Pulmonary Vascular Adaptation Research Articles

Pulmonary vascular remodeling and right ventricular adaptation in precapillary pulmonary hypertension

Background: In precapillary pulmonary hypertension (PH) as pulmonary arterial hypertension (PAH), chronic thromboembolic PH (CTPEH) and PH due to hypoxia and lung disease (HPH) the different pathomechanisms of vascular remodeling result in different right ventricular (RV) adaptation. Routine clinical factors which could predict vascular remodeling are lacking. Purpose: Our aim was to investigate the differences in parameters of pulmonary vascular remodeling and RV adaptation in subgroups of precapillary PH and to correlate the severity of PH with these parameters. Methods: Fifty-one patients (age 57±15 years) with precapillary PH (PAH N=18, CTEPH N=15, HPH N=18;) underwent right heart catheterization (RHC) and results of RHC, echocardiography and laboratory tests were analyzed retrospectively. Results: The majority of parameters did not show difference among PH groups, but diastolic PAP was higher in PAH than in CTEPH and HPH (p<0.05) and RV outflow tract velocity time integral (RVOT VTI) and RV stroke work index were increased in PAH compared to HPH (p<0.05). Pulmonary vascular resistance (PVR) showed a significant relation to pulmonary arterial compliance (PAC) in the total cohort (p<0.05, r=–0.661) and in all subgroups (PAH p<0.05, r=–0.70; CTEPH p<0.05, r=–0.525; HPH p<0.05, r=–0.793). In PAH, all parameters including RVOT VTI and acceleration time (AT), tricuspid annular plane systolic excursion, RV diameter and right atrial area showed correlations with PVR. In the HPH group, only RVOT AT had a correlation with PVR, but no parameters in the CTEPH group showed a relationship to other factors. Conclusion: In precapillary PH the different degree of RV adaptation in the subgroups is shown by RVSWI as an invasive parameter. The severity of PH is related to PAC in precapillary PH. Some parameters can better characterize the severity of vascular and cardiac changes in PAH than in CTEPH or HPH.

Pulmonary vascular function at exercise in systemic sclerosis: A case-control study

Systemic sclerosis (SSc) is a severe form of associated pulmonary arterial hypertension (PAH), for which annual screening is recommended based on resting echocardiography. While the latter may be normal in the early stages of PAH, exercise echocardiography (Ex-Echo) may provide additional insights on pulmonary vascular function. However, the clinical use of Ex-Echo is limited by methodological concerns. Although it is currently admitted that pulmonary arterial pressure (PAP) at exercise should be interpreted relative to flow change, few studies investigated the relationship between PAP and cardiac output (CO) during exercise in SSc patients. We sought to explore exercise-induced changes in the pulmonary circulation by pressure-flow relationship in SSc patients compared with healthy subjects. SSc patients without overt lung or heart involvement, and healthy subjects underwent symptom-limited Ex-Echo to generate multipoint relationship between meanPAP (PAPm) and CO. Conventional markers of RV function were also recorded during exercise. Forty-two patients and 47 controls were included. At peak exercise, patients had lower PAP, lower CO, but higher PAPm to CO ratio (TPR) than controls ( Table 1 ). The slope of PAPm to CO relationship (P/Q slope) was higher in patients ( Fig. 1 ), but this was not significant after correction for age. Age was an independent determinant for the P/Q slope, but did not affect the difference in peak-exercise TPR. Markers of RV function (TAPSE, S wave velocity, and IVA) were lower in patients at exercise. SSc patients presented with different pulmonary vascular and myocardial adaptation to exercise compared with healthy individuals. In contrast with P/Q slope, changes in peak TPR were not influenced by age. This pattern may be observed in patients without evidence of cardiac or pulmonary involvement and explain, at least in part, lower exercise capacity in these patients.

