endothelin-1 and Hepatopulmonary-Syndrome

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.

Topics: Animals; Early Diagnosis; Endothelin-1; Hepatopulmonary Syndrome; Humans; Liver Cirrhosis; Lung; Nitric Oxide; Nitric Oxide Synthase Type II; Nitric Oxide Synthase Type III; Predictive Value of Tests; Prognosis; Pulmonary Artery; Pulmonary Circulation; Vasodilation

Pulmonary vascular abnormalities occurring in the setting of liver disease have been increasingly recognized as important clinical entities that influence survival and liver transplant candidacy in affected patients. The most common such abnormality, the hepatopulmonary syndrome, is found in 15% to 20% of patients with cirrhosis. These disorders have no effective medical therapies. Experimental models of hepatopulmonary syndrome have identified a sequence of hepatic and pulmonary endothelial alterations that lead to nitric oxide and carbon monoxide-mediated intrapulmonary vasodilatation. A key role for shear stress-mediated pulmonary endothelial endothelin B receptor overexpression and cholangiocyte ET-1 production and release has emerged as a mechanism for local nitric oxide production in the lung. How these alterations are influenced by bacterial translocation and the systemic hyperdynamic circulatory state and whether similar changes occur in human disease are areas of ongoing investigation.

Topics: Animals; Common Bile Duct; Endothelin-1; Hepatopulmonary Syndrome; Humans; Ligation; Liver; Liver Cirrhosis; Rats

Aim To determine the role of endothelin (ET)-1 in predicting hepatopulmonary syndrome (HPS) in patients with liver cirrhosis. Methods A cross sectional study involving 80 liver cirrhosis patients aged 18 years or older was conducted in Adam Malik General Hospital Medan, Indonesia between July 2017 and June 2018. HPS diagnosis was confirmed from the presence of liver cirrhosis, abnormal oxygenation, and intrapulmonary vascular dilatations (IPVD). ET-1 level was measured from serum sample using ELISA method. Patients with coexisting primary pulmonary pathology and intrinsic heart disease were active smokers, and those who declined to participate were excluded. Statistical analysis was conducted at 95% confidence interval. p<0.05 was considered significant. Results Majority the patients were male (56.3%) and had higher educational background (62.5%). Mean age of the patients was 51.3 (SD=12.6) years. The prevalence of HPS was 21.2%. The patients with HPS had higher ET-1 level compared to those without HPS (p<0.001). The patients with hepatic encephalopathy had 2.917 times higher risk for suffering from HPS, while the patients with Child Pugh score A had lower risk (0.738 times) for having HPS compared to subjects with Child Pugh score B and C. ET-1 level >187.5 mg/L had sensitivity and specificity for predicting HPS in subjects with liver cirrhosis of 82.35% and 81.25%, respectively. Conclusion ET-1 could be used as a promising marker for HPS in patients with liver cirrhosis. ET-1 level of >187.5 mg/l had a good accuracy in predicting HPS in liver cirrhosis patient.

Topics: Adolescent; Cross-Sectional Studies; Endothelin-1; Hepatopulmonary Syndrome; Humans; Liver Cirrhosis; Male; Middle Aged; Prospective Studies

Hepatopulmonary syndrome and portopulmonary hypertension are common complications of liver disorders. This study aimed to determine roles of ET-B receptors and endothelial-derived NO synthase in the regulation of pulmonary hemodynamic in cirrhotic rats.. Male Sprague-Dawley rats were divided into the Sham and common bile duct ligation (CBDL) groups. After 28 days, animals were anesthetized, and the right ventricle, femoral artery, and vein cannulated. Then, intravenous injection of BQ-788 (a selective ET-B receptor antagonist) and L-NAME (eNOS inhibitor) were performed sequentially.. After the first injection of BQ-788, the right ventricular systolic pressure (RVSP) and mean arterial systemic pressure increased only in the Sham group. L-NAME increased RVSP in the Sham and CBDL groups, whereas mean arterial systemic pressure elevated only in the Sham group significantly. Reinjection of BQ-788 increased RVSP in the Sham group, whereas it decreased RVSP in the CBDL group. Both plasma NO metabolites and lung endothelin-1 increased in the CBDL group.. ET-B receptors on the endothelial cells play roles in the regulation of pulmonary and systemic vascular tone in normal condition through the NO-mediated pathway, whereas ET-B receptors on the smooth muscle cells have a role in the pulmonary vascular tone in liver cirrhosis.

Topics: Animals; Arterial Pressure; Endothelial Cells; Endothelin-1; Hemodynamics; Hepatopulmonary Syndrome; Liver Cirrhosis, Experimental; Male; Muscle, Smooth, Vascular; Myocytes, Smooth Muscle; Nitric Oxide; Nitric Oxide Synthase Type III; Pulmonary Artery; Pulmonary Circulation; Rats, Sprague-Dawley; Receptor, Endothelin B; Signal Transduction; Ventricular Function, Right; Ventricular Pressure

Hepatopulmonary syndrome (HPS) is a serious complication of advanced liver disease, which markedly increases mortality. Pulmonary vascular remodelling (PVR) induced by circulating mediators plays an important role in the pathogenesis of HPS, while the underlying mechanism remains undefined. In the present study, we reported that endothelin-1 (ET-1) is up-regulated and annexin A1(ANXA1) is down-regulated in HPS rat, and ET-1 decreases the ANXA1 expression in a dose-dependent manner in rat pulmonary arterial smooth muscle cells (PASMCs). Then, we showed that ANXA1 can decrease nuclear p-ERK1/2 accumulation and decrease the cyclin D1 expression, thus resulting in the subsequent inhibition of PASMCs proliferation. As previously reported, we confirmed that ET-1 decreases the ANXA1 protein levels by the carbonylation and degradation of ANXA1. In conclusion, our research links the signaling cascade of ET1-ANXA1-cell proliferation to a potential therapeutic strategy for blocking IPS-associated PVR.

