ET(A) and ET(B) receptors modulate the proliferation of human pulmonary artery smooth muscle cells

We determined the distribution of ET(A) and ET(B) receptors in pulmonary arteries from pulmonary hypertensive patients and control subjects, using in vitro autoradiography, and investigated their role in mediating the proliferative effects of endothelin-1 (ET-1) on distal human pulmonary artery smooth muscle cells (PASMCs). Distal arteries possessed more medial [(125)I]-ET-1 binding sites (105 +/- 10 versus 45 +/- 6 amol/mm(2); p < 0.001) and a greater proportion of ET(B) receptors than proximal arteries (36 +/- 3% versus 3 +/- 1%; p < 0.001). Receptor density in distal arteries and lung parenchyma was twofold greater (p < 0.05) in pulmonary hypertensive patients than in control subjects. ET-1 (10(-9)-10(-7) mol/L) stimulated DNA synthesis (147 +/- 10% of control subjects; p < 0.05) and attenuated the antiproliferative action of cicaprost and forskolin on PASMCs, these effects being mediated via ET(A) and ET(B) receptors. Serum-stimulated proliferation was attenuated by inhibiting either endogenous ET-1 release with phosphoramidon (10(-5) mol/L) or its action with PD145065 (10(-5) mol/L). Cicaprost (10(-10)-10(-7) mol/L) inhibited ET-1 release from PASMCs (49 +/- 16% of control after 24 h; p < 0.001) and increased intracellular cAMP levels, whereas ET(B) receptor stimulation selectively reduced cAMP levels. In conclusion, ET(A) and ET(B) receptors are differentially distributed in human pulmonary arteries. Both receptors promote the proliferation of PASMCs in vitro and may contribute to vascular remodeling in pulmonary hypertension.     

The role of endothelin-1 and the endothelin B receptor in the pathogenesis of hepatopulmonary syndrome in the rat

Endothelin-1 (ET-1) stimulation of endothelial nitric oxide synthase (eNOS) via pulmonary endothelial endothelin B (ET(B)) receptors and pulmonary intravascular macrophage accumulation with expression of inducible nitric oxide synthase (iNOS) and heme oxygenase-1 (HO-1) are implicated in experimental hepatopulmonary syndrome (HPS) after common bile duct ligation (CBDL). Our aim was to evaluate the role of ET-1 in the development of experimental HPS. The time course of molecular and physiological changes of HPS and the effects of selective endothelin receptor antagonists in vivo were assessed after CBDL. Effects of ET-1 on intralobar pulmonary vascular segment reactivity and on eNOS expression and activity in rat pulmonary microvascular endothelial cells (RPMVECs) were also evaluated. Hepatic and plasma ET-1 levels increased 1 week after CBDL in association with a subsequent increase in pulmonary microvascular eNOS and ET(B) receptor levels and the onset of HPS. Selective ET(B) receptor inhibition in vivo significantly decreased pulmonary eNOS and ET(B) receptor levels and ameliorated HPS. CBDL pulmonary artery segments had markedly increased ET(B) receptor mediated, nitric oxide dependent vasodilatory responses to ET-1 compared with controls and ET-1 triggered an ET(B) receptor dependent stimulation of eNOS in RPMVECs. Pulmonary intravascular macrophages also accumulated after CBDL and expressed HO-1 and iNOS at 3 weeks. Selective ET(B) receptor blockade also decreased macrophage accumulation and iNOS production. In conclusion, ET-1 plays a central role in modulating pulmonary micovascular tone in experimental HPS.     

Increased pulmonary vascular endothelin B receptor expression and responsiveness to endothelin-1 in cirrhotic and portal hypertensive rats: a potential mechanism in experimental hepatopulmonary syndrome

