Vasoconstriction Of Pulmonary Arteries Research Articles

A patient with possible TRALI who developed pulmonary hypertensive crisis and acute pulmonary edema during cardiac surgery

There are very few case reports of transfusion-related acute lung injury (TRALI) under close hemodynamic monitoring. We encountered a case of possible TRALI during on-pump coronary artery bypass grafting (CABG). A 66-year-old man who had undergone on-pump CABG was administered fresh frozen plasma (FFP). One hour after FFP transfusion, pulmonary hypertensive crisis and subsequent hypoxic decompensation occurred. A second cardiopulmonary bypass (CPB) was needed for circulatory and respiratory deterioration. Extracorporeal life support (ECLS), intraaortic balloon pumping (IABP), and nitric oxide therapy were required after the surgery. Despite the severity of the initial state, his recovery was comparatively smooth. ECLS and IABP were removed on postoperative day (POD)1; the patient was extubated and discharged from the ICU on POD7 and POD12, respectively. The diagnosis of TRALI was confirmed by human leukocyte antigen antibody detection in the administered FFP. In addition, lymphocytic immunofluorescence test showed that a cross-match of the plasma from the pooled FFP against the recipient leukocytes was positive. The clinical course of the pulmonary artery hypertension was followed by a decrease in dynamic lung compliance. The mechanism of this phenomenon is unclear. However, it might suggest the possibility of vasoconstriction or obstruction of the peripheral pulmonary artery preceding lung damage, as in the case in animal models reported previously.

86: Maternal nicotine use increases fetal pulmonary arterial vasoconstriction during hypoxemia at near term gestation in a nonhuman primate model

Maternal nicotine exposure during gestation results in metabolic and structural changes in the developing fetal lung, and abnormal lung function in newborn monkeys. We hypothesized that maternal nicotine exposure alters fetal pulmonary arterial vascular responses to hypoxemic and hyperoxemic stimuli at near-term gestation

Inhaled Treprostinil for the Treatment of Pulmonary Arterial Hypertension

Pulmonary arterial hypertension is a progressive disease characterized by vascular proliferation and vasoconstriction of the small pulmonary arteries that eventually leads to right-sided heart failure and death. Patients often initially have symptoms such as shortness of breath, fatigue, and edema; later in the disease, presyncope and syncope are common. Patients with progressive pulmonary arterial hypertension despite oral therapy and/or with severe disease typically require treatment with a prostanoid. Inhaled treprostinil (Tyvaso) is a prostacyclin analog indicated for the treatment of pulmonary arterial hypertension to increase walk distance in patients with symptoms classified as New York Heart Association functional class III. Inhaled treprostinil was approved by the Food and Drug Administration in July 2009. This article provides a brief overview of the pathophysiology of pulmonary arterial hypertension and reviews the mechanism of action, key clinical data, and the practical management of inhaled treprostinil in patients with pulmonary arterial hypertension.

Macrophage migration inhibitory factor contributes to hypoxic pulmonary vasoconstriction in rats

BackgroundHypoxic pulmonary vasoconstriction may lead to pulmonary hypertension, but the underlying mechanisms of persistent vasoconstriction are still unclear. There is evidence that pulmonary inflammation contributes to the abnormalities of function in the pulmonary artery (PA) following chronic hypoxia exposure. Macrophage migration inhibitory factor (MIF) is an important pro-inflammatory cytokine, and we found that expression of MIF was increased in the smooth muscle of PA from hypoxic pulmonary hypertensive rats. Therefore, the aim of the study was to investigate the role of MIF in modulating vasoreactivity of isolated PA rings. MethodsSprague–Dawley rats were challenged by intermittent chronic hypoxia exposure for 4weeks to establish hypoxic pulmonary hypertension models. Subsequently, immunohistochemistry and western blot assay were used to examine the MIF expression in pulmonary artery. Moreover, isometric force displacement was measured in isolated intrapulmonary artery. ResultsIn the isolated PA, our results showed that MIF mediated the enhanced pulmonary arterial vasoconstriction in response to chronic hypoxia, and the delayed hypoxic constriction in a biphasic pattern of constriction occurs in response to acute hypoxia. We also present the finding that MIF had no effect on force on its own, but concentration-dependently potentiated constrictions pre-evoked by phenylephrine under normoxic condition. The potentiation was independent of the endothelium. MIF-induced potentiation of phenylephrine-evoked constriction was partially inhibited by PKC inhibitor chelerythrine, p38 inhibitor SB 203580, ERK1/2 inhibitor U0126, respectively. ConclusionsOur results suggested that MIF enhanced vasoconstriction of pulmonary artery elicited by agonist through PKC, p38 and ERK1/2 signal pathways, which may contributes to hypoxic pulmonary vasoconstriction.

