Increased heme oxygenase activity in splanchnic organs from portal hypertensive rats: role in modulating mesenteric vascular reactivity

BACKGROUND/AIMS: We have recently demonstrated that heme oxygenase-1 is upregulated in splanchnic organs of portal hypertensive rats. In the present study, we assessed whether heme oxygenase enzymatic activity is increased in splanchnic organs of portal hypertensive rats, and the relative contribution of heme oxygenase and nitric oxide synthase to the vascular hyporeactivity in portal hypertension. METHODS: Heme oxygenase activity was measured in splanchnic organs of portal hypertensive and sham-operated rats. The effects of heme oxygenase and nitric oxide synthase inhibition on pressure responses to potassium chloride and methoxamine were assessed in perfused mesenteric vascular beds of portal hypertensive and sham-operated rats. RESULTS: Heme oxygenase activity was increased in the mesentery, intestine, liver, and spleen of portal hypertensive rats. The hyporeactivity to potassium chloride in portal hypertensive rats was overcome after simultaneous inhibition of both heme oxygenase and nitric oxide synthase, but only partially attenuated after nitric oxide synthase inhibition alone. The hyporeactivity to methoxamine was completely reversed after nitric oxide synthase blockade. CONCLUSIONS: These results demonstrate that heme oxygenase activity is increased in splanchnic organs of portal hypertensive rats. They also suggest that heme oxygenase contributes to the hyporeactivity to potassium chloride, but not to methoxamine, in portal hypertensive rats.     

The role of nitric oxide in the vascular hyporesponsiveness to methoxamine in portal hypertensive rats.

This study examined whether an increased activity of the endothelium-derived relaxing factor, nitric oxide, may account for the hyporesponsiveness to vasoconstrictors in portal hypertension. We performed dose-response curves to methoxamine, an alpha-adrenoceptor agonist, with and without N omega-nitro-L-arginine, a specific inhibitor of nitric oxide synthesis, in experimental portal hypertension. Partial portal vein-ligated or sham-operated rats were pretreated with a continuous intravenous infusion of either N omega-nitro-L-arginine (50 micrograms.kg-1.min-1) or saline. Thirty minutes after starting the infusion of N omega-nitro-L-arginine or saline an infusion of methoxamine (10, 30 and 100 micrograms.kg-1.min-1) was added. Total peripheral resistance was calculated from mean arterial pressure and cardiac index. Repeated measurements of cardiac index were performed by a thermodilution technique. In portal vein-ligated rats pretreated with saline, the increase in total peripheral resistance after methoxamine infusion was significantly less than that of sham-operated rats (0.2 +/- 0.1 vs. 1.0 +/- 0.3, 0.6 +/- 0.1 vs. 1.6 +/- 0.3 and 3.7 +/- 0.5 vs. 6.1 +/- 0.7 mm Hg.ml-1.min.100 gm, p less than 0.05, methoxamine 10, 30 and 100 micrograms.kg-1.min-1, respectively). In the presence of N omega-nitro-L-arginine, the change in total peripheral resistance after methoxamine infusion was similar in both groups (p greater than 0.05). In conclusion, this study demonstrates that a vascular hyporesponsiveness to methoxamine is present in portal vein-ligated rats and that this hyporesponsiveness is reversed by blockade of nitric oxide.(ABSTRACT TRUNCATED AT 250 WORDS)     

Systemic and splanchnic haemodynamic effects of sildenafil in an in vivo animal model of cirrhosis support for a risk in cirrhotic patients.