Effects of living at moderate altitude on pulmonary vascular function and exercise capacity in mice with sickle cell anemia

Exposure to high altitude worsens symptoms and crises in patients with sickle cell disease (SCD). However, it remains unclear if prolonged exposure to low barometric pressures exacerbates SCD etiologies or impairs quality of life. We tested the hypothesis that, relative to wild‐type (WT) mice, Berkley sickle cell mice (BERK‐SS) residing at sea level, mild (1609 m) and moderate (2438 m) altitude would have a higher rate of hemolysis, impaired cardiac function, and reduced exercise tolerance and that the level of altitude would worsen these decrements. Following 3 months of altitude exposure, right ventricular systolic pressures (RVSP) were measured (solid‐state transducer). In addition, the adaptive balance between pulmonary vascular endothelial nitric oxide synthase and endothelin was assessed in lung tissue to determine differences in pulmonary vascular adaptation and the speed/duration relationship (critical speed, CS) was used to evaluate treadmill exercise tolerance. At all altitudes, BERK‐SS mice had a significantly lower %Hct and higher total bilirubin and free hemoglobin concentration (P<0.05 for all). RVSPs in BERK‐SS were higher than WT at moderate altitude and when compared to BERK‐SS at sea level (P<0.05, for both). CS was significantly lower in BERK‐SS at mild and moderate altitude (P<0.05). BERK‐SS demonstrated exacerbated SCD complications and reduced exercise capacity associated with an increase in altitude. These results suggest that exposure to mild and moderate altitude enhances the progression of SCD in BERK‐SS mice compared to healthy WT cohorts and BERK‐SS mice at sea level and provides crucial information for the clinical counseling of SCD patients.Support or Funding InformationThis study was supported by the National Heart, Lung and Blood Institute Grants 1R01HL125642‐01A1 (Irwin DC), 1R01HL086680‐07 (Nozik‐Grayck E), 5P01HL014985‐38 (Stenmark KR), and T32‐HL007171 (Stenmark KR), Colorado Sickle Cell Treatment and Research Center (Hassell K and Nuss R).This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Effects of living at moderate altitude on pulmonary vascular function and exercise capacity in mice with sickle cell anaemia.

Sickle cell disease (SCD) results in cardiopulmonary dysfunction, which may be exacerbated by prolonged exposure to environmental hypoxia. It is currently unknown whether exposure to mild and moderate altitude exacerbates SCD associated cardiopulmonary and systemic complications. Three months of exposure to mild (1609m) and moderate (2438m) altitude increased rates of haemolysis and right ventricular systolic pressures in mice with SCD compared to healthy wild-type cohorts and SCD mice at sea level. The haemodynamic changes in SCD mice that had lived at mild and moderate altitude were accompanied by changes in the balance between pulmonary vascular endothelial nitric oxide synthase and endothelin receptor expression and impaired exercise tolerance. These data demonstrate that chronic altitude exposure exacerbates the complications associated with SCD and provides pertinent information for the clinical counselling of SCD patients. Exposure to high altitude worsens symptoms and crises in patients with sickle cell disease (SCD). However, it remains unclear whether prolonged exposure to low barometric pressures exacerbates SCD aetiologies or impairs quality of life. We tested the hypothesis that, relative to wild-type (WT) mice, Berkley sickle cell mice (BERK-SS) residing at sea level, mild (1609m) and moderate (2438m) altitude would have a higher rate of haemolysis, impaired cardiac function and reduced exercise tolerance, and that the level of altitude would worsen these decrements. Following 3months of altitude exposure, right ventricular systolic pressure was measured (solid-state transducer). In addition, the adaptive balance between pulmonary vascular endothelial nitric oxide synthase and endothelin was assessed in lung tissue to determine differences in pulmonary vascular adaptation and the speed/duration relationship (critical speed) was used to evaluate treadmill exercise tolerance. At all altitudes, BERK-SS mice had a significantly lower percentage haemocrit and higher total bilirubin and free haemoglobin concentration (P<0.05 for all). right ventricular systolic pressures in BERK-SS were higher than WT at moderate altitude and also compared to BERK-SS at sea level (P<0.05, for both). Critical speed was significantly lower in BERK-SS at mild and moderate altitude (P<0.05). BERK-SS demonstrated exacerbated SCD complications and reduced exercise capacity associated with an increase in altitude. These results suggest that exposure to mild and moderate altitude enhances the progression of SCD in BERK-SS mice compared to healthy WT cohorts and BERK-SS mice at sea level and provides crucial information for the clinical counselling of SCD patients.

Environmental Physiology and Diving Medicine.

