NO as an indicator of portal hemodynamics and the role of iNOS in increased NO production in CCl4-induced liver cirrhosis

Does Biliodigestive Anastomosis Have Any Effect on the Reversal of Hepatopulmonary Syndrome in a Biliary Cirrhosis Experimental Model?

BACKGROUND

Biliary cirrhosis is associated with hepatopulmonary syndrome (HPS), which is related to increased posttransplant morbidity and mortality.

AIMS

This study aims to analyze the pathophysiology of biliary cirrhosis and the onset of HPS.

METHODS

Twenty-one-day-old Wistar rats were subjected to common bile duct ligation and were allocated to two groups: group A (killed 2, 3, 4, 5, or 6 weeks after biliary obstruction) and group B (subjected to biliodigestive anastomosis 2, 3, 4, 5, or 6 weeks after the first procedure and killed 3 weeks later). At the killing, arterial blood was collected for the analyses, and samples from the liver and lungs were collected for histologic and molecular analyses. The gasometric parameters as well as the expression levels of ET-1, eNOS, and NOS genes in the lung tissue were evaluated.

RESULTS

From a total of 42 blood samples, 15 showed hypoxemia (pO₂ < 85 mmHg) and 17 showed an increased oxygen gradient [p (A-a) O₂ > 18 mmHg]. The liver histology revealed increased ductular proliferation after common bile duct ligation, and reconstruction of bile flow promoted decreased ductular proliferation 5 and 6 weeks post-common bile duct ligation. Pulmonary alterations consisted of decreased parenchymal airspace and increased medial wall thickness. Biliary desobstruction promoted transitory improvements 5 weeks after biliary obstruction (increased parenchymal airspace and decreased MWT-p = 0.003 and p = 0.004, respectively) as well as increased endothelin expression levels (p = 0.009).

CONCLUSIONS

The present model showed lung tissue alterations promoted by biliary obstruction. The biliodigestive anastomosis had no clear direct effects on these alterations.

Current scenario for the hepatoprotective effects of Inchinkoto, a traditional herbal medicine, and its clinical application in liver surgery: A review

Inchinkoto (ICKT) is one of the most commonly used herbal medicines as a hepatoprotective agent. Among the numerous chemical compounds included in ICKT, geniposide is the most abundant component. Geniposide, after p.o. intake, is converted to the active metabolite genipin by intestinal bacteria and is absorbed in the portal circulation. The biological properties of ICKT and genipin have been studied in numerous experiments. Administration of ICKT or genipin exerts choleretic effects through upregulation of multidrug resistance-associated protein 2 in hepatocytes. ICKT also exerts an anti-apoptotic action through inhibition of transforming growth factor-β1- or tumor necrosis factor-α-dependent signaling pathways. The excessive inflammatory response induced by various hepatic stresses is also attenuated by ICKT pre-administration. Moreover, ICKT upregulates antioxidant enzymes in the liver under conditions of oxidative stress. These experimental results suggest potential benefit of ICKT in liver disease and particularly in hepatic surgery, which justify further well-designed controlled clinical study. To date, however, clinical data regarding the benefit of ICKT for liver surgery are rare. This review article summarized and discussed recent evidence relating to the hepatoprotective effects of ICKT in the field of basic and clinical science.

S-nitrosothiol signaling regulates liver development and improves outcome following toxic liver injury

Toxic liver injury is a leading cause of liver failure and death because of the organ's inability to regenerate amidst massive cell death, and few therapeutic options exist. The mechanisms coordinating damage protection and repair are poorly understood. Here, we show that S-nitrosothiols regulate liver growth during development and after injury in vivo; in zebrafish, nitric-oxide (NO) enhanced liver formation independently of cGMP-mediated vasoactive effects. After acetaminophen (APAP) exposure, inhibition of the enzymatic regulator S-nitrosoglutathione reductase (GSNOR) minimized toxic liver damage, increased cell proliferation, and improved survival through sustained activation of the cytoprotective Nrf2 pathway. Preclinical studies of APAP injury in GSNOR-deficient mice confirmed conservation of hepatoprotective properties of S-nitrosothiol signaling across vertebrates; a GSNOR-specific inhibitor improved liver histology and acted with the approved therapy N-acetylcysteine to expand the therapeutic time window and improve outcome. These studies demonstrate that GSNOR inhibitors will be beneficial therapeutic candidates for treating liver injury.

