Postobstructive Pulmonary Vasculopathy Research Articles

Upregulation of canonical transient receptor potential channel in the pulmonary arterial smooth muscle of a chronic thromboembolic pulmonary hypertension rat model.

Chronic ligation of the left main pulmonary artery (PA) results in pulmonary vascular remodeling and sustained vasoconstriction. This method has been used to generate a postobstructive pulmonary vasculopathy model to mimic severe chronic thromboembolic pulmonary hypertension (CTEPH). The aim of this study was to examine the cellular and molecular mechanisms underlying CTEPH and to provide evidence for potential treatments. The CTEPH rat model was induced by surgical left PA ligation (LPAL). Right ventricular systolic pressure (RVSP), lung histochemistry and plasma D-dimer measurements were carried out to evaluate the model. A fluorescence microscope was used to measure the basal intracellular Ca(2+) concentration ([Ca(2+)]i) and store-operated Ca(2+) entry (SOCE) in rat distal pulmonary arterial smooth muscle cells through a Fura-2 fluorescence-based method. The expression of the canonical transient receptor potential channel 1 (TRPC1) and TRPC6 was determined by western blotting and real-time quantitative PCR in isolated distal pulmonary arteries (PA). At the time points of 2 and 5 weeks postsurgery, the RVSP showed significant increases in the LPAL groups in comparison with the respective control groups. LPAL also led to right ventricular hypertrophy (RVH), distal pulmonary arterial remodeling in unobstructed territories and persistently higher plasma D-dimer levels. Increases of the basal [Ca(2+)]i and SOCE in LPAL were associated with a clear upregulation of TRPC1 and TRPC6 expression in the distal PA. Our study demonstrated that LPAL successfully reproduced the vascular tone changes that mimic CTEPH pathogenesis. In this model, the increased RVSP and RVH are likely related to enhanced SOCE and upregulated TRPC1 and TRPC6 expression levels in the distal PA.

Regression of postobstructive vasculopathy after revascularization of chronically obstructed pulmonary artery

ObjectivesPulmonary vascular resistance decreases dramatically after pulmonary thromboendarterectomy and further improves in time. This may reflect the slow regression of postobstructive pulmonary vasculopathy. We hypothesized that postobstructive pulmonary vasculopathy may regress after reperfusion in a piglet model of chronic (5 weeks) left pulmonary artery obstruction. MethodsThe ligated left pulmonary artery was reimplanted into the pulmonary arterial trunk. Pulmonary artery blood flow and pressure were measured 2 days and 5 weeks after reperfusion. Pulmonary artery smooth muscle thickness, endothelium-dependent relaxation, and left lung endothelial nitric oxide synthase activity and expression were assessed 5 weeks after ligation (n = 10) and 5 weeks after reperfusion (n = 10), and compared with a sham group (n = 10). Patency of the anastomoses and systemic blood supply to the lung were assessed by pulmonary angiography and nonselective thoracic aortography, respectively. ResultsAngiography showed that pulmonary artery anastomoses were patent in all animals. Five weeks after reperfusion, left pulmonary blood flows were similar to those in the sham animals, and systemic blood supply to the left lung decreased. Left pulmonary vascular resistance decreased by 50% at 5 weeks after reperfusion compared with 2 days after reperfusion (P = .0009). Medial muscle thickness of the left pulmonary artery greater than 600 μm increased 5 weeks after ligation and regressed to sham values 5 weeks after reperfusion (P = .001). Endothelium-dependent relaxation was only partially restored 5 weeks after reperfusion, whereas left lung endothelial nitric oxide synthase expressions and activities returned to sham values. ConclusionsThis study shows that postobstructive pulmonary vasculopathy induced by ligation of the pulmonary artery for 5 weeks regresses after reperfusion, accounting for the progressive improvement in hemodynamics after thromboendarterectomy.

