Development Of Primary Pulmonary Hypertension Research Articles

P111: Estrogen does not attenuate hypoxic pulmonary vasoconstriction

Background: Sex differences exist between men and women in a variety of organ systems. Primary pulmonary hypertension (PPH) is a clinically important disease exhibiting this sexual dimorphism. Due the gender difference in this disease, many studies have investigated the role of sex hormones in the development of PPH. Females have been noted to exhibit less severe pulmonary hypertension during chronic hypoxia as compared to men, which has lead to the investigation of estrogen in the hypoxic response. We hypothesize that endogenous estrogen will attenuate hypoxic pulmonary vasoconstriction (HPV) in acute hypoxia. To study this, isometric force displacement was measured in isolated rat pulmonary artery rings of normal and ovarectomized females. Methods: Normal and ovarectomized adult female (250-350g) Sprague-Dawley rat pulmonary arteries (n=8/group) were isolated and suspended in physiologic organ baths. Pulmonary arteries were pre-contracted with phenylephrine prior to 60 min hypoxia. Force displacement was continuously recorded. Data (mean+/-SEM) was analyzed with two-way analysis of variance with post-hoc Bonferroni test and unpaired student’s t-test. Results: Normal female and ovarectomized females exhibited similar phase II vasoconstriction during acute hypoxia. Maximum phase II vasoconstriction for normal females was 105.41 ± 7.61% vs. 106.94 ± 19.18% for ovarectomized females (P=.9424). Conclusions: We conclude that endogenous estrogen exposure does not alter pulmonary vasoreactivity during acute hypoxia. Although studies have shown that there is a role of endogenous and exogenous estrogen in attenuation of pulmonary hypertension, our Results indicate that chronic exposure to estrogen does not affect the acute response to hypoxia by pulmonary arteries.

Transforming Growth Factor-βs and Vascular Disorders

Transforming growth factor-β (TGF-β) superfamily members, TGF-β and bone morphogenetic proteins (BMPs), are potent regulatory cytokines with diverse functions on vascular cells. They signal through heteromeric type I and II receptor complexes activating Smad-dependent and Smad-independent signals, which regulate proliferation, differentiation, and survival. They are potent regulators of vascular development and vessel remodeling and play key roles in atherosclerosis and restenosis, regulating endothelial, smooth muscle cell, macrophage, T cell, and probably vascular calcifying cell responses. In atherosclerosis, TGF-β regulates lesion phenotype by controlling T-cell responses and stimulating smooth muscle cells to produce collagen. It contributes to restenosis by augmenting neointimal cell proliferation and collagen accumulation. Defective TGF-β signaling in endothelial cells attributable to mutations in endoglin or the type I receptor ALK-1 leads to hereditary hemorrhagic telangiectasia, whereas defective BMP signaling attributable to mutations in the BMP receptor II has been associated with development of primary pulmonary hypertension. The development of mouse models with either cell type–specific or general inactivation of TGF-β/BMP signaling has started to reveal the importance of the regulatory network of TGF-β/BMP pathways in vivo and their significance for atherosclerosis, hereditary hemorrhagic telangiectasia, and primary pulmonary hypertension. This review highlights recent findings that have advanced our understanding of the roles of TGF-β superfamily members in regulating vascular cell responses and provides likely avenues for future research that may lead to novel pharmacological therapies for the treatment or prevention of vascular disorders.

Early Diagnosis of Pulmonary Circulatory Disorders in Acute Lung Lesions in Critically Ill Patients

The most severe sequels of acute lung lesions are manifested by the impairment of ventilation-perfusion relations, by the development of primary pulmonary hypertension, by circulatory disorders and the increased content of extravascular fluid in the lung, whose diagnosis is extremely difficult. The purpose of the study was to access the capacities of early diagnosis of systemic hemodynamic and pulmonary circulatory disorders in acute lung lesion in patients with critical states. Hydro- and hemodynamics was evaluated in 32 persons in the early phase of intoxications with neurotropic poisons, in 15 with severe concomitant injury, and in 22 patients with critical states intensively treated cardiac surgery. Hemodynamics was determined, by concomitantly using the integral body rheography technique after M. I. Tishchenko and transthoracic impedance cardiogra-phy. The rheographic techniques could evaluate the state of systemic hemodynamics, the nature and effectiveness of pulmonary pulsatile blood flow, that depended on pulmonary hypertension, and increased thoracic fluid. The determination of the level of lactate and its arterial and venous blood ration with consideration of lactate clearance enabled the authors to evaluate both the effectiveness of systemic perfusion and impaired metabolic processes in the lung. Drastically decreased pulsatile blood flow, ineffective volumetric load, low oxygenation index, increased thoracic fluid volume, and the ratios of the arterial to venous blood concentration of lactate with its normal clearance may be early signs of acute lung lesion.