OBJECTIVES: Sildenafil is a selective inhibitor of the cGMP-specific phosphodiesterase type V (PDE-V) in the corpus cavernosum. PDE-V is also present in the mesenteric artery. Cirrhosis is complicated by a splanchnic vasodilation attributed to a local overproduction of nitric oxide (NO). As sildenafil potentiates the effects of NO, it may further decrease mesenteric vascular tone and increase portal venous blood flow. The aim is to evaluate the effects of sildenafil on the systemic and splanchnic haemodynamics in an experimental model of cirrhosis. METHODS: Secondary biliary cirrhosis was induced in male Wistar rats by common bile duct ligation (CBDL, n=8); control rats were sham-operated (sham, n=7). The mean arterial pressure (MAP), portal venous pressure (PVP) and arterial mesenteric blood flow (MBF) were measured after intramesenteric (0.01-10 mg/kg) and after intravenous (i.v.) (0.01-10 mg/kg) administration of sildenafil. RESULTS: Baseline PVP was significantly higher in CBDL than in sham rats, whereas baseline MAP tended to be lower and MBF tended to be higher in CBDL compared with sham rats. Both intramesenteric and i.v. injection of sildenafil significantly decreased MAP and increased MBF and PVP in a dose-dependent way. The decrease in MAP was significantly less important in CBDL than in sham rats. The increase in MBF was importantly lower in CBDL than in sham rats. PVP tended to increase more significantly in sham rats than in CBDL. CONCLUSION: Sildenafil increases MBF and PVP and induces systemic hypotension. The effects are less pronounced in cirrhosis, suggesting vascular hyporesponsiveness to sildenafil. Although the rise in PVP in cirrhotic animals is smaller than in controls, it may present a risk for haemorrhagic complications. Further studies are necessary before prescribing sildenafil to patients with cirrhosis.     

Modulation of the hyperdynamic circulation of cirrhotic rats by nitric oxide inhibition.

The effects of NG-monomethyl-L-arginine (L-NMMA), an inhibitor of nitric oxide (NO) biosynthesis on the splanchnic and systemic circulation, were investigated in rats with cirrhosis induced by carbon tetrachloride. Portal hypertension in these rats was accompanied by decreased arterial blood pressure and peripheral vascular resistance as well as by splanchnic vasodilation with increased portal venous inflow and decreased splanchnic resistance. Intravenous bolus administration of L-NMMA (25 mg/kg) significantly increased systemic blood pressure and decreased cardiac output. L-NMMA also significantly increased systemic and splanchnic vascular resistance; whereas blood flow to the stomach, small intestine, colon, pancreas, mesentery, spleen, and kidney was decreased significantly. L-NMMA did not alter the portal pressure or portosystemic shunting in these cirrhotic rats, yet portal vascular resistance increased, suggesting effects on the intrahepatic and collateral circulation. Pretreatment with L-arginine (300 mg/kg) prevented the hemodynamic changes induced by L-NMMA. These findings support the concept that local excess formation of NO contributes to changes in splanchnic circulation associated with portal hypertension in cirrhosis.     

Effects of inhibition of nitric oxide formation on regional blood flow in experimental myocardial infarction.

BACKGROUND. Large myocardial infarction is associated with reactive hypertrophy and dilation of the left ventricle, depressed coronary flow reserve, and the development of heart failure including systemic vasoconstriction. We hypothetized that changes in endothelial function, e.g., in the synthesis or action of nitric oxide in the coronary and peripheral vasculatures, might be involved in the depressed coronary flow reserve and increased systemic vascular resistance observed in postinfarction myocardial hypertrophy and failure. METHODS AND RESULTS. The regional blood flow changes that occur as a result of inhibiting the basal release of nitric oxide with NG-monomethyl-L-arginine (L-NMMA) and how this regional pattern may be altered in large MI (infarct size, 30-51% of left ventricle) were examined. Measurements were made 24 hours and 8 weeks after myocardial infarction or sham operation in conscious rats. The left ventricular end-diastolic pressure and effects of L-NMMA on left ventricular end-diastolic pressure was similar 24 hours and 8 weeks after myocardial infarction. The effects of L-NMMA (30 mg/kg i.v.) on heart rate and blood pressure were similar in infarcted and sham animals. L-NMMA exerted a marked vasoconstriction in the renal, splanchnic, cutaneous, and cerebral circulations of similar magnitude in sham-operated rats and animals with myocardial infarction. The coronary vasoconstrictor effect of L-NMMA was attenuated significantly in the hypertrophied right and noninfarcted left ventricle of 8-week-old infarcted rats (p less than 0.01 versus sham-operated animals) but not 24 hours after induction of myocardial infarction when cardiac hypertrophy has not yet developed. The increase in left ventricular coronary resistance in 8-week-old infarcted animals was inversely related to infarct size (r = -0.787, p = 0.012, n = 9). Nitroglycerin exerted similar increases in coronary blood flow in rats with chronic myocardial infarction and sham-operated animals, arguing against a reduced vascular responsiveness to nitric oxide. Transmission electron microscopy of coronary resistance vessels in 8-week-old infarcted animals did not reveal endothelial abnormalities. CONCLUSIONS. These data suggest that the basal release of nitric oxide in the renal, intestinal, and cutaneous circulations is not affected adversely in this model of myocardial infarction and failure. However, the blunted coronary vasoconstrictor effect of L-NMMA late after large myocardial infarction supports the view that the basal release of nitric oxide is impaired in postinfarction reactive cardiac hypertrophy.     

