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.     

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.     

Vascular endothelial growth factor in diabetes induced early retinal abnormalities

Increased vascular permeability and blood flow alterations are characteristic features of diabetic retinal microangiopathy. The present study investigated vascular endothelial growth factor (VEGF) and its interactions with endothelin (ET) 1 and 3, endothelial, and inducible nitric oxide synthase (eNOS, iNOS) in mediating diabetes induced retinal vascular dysfunction. Male Sprague Dawley rats with streptozotocin (STZ) induced diabetes, with or without VEGF receptor signal inhibitor SU5416 treatment (high or low dose) were investigated after 4 weeks of follow-up. Colour Doppler ultrasound of the ophthalmic/central retinal artery, retinal tissue analysis with competitive RT-PCR and microvascular permeability were studied. Diabetes caused increased microvascular permeability along with increased VEGF mRNA expression. Increased vascular permeability was prevented by SU5416 treatment. Diabetic animals showed higher resistivity index (RI), indicative of vasoconstriction with increased ET-1 and ET-3 mRNA expression, whereas eNOS and iNOS mRNA expressions were un-affected. SU5416 treatment corrected increased RI via increased iNOS in spite of increased ET-1, ET-3 and VEGF mRNA expression. Cell culture (HUVEC) studies indicate that in part, an SU5416 induced iNOS upregulation may be mediated though a MAP kinase signalling pathway. The present data suggest VEGF is important in mediating both vasoconstriction and permeability in the retina in early diabetes.     

Quantitative analysis of endothelin and nitric oxide synthase in rat model of postobstructive pulmonary vasculopathy

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

Prevention of gram-negative translocation reduces the severity of hepatopulmonary syndrome

Hepatopulmonary syndrome (HPS) is characterized by intrapulmonary vascular dilatations and an increased alveoloarterial oxygen difference (AaPO(2)). These abnormalities are related to augmented pulmonary nitric oxide (NO) production, dependent primarily on increases in the expression and activity of inducible NO-synthase (iNOS) within pulmonary intravascular macrophages and, to a lesser extent, of endothelial NOS (eNOS). Production of iNOS by pulmonary intravascular macrophages might be related to translocated gut bacteria present in the pulmonary circulation. To test this hypothesis, we determined whether macrophage sequestration, lung iNOS expression and activity, and HPS severity were decreased after norfloxacin was given for 5 weeks to prevent Gram-negative bacterial translocation in rats with common bile duct ligation-induced cirrhosis. Norfloxacin decreased the incidence of Gram-negative translocation from 70 to 0% and the percentage of pulmonary microvessels containing more than 10 macrophages from 52 +/- 7 to 21 +/- 8% (p < 0.01). AaPO(2) and cerebral uptake of intravenous (99m)Tc-labeled albumin macroaggregates (reflecting intrapulmonary vascular dilatations) were intermediate to those of untreated cirrhotic and sham-operated rats. The activity and expression of lung iNOS, but not eNOS, were reduced to normal. Norfloxacin may reduce HPS severity by inhibiting Gram-negative bacterial translocation, thereby decreasing NO production by pulmonary intravascular macrophages. Bacterial translocation may be the key to the pathogenesis of HPS.     

Evidence against the hypothesis that endothelial endothelin B receptor expression is regulated by relaxin and pregnancy

The endothelial endothelin B (ET(B)) receptor subtype is critical for renal vasodilation induced by relaxin in nonpregnant rats and during pregnancy (the latter via endogenous circulating relaxin). Here we tested whether expression of vascular ET(B) receptor protein is regulated by relaxin. Small renal arteries were harvested from virgin and midterm pregnant rats as well as nonpregnant rats that were administered recombinant human relaxin (rhRLX) at 4 mug/h or vehicle for 5 d or 4-6 h. Small renal arteries dissected from additional virgin rats were incubated in vitro with rhRLX or vehicle for 3 h at 37 C. ET(B) expression was also evaluated in cultured human endothelial cells: aortic, coronary, umbilical vein, and dermal microvascular endothelial cells. Cells were incubated for 4, 8, or 24 h with rhRLX (5, 1, or 0.1 ng/ml) or vehicle. ET(B) protein expression in arteries and cells was evaluated by Western analysis. No regulation of ET(B) expression was observed in small renal arteries in any of the experimental protocols, nor was there an increase in the vasorelaxation response to ET-3 in small renal arteries incubated in vitro with rhRLX. rhRLX only sporadically altered ET(B) expression in human coronary artery endothelial cells and human umbilical vein endothelial cells at certain time points or doses, and no regulation was observed in human aortic endothelial cells or human dermal microvascular endothelial cells. These results suggest that regulation of ET(B) receptor protein has little or no role in relaxin stimulation of the endothelial ET(B)/nitric oxide vasodilatory pathway.     