Pulmonary Hypertension Associated With Left Heart Disease: Characteristics, Emerging Concepts, and Treatment Strategies

Left heart disease (LHD) represents the most common causes of pulmonary hypertension (PH). Whether caused by systolic or diastolic dysfunction or valvular heart disease, a hallmark of PH associated with LHD is elevated left atrial pressure. In all cases, the increase in left atrial pressure causes a passive increase in pulmonary pressure. In some patients, a superimposed active component caused by pulmonary arterial vasoconstriction and vascular remodeling may lead to a further increase in pulmonary arterial pressure. When present, PH is associated with a worse prognosis in patients with LHD. In addition to local abnormalities in nitric oxide and endothelin production, gene modifiers such as serotonin polymorphisms may be associated with the pathogenesis of PH in LHD. Optimizing heart failure regimens and corrective valve surgery represent the cornerstone of the treatment of PH in LHD. Recent studies suggest that sildenafil, a phosphodiesterase-5 inhibitor, is a promising agent in the treatment of PH in LHD. Unloading the left ventricle with circulatory support may also reverse severe PH in patients with end-stage heart failure allowing candidacy to heart transplantation.

Hemoglobin-based Oxygen Carriers for Reversing Hypotension and Shock

Hemoglobin-based Oxygen Carriers for Reversing Hypotension and Shock

Ceramide inhibits Kv currents and contributes to TP-receptor-induced vasoconstriction in rat and human pulmonary arteries

Neutral sphingomyelinase (nSMase)-derived ceramide has been proposed as a mediator of hypoxic pulmonary vasoconstriction (HPV), a specific response of the pulmonary circulation. Voltage-gated K(+) (K(v)) channels are modulated by numerous vasoactive factors, including hypoxia, and their inhibition has been involved in HPV. Herein, we have analyzed the effects of ceramide on K(v) currents and contractility in rat pulmonary arteries (PA) and in mesenteric arteries (MA). The ceramide analog C6-ceramide inhibited K(v) currents in PA smooth muscle cells (PASMC). Similar effects were obtained after the addition of bacterial sphingomyelinase (SMase), indicating a role for endogenous ceramide in K(v) channel regulation. K(v) current was reduced by stromatoxin and diphenylphosphine oxide-1 (DPO-1), selective inhibitors of K(v)2.1 and K(v)1.5 channels, respectively. The inhibitory effect of ceramide was still present in the presence of stromatoxin or DPO-1, suggesting that this sphingolipid inhibited both components of the native K(v) current. Accordingly, ceramide inhibited K(v)1.5 and K(v)2.1 channels expressed in Ltk(-) cells. Ceramide-induced effects were reduced in human embryonic kidney 293 cells expressing K(v)1.5 channels but not the regulatory subunit K(v)β2.1. The nSMase inhibitor GW4869 reduced the thromboxane-endoperoxide receptor agonist U46619-induced, but not endothelin-1-induced pulmonary vasoconstriction that was partly restored after addition of exogenous ceramide. The PKC-ζ pseudosubstrate inhibitor (PKCζ-PI) inhibited the K(v) inhibitory and contractile effects of ceramide. In MA ceramide had no effect on K(v) currents and GW4869 did not affect U46619-induced contraction. The effects of SMase were also observed in human PA. These results suggest that ceramide represents a crucial signaling mediator in the pulmonary vasculature.

