Effect of terlipressin on in vitro vascular hyporeactivity of portal hypertensive rats

Backgrounds/Aims: Isolated vessels of portal hypertensive rats exhibit decreased responsiveness to vasoconstrictors. The vasopressin analogue terlipressin analogue terlipressin is used in the treatment of portal hypertension since it is known to reduce portal pressure, an effect that is thought to arise from splanchnic vasoconstriction via stimulation of vasoconstrictor V₁ receptors. This study assessed the effect of terlipressin on the in vitro vascular reactivity of portal hypertensive rats to the α-adrenoceptor agonist methoxamine.Methods: Portal hypertension was produced by portal vein ligation. Sham-operated rats served as controls. In isolated perfused mesentric arteries of portal vien ligated and sham-operated rats pressor responses to methoxamine (3 nmol-3 μmol) were determined in the absence and presence of the nitric oxide synthase inhibitor N^g-nitro-L-arginine methyl ester (L-NAME; 100 μM), terlipressin or the selective V₂ receptor agonist desmopressin (each 0.5 μM). In addition, the direct pressor properties of terlipressin (3 pmol-100 nmol) were compared to arginine vasopressin (3 pmol-1 nmol) in vessels of normal rats.Results: Mesenteric vessels of portal vein ligated rats were markedly hyporeactive to methoxamine, even in the presence of L-NAME. Terlipressin alone reduced and in combination with L-NAME abolished the difference in reactivity to methoxamine between the portal vein ligated and sham-operated groups, while desmopressin was ineffective. Arginine vasopressin potently contracted vessels of normal rats with a threshold dose of 10 pmol and was maximally effective at 300 pmol. In contrast, terlipressin failed to produce pressor responses up to 100 nmol.Conclusions: Hyporeactivity of mesenteric vessels of portal vein ligated rats to methoxamine is predominantly independent of nitric oxide. Terlipressin alone ameliorates and in combination with L-NAME abolishes the hyporesponsiveness to methoxamine presumably by inhibiting the nitric oxide-independent mechanism that underlies the reduced responsiveness to methoxamine in portal hypertension. This effect of terlipressin appears to be independent of stimulation of V₂ as well as vasoconstrictor V₁ receptors.     

Heme oxygenase attenuates oxidative stress and inflammation, and increases VEGF expression in portal hypertensive rats

BACKGROUND/AIMS: The pathophysiological significance of heme oxygenase-1 up-regulation in portal hypertension is not completely understood. In this study, we determined the role of heme oxygenase-1 on oxidative stress, inflammation, angiogenesis, and splanchnic hemodynamics in rats with portal hypertension induced by partial portal vein ligation. METHODS: Rats were treated with the heme oxygenase inhibitor SnMP or vehicle for 7 days. Then, oxidative stress was quantified by superoxide anion production, and inflammatory response was assessed by immunofluorescence. Expression of angiogenesis mediators was determined by western blotting, and the extent of portosystemic collaterals by radioactive microspheres. Hemodynamic studies were performed by flowmetry. RESULTS: Oxidative stress was significantly increased in the mesentery of portal hypertensive rats, as compared with sham-operated controls. In portal hypertensive rats, chronic heme oxygenase inhibition (1) potentiated oxidative stress and inflammation, (2) significantly decreased VEGF expression, without modifying the extent of collaterals or the splanchnic neovascularization, and (3) significantly decreased superior mesenteric artery blood flow and portal pressure. CONCLUSIONS: This study demonstrates that heme oxygenase plays an important (beneficial) role attenuating oxidative stress and inflammation, but it also plays a detrimental role in stimulating VEGF production, and contributing to the development of hyperdynamic splanchnic circulation in rats with portal hypertension.     

