Pulsatile flow dynamics maintain pulmonary artery architecture.

For decades the pulmonary circulation was not considered as important as the systemic ("greater") circulation. However, pulmonary hypertension can arise because of many diseases of the heart and lung. Therefore, increasing efforts in research have been undertaken leading to a profound increase in understanding pulmonary vascular physiology and pathophysiology. This review discusses basic physiology, clinical concepts, and treatment options for pulmonary hypertension and the related right ventricular heart failure focusing on secondary pulmonary hypertension in patients during anesthetic procedures. Physiology of Pulmonary Circulation The pulmonary vascular bed is a high-flow, low-pressure circulation system. Pulmonary vessels have less resistance in comparison to the systemic circulation under normal conditions because of higher compliance of pulmonary precapillary arterioles with a thinner media and less smooth muscle cells (SMCs) compared with the corresponding systemic arterioles. In addition, the cross-sectional area of the pulmonary vascular bed is large and highly distensible with recruitable vessels available to accommodate increase in flow resulting in low pressure and low resistance. In contrast to the systemic arteries, pulmonary vessels constrict with hypoxia (Euler-Liljestrand reflex) and relax in the presence of hyperoxia. Furthermore, changes in cardiac output (CO), airway pressure, and gravity affect the pulmonary more than the systemic circulation. Increases in CO distend open vessels and recruit previously closed vessels. Therefore, the cross-sectional area of pulmonary circulation enlarges and results in a decrease in pulmonary vascular resistance (PVR). An increase in CO has very little effect on pulmonary arterial pressure (PAP) because of the recruitment and distension of pulmonary vessels. An increased PAP or left atrial pressure (LAP) may also distend and recruit pulmonary vessels. Clinically, this means that enhanced CO caused by the administration of inotropic drugs or enlarged blood volume will passively decrease PVR. The contribution of intra- and extraalveolar vessels accounts for the unique U-shaped relationship between lung volume and PVR, which is minimal at functional residual capacity and increased at large and small lung volumes (Fig. 1). Clinically, this may be observed when hyperinflation of the lungs greatly increases PVR.Figure 1: Relationship between lung volume and pulmonary vascular resistance (PVR) (123). RV = residual volume, FRC = functional residual capacity, TLC = total lung capacity.Gravity influences the distribution of blood flow in the pulmonary circulation. Blood flow as well as ventilation increases in the dependent areas of the lung. The relationship between alveolar and hydrostatic pressure implies important clinical consequences. Patients with unilateral lung disease should be positioned with the diseased side up as was already shown by Remolina et al. (1). Lying with the sick lung dependent resulted in the worst gas exchange and the lowest arterial oxygen pressure (1). Application of high levels of positive end-expiratory pressure (PEEP) will narrow the capillaries in the well-ventilated lung areas and divert flow to less well-ventilated or nonventilated areas. Therefore, a decrease in PaO2 is the consequence. Constantly changing hemodynamics, mechanical forces, and hormonal environment influence the vascular endothelium and the underlying SMCs. Under normal circumstances, the interaction between endothelium and SMCs results in a low vascular resistance in the pulmonary circulation. An increasing number of molecules seem to be involved in these biochemical transductions: L-arginine-nitric oxide (NO)-cyclic-3′-5′guanosine monophosphate (cGMP) pathway seems to have a predominant role (2). Physiological agonists such as bradykinin and acetylcholine as well as mechanical stress derived from pulmonary blood flow can activate endothelial cells. This results in oxidation of the guanidino-nitrogen atom of the amino acid L-arginine by the constitutive NO synthase to form and release NO. NO diffuses from endothelial cells to the SMCs, and produces relaxation by activating guanylate cyclase with increasing intracellular cGMP (2). Pulmonary endothelial cells (surface area of 200 m2 in the adult) have a very strategic location: they are exposed to the entire CO, link the pulmonary and systemic circulation, and also regulate SMC tone by signaling to the vascular wall. Endothelial cells both seem to sense local shear stress and to initiate a response (e.g., production of NO) in order to accommodate rapid changes of blood flow. NO and prostacyclin (PGI2) support oxygenation and lung inflation in dilating the pulmonary vasculature after birth, keeping a key regulatory role in the lung because of its prompt, local powerful action compared with a brief half-life time (3). Pathophysiology of Pulmonary Hypertension It is now understood that the balance between vasoconstrictors and vasodilators and mitogenic and antimitogenic factors derived from the endothelium is disturbed in situations with an increase in PAP (4, 5). Endothelial dysfunction is promoted by hypoxia, acidosis, free radicals (6), inflammatory mediators, shear stress caused by increased pulmonary blood flow from left-to-right intracardiac shunt (7), and fibrin from thromboembolism (8). There is no widely accepted range for normal PAP. However, mean PAP >25 mm Hg (normal 15 mm Hg) at rest or >30 mm Hg with exercise is generally accepted as indicative for pulmonary hypertension (9). The enhanced pressure in the pulmonary circulation is associated with an increase in PVR and results in a progressive inability of the right ventricle (RV) to sustain its output leading to RV hypertrophy and RV failure depending from acute or chronic changes (4). In a study by Vizza et al. (10), prevalence of RV dysfunction (defined as RV ejection fraction [RVEF] <45%) was significantly higher in patients with pulmonary hypertension compared with all other groups with end-stage pulmonary disease. Determination of PVR is difficult in clinical settings even if the respective variables such as LAP, mean PAP, pulmonary capillary wedge pressure (PCWP), and thermodilution CO are measured directly because of their intrinsic inaccuracies. Therefore, indirect estimations use the equation: Normal PVR is approximately 1.1–1. 