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.     

In vitro and in vivo vascular responses to the L-type calcium channel activator, Bay K 8644, in rats with cirrhosis

A substance which increases the entry of extracellular calcium into arterial smooth muscle may decrease cirrhosis-induced vasodilation. The aim of the present study was to measure the effects of the L-type Ca²⁺ channel activator, Bay K 8644, on the haemodynamics of rats with cirrhosis. Vascular reactivity to this substance was also investigated. Splanchnic and systemic haemodynamic responses to Bay K 8644 (50 μg/kg) were measured in cirrhotic and normal rats. Contraction induced by 0.1 μmol/L Bay K 8644 was measured in arterial rings (aorta and superior mesenteric artery) from cirrhotic and normal rats. In cirrhotic rats, Bay K 8644 significantly decreased portal pressure (15%) and portal tributary blood flow (24%), significantly increased portal territory vascular resistance (54%) and did not significantly change hepatocollateral vascular resistance. Bay K 8644 significantly increased arterial pressure (7%) and systemic vascular resistance (24%) and did not change the cardiac index. In normal rats, Bay K 8644 significantly increased vascular resistance (150%) in portal, hepatocollateral and systemic territories and significantly decreased the cardiac index (44%). Changes in portal territory, hepatocollateral and systemic vascular resistances were significantly less marked in cirrhotic than in normal rats. In rings from the aorta and superior mesenteric artery, Bay K 8644-induced contraction was significantly lower in cirrhotic than in normal rats. In conclusion, in rats with cirrhosis, Bay K 8644 administration reduced vasodilation in splanchnic and systemic arteries and did not affect hepatocollateral vascular resistance. The Bay K 8644-induced reduction in splanchnic vasodilation caused a decrease in portal hypertension. This study also shows that Bay K 8644-induced vascular contraction was less marked in cirrhotic than in normal rats, in systemic and splanchnic vascular beds.     

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.     

The role of nitric oxide in the pathogenesis of systemic and splanchnic vasodilation in cirrhotic rats before and after the onset of ascites.

BACKGROUND: The role of nitric oxide (NO) in the pathogenesis of splanchnic arterial vasodilation in cirrhosis has been recently debated by some experimental studies. AIMS: We investigated the role of NO in the pathogenesis of the splanchnic arterial vasodilation along the course of CCl(4)-induced experimental cirrhosis. METHODS: We analyzed the effect on mean arterial pressure (MAP), cardiac output (CO), total peripheral resistance (TPR), and resistance in the superior mesenteric artery (RSMA), before and after the administration of a unspecific NO synthase (NOS) inhibitor (Nomega-nitro-L-arginine-methyl-ester, L-NAME) and a specific NOS2 inhibitor (L-N-(1-iminoethyl)-lysine, L-NIL) to cirrhotic rats with and without ascites, and to control rats. NOS2 and NOS3 protein expression was also assessed in systemic and splanchnic arteries of these animals. RESULTS: L-NAME in cirrhotic rats markedly improved MAP, and TPR and decreased CO regardless of whether they had ascites or not. L-NIL did not produce any significant effect on systemic haemodynamics in control and cirrhotic rats. NOS3 overexpression in the aorta of cirrhotic animals paralleled the progression of the liver disease. L-NAME increased RSMA in cirrhotic rats, but this effect was much less intense in rats with ascites. L-NIL had an effect only on RSMA in rats with ascites, which was of a similar extent to that produced by L-NAME. Western blot experiment showed a faint overexpression of NOS3 in the mesenteric artery of cirrhotic rats with and without ascites and a clear induction of NOS2 only in the mesenteric artery of rats with ascites. Conclusions: These results indicate that NO contributes significantly to the pathogenesis of arterial splanchnic circulation in the early stages of experimental cirrhosis but has only a minor role in its maintenance after the development of ascites. Furthermore, the expression of the different NOS isoforms varies along the course of the liver disease.     

