Effects of nitric oxide and cyclooxygenase inhibition on splanchnic hemodynamics in portal hypertension

Selective cyclooxygenase inhibition by SC-560 improves hepatopulmonary syndrome in cirrhotic rats

Objective

Hepatopulmonary syndrome (HPS) is characterized by hypoxia in patients with chronic liver disease. The mechanism of HPS includes pulmonary vasodilatation, inflammation, and angiogenesis. Prostaglandins synthesized by cyclooxygenases (COX) participate in vascular responsiveness, inflammation and angiogenesis, which can be modulated by COX inhibitors. We therefore evaluated the impact of COX inhibition in rats with common bile duct ligation (CBDL)-induced liver cirrhosis and HPS.

Methods

Cirrhotic rats were randomly allocated to receive non-selective COX inhibitor (indomethacin), selective COX-1 inhibitor (SC-560), or COX-2 inhibitor (celecoxib) for 14 days. After that, hemodynamic parameters, severity of hypoxia and intrapulmonary shunts, liver and renal biochemistry parameters, histological finding and protein expressions were evaluated.

Results

Non-selective COX inhibition by indomethacin improved hepatic fibrosis and pulmonary inflammation in cirrhotic rats with HPS. It also decreased mean arterial blood pressure, portal pressure, and alleviated hypoxia and intrapulmonary shunts. However, indomethacin increased mortality rate. In contrast, selective COX inhibitors neither affected hemodynamics nor increased mortality rate. Hypoxia was improved by SC-560 and celecoxib. In addition, SC-560 decreased intrapulmonary shunts, attenuated pulmonary inflammation and angiogenesis through down-regulating COX-, NFκB- and VEGF-mediated pathways.

Conclusion

Selective COX-1 inhibitor ameliorated HPS by mitigating hypoxia and intrapulmonary shunts, which are related to anti-inflammation and anti-angiogenesis.

The Gastrointestinal Circulation: Physiology and Pathophysiology

The gastrointestinal (GI) circulation receives a large fraction of cardiac output and this increases following ingestion of a meal. While blood flow regulation is not the intense phenomenon noted in other vascular beds, the combined responses of blood flow, and capillary oxygen exchange help ensure a level of tissue oxygenation that is commensurate with organ metabolism and function. This is evidenced in the vascular responses of the stomach to increased acid production and in intestine during periods of enhanced nutrient absorption. Complimenting the metabolic vasoregulation is a strong myogenic response that contributes to basal vascular tone and to the responses elicited by changes in intravascular pressure. The GI circulation also contributes to a mucosal defense mechanism that protects against excessive damage to the epithelial lining following ingestion of toxins and/or noxious agents. Profound reductions in GI blood flow are evidenced in certain physiological (strenuous exercise) and pathological (hemorrhage) conditions, while some disease states (e.g., chronic portal hypertension) are associated with a hyperdynamic circulation. The sacrificial nature of GI blood flow is essential for ensuring adequate perfusion of vital organs during periods of whole body stress. The restoration of blood flow (reperfusion) to GI organs following ischemia elicits an exaggerated tissue injury response that reflects the potential of this organ system to generate reactive oxygen species and to mount an inflammatory response. Human and animal studies of inflammatory bowel disease have also revealed a contribution of the vasculature to the initiation and perpetuation of the tissue inflammation and associated injury response.

Arachidonic acid metabolites and endothelial dysfunction of portal hypertension

Increased resistance to portal flow and increased portal inflow due to mesenteric vasodilatation represent the main factors causing portal hypertension in cirrhosis. Endothelial cell dysfunction, defined as an imbalance between the synthesis, release, and effect of endothelial mediators of vascular tone, inflammation, thrombosis, and angiogenesis, plays a major role in the increase of resistance in portal circulation, in the decrease in the mesenteric one, in the development of collateral circulation. Reduced response to vasodilators in liver sinusoids and increased response in the mesenteric arterioles, and, viceversa, increased response to vasoconstrictors in the portal-sinusoidal circulation and decreased response in the mesenteric arterioles are also relevant to the pathophysiology of portal hypertension. Arachidonic acid (AA) metabolites through the three pathways, cyclooxygenase (COX), lipoxygenase, and cytochrome P450 monooxygenase and epoxygenase, are involved in endothelial dysfunction of portal hypertension. Increased thromboxane-A2 production by liver sinusoidal endothelial cells (LSECs) via increased COX-1 activity/expression, increased leukotriens, increased epoxyeicosatrienoic acids (EETs) (dilators of the peripheral arterial circulation, but vasoconstrictors of the portal-sinusoidal circulation), represent a major component in the increased portal resistance, in the decreased portal response to vasodilators and in the hyper-response to vasoconstrictors. Increased prostacyclin (PGI2) via COX-1 and COX-2 overexpression, and increased EETs/heme-oxygenase-1/K channels/gap junctions (endothelial derived hyperpolarizing factor system) play a major role in mesenteric vasodilatation, hyporeactivity to vasoconstrictors, and hyper-response to vasodilators. EETs, mediators of liver regeneration after hepatectomy and of angiogenesis, may play a role in the development of regenerative nodules and collateral circulation, through stimulation of vascular endothelial growth factor (VEGF) inside the liver and in the portal circulation. Pharmacological manipulation of AA metabolites may be beneficial for cirrhotic portal hypertension.

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.

Nitric oxide and prostaglandin as mediators in the pathogenesis of hyperkinetic circulatory state in a model of endotoxemia-induced portal hypertension

AIMS

To evaluate the participation of nitric oxide (NO) and prostaglandin (PGI2) on hyperdynamic state in endotoxemia-induced portal hypertension (EIP) induced by chronic endotoxemia.

METHODS

The portal pressure (PP) and mean arterial pressure (MAP) were recorded, in vivo before and after administration of L-NAME (NOS inhibitor) and indomethacin (specific blocker of COX). The vasoactive responses to acetylcholine of thoracic rat aortic rings were studied in vitro before and after nitric oxide and cyclooxygenase blockade using multichannel organ bath. The mRNA expression for isoforms of (cyclooxygenase) COX and nitric oxide synthase (NOS) were analyzed using RT-PCR.

RESULTS

Administration of both L-NAME and indomethacin in EIP rabbits significantly reduced (p < 0.05) the PP and reversed the MAP to normal as compared to sham-operated (SO) rabbits. There was impaired vasodilatory response to acetylcholine in EIP rabbits. L-NAME caused a significant reduction in acetylcholine-induced vasorelaxation in SO rabbits than EIP due to preexisting hyperemia in EIP. Indomethacin partially restored vasoresponsiveness to acetylcholine in EIP group. The mRNA expression of eNOS (endothelial NOS) and COX-1 (constitutive COX) were significantly higher in SO than EIP rabbits. iNOS (inducible NOS) and COX-2 (inducible COX) mRNA expression was seen only in EIP rabbits.

CONCLUSIONS

A significant component of acetylcholine-mediated vasorelaxation in EIP model is modulated by eNOS. There was increased production of contractile prostaglandin in EIP rabbits. iNOS and COX-2 play an important role in the hemodynamic abnormalities of PHT. This novel model of PHT produced by chronic splanchnic endotoxemia in rabbit, mimics impaired vasodilation and vasoreactivity akin to other models of PHT.