4 Wood units or about 90–120 dynes · s · cm−5, and a PVR >300 dynes · s · cm−5 is indicative of pulmonary hypertension. Pulmonary blood flow and volume are not always equal to or correlated with CO, because of intracardiac or other shunts. Vascular Remodeling Chronic pulmonary hypertension leads to structural alterations of the pulmonary vasculature and to a progression of histological changes known as "vascular remodeling" (11). Under physiological conditions, pulmonary arterioles are thin-walled vessels with the media occupying only 7% of the vessel thickness. The major finding in remodeled vessels caused by a chronic stimulus like hypoxia is the increase in SMCs in already muscularized arteries and extension of SMCs into vessels that are normally thin and nonmuscular (12) and thickening of the adventitial layer (13). Thickening of the adventitial layer is the result of marked proliferation of the fibroblasts, which has been shown to be modulated by protein kinase C and mitogen-activated protein kinase (14). After the proliferative response, there is an increase in adventitial connective tissue including a switch in SMC phenotype to a more synthetic cell that is responsible for deposition of increased connective tissue (12). This deposition of most notably collagen is probably a protective mechanism strengthening the vascular wall against the increase in intravascular pressure (15). Additionally, damage to intimal endothelium as well as intimal hyperplasia and fibrosis can be detected (5). The central regulatory function of the pulmonary endothelium is underlined by the fact that a dysfunctional endothelium can influence the development of pulmonary hypertension at the levels of coagulation control, vasomotor tone, and pulmonary vascular remodeling (16). The major stimulus for remodeling is hypoxia (17). The increase in PVR is predominantly caused by the hypoxic pulmonary vasoconstriction (HPV), which resides primarily distal to lobar arteries and proximal to the capillaries and occurs in resistance arterioles 30–300 μm in diameter (18). Pulmonary arteriolar SMC oxygen-sensitive voltage-dependent potassium channels seem to have an important role for initiating HPV (19). Inhibition of these channels by decreased PO2 inhibits outward potassium current, causing membrane depolarization and calcium entry through voltage-dependent calcium channels (19). The main determinant of HPV is alveolar PO2, but mixed venous PO2 contributes to approximately 20% of the response (19). HPV is inhibited by substances such as substance P, atrial natriuretic peptides, by mediators such as PGI2 and NO, by increased LAP, by increased alveolar pressure, and by alkalosis. Enhanced HPV, however, could be observed with acidosis, by using epidural anesthesia and by inhibition of cyclooxygenase or NO synthase (19). Subsequent increases in PAP are predominantly caused by vascular remodeling as well as secondary polycythemia. Proliferation and differentiation of pericytes and intermediate cells to SMCs are a consequence of chronic exposure to hypoxia followed by elastin and collagen synthesis and deposition (20). In addition, vasomotor function may be altered in these remodeled vessels (20). Among the candidates of biochemical mediators of hypoxia-induced pulmonary hypertension are voltage-gated potassium channels, mitochondrial oxygen sensing, and an imbalance in vasoactive factors (see below) (21). Remodeling also happens in inflammation secondary to sepsis (22) and in patients with chronic lung disease (23) and adult respiratory distress syndrome (ARDS) (24). The inflammation process and increased blood flow lead to vascular remodeling by damaging endothelial cells and disturbs the sensitive balance of pulmonary tone. Under physiological conditions, these cells eliminate factors that initiate SMC proliferation such as angiotensin II, endothelin, thromboxane A2, prostaglandin H2 and O2−(25). Alternatively, damaged endothelial cells may fail to produce inhibitory factors, possible heparin-like substances, which normally decrease SMC proliferation. Removal of the inciting stimulus can lead to reversal of structural changes. Etiology of Pulmonary Hypertension Pulmonary hypertension is caused by a variety of acute and chronic pulmonary diseases with an increase in PAP (Table 1). In contrast to secondary pulmonary hypertension, primary pulmonary hypertension (PPH) is not related to a known underlying disease.Table 1: World Health Organization Diagnostic Classification of Pulmonary Hypertension (1998) (21)PPH PPH is rare (1–2 per million in the general population), affects more women than men (1.7:1), sometimes has a familial link (6% of all cases), and has a poor prognosis (median survival 2–3 yr after diagnosis). PAP usually is >60 mm Hg in these patients (9, 26). PPH is a diagnosis of exclusion, because it is idiopathic. Hypoxemia and increased PVR resulting in an increased PAP can lead to RV failure and death. Altered vasoreactivity alone is not responsible for PPH. Vascular remodeling contributes to the vasculopathic process. However, regression of extensive changes caused by hypertension can occur. Secondary Pulmonary Hypertension Secondary pulmonary hypertension is more common, the increases in PAP are generally less severe (mean PAP <40 mm Hg) (26), and it is also more frequently seen in the perioperative period. Therefore, in this review, we have focused on secondary forms of pulmonary hypertension. Most cases of pulmonary hypertension are secondary to cardiac or pulmonary disease (Table 1) and may be reversible in some cases. Clinical manifestations might be overshadowed by the symptoms of the underlying disease (Table 2). Blood vessel changes are not confined to PPH but are also found in many forms of secondary pulmonary hypertension. Congenital cardiac disease with an atrial or ventricular septal defect causes an increase in pulmonary blood flow. Over time, in response to the increased blood flow, the PVR is increased and eventually will exceed systemic vascular resistance (SVR). Under these conditions, blood flow is shunted from right to left, often referred to as Eisenmenger syndrome. In contrast, high-pressure shunts such as those associated