Topics: Animals; Annexin A1; Cell Proliferation; Cells, Cultured; Cyclin D1; Down-Regulation; Endothelin-1; Hepatopulmonary Syndrome; Inflammation; MAP Kinase Signaling System; Muscle, Smooth, Vascular; Myocytes, Smooth Muscle; Phenotype; Protein Carbonylation; Pulmonary Artery; Rats; Rats, Sprague-Dawley; Signal Transduction; Up-Regulation

Hepatopulmonary syndrome (HPS) is characterized by oxygen desaturation and increased intrapulmonary shunting formation in cirrhosis. Due to an unclarified mechanism, there is still no effective therapy except liver transplantation. Recent studies revealed that pulmonary angiogenesis may participate in pathogenesis, in which nitric oxide (NO) and vascular endothelial growth factor (VEGF) play roles. Pioglitazone, a peroxisome proliferator-activated receptor gamma agonist, exerts anti-angiogenesis effect. However, whether pioglitazone influences pulmonary angiogenesis, shunting and HPS remains unexplored.. Cirrhosis with HPS was induced in Spraque-Dawley rats with common bile duct ligation (CBDL). Pioglitazone (10 mg/kg/day, oral gavage) or vehicle was administered from 8th to 28th day post CBDL. On the 28th day, the mortality rate, hemodynamic parameters, concentrations of plasma glucose and liver biochemistry parameters, and arterial blood gas data were evaluated. Lungs were dissected for protein expression analyses. In another series, intrapulmonary shunting degree was determined by color microsphere method in paralleled groups.. The survival rates were similar in HPS rats with or without pioglitazone administration. Pioglitazone did not influence the hemodynamic parameters, glucose and liver biochemistry levels, oxygen saturation and alveolar arterial gradient, but significantly down-regulated pulmonary VEGF protein expression, endothelial NO synthase (eNOS) activation, and decreased intrapulmonary shunts. Pioglitazone significantly decreased intrapulmonary shunts as compared with the vehicle (18.1 ± 4.5 vs. 9.8 ± 3.6, p = 0.015).. Pioglitazone down-regulated VEGF, eNOS and decreased intrapulmonary shunts without improving oxygenation. The current finding suggests a multifactorial mechanism of HPS that could not be successfully overcome merely by pioglitazone-induced anti-angiogenesis and shunting reduction.

Topics: Angiogenesis Inhibitors; Animals; Endothelin-1; Hepatopulmonary Syndrome; Liver Cirrhosis; Male; Nitric Oxide; Pioglitazone; Rats; Rats, Sprague-Dawley; Thiazolidinediones; Vascular Endothelial Growth Factor A

To investigate possible abnormalities of vasoactive compounds, nitrative stress, and antioxidant activity of paraoxonase (PONa) in human hepatopulmonary syndrome (HPS), we determined endothelin-1 (ET), nitric oxide (NOx) metabolites, PONa alongside crude plasma nitrotyrosine (NT) as surrogate marker of nitrative stress.. Liver cirrhosis (LC) patients with HPS (n = 12) were matched by age, sex, and Child-Pugh score to LC patients without HPS (n = 15) and to healthy controls (CTR) (n = 15); plasma NO2(-) (nitrite) (vascular metabolite), NO3(-) (nitrate) (inflammatory metabolite), and PONa were determined by a colorimetric assay, ET, and NT by immunoassays.. HPS patients showed higher level of ET (p = 0.0002), NO2(-) (p = 0.002), NO3(-) (p = 0.0001), NT (p < 0.0001), and lower PONa (p = 0.0004) than CTR; post-hoc analysis revealed greater ET (p < 0.05) and NO3(-) (p < 0.005) in LC patients with HPS than in LC patients without HPS. NT correlated to Child-Pugh score within HPS (p = 0.04) and LC (p = 0.02).. Our HPS patients are characterized by elevated plasma levels of ET and NOx metabolites and lower PONa. Reduced PONa alongside elevated NO3(-) and NT suggests that defective antioxidation may favor nitrative stress and both may be implicated in the pathogenesis of HPS.

Topics: Aged; Aryldialkylphosphatase; Biomarkers; Cross-Sectional Studies; Endothelin-1; Female; Hepatopulmonary Syndrome; Humans; Italy; Liver Cirrhosis; Male; Middle Aged; Nitrates; Nitric Oxide; Nitrites

Pulmonary vascular dilation and angiogenesis underlie experimental hepatopulmonary syndrome (HPS) induced by common bile duct ligation (CBDL) and may respond to receptor tyrosine kinase (RTK) inhibition. Vascular endothelial growth factor-A (VEGF-A) expression occurs in proliferating cholangiocytes and pulmonary intravascular monocytes after CBDL, the latter contributing to angiogenesis. CBDL cholangiocytes also produce endothelin-1 (ET-1), which triggers lung vascular endothelin B receptor-mediated endothelial nitric oxide synthase (eNOS) activation and pulmonary intravascular monocyte accumulation. However, whether RTK pathway activation directly regulates cholangiocyte and pulmonary microvascular alterations in experimental HPS is not defined. We assessed RTK pathway activation in cholangiocytes and lung after CBDL and the effects of the type II RTK inhibitor sorafenib in experimental HPS. Cholangiocyte VEGF-A expression and ERK activation accompanied proliferation and increased hepatic and circulating ET-1 levels after CBDL. Sorafenib decreased each of these events and led to a reduction in lung eNOS activation and intravascular monocyte accumulation. Lung monocyte VEGF-A expression and microvascular Akt and ERK activation were also found in vivo after CBDL, and VEGF-A activated Akt and ERK and angiogenesis in rat pulmonary microvascular endothelial cells in vitro. Sorafenib inhibited VEGF-A-mediated signaling and angiogenesis in vivo and in vitro and improved arterial gas exchange and intrapulmonary shunting. RTK activation in experimental HPS upregulates cholangiocyte proliferation and ET-1 production, leading to pulmonary microvascular eNOS activation, intravascular monocyte accumulation, and VEGF-A-mediated angiogenic signaling pathways. These findings identify a novel mechanism in cholangiocytes through which RTK inhibition ameliorates experimental HPS.