Chronological changes in renal vascular reactivity in portal hypertensive rats

BACKGROUND

Circulatory dysfunction in portal hypertension is characterized by increased cardiac output, decreased systemic vascular resistance, a fall in mean arterial pressure secondary to splanchnic and systemic vasodilation and hence renal hypoperfusion. Previous studies have disclosed that renal vasculatures of portal hypertensive rats had lower perfusion pressure and hyporesponsiveness to endogenous vasoconstrictors. However, the sequences of altered renal haemodynamics have never been described. This study aimed to explore the evolution of renal vascular hyporeactivity and associated mechanisms during portal hypertension.

MATERIALS AND METHODS

All rats were randomized into partial portal vein ligation (PVL) or shamed surgery. Isolated kidney perfusion was performed at postoperative day 1, 4, 7 and 14, respectively, to evaluate chronologically renal vascular response to endothelin-1. Renal arteries and kidneys were harvested for further analysis.

RESULTS

Impaired renal vascular reactivity to endothelin-1 developed 1 week following PVL. There were extensive up-regulations of vasodilative nitric oxide synthase (NOS) and cyclooxygenase-2 in renal arteries of PVL rats. Among them, the changes in endothelial NOS paralleled with the evolution of renal vascular hyporesponsiveness. Preincubation of NOS inhibitor attenuated the renal vascular hyporeactivity in PVL rats. Up-regulated NOS and down-regulated cyclooxygenase-2 in kidneys of PVL rats might play a critical role to maintain renal circulation and body fluid homoeostasis in response to systemic hypotension.

CONCLUSIONS

This investigation highlights the versatile nature of renal vasculatures in portal hypertension, which is replete with compensatory mechanisms. It may help to unveil potential mechanisms of severe renal dysfunction in advanced liver disease.

Role of endothelial nitric oxide synthase in the development of portal hypertension in the carbon tetrachloride-induced liver fibrosis model

Portal hypertension (PHT) is a complication of liver cirrhosis and directly increases mortality and morbidity by increasing the propensity of venous hemorrhage. There are two main underlying causations for PHT, increased hepatic resistance and systemic hyperdynamic circulation. Both are related to localized aberrations in endothelial nitric oxide synthase (eNOS) function and NO biosynthesis. This study investigates the importance of eNOS and systemic hyperdynamic-associated hyperemia to better understand the pathophysiology of PHT. Wild-type and eNOS(-/-) mice were given the hepatotoxin CCl(4) for 4-12 wk. Hepatic fibrosis was determined histologically following collagen staining. Portal venous pressure, hepatic resistance, and hyperemia were determined by measuring splenic pulp pressure (SPP), hepatic portal-venous perfusion pressure (HPVPP), abdominal aortic flow (Qao), and portal venous flow (Qpv). Hepatic fibrosis developed equally in wild-type and eNOS(-/-) CCl(4)-exposed mice. SPP, Qao, and Qpv increased rapidly in wild-type CCl(4)-exposed mice, but HPVPP did not. In eNOS(-/-) CCl(4) mice, Qao was not increased, SPP was partially increased, and HPVPP and Qpv were increased nonsignificantly. We concluded that the systemic hyperemia component of hyperdynamic circulation is eNOS dependent and precedes increased changes in hepatic resistance. Alternative mechanisms, possibly involving cyclooxygenase, may contribute. eNOS maintains normal hepatic resistance following CCl(4)-induced fibrosis. Consequently, increased portal pressure following chronic CCl(4) exposure is linked to hyperdynamic circulation in wild-type mice and increased hepatic resistance in eNOS(-/-) mice.