with truncus arteriosus, ventricular septal defects, or patent ductus arteriosus (28) cause pulmonary hypertension much earlier and it is often more severe.Table 2: Common Symptoms and Signs of Pulmonary Hypertension (27)The relevance of pulmonary hypertension in the perioperative period was shown in a study by Reich et al. (29). In patients undergoing coronary artery bypass grafting with cardiopulmonary bypass (CPB), the development of pulmonary hypertension was a significant predictor of increased mortality and perioperative myocardial infarction (29). The severity of the observed vasoconstriction correlates with the extent of CPB-induced endothelial injury (30). Levels of thromboxane A2(31) and endothelin (32) were increased after CPB, whereas PGI2 and NO levels were reduced (33). For a long time, it was thought that CPB did not cause any pulmonary endothelial injury due to ischemia-reperfusion because of the protection via the vasa vasorum of the bronchial circulation. It has been shown, however, that total CPB may cause complete cessation and reestablishment of pulmonary artery flow, with inadequate pulmonary endothelial blood supply by the vasa vasorum, resulting in an ischemia-reperfusion injury (34). The intraoperative injury and postoperative endothelial dysfunction of the pulmonary endothelium is promoted by the following factors (2): Preoperative status of the pulmonary vascular bed, i.e., pulmonary hypertension, valvular pathology; chronic obstructive pulmonary disease, pulmonary thromboembolism, and shear stress caused by increases in pulmonary blood flow and pressure of left-right intracardiac shunt. Bando et al. (35) demonstrated in patients with congenital heart disease that preoperative pulmonary hypertension, absence of mixed venous saturation monitoring, and absence of prophylactic α-blockade significantly increased postoperative pulmonary hypertension. Intraoperative vasospastic stimuli, such as hypoxia, hypercarbia, acidosis, duration of total CPB, ischemia-reperfusion injury, free radical formation, inflammatory mediators, pulmonary leukosequestration, excess thromboxane or endothelin production, and microemboli. Postoperative factors such as adrenergic tone, atelectasis, and HPV. Other examples of pulmonary hypertension during anesthesia are shown in Table 3.Table 3: Occurrence of Pulmonary Hypertension During Anesthesia (36)Symptoms and Diagnosis of Pulmonary Hypertension The most common clinical signs of pulmonary hypertension are dyspnea and fatigue (9) (see also Table 2). These major symptoms might be explained through the associated decrease in CO; however, an exact etiology is still missing. On physical examination, a prominent P2 heart sound, a tricuspid regurgitation murmur, an atrial (S3), or ventricular (S4) heart sound might be heard. The chest radiograph can display an enlarged main pulmonary artery and enlarged hilar vessels, whereas the electrocardiogram shows a right axis deviation suggesting right ventricular hypertrophy. However, the validity of acute changes in the electrocardiogram attributed to right heart insufficiency in the intraoperative period is limited. Transesophageal echocardiography (TEE) as a more advanced technique diagnoses pulmonary hypertension indirectly attributed to RV enlargement, paradoxical interatrial and interventricular movement, partial systolic closure of pulmonary valve, tricuspid regurgitation, and an increased RV systolic pressure (Fig. 2). There are two approaches to obtaining hemodynamic measurements using TEE. By using spatial imaging methods, cardiac chamber volumes can be estimated to obtain both preload and stroke volume. In addition, Doppler-based methods can be used to estimate both right ventricular filling and CO (37). Because of the inherent difficulty in developing a simple geometric model of the RV, regression equations may inaccurately predict ventricular volumes. In addition, TEE measurements are further altered by changing loading conditions, which alter both the size and geometry of the RV. Although TEE evaluation of RV volume can be difficult to determine in adults, high-quality images are routinely obtained in pediatric patients. One of the main limitations on further use of TEE is the availability of equipment as well as costs of echocardiography machines and probes, and expertise (37). The definitive diagnosis is obtained by right heart catheterization with direct measurement of PAP, right atrial pressure (RAP), PCWP, and CO.Figure 2: Transesophageal echocardiography for diagnosis of pulmonary hypertension. Dilated right ventricle (RV) in the midesophageal four chamber view. The figure shows the classical septal (S) interventricular shift to the left side. RA = right atrium, LA = left atrium, LV = left ventricle.RV and Pulmonary Hypertension Like the pulmonary circulation, the RV was not considered as important as the left ventricle (LV) in maintaining normal hemodynamics and counted for a long time as a "quantite negliable" (38). Today it is recognized that RV and LV are interdependent and both have vitally important functions. The RV is a thin-walled, highly compliant, but poorly contractile chamber. Under normal loading conditions and when function is not compromised, RV ejects blood against 25% of the afterload of the LV, resulting in a smaller RV wall thickness (39). The RV is bound by the RV free wall and the interventricular septum. Failure of the septum (e.g., because of ischemia) to contract normally will decrease RV systolic function. Blood supply for the RV and the septum depends mostly on whether a right or left dominant, or a "balanced" coronary circulation is present. Usually the right and the left anterior descending coronary artery supply the septum and parts of the free wall of the RV. The continuous pressure gradient between the aorta and the RV (coronary perfusion pressure) is responsible for the coronary blood flow to the RV free wall throughout systole and diastole (40). Therefore, the RV blood/oxygen supply is proportional to the systemic pressure but inversely proportional to the RV pressure. Systemic hypotension or increased RV pressure results in a decreased RV coronary perfusion pressure (41). Vlahakes et al. (42) previously showed that right heart performance is directly related to systemic pressure during pulmonary