BACKGROUND/AIMS: In experimental hepatopulmonary syndrome (HPS), hepatic endothelin-1 (ET-1) release during common bile duct ligation (CBDL) and ET-1 infusion in pre-hepatic portal hypertension after portal vein ligation (PVL) initiate vasodilatation through an endothelin B receptor mediated increase in pulmonary endothelial nitric oxide synthase (eNOS). We evaluated if pulmonary ET receptor expression changes in experimental cirrhosis and portal hypertension and confers susceptibility to HPS.METHODS: In normal, PVL and CBDL animals, lung ET receptor expression and localization were assessed and ET receptor levels and functional analysis of ET-1 effects on eNOS levels were evaluated in intralobar pulmonary artery (PA) and aortic (AO) segments. Normal rats underwent evaluation for HPS after ET-1 infusion.RESULTS: There was a selective increase in ET(B) receptor expression in the pulmonary vasculature from PVL and CBDL animals. ET-1 stimulated NO production and an ET(B) receptor mediated increase in eNOS levels in PA segments from PVL and CBDL animals, but not normal animals. ET-1 did not alter lung eNOS levels or cause HPS in normal rats.CONCLUSIONS: ET(B) receptor expression and ET-1 mediated eNOS and NO production are enhanced in the lung vasculature in cirrhotic and portal hypertensive animals and correlate with in vivo susceptibility to ET-1 mediated HPS.     

Endothelin-1 induces vasoconstriction on portal-systemic collaterals of portal hypertensive rats

Portal hypertension is associated with increased hepatic and collateral resistance to an increased portal blood flow. Endothelin-1 (ET-1) can induce intrahepatic vasoconstriction and consequently increase portal pressure. It is unknown if ET-1 also modulates portal pressure by a direct vasoconstrictive effect on collaterals. This study investigated the collateral vascular responses to ET-1, the receptors in mediation, and the regulation of ET-1 action by nitric oxide and prostaglandin. The portal-systemic collaterals of partially portal vein-ligated rats were tested by in situ perfusion. The concentration-response curves of collaterals to graded concentrations of ET-1 (10(-10)-10(-7) mol/L) with or without BQ-123 (ET(A) receptor antagonist, 2 x 10(-6) mol/L), BQ-788 (ET(B) receptor antagonist, 10(-7) mol/L) or both were recorded. In addition, the collateral responses to ET-1 with preincubation of n(omega)-nitro-L-arginine (NNA; 100 mol/L), indomethacin (INDO; 10 mol/L), or in combination were performed. ET-1 increased the perfusion pressure of collaterals and its effect was significantly suppressed by BQ-123 alone and BQ-123 plus BQ-788, but not BQ-788 alone (P <.05). Incubation with NNA, INDO, or both significantly enhanced the response of collaterals to ET-1 (P < .05). These results show that ET-1 produces a direct vasoconstrictive effect on the collateral vessels of portal hypertensive rats. This effect is mediated by ET(A,) but not ET(B), receptors. Both nitric oxide and prostaglandin modulate the collateral vascular response to ET-1 and may therefore participate in the development and maintenance of portal hypertension.     

Gene transfer of endothelial nitric oxide synthase to the lung of the mouse in vivo. Effect on agonist-induced and flow-mediated vascular responses.

The effects of transfer of the endothelial nitric oxide synthase (eNOS) gene to the lung were studied in mice. After intratracheal administration of AdCMVbetagal, expression of the beta-galactosidase reporter gene was detected in pulmonary airway cells, in alveolar cells, and in small pulmonary arteries. Gene expression with AdCMVbetagal peaked 1 day after administration and decayed over a 7- to 14-day period, whereas gene expression after AdRSVbetagal transfection peaked on day 5 and was sustained over a 21- to 28-day period. One day after administration of AdCMVeNOS, eNOS protein levels were increased, and there was a small reduction in mean pulmonary arterial pressure and pulmonary vascular resistance. The pressure-flow relationship in the pulmonary vascular bed was shifted to the right in animals transfected with eNOS, and pulmonary vasodepressor responses to bradykinin and the type V cGMP-selective phosphodiesterase inhibitor zaprinast were enhanced, whereas systemic responses were not altered. Pulmonary vasopressor responses to endothelin-1 (ET-1), angiotensin II, and ventilatory hypoxia were reduced significantly in animals transfected with the eNOS gene, whereas pressor responses to norepinephrine and U46619 were not changed. Systemic pressor responses to ET-1 and angiotensin II were similar in eNOS-transfected mice and in control mice. Intratracheal administration of AdRSVeNOS attenuated the increase in pulmonary arterial pressure in mice exposed to the fibrogenic anticancer agent bleomycin. These data suggest that transfer of the eNOS gene in vivo can selectively reduce pulmonary vascular resistance and pulmonary pressor responses to ET-1, angiotensin II, and hypoxia; enhance pulmonary depressor responses; and attenuate pulmonary hypertension induced by bleomycin. Moreover, these data suggest that in vivo gene transfer may be a useful therapeutic intervention for the treatment of pulmonary hypertensive disorders.     