Adenosine receptor blockade reduces splanchnic hyperemia in cirrhotic rats.

To explore a possible role for adenosine in the pathogenesis of the splanchnic hyperemia of cirrhosis, we administered 8-phenyltheophylline, a specific adenosine receptor antagonist, to rats with biliary cirrhosis caused by bile duct ligation and to control sham-operated rats. Micro-Doppler flow studies showed that a 10-mumol/kg dose of 8-phenyltheophylline completely abolished the superior mesenteric hyperemic response to infusions of exogenous adenosine in both cirrhotic and control rats. Analysis of regional blood flows by radioactive microspheres demonstrated that this dose of 8-phenyltheophylline in cirrhotic rats significantly increased portal tributary vascular resistance by 60% and decreased portal tributary blood flow by 26%. This decrease was entirely the result of a 42% reduction in the intestinal blood flow. 8-phenyltheophylline did not affect cardiac output, arterial pressure or any other extrasplanchnic hemodynamic variables in cirrhotic rats. No detectable effect of 8-phenyltheophylline was seen in sham-operated rats. These results suggest that adenosine may be involved in the genesis of splanchnic hyperemia in cirrhotic rats.     

Intraportal administration of glyceryl trinitrate or nitroprusside exerts more systemic than intrahepatic effects in anaesthetised cirrhotic rats.

BACKGROUND/AIMS: Increased intrahepatic vascular tone can be pharmacologically manipulated in isolated cirrhotic livers. Intrahepatic endothelial dysfunction may lead to a decreased production of the potent endogenous vasodilator nitric oxide in cirrhotic livers. The aims of the study were to determine whether portal pressure can be lowered in vivo by injecting nitric oxide donors glyceryl trinitrate or nitroprusside directly in the portal vein and whether this is related to a decrease in intrahepatic resistance. METHODS: In anaesthetised CCl4 cirrhotic rats, intraportal doses of glyceryl trinitrate 0.5, 1 or 5 microg/kg/ min or nitroprusside 1, 5 or 10 microg/kg/min did not decrease portal pressure but only arterial pressure. Systemic and splanchnic haemodynamics were measured before and during 15 min intraportal infusion of glyceryl trinitrate 10 microg/kg/min or nitroprusside 20 microg/kg/min. RESULTS: Glyceryl trinitrate decreased portal pressure from 14.0+/-1.1 to 11.8+/-1.4 mm Hg, splanchnic perfusion pressure from 102+/-10 to 74+/-5 mm Hg and portal sinusoidal flow from 2.11+/-0.38 to 1.70+/-0.35 ml/min/g liver (all p<0.05). Nitroprusside did not decrease portal pressure significantly but led to a reduction of the splanchnic perfusion pressure (104+/-9 to 66+/-7 mm Hg) and the portal sinusoidal flow (2.39+/-0.50 to 1.77+/-0.31 ml/min/g liver; all p<0.05). Portal sinusoidal resistance was not altered by either drug. CONCLUSIONS: Intraportal infusion of nitric oxide donors decreased arterial pressure more than portal pressure. Portal sinusoidal resistance remained unaffected, but the liver parenchyma became less perfused with high doses. The systemic effects of nitric oxide donating drugs prevailed.     