hypertension. RV function is very sensitive to increased RV preload or afterload, septic shock, coexistent LV dysfunction, or right coronary artery occlusive disease (43, 44). In a fundamental study, Urabe et al. (45) demonstrated that an increase in the afterload of the RV resulted in a rightward shift of the relationship between perfusion pressure and regional shortening. Also, end-diastolic segment lengths increased significantly after banding of the pulmonary artery. In contrast to LV performance, RV function is relatively sensitive to increases in afterload. Acute increase in mean PAP above approximately 40 mm Hg results in a significant decrease in RVEF even in the presence of a normal RV contractility. However, gradual increases in afterload are well tolerated, because the RV has time to assemble new sarcomeres in parallel to increase wall thickness (39). In the presence of decreased RV contractility, the RV is even more susceptible to acute increases in afterload. The decrease in RVEF results from a disproportionate increase in end-systolic volume compared with end-diastolic volume (41). The RV is less preload-responsive than the LV such that a given increase in preload results in a smaller increase in stroke work. Therefore, attempts at volume loading may be less effective in increasing RV output compared with volume loading of the In addition, volume loading may even the of RV oxygen (41). Vlahakes that two important in the of right heart RV afterload be reduced and systemic pressure be or Normal and are for maintaining normal RV function The of is as important for RV as it is for LV RV performance is by both intrinsic factors of the RV as well as factors afterload, of the pressure, right coronary artery perfusion pressure, LV performance, and the contractile of the interventricular of the LV function like coronary artery disease, heart valvular heart disease, or systemic hypertension influence RV function by ventricular Also, a RV and right can shift the interatrial and interventricular septum and the left and LV end-diastolic volume. venous pressure not on RV filling pressure and volume because it is dependent on the compliance of the RV in the tricuspid methods, and imaging are and more in the RV RV dysfunction caused by increased PAP was demonstrated in patients with chronic pulmonary disease and in patients ventilation can also RV the interventricular septum paradoxical resulting in right heart and decreased LV chamber size In postoperative a decrease in RVEF is observed at levels because of of alveolar vessels and increase in RV afterload significant was between RVEF and increasing of airway pressure by ventilation of the underlying disease has Because symptoms often arise in pulmonary hypertension, the after of signs of RV insufficiency is yr in for lung disease, as well as systemic for chronic lung are of of pulmonary hypertension. of which causes and and for can also definitive of congenital heart diseases can and mortality from postoperative pulmonary hypertension common clinical is the of the right heart because of chronic left heart In this of the LV has of the right heart by means of coronary or coronary artery bypass treatment and should PVR, which can be with the following and factors the pulmonary oxygenation with oxygen of respiratory acidosis, mm Hg) of a to of respiratory of the lung of release caused by stress and of options for RV dysfunction with increased PVR whereas positive inotropic drugs are the treatment of in RV dysfunction with normal PVR. of RV of RV preload should be considered if central venous pressure is mm Hg It is however, that preload of the RV should be estimated by a simple volume in an increase in mean arterial blood pressure and can increase RVEF with volume if RV is normal and PAP is increased only However, administration of volume also can have in patients with right heart treatment in for (defined as patients no increase in to the with central venous pressure mm of RV of the of the pulmonary circulation of CO and RV failure previously or vasodilators should be keeping in to a significant decrease in the decrease in the in RV stroke volume, systemic hypotension can be the consequence. is thought to produce by calcium channels has other such as the to NO synthase activate and release in both endothelial and SMCs. of SMCs is by both release of NO and direct of SMCs has a half-life it is relatively for the pulmonary circulation. It has been shown to be a and of other drugs to produce pulmonary in of patients with PPH a but there are no observed because of the small In contrast to treatment with that to reduced PAP and PVR in patients with secondary pulmonary hypertension treatment did not any This might be explained by the fact that on their to vascular remodeling The angiotensin reduced PAP and PVR in patients with secondary pulmonary hypertension 4 after have been shown to be effective in the treatment of pulmonary hypertension secondary to connective tissue vascular disease but not in patients with treatment was because of the on venous The of with calcium in secondary pulmonary hypertension seems to on the of PAP, i.e., the higher the of PAP, the less effective the of to the of on PAP in patients with pulmonary showed that a in PAP in of The in PAP in patients with the and the in PAP with clinical Although these drugs have shown their they have severe if used it is that calcium treatment should be to to Patients with pulmonary hypertension and severe clinical right heart failure (mean mm CO should be from treatment with calcium because of the inotropic of these by or more responsible for the of monophosphate leading to an increased of these with increased LV and pulmonary given have been used in patients with pulmonary hypertension after cardiac was shown for cardiac patients with increased PVR to pulmonary systemic It also seems to have an pulmonary effect to The PGI2 was in to PAP in PPH It is by the vascular endothelium and via prostaglandin to cyclase with following increase of PGI2 production is in patients with pulmonary hypertension of PGI2 may in to these are an inhibition of both and SMC proliferation from treatment of PGI2 or its also PAP in pulmonary hypertension of the pulmonary hypertension after heart in or pulmonary hypertension secondary to connective tissue diseases in a