Review: Vasoconstrictors for the treatment of portal hypertension

Vasoconstrictors have long been used in an attempt to mitigate the effects of portal hypertension. In this review, we discuss the current understanding of portal hypertension and the use of vasoconstrictors in the management of its sequlae, including variceal hemorrhage, hepatorenal syndrome, and paracentesis-induced circulatory dysfunction. Experimental and clinical evidence for the use of vasoconstrictors is considered, and several exciting recent developments are reviewed.

2-Arachidonoylglycerol, an endogenous cannabinoid receptor agonist, in various rat tissues during the evolution of experimental cholestatic liver disease

BACKGROUND/AIM

Changes in tissue levels of 2-arachidonoylglycerol (2-AG), an endocannabinoid, during the evolution of bile duct ligation (BDL) may indicate that endocannabinoids have a role in the hemodynamic changes that occur in this condition.

METHODS

2-AG levels, in various organs and vascular beds of BDL rats, 2 and 4 weeks post surgery, were determined. Untouched and sham-operated (SO) rats were used as controls.

RESULTS

2-AG content of a specific organ was not a static finding and depended on the rat's age, the time from the surgical procedure and the type of procedure. The most pronounced changes were observed in BDL rats 4 weeks post surgery. In these rats, hepatic, pulmonary, cardiac and renal medullary and papillary 2-AG levels were highest observed. No changes in splenic, aortic and renal cortical 2-AG levels were observed. In addition a stepwise increase in 2-AG levels from the cortex to the papilla was detected and was followed by a decrease in creatinine clearance.

CONCLUSIONS

2-AG probably has a role in the pathophysiologic changes in the liver, heart, lung and kidney that follows BDL.

Vascular actions of the prostacyclin receptor antagonist BAY 73-1449 in the portal hypertensive rat

We have investigated the actions of the postacyclin receptor antagonist BAY 73-1449 on shunt vessel development and shunt flow in the portal vein ligated portal hypertensive Wistar rat in vivo. BAY 73-1449 (0.1-1 mg/kg), given intravenously, did not significantly reduce mesenteric inflow, but significantly reduced splenic shunt vessel outflow, compared to the effects of vehicle, in anaesthetized portal vein ligated rats as measured by shunt vessel conductance. There were no differences between portal vein ligated animals treated, beginning just before portal vein ligation, with vehicle for 7 days and animals treated for 7 days with BAY 73-1449 (1-5 mg/kg, s.c.) in the degree of porto-systemic shunting, as measured by the radioactive microsphere technique in anaesthetized rats. Portal pressure was similar in animals treated with vehicle or BAY 73-1449. It is concluded that the prostacyclin receptor antagonist BAY 73-1449 can acutely reduce shunt vessel blood flow in portal hypertensive rats.

Modifications produced by indomethacin and L-NAME in the effect of ultralow-dose aspirin on platelet activity in portal hypertension

In our previous study, we demonstrated the effect of ultralow-dose aspirin (ULDA) on platelet activity and bleeding in rats with portal hypertension (PHT) produced by portal vein ligation (PVL). This paper reports modifications in this effect caused by blocking NO production by nitro arginine methyl ester (NAME) and cyclooxygenase (COX) activity with indomethacin. PVL rats and sham-operated controls were treated with placebo, indomethacin or NAME and 30 min thereafter with placebo or ULDA treatment. Platelet activity was studied by a model of in vivo laser-induced thrombus production in the mesenteric circulation, induced hemorrhage time (IHT) and platelet aggregation ex vivo induced by adenosine diphosphate in an aggregometer. The PVL group receiving placebo showed a decreased platelet activity with prolonged IHT, an effect that was reversed by ULDA. Indomethacin induced a decreased platelet activity in the control rats and a prolonged IHT. In PHT with ULDA, in vivo platelet activity was enhanced but the normalization of IHT observed in rats without indomethacin was blunted. The addition of NAME normalized the diminished in vivo platelet aggregation and increased the IHT observed in PVL animals. These changes decreased the effect of ULDA in both sham-operated and PVL animals. The effect of indomethacin was more clearly modified by ULDA than the effect of NAME, thus suggesting that modifications in the COX pathway might alter the effect of ULDA. The simultaneous administration of indomethacin and ULDA could inhibit its beneficial effect on bleeding in rats with PHT.

Effect of verapamil on nitric oxide synthase in a portal vein-ligated 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 N^w–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 N^w- 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.

Role of PGI2 in the formation and maintenance of hyperdynamic circulatory state of portal hypertensive rats

AIM: To investigate the role of prostacyclin (PGI₂) and nitric oxide (NO) in the development and maintenance of hyperdynamic circulatory state of chronic portal hypertensive rats.

METHODS: Ninety male Sprague-Dawley rats were divided into three groups: intrahepatic portal hypertension (IHPH) group by injection of CCl₄, prehepatic portal hypertension (PHPH) group by partial stenosis of the portal vein and sham-operation control (SO) group. One week after the models were made, animals in each group were subdivided into 4 groups: saline controlled group (n = 23), Nω-nitro-L-arginine (L-NNA)group (n = 21) group, indomethacin (INDO) group (n = 22) and high-dose heparin group (n = 24). The rats were administrated 1mL of saline, L-NNA (3.3 mg/kg·d) and INDO (5 mg/kg·d) respectively through gastric tubes for one week,then heparin (200 IU/Kg/min) was given to rats by intravenous injection for an hour. Splanchnic and systemic hemodynamics were measured using radioactive microsphere techniques. The serum nitrate/nitrite(NO₂^-/NO₃^-) levels as a marker of production of NO were assessed by a colorimetric method, and concentration of 6-keto-PGF1α, a stable hydrolytic product of PGI₂, was determined by radioimmunoassay.

RESULTS: The concentrations of plasma 6-keto-PGF1α (pg/mL) and serum NO₂^-/NO₃^- (μmol/L) in IHPH rats (1123.85±153.64, 73.34±4.31) and PHPH rats (891.88±83.11, 75.21±6.89) were significantly higher than those in SO rats(725.53±105.54, 58.79±8.47) (P<0.05). Compared with SO rats, total peripheral vascular resistance (TPR) and splanchnic vascular resistance (SVR) decreased but cardiac index (CI) and portal venous inflow (PVI) increased obviously in IHPH and PHPH rats (P<0.05). L-NNA and indomethacin could decrease the concentrations of plasma 6-keto-PGF1α and serum NO₂^-/NO₃^-in IHPH and PHPH rats (P<0.05) .Meanwhile, CI, FPP and PVI lowered but MAP,TPR and SVR increased(P<0.05). After deduction of the action of NO, there was no significant correlation between plasma PGI₂ level and hemodynamic parameters such as CI, TPR, PVI and SVR. However, after deduction of the action of PGI₂, NO still correlated highly with the hemodynamic parameters, indicating that there was a close correlation between NO and the hemodynamic parameters. After administration of high-dose heparin, plasma 6-keto-PGF₁α concentrations in IHPH, PHPH and SO rats were significantly higher than those in rats administrated vehicle (P<0.05). On the contrary, levels of serum NO₂^-/NO₃^- in IHPH, PHPH and SO rats were significantly lower than those in rats administrated Vehicle (P<0.05). Compared with those rats administrated vehicle, the hemodynamic parameters of portal hypertensive rats, such as CI and PVI, declined significantly after administration of high-dose heparin (P<0.05), while TPR and SVR increased significantly (P<0.05).

CONCLUSION: It is NO rather than PGI₂ that is a mediator in the formation and maintenance of hyperdynamic circulatory state of chronic portal hypertensive rats.