Glomerular hypertension and hyperfiltration in adrenocorticotrophin-induced hypertension in rats: the role of nitric oxide

OBJECTIVE: To determine the effects on pre- and post-glomerular vascular resistance of adrenocorticotrophin (ACTH)-induced hypertension in rats, before and after blockade of nitric oxide formation. DESIGN: Four groups of Sprague-Dawley rats were studied. Measurements were made in ACTH- (Synacthen Depot, 0.25 mg/kg twice daily for 8 days) and sham-treated anaesthetized rats, before and after either Nomega-nitro-L-arginine (L-NNA, 6 mg/kg) or vehicle. METHODS: Whole-kidney and single-nephron haemodynamics and function were measured. Glomerular capillary pressure was estimated from tubular stop-flow pressure measurements. RESULTS: Blood pressure (P < 0.001), renal blood flow (RBF, P < 0.05) and glomerular filtration rate (P < 0.01) were increased following ACTH treatment compared with sham. There were no differences in either total renal, or pre- or post-glomerular vascular resistances, but stop-flow-estimated glomerular capillary pressure was elevated (P < 0.001) as was single-nephron glomerular filtration rate (SNGFR) (P < 0.001) and single-nephron blood flow (P < 0.01 ) in the ACTH- compared to the sham-treated rats. L-NNA treatment increased blood pressure by a similar extent in both ACTH- and sham-treated rats, but reduced RBF (P < 0.05) and glomerular filtration rate (GFR) (P < 0.05) more in the ACTH group; similar changes were seen in single-nephron values. L-NNA increased pre- and post-glomerular resistances to a greater extent in the ACTH group. CONCLUSIONS: ACTH-induced hypertension produced glomerular hypertension and hyperfiltration, which may be due to nitric oxide-related vasodilatation of the renal vasculature.     

先天性心脏病患儿血浆ET—1水平影响因素的监测及意义

选择69例左向右分流的先天性心脏病（CHD）患儿抽取股静脉血。其中伴有中、重度肺动脉高压（肺高压）的17例患儿给予卡托普利1mg/(kg.d)口服,治疗15天后再抽血,用放免法测定样品中内皮素-1（ET-1）含量。结果①肺血流量增加,血浆ET-1水平亦增加,达正常对照的2倍多（83.46±24.56pg/ml,38.53±11.93pg.ml,P＜0.001）;②CHD并肺高压者血浆ET-1水平（90.15±22.56pg/ml)较无肺高压者（65.44±6.33pg/ml）明显增高（P＜0.001）,ET-1含量随肺动脉压力的升高而增加;③卡托普利可使患儿的平均肺动脉压及血浆ET-1水平有下降趋势,但与治疗前比较无统计学差异（P＞0.05）。认为卡托普利可预防或延缓肺动脉高压的形成和发展,具有重要的临床意义。     

ZD1611, an orally active endothelin-A receptor antagonist, prevents chronic hypoxia-induced pulmonary hypertension in the rat.

Endothelin-1 (ET-1) is a potent vasoconstrictor and comitogen implicated in the pathogenesis of pulmonary hypertension (PH). We evaluated the effects of an ET(A)receptor-selective antagonist, ZD1611, on hypoxia-induced PH in rats. and paradigms were established in which rats were administered placebo or ZD1611 (1-3 mg/kg, q.i.dpo) concomitant with hypoxic exposure (10% O(2)1 ATM) for 14 days or beginning after 7-day hypoxic exposure for 21 days. Compared with normoxic controls, hypoxic exposure plus placebo increased (P<0.05) hematocrit, mass ratio of right ventricle over left ventricle plus septum (RV/LV+S), and right intraventricular peak systolic pressure (RVSP). These latter two effects were decreased (P<0.05) by ZD1611 in both experimental paradigms [RV/LV+S(%)::RVSP(%); prophylactic, 14::32; therapeutic, 28::37]. Hypoxic exposure did not change mean systemic arterial pressure (MSAP). ZD1611 did not affect MSAP, plasma ET-1 concentrations, or blood gases measured when rats respired room air. In mechanistic studies, ZD1611 decreased (P<0.01) smooth muscle hypertrophy of small pulmonary arteries and abolished hypoxia-induced decreases in sensitivity and maximum contraction to ET-1 in isolated extralobar branch pulmonary artery. In conclusion, the ET(A)receptor-selective antagonist, ZD1611, attenuates hypoxia-induced PH in the rat.     