To be EndMT or not to be, that is the question in pulmonary hypertension.

Individuals with single ventricle congenital heart disease (CHD) undergo multiple staged surgical palliations. Staged single ventricle palliation with a superior cavopulmonary connection (SCPC) in infancy followed by a Fontan in early childhood relies on passive, unobstructed pulmonary blood flow and normal pulmonary vasculature. We hypothesized that patients with echocardiographic identification of retrograde flow in a branch pulmonary artery (PA) after SCPC or Fontan are at increased risk for adverse outcomes. We conducted a retrospective chart review of patients seen at Children's Wisconsin from 1999 to 2019. Inclusion criteria included a history of single ventricle congenital heart disease and surgical palliation with a superior cavopulmonary connection (SCPC). We created two cohorts based on transthoracic echocardiographic identification of branch PA flow patterns: those with color Doppler-defined pulmonary artery flow reversal (PA reversal cohort) and those with normal anterograde flow (Non-reversal cohort). We identified 21 patients in the PA reversal cohort and 539 patients in the Non-reversal cohort. The PA reversal cohort had increased hospital length of stay after SCPC palliation (p < 0.001) and decreased transplant-free survival (p = 0.032), but there was no difference in overall survival (p = 0.099). There was no difference in hospital length of stay after Fontan (p = 0.17); however, the PA reversal cohort was significantly less likely to progress to Fontan palliation during early childhood (p = 0.005). Echocardiographic color Doppler identification of branch PA flow reversal in patients with single ventricle physiology is a high-risk indicator for adverse short- and long-term outcomes.