QUANTITATIVE ANALYSIS OF ENDOTHELIN AND NITRIC OXIDE SYNTHASE IN RAT MODEL OF POSTOBSTRUCTIVE PULMONARY VASCULOPATHY

There is increasing evidence that endothelin (ET) and endothelial nitric oxide synthase (eNOS) may contribute various kinds of pulmonary vascular remodeling, including postobstructive pulmonary vasculopathy (POPV), which resulted from chronic ligation of unilateral pulmonary artery. The aim of this study was to investigate the expression of ET-1, ET-A receptor, ET-B receptor, and eNOS quantitatively in POPV rats. One month after a left thoracotomy with either left main pulmonary artery ligation (ligated group) or no ligation (control group), rat pulmonary arteries and lungs were used for Western blot analysis using specific antibodies against ET-1, ET-A receptor, ET-B receptor, and eNOS. ET-A receptor was more highly expressed in the pulmonary arteries of ligated rats compared to the control. The expression of ET-1, ET-B receptor,and eNOS was not different between ligated and control rats. These findings suggest that ET-A receptor overexpression would play a main role for pulmonary arterial remodeling in POPV rats, whereas eNOS may serve as a compensatory mediator.

Altered reactivity of pulmonary vessels in postobstructive pulmonary vasculopathy.

Chronic ligation of one pulmonary artery results in pulmonary vascular remodeling and bronchial angiogenesis, collectively known as postobstructive pulmonary vasculopathy (POPV). To investigate pulmonary vascular reactivity in POPV, we ligated the left main pulmonary artery of guinea pigs and, after 1-10 mo, prepared explants by inflating lungs with agarose and sectioning them into approximately 1-mm-thick slices; we measured areas of pulmonary vessels and determined contractile responses to histamine and serotonin (5-HT) and relaxant responses to ACh and sodium nitroprusside. We found maximal contractions of arteries to 5-HT (24. 4 +/- 2.6%) and of veins to histamine (53.9 +/- 4.7%) were significantly increased in POPV of 3-mo duration compared with those of controls (16.8 +/- 1.5 and 40.8 +/- 5.0%, respectively). Relaxation of arteries with ACh was enhanced at 10 mo but not at 1 mo after ligation. Relaxation with sodium nitroprusside was increased in veins at 1 mo after ligation but was not altered in arteries. Morphometry revealed reduced diameters of arteries and veins without increased medial thickness. Our data suggest that the enhanced contractile responses of pulmonary vessels to histamine and 5-HT in POPV were not a result of endothelial dysfunction or of structural alterations but might be caused by as-yet-undiscovered mechanisms.

PULMONARY VASCULAR REMODELING DISTAL TO PULMONARY ARTERY LIGATION IS ACCOMPANIED BY UPREGULATION OF ENDOTHELIN RECEPTORS AND NITRIC OXIDE SYNTHASE

There is increasing evidence that the pathogenesis and progression of many forms of pulmonary vasculopathy are related to abnormalities in endothelial mediators, including endothelin-1 (ET-1) and nitric oxide (NO). Using a rat model of chronic unilateral pulmonary artery ligation, we investigated the role of ET-1 and NO in postobstructive pulmonary vasculopathy (POPV). Eight months after a left thoracotomy with either left main pulmonary artery ligation (ligated group) or no ligation (sham group), rat lungs, including those contralateral to the ligation (hyperperfused group), were fixed and mounted for histologic sectioning. Morphometric measurements were carried out by computer-assisted image analysis and immunohistochemical staining was performed using specific antibodies against ET-1, ETA, and EBB receptors, and endothelial NO synthase (eNOS). Compared to sham lungs, the ligated lungs showed (1) an increase in muscular, adventitial, and intimal thickness of pulmonary artery; (2) increase in external diameter of the bronchial artery (39.8+/-2.2 mum vs.16.8+/-0.9 mum in sham group; P <. 005) and number of bronchial arteries per bronchiole (3.21+/-mu0.26vs.1.86+/-mu0.21 in sham group; P <. 001); and (3) increase in the intensity of eNOS and ETA, B receptor immunoreactivity. No morphometric or immunohistochemical differences were observed between the hyperperfused and sham lungs. These ndings suggest that increased synthesis of endothelial NO may serve as a compensatory mediator in ET-1 mediated vascular remodeling.