Increased neuronal nitric oxide synthase interaction with soluble guanylate cyclase contributes to the splanchnic arterial vasodilation in portal hypertensive rats

Splanchnic arterial vasodilation represents the pathophysiological hallmark of the hemodynamic dysfunction observed in portal hypertensive states. The role of neuronal nitric oxide synthase (nNOS) in the splanchnic arterial vasodilation remains to be elucidated. We therefore investigated: (i) if nNOS is involved in the splanchnic arterial vasodilation; and (ii) the possible interaction of nNOS with soluble guanylate cyclase (sGC) in superior mesenteric arterial (SMA) beds in portal hypertensive rats. Portal hypertension was induced by partial portal vein ligation (PVL). To determine the role of nNOS, we removed endothelial layer and measured contractile response and nitric oxide (NO) release in the presence or absence of 7-nitroindazole (7-NI, 10 muM), an nNOS-specific inhibitor. In endothelium-removed vessels, nNOS inhibitor significantly increased the contractile response to methoxamine in SMA beds isolated from the portal hypertensive rats, compared to non-treated SMA beds (106.8 +/- 10.7 vs 86.8 +/- 7.2 mmHg, P = 0.003). This effect of nNOS inhibitor was accompanied with decreased NO production in SMA of portal hypertensive rats (321.3 +/- 18.6 vs 139.5 +/- 16.9 pmol/mL/min, P = 0.0001). Unlike endothelial NOS that is located in endothelial cells, nNOS protein is highly expressed in smooth muscle layers of SMA. Furthermore, there was a significant increase in ~90 kDa nNOS protein in the portal hypertensive group, compared to the sham-operated group (P < 0.01). Interestingly, this 90 kDa nNOS was coimmunoprecipitated with sGC. In conclusion, increased nNOS expression in smooth muscle layers of arteries in the splanchnic circulation may be an additional and more efficient pathway for the activation of sGC by NO, which sustains arterial vasodilation.     

Mesenteric vasoconstriction triggers nitric oxide overproduction in the superior mesenteric artery of portal hypertensive rats

BACKGROUND & AIMS: Vasoconstriction of the superior mesenteric artery (SMA) is the earliest hemodynamic event occurring after partial portal vein ligation (PVL). We tested the hypothesis that this early vasoconstriction of the SMA may initiate eNOS up-regulation in PVL. METHODS: Portal hypertension with or without mesenteric vasoconstriction was induced by differentially calibrated stenosis of the portal vein (PVL-20G and PVL-18G, respectively). In a separate group of rats, mesenteric vasoconstriction was achieved by renal artery ligation. Sham-operated rats were used as controls. Effects of vasoconstriction of the SMA in PVL and RAL rats were evaluated by measuring perfusion pressure changes in isolated SMA beds in response to methoxamine, nitric oxide synthase activity, and eNOS protein expression. Mean arterial pressure, portal pressure, and SMA blood flow were measured by catheterization and Doppler flowmetry. SMA vascular resistance was calculated from arterial pressure, portal pressure, and SMA flow. RESULTS: There was a significant increase in SMA vascular resistance in PVL-20G (2.33 +/- 0.13 vs. 1.22 +/- 0.03 mm Hg/% flow; P < 0.05) and RAL (2.32 +/- 0.18 vs. 1.18 +/- 0.02 mm Hg/% flow; P < 0.05) but not in PVL-18G, showing mesenteric vasoconstriction in both PVL-20G and RAL groups. The mesenteric vasculature of PVL-20G and RAL animals showed hyporeactivity to methoxamine (P < 0.01). Whereas both PVL groups were portal hypertensive (P < 0.01), RAL rats were not. The SMA hyporeactivity of PVL-20G and RAL rats was corrected by N(G)()-monomethyl-L-arginine, and nitric oxide synthase enzyme activity was significantly higher in PVL-20G and RAL rats (P < 0.05). CONCLUSIONS: Mesenteric arterial vasoconstriction plays a triggering role in up-regulation of eNOS catalytic activity in the SMA of portal hypertensive rats.     