Calcium dynamics and intercellular communication in arterial smooth muscle cells

Pulmonary arterial hypertension (PAH) is a syndrome in which pulmonary arterial obstruction increases pulmonary vascular resistance, which leads to right ventricular (RV) failure and a 15% annual mortality rate. The present review highlights recent advances in the basic science of PAH. New concepts clarify the nature of PAH and provide molecular blueprints that explain how PAH is initiated and maintained. Five basic science concepts provide a framework to understand and treat PAH: (1) Endothelial dysfunction creates an imbalance that favors vasoconstriction, thrombosis, and mitogenesis. Restoration of this balance by inhibition of endothelin and thromboxane or augmentation of nitric oxide (NO) and prostacyclin is the paradigm on which most current therapy is based. (2) PAH has a genetic component. Mutations (bone morphogenetic protein receptor-2 [BMPR2]) and single-nucleotide polymorphisms (SNPs; ion channels and transporter genes) predispose to PAH. (3) Excess proliferation, impaired apoptosis, and glycolytic metabolism in pulmonary artery smooth muscle, fibroblasts, and endothelial cells suggest analogies to cancer. Many experimental therapies reduce PAH by decreasing the proliferation/apoptosis ratio; these include inhibitors of pyruvate dehydrogenase kinase (PDK), serotonin transporters (SERT), survivin, 3-hydroxy-3-methylglutaryl coenzyme A reductase, transcription factors (hypoxia-inducible factor [HIF]-1α and nuclear factor of activated T lymphocytes [NFAT]), and tyrosine kinases. Augmentation of voltage-gated K+ channels (Kv1.5) and BMPR2 signaling also addresses this imbalance. Tyrosine kinase inhibitors used to treat cancer are currently in phase 1 PAH trials. (4) Refractory vasoconstriction may occur due to rho kinase activation. Fewer than 20% of PAH patients respond to conventional vasodilators; however, refractory vasoconstriction may respond to rho kinase inhibitors. (5) The RV can be targeted therapeutically. Although increased afterload initiates RV failure, which is the major cause of death/dysfunction in PAH, the RV may be amenable to cardiac-targeted therapies. The RV in PAH has features of ischemic, hibernating myocardium. Guided by these new …

See related article, pages 1323–1330 Serotonin (5-HT, 5-hydroxytryptamine) has long been recognized as one of the most potent naturally occurring pulmonary vasoconstrictors.1 It was first implicated in the pathogenesis of pulmonary arterial hypertension (PAH) after an outbreak of the disease in Switzerland in the 1960’s among patients taking aminorex fumarate, an appetite suppressant that inhibits serotonin uptake by platelets.2 Since that time further outbreaks of PAH have been identified in Europe and the USA associated with the use of fenfluramine-derivate anorexigens,3–5 eventually leading to their withdrawal from the world market in 1997. Although this was, at least in retrospect, a predictable tragedy, it has ironically opened avenues of research into the biology of serotonin signaling in PAH. As fenfluramine-derivatives are substrates for the serotonin transporter (5-HTT, SERT) proteins,6 this suggests that abnormal SERT expression or functional activity could play a role in the pathogenesis of PAH. There is now a body of evidence supporting this hypothesis that provides hope for the development of effective therapeutic strategies targeting specific components of this signaling pathway in patients with these diseases. Most of the serotonin produced in the body is secreted by enterochromaffin cells of the intestine into the portal circulation where it is partially metabolized by the liver. However, levels of free circulating serotonin are maintained in the low nanomolar range through energy-dependent SERT-mediated transport into platelets. This led some researchers to hypothesize that fenfluramines might cause PAH by increasing free plasma levels of serotonin. However, this hypothesis is inconsistent with the observation that chronic treatment with fenfluramine-derivatives if anything reduces plasma levels of serotonin.6 This suggests that other SERT-related effects promote PAH in susceptible patients. This is supported by the observation that patients with idiopathic PAH have increased frequency of the so called L-type polymorphism …

Neonatal hypoxic pulmonary hypertension causes increases and spatial changes in tropoelastin expression in pulmonary arteries. However, it is not clear if this is due to recruitment of quiescent smooth muscle cells (SMC) into an elastin-producing phenotype or persistence of the fetal pattern of tropoelastin gene expression. We evaluated the distribution and relative concentration of tropoelastin mRNA in intralobar pulmonary arteries from late gestation fetuses and in animals exposed to hypobaric hypoxia (430 mmHg) from birth for 1, 3, 7, or 14 d, as well as in age-matched and adult room air-breathing controls. In situ hybridization demonstrated that tropoelastin mRNA was distributed throughout the entire radius of the pulmonary vessel wall in the fetus and newborn calf. By 15 d of age, only cells in the inner third of the media expressed tropoelastin mRNA, and by adulthood no tropoelastin mRNA was detected in the vessel wall. These findings demonstrated that tropoelastin expression shuts off in a spatially specific pattern, moving from the abluminal to the luminal side of the medial in the neonatal pulmonary artery when pressures and resistance are falling. In the aorta of 15-d-old calves, tropoelastin mRNA expression was seen equally throughout the media, indicating tissue-specific regulation of elastin in the neonatal period. In contrast, intralobar pulmonary arteries from calves exposed to hypoxia, which prevented the normal postnatal decline in pulmonary artery pressure, maintained the fetal pattern and levels of tropoelastin mRNA expression at all time points. Thus, rather than causing a recruitment of SMC into an elastin-producing phenotype, neonatal pulmonary hypertension caused a persistence of the fetal pattern of tropoelastin expression in medial SMC. Cell-free translation showed that the same tropoelastin isoforms were made by mRNA from control and hypertensive calves and, unlike the ligamentum nuchae, did not change during the transition from fetal to neonatal life. We conclude that pulmonary hypertension in the neonate perturbs the normal postpartum repression of tropoelastin expression resulting in a persistence of the fetal spacial and isoform patterns of tropoelastin gene expression.