阿托伐他汀对慢性阻塞性肺疾病合并肺动脉高压患者的影响

目的:评价阿托伐他汀对慢性阻塞性肺疾病(COPD)合并慢性肺源性心脏病(简称肺心病)患者肺动脉高压(PH)的影响。方法:55例COPD合并慢性肺心病、PH患者随机分为2组:阿托伐他汀组(AL组,27例)和常规治疗组(28例)。2组患者均接受常规治疗,阿托伐他汀组口服阿托伐他汀,20mg/d。分别观察阿托伐他汀组及常规治疗组治疗前、治疗后6个月血浆中一氧化氮(nitric oxide,NO)、内皮素I(endothelin-1,ET-1)、超声心动图变化。结果:阿托伐他汀组治疗6个月后ET-1、PH较治疗前和常规治疗组治疗6个月时明显下降(P<0.05)、内源性一氧化氮(NO)明显升高(P<0.05)。常规治疗组治疗前、治疗后6个月上述指标比较差异无统计学意义(P>0.05)。结论:阿托伐他汀可调节NO及ET-1的分泌,有效降低PH。     

Changes in capillary shear stress in skeletal muscles exposed to long-term activity: role of nitric oxide

OBJECTIVE: The purpose of this study was to establish whether suppression of angiogenesis by nitric oxide synthase (NOS) inhibition in skeletal muscles exposed to long-term activity can be explained by changes in capillary shear stress linked to the lack of nitric oxide production. METHODS: Capillary shear stress was calculated from diameters (d) and red blood cell velocities (V(rbc)) measured at rest and after acute contractions in epi-illuminated extensor digitorum longus muscles of control rats and those in which ankle flexors had been stimulated via implanted electrodes (10 Hz, 8 h x day(-1)) for 2 or 7 days without and with inhibition of nitric oxide synthase activity by N(omega)-nitro-L-arginine (L-NNA, 3-4 mg x day(-1) in drinking water). RESULTS: Neither chronic electrical stimulation nor L-NNA treatment altered capillary diameters. Capillary V(rbc) and shear stress (SS) were doubled in muscles after 2 days stimulation (298 +/- 22 microm x s(-1) and 11.4 +/- 1.0 dyne x cm(-2), respectively, p < .005) compared to controls (148 +/- 18 microm x s(-1) and 5.6 +/- 0.8 dyne x cm(-2)) but normalized after 7 days (153 +/- 27 microm x s(-1) and 6.2 +/- 1.0 dyne x cm(-2)), when the capillary bed is known to be enlarged. L-NNA, which increased blood pressure in all treated animals, abolished the increase in capillary SS after 2 days stimulation and decreased SS after 7 days. CONCLUSIONS: These data support a role for NO in the early elevation of capillary shear stress that initiates angiogenesis in stimulated muscles, likely via modulation of upstream vascular resistance, and could explain the lack of capillary growth in stimulated muscles when nitric oxide generation is suppressed.     

Endothelins and endothelin receptor antagonists: therapeutic considerations for a novel class of cardiovascular drugs

The 21-amino acid peptide endothelin-1 (ET-1) is the predominant isoform of the endothelin peptide family, which includes ET-2, ET-3, and ET-4. It exerts various biological effects, including vasoconstriction and the stimulation of cell proliferation in tissues both within and outside of the cardiovascular system. ET-1 is synthesized by endothelin-converting enzymes (ECE), chymases, and non-ECE metalloproteases; it is regulated in an autocrine fashion in vascular and nonvascular cells. ET-1 acts through the activation of G(i)-protein-coupled receptors. ET(A) receptors mediate vasoconstriction and cell proliferation, whereas ET(B) receptors are important for the clearance of ET-1, endothelial cell survival, the release of nitric oxide and prostacyclin, and the inhibition of ECE-1. ET is activated in hypertension, atherosclerosis, restenosis, heart failure, idiopathic cardiomyopathy, and renal failure. Tissue concentrations more reliably reflect the activation of the ET system because increased vascular ET-1 levels occur in the absence of changes in plasma. Experimental studies using molecular and pharmacological inhibition of the ET system and the first clinical trials have demonstrated that ET-1 takes part in normal cardiovascular homeostasis. Thus, ET-1 plays a major role in the functional and structural changes observed in arterial and pulmonary hypertension, glomerulosclerosis, atherosclerosis, and heart failure, mainly through pressure-independent mechanisms. ET antagonists are promising new agents in the treatment of cardiovascular diseases.     

