IPA (-log EC(50) 6.09; maximum 58% reversal of induced contraction). Comparable differences between MPA and IPA were seen for SIN-1 (NO donor) and levcromakalim (K(ATP) channel opener). 4. KRN2391 was equipotent in MPA from control and pulmonary hypertensive rats but, when glibenclamide (10 micromol/L) was present, KRN2391 was six-fold less potent in preparations from pulmonary hypertensive than control rats. An eight-fold reduction in potency was seen for SIN-1 (no glibenclamide) in arteries from pulmonary hypertensive rats, confirming previous findings with other NO donors. 5. It is concluded that the dual mechanism of action of KRN2391 accounts for the finding that this drug is equally potent in pulmonary arteries from pulmonary hypertensive and control rats. In the context of pulmonary hypertension, this property of the drug could give it an advantage over drugs that act solely as NO donors because these decline in potency, at least in animal models of this disease.

Perindopril, an angiotensin converting enzyme inhibitor, in pulmonary hypertensive rats: comparative effects on pulmonary vascular structure and function

1. Hypoxic pulmonary hypertension in rats (10% O2, 4 weeks) is characterized by changes in pulmonary vascular structure and function. The effects of the angiotensin converting enzyme inhibitor perindopril (oral gavage, once daily for the 4 weeks of hypoxia) on these changes were examined. 2. Perindopril (30 mg kg-1 d-1) caused an 18% reduction in pulmonary artery pressure in hypoxic rats. 3. Structural changes (remodelling) in hypoxic rats included increases in (i) critical closing pressure in isolated perfused lungs (remodelling of arteries <50 microm o.d.) and (ii) medial wall thickness of intralobar pulmonary arteries, assessed histologically (vessels 30 - 100 and 101 - 500 microm o.d.). Perindopril 10 and 30 mg kg-1 d-1 attenuated remodelling in vessels < or = 100 microm (lungs and histology), 30 mg kg-1 d-1 was effective in vessels 101 - 500 microm but neither dose prevented hypertrophy of main pulmonary artery. 3 mg kg-1 d-1 was without effect. 4. Perindopril (30 mg kg-1 d-1) prevented the exaggerated hypoxic pulmonary vasoconstrictor response seen in perfused lungs from hypoxic rats but did not prevent any of the functional changes (i.e. the increased contractions to 5-HT, U46619 (thromboxane-mimetic) and K+ and diminished contractions to angiotensins I and II) seen in isolated intralobar or main pulmonary arteries. Acetylcholine responses were unaltered in hypoxic rats. 5. We conclude that, in hypoxic rats, altered pulmonary vascular function is largely independent of remodelling. Hence any drug that affects only remodelling is unlikely to restore pulmonary vascular function to normal and, like perindopril, may have only a modest effect on pulmonary artery pressure.