Extracellular matrix (ECM) protein receptors, or integrins, participate in vascular remodeling and the systemic myogenic response. Synthetic ligands and ECM fragments regulate the vascular smooth muscle cell contractile state by altering intracellular Ca2+ levels ([Ca2+]i). Information on the Ca2+ effect of integrins in vascular smooth muscle cells is limited, but nonexistent in pulmonary arterial smooth muscle cells (PASMCs). We therefore characterized integrin expression in endothelium-denuded pulmonary arteries, and explored [Ca2+]i mobilization pathways induced by soluble ligands in rat PASMCs. Reverse transcriptase-PCR showed mRNA expression of integrins alpha1, alpha2, alpha3, alpha4, alpha5, alpha7, alpha8, alpha(v), beta1, beta3, and beta4, and immunoblots of alpha5, alpha(v), beta1, and beta3 confirmed protein expression. Exposure of PASMCs to integrin-binding peptides (0.5 mM) containing the arginine-glycine-aspartate (RGD) motif elicited [Ca2+]i responses with an order of potency of GRGDNP > GRGDSP > GRGDTP = cyclo-RGD. Pharmacological analysis revealed that the GRGDSP-induced Ca2+ response was unrelated to Ca2+ influx and the inositol triphosphate receptor-gated Ca2+ store, but partially blocked by ryanodine or inhibition of lysosome-related acidic organelles with bafilomycin A1. Simultaneous inhibition of both pathways was necessary to abolish the response. GRGDSP treatment increased cyclic ADP-ribose, the endogenous activator of ryanodine receptors, by 70%. GRGDSP also rapidly reduced Lysotracker Red accumulation, confirming direct modulation of acidic organelles. These data are the first demonstration of integrin-mediated Ca2+ regulation in PASMCs. The presence of an array of integrins, and activation of ryanodine-sensitive Ca2+ stores and lysosome-like organelles by GRGDSP suggest important roles for integrin-dependent Ca2+ signaling in regulating PASMC function.

Blood vessels are permanently subjected to mechanical forces in the form of stretch, encompassing cyclic mechanical strain due to the pulsatile nature of blood flow and shear stress. Significant variations in mechanical forces, of physiological or physiopathological nature, occur in vivo. These are accompanied by phenotypical modulation of smooth muscle cells and endothelial cells, producing structural modifications of the arterial wall. In all the cases, vascular remodelling can be allotted to a modification of the tensional strain or shear, and underlie a trend to reestablish baseline mechanical conditions. Vascular cells are equipped with numerous receptors that allow them to detect and respond to the mechanical forces generated by pressure and shear stress. The cytoskeleton and other structural components have an established role in mechanotransduction, being able to transmit and modulate tension within the cell via focal adhesion sites, integrins, cellular junctions and the extracellular matrix. Mechanical forces also initiate complex signal transduction cascades, including nuclear factor-kappaB and mitogen-activated protein kinase pathways, leading to functional changes within the cell.

endothelial progenitor cells (EPCs) are a unique cell type found circulating in the peripheral blood with the capacity to become mature endothelial cells. EPCs can be released from many sources including the bone marrow, adipose tissue, the vessel wall, as well as potentially the spleen, liver, and

should decrease pulmonary artery pressure (PAP) and pulmonary vascular resistance (PVR), without affecting systemic arterial pressure (SAP), and potentially improve oxygenation by redistributing pulmonary blood flow to ventilated areas of lung. INO (INO Therapeutics Inc., Clinton NJ) possesses these properties and has gained approval from the Food and Drug Administration (FDA) for the care of neonates with acute lung injury and pulmonary hypertension (PH), and widespread clinical acceptance (but not FDA approval) for adults with PH with or without lung injury. Delivered as a gas, INO is preferentially distributed to the ventilated areas of the lung, where it produces relaxation of pulmonary vascular smooth muscle via activation of guanylate cyclase and the conversion of guanosine-5-triphosphate to cyclic guanosine monophosphate. 1 Absorbed INO is rapidly inactivated by hemoglobin, thereby preventing systemic effects and confining its vasodilator properties to the pulmonary circulation. 1 The search for inhaled selective pulmonary vasodilators was an active area of research, particularly in Europe and Australia, before the widespread publicity and testing of INO in the early 1990s. However, research on this subject appears to have declined inversely with the growing acceptance and use of INO. Until FDA approval had been granted, INO had been supplied free of charge in the United States on an investigational-drug basis. However, after FDA approval, the cost of treatment with INO became very expensive. This prompted a search at our institution for alternative agents to INO. The purpose of this article is to review the published experience concerning alternative inhaled vasodilators and, when possible, compare their reported efficacy with that of INO.