Hydrogen Peroxide Regulates Extracellular Superoxide Dismutase Activity and Expression in Neonatal Pulmonary Hypertension

We previously demonstrated that superoxide and H(2)O(2) promote pulmonary arterial vasoconstriction in a lamb model of persistent pulmonary hypertension of the newborn (PPHN). Because extracellular superoxide dismutase (ecSOD) augments vasodilation, we hypothesized that H(2)O(2)-mediated ecSOD inactivation contributes to pulmonary arterial vasoconstriction in PPHN lambs. ecSOD activity was decreased in pulmonary arterial smooth muscle cells (PASMCs) isolated from PPHN lambs relative to controls. Exposure to 95% O(2) to mimic hyperoxic ventilation reduced ecSOD activity in control PASMCs. In both cases, these events were associated with increased protein thiol oxidation, as detected by the redox sensor roGFP. Accordingly, exogenous H(2)O(2) decreased ecSOD activity in control PASMCs, and PEG-catalase restored ecSOD activity in PPHN PASMCs. In intact animal studies, ecSOD activity was decreased in fetal PPHN lambs, and in PPHN lambs ventilated with 100% O(2) relative to controls. In ventilated PPHN lambs, administration of a single dose of intratracheal PEG-catalase enhanced ecSOD activity, reduced superoxide levels, and improved oxygenation. We propose that H(2)O(2) generated by PPHN and hyperoxia inactivates ecSOD, and intratracheal catalase enhances enzyme function. The associated decrease in extracellular superoxide augments vasodilation, suggesting that H(2)O(2) scavengers may represent an effective therapy in the clinical management of PPHN.

Pulmonary Hypertension in COPD: Pathophysiology and Therapeutic Targets

The incidence of mild to moderate pulmonary hypertension (PH) is highly prevalent, reaching to 50% in advanced chronic obstructive pulmonary disease (COPD). However, a subpopulation (1-4% in most studies) with grim prognosis despite moderate airflow limitation, present with "out-of-proportion" severe PH, is arbitrarily defined by a mean PH ≥ 40 mmHg, at rest. The sequence of changes that lead to PH in COPD begins at early disease stages by the impairment of endothelial function, which is associated with impaired release of endothelium-derived vasodilating (nitric oxide, prostacyclin) and vasoconstrictive agents (endothelin-1) and imbalance among them. PH in COPD is caused by vasoconstriction and remodelling of pulmonary arteries, which is characterized by the intimal proliferation of poorly differentiated smooth muscle cells and the deposition of elastic and collagen fibres. Hypoxia, inflammation and toxic effects of cigarette smoke, independently or additively interacting, are confirmed factors leading to PH. To date, long-term supplemental oxygen remains the primary treatment in COPD patients with PH. The administration of new vasodilators (prostanoids, endothelin-1 receptor antagonists and phosphodiesterase-5 inhibitors) dedicated to idiopathic pulmonary arterial hypertension in the disproportionate subgroup of patients with "out-of-proportion" PH may be considered in the setting of clinical trials. The use of these drugs in COPD patients with PH < 40 mmHg may worsen gas exchange, and to date, has no proven benefit. Future treatments must target more directly pathogenetic mechanisms. Therefore, novel agents have been proposed and are under active investigation, including 5-HT receptor antagonists, Rho-kinase inhibitors, statins and stem cell therapy.