Effects of endothelin-1 on portal-systemic collaterals of common bile duct-ligated cirrhotic rats

BACKGROUND/AIMS

Endothelin-1 (ET-1) may induce intrahepatic vasoconstriction and consequently increase portal pressure. Endothelin-1 has been shown to exert a direct vasoconstrictive effect on the collateral vessels in partially portal vein-ligated rats with a high degree of portal-systemic shunting. This study investigated the collateral vascular responses to ET-1, the receptors in mediation and the regulation of ET-1 action by nitric oxide and prostaglandin in cirrhotic rats with a relatively low degree of portal-systemic shunting.

METHODS

The portal-systemic collaterals of common bile duct-ligated (BDL) cirrhotic rats were tested by in situ perfusion. The concentration-response curves of collaterals to graded concentrations of ET-1 (10(-10)-10(-7) m) with or without BQ-123 (ET(A) receptor antagonist, 2 x 10(-6) m), BQ-788 (ET(B) receptor antagonist, 10(-7) m) or both were recorded. In addition, the collateral responses to ET-1 with preincubation of N(omega)-nitro-L-arginine (NNA, 10(-4) M), indomethacin (INDO, 10(-5) M) or in combination were assessed.

RESULTS

Endothelin-1 significantly increased the perfusion pressures of portal-systemic collaterals. The ET-1-induced constrictive effects were inhibited by BQ-123 or BQ-123 plus BQ-788 but not by BQ-788 alone. The inhibitory effect was greater in the combination group. Pretreatment of NNA or NNA plus INDO equivalently enhanced the response of ET-1 while pretreatment of INDO alone exerted no effect.

CONCLUSION

Endothelin-1 has a direct vasoconstrictive effect on the collaterals of BDL cirrhotic rats, mainly mediated by ET(A) receptor. Endogenous nitric oxide may play an important role in modulating the effects of ET-1 in the portal-systemic collaterals of BDL cirrhotic rats.

Eicosanoids in cirrhosis and portal hypertension

In the last decade, the knowledge of the pathogenesis of portal hypertension and cirrhosis has increased dramatically. In portal hypertension, almost all the known vasoactive systems/substances are activated or increased and the most recent studies have stressed the importance of the endothelial factors, in particular, prostaglandins. Prostaglandins are formed following the oxygenation of arachidonic acid by the cyclooxygenase (Cox) pathway. An important consideration in portal hypertension and cirrhosis in the periphery is the altered hemodynamic profile and its contributory role in controlling endothelial release of these vasoactive substances. Prostaglandins are released from the endothelium in response to both humoral and mechanical stimuli and can profoundly affect both intrahepatic and peripheral vascular resistance. Within the liver, intrahepatic resistance is altered due to a diminution in sinusoidal responsiveness to vasodilators and an increase in prostanoid vasoconstrictor responsiveness. This review will examine the contributory role of both hormonal and/or hemodynamic force-induced changes in prostaglandin production and signaling in cirrhosis and portal hypertension and the consequence of these changes on the structural and functional response of both the vasculature and the liver.

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.

Longitudinal prostaglandin E(2) generation in various organs during evolution of experimental portal hypertension

It has been suggested that the arteriolar vasodilatation and hyperdynamic circulation observed in rats with partial portal vein ligation (PPVL) is caused by increased splanchnic and systemic delivery of vasodilator substances. The aims of our study were to determine organ-specific generation of prostaglandin E(2) (PGE(2)) in rats with PPVL during the evolution of portal hypertension. Rats with PPVL and sham-operated (S) rats were studied in the first, third, fourth and 14th postoperative days. They were anesthetized and splenic pulp pressure and blood pressure were measured. Spleen, colon and lungs were removed and the splenic, pulmonary and mucosal colonic PGE(2) were determined. All PPVL rats developed sequential hemodynamic changes compatible with evolving portal hypertension. Splenic pulp pressure was higher in PPVL rats compared with S rats during all days of the study. Within the group of PPVL the splenic pulp pressure was higher in the first postoperative day and decreased in the ensuing days. No changes in splenic and colonic PGE(2) generation were noted during the study period. Pulmonary PGE(2) generation increased significantly in the first postoperative day in PPVL rats compared with S rats. However, similar increase was observed on the third postoperative day in S rats. PGE(2) probably has no role in splanchnic hemodynamic changes during evolution of portal hypertension. Pulmonary PGE(2) generation may increase as a response to increased portal pressure, or to abdominal surgery.

Endothelial COX-1 and -2 differentially affect reactivity of MVB in portal hypertensive rats

Expression of constitutive and inducible cyclooxygenase (COX-1 and COX-2, respectively) and the role of prostanoids were investigated in the aorta and mesenteric vascular bed (MVB) from the portal vein-ligated rat (PVL) as a model of portal hypertension. Functional experiments were carried out in MVB from PVL and sham-operated rats in the absence or presence of the nonselective COX inhibitor indomethacin or the selective inhibitors of COX-1 (SC-560) or COX-2 (NS-398). Western blots of COX-1 and COX-2 proteins were evaluated in aorta and MVB, and PGI(2) production by enzyme immunoassay of 6-keto-PGF(1alpha) was evaluated in the aorta. In the presence of functional endothelium, decreased contraction to norepinephrine (NE) and increased vasodilatation to ACh were observed in MVB from PVL. Exposure of MVB to indomethacin, SC-560, or NS-398 reversed the hyporeactivity to NE and the increased endothelial vasodilatation to ACh in PVL, with NS-398 being more potent than the other two inhibitors. Upregulation of COX-1 and COX-2 expressions was detected in aorta and MVB from PVL portal hypertensive rats, and increased production of 6-keto-PGF(1alpha) was observed in aorta from portal hypertensive rats. These results suggest that generation of endothelial vasodilator prostanoids, from COX-1 and COX-2 isoforms, accounts for the increased mesenteric blood flow in portal hypertension.

Prostaglandin H synthase and vascular function

Prostaglandin H synthase (PGHS) is a rate-limiting enzyme in the production of prostaglandins and thromboxane, which are important regulators of vascular function. Under normal physiological conditions, PGHS-dependent vasodilators (such as prostacyclin) modulate vascular tone. However, PGHS-dependent vasoconstriction (mediated by thromboxane and/or its immediate precursor, PGH(2)) predominates in some vascular pathologies (eg, systemic hypertension, diabetes, cerebral ischemia, and aging). This review will discuss the role of PGHS-dependent modulation of vascular function in a number of vascular beds (systemic, pulmonary, cerebral, and uterine) with an emphasis on vascular pathophysiology. Moreover, the specific contributions of the different isoforms (PGHS-1 and PGHS-2) are discussed. Understanding the role of PGHS in vascular function is of particular importance because they are the targets of the commonly used nonsteroidal antiinflammatory drugs (NSAIDs), which include aspirin and ibuprofen. Importantly, with the advent of specific PGHS-2 inhibitors for treatment of conditions such as chronic inflammatory disease, it is an opportune time to review the data regarding PGHS-dependent modulation of vascular function.

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.