Nordexfenfluramine causes more severe pulmonary vasoconstriction than dexfenfluramine

The anorectic agent dexfenfluramine (dex) causes the development of primary pulmonary hypertension in susceptible patients by an unknown mechanism. We compared the effects of dex with those of its major metabolite, nordexfenfluamine (nordex), in the isolated perfused rat lung and in isolated rings of resistance pulmonary arteries. Nordex caused a dose-dependent and more intense vasoconstriction, which can be inhibited by the nonspecific 5-hydroxytryptamine type 2 (5-HT(2)) blocker ketanserin. Similarly a rise in cytosolic calcium concentration ([Ca(2+)](i)) in dispersed pulmonary artery smooth muscle cells (PASMCs) induced by nordex could be prevented by ketanserin. Unlike prior observations with dex, nordex did not inhibit K(+) current or cause depolarization in PASMCs. Removal of Ca(2+) from the tissue bath or addition of nifedipine (1 microM) reduced ring contraction to nordex by 60 +/- 9 and 63 +/- 4%, respectively. The addition of 2-aminoethoxydiphenyl borate (2-APB), a blocker of store-operated channels and the inositol 1,4,5-trisphosphate receptor, caused a dose-dependent decrease in the ring contraction elicited by nordex. The combination of 2-APB (10 microM) and nifedipine (1 microM) completely ablated the nordex contraction. Likewise the release of Ca(2+) from the sarcoplasmic reticulum by cyclopiazonic acid markedly reduced the nordex contraction while leaving the KCl contraction unchanged. We conclude that nordex may be responsible for much of the vasoconstriction stimulated by dex, through the activation of 5-HT(2) receptors and that the [Ca(2+)](i) increase in rat PASMCs caused by dex/nordex is due to both influx of extracellular Ca(2+) and release of Ca(2+) from the sarcoplasmic reticulum.

Genetic aspect of pulmonary arterial hypertension

This paper concentrates on the genetic aspects of pulmonary arterial hypertension (PAH), a diagnostically based subclass of pulmonary hypertension that includes primary pulmonary hypertension (PPH). During the past year, patients with familial and sporadic PPH were found to have germline heterozygous missense, nonsense and frameshift mutations in bone morphogenetic protein receptor II (BMPRZ). Mutations in BMPR2, a member of the transforming growth factor-β (TGF-β) receptor superfamily, are predicted to interrupt the bone morphogenetic protein (BMP) signalling pathway, resulting in proliferation, rather than apoptosis of cells within small arterioles. Mechanistically, haploinsufficiency was found by using in vitro gene expression experiments, but a dominant-negative mechanism has not been excluded. The failure to find BMPR2 mutations in all families with familial PPH and in all patients with sporadic PPH suggests that other genes remain to be identified. Mutations in ALK1, a TGF-β type 1 receptor, previously known to cause type 2 hereditary haemorrhagic telangiectasia (HHT), have also been reported in a few HHT families with clinical and histological features of PPH. The clinical development of PPH, as in neoplasia, appears to require ‘two hits’. The two hits can be provided either by genetic or environmental factors.

Anorexigens and Pulmonary Hypertension in the United States

The use of appetite suppressants in Europe has been associated with the development of primary pulmonary hypertension (PPH). Recently, fenfluramine appetite suppressants became widely used in the United States but were withdrawn in September 1997 because of concerns over adverse effects. We conducted a prospective surveillance study on patients diagnosed with pulmonary hypertension at 12 large referral centers in North America. Data collected on patients seen from September 1, 1996, to December 31, 1997, included the cause of the pulmonary hypertension and its severity. Patients with no identifiable cause of pulmonary hypertension were classed as PPH. A history of drug exposure also was taken with special attention on the use of antidepressants, anorexigens, and amphetamines. Five hundred seventy-nine patients were studied, 205 with PPH and 374 with pulmonary hypertension from other causes (secondary pulmonary hypertension [SPH]). The use of anorexigens was common in both groups. However, of the medications surveyed, only the fenfluramines had a significant preferential association with PPH as compared with SPH (adjusted odds ratio for use > 6 months, 7.5; 95% confidence interval, 1.7 to 32.4). The association was stronger with longer duration of use when compared to shorter duration of use and was more pronounced in recent users than in remote users. An unexpectedly high (11.4%) number of patients with SPH had used anorexigens. The magnitude of the association with PPH, the increase of association with increasing duration of use, and the specificity for fenfluramines are consistent with previous studies indicating that fenfluramines are causally related to PPH. The high prevalence of anorexigen use in patients with SPH also raises the possibility that these drugs precipitate pulmonary hypertension in patients with underlying conditions associated with SPH.