Expression of inducible nitric oxide (NO) synthase but not prevention by its gene ablation of hepatocarcinogenesis with fibrosis caused by a choline-deficient, L-amino acid-defined diet in rats and mice

Expression of inducible nitric oxide synthase (iNOS) and effects of iNOS gene ablation on the hepatocarcinogenesis associated with fibrosis caused by a choline-deficient, L-amino acid-defined (CDAA) diet, were examined in male F344 rats and C57BL/6J wild-type and iNOS-/- mice. Western blot, RT-PCR and immunohistochemical analyses revealed increased expression of iNOS protein and mRNA in the livers of rats and wild-type mice fed a CDAA diet for 12-80 weeks, associated with elevated serum NO(x) and liver nitrotyrosine levels. iNOS-/- mice demonstrated greater liver injury and fibrosis in the early stage than their wild-type counterparts, but this did not significantly affect the incidence and multiplicity of altered foci, adenomas and hepatocellular carcinomas in spite of immunohistochemical iNOS expression in these lesions. Results suggested no major determinant roles of the expressed iNOS in the development of liver tumors caused by the CDAA diet.

Overexpression of inducible nitric oxide synthase in gastric mucosa of rats with portal hypertension: correlation with gastric mucosal damage

BACKGROUND

An increased biosynthesis of nitric oxide (NO) has been implicated in the hyperdynamic circulation and development of collaterals of portal hypertension (PHT) because of its potent vasodilatory effects. NO is synthesized from L-arginine by three different isozymes of nitric oxide synthase (nNOS, iNOS and eNOS). Thus, the expression of inducible NOS (iNOS) might account for NO overproduction in PHT. However, in previous investigations, the role of iNOS in the pathogenesis of PHT gastropathy remained controversial. Our current study was in both molecular and protein levels to determine whether the expression of iNOS is responsible for PHT gastropathy.

MATERIALS AND METHODS

PHT was induced experimentally by partial ligation of the portal vein. Fourteen days after partial ligation of the portal vein, the rats were randomly assigned to receive either vehicle or L-NAME (NOS inhibitor) at doses of 5 mg/kg/day, 10 mg/kg/day, or 25 mg/kg/day by gastric lavage twice a day for 1 week. Sham operated rats served as controls. Northern hybridization and in situ hybridization are used to compare the expression of gastric mucosa iNOS mRNA in the PHT rats and the controls. NO was measured by the Griess method after reduction of nitrate to nitrite with nitrate reductase. Immunohistochemical staining was carried out to detect the iNOS protein. In addition, the severity of gross gastric mucosal lesions was evaluated macroscopically by a gross ulcer index.

RESULTS

The iNOS expression at both mRNA and protein was prominently increased in PHT rats, accompanied with the enhanced NO production. The gastric mucosa iNOS mRNA and serum NO levels were significantly decreased after L-NAME administration (P < 0.05). However, the markedly reduced gastric mucosal damage in PHT rats was observed only at high does of L-NAME (25 mg/kg/day) administration.

CONCLUSION

PHT triggers overexpression of iNOS mRNA and proteins in rat gastric mucosa, but that this alone does not account for PHT gastropathy.

Intrapulmonary vascular dilatation and nitric oxide in hypoxemic rats with chronic bile duct ligation

BACKGROUND/AIMS

Nitric oxide (NO) has been suggested as the major cause of pulmonary vascular dilatation and hypoxemia in hepatopulmonary syndrome (HPS). The aim of this study was to assess the effect of NO on arterial oxygenation in rats with common bile duct ligation (CBDL rats), a model of HPS.

METHODS

Arterial blood gases were measured in 44 CBDL rats and 44 Sham rats under unrestrained conditions. Intrapulmonary shunting was assessed with (141)Ce-labeled microspheres (15-mum diameter) and serum nitrate/nitrite levels were measured by HPLC. The effect of NOS inhibition on A-aDO(2) was studied using L-NAME.

RESULTS

A decrease of PaO(2) below 82.7 mmHg (the mean value-2sigma in Sham rats) was seen in 43% of CBDL rats. Intrapulmonary shunting was greater in CBDL rats than in Sham rats (P<0.001). A correlation between the extent of shunting and A-aDO(2) was found in all animals studied (r=0.89, P<0.001, n=16). Serum levels of nitrate/nitrite increased significantly across the lungs, and the increase was significantly correlated with A-aDO(2) in the total population of animals studied. Administration of L-NAME to CBDL rats achieved a significant improvement of A-aDO(2).