Inhibition of prostacyclin by indomethacin ameliorates the splanchnic hyposensitivity to glypressin in haemorrhage-transfused common bile duct-ligated rats

Prostacyclin (PGI2) is an important contributor to the mediation of hyporeactivity to vasoconstrictors and the development of hyperdynamic circulation in portal hypertensive states. Inhibition of PGI2 synthesis in haemorrhage-transfused partially portal vein-ligated rats could ameliorate the splanchnic hyposensitivity to glypressin, a long-acting vasopressin analogue. This study investigated whether the hyposensitivity to glypressin also exists in rats with common bile duct ligation (BDL) and whether the inhibition of PGI2 synthesis by indomethacin could potentiate the portal-hypotensive effect of glypressin in bleeding BDL rats. Two series of BDL rats were used. Series 1 investigated the haemodynamic effects of low dose glypressin (0.07 mg kg-1) in BDL rats with or without bleeding by catheterization. In series 2, haemodynamic parameters were measured in stable or bleeding BDL rats that were receiving intravenously high dose glypressin (0.2 mg kg-1) or indomethacin (5 mg kg-1) followed by high dose glypressin. In rats with a hypotensive haemorrhage, 4.5 mL of blood was withdrawn and 50% of the withdrawn blood was reinfused before the administration of glypressin or indomethacin. Splanchnic hyposensitivity to glypressin was demonstrated in haemorrhage-transfused BDL rats receiving high, but not low, doses of glypressin. Indomethacin infusion did not cause significant systemic and portal haemodynamic changes in bleeding BDL rats (P > 0.05). The addition of indomethacin significantly enhanced the portal-hypotensive effects of glypressin (P < 0.05) and potentiated the increases in mean arterial pressure induced by glypressin infusion (P < 0.001) in bleeding BDL rats. Splanchnic hyposensitivity to glypressin observed in haemorrhage-transfused BDL rats could be ameliorated by the addition of indomethacin, suggesting a role of endogenous PGI2 in its pathophysiology.

Diagnosing portal hypertension

It is important to diagnose portal hypertension owing to its devastating complications. Clinicians need to be able to recognize physical signs and symptoms associated with portal hypertensive states. When in doubt, appropriate diagnostic measures need to be performed and a definite diagnosis made. Hepatic venous pressure gradient (HVPG) is often used as a surrogate measurement of portal pressure. HVPG can be obtained safely and conveniently on an outpatient basis. It can also be used to assess efficacy of various treatment modalities. Knowledge of pathophysiology of portal hypertension has provided the basis for further trials in both novel treatment modalities and diagnostic methods.

Hepatorenal failure

Since the description of HRS more than 100 years ago, significant advances have been made in understanding the pathophysiology of HRS and in the management of these patients. There is now a therapeutic armamentarium: medical (ornipressin plus plasma volume expansion), radiographic (TIPS shunt), and surgical (liver transplantation). The diagnosis of HRS is no longer synonymous with a death sentence; instead, it is a therapeutic challenge, and a coordinated approach by intensivists, hepatologists, nephrologists, interventional radiologists, and transplant surgeons is needed to continue to improve the prognosis of cirrhotic patients presenting with HRS. Increased understanding of HRS will allow preventative rather than therapeutic measures to be used. As in all fields of medicine, these advances will come only with innovative clinical investigation.

Effects of vasopressin on portal-systemic collaterals in portal hypertensive rats: role of nitric oxide and prostaglandin

This study investigated the effect of vasopressin on portal-systemic collaterals in portal hypertensive rats and the influence of nitric oxide (NO) and prostaglandin on the responsiveness of collateral vessels to vasopressin. The vascular responsiveness to graded concentrations of vasopressin was tested with or without the incubation of n(omega)-nitro-L-arginine (NNA) (100 micromol/L) and/or indomethacin (10 micromol/L) in perfused collateral vascular beds of rats with portal hypertension induced by partial portal vein ligation. In addition, concentration-response curves to vasopressin with incubation of a vasopressin V(1) receptor antagonist d(CH(2))(5)Tyr(Me) arginine vasopressin and concentration-response curves to a V(2) receptor agonist 1-desamino-8-D-arginine vasopressin were performed. Vasopressin significantly increased the perfusion pressure of collaterals, and this effect was suppressed by the addition of the V(1) receptor antagonist. Perfusion with the V(2) receptor agonist had no effect on the collaterals. Incubation with NNA, indomethacin, or both significantly potentiated the response of collaterals to vasopressin. In addition, the pressor response to vasopressin in the combination group was significantly higher than that in the NNA-alone group. The results show that vasopressin produces a direct vasoconstrictive effect on the portal-systemic collaterals of portal hypertensive rats. This effect is mediated by the vasopressin V(1,) but not V(2), receptors. The attenuation of the response to vasopressin by NO and prostaglandin suggest a function role of both mediators in the regulation of the portal-systemic collateral circulation in portal hypertensive rats.

Effects of sustained-release lanreotide on hemodynamics in rats with portal vein stenosis

BACKGROUND/AIMS

Somatostatin and its analogue have been shown to provide beneficial effects in the management of portal hypertension and hyperdynamic circulation. The current study was undertaken to evaluate the effects of lanreotide, a sustained-release somatostatin analogue, on hemodynamics in rats with portal hypertension.

METHODS

Immediately after portal vein stenosis, rats were randomly assigned to receive vehicle or a single intramuscular injection of lanreotide 10 mg/kg. Hemodynamic measurements (radioactive microsphere technique) with portal systemic shunts determinations were performed on the 4th and 8th day after surgery, respectively.

RESULTS

On the 4th day after surgery, rats treated with lanreotide had significantly lower cardiac index and higher systemic vascular resistance than rats treated with vehicle, while these values were no different on the 8th day after portal vein stenosis. In contrast, the elevation of portal pressure, portal tributary blood flow, and splanchnic fraction of cardiac output had ameliorated following lanreotide administration associated with an increase in splanchnic arterial resistance. Portal systemic shunts were lower in rats receiving lanreotide than in rats receiving vehicle.

CONCLUSION

The current study showed that a single injection of sustained-release lanreotide in rats with portal vein stenosis delayed the development of peripheral arterial vasodilatation and hyperdynamic circulation, while it modified the evolution of portal hypertension and splanchnic hyperemia. This treatment also prevents, in part, the development of portal systemic shunts in rats with portal vein stenosis.

Factors mediating the hemodynamic effects of tumor necrosis factor-alpha in portal hypertensive rats

Nitric oxide, prostacyclin, and glucagon have been implicated in promoting the hyperdynamic circulatory state of portal hypertension. Recent evidence also indicates that increased tumor necrosis factor-alpha (TNF-alpha) production is involved in the pathogenesis of this hemodynamic abnormality. This study was aimed at investigating in rats with portal vein stenosis (PVS) the effects on splanchnic hemodynamics of blocking circulating TNF-alpha and the factors mediating the vascular action of this cytokine in this setting. Anti-TNF-alpha polyclonal antibodies or placebo was injected into rats (n = 96) before and 4 days after PVS (short-term inhibition) and at 24 h and 4, 7, 10 days after PVS (long-term inhibition). Short-term TNF-alpha inhibition reduced portal venous inflow and cardiac index and increased splanchnic and systemic resistance. Portal pressure was unchanged, but portal-systemic shunting was decreased. After long-term TNF-alpha inhibition, portal venous inflow and portal pressure were unchanged, but arterial pressure and systemic resistance rose significantly. Anti-TNF-alpha PVS rats exhibited lower increments of systemic resistance after Nomega-nitro-L-arginine methyl ester and indomethacin administration and lower serum levels of TNF-alpha, nitrates-nitrites, and 6-keto-PGF1alpha, both over the short and the long term. Serum glucagon levels rose after long-term inhibition. In conclusion, the specific role played by TNF-alpha in the development of the hyperdynamic state of portal hypertension appears to be mainly mediated through an increased release of nitric oxide and prostacyclin. Maintenance of the splanchnic hyperemia after long-term TNF-alpha inhibition could be due to a compensatory release of glucagon.