Role of Lipoxygenase Metabolites of Arachidonic Acid in Enhanced Pulmonary Artery Contractions of Female Rabbits

Pulmonary arterial hypertension is characterized by elevated pulmonary artery pressure and vascular resistance. In women the incidence is 4-fold greater than that in men. Studies suggest that sustained vasoconstriction is a factor in increased vascular resistance. Possible vasoconstrictor mediators include arachidonic acid-derived lipoxygenase (LO) metabolites. Our studies in rabbits showed enhanced endothelium-dependent contractions to arachidonic acid in pulmonary arteries from females compared with males. Because treatment with a nonspecific LO inhibitor reduced contractions in females but not males, the present study identified which LO isoform contributes to sex-specific pulmonary artery vasoconstriction. The 15- and 5- but not 12-LO protein expressions were greater in females. Basal and A23187-stimulated release of 15-, 5-, and 12-hydroxyeicosatetraenoic acids (HETEs) from females and males were measured by liquid chromatography/mass spectrometry. Only 15-HETE synthesis was greater in females compared with males under both basal and stimulated conditions. Vascular contractions to 15-HETE were enhanced in females compared with males (maximal contraction: 44±6%versus 25±3%). The specific 15-LO inhibitor PD146176 (12 μmol/L) decreased arachidonic acid-induced contractions in females (maximal contraction: 93±4% versus 57±10%). If male pulmonary arteries were incubated with estrogen (1 μmol/L, 18 hours), protein expression of 15-LO and 15-HETE production increased. Mechanisms to explain the increased incidence of pulmonary hypertension in women are not known. Results suggest that the 15-LO pathway is different between females and males and is regulated by estrogen. Understanding this novel sex-specific mechanism may provide insight into the increased incidence of pulmonary hypertension in females.

Idiopathic pulmonary arterial hypertension: An avian model for plexogenic arteriopathy and serotonergic vasoconstriction

Idiopathic pulmonary arterial hypertension (IPAH) is a disease of unknown cause that is characterized by elevated pulmonary arterial pressure and pulmonary vascular resistance attributable to vasoconstriction and vascular remodeling of small pulmonary arteries. Vascular remodeling includes hypertrophy and hyperplasia of smooth muscle (medial hypertrophy) accompanied in up to 80% of the cases by the formation of occlusive plexiform lesions (plexogenic arteriopathy). Patients tend to be unresponsive to vasodilator therapy and have a poor prognosis for survival when plexogenic arteriopathy progressively obstructs their pulmonary arteries. Research is needed to understand and treat plexogenic arteriopathy, but advances have been hindered by the absence of spontaneously developing lesions in existing laboratory animal models. Young domestic fowl bred for meat production (broiler chickens, broilers) spontaneously develop IPAH accompanied by semi-occlusive endothelial proliferation that progresses into fully developed plexiform lesions. Plexiform lesions develop in both female and male broilers, and lesion incidences (lung sections with lesions/lung sections examined) averaged approximately 40% in 8 to 52 week old birds. Plexiform lesions formed distal to branch points in muscular interparabronchial pulmonary arteries, and were associated with perivascular mononuclear cell infiltrates. Serotonin (5-hydroxytryptamine, 5-HT) is a potent vasoconstrictor and mitogen known to stimulate vascular endothelial and smooth muscle cell proliferation. Serotonin has been directly linked to the pathogenesis of IPAH in humans, including IPAH linked to serotonergic anorexigens that trigger the formation of plexiform lesions indistinguishable from those observed in primary IPAH triggered by other causes. Serotonin also plays a major role in the susceptibility of broilers to IPAH. This avian model of spontaneous IPAH constitutes a new animal model for biomedical research focused on the pathogenesis of IPAH and plexogenic arteriopathy.