CONCLUSIONS

These results suggest that pulmonary vascular dilatation due to NO leads to hypoxemia in CBDL rats.

The role of nitric oxide synthase isoforms in extrahepatic portal hypertension: studies in gene-knockout mice

BACKGROUND & AIMS

Considerable debate exists concerning which isoform of nitric oxide synthase (NOS) is responsible for the increased production of NO in PHT. We used the portal vein ligation model of PHT in wild-type and eNOS- or iNOS-knockout mice to definitively determine the contribution of these isoforms in the development of PHT.

METHODS

The portal vein of wild-type mice, or those with targeted mutations in the nos2 gene (iNOS) or the nos3 gene (eNOS), was ligated and portal venous pressure (Ppv), abdominal aortic blood flow (Qao), and portosystemic shunt determined 2 weeks later.

RESULTS

In wild-type mice, as compared with sham-operated controls, portal vein ligation (PVL) resulted in a time-dependent increase in Ppv (7.72 +/- 0.37 vs 17.57 +/- 0.51 cmH(2)O, at 14 days) concomitant with a significant increase in Qao (0.12 +/- 0.003 vs 0.227 +/- 0.005 mL/min/g) and portosystemic shunt (0.47% +/- 0.01% vs 84.13% +/- 0.09% shunt). Likewise, PVL in iNOS-deficient mice resulted in similar increases in Ppv, Qao, and shunt development. In contrast, after PVL in eNOS-deficient animals, there was no significant change in Ppv (7.52 +/- 0.22 vs 8.07 +/- 0.4 cmH(2)0) or Qao (0.111 +/- 0.01 vs 0.14 +/-.023 mL/min/g). However, eNOS (-/-) mice did develop a substantial portosystemic shunt (0.33% +/- 0.005% vs 84.53% +/- 0.19% shunt), comparable to that seen in wild-type animals after PVL.

CONCLUSIONS

These data support a key role for eNOS, rather than iNOS, in the pathogenesis of PHT.

Endothelial, but not the inducible, nitric oxide synthase is detectable in normal and portal hypertensive rats

BACKGROUND

Chronic portal hypertension is accompanied by a nitric oxide (NO) dependent vasodilation. Three isoforms of NO producing synthases (NOS) are characterized: neuronal NOS (nNOS), endothelial NOS (eNOS) and inducible NOS (iNOS). Sources of increased NO levels in chronic hypertension is disputed.

METHODS

To determine eNOS and iNOS expression in different organs of portal hypertensive and control rats, we divided Sprague-Dawley rats in 6 groups: (1). Partial portal vein ligated rats, (2). Bile duct ligated rats, (3). Carbon tetrachloride treated rats, (4). Sham operated rats, (5). Untreated control rats, and (6). LPS treated rats. Immunohistochemistry (IHC) and immunoblotting (IB) using antibodies against eNOS or iNOS were carried out on samples from thymus, aorta, heart, lung, oesophagus, liver, spleen, kidney, pancreas, small and large intestine.

RESULTS

IHC revealed an even eNOS expression in all groups. Expression of iNOS was restricted to macrophages in organs of LPS treated and the thymus of rats. IB mirrored these results.

CONCLUSION

In chronic portal hypertension, the main source for NO production depends on eNOS activity.

Differential expression and localization of nitric oxide synthases in cirrhotic livers of bile duct-ligated rats

Increased vascular nitric oxide (NO) production has been implicated in the pathogenesis of the hyperdynamic circulation in liver cirrhosis. This study investigated the expression of three isoforms of NO synthase (NOS) in rat cirrhotic livers. Cirrhosis was induced by chronic bile duct ligation (BDL). NOS enzyme activity was assessed by L-citrulline generation. Competitive RT-PCR was performed to detect the mRNA levels of NOS. In situ hybridization was done to localize NOS mRNA. Protein expression of NOS was evaluated by Western blotting and immunohistochemistry. The L-citrulline assay showed that constitutive NOS (cNOS) enzymatic activity was decreased, while inducible NOS (iNOS) activity was increased in BDL livers. Both endothelial NOS (eNOS) and neuronal NOS (nNOS) mRNA were detected in BDL and sham rats, but with enhanced expression in BDL rats. eNOS protein was redistributed with less expression in sinusoidal endothelial cells, but the total levels in liver were not changed. nNOS was induced in hepatocytes of BDL rats, in contrast to only a weak signal observed around some blood vessels in sham livers. Intense mRNA and protein expression of iNOS was induced in livers of BDL rats and was localized in hepatocytes, with no or a negligible amount in control livers. In conclusion, iNOS was induced in cirrhotic liver with its activity increased. In contrast, cNOS activity was impaired, regardless of unchanged eNOS protein levels and enhanced nNOS expression. These results suggest that all three types of NOS have a role in cirrhosis, but their expression and regulation are different.