Prostanoid production in endothelial and Kupffer liver cells from monocrotaline intoxicated rats

A single dose of monocrotaline, a pyrrolizidine alkaloid, was injected into rats in order to produce 25 (Group I) and 45 (Group II) days later a progressive and so called delayed liver injury. The present study investigated the prostanoid production of Kupffer cells and endothelial cells separated from Monocrotaline and saline (Group III) injected rat livers. Kupffer cells: formation of 6 keto Prostaglandin F1 alpha, the major prostacycline metabolite, gradually decreased in Groups I vs II (P < 0.01) and in both Groups I and II vs Controls (P < 0.01). In addition Prostaglandin F2 alpha showed a significant increase in Groups I and II when compared to Group III, (P < 0.001), and Thromboxane B2 was present in both Groups of Monocrotaline treated animals, while it was not detectable in the control Group III. Endothelial cells: 6 keto Prostaglandin F1 alpha decreased in Groups 1 vs II. This differences was significant when compared, and compared to controls (Group III, P < 0.001). Prostaglandin E2 was detected only in Groups I and II. Prostaglandin F2 alpha and Thromboxane B2 could not be detected in any Group. Ultramicroscopy showed morphological cell damage in nonparenchymal cells in Monocrotaline intoxication in Group II, rats sacrificed 45 days after the injection, while it shows normal features in those treated animals sacrificed 25 days after the injection, as well as in control group.

CONCLUSION

A single Monocrotaline injection produces, 25 and 45 days later, severe and progressive alterations in the prostanoid production in Kupffer and Endothelial cells, while ultramicroscopic alterations was only observed 45 days after the injection of Monocrotaline. A decreased production of vasodilators and the presence of vasoconstrictor prostanoids that can participate in the production of the circulatory derangements enhancing liver injury and portal hypertension were also observed.

Vasopressin reverses mesenteric hyperemia and vasoconstrictor hyporesponsiveness in anesthetized portal hypertensive rats

We recently reported that vasopressin analogues correct the in vitro vascular hyporeactivity to adrenergic vasoconstrictors in portal hypertensive rats. The aim of the present study was to determine whether vasopressin reduces splanchnic blood flow in portal vein-ligated (PVL) rats by restoring vasoconstrictor responsiveness in vivo. The ultrasonic transit time-shift technique was used for blood flow measurements. At basal conditions, blood flow through the superior mesenteric artery was elevated 1.6-fold in PVL rats as compared with sham-operated (SHAM) control rats. PVL rats also exhibited blunted mesenteric constrictor responses to the adrenoceptor agonist, phenylephrine (0.03-1 micromol x min(-1) x kg(-1)). Terlipressin (2-20 microg x k(-1)) and arginine vasopressin (3-300 pmol x min(-1) x kg(-1)) dose-dependently reduced, and at the highest doses, even abolished, the difference in mesenteric blood flow (MBF) between PVL and SHAM rats. When expressed as percent changes relative to baseline, mesenteric arterial responses to terlipressin and arginine vasopressin were found to be enhanced in PVL rats as compared with SHAM rats. Moreover, pretreatment with terlipressin (20 microg x kg(-1)) reversed the mesenteric hyporesponsiveness to phenylephrine of PVL rats. These vasopressin effects were independent of the nitric oxide (NO) pathway, because they were not mimicked by inhibition of NO synthesis with N(G)-nitro-L-arginine methyl ester (L-NAME) (0.1-10 mg x kg(-1)). These data indicate that pharmacological doses of vasopressin reverse the splanchnic hyperemia by restoring the responsiveness to adrenergic vasoconstrictors in portal hypertensive rats.

Underlying mechanisms of portal hypertensive gastropathy

Gastric mucosal lesions are frequently observed in patients with liver cirrhosis and portal hypertension. Similar lesions can be observed in experimental portal hypertension. This review summarizes our current knowledge of the pathophysiology of portal hypertensive gastropathy, with a particular focus on the microcirculatory disturbances that characterize this condition. The stomach of cirrhotic patients exhibits an increased susceptibility to injury induced by several irritants. Similarly, the stomach of portal hypertensive animals is less resistant to injury. One of the most important factors contributing to the increased susceptibility to damage is an impaired hyperemic response when the epithelium is exposed to irritants. This appears to be related to a reduction in mucosal prostaglandin production and to altered microcirculatory responsiveness to nitric oxide. Nitric oxide overproduction in portal hypertension may have direct effects on gastric blood flow regulation. Elevated production of tumor necrosis factor-alpha by gastric mucosa in portal hypertensive rats has also been shown to contribute to mucosal injury. A better understanding of the pathogenesis of portal hypertensive gastropathy may lead to development of specific therapeutic interventions for this condition.

Effects of L-arginine on the systemic, mesenteric, and hepatic circulation in patients with cirrhosis

Nitric oxide (NO) is known to play an important role in modulating both the hepatic and mesenteric circulation under physiological and pathological conditions. We investigated how L-arginine, a precursor of NO, modifies the hepatic and mesenteric circulation in patients with cirrhosis. The study design was a single-blind controlled study. We measured the systemic and portal hemodynamics before and following intravenous L-arginine and saline infusion using pulsed Doppler ultrasonography in 20 patients with cirrhosis, and then the effects were compared with those found in 20 healthy subjects. In these patients, the effects of L-arginine on hepatic circulation were investigated using hepatic catheterization. L-Arginine infusion induced systemic vasodilation in both the healthy controls and the cirrhotic patients in a similar hemodynamic manner. In these patients, the L-arginine-induced increase in the portal flow was significantly higher than that of cardiac output (CO); however, the relation was the inverse in healthy subjects. Moreover, the L-arginine-induced increase in the portal flow was greater in the cirrhotic patients than that seen in healthy subjects. As a result, L-arginine infusion was thus found to selectively augment the hepatopetal portal blood flow in the cirrhotic liver. In patients, L-arginine infusion induced marked hepatic vasodilation as demonstrated by the reduced hepatic sinusoidal resistance (HSR) and increased estimated hepatic blood flow (EHBF) associated with the ameliorated intrinsic clearance of indocyanine green. Despite the fall in HSR, the hepatic venous pressure gradient (HVPG) increased following L-arginine infusion. The mesenteric and hepatic vascular areas of cirrhosis exhibited an increased susceptibility to the dilator action of L-arginine. These findings suggest that the enhanced NO production in the splanchnic vascular area has an important role in the hepatic circulation in patients with cirrhosis.

Enhanced cyclooxygenase-1 expression within the superior mesenteric artery of portal hypertensive rats: role in the hyperdynamic circulation

Portal hypertension (PHT) is characterized by splanchnic hyperemia due to enhanced production of vasodilator substances. Enhanced vasodilation and increased splanchnic blood flow contribute to the elevated portal pressure characteristic of PHT. The aim of this study was to determine whether cyclooxygenase (Cox) expression is altered in PHT vessels and whether chronic inhibition of this enzyme impacts on splanchnic blood flow in PHT. PHT was created in Sprague-Dawley rats by a partial portal vein ligation. Control animals were sham operated. Plasma 6-keto-PGF1alpha (prostaglandin F1alpha) levels were significantly elevated in PHT after 2 days as compared with sham and remained elevated up to day 15. Treatment with indomethacin (2 mg/kg i.p. daily for 15 days) resulted in a significant decrease in 6-keto-PGF1alpha levels, which was concomitant with a significant decrease in superior mesenteric artery blood flow (Qsma) after 15 days in PHT rats. Cox-I expression was differentially enhanced in the PHT superior mesenteric artery and thoracic aorta during the development and progression of PHT. In contrast, Cox-II messenger RNA (mRNA) and protein expression was not detected in either of these vessels throughout the development of PHT. These data suggest that PHT is associated with enhanced Cox-I expression within the splanchnic vasculature concomitant with elevated plasma prostacyclin levels and a significant pressor response to indomethacin in PHT animals. We conclude that enhanced Cox-I expression results in increased prostacyclin levels that partially contribute to the maintenance of the hyperemia typical of PHT.