Topics: Animals; Common Bile Duct; Disease Models, Animal; Endothelin-1; Endothelium, Vascular; Hepatopulmonary Syndrome; Ligation; Lung; Male; Neovascularization, Pathologic; Niacinamide; Nitric Oxide Synthase Type III; Phenylurea Compounds; Protein Kinase Inhibitors; Rats; Rats, Sprague-Dawley; Receptor Protein-Tyrosine Kinases; Signal Transduction; Sorafenib; Vascular Endothelial Growth Factor A

Hepatopulmonary syndrome (HPS) is a chronic hepatic complication characterized by defect in arterial oxygenation induced by pulmonary vascular dilatation and vasoactive substances in the setting of chronic liver disease (CLD). This study is to investigate the abnormality of hemodynamic and vasoactive substances in hepatopulmonary syndrome.. From September 2007 to September 2012, 58 patients with HPS in the General Surgery Department and Transplantation Center of Renji Hospital were enrolled for the case-control study. HPS patients enrolled were referred to as group H, CLD without HPS to as group C and case controls to as group N. Hemodynamic parameters of the systemic and pulmonary circulations as well as vasoactive substances in the radial and pulmonary arteries were measured in all patients. Univariate and multiple regression analysis were performed afterwards.. The mean pulmonary arterial pressure, pulmonary artery wedge pressure, systemic vascular resistance and pulmonary vascular resistance (PVR) in HPS patients were significantly lower than those in CLD patients without HPS (p < 0.05). The nitrite-to-nitrate ratio (NO2-/NO3-), endothelin-1 (ET-1) and tumor necrosis factor-α (TNF-α) in the radial and pulmonary arteries differed significantly among group H, group C and case controls (group N) separately (p < 0.05). The vasoactive intestinal peptide and 6-keto-prostaglandin-F1α in the radial and pulmonary arteries of group H were significantly higher than those in group N (p < 0.05). The NO2(-)/NO3(-) levels correlated negatively with PVR (r = -0.535, p < 0.05) and Endothelin-1 (r = -0.624, p < 0.05). CO (p < 0.05), CI (p < 0.05), SI (p < 0.05) and TNF-α (p < 0.05) level are considered significantly when performed with multiple regression analysis.. The CO increases and PVR decreases in HPS patients. The abnormally elevated NO2-/NO3- level in the pulmonary circulation leads to pulmonary vasodilation. ET-1 may induce nitric oxide synthesis and correlated negatively with PVR in HPS. CO, CI, SI and TNF-α level are independent risk factors for HPS patients' survival.

Topics: 6-Ketoprostaglandin F1 alpha; Case-Control Studies; Endothelin-1; Female; Hemodynamics; Hepatopulmonary Syndrome; Humans; Male; Middle Aged; Nitric Oxide; Pulmonary Artery; Pulmonary Circulation; Radial Artery; Risk Factors; Tumor Necrosis Factor-alpha; Vascular Resistance; Vasoactive Intestinal Peptide; Vasodilation

Hepatic production and release of endothelin-1 (ET-1) binding to endothelin B (ETB) receptors, overexpressed in the lung microvasculature, is associated with accumulation of pro-angiogenic monocytes and vascular remodeling in experimental hepatopulmonary syndrome (HPS) after common bile duct ligation (CBDL). We have recently found that lung vascular monocyte adhesion and angiogenesis in HPS involve interaction of endothelial C-X3-C motif ligand 1 (CX3CL1) with monocyte CX3C chemokine receptor 1 (CX3CR1), although whether ET-1/ETB receptor activation influences these events is unknown. Our aim was to define if ET-1/ETB receptor activation modulates CX3CL1/CX3CR1 signaling and lung angiogenesis in experimental HPS. A selective ETB receptor antagonist, BQ788, was given for 2 weeks to 1-week CBDL rats. ET-1 (±BQ788) was given to cultured rat pulmonary microvascular endothelial cells overexpressing ETB receptors. BQ788 treatment significantly decreased lung angiogenesis, monocyte accumulation, and CX3CL1 levels after CBDL. ET-1 treatment significantly induced CX3CL1 production in lung microvascular endothelial cells, which was blocked by inhibitors of Ca(2+) and mitogen-activated protein kinase (MEK)/ERK pathways. ET-1-induced ERK activation was Ca(2+) independent. ET-1 administration also increased endothelial tube formation in vitro, which was inhibited by BQ788 or by blocking Ca(2+) and MEK/ERK activation. CX3CR1 neutralizing antibody partially inhibited ET-1 effects on tube formation. These findings identify a novel mechanistic interaction between the ET-1/ETB receptor axis and CX3CL1/CX3CR1 in mediating pulmonary angiogenesis and vascular monocyte accumulation in experimental HPS.