血红素氧合酶/一氧化碳系统在心肌缺血再灌注损伤中的保护机制

血红素氧合酶是血红素降解的限速酶,可将血红素分解为等摩尔的胆绿素、铁和一氧化碳。血红素氧合酶/一氧化碳系统在心肌缺血再灌注中通过血管舒张、抗氧化、抗炎、抗凋亡和抗心律失常作用发挥其保护心肌和心功能的作用。并且其与一氧化氮合酶/一氧化氮系统具有相互调节作用。     

Nitric oxide mediates hyporeactivity to vasopressors in mesenteric vessels of portal hypertensive rats.

Increased levels of circulating vasodilators have been claimed to be the causative factor in the hyporesponsiveness to endogenous vasopressors in portal hypertension. To investigate whether this hyporeactivity to vasopressors is also present in an in vitro system perfused with a synthetic medium, the responsiveness to graded concentrations of norepinephrine, arginine-vasopressin, and potassium chloride was tested in perfused superior mesenteric arterial beds of normal rats and rats with portal hypertension induced by partial portal vein ligation (PVL). The same vasopressors were tested after incubation of vessel preparations with the stereo-specific nitric oxide formation inhibitor N omega-nitro-L-arginine (NNA, 10(-4) mol/L). Vessel preparations of PVL compared with normal rats (n = 8 per group and vasopressor) expressed a significant (P less than 0.05) hyporeactivity to norepinephrine, arginine-vasopressin, and potassium chloride over a wide range of concentrations. This hyporesponsiveness was overcome by preincubating vessel preparations with NNA. In summary, portal hypertension is accompanied by a significant in vitro hyporeactivity of splanchnic vessels to norepinephrine, arginine-vasopressin, and potassium chloride, and secretion of nitric oxide in this preparation seems responsible for this blunted response.     

Simvastatin treatment improves liver sinusoidal endothelial dysfunction in CCl4 cirrhotic rats

BACKGROUND/AIMS: Sinusoidal endothelial dysfunction with decreased nitric oxide (NO) production contributes to increased hepatic resistance in cirrhosis. Statins improve endothelial dysfunction in peripheral vasculature. This study was designed to characterize the hemodynamic and molecular effects of statins in cirrhotic rats. METHODS: Systemic and splanchnic hemodynamics were evaluated in CCl(4) ascitic cirrhotic rats treated with placebo or simvastatin (25 mg/kg/day, for 3 days), at baseline and after volume expansion. Vascular responses of liver vasculature were evaluated after isolation and perfusion of the liver. RESULTS: There were no differences in baseline hemodynamics in rats treated with simvastatin or placebo. However, in rats treated with simvastatin the increase in portal pressure induced by volume expansion was significantly attenuated. In isolated and perfused cirrhotic livers simvastatin pre-treatment significantly attenuated the pressure response to methoxamine, and significantly improved paradoxical vasoconstriction induced by acetylcholine. These effects were not observed in the presence of a nitric oxide synthase inhibitor. Simvastatin increased eNOS expression, Akt-dependent eNOS phosphorylation and cGMP liver content. CONCLUSIONS: The administration of simvastatin might constitute a new way to selectively increase NO availability in the cirrhotic liver circulation and, therefore improve the vascular disturbances that contribute to portal hypertension.     

Hyperkinetic circulation and decreased sensitivity to vasoconstrictors following portacaval shunt in the rat. Effects of chronic nitric oxide inhibition.

BACKGROUND/AIMS: This study aimed to investigate: (i) whether the hyperkinetic circulation that develops after portacaval shunt is associated with decreased vascular sensitivity to vasoconstrictors and (ii) the role of nitric oxide on its pathogenesis. METHODS: Portacaval-shunted and sham-operated rats received long-term treatment with the nitric oxide inhibitor L-NAME (osmotic minipump) or its inactive enantiomer D-NAME. Measurements of arterial pressure, cardiac output and superior mesenteric artery blood flow (transit-time flow probe) were done 4 days later in baseline conditions and after increasing doses of methoxamine. Peripheral and superior mesenteric vascular resistance were calculated. RESULTS: Portacaval shunted rats showed a significantly lower peripheral and superior mesenteric vascular resistance and a significant reduction in their response to incremental doses of methoxamine than sham-operated controls. Chronic nitric oxide inhibition attenuated the systemic but not the splanchnic vasodilatation and totally corrected the hyposensitivity to methoxamine of portacaval-shunted rats. However, they still had a significantly lower peripheral and superior mesenteric vascular resistance than sham-operated rats. CONCLUSIONS: This study shows that the splanchnic and systemic hyporesponsiveness to methoxamine observed in portacaval-shunted rats could be explained by an excess of nitric oxide. However, other factors may be involved in maintaining splanchnic and systemic vasodilatation despite NO-inhibition.     