Drug-induced respiratory disorders: incidence, prevention and management.

Various drugs are associated with adverse respiratory disorders (ARDs) ranging in severity from mild, moderate to severe and even fatal. Cardioselective and nonselective beta-blockers, calcium antagonists and dipyridamole can induce asthma. ACE inhibitors are mainly associated with cough. Amiodarone is related to a form of interstitial pneumonitis (IP) which can be fatal, tocainidine and flecainidine to a form of IP, and hydrochlorothiazide to a form of IP and pulmonary oedema. Antiasthmatic drugs can be associated with a paradoxical bronchospasm, while leukotriene antagonists are linked to the development of Churg-Strauss syndrome. Nonsteroidal anti-inflammatory drugs including aspirin (acetylsalicylic acid) may induce asthma. Gold is mainly related to IP, penicillamine to IP, systemic lupus erythematosus, bronchiolitis obliterans, and Goodpasture's syndrome. Acute respiratory reactions to nitrofurantoin include dyspnoea, cough, IP, and pleural effusion while IP and fibrosis are common in chronic reactions. Other antibacterials mainly evoke pneumonitis, pulmonary infiltrates and eosinophilia, and bronchiolitis obliterans. ARDs are similar for most categories of cytotoxic agents, with chronic pneumonitis and fibrosis being the most common. Noncardiogenic pulmonary oedema occurs as the most common respiratory complication in opioid agonist addiction. Psychotropic drugs such as phenothiazides, butyrophenones and tricyclic antidepressants can also induce pulmonary oedema. Oral contraceptives may produce asthma exacerbation, while long term use and/or high doses of postmenopausal hormone replacement therapy increase the risk of asthma. Bromocriptine is mainly associated with pleural effusion, while methysergide is usually associated with pleural effusion and fibrosis. Some anorectic agents have been linked to the development of primary pulmonary hypertension. The possibility of the occurrence of ARDs should be taken into account in each individual patient. Although in most cases the adverse effects are unpredictable, they can be reduced to a minimum or prevented if some drugs are avoided or stopped in time.

Dexfenfluramine increases pulmonary artery smooth muscle intracellular Ca2+, independent of membrane potential.

The anorexic agent dexfenfluramine causes the development of primary pulmonary hypertension in susceptible patients by an unknown mechanism that may include changes in K+-channel activity and intracellular Ca2+ concentration ([Ca2+]i). We investigated the dose-dependent effects of dexfenfluramine on [Ca2+]i, K+ current, and membrane potential in freshly dispersed rat pulmonary artery smooth muscle cells. Dexfenfluramine caused a dose-dependent (1-1,000 microM) increase in [Ca2+]i, even at concentrations lower than those necessary to inhibit K+ currents (10 microM) and cause membrane depolarization (100 microM). The [Ca2+]i response to 1 and 10 microM dexfenfluramine was completely abolished by pretreatment of the cells with 0.1 microM thapsigargin, whereas the response to 100 microM dexfenfluramine was reduced. CoCl2 (1 mM), removal of extracellular Ca2+, and pretreatment with caffeine (1 mM) reduced but did not abolish the response to 100 microM dexfenfluramine. We conclude that dexfenfluramine increases [Ca2+]i in rat pulmonary artery smooth muscle cells by both release of Ca2+ from the sarcoplasmic reticulum and influx of extracellular Ca2+.