Nitric oxide-dependent and -independent vascular hyporeactivity in mesenteric arteries of portal hypertensive rats

1. Increased production of nitric oxide (NO) has been suggested to underlie both the vascular hyporeactivity to vasoconstrictors and the splanchnic vasodilatation seen in portal hypertension. This study assessed the role of NO in the vasoconstrictor hyporeactivity of portal vein-ligated (PVL) rats in isolated and in situ perfused mesenteric arterial beds. 2. Isolated perfused mesenteric arteries of PVL rats were significantly less reactive to noradrenaline (NA), methoxamine (METH), arginine vasopressin (AVP) and endothelin-1 (ET-1) than those from sham-operated (Sham) rats. 3. Blockade of NO synthesis with NG-nitro-L-arginine methyl ester (L-NAME, 100 microM) in isolated perfused mesenteric arteries from PVL rats restored the reactivity to bolus injections of AVP and ET-1, but had little effect on the hyporeactivity to NA or METH. Cyclo-oxygenase inhibition with indomethacin (5 microM) likewise did not restore reactivity to METH of isolated perfused mesenteric arteries of PVL rats. 4. The hyporeactivity to METH seen in isolated perfused mesenteric arteries from PVL rats was reduced by low concentrations of AVP (20 nM) or ET-1 (1 nM) which per se caused only a slight increase in perfusion pressure. When L-NAME (100 microM) was combined with AVP (20 nM) or ET-1 (1 nM), respectively, reactivity to METH of isolated perfused mesenteric arteries of PVL rats was restored to the level seen in Sham rats. These effects of AVP and ET-1 were not mimicked by precontracting the vessels with 5-hydroxytryptamine (5 microM). 5. The differential effects of L-NAME and AVP on the hyporesponsiveness to methoxamine and AVP were corroborated by experiments performed with the in situ perfused mesenteric vascular bed preparation. 6. These data indicate that both NO-dependent and NO-dependent mechanisms are involved in the vasoconstrictor hyporesponsiveness of mesenteric arteries from portal hypertensive rats. The hyporeactivity to AVP and ET-1 is mediated by NO whereas the reduced responsiveness to adrenoceptor agonists appears to be predominantly NO-independent AVP and ET-1, in addition, seem to inhibit the NO-independent mechanism of vascular hyporeactivity, since the hyporesponsiveness to METH was reduced in the presence of AVP or ET-1 and abolished by the combination of these peptides with L-NAME.

Pathophysiology of portal hypertension

Portal hypertension is a common clinical syndrome associated with chronic liver diseases and is characterized by a pathological increase in portal pressure. Increase in portal pressure is because of an increase in vascular resistance and an elevated portal blood flow. The site of increased intrahepatic resistance is variable and is dependent on the disease process. The site of obstruction may be: pre-hepatic, hepatic, and/or post-hepatic. In addition, part of the increased intrahepatic resistance is because of increased vascular tone. Another important factor contributing to increased portal pressure is elevated blood flow. Peripheral vasodilatation initiates the classical profile of decreased systemic resistance, expanded plasma volume, elevated splanchnic blood flow and elevated cardiac index. The elevated portal pressure leads to formation of portosystemic collaterals and oesophageal varices. Pharmacotherapy for portal hypertension is aimed at reducing both intrahepatic vascular tone and elevated splanchnic blood flow.

Pathophysiology of portal hypertension

Portal hypertension is a common clinical syndrome associated with chronic liver diseases, and is characterized by a pathological increase in portal pressure that leads to the formation of portosystemic collaterals resulting in shunting of portal blood into the systemic circulation. The increase in portal pressure is due to an increase in vascular resistance and an elevated portal blood flow. The site of increased resistance is variable, and dependent upon the disease process. The site of relative obstruction may be prehepatic, hepatic, or posthepatic. There are several intrahepatic lesions that lead to increased resistance. Some of these lesions are irreversible, like fibrosis, regenerating nodules, and capillarization of the space of Disse; however, there is a functional component, increased vascular tone, which contributes to increased intrahepatic resistance and is potentially reversible. Another important factor contributing to the increased portal pressure is elevated portal blood flow. Peripheral vasodilatation initiates the classical profile of decreased systemic resistance, expanded plasma volume, elevated splanchnic blood flow, and elevated cardiac index, which characterize the hyperdynamic circulatory state. This hyperdynamic circulation is responsible for various complications of portal hypertension.

Endothelial calcium-calmodulin dependent nitric oxide synthase in the in vitro vascular hyporeactivity of portal hypertensive rats

BACKGROUND/AIMS

Increased nitric oxide production has been implicated in impaired vascular responsiveness to vasoconstrictors in portal hypertension. However, there is no firm evidence concerning the involved nitric oxide synthase isoform. The present study investigated the possible contribution of one nitric oxide synthase isoform, the endothelial constitutive Ca2+-calmodulin dependent, in the overproduction of nitric oxide in portal hypertension.

METHODS

Vascular responses to norepinephrine and acetylcholine were evaluated in isolated thoracic aortic rings from normal and portal vein stenosed rats.

RESULTS

An impaired concentration-dependent contraction to norepinephrine was observed in intact rings from portal hypertensive rats compared to controls. The hyporeactivity to norepinephrine was reversed after endothelium denudation, the inhibition of nitric oxide synthase with L-NOARG or the inhibition of calmodulin with W-7, but not after pre-incubation with indomethacin. Stimulation of intact rings with norepinephrine after the inhibition of calmodulin with calmidazolium was followed by a decreased vascular response in vessels from normal rats but not in those from portal hypertensive rats. Stimulation of intact rings with norepinephrine in a Ca2+-free medium was followed by a decreased vascular response in vessels from both portal hypertensive and normal rats. No difference in vasoconstrictive responses was observed between the two groups after calmidazolium or in a Ca2+-free medium. Relaxation induced by acetylcholine in norepinephrine-precontracted rings was more marked in rings from portal hypertensive rats than in controls. No differences in the vasodilator responses were observed after relaxations had been inhibited by the removal of the endothelium, pre-incubation with L-NOARG, indomethacin, W-7 or calmidazolium and in a Ca2+-free medium.

CONCLUSIONS

This study demonstrates the involvement of the endothelial constitutive Ca2+-calmodulin dependent nitric oxide synthase isoform in the overproduction of nitric oxide in portal hypertension.

Aminoguanidine corrects hyperdynamic circulation without ameliorating portal hypertension and portal hypertensive gastropathy in anesthetized portal hypertensive rats

BACKGROUND/AIMS

Portal hypertension and hyperdynamic circulation (i.e. generalized vasodilation and increased cardiac output and regional organ blood flows) may play an important role in the development of portal hypertensive gastropathy. This study investigated the effect of chronic administration of aminoguanidine, a selective inducible nitric oxide synthase inhibitor, to portal hypertensive rats on hemodynamics and the development of portal hypertensive gastropathy.