Analysis of pulmonary heme oxygenase-1 and nitric oxide synthase alterations in experimental hepatopulmonary syndrome

BACKGROUND & AIMS: Cirrhosis and portal hypertension due to chronic common bile duct ligation reproduce the features of human hepatopulmonary syndrome, whereas portal hypertension alone due to partial portal vein ligation does not. Nitric oxide contributes to experimental hepatopulmonary syndrome, but the nitric oxide synthase forms involved remain controversial. Recently, increased pulmonary heme oxygenase-1 expression and carbon monoxide production have also been found after common bile duct ligation. Our aim was to explore the role of the heme oxygenase-1/carbon monoxide pathway in the pathogenesis of experimental hepatopulmonary syndrome. METHODS: Pulmonary heme oxygenase-1 expression and distribution were assessed in sham; 3-week partial portal vein ligation; and 1-, 2-, 3-, 4-, and 5-week common bile duct ligation animals by Northern, Western and immunohistochemical analysis relative to endothelial and inducible nitric oxide synthase levels and to hepatopulmonary syndrome development. In vivo heme oxygenase enzyme inhibition with tin protoporphyrin IX in common bile duct ligation animals was used to define effects on intrapulmonary vasodilatation and arterial blood gases. RESULTS: Heme oxygenase-1 expression in pulmonary intravascular monocytes/macrophages and arterial carboxyhemoglobin levels increased progressively from 3 to 5 weeks after common bile duct ligation relative to controls (5-week protein levels were 15.94 +/- 1.75-fold those of sham animals; P < 0.001). Inducible nitric oxide synthase increased transiently in pulmonary intravascular monocytes/macrophages in 3-week common bile duct ligation animals, whereas pulmonary microvascular endothelial nitric oxide synthase increases began at 2 weeks and correlated with the onset of hepatopulmonary syndrome. Tin protoporphyrin treatment normalized carboxyhemoglobin and improved arterial blood gases and intrapulmonary vasodilatation, reflecting partial reversal of hepatopulmonary syndrome. CONCLUSIONS: The heme oxygenase-1/carbon monoxide system is an important contributor to the progression of experimental hepatopulmonary syndrome in addition to alterations in the endothelial nitric oxide synthase/nitric oxide pathway.     

Effect of verapamil on nitric oxide synthase in a portal veinligated rat model： Role of prostaglandin

AIM: To investigate the effects of verapamil on nitric oxide (NO) synthesis in a portal vein-ligated rat model. METHODS: Systemic and splanchnic hemodynamics were measured by radiolabeled microspheres in portal hypertensive rats after acute administration of verapamil (2 mg/kg) on chronic treatment with Nw-nitro-L-arginine (NNA)(80 mg/kg) and/or indomethacin (2 mg/kg) . RESULTS: Verapamil (2 mg/kg) caused a marked fall in both arterial pressure and cardiac output accompanied by an insignificant change in the portal pressure and no change in portal venous inflow. This result suggested that verapamil did not cause a reduction in portal vascular resistance of portal hypertensive rats, which was similar between NW- nitro-L-arginine-treated and indomethacin-treated groups. CONCLUSION: In portal hypertensive rats pretreated with NNA and/or indomethacin, acute verapamil administration can not reduce the portal pressure, suggesting that NO and prostaglandin play an important role in the pathogenesis of splanchnic arterial vasodilation in portal hypertension.     