Topics: Animals; Calcium Signaling; Cells, Cultured; Chemokine CX3CL1; Endothelial Cells; Endothelin-1; Hepatopulmonary Syndrome; Lung; Male; MAP Kinase Signaling System; Neovascularization, Pathologic; Rats; Rats, Sprague-Dawley; Receptor, Endothelin B

Liver dysfunction has been recognized to influence the lung in many different clinical situations, although the mechanisms for these effects are not well understood. One increasingly recognized interaction, the hepatopulmonary syndrome (HPS) occurs in the context of cirrhosis and results when alveolar microvascular dilation causes arterial gas exchange abnormalities and hypoxemia. HPS occurs in up to 30% of patients with cirrhosis and significantly increases mortality in affected patients. Currently, liver transplantation is the only curative therapy. Experimental biliary cirrhosis induced by common bile duct ligation (CBDL) in the rat reproduces the pulmonary vascular and gas exchange abnormalities of human HPS and has been contrasted with other experimental models of cirrhosis in which HPS does not develop. Microvascular dilation, intravascular monocyte infiltration, and angiogenesis in the lung have been identified as pathologic features that drive gas exchange abnormalities in experimental HPS. Our recent studies have identified biliary epithelium and activation and interaction between the endothelin-1 (ET-1)/endothelial endothelin B (ETB) receptor and CX3CL1/CX3CR1 pathways as important mechanisms for the observed pathologic events. These studies define novel interactions between the lung and liver in cirrhosis and may lead to effective medical therapies.

Topics: Animals; Cells, Cultured; Cytokines; Endothelin-1; Gene Expression Regulation; Hepatopulmonary Syndrome; Humans; Rats

Hepatopulmonary syndrome is a pulmonary vascular complication of cirrhosis in which intrapulmonary vasodilatation (IPV) results in hypoxemia. Endothelin-1 (ET-1), produced by proliferating cholangiocytes, has been identified as a mediator of IPV in an animal model of HPS, but the pathophysiology of IPV in humans has not been defined.. The purpose of this study was to assess whether cirrhosis with IPV, which often leads to HPS, is associated with increased hepatic venous ET-1 blood levels.. We performed a prospective cohort pilot study of 40 patients with liver disease undergoing transjugular liver biopsy from November 1, 2008 to September 1, 2009. Patients were categorized according to absence (-) or presence (+) of IPV as determined by bubble-contrasted echocardiography. Hepatic venous blood was assayed for ET-1 by ELISA. The percent volume of cholangiocytes in the liver biopsy specimen was determined by morphometric analysis, as a measure of bile duct proliferation.. Nine subjects were excluded, due to absence of cirrhosis (6) and patent foramen ovale (3). Of the remaining 31 subjects, IPV was present in 18 (58%). Median hepatic venous ET-1 was higher with IPV+ than IPV- at levels of 9.1 pg/mL (range 7.5-11.7) versus 2.1 pg/mL (1.3-5.6), respectively (P = 0.004). ET-1 levels correlated positively with cholangiocyte percent volume (r = 0.72, P < 0.001) but not with measures of liver dysfunction (bilirubin, INR, MELD score, or hepatic venous pressure gradient).. In human cirrhosis, increased hepatic venous ET-1 is associated with IPV and increased hepatic cholangiocyte volume.

Topics: Bile Ducts; Cell Proliferation; Cross-Sectional Studies; Dilatation, Pathologic; Endothelin-1; Female; Hepatic Veins; Hepatopulmonary Syndrome; Humans; Immunohistochemistry; Liver Cirrhosis; Male; Middle Aged; Pilot Projects; Prospective Studies; Pulmonary Veins; Vasodilation

Experimental hepatopulmonary syndrome (HPS) after common bile duct ligation (CBDL) in rat is accompanied by increased lung vascular endothelial endothelin B (ETB) receptor expression and increased circulating levels of endothelin-1 (ET-1). The onset of HPS is hypothesized to be triggered by ET-1/ETB receptor activation of endothelial nitric oxide synthase (eNOS)-derived NO production in the pulmonary endothelium. However, whether functional pulmonary vascular ETB receptors are required for the development of experimental HPS is not defined. We evaluated the effects of vascular ETB receptor deficiency on the development of experimental HPS. The molecular and physiological alterations of HPS were compared in 2-wk CBDL wild-type and ETB receptor-deficient (transgenic sl/sl) rats. Relative to wild-type rats, basal hepatic and plasma ET-1 levels were elevated in sl/sl controls although, unlike wild-type animals circulating ET-1 levels, did not increase further after CBDL in sl/sl animals. In contrast to wild-type animals, ETB receptor-deficient rats did not develop increased Akt and eNOS expression and activation and did not develop gas exchange abnormalities of HPS after CBDL. There was a similar degree of pulmonary intravascular monocyte accumulation in both 2-wk CBDL sl/sl and wild-type animals. In conclusion, ETB receptor deficiency inhibits lung Akt/eNOS activation and prevents the onset of experimental HPS after CBDL. This effect is independent of inhibition of pulmonary intravascular monocyte accumulation. These results demonstrate that ET-1/ETB receptor signaling plays a key role in the initiation of experimental HPS.