Mutations in transforming growth factor-beta (TGF-beta) receptor superfamily members underlie conditions characterized by vascular dysplasia. Mutations in endoglin and activin-like kinase receptor 1 (ALK1) cause hereditary hemorrhagic telangiectasia, whereas bone morphogenetic protein type II receptor (BMPR-II) mutations underlie familial pulmonary arterial hypertension. To understand the functional roles of these receptors, we examined their relative contributions to BMP signaling in human pulmonary artery endothelial cells (HPAECs). BMP9 potently and selectively induced Smad1/5 phosphorylation and Id gene expression in HPAECs. Contrary to expectations, BMP9 also stimulated Smad2 activation. Furthermore, BMP9 induced the expression of interleukin 8 and E-selectin. Using small interfering RNA, we demonstrate that the type I receptor, ALK1, is essential for these responses. However, small interfering RNA and inhibitor studies showed no involvement of ALK5 or endoglin. We further demonstrate that, of the candidate type II receptors, BMPR-II predominantly mediated IL-8 and E-selectin induction and mitogenic inhibition by BMP9. Conversely, activin receptor type II (ActR-II) contributed more to BMP9-mediated Smad2 activation. Only abolition of both type II receptors significantly reduced the Smad1/5 and Id responses. Both ALK1 and BMPR-II contributed to growth inhibition of HPAECs, whereas ActR-II was not involved. Taken together, our findings demonstrate the critical role of type II receptors in balancing BMP9 signaling via ALK1 and emphasize the essential role for BMPR-II in a subset of BMP9 responses (interleukin 8, E-selectin, and proliferation). This differential signaling may contribute to the contrasting pathologies of hereditary hemorrhagic telangiectasia and pulmonary arterial hypertension.

The high morbidity and mortality in congenital diaphragmatic hernia (CDH) are attributed to severe pulmonary hypoplasia and persistent pulmonary hypertension (PH). PH is characterized by structural changes in pulmonary arteries, resulting in adventitial and medial thickness. These effects are triggered by abnormal apoptosis and proliferation of pulmonary vascular endothelial and smooth muscle cells (SMCs). Apelin (APLN), a target gene of bone morphogenic protein receptor 2 (BMPR2), is known to play an important and manifold role in regulating pulmonary homeostasis promoting endothelial cell (EC) survival, proliferation and migration. In addition to these autocrine effects of apelin, it displays a paracrine function attenuating the response of pulmonary SMCs to growth factors and promoting apoptosis. Apelin exerts its effect via its G-protein-coupled receptor (APLNR) and is solely expressed by pulmonary vascular EC, whereas APLNR is co-localized in pulmonary ECs and SMCs. Dysfunction of BMPR2 and downstream signalling have been shown to disturb the crucial balance of proliferation of SMCs contributing to the pathogenesis of human and experimentally induced PH. We designed this study to investigate the hypothesis that apelin and APLNR signalling are disrupted in the pulmonary vasculature of rats in nitrofen-induced CDH. Pregnant rats were exposed to nitrofen or vehicle on D9 of gestation. Foetuses were sacrificed on D21 and divided into nitrofen and control group (n = 32). Pulmonary RNA was extracted and mRNA levels of APLN and APLNR were determined by quantitative real-time PCR. Protein expression of apelin and APLNR was investigated by western blotting. Confocal immunofluorescence double staining for apelin, APLNR and SMCs were performed. Relative mRNA level of APLN and APLNR were significantly decreased in the CDH group compared to control lungs. Western blotting and confocal microscopy confirmed the qRT-PCR results showing decreased pulmonary protein expression of apelin and APLNR in lungs of nitrofen-exposed foetuses compared to controls. This study provides striking evidence of markedly decreased gene and protein expression of apelin and its receptor APLNR in the pulmonary vasculature of nitrofen-induced CDH. The disruption of the apelin-APLNR signalling axis in the pulmonary vasculature may lead to extensive vascular remodelling and contribute to PPH in the nitrofen-induced CDH model.

Lysophospholipid mediators in the vasculature

In this study, we compared the effect of the essential oil of Citrus bergamia Risso [bergamot, bergamot essential oil (BEO)] on the intracellular Ca levels in vascular endothelial (EA) and mouse vascular smooth muscle (MOVAS) cells, using the fura-2 fluorescence technique. BEO caused an initial transient increase in intracellular Ca concentration ([Ca]i) in EA cells, followed by a decrease, whereas it induced a sustained increase in [Ca]i in MOVAS cells. Linalyl acetate (LA) as a major component of BEO-induced [Ca]i mobilization was similar to BEO in EA cells. The increase of [Ca]i by LA was higher in EA cells than in MOVAS cells. [Ca]i rise induced by extracellular Ca application was significantly blocked by BEO or LA in EA cells but not in MOVAS cells, suggesting that BEO and LA block Ca influx in EA cells. The present results suggest that BEO and LA differentially modulate intracellular Ca levels in vascular endothelial and smooth muscle cells. In addition, blockade of Ca influx by BEO and LA in EA cells may explain the protective effects of BEO on endothelial dysfunction associated with cardiovascular disease.