The role of nitric oxide in the inhibition of gastric epithelial proliferation in portal hypertensive rats

BACKGROUND/AIM: Portal hypertension is associated with inhibition of gastric epithelial proliferation and increased gastric nitric oxide synthase activity. Whether the nitric oxide inhibits gastric epithelial proliferation is unclear. METHODS: Portal vein ligation was performed to induce portal hypertension in rats. The rats were treated for 7 days with either vehicle or N(G)-nitro-L-arginine methyl ester (L-NAME) at 5 mg/kg or 25 mg/kg doses (gastric gavage, twice a day). Sham-operated rats treated with vehicle served as controls. Hemodynamic parameters were measured using radiolabeled microspheres in anesthetized animals. Gastric epithelial proliferation was assessed by evaluating the proliferative cell nuclear antigen labeling index. RESULTS: The cardiac index and gastric fundic blood flow were higher, and the gastric fundic proliferative cell nuclear antigen labeling index was lower in the portal hypertensive rats than in the controls. In portal hypertensive rats, the 5 mg/kg dose of L-NAME decreased the cardiac index and increased the gastric fundic proliferative cell nuclear antigen labeling index to levels similar to those found in the controls, but did not affect gastric fundic blood flow significantly. The 25 mg/kg dose of L-NAME further decreased both the cardiac index and the gastric fundic blood flow, but did not affect the gastric proliferative cell nuclear antigen labeling index significantly. CONCLUSIONS: In portal hypertensive rats, the correction of systemic hyperdynamic circulation by NO inhibition is associated with normalization of gastric epithelial proliferation. Excessive nitric oxide may inhibit gastric epithelial proliferation in portal hypertension.     

The role of nitric oxide in the reduction of protein kinase C-induced contractile response in aortae from rats with portal hypertension

BACKGROUND/AIMS: Protein kinase C plays a role in the regulation of vascular cell contraction but its activity may be reduced by nitric oxide. In portal hypertension, the exact mechanism by which nitric oxide induces vascular hyporeactivity to vasoconstrictors is unclear. The aim of this study was to investigate the role of the interaction of nitric oxide and protein kinase C in the vascular reactivity in isolated aortae from portal vein-stenosed rats. METHODS/RESULTS: The contractile response to phorbol 12,13-dibutyrate, a protein kinase C activator, was significantly reduced in portal vein-stenosed aortae compared to sham-operated aortae. Preincubation with N-nitro-L-arginine or endothelium removal enhanced the response to phorbol 12,13-dibutyrate. The hyporesponsiveness to phorbol 12,13-dibutyrate in portal vein-stenosed rat aortae was only corrected after endothelium removal. The time course of contractions induced by phorbol 12,13-dibutyrate showed that the contraction was maintained for 2 h in sham-operated aortae and decreased to baseline in portal vein-stenosed rat aortae. This decrease was inhibited by N-nitro-L-arginine preincubation or endothelium removal. Protein kinase C downregulation caused a more marked reduction of phenylephrine-induced contraction in portal vein-stenosed aortae than in sham-operated aortae. The time course of total nitric oxide synthase activity in the presence of phorbol 12,13-dibutyrate showed a decrease in nitric oxide synthase activity after 30 min in both groups. Nitric oxide synthase activity remained stable for 120 min in sham-operated aortae but returned to basal level in portal vein-stenosed aortae. CONCLUSIONS: Hyporeactivity to vasoconstrictors in portal vein-stenosed rat aortae may be due, in part, to a decrease in protein kinase C activation caused by nitric oxide overproduction.     

Relationships between NOS2 and HO-1 in liver of rats with chronic bile duct ligation.