Increased Reactivity to Endothelin of Pulmonary Arteries in Long-term Post-obstructive Pulmonary Vasculopathy in Rats

Post-obstructive pulmonary vasculopathy (POPV) describes the constellation of findings following chronic ligation of one pulmonary artery, including bronchial angiogenesis, pulmonary vasculopathy and increased vasoreactivity to pharmacologic agents. Previously, we found in rats with POPV of 28 days duration that maximal responses to endothelin-1 (ET-1) and ET-3 of pulmonary arteries but not veins were increased, and that relaxation of arteries to ET-1 was reduced, attributable to an elevated proportion of ETAover ETBreceptors. To determine the reactivity of pulmonary vessels and airways to ET in protracted POPV, we ligated the left main pulmonary artery of nine rats. Eleven months later, using a lung explant technique, we compared contractile responses of pulmonary vessels and airways to ET-1 and ET-3 in POPV lungs with controls. Morphometric measurements were made on the vessels, and immunoreactivity to ET-1 and endothelin converting enzyme (ECE-1) studied. We found contractile responses to ET-1 and ET-3 significantly increased in arteries, but not veins or airways. Morphometry showed arteries and veins had reduced diameters with muscle thickening only in veins. Expression of ET-1 and ET-3 in vascular endothelial cells and airway epithelial cells were not altered significantly. Our data suggest that protracted POPV selectively enhanced the contractility of pulmonary arteries to ET, and is not attributable to medial muscle thickening.

Endothelin reactivity and receptor profile of pulmonary vessels in postobstructive pulmonary vasculopathy

Chronic ligation of one pulmonary artery results in pulmonary vascular remodeling and bronchial angiogenesis, collectively known as postobstructive pulmonary vasculopathy (POPV). To determine whether the reactivity of pulmonary vessels to endothelins (ET) was altered in POPV and to explore potential mechanisms, we ligated the left main pulmonary artery of 18 rats. Four weeks later, using a lung explant technique, we compared POPV lungs with controls for contractile responses of intrapulmonary vessels to ET-1 and ET-3 and for relaxant responses to ET-1 and sodium nitroprusside (SNP) after precontraction with U-46619. Morphometric measurements were made on vessels studied pharmacologically. Competition receptor binding studies with 125I-labeled ET-1 and unlabeled ET-1 and BQ-123 were performed using membrane proteins of pulmonary vessels. We found, in arteries, that contractile responses to ET-1 and ET-3 were significantly increased and that relaxant responses to ET-1 but not to SNP were reduced; in veins, only relaxation to SNP was increased. Morphometry showed that arteries and veins in POPV had reduced diameters without altered muscle thickness. Receptor binding studies showed that the proportion of ETA receptors in arteries was significantly increased in POPV (66%) vs. controls (54%). We conclude that, in POPV, the increase in reactivity to ET-1 and ET-3 is primarily related to an augmented proportion of ETA receptors.

Respiratory mechanics and gas exchange in postobstructive pulmonary vasculopathy

Chronic unilateral pulmonary artery ligation induces formation of new bronchial collateral vessels in the affected lung. These vessels form precapillary anastomoses with the pulmonary circulation and the lung is perfused with arterial blood. Inspired gas is diverted to the contralateral lung to maintain the ventilation/perfusion ratio (VA/Q) and gas exchange. This study was designed to determine the mechanism responsible for this shift of ventilation, which has not previously been investigated. We studied six dogs, before and 6 months after ligation of the left main pulmonary artery. We measured pulmonary resistance (RL) and elastance (EL), minute ventilation (VE), O2 consumption (VO2) and CO2 production (VCO2) of the right and left lungs. We also examined the effect of CO2, atropine and isoproterenol on RL and EL. In the lung with ligated pulmonary artery: 1) VE was significantly reduced; 2) RL and EL were increased and were unresponsive to CO2, atropine and isoproterenol; and 3) VO2 decreased more than VCO2 and, consequently, respiratory quotient (RQ) was greater than 1. We conclude that, with chronic pulmonary artery obstruction, ventilation shifts to the contralateral lung because of an increase in RL and EL not related to airway smooth muscle tone.

Myoendothelial junctional complexes in postobstructive pulmonary vasculopathy: a quantitative electron microscopic study.