Man’s experience and exploration of the underwater environment has been recorded from ancient times and today encompasses large sections of the population for sport enjoyment, recreational and commercial purpose, as well as military strategic goals. Knowledge, respect and maintenance of the underwater world is an essential development for our future and the knowledge acquired over the last few dozen years will change rapidly in the near future with plans to establish secure habitats with specific long-term goals of exploration, maintenance and survival. This summary will illustrate briefly the physiological changes induced by immersion, swimming, breath-hold diving and exploring while using special equipment in the water. Cardiac, circulatory and pulmonary vascular adaptation and the pathophysiology of novel syndromes have been demonstrated, which will allow selection of individual characteristics in order to succeed in various environments. Training and treatment for these new microenvironments will be suggested with description of successful pioneers in this field. This is a summary of the physiology and the present status of pathology and therapy for the field.

PBX transcription factors drive pulmonary vascular adaptation to birth.

A critical event in the adaptation to extrauterine life is relaxation of the pulmonary vasculature at birth, allowing for a rapid increase in pulmonary blood flow that is essential for efficient gas exchange. Failure of this transition leads to pulmonary hypertension (PH), a major cause of newborn mortality associated with preterm birth, infection, hypoxia, and malformations including congenital diaphragmatic hernia (CDH). While individual vasoconstrictor and dilator genes have been identified, the coordination of their expression is not well understood. Here, we found that lung mesenchyme-specific deletion of CDH-implicated genes encoding pre-B cell leukemia transcription factors (Pbx) led to lethal PH in mice shortly after birth. Loss of Pbx genes resulted in the misexpression of both vasoconstrictors and vasodilators in multiple pathways that converge to increase phosphorylation of myosin in vascular smooth muscle (VSM) cells, causing persistent constriction. While targeting endothelin and angiotensin, which are upstream regulators that promote VSM contraction, was not effective, treatment with the Rho-kinase inhibitor Y-27632 reduced vessel constriction and PH in Pbx-mutant mice. These results demonstrate a lung-intrinsic, herniation-independent cause of PH in CDH. More broadly, our findings indicate that neonatal PH can result from perturbation of multiple pathways and suggest that targeting the downstream common effectors may be a more effective treatment for neonatal PH.

Telemetric monitoring of blood flow and pressure in a chronic lamb model (862.7)

The lamb is an excellent model for the study of cardiopulmonary dynamics in small children. Steady state measurements of cardiovascular parameters such as blood pressure and blood flow in undisturbed subjects are challenging to acquire but essential in the continuous monitoring of cardiopulmonary and systemic interactions. We have established a chronic lamb model that incorporates a telemetry system (Transonic EndoGear Inc, Davis CA) capable of measuring up to five variables in the same animal. This provides a new opportunity to record uninterrupted comprehensive cardiovascular performance over an extended period of time. This telemetry system uses a Doppler‐based flowmeter that allows measurements of flow velocity using endo‐, epi and peri‐vascular mounted flowprobes. Blood pressure is measured with endovascular 3F solid‐sate pressure catheters. With this system, we have applied perivascular Doppler flowprobes in the superior vena cava, endovascular flowprobes in the main pulmonary artery and epivascular flowprobes on the aorta as well as endovascular blood pressure catheters in the left internal mammary artery, main pulmonary artery, and right atrium. The EndoGear system enables the chronic invasive monitoring of critical cardiovascular variables in untethered and unrestrained lambs for extended periods, providing new insight about the time course of postnatal pulmonary vascular adaptation.

Delayed Pulmonary Arterial Hypertension in Relation to Pulmonary Damage Score after Pneumonectomy under Protective Ventilation: Experimental Study

Objective: To characterize pulmonary hemodynamic changes in relation to lung injury at 2 time points [48 h (H48) and 168 h (H168)] after pneumonectomy under intraoperative protective ventilation in order to improve postpneumonectomy pulmonary edema (PPE) prevention. Method: Fifteen pigs (25 ± 1.9 kg) were randomly allocated to nonsurgical (control, n = 5) and surgical (H48 and H168) groups. A left pneumonectomy under volume-controlled one-lung ventilation (OLV) (low tidal volume, positive end-expiratory pressure = 4 cm H₂O, inspired oxygen fraction = 50%) was performed in surgical animals. Mean pulmonary artery pressure (MPAP) and pulmonary artery occlusion pressure were recorded. Pulmonary vascular resistance (PVR) was calculated. Pulmonary damage score (PDS) and bronchoalveolar albumin level were evaluated. Data were collected after induction (T0), after OLV (T1), after left pneumonectomy (T2), and at H48 or H168 (T3). Results: Pneumonectomy caused precapillary pulmonary arterial hypertension (PAH) measured at T3 H48 (36.2 ± 3.67 mm Hg). PAH was delayed temporarily (both after OLV and after pneumonectomy) (p < 0.001), and linked with PVR (r = 0.93; p < 0.05). PDS and bronchoalveolar albumin level varied with MPAP (r = 0.76; p < 0.001 and r = 0.55; p < 0.05). Conclusion: Given that PAH is delayed and related to PVR increase, indicating secondary pulmonary vascular bed adaptation limits, pharmacological treatment should focus on a delayed failure in pulmonary capacitance in patients at risk of PPE.