N-乙酰半胱氨酸对COPD患者血中血管内皮素、一氧化氮的影响

目的探讨N-乙酰半胱氨酸对慢性阻塞性肺疾病（COPD）患者血清中血管内皮素及一氧化氮水平的影响。方法AECOPD患者60例，随机分为对照组及NAC组，测定两治疗组治疗前、后血浆内皮素-1（ET—1）和一氧化氮（NO）含量的变化。结果两组治疗后ET—1含量均低于治疗前，而NO高于治疗前（P（0．05）；但所有这些变化均以N-乙酰半胱氨酸组的变化程度更明显（P（0．01）。结论N-乙酰半胱氨酸有助于COPD患者维持体内舒血管因子及缩血管因子平衡，可能对肺动脉高压的形成有一定的预防作用。     

The therapeutic potential of endothelin receptor antagonists in cardiovascular disease

Endothelin (ET)-1, a 21-amino acid peptide, is the predominant isoform of the endothelin peptide family. ET-1 is ubiquitously expressed and stimulates vasoconstriction and cell proliferation. Enzymes such as endothelin converting enzymes (ECE), chymases, and non-ECE metalloproteinases contribute to the synthesis of ET-1, which is regulated in an autocrine fashion in vascular and nonvascular cells. Endothelin ET(A) receptors mediate vasoconstriction and cell proliferation, whereas ET(B) receptors are involved in the clearance of ET-1, inhibition of endothelial apoptosis, release of nitric oxide and prostacyclin, and inhibition of ECE-1 expression. Most cardiovascular diseases, such as arterial hypertension, atherosclerosis, restenosis, heart failure, idiopathic cardiomyopathy, pulmonary hypertension, and renal failure are associated with local activation of the endothelin system. Experimental studies and first clinical trials suggest that ET-1 is importantly involved in the functional and structural changes in the cardiovascular system, and that many of the actions of ET-1 are mediated through pressure-independent mechanisms. Endothelin antagonists promise to be successful as a new class of drugs for the treatment of cardiovascular diseases.     

Protective effects of a dual endothelin converting enzyme/neutral endopeptidase inhibitor on the development of pulmonary hypertension secondary to cardiac dysfunction in the rat

Endothelium‐derived nitric oxide (NO) and endothelin (ET)‐1 interact to regulate the vascular tone in pulmonary hypertension (PH). We investigated the protective effects of an orally active, dual endothelin converting enzyme (ECE)/neutral endopeptidase (NEP) inhibitor/CGS 26393 on pulmonary vascular remodeling and pulmonary expressions of ET‐1 and endothelial nitric oxide synthase (eNOS) during the development of PH secondary to cardiac dysfunction. Significant increases in the mean pulmonary arterial pressure, pulmonary arteriolar medial thickness, and pulmonary expression of ET‐1 were seen in rats subjected to aortic banding for 4 weeks, compared with sham‐operated rats. Treatment with CGS 26393 (30 mg/kg, twice daily, p.o.) began on 1 day after aortic banding. CGS 26393 treated rats had lower mean pulmonary arterial pressure (15 ± 1 mmHg, mean ± SEM, P < 0.05) compared to vehicle‐treated rats (37 ± 1 mmHg). It also normalized pulmonary arteriolar medial thickness and reduced the levels of pulmonary ET‐1 and big ET‐1 by 55% (P < 0.05) and 28% (P < 0.01), respectively, when compared with vehicle‐treated animals. Meanwhile, the expressions of eNOS mRNA and eNOS protein and cGMP levels in the lung of CGS 26393‐treated rats were increased by 62% (P < 0.05), 100% (P < 0.05), and 32% (P < 0.01), respectively, compared to the vehicle‐treated rats. These results suggest that CGS 26393 could offer preventive effects on the development of PH by ameliorating pulmonary remodeling, decreasing ET‐1 production, and up‐regulating eNOS and cGMP in aorta‐banded rats. However, the molecular mechanisms by which treatment with CGS 26393 results in altered expressions of eNOS and cGMP awaits further investigation. Pediatr Pulmonol. 2010;45:1076–1085. © 2010 Wiley‐Liss, Inc.     