内皮素-1在大鼠肝肺综合征发病机制中的作用

目的 探讨内皮素-1(ET-1)在大鼠肝肺综合征(HPS)发病机制中的作用.方法 应用放免法检测HPS大鼠血浆和肝、肺组织匀浆中ET-1的水平.结果 ①HPS大鼠血浆和肝组织、肺组织匀浆中ET-1水平动态升高.②各阶段血浆和肝、肺组织匀浆中ET-1水平与谷丙转氨酶(ALT)、总胆红素(TBIL)呈正相关.结论 在HPS形成过程中,血浆和肝、肺组织匀浆中ET-1水平持续升高,与肝功能损害有关,提示ET-1可能参与HPS的发生.肺组织匀浆中升高的ET-1可能更多地通过与在肺血管表达增强的内皮素受体B(ETRB)结合从而扩张肺血管.     

Pulmonary Expression of iNOS and HO-1 Protein Is Upregulated in a Rat Model of Prehepatic Portal Hypertension

Portal hypertension is associated with a wide range of pulmonary pathophysiologies, ranging from portopulmonary hypertension to hepatopulmonary syndrome. Although the clinical and pathological features of pulmonary dysfunction in this setting have been extensively characterized, the underlying biology is not well understood. Specifically, the role of mediators that regulate mesenteric vascular hemodynamics in portal hypertension, such as nitric oxide and endothelin, have not been studied in the lung. Using a rat model of prehepatic portal hypertension with preserved hepatic function, we examined pulmonary elaboration of endothelial nitric oxide synthase (NOS), inducible NOS, heme oxygenase- 1 (HO-1), heme oxygenase-2 (HO-2), endothelin-1 mRNA, and protein. In comparison to sham controls, portal hypertensive animals exhibited significantly increased pulmonary iNOS and HO-1 mRNA and protein. Cyclic GMP was significantly increased in portal hypertensive lung tissue, suggesting activation of guanylyl cyclase by the endproducts of iNOS and/or HO-1 activity. Using immunohistochemical analysis, iNOS expression was localized to the vascular endothelium, while HO-1 localized to bronchiolar epithelium and macrophages. These results suggest that production of nitric oxide and carbon monoxide may contribute to the pulmonary pathology associated with portal hypertension.     

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.     

Functional link between ETB receptors and eNOS maintain tissue oxygenation in the normal liver

OBJECTIVE: Endothelins and their receptors play a crucial role in regulating liver microcirculation in pathophysiological conditions. The authors investigated the functional significance of the coupling of ET(B) receptors and eNOS in maintaining regional perfusion and tissue oxygenation in the normal liver. METHODS: The effect of endothelin-1 or the ET(B) agonist IRL1620 on oxygen consumption was determined in isolated perfused liver and isolated hepatocytes. Oxygen delivery to the liver tissue was determined in vivo. Following eNOS or iNOS blockade, either ET-1 or IRL1620 was infused via the portal vein. Hepatic tissue oxygenation, redox state, and microcirculation were investigated by intravital microscopy. Injury was estimated by serum LDH. RESULTS: Although IRL1620 and endothelin-1 increased oxygen consumption in isolated hepatocytes, in intact liver, endothelin decreased oxygen consumption while IRL1620 produced no change. In vivo, ET(B) stimulation modestly altered hepatic tissue P(O(2)), redox potential, and microcirculation. eNOS inhibition and ET(B) activation dramatically reduced microcirculatory blood flow, oxygen supply, and increased LDH release. Inhibition of iNOS resulted in small but not significant changes in these parameters. Concomitant ET(A)/ET(B) receptor activation increased microcirculatory failure and decreased tissue oxygen even without NOS inhibition. In contrast, hepatocellular injury was significantly increased following eNOS inhibition. CONCLUSIONS: Coupling between ET(B) receptor stimulation and eNOS activation decreases sinusoidal constriction and plays a functionally important role in maintaining microcirculation and tissue oxygenation in the normal liver.     