Stress Echocardiography in Regurgitant Valve Disease

Because of its wide availability, low cost, versatility, and clinical use, stress echocardiography has become increasingly recognized as a valuable tool in the assessment of patients with regurgitant valvular heart disease. Exercise testing is favored compared with pharmacological stress testing for risk stratification in asymptomatic patients and can identify what might otherwise be considered as a moderate valve disease. It has been shown to provide insights into exertional symptoms disproportionate to resting hemodynamics in these patients and to facilitate individual risk stratification. Aggravation of valvular regurgitation severity, exercise-induced pulmonary hypertension (PHT), impaired left ventricular (LV) contractile reserve, inducible ischemia, dynamic LV dyssynchrony, and altered exercise capacity, together with the development of symptoms during exercise echocardiography, provide the clinician with straightforward prognostic information, therefore enabling a more accurate definition of the optimal timing of intervention in patients with valvular regurgitation.1,2 In contrast, dobutamine stress echocardiography has little value in cases of valvular regurgitation. Dobutamine infusion is almost systematically associated with a decrease in the severity of regurgitation; however, it might be of interest in the detection of LV contractile reserve and inducible ischemia. The most common form of exercise used in conjunction with echocardiography is immediate postexercise imaging on a treadmill or upright bicycle ergometer. However, semisupine exercise testing on an appropriate tilted table allows continuous echocardiographic monitoring, which represents an advantageous tool for quantifying changes in valvular regurgitation severity, LV function, and pulmonary pressure (Table). This exercise stress echocardiography modality (ie, per-exercise echocardiography) is the most used in Europe, and we strongly suggest this approach in the setting of valvular heart disease to detect evanescent changes. A symptom-limited graded exercise test is recommended, and ≥80% of the age-predicted upper heart rate should be reached in the absence of symptoms. The test is adapted to the clinical conditions …

Pulmonary vascular adaptation to high-altitude living

When a rat is exposed to a low oxygen (10%) atmosphere, pulmonary artery pressure rises over a few days to reach a new level around 2 to 3-fold above that in a normal oxygen atmosphere. The rise in pulmonary artery pressure is accompanied by structural changes in the pulmonary vasculature that include the expansion of the smooth muscle in pulmonary arteries and arterioles and extension to previously unmuscularised vessels. The right ventricle undergoes hypertrophy. This response of the pulmonary circulation to hypoxia is typical of most mammals, including humans. There is, however, considerable inter-species and within species variation in the magnitude of the response. For example, Tibetans, who have lived at altitude for many thousands of years, exhibit a lower pulmonary artery pressure at altitude than more recent arrivals, such as the Han Chinese. Recognition of this differential response has prompted studies comparing the activity of candidates, including components of nitric oxide signalling pathway, in cohorts of subjects at high altitude. Access to high-throughput sequencing has enabled studies comparing genome sequences in these cohorts. Understanding the genomic variants that underlie susceptibility to hypoxia-induced pulmonary hypertension can signpost druggable signalling pathways that might be exploited to ameliorate the effects of exposure to hypoxia – and may also be useful in diseases where hypoxia is a pathological factor (such as COPD) or in intensive care situations.

A brief overview of mouse models of pulmonary arterial hypertension: problems and prospects

Many chronic pulmonary diseases are associated with pulmonary hypertension (PH) and pulmonary vascular remodeling, which is a term that continues to be used to describe a wide spectrum of vascular abnormalities. Pulmonary vascular structural changes frequently increase pulmonary vascular resistance, causing PH and right heart failure. Although rat models had been standard models of PH research, in more recent years the availability of genetically engineered mice has made this species attractive for many investigators. Here we review a large amount of data derived from experimental PH reports published since 1996. These studies using wild-type and genetically designed mice illustrate the challenges and opportunities provided by these models. Hemodynamic measurements are difficult to obtain in mice, and right heart failure has not been investigated in mice. Anatomical, cellular, and genetic differences distinguish mice and rats, and pharmacogenomics may explain the degree of PH and the particular mode of pulmonary vascular adaptation and also the response of the right ventricle.