Hepatic and splanchnic nitric oxide activity in patients with cirrhosis

BACKGROUND: In animal models of cirrhosis, altered activity of nitric oxide (NO) has been implicated in the pathogenesis of increased intrahepatic portal vascular resistance and abnormal mesenteric vasodilatation. AIMS: To investigate NO activity in the liver and splanchnic vascular bed of patients with cirrhosis. METHODS: Activity of the calcium dependent constitutive and calcium independent inducible isoforms of NO synthase (cNOS and iNOS, respectively) was assayed biochemically in biopsy specimens of liver and a vascular portion of the greater omentum (representative of mesenteric vasculature) obtained from patients with cirrhosis undergoing liver transplantation (n=14) and non-cirrhotic control patients undergoing liver resection for metastases (n=9). The concentration of NO metabolites (NO2 + NO3) in portal and peripheral venous plasma was measured. RESULTS: The activity of cNOS was lower in cirrhotic compared with non-cirrhotic subjects for both liver and omentum. Hepatic and omental iNOS activities did not differ significantly between the two groups. Portal (NO2 + NO3) was threefold higher in cirrhotic than non-cirrhotic patients, but no differences were observed in systemic venous samples from the two groups. CONCLUSIONS: The activity of cNOS is diminished in the cirrhotic human liver. The resultant decrease in constitutive NO release may promote an increase in the intrahepatic portal vascular resistance. Elevated portal venous (NO2 + NO3) indicates enhanced splanchnic vascular release of NO in cirrhotic patients, but the absence of increased NOS activity in the mesenteric vasculature suggests differential regulation of NO synthesis within the splanchnic vascular bed.     

NAD(P)H oxidase modulates angiogenesis and the development of portosystemic collaterals and splanchnic hyperaemia in portal hypertensive rats

BACKGROUND: Recent studies have shown the presence of vascular endothelial growth factor (VEGF)-dependent splanchnic angiogenesis in experimental models of portal hypertension, and the role of such neovascularisation on the development of both portosystemic collaterals and hyperdynamic splanchnic circulation. However, the mechanisms modulating angiogenesis in portal hypertension are unknown. Experimental evidence indicates that NAD(P)H oxidase is required for VEGF-induced angiogenesis. Interestingly, we have recently shown that splanchnic NAD(P)H oxidase activity is significantly increased in portal hypertensive rats. Therefore, it could be possible that activated NAD(P)H oxidases modulate angiogenesis in portal hypertension. AIM: To determine the effects of chronic NAD(P)H oxidase inhibition on angiogenesis and splanchnic haemodynamics in portal hypertensive rats. METHODS: Partial portal vein-ligated and sham-operated rats were treated with the NAD(P)H oxidase inhibitor apocynin, or with vehicle for 5 days. Then, the expression of angiogenesis markers (western blotting), the formation of portosystemic collaterals (radioactive microspheres) and the production of superoxide anion (lucigenin-enhanced chemiluminescence) were determined. Mean arterial pressure, portal pressure, and superior mesenteric arterial blood flow and resistance were also measured. RESULTS: In portal hypertensive rats, NAD(P)H oxidase blockade significantly decreased portosystemic collateral formation, and superior mesenteric arterial flow. It also reduced the splanchnic expression of VEGF, VEGF receptor-2 and CD31, and attenuated the increased production of superoxide, compared with vehicle. CONCLUSIONS: NAD(P)H oxidase plays an important role in experimental portal hypertension, modulating splanchnic angiogenesis, the formation of portosystemic collaterals and the development of splanchnic hyperdynamic circulation. These results suggest that NAD(P)H oxidase may represent a new target in the treatment of portal hypertension.     

Hemodynamic characterization of arterialized and nonarterialized liver transplants in the rat.

Persistent hyperkinetic circulation after liver transplantation has been described in humans, but similar changes have not been well characterized in the rat model. This study aimed to investigate the hemodynamics of the systemic and splanchnic circulations in both arterialized and nonarterialized hepatic allografts. Orthotopic liver transplantation was performed in four groups of Sprague-Dawley rats. Group A comprised sham-operated rats with hepatic artery ligation that did not receive transplants; group B comprised rats that received transplants without arterialization; group C comprised sham-operated rats with intact hepatic artery that did not receive transplants; and group D comprised rats that received transplants with arterialization. Blood flow measurements were performed three weeks after the surgical procedure, using the radioactive microsphere method. The results showed that rats that received transplants exhibited a significantly higher cardiac index and lower systemic vascular resistance than the control rats. Splanchnic hyperemia was also present with increased mesenteric blood flow. However, there was no difference in hemodynamics between rats that received arterialized transplants and those that received nonarterialized transplants. Arterial collateral vessels from adjacent tissues were observed in the nonarterialized grafts; this was confirmed histologically. It is concluded that rats that undergo orthotopic liver transplantation exhibit hyperdynamic circulation, regardless of the arterial reconstruction procedure, possibly due to extensive collateral formation in the hepatosplanchnic circulation.     