Effect of Serotonin Reuptake Inhibitors on Pulmonary Hemodynamics in Humans

BackgroundSerotonin promotes pulmonary arterial vasoconstriction and pulmonary arterial smooth muscle cell proliferation, thereby having the potential to increase pulmonary arterial blood pressure. Although serotonin reuptake inhibitors (SRIs) might inhibit further deterioration in patients with manifest pulmonary arterial hypertension, they may induce pulmonary hypertension in healthy newborns after fetal exposure. As it is unclear whether treatment with SRIs affects pulmonary hemodynamics in adults without pulmonary hypertension, the aim of the present study was to investigate the effect of SRIs on pulmonary hemodynamics in such subjects.MethodsSixteen patients with stable angina pectoris scheduled for first time coronary artery bypass grafting were included in the study. Of these 8 were currently treated with an SRI (the SRI group) and 8 were not (the control group). Pulmonary arterial pressures were measured before induction of anesthesia by means of a pulmonary artery catheter. Serotonin transporter and 5-HT2A receptor gene polymorphisms and platelet 5-HT2A receptor expression were studied to elucidate their possible role as modifying factors.ResultsNo patients in any of the groups had pulmonary arterial hypertension. Mean pulmonary artery pressure was 15.0 mmHg in the SRI group and 14.5 mmHg in the control group (P = 0.50; 95% confidence interval for the difference, -2.9 to +3.9 mmHg). Neither were there any significant differences between the groups for any of the other hemodynamic variables studied. The various gene polymorphisms and the extent of platelet 5-HT2A receptor expression did not influence the hemodynamic variables.ConclusionsSRI treatment did not significantly influence pulmonary hemodynamics in patients without pulmonary hypertension.KeywordsSerotonin; Selective serotonin reuptake inhibitors; Pulmonary hemodynamics; Pulmonary hypertension

Preliminary Experience in the Use of Preoperative Echo-guided Left Stellate Ganglion Block in Patients Undergoing Cardiac Surgery

Pulmonary arterial (PA) vasoconstriction in cardiac surgery can originate from the action of combined humoral, endothelial, and sympathetic tone changes. The consequence of PA vasoconstriction is pulmonary hypertension (PHT) and, when present after cardiopulmonary bypass (CPB), can predispose to right ventricular dysfunction. Right ventricular dysfunction after CPB is a serious complication with high mortality rates. The extent to which sympathetic blockade could reduce PA vasoconstriction and reduce PHT is unknown. Pharmacologic stellate ganglion block (SGB) has been associated with a reduction in PHT, but its role and mechanism in cardiac surgery have not been described. Thus, the goal of the study was to test the hypothesis that echo-guided left SGB, performed before the induction of general anesthesia, could prevent PA pressure increases during CPB weaning. A prospective cohort study in cardiac surgical patients. A tertiary care university hospital. Forty cardiac surgical patients. A left SGB was performed immediately before the induction of general anesthesia under ultrasound guidance and was compared with matched control patients. Standard hemodynamic and electrocardiographic monitoring was performed, and blood gas samples were drawn at specific predetermined time points for analysis. Rhythm disorders, echocardiographic parameters that included wall motion abnormalities, and biochemical parameters of myocardial ischemia were measured by an observer blinded to the allocated group. Marked improvement in the PaO(2)/F(I)O(2) ratio in the SGB group was observed (mean difference = 77 mmHg, p = 0.0001). There were no differences between the groups in PA pressure over time during the procedure; central venous pressure was higher in the SGB group (p =0.0184). Reductions of right ventricular fractional area change (p = 0.0331) and tricuspid annulus displacement (p = 0.0048) were observed in the SGB group. The CK-MB was 1.5 times higher in the SGB group (p = 0.0211), but no patients developed myocardial infarction. Left SBG was associated with improved oxygenation that could partially explain its mechanism in acute PHT. Further studies are necessary to evaluate the usefulness of this technique in patients with a high risk of PHT during separation from CPB.