CGMP Inhibits TGF-β Signaling by Sequestering Smad3 with Cytosolic β2-Tubulin in Pulmonary Artery Smooth Muscle Cells

Atrial natriuretic peptide (ANP) and TGF-β play counterregulatory roles in pulmonary vascular adaptation to chronic hypoxia. We have demonstrated that ANP-cyclic GMP (cGMP)-protein kinase G (PKG) signaling inhibits TGF-β signaling by blocking TGF-β-induced nuclear translocation of mothers against decapentaplegic homolog (Smad)3 in pulmonary artery smooth muscle cells (PASMC). The current study tested the novel hypothesis that activation of the ANP-cGMP-PKG pathway limits TGF-β-induced Smad3 nuclear translocation by enhancing Smad3 binding to cytosolic anchoring proteins in isolated pulmonary artery smooth muscle cells. Cells were pretreated with vehicle or cGMP and then exposed to TGF-β1 treatment. Cytosolic fractions were isolated and immunoprecipitated with a selective anti-Smad3 antibody. Differential proteomic analysis of the cytosolic Smad3-interacting proteins by two-dimensional differential in-gel electrophoresis and mass spectroscopy followed by coimmunoprecipitation and immunostaining demonstrated that Smad3 was bound to β2-tubulin in a TGF-β1/cGMP-dependent manner: binding of Smad3 to β2-tubulin was decreased by TGF-β1 and increased by cGMP treatment. A site-directed mutagenesis study demonstrated that mutating Smad3 at Thr388, but not Ser309, two potential sites of PKG-induced hyperphosphorylation, inhibited cGMP-induced Smad3 binding to β2-tubulin. Further, luciferase reporter analysis showed that muation of T388 in Smad3 abolished the inhibitory effect of cGMP on TGF-β1-induced plasminogen activator inhibitor-1 (PAI-1) transcription. In addition, disruption of β2-tubulin with the microtubule depolymerizers nocodazole and colchicine promoted Smad3 dissociation from β2-tubulin, increased both TGF-β1-induced Smad3 nuclear translocation and PAI-1 mRNA expression, and abolished the inhibitory effects of cGMP on these processes. In contrast, the microtubule stabilizers paclitaxel and epothilone B increased cytosolic Smad3 binding to β2-tubulin and enhanced the inhibitory effect of cGMP on Smad3 nuclear translocation and PAI-1 expression in response to TGF-β1. These provocative findings suggest that sequestering Smad3 by β2-tubulin in cytosol is a key mechanism by which ANP-cGMP-PKG signaling interferes with downstream signaling from TGF-β and thus protects against pulmonary arterial remodeling in response to hypoxia stress.

Transforming growth factor-β signaling mediates hypoxia-induced pulmonary arterial remodeling and inhibition of alveolar development in newborn mouse lung

Hypoxia causes abnormal neonatal pulmonary artery remodeling (PAR) and inhibition of alveolar development (IAD). Transforming growth factor (TGF)-beta is an important regulator of lung development and repair from injury. We tested the hypothesis that inhibition of TGF-beta signaling attenuates hypoxia-induced PAR and IAD. Mice with an inducible dominant-negative mutation of the TGF-beta type II receptor (DNTGFbetaRII) and nontransgenic wild-type (WT) mice were exposed to hypoxia (12% O(2)) or air from birth to 14 days of age. Expression of DNTGFbetaRII was induced by 20 microg/g ZnSO(4) given intraperitoneally daily from birth. PAR, IAD, cell proliferation, and expression of extracellular matrix (ECM) proteins were assessed. In WT mice, hypoxia led to thicker, more muscularized resistance pulmonary arteries and impaired alveolarization, accompanied by increases in active TGF-beta and phosphorylated Smad2. Hypoxia-induced PAR and IAD were greatly attenuated in DNTGFbetaRII mice given ZnSO(4) compared with WT control mice and DNTGFbetaRII mice not given ZnSO(4). The stimulatory effects of hypoxic exposure on pulmonary arterial cell proliferation and lung ECM proteins were abrogated in DNTGFbetaRII mice given ZnSO(4). These data support the conclusion that TGF-beta plays an important role in hypoxia-induced pulmonary vascular adaptation and IAD in the newborn animal model.