Topics: Animals; Animals, Genetically Modified; Cholestasis; Endothelin-1; Gene Deletion; Gene Expression Regulation; Genetic Predisposition to Disease; Heme Oxygenase-1; Hepatopulmonary Syndrome; Liver; Male; Nitric Oxide Synthase Type III; Oncogene Protein v-akt; Rats; Rats, Wistar; Receptor, Endothelin B

To observe the changes of systemic and pulmonary hemodynamics and the plasma levels of inducible nitric oxide synthase (iNOS) and endothelin-1 (ET-1) and investigate their association in patients with hepatopulmonary syndrome (HPS).. Twenty-six patients with HPS undergoing orthotopic liver transplantation (OLT) were enrolled in this study with 20 patients without hypoxemia as the control group. Blood samples were taken one day before OLT to measure the plasma levels of iNOS and ET-1 using fluorescence quantitative polymerase chain reaction (FQ-PCR) and radioimmunoassay, respectively, with 10 healthy volunteers serving as the healthy control group. Before the operation for OLT, the parameters of systemic and pulmonary hemodynamics were monitored after anesthesia induction.. The systemic and pulmonary hemodynamics in patients without hypoxemia was characterized by high cardiac output and low resistance, and by comparison, the patients with HPS showed even higher cardiac output and lower mean pulmonary artery pressure, pulmonary artery wedge pressure, systemic vascular resistance and pulmonary vascular resistance. The two patient groups had comparable plasma iNOS and ET-1 levels, which were both higher than those in the healthy control group.. The hemodynamics in patients with end-stage liver disease exhibit a pattern of high cardiac output and low resistance, which is more obvious in HPS patients possibly in association with elevated plasma levels of iNOS and ET-1.

Topics: Adult; Aged; Case-Control Studies; Endothelin-1; Female; Hemodynamics; Hepatopulmonary Syndrome; Humans; Male; Middle Aged; Nitric Oxide Synthase Type II; Pulmonary Circulation; Young Adult

This report describes a case of Abernethy malformation associated with hepatopulmonary syndrome, which was resolved after shunt ligation. The clinical course indicated that hepatopulmonary syndrome can develop in Abernethy malformation in which liver function and portal pressure is normal, and liver transplantation is not the exclusive therapy for hepatopulmonary syndrome. The levels of endotoxin and endothelin 1 in the shunt blood were high, whereas those of tumor necrosis factor alpha and interleukin-1beta were within reference range. Although pathogenesis of hepatopulmonary syndrome remains unknown, the findings in this case suggest that bacterial translocation as well as elevated endothelin 1 may play a causal role in development of hepatopulmonary syndrome.

Topics: Biomarkers; Blood Gas Analysis; Child, Preschool; Congenital Abnormalities; Endothelin-1; Follow-Up Studies; Hepatopulmonary Syndrome; Humans; Ligation; Male; Portal System; Portal Vein; Risk Assessment; Severity of Illness Index; Tomography, X-Ray Computed; Treatment Outcome; Ultrasonography, Doppler

The hepatopulmonary syndrome (HPS) results from intrapulmonary vasodilation in the setting of cirrhosis and portal hypertension. In experimental HPS, pulmonary endothelial endothelin B (ET(B)) receptor overexpression and increased circulating endothelin-1 (ET-1) contribute to vasodilation through enhanced endothelial nitric oxide synthase (eNOS)-derived nitric oxide (NO) production. In both experimental cirrhosis and prehepatic portal hypertension, ET(B) receptor overexpression correlates with increased vascular shear stress, a known modulator of ET(B) receptor expression. We investigated the mechanisms of pulmonary endothelial ET(B) receptor-mediated eNOS activation by ET-1 in vitro and in vivo. The effect of shear stress on ET(B) receptor expression was assessed in rat pulmonary microvascular endothelial cells (RPMVECs). The consequences of ET(B) receptor overexpression on ET-1-dependent ET(B) receptor-mediated eNOS activation were evaluated in RPMVECs and in prehepatic portal hypertensive animals exposed to exogenous ET-1. Laminar shear stress increased ET(B) receptor expression in RPMVECs without altering mRNA stability. Both shear-mediated and targeted overexpression of the ET(B) receptor enhanced ET-1-mediated ET(B) receptor-dependent eNOS activation in RPMVECs through Ca(2+)-mediated signaling pathways and independent of Akt activation. In prehepatic portal hypertensive animals relative to control, ET-1 administration also activated eNOS independent of Akt activation and triggered HPS. These findings support that increased pulmonary microvascular endothelial ET(B) receptor expression modulates ET-1-mediated eNOS activation, independent of Akt, and contributes to the development of HPS.

Topics: Animals; Calcium; Cells, Cultured; Endothelial Cells; Endothelin-1; Gene Expression; Hepatopulmonary Syndrome; Lung; Microcirculation; Nitric Oxide Synthase Type III; Proto-Oncogene Proteins c-akt; Rats; Receptor, Endothelin B; Signal Transduction; Stress, Mechanical

To evaluate the role of intestinal endotoxemia in the genesis of hepatopulmonary syndrome.. A rat model of cirrhosis was prepared with the method of compound factors. At the end of the eighth week, rats with cirrhosis were treated with 300 microg LPS/100 g body weight, and 1 g/rat of glycine about four h prior to LPS. After three h of LPS treatment, blood and tissues were collected for various measurements. Kupffer cells were isolated from male Wistar rats and cultured, and divided into five groups. Supernatant was harvested at 3 h after treatment with LPS for measurement of tumor necrosis factor-alpha (TNF-alpha).. Our results showed that in rats with cirrhosis, slowed and deepened breath with occasional pause was. PaO2, PaCO2 and standard bicarbonate (SB) in arterial blood were decreased. Arterial O2 and actual bicarbonate (AB) were markedly decreased. There was a close correlation between decreased O2 and endotoxin. Metabolic acidosis accompanying respiratory alkalosis was the primary type of acid-base imbalance. The alveolar-arterial oxygen gradient was sharply widened. Massive accumulation of giant macrophages in the alveolar spaces and its wall and widened alveolar wall architecture were observed. The number of bacterial translocations in mesenteric lymph nodes increased. The ratio of TC99M-MAA brain-over-lung radioactivity rose. Endotoxin, and TNF-alpha, endothelin-1 (ET-1), nitric oxide (NO) in plasma and ET-1, carbon monoxide (CO) in lung homogenates increased. After administration of a given dosage of LPS in rats with cirrhosis, various pathological parameters worsened. Plasma level of endotoxin was related to TNF-alpha, ET-1, NO in plasma and ET-1, NO, CO in lung homogenates. TNF-alpha level was related to ET-1 and NO in plasma and lung homogenates and CO in lung homogenate as well. The level of TNF-alpha increased after infusion of LPS into culture supernatant of Kupffer cells in vitro. However, TNF-alpha significantly decreased after pretreatment with glycine, PD98059 and SB212850. Glycine could antagonize the effect of LPS in vivo and in vitro.. Intestinal endotoxemia accompanying by cirrhosis may be an important mechanism in the development of hepatopulmonary syndrome in rats. Overproduction of TNF-alpha due to endotoxin stimulation of Kupffer cells via mitogen-activated protein kinase (MAPK) signal transduction pathway may be a major mechanism mediating the pathologic alterations of hepatopulmonary syndrome.