Synergism between Ca2+ and Rho‐kinase signaling during pulmonary arterial vasoconstriction in chronic hypoxic newborn lamb

Pulmonary artery (PA) contractility is mediated in large part by increases in cytosolic Ca2+, which activates myosin light chain (MLC) kinase and in turn phosphorylates myosin light chain20 (MLC20). Rho‐kinase further enhances phosphorylation of MLC20 and contractility through inhibition of MLC phosphatase. We hypothesized that Ca2+ and Rho‐kinase signaling synergistically regulate pulmonary vascular tone in chronically hypoxic (CH) newborn lambs. This hypothesis was tested by performing wire myography on serotonin (5‐HT) stimulated PA rings isolated from 12 to 17 day old lambs maintained at high altitude (3801 m) for the final 100 days of gestation and after birth (CH). 5‐HT elicited dose‐dependent contractions were attenuated with various Ca2+ entry or Rho‐kinase blockers. Voltage dependent and independent Ca2+ entry was inhibited with 30 μM KB‐R7943 (KBR), 100 μM flufenamate (FFA), 30 μM SN‐6, or 10 μM nifedipine (NIF) in the absence or presence of 50 μM SKF‐96365 (SKF). Rho‐kinase was inhibited with 10 μM fasudil or Y27632. The potency order for the Ca2+ entry antagonists was KBR ≥ NIF+SKF ≫ NIF &gt; FFA ≫ SN‐6, whileY27632 &gt; fasudil. Fasudil substantially augmented the inhibitory action of the Ca2+ entry blockers. These findings support the rationale for treating pulmonary hypertension with medications that target both Ca2+ and Rho‐kinase pathways. NIH P01HD031226, R01HD003807 (LDL), R01HL95973 (AB)

Neprilysin Peptidase‐Independent Complex Formation In Pulmonary Artery Smooth Muscle Cells

Pulmonary hypertension (PHTN) results from vasoconstriction and remodeling of pulmonary arteries (PA), including accumulation and migration of smooth muscle cells (SMCs). We found that the activity/expression of the transmembrane peptidase neprilysin (NEP) is decreased in chronic hypoxic PHTN, and that chronically hypoxic NEP null mice have increased pulmonary vascular remodeling. We hypothesize that, besides peptidase effects, the peptidase‐independent mechanisms of NEP, mediated through coupling of NEP to intracellular proteins, are important in mediating the effects of NEP in PA SMCs.Silver‐stained gels of C57BL/6 wt mouse PA SMCs, co‐immunoprecipitated with an antibody to NEP, show bands of 40, 55, 65, 75, 90 and 150 kD. Western analyses (n=2–5) show that NEP forms complexes with the MAPK ERK1/2 and the protein kinase Lyn. Human PA SMCs show similar results. Future studies will investigate the growth‐ and migratory‐inhibitory properties of these complexes, as well as characterize NEP complexes with other proteins. These findings indicate that peptidase‐independent mechanisms may contribute to the mechanisms of action of NEP and may aid in understanding NEP's involvement in preventing/reversing pulmonary vascular remodeling, and in designing treatment and prevention strategies for PHTN.Research Support: NHLBI RO1 HL‐078929‐01 and PPG HL‐014985, UCD Dept. of Medicine, and the VA.

Role of the G-protein and tyrosine kinase--Rho/ROK pathways in 15-hydroxyeicosatetraenoic acid induced pulmonary vasoconstriction in hypoxic rats

It has been previously reported by us that hypoxia activates lung 15-lipoxygenase (15-LO), which catalyzes arachidonic acid to 15-hydroxyeicosatetraenoic acid (15-HETE), leading to the constriction of pulmonary artery (PA). Rho-associated serine/threonine kinase (ROK), a downstream effector of small GTPase RhoA that may be modulated by G-protein and tyrosine kinase, plays an important role in smooth muscle contraction. However, whether the 15-HETE induced PA vasoconstriction involves the Rho/ROK pathway remains to be demonstrated. Therefore, we studied the contribution of ROK as well as G-protein and tyrosine kinase to the 15-HETE induced pulmonary vasoconstriction using PA ring technique, RNA interference technology, RP-HPLC, western blot and RT-PCR combined with the blockers. The hypoxia-induced expression of ROK is regulated by 15-HETE in rat PA smooth muscle cells (PASMCs), leading to vasoconstriction. The up-regulation of ROK expression caused by 15-HETE appears to be mediated by the G-protein and tyrosine kinase pathways. The translocation of ROK2 from the nucleus to the cytoplasm during hypoxia exposure relies on the mechanism for 15-HETE production. These results suggest that 15-HETE may mediate the up-regulation of ROK expression through G-protein and tyrosine kinase pathways under hypoxic condition, leading to PA vasoconstriction.