ANP signaling inhibits TGF-β-induced Smad2 and Smad3 nuclear translocation and extracellular matrix expression in rat pulmonary arterial smooth muscle cells

Atrial natriuretic peptide (ANP) and transforming growth factor (TGF)-beta play important counterregulatory roles in pulmonary vascular adaptation to chronic hypoxia. To define the molecular mechanism of this important interaction, we tested whether ANP-cGMP-protein kinase G (PKG) signaling inhibits TGF-beta1-induced extracellular matrix (ECM) expression and defined the specific site(s) at which this molecular merging of signaling pathways occurs. Rat pulmonary arterial smooth muscle cells (PASMCs) were treated with ANP (1 muM) or cGMP (1 mM) with or without pretreatment with PKG inhibitors KT-5823 (1 muM) or Rp-8-bromo-cGMP (Rp-8-Br-cGMP 50 muM), then exposed to TGF-beta1 (1 ng/ml) for 5-360 min (for pSmad nuclear translocation and protein analysis) or 24 h (for ECM mRNA expression). Nuclear translocation of pSmad2 and pSmad3 was assessed by fluorescent confocal microscopy. ANP and cGMP inhibited TGF-beta1-induced pSmad2 and pSmad3 nuclear translocation and expression of periostin, osteopontin, and plasminogen activator inhibitor-1 mRNA and protein, but not TGF-beta1-induced phosphorylation of Smad2 and Smad3. KT-5823 and Rp-8-Br-cGMP blocked ANP/cGMP-induced activation of PKG and inhibition of TGF-beta1-stimulated nuclear translocation of pSmad2 and pSmad3 in PASMCs. These results reveal for the first time a precise site at which ANP-cGMP-PKG signaling exerts its antifibrogenic effect on the profibrogenic TGF-beta1 signaling pathway: by blocking TGF-beta1-induced pSmad2 and pSmad3 nuclear translocation and ECM expression in PASMCs. Blocking nuclear translocation and subsequent binding of pSmad2 and pSmad3 to TGF-beta-Smad response elements in ECM genes may be responsible for the inhibitory effects of ANP on TGF-beta-induced expression of ECM molecules.

Atrial natriuretic peptide-dependent modulation of hypoxia-induced pulmonary vascular remodeling

Hypoxic stress upsets the balance in the normal relationships between mitogenic and growth inhibiting pathways in lung, resulting in pulmonary vascular remodeling characterized by hyperplasia of pulmonary arterial smooth muscle cells (PASMCs) and fibroblasts and enhanced deposition of extracellular matrix. Atrial natriuretic peptide (ANP) reduces pulmonary vascular resistance and attenuates hypoxia-induced pulmonary hypertension in vivo and PASMC proliferation and collagen synthesis in vitro. The current study utilized an ANP null mouse model ( Nppa−/−) to test the hypothesis that ANP modulates the pulmonary vascular and alveolar remodeling response to normobaric hypoxic stress. Nine-10 wk old male ANP null ( Nppa−/−) and wild type nontransgenic (NTG) mice were exposed to chronic hypoxia (10% O 2, 1 atm) or air for 6 wks. Measurement: pulmonary hypertension, right ventricular hypertrophy, and pulmonary arterial and alveolar remodeling were assessed. Hypoxia-induced pulmonary arterial hypertrophy and muscularization were significantly increased in Nppa−/− mice compared to NTG controls. Furthermore, the stimulatory effects of hypoxia on alveolar myofibroblast transformation (8.2 and 5.4 fold increases in Nppa−/− and NTG mice, respectively) and expression of extracellular matrix molecule (including osteopontin [OPN] and periostin [PN]) mRNA in whole lung were exaggerated in Nppa−/− mice compared to NTG controls. Combined with our previous finding that ANP signaling attenuates transforming growth factor (TGF)-β-induced expression of OPN and PN in isolated PASMCs, the current study supports the hypothesis that endogenous ANP plays an important anti-fibrogenic role in the pulmonary vascular adaptation to chronic hypoxia.