Topics: Acid-Base Imbalance; Acidosis; Animals; Bacterial Translocation; Brain; Carbon Monoxide; Endothelin-1; Endotoxemia; Hepatopulmonary Syndrome; Kupffer Cells; Lipopolysaccharides; Liver Cirrhosis; Lung; Male; MAP Kinase Signaling System; Nitric Oxide; Rats; Rats, Wistar; Respiratory Mechanics; Sulfhydryl Compounds; Technetium Tc 99m Aggregated Albumin; Tumor Necrosis Factor-alpha

Hepatic production and release of endothelin 1 plays a central role in experimental hepatopulmonary syndrome after common bile duct ligation by stimulating pulmonary endothelial nitric oxide production. In thioacetamide-induced nonbiliary cirrhosis, hepatic endothelin 1 production and release do not occur, and hepatopulmonary syndrome does not develop. However, the source and regulation of hepatic endothelin 1 after common bile duct ligation are not fully characterized. We evaluated the sources of hepatic endothelin 1 production after common bile duct ligation in relation to thioacetamide cirrhosis and assessed whether transforming growth factor beta1 regulates endothelin 1 production.. Hepatopulmonary syndrome and hepatic and plasma endothelin 1 levels were evaluated after common bile duct ligation or thioacetamide administration. Cellular sources of endothelin 1 were assessed by immunohistochemistry and laser capture microdissection of cholangiocytes. Transforming growth factor beta1 expression and signaling were assessed by using immunohistochemistry and Western blotting and by evaluating normal rat cholangiocytes.. Hepatic and plasma endothelin 1 levels increased and hepatopulmonary syndrome developed only after common bile duct ligation. Hepatic endothelin 1 and transforming growth factor beta1 levels increased over a similar time frame, and cholangiocytes were a major source of each peptide. Transforming growth factor beta1 signaling in cholangiocytes in vivo was evident by increased phosphorylation and nuclear localization of Smad2, and hepatic endothelin 1 levels correlated directly with liver transforming growth factor beta1 and phosphorylated Smad2 levels. Transforming growth factor beta1 also stimulated endothelin 1 promoter activity, expression, and production in normal rat cholangiocytes.. Cholangiocytes are a major source of hepatic endothelin 1 production during the development of hepatopulmonary syndrome after common bile duct ligation, but not in thioacetamide-induced cirrhosis. Transforming growth factor beta1 stimulates cholangiocyte endothelin 1 expression and production. Cholangiocyte-derived endothelin 1 may be an important endocrine mediator of experimental hepatopulmonary syndrome.

Topics: Animals; Base Sequence; Biomarkers; Biopsy, Needle; Blood Gas Analysis; Blotting, Northern; Blotting, Western; Cells, Cultured; Disease Models, Animal; Endothelin-1; Hepatopulmonary Syndrome; Immunohistochemistry; Liver Function Tests; Male; Molecular Sequence Data; Probability; Random Allocation; Rats; Rats, Sprague-Dawley; Reference Values; Reverse Transcriptase Polymerase Chain Reaction; Sensitivity and Specificity; Transforming Growth Factor beta; Transforming Growth Factor beta1

Rats with chronic bile duct ligation (CBDL) and portal vein ligation (PVL) are used as models of portal hypertension. CBDL rats show hypoxemia with intrapulmonary vasodilatation (IPVD), and are recognized as a model of hepatopulmonary syndrome (HPS), while PVL rats are normoxemic. We investigated the differences in arterial oxygenation between these models, and the key factors leading to HPS.. Forty-eight Sprague-Dawley rats were prepared as CBDL or PVL models, or as Sham rats. Arterial oxygenation, hemodynamics (reference sample method), and IPVD were simultaneously evaluated in conscious and unrestrained animals, using (141)Ce- or (113)Sn-labeled microspheres (15 microm in diameter), respectively. Endothelin-1 (ET-1) and nitrate/nitrite (end products of nitric oxide; NOx) production by the lung tissue (increment across the lungs) was also determined.. The extent of IPVD was similar in both models, but hypoxemia was only observed in CBDL rats. The ET-1 level and the increment in NOx were significantly increased in CBDL rats, and the increment was directly correlated with impairment of oxygenation. Blood flow through the bronchial arteries (anatomical shunting) was increased in CBDL rats, reaching more than three times the level in PVL rats or Sham rats.. These results support the hypothesis that NO derived from the lung tissues contributes to hypoxemia, and IPVD appears to be a prerequisite for impaired oxygenation. The considerable increase of anatomical shunting may potentially contribute to impaired oxygenation in CBDL rats.