Thrombin activation of proteinase‐activated receptor 1 potentiates the myofilament Ca2+ sensitivity and induces vasoconstriction in porcine pulmonary arteries

Thrombus formation is commonly associated with pulmonary arterial hypertension (PAH). Thrombin may thus play an important role in the pathogenesis and pathophysiology of PAH. Hence, we investigated the contractile effects of thrombin and its mechanism in pulmonary artery. The cytosolic Ca(2+) concentrations ([Ca(2+)](i)), 20 kDa myosin light chain (MLC20) phosphorylation and tension development were evaluated using the isolated porcine pulmonary artery. Thrombin induced a sustained contraction in endothelium-denuded strips obtained from different sites of a pulmonary artery, ranging from the main pulmonary artery to the intrapulmonary artery. In the presence of endothelium, thrombin induced a transient relaxation. The contractile effect of thrombin was abolished by either a protease inhibitor or a proteinase-activated receptor 1 (PAR(1)) antagonist, while it was mimicked by PAR(1)-activating peptide (PAR(1)AP), but not PAR(4)AP. The thrombin-induced contraction was associated with a small elevation of [Ca(2+)](i) and an increase in MLC20 phosphorylation. Thrombin and PAR(1)AP induced a greater increase in tension for a given [Ca(2+)](i) elevation than that obtained with high K(+)-depolarization. They also induced a contraction at a fixed Ca(2+) concentration in alpha-toxin-permeabilized preparations. The present study revealed a unique property of the pulmonary artery. In contrast to normal arteries of the systemic circulation, thrombin induces a sustained contraction in the normal pulmonary artery, by activating PAR(1) and thereby increasing the sensitivity of the myofilament to Ca(2+). This responsiveness of the pulmonary artery to thrombin may therefore contribute to the pathogenesis and pathophysiology of PAH.

Impaired Vasoconstriction and Nitric Oxide-Mediated Relaxation in Pulmonary Arteries of Hypoxia- and Monocrotaline-Induced Pulmonary Hypertensive Rats

Pulmonary hypertension (PH) is a life-threatening disease with unclear vascular mechanisms. We tested whether PH involves abnormal pulmonary vasoconstriction and impaired vasodilation. Male Sprague-Dawley rats were exposed to hypoxia (9% O(2)) for 2 weeks or injected with single dose of monocrotaline (MCT, 60 mg/kg s.c.). Control rats were normoxic or injected with saline. After the hemodynamic measurements were performed, pulmonary and mesenteric arteries were isolated for measurement of vascular function. Hematocrit was elevated in hypoxic rats. Right ventricular systolic pressure and Fulton's Index [right/(left + septum) ventricular weight] were greater in hypoxic and MCT-treated rats than in normoxic rats. Pulmonary artery contraction by phenylephrine and 96 mM KCl was less in hypoxic and MCT-treated rats than in normoxic rats. Acetylcholine-induced relaxation was less in the pulmonary arteries of hypoxic and MCT-treated rats than of normoxic rats, suggesting reduced effects of endothelium-derived vasodilators. The nitric oxide synthase inhibitor, N(omega)-nitro-l-arginine methyl ester, and the guanylate cyclase inhibitor, 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one, inhibited acetylcholine relaxation, suggesting that it was mediated by nitric oxide (NO)-cGMP. The NO donor sodium nitroprusside caused less relaxation in the pulmonary arteries of hypoxic and MCT-treated than of normoxic rats, suggesting decreased responsiveness of vascular smooth muscle cells (VSMCs) to vasodilators. Phenylephrine and KCl contraction and acetylcholine and sodium nitroprusside relaxation were not different in the mesenteric arteries from all groups. In lung tissue sections, the wall thickness of pulmonary arterioles was greater in hypoxic and MCT-treated rats than in normoxic rats. The specific reductions in pulmonary, but not systemic, arterial vasoconstriction and vasodilation in hypoxia- and MCT-induced PH are consistent with the possibility of de-differentiation of pulmonary VSMCs to a more proliferative/synthetic and less contractile phenotype in PH.