Dominant negative mutation of the TGF-β receptor blocks hypoxia-induced pulmonary vascular remodeling

The present study utilized a novel transgenic mouse model that expresses an inducible dominant negative mutation of the transforming growth factor (TGF)-beta type II receptor (DnTGFbetaRII mouse) to test the hypothesis that TGF-beta signaling plays an important role in the pathogenesis of chronic hypoxia-induced increases in pulmonary arterial pressure and vascular and alveolar remodeling. Nine- to 10-wk-old male DnTGFbetaRII and control nontransgenic (NTG) mice were exposed to normobaric hypoxia (10% O2) or air for 6 wk. Expression of DnTGFbetaRII was induced by drinking 25 mM ZnSO4 water beginning 1 wk before hypoxic exposure. Hypoxia-induced increases in right ventricular pressure, right ventricular mass, pulmonary arterial remodeling, and muscularization were greatly attenuated in DnTGFbetaRII mice compared with NTG controls. Furthermore, the stimulatory effects of hypoxic exposure on pulmonary arterial and alveolar collagen content, appearance of alpha-smooth muscle actin-positive cells in alveolar parenchyma, and expression of extracellular matrix molecule (including collagen I and III, periostin, and osteopontin) mRNA in whole lung were abrogated in DnTGFbetaRII mice compared with NTG controls. Hypoxic exposure had no effect on systemic arterial pressure or heart rate in either strain. These data support the hypothesis that endogenous TGF-beta plays an important role in pulmonary vascular adaptation to chronic hypoxia and that disruption of TGF-beta signaling attenuates hypoxia-induced pulmonary hypertension, right ventricular hypertrophy, pulmonary arterial hypertrophy and muscularization, alveolar remodeling, and expression of extracellular matrix mRNA in whole lung.

Developmental Expression of Vasoactive and Growth Factors in Human Lung. Role in Pulmonary Vascular Resistance Adaptation at Birth

The factors that mediate the postnatal fall in pulmonary vascular resistance, which is crucial for normal gas exchange, are not fully understood. The endothelium has been implicated in this phenomenon, through the release of vasorelaxant factors such as nitric oxide (NO). Human pulmonary expression of endothelial NO synthase increases up to 31 wk of gestation, together with vascular endothelial growth factor (VEGF), and both factors potently mediate pulmonary angiogenesis and vasorelaxation. During the perinatal period, when pulmonary vasodilatation is maximal, endothelial NO synthase and VEGF are weakly expressed. This raises the involvement of vasorelaxant factors other than NO at birth. One candidate is endothelial-derived hyperpolarizing factor, which induces smooth muscle cell hyperpolarization by activating K(ATP) channels. The marked vasorelaxation induced by activation of these channels in newborn animals, and their strong perinatal expression in the human lung, suggest their involvement during this phase. Another candidate is endothelin (ET)-1, together with its receptors ET-A and ET-B. ET-A receptors are located exclusively on smooth muscle cells and mediate vasoconstriction, whereas ET-B receptors mediate vasoconstriction when located on smooth muscle cells and vasodilatation when located on endothelial cells. ET-B receptors, which are strongly expressed in the human fetal lung both at the end of gestation and after birth, may be involved in perinatal pulmonary vasodilatation. Thus, in human fetal lung, K(ATP) channels and ET-B receptors could be important in mediating the perinatal pulmonary vasodilatation crucial for adapting the pulmonary circulation to extrauterine life.

Transition from placental to air breathing stimulates haem‐oxygenase‐1 expression without functional consequence for pulmonary vascular adaptation in pigs and mice

1. In systemic vessels, haem-oxygenase (HO) is induced during oxidative stress and known to modulate vasodilatation and vascular remodelling. At birth, with the transition from placental to air breathing, the pulmonary vessels are exposed to oxidative stress and undergo well-documented remodelling processes. Thus, we investigated the role of HO in the lung during adaptation to extra-uterine life using a pig and mouse model. In addition to the novel data presented with regard to one isoform, HO-1, this study is among the first to describe the pulmonary vascular remodelling in the mouse after birth. 2. We show, for the first time, that another isoform, HO-2, is present constitutively at birth and HO-1 protein is induced in the porcine and murine lung after birth in vascular and airway structures, peaking at 14 days in the pig and at about 4 days in the mouse. Furthermore, we show that HO-1 mRNA declines after birth in the mouse lung. 3. Inhibitors of HO did not modify vasodilator responses in vessels from 14-day-old pigs. 4. Moreover, lungs from HO-1-deficient mice developed normally after birth. 5. HO-1 is induced at birth but plays no role in the development of vasodilator responses or remodelling that occurs at this time. These data suggest that HO-1 expression at birth is a redundant response to oxidative stress in the lungs of healthy mammals. However, it remains possible that this pathway protects if complications occur during or after birth.