Topics: Animals; Arteries; Disease Models, Animal; Endothelin-1; Hepatopulmonary Syndrome; Hypertension, Portal; Hypoxia; Lung; Male; Microspheres; Nitrates; Nitrites; Oxygen; Rats; Rats, Sprague-Dawley; Vasodilation

The correlation between pulmonary endothelin receptors and alveolar-arterial oxygen gradient (A-aDO2) in rats with hepatopulmonary syndrome was investigated. Animals were divided into 2 groups: Sham-operated (Sham) group and common bile duct ligation (CBDL) group. Arterial blood gas was evaluated by a blood gas analyzer. The concentrations of ET-1 in blood and lung tissue sample were evaluated by radioimmunoassay. The distribution and expression of two kinds of subtype receptor of ET-1, ETRA and ETRB were examined by in situ hybridization. The results showed that the level of A-aDO2 was higher in CBDL group than that in Sham group (P < 0.05). The levels of plasma and pulmonary ET-1 in CBDL group were both higher than in Sham group (P < 0.05). There was no significant difference in average A of ETRA between two groups by imaging analysis (0.21 +/- 0.06 vs 0.22 +/- 0.08, P > 0.05), while that of ETRB was higher in CBDL group than in Sham group (0.58 +/- 0.16 vs 0.28 +/- 0.07, P < 0.05). The expression of ETRB in lung was positively correlated with A-aDO2 (P < 0.05). It was concluded that the widened A-aDO2 may be related with enhancement of the expression of ETRB in lung.

Topics: Animals; Endothelin-1; Hepatopulmonary Syndrome; Lung; Male; Oxygen; Pulmonary Alveoli; Rats; Rats, Wistar; Receptor, Endothelin A; Receptor, Endothelin B

Common bile duct ligation (CBDL) triggers a molecular cascade resulting in the hepatopulmonary syndrome (HPS). Both increased hepatic endothelin-1 (ET-1) production and pulmonary vascular ET(B) receptor expression with stimulation of endothelial nitric oxide synthase and TNF-alpha mediated inducible nitric oxide synthase and heme oxygenase-1 expression in pulmonary intravascular macrophages occur. Whether biliary cirrhosis is unique in triggering ET-1 and TNF-alpha alterations and HPS is unknown. We evaluated for HPS in rat prehepatic portal hypertension [partial portal vein ligation (PVL)], biliary (CBDL) and nonbiliary [thioacetamide treatment (TAA)] cirrhosis, and assessed ET-1 infusion in normal and PVL animals. Control, PVL, CBDL, TAA-treated, and ET-1-infused PVL animals had ET-1 and TNF-alpha levels measured and underwent molecular and physiological evaluation for HPS. HPS developed only in biliary cirrhosis in association with increased plasma ET-1 and TNF-alpha levels and the development of established molecular changes in the pulmonary microvasculature. In contrast, PVL did not increase ET-1 or TNF-alpha levels and TAA treatment increased TNF-alpha levels alone, and neither resulted in the full development of molecular or physiological changes of HPS despite portal pressure increases similar to those after CBDL. Exogenous ET-1 increased TNF-alpha levels and triggered HPS after PVL. Combination of ET-1 and TNF-alpha overproduction is unique to biliary cirrhosis and associated with experimental HPS. ET-1 infusion increases TNF-alpha levels and triggers HPS in prehepatic portal hypertension. ET-1 and TNF-alpha interact to trigger pulmonary microvascular changes in experimental HPS.

Topics: Animals; Endothelin-1; Heme Oxygenase (Decyclizing); Heme Oxygenase-1; Hepatopulmonary Syndrome; Hypertension, Portal; Ligation; Liver Cirrhosis; Liver Cirrhosis, Biliary; Lung; Male; Nitric Oxide Synthase; Nitric Oxide Synthase Type II; Nitric Oxide Synthase Type III; Portal Vein; Rats; Rats, Sprague-Dawley; Thioacetamide; Tumor Necrosis Factor-alpha

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.

Topics: Animals; Biomarkers; Common Bile Duct; Endothelin Receptor Antagonists; Endothelin-1; Endothelium, Vascular; Hepatopulmonary Syndrome; Ligation; Male; Nitric Oxide Synthase; Nitric Oxide Synthase Type III; Pulmonary Artery; Rats; Rats, Sprague-Dawley; Receptor, Endothelin B

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.. 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.. 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.. 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.

Topics: Animals; Common Bile Duct; Endothelin-1; Endothelium, Vascular; Hepatopulmonary Syndrome; Hypertension, Portal; Ligation; Liver Cirrhosis; Male; Nitric Oxide; Nitric Oxide Synthase; Nitric Oxide Synthase Type III; Portal Vein; Pulmonary Artery; Pulmonary Circulation; Rats; Rats, Sprague-Dawley; Receptor, Endothelin B