An increased expression and activity of the heme oxygenase-1 (HO-1) in the liver has been observed in models of hepatic damage. Nitric oxide (NO) seems to be involved in HO-1 regulation. The aim of this work is to assess HO-1 induction and heme oxygenase (HO) activity in rats with bile duct ligation (BDL). We have assessed the effect of chronic inhibition of the NO synthesis by N(G)-nitro-l-arginine methyl ester (l-NAME) on HO-1 induction and HO activity. In the BDL animals, compared with sham-operated ones, we found an increased plasma nitrite and bilirubin concentration, and a marked liver expression of inducible nitric oxide synthase and HO-1, assessed by both Western blot and immunohistochemistry. Chronic l-NAME treatment prevented plasma nitrite increase in animals subjected to BDL. BDL animals treated with l-NAME, compared with untreated BDL rats, showed an important decrease in HO-1 expression and in HO activity (assessed as a decreased plasma bilirubin and bilirubin excretion). In conclusion, our experiments show parallel changes in expression and activity of HO-1 and NOS2 activity in the BDL model of liver damage and suggest that increased NO production is involved in HO-1 overexpression.     

肝硬化大鼠内脏血管壁NOS分布的免疫组化研究

目的：观察肝硬化门静脉高压大鼠内脏动、静脉血管壁一氧化氮合酶（ＮＯＳ）的分布及染色强度变化,探讨ＮＯ在门静脉高压形成机制中的作用。方法：采用免疫组化染色法,应用两种ＮＯＳ特异性抗体,分别观察内皮型（ｅＮＯＳ）和诱生型（ｉＮＯＳ）ＮＯＳ的变化特点,并结合计算机图象分析系统对染色强度进行量化处理。结果：肝硬化大鼠肠系膜上动脉（ＳＭＡ）ｉＮＯＳ和ｅＮＯＳ染色强度与对照组相比均显著增加（Ｐ＜０．０１）,其中以ｅＮＯＳ增加更为明显。而两组门静脉（ＰＶ）ＮＯＳ染色强度则无明显差异（Ｐ＞０．０５）。肝硬化组ＳＭＡ的ＮＯＳ染色强度明显高于ＰＶ（Ｐ＜０．０５）。结论：ＮＯＳ在内脏血管表达增多,以及在ＳＭＡ的表达高于ＰＶ,提示ＮＯ可能主要通过扩张内脏动脉、增加内脏血流量而参与门静脉高压的形成。     

肝硬化大鼠内脏血管一氧化氮合酶基因表达及活性的动静脉差异

目的观察肝硬化内脏血管一氧化氮合酶(NOS)表达及活性的动静脉差异在门静脉高压形成机制中的意义.方法以四氯化碳皮下注射制备大鼠门静脉高压模型,应用免疫组织化学、化学发光以及RT-PCR分别检测大鼠门静脉(PV)和肠系膜动脉(MA)组织NOS的分布、活性及基因表达.结果肝硬化组大鼠PV和MA血管各层均有iNOS分布,而eNOS则局限于内皮层.肝硬化大鼠内脏血管NOS活性[pmol.min-1.mg-1.蛋白(PV 23.82±2.48,MA 43.46±4.93)]及mRNA表达均较对照组(PV 16.48±1.54,MA 16 95±2.34)显著升高(P＜0.05与0.01);同时肝硬化大鼠MA的总NOS活性和eNOS活性及eNOS mRNA表达均显著高于PV(P＜0.01).结论内脏血管eNOS亚型活性及表达增加可能在肝硬化时NO产生增多中起主要作用,而NOS活性及表达在MA与PV之间的动静脉差异,可能是NO参与门脉高压形成的重要机制之一.     