Postobstructive pulmonary vasculopathy (POPV), produced by chronic unilateral ligation of one pulmonary artery, is characterized by (1) marked proliferation of bronchial collateral vessels, (2) increased pulmonary vascular resistance, and (3) hyperreactivity of arteries to serotonin and of veins to histamine. Electron microscopic examination of the vessels in POPV suggested an increase in myoendothelial junctional complexes (MEJC). To quantitate this change, the number of MEJC in the vessel walls of the left lung was compared with that of the right lung in 16 dogs after ligation of the left main pulmonary artery for 8.4 +/- 1.6 (SE) months. The lungs were fixed by airway instillation of 3% glutaraldehyde. Electron micrographs were taken of pulmonary arteries, capillaries, and veins and of bronchial vessels, and their external diameter and length of endothelial basal lamina were measured. The MEJC were counted and expressed as number per length of basal lamina and typed: Type I consisted of endothelial processes, type II of smooth muscle or pericyte processes, and type III of processes from each cell type. The results demonstrated that the vasculature from the control lung had the smallest number of MEJC and the majority were type I. With ligation, there was a significant increase (p < .01) in the number of MEJC for each type of vessel examined, but no significant change in the distribution of the type. In addition, no correlation was found between the number of MEJC and vascular diameter. It can be concluded that MEJC are increased in each region of the lung's vasculature in POPV and that they may play a role in the proliferative response of the bronchial vasculature, the remodeling of the pulmonary vasculature, and the pulmonary vascular hyperreactivity of this model.

Altered mechanical properties of lung parenchyma in postobstructive pulmonary vasculopathy

Postobstructive pulmonary vasculopathy (POPV) produced by chronic unilateral ligation of one pulmonary artery, results in perfusion of the pulmonary capillaries with systemic arterial blood. As a consequence, gas exchange occurs primarily in the contralateral nonligated lung. To determine whether the mechanical properties of the lung parenchyma are changed in POPV, we compared five dogs with chronic ligation of the left main pulmonary artery with five control dogs. Separate measurements of left and right lung airway flows, tracheal pressures, and alveolar pressures were made during mechanical ventilation at frequencies between 5 and 40 breaths/min. We calculated pulmonary elastance (EL) and pulmonary (RL), airway (Raw), and tissue (Rti) resistances. At all frequencies, dogs with POPV had higher left (ligated) EL and Rti and lower right (normal) lung Rti but similar EL compared with the respective lungs from control animals. Raw was the same in both lungs. Histology showed visceral pleura thickening and encroachment of new bronchial collaterals and lymphatics on the parenchyma of the ligated lungs. The contralateral lungs were entirely normal. We conclude that in POPV 1) there is an increase, in the ligated lung, of both EL and RL, the latter likely due to histological changes of the lung parenchyma, and 2) there is a reduction of Rti in the contralateral lung.

Endothelin-1-like immunoreactivity in postobstructive pulmonary vasculopathy.

Postobstructive pulmonary vasculopathy (POPV) is produced by chronic ligation of one pulmonary artery and results in bronchial collateral vessel proliferation and pulmonary arterial abnormalities. The role of endothelin-1 (ET-1), a potent vasoconstrictor peptide, was investigated in a canine model of POPV using radioimmunoassay and immunohistochemistry. The left main pulmonary artery of 9 dogs was ligated, and 3 months (n = 3) and 15 months (n = 6) later, ET-1 levels were measured by radioimmunoassay of plasma samples from left and right pulmonary arteries and veins. In addition, tissues from control and ligated lungs were fixed in Bouin's solution embedded in paraffin and stained with antiserum to ET-1. Plasma ET-1 levels distal to the ligation were not different from those of the control pulmonary artery (1.7 pg/ml in the ligated lungs vs. 1.4 pg/ml in the controls; NS). ET-1-like immunoreactivity was localized mainly to the epithelium in both control and ligated lungs, but the pulmonary arteries and the new bronchial vessels stained more intensely in the ligated lungs. The sections immunostained with ET-1 antiserum preabsorbed with synthetic ET-1 did not stain. These results suggest that ET-1 may play a role in the bronchial neovascularization and the pulmonary arterial thickening characteristic of POPV.

Bronchial collateral vessel micropuncture pressure in postobstructive pulmonary vasculopathy.

Postobstructive pulmonary vasculopathy, produced by chronic ligation of one pulmonary artery, markedly increases bronchial blood flow. Previously, using arterial and venous occlusion, we determined that bronchial collaterals enter the pulmonary circuit at the distal end of the arterial segment. In this study, we tested the hypothesis that pressure in bronchial collaterals (Pbr) closely approximates that at the downstream end of the arterial segment (Pao). We pump perfused [111 +/- 10 (SE) ml/min] left lower lobes of seven open-chest live dogs 3-15 mo after ligation of the left main pulmonary artery. Bronchial blood flow was 122 +/- 16 ml/min. We measured pulmonary arterial and venous pressures and, by arterial and venous occlusion, respectively, Pao and the pressure at the upstream end of the venous segment (Pvo). Pbr was obtained by micropuncture of 34 pleural surface bronchial vessels 201 +/- 16 microns in diameter. We found that Pbr (14.4 +/- 1.0 mmHg) was similar to Pao (15.0 +/- 0.8 mmHg) but differed significantly (P < 0.01) from Pvo (11.3 +/- 0.5 mmHg). In addition, Pbr was independent of systemic arterial pressure and bronchial vessel diameter. Light and electron microscopy revealed that, in the lobes with the ligated pulmonary artery, the new bronchial collaterals entered the thickened pleura from the parenchyma via either bronchovascular bundles or interlobular septa and had sparsely muscularized walls. We conclude that, in postobstructive pulmonary vasculopathy, bronchial collateral pressure measured by micropuncture is very close to the pressure in precapillary pulmonary arteries and that most of the pressure drop in the bronchial collaterals occurs in vessels > 350 microns in diameter.