Impact of PTEN expression on the outcome of hepatitis C virus-positive cirrhotic hepatocellular carcinoma patients: possible relationship with COX II and inducible nitric oxide synthase

PTEN, a novel tumor suppressor, functions as a regulator of both cell cycle progression and apoptosis. PTEN gene is frequently mutated or deleted in several malignancies including human hepatocellular carcinoma (HCC). The clinical significance and prognostic value of PTEN expression in HCC or in the surrounding non-cancerous parenchyma remain obscure. Using immunohistochemistry, we analyzed the PTEN protein expression in 46 tissue sections collected from surgically resected hepatitis C virus (HCV)-positive cirrhotic HCC patients. Although the surrounding normal liver tissue was strongly expressing PTEN in 42 cases (91.3%), the immunostaining intensity was low in 29 (63.1%) and high in 17 (36.9%) of the HCCs. Additionally a significant positive correlation was identified between low PTEN expression in the HCC and increased expression of iNOS and COX II in the surrounding liver. The overall survival was significantly longer for the HCC-patients with high PTEN expression than patients with low PTEN expression. Univariate analysis revealed PTEN expression as an independent prognostic factor for patients survival. By Western blot analysis we also found that the Akt/PKB signaling, which is negatively regulated by PTEN, was upregulated in the HCCs in comparison to its expression in the surrounding liver tissue. These results demonstrate that downregulation of PTEN in the tumor is an important step in HCV-positive cirrhotic hepatocarcinogenesis and might result in concomitant upregulation of iNOS and COX II in the surrounding liver in favor of tumor promotion.

Intestinal expressions of eNOSmRNA and iNOSmRNA in rats with acute liver failure

AIM: To observe the gene expression change of eNOSmRNA and iNOSmRNA in the small and large intestines with acute liver failure (ALF), and to reveal the biological function of NO on the pathogenesis of ALF and multiple organs dysfunction at the molecular level.

METHODS: Sixty male Wistar rats were selected, weighing from 250 g to 350 g, and divided into 5 groups randomly: SO, ALF (6 h, 12 h), L-Arg, L-NAME, L-Arg and L-NAME, each group with 10 rats. The dose of L-Arg was 300 mg•kg¯¹, and L-NAME was 30 mg•kg¯¹, the reagents diluted by normal saline were injected through tail vein 30 minutes pre- and post-operation. The rats in the ALF group were respectively sacrificed postoperatively at 6 h, 12 h, and the rats in the other groups were sacrificed postoperatively at 6 h. The tissues of small and large intestines were harvested in 4% paraforaldehyde containing the reagent of DEPC and fixed at 6 h, embedded in paraffin, and 4 μm section was cut. The expression of eNOSmRNA and iNOSmRNA in these tissues was determined with in situ hybridization, and analyzed with the imaging analysis system of CMM-3 and SPSS statistical software.

RESULTS: The expression of eNOSmRNA in the large intestine and iNOSmRNA in the small and large intestines increased significantly at 6 h after ALF, but the expression of iNOSmRNA in the small and large intestines reduced notably at 12 h after ALF (P ＜ 0.05); the expression of eNOSmRNA in the large intestine and iNOSmRNA in the small and large intestines decreased significantly with the reagents of L-Arg at 6 h ALF, but the expression of eNOSmRNA and iNOSmRNA in the small and large intestines decreased totally with the reagents of L-NAME or association with L-Arg 6 h ALF.