METHODS

Partial portal vein-ligated or sham-operated rats were randomly assigned to receive either placebo (distilled water) or aminoguanidine (approximately 100 mg/kg per day subcutaneously) for 2 days prior to and 14 days. Hemodynamic studies with a thermodilution technique and gastric morphometric analysis were performed at 14 days after the operation.

RESULTS

In rats given placebo, portal vein-ligated rats had a significantly lower mean arterial pressure and systemic vascular resistance associated with a significantly higher cardiac index and portal pressure than sham-operated rats (p<0.05). In portal vein-ligated rats aminoguanidine induced a significant increase in mean arterial pressure and systemic vascular resistance accompanied by a significant decrease in cardiac index (p<0.05) without changes in portal pressure (p>0.05). Despite persistence of portal hypertension, the aminoguanidine-treated portal vein-ligated rats had similar mean arterial pressure, cardiac index, and systemic vascular resistance as seen in placebo-treated sham-operated rats. The mean cross-sectional area of gastric mucosal vessels was significantly higher in placebo-treated portal vein-ligated than in placebo-treated sham-operated rats (p<0.05). Treatment with aminoguanidine did not induce changes in the mean cross-sectional area of gastric mucosal vessels in either portal vein-ligated or sham-operated rats (p>0.05).

CONCLUSIONS

The results show that in portal hypertensive rats long-term aminoguanidine therapy corrects the hyperdynamic circulation without inducing changes in portal pressure and ameliorating the development of portal hypertensive gastropathy. This study suggests that, instead of correcting hyperdynamic circulation, treatment of portal hypertensive gastropathy should be aimed at reducing portal pressure.

Bilioenteric anastomosis reverses hyperkinetic circulation in bile duct-ligated cirrhotic rats

BACKGROUND/AIMS

The chronic bile duct-ligated rat is used to study hemodynamic changes in cirrhosis but suffers from total biliary obstruction and deep jaundice. The extent of reversibility of hemodynamics and histology following bile flow reconnection is controversial. We aimed to characterize the hemodynamics and histology of bile duct-ligated cirrhotic rats in which bile flow was reconnected by a Roux-en-y choledochojejunostomy.

METHODS

Operations created four groups: double sham (control), bile duct ligated, and two reconnected groups. Cardiac index and regional blood flows were measured by radioactive microspheres 4 weeks following the last operation in the first three groups and 8 weeks afterwards in the second reconnected group. Liver histology was assessed by a computer-aided scoring program.

RESULTS

Cardiac index, mean arterial pressure, and systemic vascular resistance in the reconnected groups were different from bile duct-ligated rats and returned to control values. Portal pressures in the reconnected groups (4-weeks, 10.0 +/- 0.5 and 8-week, 9.7 +/- 0.6 mmHg) were significantly lower than in bile-duct-ligated rats (13.7 +/- 0.6) but remained elevated compared to controls (7.0 +/- 0.3). Portal pressure in the reconnected rats was correlated with cardiac index and mesenteric blood flow, r = 0.66 and r = 0.45, respectively. Liver histology was improved in the reconnected rats, with decreased bile duct proliferation, fibrosis and apoptosis.

CONCLUSIONS

We conclude that many of the histological features of secondary biliary cirrhosis are reversible after bilioenteric anastomosis. Furthermore, the hyperdynamic circulation is also largely reversible and is related to the degree of portal hypertension.

Anatomical differences in responsiveness to vasoconstrictors in the mesenteric veins from normal and portal hypertensive rats

The present study evaluates the effects of pre-hepatic portal hypertension, induced in rats by partial portal vein ligation, on the responsiveness of rostral (proximal) and caudal (distal) rings from the mesenteric vein. The anatomical origin of the sample influenced the response to vasoconstrictors in sham-operated animals, and this pattern of reactivity was specifically modified in portal-ligated rats. In veins from sham-operated rats, contraction induced by a submaximal concentration of KCl (60 mM) was greater in proximal than in distal rings. Vasopressin and 5-hydroxytryptamine contracted mainly distal rings, methoxamine showed a greater effect on proximal rings, and endothelin-1 and angiotensin-II contracted vein rings independently of their anatomical origin. In veins from portal hypertensive rats, response to KCl (60 mM) were increased in distal rings, and all rings exhibited enhanced reactivity to vasopressin and 5-hydroxyptyptamine as well as attenuation of the response to methoxamine. Responses to endothelin-1 were decreased in proximal vein rings from portal hypertensive rats whereas responses to angiotensin-II were not influenced by the anatomical origin. Incubation with atropine, propranolol or indomethacin, did not modify the responses to vasopressin and 5-hydroxytryptamine in tissues from either sham-operated or portal hypertensive animals. Likewise, the hyporeactivity to methoxamine and endothelin-1 in rings from portal hypertensive rats persisted in the presence of the nitric oxide inhibitor NG-nitro-L-arginine methyl ester. These results suggest the physiological existence of anatomical differences in the responsiveness to vasoconstrictors throughout the mesenteric vein and that changes in the responsiveness of the mesenteric vein induced by portal hypertension are specific for each agonist and possibly result from individual variations at a receptor or post-receptor level.

Haemodynamic and hormonal responses to long-term inhibition of nitric oxide synthesis in rats with portal hypertension

In portal hypertension, the role of the vasorelaxant nitric oxide (NO) in long-term splanchnic and systemic vascular tone regulation is unclear. This study examined the effects of long-term administration of a NO synthesis inhibitor on haemodynamics in portal hypertensive rats. Rats were randomly assigned to receive either water (placebo) or 100 mg/kg.day of oral N-nitro-L-arginine methylester (L-NAME) for 28 days. At 14 days, the portal vein was ligated in 10 rats from each group. At 28 days, splanchnic and systemic blood flows were measured in 20 normal and 20 portal vein stenosed rats. Plasma atrial natriuretic peptide (ANP) concentrations as well as plasma and urinary cyclic guanosine monophosphate (cGMP) levels were also measured. Porto-systemic shunts were measured in other portal vein stenosed animals that had or had not received L-NAME. Portal vein stenosed rats that received L-NAME had significantly lower portal tributary blood flow and percentages of portal-systemic shunting (7.3 +/- 0.5 versus 3.7 +/- 0.2 ml/min.100 g and 96 +/- 1 versus 68 +/- 5%, respectively) and higher hepatocollateral vascular resistance (147 +/- 10 versus 295 +/- 30 dyn.s.cm-5.100 g.10(3), respectively) than placebo portal vein stenosed rats. Portal pressure, ANP and cGMP levels did not differ between the groups. Arterial pressure was significantly higher and cardiac index lower after L-NAME than after placebo. Normal rats had similar but less marked L-NAME-induced responses than portal hypertensive rats. The presence of a long-term L-NAME-induced vasoconstriction in collateral vessels and splanchnic and systemic arterioles in portal vein stenosed rats indicates that a NO-mediated vasodilator tone may contribute to the development and the maintenance of collateral circulation as well as splanchnic and systemic vasodilation in portal hypertension. Moreover, the NO-mediated vasodilator tone in portal hypertensive animals seems to be increased.