To investigate the expression of ET-1 mRNA in the lung of rats with hepatopulmonary syndrome.. Male Sprague-Dawley rats were divided into four groups: SO, IHPH, PHPH and PCS. Two weeks after production of rat models, all measurements were performed. Arterial blood gas was analyzed. The concentrations of NO and ET-1 in lungs were measured by using radioimmunoassay. In situ hybridization, ET-1 mRNA expressions were detected in lung tissue sections with digoxin-labeled ET-1 oligonucleotide probes. Liver and lung tissues and all the results of in situ hybridization were analyzed by one pathologist. At a magnification of 10 x 40, percent areas of positive stains were detected to indicate the expressions of ET-1 mRNA in the arteries, capillaries and branches.. Arterial blood gas analysis showed that PaO(2) (mmHg) decreased more significantly in IHPH (73.85 +/- 6.51) rats than in PHPH (97.39 +/- 1.33), PCS (95.23 +/- 2.22) and SO rats (99.05 +/- 0.75). Alveolar-arterial oxygen gradient (A-aG) (mmHg) increased more significantly in IHPH rats (32.99 +/- 6.57) than in PHPH (4.98 +/- 1.69), PCS (6.51 +/- 2.04) and SO rats (3.23 +/- 0.81). Changes of vascular active substance in plasma and lung indicated that the level of lung NO of IHPH (19.78 +/- 5.33) was increased significantly more than that of PHPH (13.21 +/- 3.99) and PCS (13.89 +/- 3.16). These levels in lung homogenate increased more significantly than those SO (8.71 +/- 1.68). The levels of ET-1 in IHPH rats (195.1 +/- 36.2) was significantly lower than in PHPH (234.8 +/- 71.0), PCS (240.4 +/- 66.5) and SO rats (271.8 +/- 40.6). ET-1 mRNA in situ hybridization showed that there was no significant difference in positive expression of ET-1 mRNA in alveolar arteries and small bronchi. The expression of ET-1 mRNA was significantly lower in alveolar capillary endothelia (5.12 +/- 1.27) than in PHPH (7.43 +/- 0.83), PCS (7.07 +/- 0.86) and SO (7.81 +/- 1.98) rats.. The low expressions of ET-1 mRNA in HPS rat alveolar capillary endothelia accompanied by decreased ET-1 levels in lung may play an important role in the mechanism of HPS.

Topics: Animals; Disease Models, Animal; Endothelin-1; Hepatopulmonary Syndrome; Image Processing, Computer-Assisted; In Situ Hybridization; Lung; Male; Nitrates; Nitrites; Rats; Rats, Sprague-Dawley; RNA, Messenger

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.

Topics: Animals; Bile Duct Diseases; Body Fluids; Cattle; Cells, Cultured; Common Bile Duct; Cysts; Endothelin-1; Endothelium, Vascular; Hepatopulmonary Syndrome; Ligation; Male; Nitric Oxide Synthase; Nitric Oxide Synthase Type III; Nitrites; Pulmonary Artery; Rats; Rats, Sprague-Dawley; RNA, Messenger

Topics: Animals; Bile Ducts; Endothelin-1; Hepatopulmonary Syndrome; Homeostasis; Hypertension, Portal; Ligation; Lung; Pulmonary Circulation; Rats

Biliary cirrhosis in the rat triggers intrapulmonary vasodilatation and gas exchange abnormalities that characterize the hepatopulmonary syndrome. This vasodilatation correlates with increased levels of pulmonary microcirculatory endothelial nitric oxide synthase (eNOS) and hepatic and plasma endothelin-1 (ET-1). Prehepatic portal hypertension induced by portal vein ligation (PVL) does not cause similar changes, suggesting that ET-1 in cirrhosis may modulate pulmonary eNOS and vascular tone. We assessed whether ET-1 altered eNOS expression and nitric oxide production in bovine pulmonary artery endothelial cells (BPAECs) and if a 2-wk low-level intravenous ET-1 infusion in PVL animals modulated pulmonary eNOS levels, microcirculatory tone, and gas exchange. ET-1 caused a 2.5-fold increase in eNOS protein in BPAECs, inhibitable with an endothelin B receptor antagonist, and an increase in eNOS mRNA and nitrite production. ET-1 infusion in PVL animals caused increased pulmonary eNOS levels, intrapulmonary vasodilatation, and gas exchange abnormalities without increasing pulmonary arterial pressure. ET-1 produced during hepatic injury may contribute to the hepatopulmonary syndrome by modulating eNOS and inducing pulmonary microcicrulatory vasodilatation.

Topics: Animals; Blotting, Western; Cattle; Cell Division; Cells, Cultured; Disease Models, Animal; Endothelin-1; Endothelium, Vascular; Gene Expression Regulation, Enzymologic; Hepatopulmonary Syndrome; Hypertension, Portal; Injections, Intravenous; Liver; Liver Cirrhosis, Experimental; Male; Nitric Oxide Synthase; Nitric Oxide Synthase Type III; Pulmonary Artery; Pulmonary Circulation; Pulmonary Gas Exchange; Rats; Rats, Sprague-Dawley; Receptor, Endothelin B; Receptors, Endothelin; RNA, Messenger; Vasodilation

Models of hepatopulmonary syndrome require both hepatic injury and portal hypertension to develop pulmonary microvascular and gas exchange abnormalities. Recently, increased endothelin-1 levels associated with vasodilatation, have been observed in cirrhosis. We investigated endothelin-1 production in common bile duct ligated animals with hepatopulmonary syndrome in comparison to partial portal vein ligated animals that do not develop hepatopulmonary syndrome.. Organ and plasma endothelin-1 were measured in sham, bile duct ligated and portal vein ligated rats, and Northern analysis and immunohistochemistry were performed in liver. Plasma endothelin-1 levels were correlated with pulmonary endothelial nitric oxide synthase levels and alveolar-arterial oxygen gradients.. Hepatic and plasma endothelin-1 increased only after bile duct ligation, and were accompanied by increased hepatic endothelin-1 mRNA and increased endothelin-1 protein in biliary epithelium. Plasma endothelin-1 levels correlated directly with both pulmonary endothelial nitric oxide synthase levels and alveolar-arterial gradients.. Enhanced hepatic production and increased plasma levels of endothelin-1 occur after bile duct ligation, but not after portal vein ligation, and correlate with associated molecular and gas exchange alterations in the lung. Endothelin-1 may contribute to the pathogenesis of hepatopulmonary syndrome.

Topics: Animals; Bile Ducts; Endothelin-1; Fluorescent Antibody Technique; Hepatopulmonary Syndrome; Ligation; Liver; Lung; Male; Nitric Oxide Synthase; Nitric Oxide Synthase Type III; Portal Vein; Pulmonary Gas Exchange; Rats; Rats, Sprague-Dawley