CONCLUSION: The expression of eNOSmRNA in the large intestine increased notably at the early stage of ALF, NO induced by the enzyme of eNOS from the transplantation of eNOSmRNA can protect the function of the large intestine, the high expression of iNOSmRNA is involved in the damaged function of the small and large intestines. NO precursor can reduce the expression of iNOSmRNA in the small and large intestines and the damage to intestines; NOS inhibitor or association with NO precursor can totally lower the expression of eNOSmRNA and iNOSmRNA in the small and large intestines, it cannot notably influence the NOS inhibitor in the gene expression of eNOSmRNA and iNOSmRNA to supply the additional NO precursor.

Role of nitric oxide in hepatopulmonary syndrome in cirrhotic rats

The hepatopulmonary syndrome (HPS) is characterized by intrapulmonary vascular dilatations and an increased alveolar-arterial oxygen difference (AaPO(2)). Exhaled nitric oxide (NO) concentrations are elevated, suggesting that pulmonary NO overproduction may be the mechanism underlying HPS. We investigated whether common bile duct ligation in rats results in lung NO overproduction and whether normalization of NO synthesis by a 6-wk course of N(G)-nitro-L-arginine methyl ester (L-NAME) (5 mg x kg(-)(1) x d(-)(1)) prevents HPS. Untreated cirrhotic rats showed increases in AaPO(2) and in cerebral uptake of intravenous (99m)Tc-labeled albumin macroaggregates (indicating intrapulmonary vascular dilatations), with decreases in pulmonary vascular resistance and in pulmonary vasoconstriction induced by angiotensin II and hypoxia. Increases were found in exhaled NO; pulmonary total and calcium-dependent NO synthase (NOS) activities; and pulmonary expression of inducible and, to a lesser extent, endothelial NOS. Accumulation of intravascular macrophages accounted for the inducible NOS expression. L-NAME normalized AaPO(2), brain radioactivity, pulmonary vascular resistance, reactivity to hypoxia and angiotensin II, exhaled NO, and NOS activities. These findings suggest that HPS and the associated reduced response to pulmonary vasoconstrictors seen in untreated cirrhotic rats are related to increased pulmonary NO production dependent primarily on increases in the expression and activities of inducible NOS within pulmonary intravascular macrophages.

Effect of nitric oxide synthase inhibition on Schistosoma japonicum egg-induced granuloma formation in the mouse liver

Nitric oxide (NO) plays diverse roles in a variety of pathological processes. We investigated the role of NO in Schistosoma japonicum egg-induced granuloma formation in a mouse hepatic model. Immunohistological analysis revealed that there is the most intense and extensive inducible nitric oxide (iNOS) expression 2 weeks after egg implantation, and thereafter it decreased considerably with time. Treatment with nitric oxide synthase inhibitors, NIL (L-N6- (iminoethyl)-lysine) or N(omega)-nitro-L-arginine methyl ester (L-NAME), resulted in two different types of unusual granulomas at 2 weeks. One type showed suppressed fibrosis, while another showed foreign body-type multinuclear cell formation which frequently appeared particularly when 50 microg/ml NIL was given. At 3 weeks following treatment, fibrotic granulomas with scanty peripheral cellularity was obvious. However, there were no apparent changes after this period (at 4 weeks). Cytokine analysis in NIL-treated mice showed a significant increase of IL-4 and IL-13 production at 2 weeks. These findings indicated that nitric oxide contributes to granuloma development during the early stages, probably through the regulation of Th2 cytokine production.

Role of nitric oxide (NO) in pulmonary dysfunction associated with experimental cirrhosis

We examined the functional role of nitric oxide (NO) and nitric oxide synthase (NOS) isoforms in the pulmonary dysfunction seen in cirrhosis. Lungs were isolated from control and carbon tetrachloride (CCl(4))-induced cirrhotic rats and perfused at constant flow with a whole blood mixture. Ventilation with hypoxic gas resulted in attenuated hypoxic pulmonary vasoconstriction (HPV) in lungs from cirrhotic animals. Administration of the non-selective NOS inhibitor N-omega-Nitro-L-Arginine (L-NNA) resulted in HPV responses that were not different between groups. However, inhibition of inducible nitric oxide synthase (iNOS) did not restore cirrhotic HPV responses. Lungs from cirrhotic rats demonstrated enhanced endothelial-dependent vasodilation to vasopressin when preconstricted with hypoxia but not when preconstricted with thromboxane mimetic. Western blot analysis failed to demonstrate differences in pulmonary endothelial NOS (eNOS) or iNOS levels between groups. Our data suggest that, while NO may play a role in mediating the reduced pulmonary vasoreactivity observed in cirrhosis, other vasoactive factors are likely also important modulators of the pulmonary dysfunction seen in this disease.