Biliary cyst fluid from common bile duct-ligated rats stimulates endothelial nitric oxide synthase in pulmonary artery endothelial cells: a potential role in hepatopulmonary syndrome

The hepatopulmonary syndrome (HPS) results from pulmonary microvascular dilatation in cirrhosis and is associated with increased pulmonary endothelial nitric oxide synthase (eNOS) levels. In the common bile duct ligation (CBDL) model, endothelin-1 (ET-1) released from the liver contributes to the rise in pulmonary eNOS and intrapulmonary vasodilatation. Whether substances, including ET-1, are found in the biliary tree and selectively enter the circulation after CBDL to influence the pulmonary vasculature is unknown. We assessed if control bile and fluid obtained from the obstructed biliary tree in CBDL animals contains ET-1 and alters eNOS expression and activity in bovine pulmonary artery endothelial cells (BPAECs). Control bile and biliary cyst fluid contained concentrations of ET-1 25- to 42-fold normal plasma levels, and hepatic venous concentrations of ET-1 were selectively increased after CBDL. Biliary cyst fluid caused a dose-dependent induction of eNOS messenger RNA (mRNA) (1.9-fold control), protein (2.5-fold control), and enzyme activity (2.2-fold control) maximal at a 1:10 dilution. The increases were associated with enhanced nitric oxide (NO) production (3.1-fold control) and were inhibitable with an ET(B) receptor antagonist. Bile from sham and portal vein-ligated animals did not increase eNOS expression and at dilutions of 1:100 and 1:10 caused cell toxicity. These results show that bile and biliary cyst fluid contain high concentrations of ET-1 that are specifically increased in hepatic venous blood after CBDL. Biliary cyst fluid increases eNOS expression and activity in an ET(B) receptor-dependent manner in BPAECs. The findings suggest a novel mechanism for the susceptibility of CBDL animals to the HPS.     

内皮素和内皮衍化的松弛因子在高血压发病上的作用

给予Ｗｉｓｔａｒ大鼠腹腔注射ＥＤＲＦ合成抑制剂（ＬＮＮＡ）２８ｄ，可诱发大鼠产生持续性高血压伴ＥＴ水平增高，ＥＴ／ｃＧＭＰ比值增大，主动脉环对ＥＴ的收缩反应明显增高，对乙酰胆碱（Ａｃｈ）舒张反应明显减低。然而同时给于Ｌ－精氨酸或ＥＴ抗血清可使血压降至正常，ＥＴ水平明显降低ＥＴ／ｃＧＭＰ比值缩小，使主动脉环对ＥＴ收缩反应减低，对Ａｃｈ舒张反应增加。     

Role for endothelin-1-induced superoxide and peroxynitrite production in rebound pulmonary hypertension associated with inhaled nitric oxide therapy

Our previous studies have demonstrated that inhaled nitric oxide (NO) decreases nitric oxide synthase (NOS) activity in vivo and that this inhibition is associated with rebound pulmonary hypertension upon acute withdrawal of inhaled NO. We have also demonstrated that inhaled NO elevates plasma endothelin-1 (ET-1) levels and that pretreatment with PD156707, an ETA receptor antagonist, blocks the rebound hypertension. The objectives of this study were to further elucidate the role of ET-1 in the rebound pulmonary hypertension upon acute withdrawal of inhaled NO. Inhaled NO (40 ppm) delivered to thirteen 4-week-old lambs decreased NOS activity by 36.2% in control lambs (P<0.05), whereas NOS activity was preserved in PD156707-treated lambs. When primary cultures of pulmonary artery smooth muscle cells were exposed to ET-1, superoxide production increased by 33% (P<0.05). This increase was blocked by a preincubation with PD156707. Furthermore, cotreatment of cells with ET-1 and NO increased peroxynitrite levels by 26% (P<0.05), whereas preincubation of purified human endothelial nitric oxide synthase (eNOS) protein with peroxynitrite generated a nitrated enzyme with 50% activity relative to control (P<0.05). Western blot analysis of peripheral lung extracts obtained after 24 hours of inhaled NO revealed a 90% reduction in 3-nitrotyrosine residues (P<0.05) in PD156707-treated lambs. The nitration of eNOS was also reduced by 40% in PD156707-treated lambs (P<0.05). These data suggest that the reduction of NOS activity associated with inhaled NO therapy may involve ETA receptor-mediated superoxide production. ETA receptor antagonists may prevent rebound pulmonary hypertension by protecting endogenous eNOS activity during inhaled NO therapy.     