Increased resistance in postobstructive pulmonary vasculopathy: structure-function relationships

Postobstructive pulmonary vasculopathy (POPV) was produced by chronic ligation (120 days) of the left main pulmonary artery of seven dogs. To explain the abnormal physiological changes found using arterial and venous occlusion (AVO) in POPV (J. Appl. Physiol. 69: 1022-1032, 1990), the light-microscopic morphology, morphometry (n = 5), and ultrastructure (n = 6) of ligated left lower lobes were compared with contralateral control right lower lobes. First, there was a proliferation of bronchial vessels around pulmonary vessels and airways to explain bronchial blood flow rates of 330 ml/min in left lower lobes. The walls of the bronchial vessels contained smooth muscle with minimal elastic tissue and prominent myoendothelial junctions. Second, focal bronchopulmonary anastomoses were seen in pulmonary arteries approximately equal to 100 microns diam, which is consistent with our conclusion that the major site of communication is at the precapillary level and suggests that the limit between arterial and middle segments defined by AVO may lie in arteries of approximately equal to 100 microns. Third, to explain the increased arterial resistance in POPV, the pulmonary arteries had an increased percent medial muscle thickness, peripheral muscularization, and focal intimal thickening but had no plexiform lesions. The ultrastructure of the arteries revealed new intimal cells and numerous myoendothelial junctions rarely found in controls. Capillaries and veins were only subtly altered. Fourth, the hyperreactivity of arteries to serotonin and of veins to histamine found using AVO was partially explained by the increased medial thickness and decreased diameter but may also be due to increased receptor concentration or related to the myoendothelial junctions. We conclude that most of the hemodynamic alterations in POPV are related to morphological abnormalities and that this model has clinical and experimental relevance in the study of bronchopulmonary vascular interactions.

Segmental vascular resistance in postobstructive pulmonary vasculopathy

Chronic unilateral pulmonary arterial ligation has been touted as a model of arteriopathy resulting in a tremendous increase in anastomotic bronchial flow (Qbr) via collaterals. To investigate its effects on the pulmonary vasculature, we ligated the left main pulmonary artery of seven dogs and 120 days later pump perfused their left lower lobes (LLL) via a cannula in the pulmonary artery at pulmonary arterial flow (Qpa) of 250 ml/min. We measured Qbr (330 ml/min) and compared LLL with control contralateral right lower lobes (RLL) and three LLL from normal dogs. Pressure-flow (P-Q) curves were obtained by varying Qpa. With arterial and venous occlusion we measured total, arterial, venous, and middle segment resistances under baseline conditions, after serotonin and histamine, either with or without Qpa and with antegrade and retrograde Qbr. Light microscopy was done postmortem. The slope of the P-Q curve was 33.4 mmHg.l-1.min in the ligated lobes compared with 15.9 in the controls, attributable by the occlusion technique mainly to a rise in arterial resistance (22.4 mmHg.l-1.min compared with 7.4 in the controls) with a small rise in venous resistance. This was explained by significant arterial medial muscle thickening and some loss of LLL volume. The arterial segment was markedly hypersensitive to serotonin, and the venous segment was mildly hypersensitive to histamine compared with controls. The occlusion data also enabled us to model the point of entry of the bronchial circulation into the pulmonary circuit at the precapillary level and to calculate bronchial vascular resistance. We conclude that postobstructive vasculopathy substantially raises pulmonary vascular resistance, mainly upstream from the site of entry of the bronchial circulation. The role of the latter may be to keep it from rising excessively in the segments it perfuses, i.e., the middle and venous ones.