Characterisation of portal hypertension models by microspheres in anaesthetised rats: a comparison of liver flow

Several portal hypertensive animal models are available and frequently used for haemodynamic studies. The portal venous inflows, measured with microspheres in pentobarbital anaesthetised rats, are compared here. The partial portal vein ligation model is characterised by a high portal venous inflow, together with extensive portal systemic shunting, at the cost of portal sinusoidal flow. In carbon tetrachloride-induced micronodular cirrhosis, portal sinusoidal flow, which reaches liver parenchyma, is high, and this is more pronounced in the presence of ascites. In bile duct ligation and excision-induced cirrhosis, an increase in liver weight was not equally followed by an increase in portal sinusoidal flow, pointing to a relatively underperfused liver.

Endothelial dysfunction in cirrhosis and portal hypertension

Portal hypertension (PHT) is a common clinical syndrome associated with chronic liver diseases; it is characterized by a pathological increase in portal pressure. Pharmacotherapy for PHT is aimed at reducing both intrahepatic vascular tone and elevated splanchnic blood flow. Due to the altered hemodynamic profile in PHT, dramatic changes in mechanical forces, both pressure and flow, may play a pivotal role in controlling endothelial and vascular smooth muscle cell signaling, structure, and function in cirrhotics. Nitric oxide, prostacyclin, endothelial-derived contracting factors, and endothelial-derived hyperpolarizing factor are powerful vasoactive substances released from the endothelium in response to both humoral and mechanical stimuli that can profoundly affect both the function and structure of the underlying vascular smooth muscle. This review will examine the contributory role of hormonal- and mechanical force-induced changes in endothelial function and signaling and the consequence of these changes on the structural and functional response of the underlying vascular smooth muscle. It will focus on the pivotal role of hormonal and mechanical force-induced endothelial release of vasoactive substances in dictating the reactivity of the underlying vascular smooth muscle, i.e., whether hyporeactive or hyperreactive, and will examine the extent to which these substances may exert a protective and/or detrimental influence on the structure of the underlying vascular smooth muscle in both a normal hemodynamic environment and following hemodynamic perturbations typical of PHT and cirrhosis. Finally, it will discuss the intracellular processes that regulate the release/expression of these vasoactive substances and that control the transformation of this normally protective cell to one that may promote the development of vasculopathy in PHT.

Effects of lipopolysaccharide on TNF-alpha production, hepatic NOS2 activity, and hepatic toxicity in rats with cirrhosis

BACKGROUND/AIMS

Septic shock results in high mortality in patients with cirrhosis. Nitric oxide synthase 2 (NOS2) is induced by bacterial lipopolysaccharides (LPS) and plays a major role in the inflammatory response to bacterial infections. Little is known about the regulation of NOS2 in cirrhosis under septic conditions. Thus, the aim of this study was to determine tissue NOS2 activity, serum nitrate and tumor necrosis factor (TNF-alpha) levels and hepatic toxicity in cirrhotic rats after LPS administration.

METHODS

Serum nitrates, TNF-alpha and transaminases were determined after LPS-administration in rats with secondary biliary cirrhosis and in sham-operated rats. Liver, lung, aortic and peritoneal macrophage NOS2 activities were determined by converting L[14C] arginine into L[14C] citrulline in a calcium free medium. Nitrate and TNF-alpha production were determined in a culture medium of peritoneal macrophages after in vivo LPS administration.

RESULTS

LPS (1.5 mg/kg) induced 50% mortality in cirrhotic rats and no mortality in sham-operated rats. After LPS, TNF-alpha, nitrate and transaminase levels were significantly higher in cirrhotic rats compared to sham-operated rats. After LPS administration, there were no differences in NOS2 activity in the aorta, lungs, or peritoneal macrophages of the two groups, whereas NOS2 activity was significantly higher in the cirrhotic liver compared to the normal liver.