International experience with trisomy 21 infants placed on extracorporeal membrane oxygenation.

To characterize the international experience concerning neonates with trisomy 21 (T21) managed with extracorporeal membrane oxygenation (ECMO), and to compare and contrast this group of patients to the neonatal ECMO population as a whole. Data from the Extracorporeal Life Support Organization for newborn infants placed on ECMO between January 1984 and June 1999 were analyzed. Infants with T21 were compared with the group of infants without T21. Fifteen thousand nine hundred forty-six infants, including 91 (n = 91) with the diagnosis of T21, were placed on ECMO for neonatal respiratory failure during the 14.5-year period. T21 infants were overrepresented in the ECMO population by several-fold when compared with the incidence of T21 in the general population. Eighty-seven of the 91 T21 infants were placed on ECMO after 1989. The distribution of primary diagnoses leading to ECMO differed between the groups (T21 vs non-T21): primary persistent pulmonary hypertension, 47.3% versus 13%; meconium aspiration syndrome, 23.1% versus 32.9%; sepsis, 7.7% versus 13.2%; congenital diaphragmatic hernia, 7.7% versus 19.9%; and respiratory distress syndrome, 3.3% versus 7.9%. Although survival to discontinuation of ECMO was similar in the 2 groups, likelihood of survival to discharge was decreased for T21 infants (65.9% vs 75.6%) because of increased post-ECMO mortality. Extracorporeal Life Support Organization registry data suggests that T21 infants are at a significantly higher risk of being placed on ECMO for neonatal respiratory failure than the general population, perhaps as a result of delayed extrauterine pulmonary vascular adaptation, as manifested in the high rate of primary persistent pulmonary hypertension as the primary diagnosis. There may have been a shift in attitude regarding the use of ECMO in the T21 patient after 1989. Although most T21 patients placed on ECMO will survive, the prognosis is more guarded in this population when compared with all infants so managed. The long-term neurodevelopmental outcome of this group of T21 ECMO survivors is currently unknown.

Cyclic-GMP-binding, cyclic-GMP-specific phosphodiesterase (PDE5) gene expression is regulated during rat pulmonary development.

Increased nitric oxide (NO) production plays a critical role in the mammalian pulmonary vascular adaptation to extrauterine life. NO activates soluble guanylate cyclase, increasing intracellular cGMP concentrations, thereby inducing relaxation of vascular smooth muscle. cGMP is inactivated by cyclic nucleotide phosphodiesterases (PDEs). One PDE isozyme, PDE5, specifically hydrolyzes cGMP, is abundant in lung tissues, and modifies the pulmonary vasodilatory response to exogenous NO. To investigate the regulation of PDE5 gene expression during pulmonary development, PDE5 mRNA levels, as well as cGMP-metabolizing PDE enzyme activity, were measured in the lungs of perinatal and adult rats. RNA blot hybridization revealed that PDE5 mRNA was detectable in fetal lung tissue as early as 18.5 d of the 22-d term gestation and reached maximal levels in neonatal lungs. mRNA levels in adult rat lungs were 3-4-fold less than the levels measured in lungs of 1- and 8-d-old rats. Pulmonary cGMP hydrolytic activity in 1-d-old animals was 30-fold greater than the cGMP hydrolytic activity of adult rat lungs. Zaprinast, a specific PDE5 antagonist, inhibited 52 and 56% of cGMP hydrolytic activity in lungs of 1- and 8-d-old rats, respectively, but only 18% of the activity in adult lungs. In situ hybridization revealed that PDE5 mRNA transcripts were present in the vascular smooth muscle cells of neonatal and adult lungs. PDE5 mRNA was also detected in the alveolar walls of neonatal rat lungs. These results demonstrate that the gene encoding PDE5 is abundantly expressed in the lungs of perinatal rats, and is available to participate in the mammalian pulmonary vascular transition to extrauterine life. Extravascular PDE5 gene expression in neonatal lungs suggests a potentially important nonvascular role for this enzyme during pulmonary development.