不同HO-1表达水平对糖尿病模型大鼠血管舒张功能及NOS的影响

目的 探讨改变血红素加氧酶-1(HO-1)表达水平对糖尿病(DM)大鼠血管舒张功能的影响及与一氧化氮合酶(NOS)/一氧化氮(NO)的关系.方法 以链脲佐菌素(STZ)诱导DM大鼠模型.SD大鼠分成4组:对照组、DM组、正铁血红素(HO-1诱导剂)组、锌原卟啉(HO-1抑制剂)组.应用离体血管张力检测技术观察胸主动脉舒张功能变化;RT-PCR法及比色法分别检测血管组织和血清中诱生型NOS(iNOS)及内皮型NOS(eNOS)的表达和NO含量.结果 与DM组相比,正铁血红素组血管环对乙酰胆碱舒张百分率有所提高,而锌原卟啉组血管舒张反应继续下降.应用正铁血红素可在提高DM大鼠血管和血清eNOS表达的同时降低iNOS/NO表达;而锌原卟啉组血清中iNOS活性及其在血管组织表达均增高.结论 提高HO-1的表达水平有益于改善DM大鼠血管舒张反应失调,这种保护作用与抑制iNOS/NO的生成、上调eNOS表达水平有关.     

Intestinal endotoxemia plays a central role in development of hepatopulmonary syndrome in a cirrhotic rat model induced by multiple pathogenic factors

AIM： To characterize the correlation between severity of hepatopulmonary syndrome （HPS） and degree of hepatic dysfunction, and to explore how intestinal endotoxemia （IETM） affects the development of HPS in cirrhotic rats.
METHODS： Male Wister rats were fed with a diet containing maize flour, lard, cholesterol, and alcohol and injected subcutaneously with CCl4 oil solution every two days for 8 wk to induce typical cirrhosis and development of HPS. The animals were also given a nitric oxide （NO） production inhibitor, N^ω-nitro-L-arginine methyl ester （L-NAME） intraperitoneally, and an iNOS inhibitor, aminoguanidine hydrochloride （AG） via gavage daily from the end of the 4th wk to the end of the 6th or 8th wk, or a HO-1 inhibitor, zinc protoporphyrin （ZnPP） intraperitoneally 12 h prior to killing. Blood, liver and lung tissues were sampled.
RESULTS： Histological deterioration of the lung paralleled to that of the liver in the cirrhotic rats. The number of pulmonary capillaries was progressively increased from 6.1 ± 1.1 （count/filed） at the 4th wk to 14.5 ± 2.4 （count/filed） at the 8th wk in the cirrhotic rats. Increased pulmonary capillaries were associated with increased blood levels of lipopolysaccharide （LPS） （0.31 ± 0.08 EU/mL vs control 0.09 ± 0.03 EU/mL）, alanine transferase （ALT, 219.1 ± 17.4 U/L vs control 5.9 ± 2.2 U/L） and portal vein pressure. Compared with normal control animals, the number of total cells in bronchoalveolar lavage fluid （BALF） of the cirrhotic rats at the 8th wk was not changed, but the number of macrophages and the ratio of macrophages to total cells were increased by nearly 2-fold, protein expression of inducible nitric oxide synthase （iNOS） and endothelial nitric oxide synthase （eNOS） started to increase significantly at the 4th wk, and reached its peak at the 8th wk in the lung of cirrhotic rats. The increase of iNOS expression appeared to be quicker than that of eNOS. NO2^-/NO3^- was also increased, which was cor     

Increased endothelin receptor B and G protein coupled kinase-2 in the mesentery of portal hypertensive rats