In vivo effects of a combined 5-HT1B receptor/SERT antagonist in experimental pulmonary hypertension

A mechanism for co-operation between the serotonin (5-hydroxytryptamine, 5-HT) transporter and 5-HT1B receptor in mediating pulmonary artery vasoconstriction and proliferation of pulmonary artery smooth muscle cells has been demonstrated in vitro. Here we determine, for the first time, the in vivo effects of a combined 5-HT1B receptor/serotonin transporter antagonist (LY393558) with respect to the development of pulmonary arterial hypertension (PAH) and its in vitro effects in human pulmonary artery smooth muscle cells (hPASMCs) derived from idiopathic PAH (IPAH) patients. We determined the effects of LY393558 as well as a selective serotonin transporter inhibitor, citalopram, on right ventricular pressure, right ventricular hypertrophy, and pulmonary vascular remodelling in wildtype mice and mice over-expressing serotonin transporter (SERT+ mice) before and after hypoxic exposure. We also compared their effectiveness at reversing PAH in SERT+ mice and hypoxic mice. Further, we examined the proliferative response to serotonin in IPAH hPASMCs. We also clarified the pharmacology of serotonin-induced vasoconstriction and 5-HT1B receptor/serotonin transporter interactions in mouse isolated pulmonary artery. Citalopram had a moderate effect at preventing and reversing experimental PAH in vivo whereas LY393558 was more effective. LY393558 was more effective than citalopram at reversing serotonin-induced proliferation in IPAH hPASMCs. There is synergy between 5-HT1B receptor and serotonin transporter inhibitors against serotonin-induced vasoconstriction in mouse pulmonary arteries. 5-HT1B receptor and serotonin transporter inhibition are effective at preventing and reversing experimental PAH and serotonin-induced proliferation of PASMCs derived from IPAH patients. Targeting both the serotonin transporter and 5-HT1B receptor may be a novel therapeutic approach to PAH.

Nox‐4 siRNA Causes Attenuation of Hypoxic Pulmonary Vasoconstriction in Bovine Pulmonary Arteries

Hypoxic pulmonary vasoconstriction (HPV) in endothelium removed bovine pulmonary arteries (BPA) is potentially mediated through the removal of a superoxide‐derived hydrogen peroxide mediated basal relaxation. To study the source of the superoxide, endothelium removed BPA rings were cultured for 48 hrs with the first 24 in the presence of either Nox‐4 or Nox‐2 siRNA. Nox‐4 siRNA caused a significant decrease in Nox‐4 expression without any effect on Nox‐2 levels. Superoxide levels and HPV were significantly reduced in BPA rings treated with Nox‐4 siRNA without affecting force development to KCl. Superoxide levels were significantly reduced with Nox‐2 siRNA treatment however, HPV and KCl force were not affected. Endothelium removed BPA rings treated with apocynin and gp91‐dstat show a decrease in superoxide levels but did not affect either KCl force or HPV. Thus Nox‐4 and not Nox‐2 may be the source for the potential superoxide derived peroxide mechanism maintaining basal relaxation during normoxia which when removed leads to HPV.Support by NIH grants HL31069, HL43023 and HL66331.