CONCLUSIONS

In rats with cirrhosis, LPS administration induces higher mortality, hepatic toxicity, hepatic NOS2 activation and TNF-alpha release than in sham-operated rats. These results confirm the harmful role of septic shock in liver disease.

A canine model of multiple portosystemic shunting

The objective of this study was to develop and describe an experimental canine model of multiple acquired portosystemic shunts (PSS) similar in nature to spontaneously occurring PSS. Sixteen dogs were used and were divided into a control (n = 6) and a diseased group (n = 10). Dogs of the diseased group were administered dimethylnitrosamine (2 mg/kg of body weight, po) twice weekly, and clinicopathologic, ultrasonographic, and hepatic scintigraphic findings were recorded during the development of hepatic disease and PSS. Surgery was then performed to permit visual verification of multiple shunts, catheter placement for portography examination, and biopsy of the liver. All diseased dogs developed severe hepatic disease and multiple PSS as documented visually at surgery and on portography. Based on this study, dimethylnitrosamine-induced portosystemic shunting appears to be an appropriate model for spontaneously occurring multiple PSS secondary to portal hypertension.

Cardiopulmonary dysfunction in cirrhosis

Cirrhosis is associated with several circulatory abnormalities. These include hyperkinetic systemic and splanchnic circulation, hepatopulmonary syndromes including pulmonary hypertension, and cirrhotic cardiomyopathy. Hepatopulmonary syndrome generally refers to hypoxaemia seen in patients with chronic liver disease and appears to be relatively common, although often subclinical. However, significant pulmonary hypertension occurs in 0.2-0.7% of cirrhotic patients. Nitric oxide and/or other vasodilators appear to be involved in the pathogenesis of hepatopulmonary syndrome through induction of pulmonary capillary dilatation which increases the alveolar-arterial oxygen gradient. Cirrhotic cardiomyopathy refers to abnormal left ventricular function which is manifested under conditions of physiological or pharmacological stress. The emergence of liver transplantation as an effective treatment for end-stage liver disease has led to recognition of previously subclinical cardiomyopathy and congestive heart failure accounts for significant morbidity and mortality after this procedure. Diminished myocardial beta-adrenergic receptor function has been shown to play an important role in the pathogenesis of this condition. The contributions of other factors including nitric oxide, catecholamines and membrane fluidity changes are under investigation. Cirrhotic patients also have an increased incidence of other cardiac abnormalities, such as endocarditis and pericardial effusions.

Lipoic acid prevents development of the hyperdynamic circulation in anesthetized rats with biliary cirrhosis

Chronic bile duct ligation is associated with the development of oxidant injury, biliary cirrhosis, portal hypertension, and a hyperdynamic circulation. We have previously demonstrated that the hyperdynamic circulation in the partial portal vein-ligated rat can be prevented by the administration of N-acetylcysteine. To extend these findings, we have examined the effect of lipoic acid, a thiol-containing antioxidant, on hemodynamics, oxidative stress, and nitric oxide (NO) production in bile duct-ligated (BDL) cirrhotic rats. Lipoic acid was given continuously in drinking water to normal and BDL rats; control rats received ordinary drinking water, and animals were studied at 24 days following surgery. Lipoic acid prevented the development of the hyperdynamic circulation (cardiac index [CI]: 15.7 +/- 2.0 vs. 29.5 +/- 2.1 mL x min-1 x 100 g-1; P <. 05) and significantly attenuated the rise in portal pressure (PP) (12.7 +/- 0.8 vs. 15.2 +/- 0.5 mm Hg; P <.05). Hepatic nitric oxide synthase (NOS) activity and plasma nitrite/nitrate concentration increased significantly following bile duct ligation, and both of these were prevented by lipoic acid. Lipoic acid had no effect on the biochemical or histological parameters of liver function in the cirrhotic group. We conclude that lipoic acid prevents the development of the hyperdynamic circulation in the rat model of biliary cirrhosis, and that this is associated with decreased synthesis of NO.