Hemodynamic and clinical correlates of endothelin-1 in chronic thromboembolic pulmonary hypertension.

BACKGROUND: In non-thromboembolic pulmonary hypertension, endothelin (ET)-1 levels are increased and correlate with the hemodynamic severity of the disease. Whether such correlations exist in chronic thromboembolic pulmonary hypertension (CTEPH) is unknown, nor whether ET-1 levels correlate with hemodynamic outcome after pulmonary endarterectomy (PEA). METHODS AND RESULTS: ET-1 levels were determined by ELISA. ET-levels were increased in 35 CTEPH patients (1.62+/-0.21 pg/ml) compared with healthy controls (n=11: 0.75+/-0.06 pg/ml, p<0.02). ET-1 levels correlated (all p<0.0001) with mean pulmonary artery pressure (mPAP) (r=0.70), cardiac index (r=-0.76), total pulmonary resistance (r=0.72), mixed venous oxygen saturation (r=-0.87), and the distance walked in the 6-min walk test (r=-0.59; p<0.005; n=23). Three months after PEA, ET-1 levels had decreased (p<0.002), and were similar between patients with and without residual pulmonary hypertension (p=0.4). Preoperative ET-1 levels, however, were higher in patients with bad postoperative outcome; that is, patients who either died because of persistent pulmonary hypertension or had residual pulmonary hypertension after PEA (2.68+/-0.48 pg/ml, and 1.13+/-0.15 pg/ml, respectively; p<0.002). The levels also correlated with hemodynamic outcome after PEA (mPAP: r=0.67, p<0.0001). By receiver-operator characteristic curve analysis, ET-1>1.77 pg/ml detected a bad postoperative outcome with a sensitivity and specificity of 79% and 85%, respectively, and a likelihood ratio of 5.2. CONCLUSION: ET-1 levels in CTEPH closely correlated with the hemodynamic and clinical severity of disease in a large cohort of patients. Preoperative ET-1 levels may be useful for better identification of patients at risk for persistent pulmonary hypertension after PEA.     

Endotoxin treatment causes an upregulation of the endothelin system in the liver: amelioration of increased portal resistance by endothelin receptor antagonism

BACKGROUND: Mechanisms underlying hepatic microcirculatory failure during endotoxemia are incompletely understood. Because endothelin-1 (ET-1) has been implicated in endotoxin-induced liver injury, we investigated the hepatic ET-1 system in endotoxin-treated rats. METHODS: Rats were treated with endotoxin (Escherichia coli lipopolysaccharide; 3 mg/kg, i.p.), and various determinations were made 24 h later. RESULTS: Endotoxin treatment caused 11.2 +/- 1.6% weight loss, a decrease in mean arterial pressure (MAP; 96 +/- 5 mmHg vs 108 +/- 3 mmHg; P < 0.05) and an increase in portal pressure (11.6 +/- 1.3 mmHg vs 7.4 +/- 1 mmHg; P < 0.02). No significant changes in the serum levels of liver enzymes or hepatocellular necrosis were observed. Endotoxin caused increases in hepatic ET-1 (from 345 +/- 31 to 565 +/- 38 pg/g; P < 0.01), ET-1 receptor density (from 179 +/- 16 to 340 +/- 26 fmol/mg; P < 0.02), and mRNA expression of preproendothelin-1, and ET(A) and ET(B) receptors. While the serum nitric oxide (nitrite +/- nitrate) concentration was increased in endotoxin-treated rats, that of ET-1 remained unchanged. A mixed ET(A)/ET(B) receptor antagonist, TAK-044 (10 mg/kg, i.v.), reduced the weight loss from 11.2 +/- 1.6% to 5.9 +/- 2.9% (P < 0.05) and the portal pressure from 11.6 +/- 1.3 mmHg to 8.6 +/- 0.7 mmHg (P < 0.05) in endotoxin-treated rats. The mixed ET(A)/ET(B) receptor antagonist also caused an increase in serum ET-1 concentration, but did not affect serum nitric oxide and MAP in endotoxin-treated rats. CONCLUSIONS: These results suggest that the upregulated hepatic ET-1 system is an important mechanism of increased portal resistance and related complications of endotoxemia.