AIM: To elucidate the mechanisms of mesenteric vasodilation in portal hypertension (PHT), with a focus on endothelin signaling. METHODS: PHT was induced in rats by common bile duct ligation (CBDL). Portal pressure (PP) was measured directly via catheters placed in the portal vein tract. The level of endothelin-1 (ET-1) in the mesenteric circulation was determined by radioimmunoassay, and the expression of the endothelin A receptor (ETAR) and endothelin B receptor (ETBR) was assessed by immunofluorescence and Western blot. Additionally, expression of G protein coupled kinase-2 (GRK2) and β-arrestin 2, which influence endothelin receptor sensitivity, were also studied by Western blot. RESULTS: PP of CBDL rats increased significantly (11.89 ± 1.38 mmHg vs 16.34 ± 1.63 mmHg). ET-1 expression decreased in the mesenteric circulation 2 and 4 wk after CBDL. ET-1 levels in the systemic circulation of CBDL rats were increased at 2 wk and decreased at 4 wk. There was no change in ETAR expression in response to CBDL; however, increased expression of ETBR in the endothelial cells of mesenteric arterioles and capillaries was observed. In sham-operated rats, ETBR was mainly expressed in the CD31+ endothelial cells of the arterioles. With development of PHT, in addition to the endothelial cells, ETBR expression was noticeably detectable in the SMA+ smooth muscle cells of arterioles and in the CD31+ capillaries. Following CBDL, increased expression of GRK2 was also found in mesenteric tissue, though there was no change in the level of β-arrestin 2. CONCLUSION: Decreased levels of ET-1 and increased ETBR expression in the mesenteric circulation following CBDL in rats may underlie mesenteric vasodilation in individuals with PHT. Mechanistically, increased GRK2 expression may lead to desensitization of ETAR, as well as other vasoconstrictors, promoting this vasodilatory effect.     

In-vivo interaction of nitric oxide and endothelin

OBJECTIVE AND METHODS: Endothelin-1 (ET-1) was initially characterized as a potent vasoconstrictor. However, the expected role of ET-1 as a major blood pressure controlling peptide could not be clearly established. Moreover, ET-1 transgenic mice are not hypertensive. We assume that counter-regulating mechanisms such as the nitric oxide (NO) system or an altered expression of endothelin receptors might cause this finding. RESULTS: An intravenous (i.v.) bolus injection of N(omega)-nitro-L-arginine methyl ester (L-NAME) resulted in a significantly higher blood pressure increase in ET-1 transgenic mice, as compared to non-transgenic littermates. On the other hand, blood pressure increased similarly after an i.v. injection of ET-1 in ET-1 transgenic mice and non-transgenic littermates. Pretreatment with dexamethasone abolished the higher blood pressure increase after L-NAME in ET-1 transgenic mice. Urinary excretion of NO metabolites was elevated in ET-1 transgenic mice and decreased significantly after dexamethasone treatment. Immunohistochemistry revealed that the inducible NO synthase (iNOS) was highly expressed in intrarenal arteries in these mice. Dexamethasone pretreatment abolished vascular iNOS expression. No vascular iNOS expression was detectable in non-transgenic littermates. Furthermore, immunohistochemistry revealed that ET-1 transgenic mice are characterized by an increased tissue density of CD4-positive lymphocytes and macrophages. Analysis of endothelin receptor expression and function revealed that the endothelin subtype A (ETA) receptor was not differently expressed in ET-1 transgenic mice as compared to age-matched littermates. The blood pressure response to an ETA receptor antagonist was likewise similar in ET-1 transgenic mice and age-matched littermates. The endothelin subtype B (ETB) receptor density was decreased in ET-1 transgenic mice. Treatment with an ETB receptor antagonist led to a non-significant slightly higher blood pressure increase in ET-1 transgenic mice as compared to controls. CONCLUSION: The endothelin receptor expression pattern and the blood pressure responses to ETA and ETB receptor antagonists could not explain the lack of hypertension in ET-1 transgenic mice. Overexpression of the human ET-1 gene causes chronic kidney inflammation with an induction of vascular iNOS expression. The induction of iNOS expression might cause a new local balance between vascular ET-1 and nitric oxide, resulting in no alterations of blood pressure.     

Endogenous endothelin in human coronary vascular function: differential contribution of endothelin receptor types A and B

Endothelin 1 mediates coronary vasoconstriction and endothelial dysfunction via endothelin receptor type A (ET(A)) activation. However, the effects of selective endothelin receptor type B (ET(B)) and combined ET(A+B) receptor blockade on coronary vasomotion are unknown. We measured coronary vascular tone and endothelium-dependent and -independent vasomotor function before and after selective infusion of BQ-788 (an ET(B) receptor antagonist) or combined infusion of BQ-788+BQ-123 (an ET(A) antagonist) into unobstructed coronary arteries of 39 patients with coronary atherosclerosis or risk factors undergoing cardiac catheterization. BQ-788 did not affect epicardial diameter but constricted the microcirculation (P<0.0001), increased coronary sinus endothelin, and reduced nitrogen oxide levels. In contrast, BQ-123+BQ-788 dilated epicardial (P<0.0001) and resistance (P=0.022) arteries. Responses to acetylcholine and sodium nitroprusside were unaffected by BQ-788 alone. Epicardial endothelial dysfunction improved after BQ-123+BQ-788 (P=0.007). Coronary microvascular responses to acetylcholine and sodium nitroprusside were unaffected by BQ-123+BQ-788. We conclude that selective ET(B) receptor antagonism causes coronary microvascular constriction, without affecting epicardial tone or endothelial function, via reduced endothelin clearance and NO availability. Combined ET(A+B) blockade dilates coronary conduit and resistance vessels and improves endothelial dysfunction of the epicardial coronary arteries. Thus, endogenous endothelin, predominantly via ET(A) receptor stimulation, contributes to basal constrictor tone and endothelial dysfunction, whereas ET(B) activation mediates vasodilation in human coronaries. Our data suggest that selective ET(A) blockade may have greater therapeutic potential than nonselective agents, particularly for treatment of endothelial dysfunction in atherosclerosis.     