Fenfluramine Potentiates Canine Pulmonary Vasoreactivity to Endothelin-1

The appetite suppressant fenfluramine, a serotonin uptake inhibitor, has been implicated in the development of primary pulmonary hypertension (PPH). The effect of fenfluramine on the pressor response to endothelin-1 (ET-1) in the canine pulmonary circulation was determined using the isolated perfused dog lung. Pulmonary vascular resistance was measured using vascular occlusion techniques. Group 1 (n=4) consisted of isolated lung lobes treated with 10−8MET-1 alone. For group 2 (n=4) and group 3 (n=4), dogs were given 15 mg fenfluramine daily for 14 days prior to sacrifice for isolated lung perfusion. In group 2, lobes were treated with 10−7Mfenfluramine after lung isolation. In group 3, the isolated lobes were treated with 10−8MET-1 similar to group 1. Acute treatment of the isolated lobes in group 2 with 10−7Mfenfluramine increased pulmonary arterial pressure. In group 3, administration of 10−8MET-1 potentiated the effect of ET-1 on post-capillary resistance relative to group 1, and elicited an increase in precapillary resistance, an effect not present in group 1. These results indicate that chronic fenfluramine exposure potentiates the pulmonary vasoconstrictor response to ET-1, and suggests that elevated levels of serotonin may «prime» the pulmonary circulation to become hyperreactive to other vasoactive substances possibly leading to the development of disease states such as primary pulmonary hypertension.

Appetite suppressants and pulmonary hypertension.

Background. Recently in France, primary pulmonary hypertension developed in a cluster of patients exposed to derivatives of fenfluramine in appetite suppressants (anorexic agents), which are used for weight control. We investigated the potential role of anorexic agents and other suspected risk factors for primary pulmonary hypertension. Methods. In a case-control study, we assessed 95 patients with primary pulmonary hypertension from 35 centers in France, Belgium, the United Kingdom, and the Netherlands and 355 controls recruited from general practices and matched to the patients' sex and age. Results. The use of anorexic drugs (mainly derivatives of fenfluramine) was associated with an increased risk of primary pulmonary hypertension (odds ratio with any anorexic-drug use, 6.3; 95 percent confidence interval, 3.0 to 13.2). For the use of anorexic agents in the preceding year, the odds ratio was 10.1 (95 percent confidence interval, 3.4 to 29.9). When anorexic drugs were used for a total of more than three months, the odds ratio was 23.1 (95 percent confidence interval, 6.9 to 77.7). We also confirmed an association with several previously identified risk factors: a family history of pulmonary hypertension, infection with the human immunodeficiency virus, cirrhosis, and use of cocaine or intravenous drugs. Conclusions. The use of anorexic drugs was associated with the development of primary pulmonary hypertension. Active surveillance for this disease should be considered, particularly since the use of anorexic drugs is expected to increase in the near future.

Appetite-suppressant drugs and the risk of primary pulmonary hypertension. International Primary Pulmonary Hypertension Study Group.

Recently, a cluster of patients was observed in France in whom primary pulmonary hypertension developed in patients exposed to derivatives of fenfluramine in appetite suppressants (anorexic agents), which are used for weight control. We investigated the potential role of anorexic agents and other suspected risk factors for primary pulmonary hypertension. In a case-control study, we assessed 95 patients with primary pulmonary hypertension from 35 centers in France, Belgium, the United Kingdom, and the Netherlands and 355 controls recruited from general practices and matched to the patients' sex and age. The use of anorexic drugs (mainly derivatives of fenfluramine) was associated with an increased risk of primary pulmonary hypertension (odds ratio with any anorexic-drug use, 6.3; 95 percent confidence interval, 3.0 to 13.2). For the use of anorexic agents in the preceding year, the odds ratio was 10.1 (95 percent confidence interval, 3.4 to 29.9). When anorexic drugs were used to a total of more than three months, the odds ratio was 23.1 (95 percent confidence interval, 6.9 to 77.7). We also confirmed an association with several previously identified risk factors: a family history of pulmonary hypertension, infection with the human immunodeficiency virus, cirrhosis, and use of cocaine or intravenous drugs. The use of anorexic drugs was associated with the development of primary pulmonary hypertension. Active surveillance for this disease should be considered, particularly since their use is expected to increase in the near future.

Possible role of prostaglandins in the pathogenesis of pulmonary hypertension

Pulmonary hypertension is known to occur at high altitudes, due to hypoxia and is considered to be more common in women taking oral contraceptives, situations known to decrease the synthesis of prostaglandin E and possibly prostacyclin with simultaneous increase in thromboxane A2 synthesis. Decreased bradykinin synthesis or persistence of foetal type of pulmonary vasculature are considered to predispose to the development of primary pulmonary hypertension. Bradykinin is a potent stimulator of prostaglandin E synthesis, a known vasodilator. Thus it is possible that primary pulmonary hypertension could be due to a fall in the synthesis of vasodilators like prostaglandin E and/or prostacyclin and a relative or absolute increase in vasoconstrictors like thromboxane A2 and/or prostaglandin F2 alpha.