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.     

Vascular,hemodynamic and renal effects of low‐dose losartan in rats with secondary biliary cirrhosis

Background: In cirrhosis, splanchnic and systemic vasodilatation induce a hyperdynamic circulatory dysfunction, portal hypertension and renal sodium retention. This vasodilatation is in part because of an impaired vascular response to α1‐adrenoceptor agonists. Recently, the angiotensin II type 1‐receptor antagonist losartan has been shown to attenuate portal hypertension. We hypothesized that losartan decreases portal pressure by counteracting the impaired vascular responsive to α1‐adrenoceptor agonists. Methods: We studied, in rats with secondary biliary cirrhosis and sham‐operated rats, the effect of 0.5 and 10 mg losartan/kg × day on aortic responsiveness to α1‐adrenoceptor stimulation with methoxamine and angiotensin II (myograph), splanchnic and systemic hemodynamics (colored microspheres), plasma noradrenaline levels and kidney function. Results: In cirrhotic rats, 10 mg losartan/kg × day completely inhibited aortic contractility to angiotensin II, decreased vascular resistance and arterial pressure and induced renal failure. In contrast, 0.5 mg losartan/kg × day only partially inhibited aortic contractility to angiotensin II, but improved aortic contractility to methoxamine, increased splanchnic and systemic vascular resistance, decreased portal pressure, decreased plasma norepinephrine levels and induced natriuresis. Conclusions: In cirrhotic rats, losartan at a very low dose increases splanchnic vascular resistance, decreases portal pressure and improves kidney function, possibly by an increased vascular responsiveness to α1‐adrenoceptor agonists.     

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.     

Lack of effect of norfloxacin on hyperdynamic circulation in bile duct‐ligated rats despite reduction of endothelial nitric oxide synthase function: result of unchanged vascular Rho‐kinase?

Background/Aims: In cirrhosis, portal hypertension is maintained by splanchnic vasodilation owing to overproduction of the vasodilator nitric oxide (NO) and defective contractile signalling by Rho‐kinase. NO overproduction is partially caused by bacterial translocation from the gut to mesenteric lymph nodes. However, the effects of intestinal bacterial decontamination on hyperdynamic circulation or vascular contractility are unknown. We investigated the haemodynamic and vascular effects of norfloxacin in rats with secondary biliary cirrhosis. Methods: Cirrhosis was induced by bile duct ligation (BDL). One group was treated with norfloxacin (20 mg/kg/day, 5 days, orally). Bacterial growth in the lymph nodes was determined on blood agar plates. Invasive haemodynamic measurements were combined with coloured microspheres. Aortic contractility was assessed myographically. Protein expression/phosphorylation was examined by Western blot analysis. Results: Norfloxacin treatment of BDL rats abolished bacterial translocation to mesenteric lymph nodes. BDL rats had hyperdynamic circulation, including portal hypertension and splanchnic vasodilation. None of these parameters was changed by norfloxacin, although norfloxacin reduced endothelial NO synthase expression and phosphorylation. The latter was associated with a diminished activity of protein kinase G (PKG), which mediates NO‐induced vasodilation. However, norfloxacin had no effect on aortic contractility to methoxamine or Ca²⁺, or the aortic expression of RhoA, Rho‐kinase and β‐arrestin 2, or the phosphorylation of the Rho‐kinase substrate moesin. Conclusions: Short‐term treatment of BDL rats with norfloxacin does not change hyperdynamic circulation or vascular contractility, despite reduction of PKG activity.