Role of Thromboxane A2 Receptor on the Effects of Oxidized LDL on Microvascular Endothelium Nitric Oxide,Endothelin‐1, and IL‐6 Production

Objective: The aim of this study was to determine to what extent thromboxane A₂ (TP) receptor mediates the effect of oxidated low‐density lipoprotein (LDL) on nitric oxide (NO), interleukin (IL)‐6, and endothelin‐1 (ET‐1) release by microvascular endothelial cells. Methods: Endothelial nitric oxide synthase (eNOS), nitrites and nitrates (NO₂/NO₃), ET‐1, and IL‐6 production were measured following human microvascular endothelial cell 1 exposure to isoprostane‐8‐epi‐PGF_2α (F₂IP), a natural agonist of the TP receptor present in oxidized LDL, or native, low‐, or medium‐oxidized LDL either with the TP‐receptor blocker, SQ29.548, or its vehicle. Results: F₂IP and both native and oxidized LDL enhanced NO₂/NO₃. F₂IP through the TP receptor stimulated eNOS (eight‐fold), while the oxidized LDL effect (two‐to five‐fold) was only partially prevented by SQ29.548. While LDL concentration and degree of oxidation synergistically and independent of SQ29.548 stimulated IL‐6, F₂IP had no effect. F₂IP induced a modest (+50%) increase in ET‐1. LDL, independent of concentration or degree of oxidation, stimulated (+120%) ET‐1 production, and this effect was only partially attenuated by SQ29.548. Conclusions: In microvascular endothelial cells, LDL concentration and degree of oxidation synergistically stimulate NO and IL‐6 production, but only NO release is largely mediated by the TP receptor. LDL facilitates ET‐1 release independent of concentration and degree of oxidation; TP‐receptor stimulation is only partially responsible for this effect.     

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.     

LPS inhibits endothelin-1-induced endothelial NOS activation in hepatic sinusoidal cells through a negative feedback involving caveolin-1

During endotoxemia, liver microcirculation disruption is characterized by a hypersensitivity to the constrictor effects of endothelin 1 (ET-1). The shift of ET-1-mediated effects toward vasoconstriction may result from depressed ET-1-mediated vasodilation through decreased ET-1-induced nitric oxide (NO) production. We have previously shown that lipopolysaccharide (LPS) pretreatment abrogates ET-1-induced endothelial nitric oxide synthase (eNOS) translocation, but its effects on eNOS activation are yet to be determined. Our aim was to assess the effects of LPS on ET-1-mediated eNOS activation in hepatic sinusoidal endothelial cells (SECs) and to investigate the molecular mechanisms involved. SECs were treated with LPS (100 ng/mL) for 6 hours followed by 30 minutes ET-1 (10 nmol/L) stimulation. LPS significantly inhibited ET-1-mediated eNOS activation. This inhibition was associated with upregulation of Caveolin-1 (CAV-1) and a shift in ET-1-mediated eNOS phosphorylation from an activation (Ser1177) to an inhibition (Thr495). LPS treatment has been shown to induce ET-1 expression and secretion from endothelial cells. We therefore investigated the role of endogenous ET-1 in the inhibition of ET-1 activation of eNOS after LPS. Antagonizing ET-1 effects and blocking its activation in LPS pretreated SECs decreased the LPS-induced overexpression of CAV-1 as well as the inhibition of ET-1-induced NOS activity. Furthermore, 6 hours of ET-1 treatment exerted the same effects on eNOS activity, phosphorylation, and CAV-1 expression as LPS treatment. In conclusion, LPS-induced suppression of ET-1-mediated eNOS activation is ET-1 dependent and suggest a pivotal role of CAV-1 in eNOS induction inhibition under stress.     