Nitric oxide synthase and heme oxygenase expressions in human liver cirrhosis

AIM:Portal hypertension is a common complication ofliver cirrhosis.Intrahepatic pressure can be elevatedin several ways.Abnormal architecture affectingthe vasculature,an increase in vasoconstrictors andincreased circulation from the splanchnic viscera intothe portal system may all contribute.It follows thatendogenous vasodilators may be able to alleviate thehypertension.We therefore aimed to investigate thelevels of endogenous vasodilators,nitric oxide(NO)andcarbon monoxide(CO)through the expression of nitricoxide synthase(NOS)and heme oxygenase(HO).METHOD:Cirrhotic(n=20)and non-cirrhotic(n=20)livers were obtained from patients whohad undergone surgery.The mRNA and proteinexpressions of the various isoforms of NOS and HOwere examined using competitive PCR,Western Blot andimmunohistochemistry.RESULTS:There was no significant change in eitherinducible NOS(iNOS)or neuronal NOS(nNOS)expressions while endothelial NOS(eNOS)was up-regulated in cirrhotic livers.Concomitantly,caveolin-1,anestablished down-regulator of eNOS,was up-regulated.Inducible HO-1 and constitutive HO-2 were found toshow increased expression in cirrhotic livers albeit indifferent localizations.CONCLUSION:The differences of NOS expressionmight be due to their differing roles in maintaining liverhomeostasis and/or involvement in the pathology ofcirrhosis.Sheer stress within the hypertensive liver mayinduce increased expression of eNOS.In turn,caveolin-1 is also increased.Whether this serves as a defensemechanism against further cirrhosis or is a consequenceof cirrhosis,is yet unknown.The elevated expressionof HO-1 and HO-2 suggest that CO may compensatein its role as a vasodilator albeit weakly.It is possiblethat CO and NO have parallel or coordinated functionswithin the liver and may work antagonistically in thepathophysiology of portal hypertension.     

Increased Gastric Bicarbonate Secretion in Portal Hypertensive Anesthetized Rats (Role of Prostaglandins and Nitric Oxide)

Gastric bicarbonate secretion might be modifiedin portal hypertension as a consequence of theintramucosal increase in prostaglandins and nitric oxidecontent. Therefore, we studied gastric bicarbonate secretion in control and portal hypertensiverats and investigated the role of prostaglandins andnitric oxide. Basal gastric bicarbonate secretion wasstudied in rats, using a gastric pH back-titration technique, two weeks after partial portal veinligation or a sham operation. The effects of thefollowing drugs were investigated: the prostaglandinsynthase inhibitor indomethacin (5 mg/kg intravenously), prostaglandin (PGE₂) (1 mg/kgintravenously), the nitric oxide synthase inhibitorsN^G-nitro-L-arginine methyl ester (LG NAME, 5mg/kg intravenously) andN^G-monomethyl-L-arginine (L-NMMA, 50 mg/kgintravenously), and the nitric oxide donor nitroprusside (5mmol/liter in the gastric perfusate). Plasma leakage inthe gastric wall was also measured after Evans blue dyeinjection in portal hypertensive and sham-operated rats pretreated by indomethacin (5 mg/kg,intravenously) and L-NAME (5 mg/kg, intravenously).Basal bicarbonate secretion was significantly increasedin portal hypertensive rats as compared to controls. After indomethacin, the bicarbonate secretionwas significantly reduced to a similar level in bothgroups. PGE₂ increased bicarbonate secretionsignificantly more in portal hypertensive rats than insham-operated rats. The NO synthase inhibitor L-NMMAsignificantly increased bicarbonate secretion in portalhypertensive rats only, while the other inhibitor,L-NAME, increased it significantly more in portalhypertensive than in the sham-operated rats. Plasma leakagein portal hypertensive rats, which was increased in thebasal condition as compared to control, was furtherenhanced by indomethacin but not by L-NAME pretreatment. The nitric oxide donor significantly reducedbicarbonate secretion in portal hypertensive rats toreach a similar level as in sham-operated rats. Basalgastric bicarbonate secretion is increased in portal hypertensive rats. This could be due to anenhanced prostaglandin mucosal level. Nitric oxide,which reduces bicarbonate secretion, may contribute tolimiting prostaglandin-induced bicarbonateoverproduction.     

Role of HSP-90 for increased nNOS-mediated vasodilation in mesenteric arteries in portal hypertension

AIM:To explore the role of heat shock protein-90 (HSP-90) for nitrergic vasorelaxation in the splanchnic circulation in rats with and without portal hypertension. METHODS: Neuronal nitric oxide synthase (nNOS) and HSP-90 were analyzed by immunofluorescence, western blotting and co-immunoprecipitation in the mesenteric vasculature and isolated nerves of portal-vein-ligated (PVL) rats and sham operated rats. In vitro perfused de-endothelialized mesenteric arterial vasculature was preconstricted with norepinep...