红芪多糖对高糖条件下人脐静脉内皮细胞功能的影响

目的研究红芪多糖（HPS）对高糖条件下人脐静脉内皮细胞（HUVEC）合成和释放一氧化氮（NO）和内皮素-1（ET-1）的影响及作用机制。方法从新鲜脐带中分离HUVEC进行鉴定、培养,细胞分为正常对照组、高糖组（30mmol／L葡萄糖）和HPS干预组。MTT比色法分析HPS对高糖诱导HUVEC增殖率的影响,流式细胞术Annexin—V／PI双染法检测细胞凋亡,硝酸盐还原酶法检测上清液中NO的水平,分光光度法检测细胞内一氧化氮合酶（NOS）、诱导型一氧化氮合酶（iNOS）的浓度,酶联免疫吸附（ELISA）法检测上清液中ET-1的含量,实时荧光定量聚合酶链反应（RT—PCR）检测细胞内皮型一氧化氮合酶（eNOS）、ET-1和c-Jun氨基末端激酶l（JNKl）mRNA的表达水平。组间差异显著性检验使用单因素方差分析,组间两两比较使用LSD法。结果高糖组在6h[（82．4±3．5）％]、24h[（68．2±1．4）％]、48h[（63．0±2．9）％]的细胞增殖率显著低于对照组（100％,P〈0．05）;HPS干预组细胞增殖率随浓度变化呈现先上升后下降的趋势,其中50mg／L[（85．34-4．6）％]、100mg／L[（89．6±1．1）％]、200mg／L[（88．8±3．6）％]HPS干预组较高糖组增加,差异具有统计学意义（均P〈0．05）;高糖组NO[（24．84±1．34）μmol／L]、NOS[（0．54±0．06）U／m1]含量较正常对照组呈现下降的趋势,iNOS[（0．133±0．015）U／m1]和ET_l[1（0．740±0．070）ng／m1]含量则在各时间点均高于对照组,HPS干预组升高不同时间点HUVEC内NO[（23．20±0．55）p．mol／L]、NOS[（0．46±0．10）U／m1]、以及降低iNOS[（0．08±0．020）U／m1]和ET-1[（0．710±0．030）μg/L]的变化,P〈0．05,使其趋向正常水平;HPS可提高高糖所致内皮细胞eNOSmRNA的水平[（0．33±0．02）比（0．23±0．04）],降低ET-1mRNA的水平（2．28±0．31比2．79±0．29）;高糖组细胞内JNK1mRNA水平表达（2．95±0．05）较正常对照组（1．00±0．00）显著增加（P〈0．05）,而HPS干预组（1．45±0．05）则较高糖组（2．95±0．05）明显减少（P〈0．05）。结论HPS对体外高糖诱导HUVEC损伤具有保护作用,这一作用可能与抑制JNK信号通路有关。     

Hepatopulmonary syndrome: Update on recent advances in pathophysiology,investigation, and treatment

Hepatopulmonary syndrome (HPS) is an important cause of dyspnea and hypoxia in the setting of liver disease, occurring in 10–30% of patients with cirrhosis. It is due to vasodilation and angiogenesis in the pulmonary vascular bed, which leads to ventilation‐perfusion mismatching, diffusion limitation to oxygen exchange, and arteriovenous shunting. There is evidence, primarily from animal studies, that vasodilation is mediated by a number of endogenous vasoactive molecules, including endothelin‐1 and nitric oxide (NO). In experimental HPS, liver injury stimulates release of endothelin‐1 and results in increased expression of ET_B receptors on pulmonary endothelial cells, leading to upregulation of endothelial NO synthase (eNOS) and subsequent increased production of NO, which causes vasodilation. In addition, increased phagocytosis of bacterial endotoxin in the lung not only promotes stimulation of inducible NO synthase, which increases NO production, but also contributes to intrapulmonary accumulation of monocytes, which may stimulate angiogenesis via vascular endothelial growth factor pathway. Despite these insights into the pathogenesis of experimental HPS, there is no established medical therapy, and liver transplantation remains the main treatment for symptomatic HPS, although selected patients may benefit from other surgical or radiological interventions. In this review, we focus on recent advances in our understanding of the pathophysiology of HPS, and discuss current approaches to the investigation and treatment of this condition.