Increased endothelial nitric oxide synthase activity in the hyperemic vessels of portal hypertensive rats

BACKGROUND/AIM

Portal hypertension is characterized by splanchnic hyperemia due to a reduction in mesenteric vascular resistance. Mediators of this hyperemia include nitric oxide. This is based on several reports indicating a marked splanchnic hyporesponsiveness in portal hypertension to vasoconstrictor stimuli both in vitro and in vivo, and a subsequent reversal using specific inhibitors of nitric oxide synthase. The objective of this study was to determine firstly whether the functional activity and/or expression of nitric oxide synthase is altered in portal hypertensive vasculature and secondly which isoenzyme form was responsible for the preferential response to nitric oxide blockade in these animals.

METHODS

We compared nitric oxide synthase functional activity in the hyperemic vasculature of sham and portal hypertensive rats (following partial portal vein ligation). Nitric oxide synthase activities were determined by measuring the conversion of L-arginine to citrulline using ion-exchange chromatography and the amount of immunodetectable nitric oxide synthase in sham and portal hypertensive vessels was determined by Western blot.

RESULTS

Ca(2+)-dependent nitric oxide synthase activity was significantly elevated (p < 0.05) in portal hypertensive particulate fractions from the superior mesenteric artery, thoracic aorta and portal vein. Vascular tissue cGMP levels and plasma nitrite levels were both significantly elevated in portal hypertension. Immunodetection with specific antisera raised against the inducible nitric oxide synthase demonstrated a lack of induction within the hyperemic vasculature. Immunodetection with antisera against endothelial nitric oxide synthase showed a significant increase in portal hypertensive portal vein only. These results demonstrate enhanced calcium-dependent nitric oxide synthase activity in portal hypertension hyperemic vessels concurrent with elevated tissue cGMP levels.

CONCLUSION

We conclude that enhanced endothelial nitric oxide synthesis may in part contribute to the hyperdynamic circulation of portal hypertension.

Energy metabolism in portal hypertension in children

This study was designed to assess resting energy expenditure (REE) and nutritional status in children with hepatic and prehepatic portal hypertension in comparison with healthy controls. Twenty-five patients with portal hypertension (PHT) and a history of variceal bleeding were compared with 14 healthy volunteers selected after matching for age and sex. PHT patients were allocated to one of two groups: 11 children with liver cirrhosis and/or chronic hepatitis, aged 14.0 +/- 3.3 y (means +/- SD) or 14 children with extrahepatic portal vein obstruction, aged 12.3 +/- 2.8 y. The control group consisted of 14 healthy children, aged 14.0 +/- 1.8 y. REE (indirect calorimetry) assessed after an overnight fast was significantly higher in PHT patients than in controls when related to body mass (143.7 +/- 29.5 and 116.1 +/- 5.9 kJ/kg, respectively; p < 0.004), lean body mass (168.0 +/- 28.9 and 146.4 +/- 14.1 kJ/kg, respectively; p < 0.02), and body surface area (7480 +/- 736 and 6590 +/- 567 kJ/1.73 m2, respectively; p < 0.001). The ratios of measured REE to basal energy expenditure calculated from standard equations (Schofield equations) indicated higher REE in PHT patients (102.24 +/- 6.90% and 93.54 +/- 4.47%, respectively; p < 0.001). Fat was the predominant source of energy in both PHT patients and controls; the percentage of nonprotein energy derived from carbohydrate oxidation was equaled: 36.04 +/- 18.84% and 37.15 +/- 15.71%, respectively. Analysis of percentage of undernutrition in PHT patients and controls revealed significant differences (44% and 21%, respectively; p < 0.001). Children with PHT are susceptible to malnutrition and have elevated REE compared with healthy controls. Fat is the principal basal state oxidative substrate for patients with PHT and healthy children.

Hyporeactivity of mesenteric resistance arteries in portal hypertensive rats

BACKGROUND/AIMS

Hyporesponsiveness to vasoconstrictors in portal hypertension has been shown to involve increased production of nitric oxide in large arteries in vitro. Small arteries (diameter 50-500 microns) are partly responsible for peripheral resistance and probably have different regulatory mechanisms from large arteries. The purpose of this study was to investigate the hyporeactivity of small mesenteric resistance arteries in portal hypertensive rats and to determine the role of nitric oxide and prostaglandins in this hyporesponsiveness.

METHODS

Third branch mesenteric arteries from normal and portal hypertensive rats obtained by portal vein ligation were isolated and suspended in myographs for isometric tension recording. Reactivity to vasoconstrictors was assessed by dose-responses to phenylephrine (Phe 10(-8) to 10(-3) M) and by potassium chloride (KCl 45 mM). Acetylcholine (Ach 10(-5) M) was administered in pre-contracted KCl 45 mM arterial rings to evaluate endothelium-dependent relaxation. Pre-incubations with N-nitro-L-arginine (L-NNA 10(-4) M, a specific inhibitor of nitric oxide synthase, or with indomethacin (10(-5) M), a specific inhibitor of cyclo-oxygenase, were performed to compare the individual roles of nitric oxide and prostaglandins in KCl 45 mM-induced contractions.

RESULTS

Impaired responses to Phe (3731 +/- 851 microN and 5971 +/- 745 microN, respectively; p < 0.05) and to KCl (2197 +/- 251 vs 2804 +/- 222 microN, respectively; p < 0.05) were observed in mesenteric resistance arterial rings from portal hypertensive rats compared to rings from normal rats. Ach-dependent relaxation did not significantly differ between normal (-25.7 +/- 5.1%) and portal hypertensive (-17.3 +/- 3.3%) rats. Indomethacin induced a similar significant increase in KCl-induced contraction in normal (3472 +/- 400 microN) and portal hypertensive (3432 +/- 654 rats. Nitric oxide synthesis inhibition had no effect in normal rats (3032 +/- 368 microN) but significantly increased KCl-induced contraction in portal hypertensive rats (3331 +/- 551 microN).

CONCLUSION

These results demonstrate the existence of a hyporesponsiveness to vasoconstrictors in small mesenteric resistance arteries of portal hypertensive rats, which seems to be due to increased production of nitric oxide.

Increased prostacyclin content in gastric mucosa of cirrhotic patients with portal hypertensive gastropathy

Plasma levels and gastric mucosal contents of prostaglandin (PG) E2 and prostacyclin were determined in cirrhotic patients with portal hypertensive gastropathy (PHG), in cirrhotic patients without PHG and in healthy controls. PGE2 and 6-keto-PGF1 alpha (a stable metabolite of prostacyclin) levels were measured in 30 cirrhotic patients and 10 controls, using radioimmunoassay. Of 30 cirrhotics, 13 had PHG of the fundus and the corpus. Plasma concentrations of 6-keto-PGF1 alpha in the cirrhotic patients were significantly higher than in the controls (p < 0.01), but there was no significant difference between cirrhotics and controls with regard to plasma levels of PGE2. The gastric mucosal contents of 6-keto-PGF1 alpha in the fundus was significantly higher in cirrhotics with PHG than those without PHG (p < 0.05) and controls (p < 0.01). However, the gastric mucosal contents of PGE2 in the fundus were not significantly different in cirrhotics with and without PHG. The gastric mucosal contents of 6-keto-PGF1 alpha significantly correlated to the plasma levels (r = 0.37, p < 0.05), but there was no significant correlation between plasma levels and gastric mucosal contents of PGE2. Since prostacyclin has vasodilator and gastric acid inhibitory effects, we speculate that high contents of prostacyclin in the gastric mucosa may have some role in the pathogenesis of PHG.

Impaired vasodilatory responses in the gastric microcirculation of anesthetized rats with secondary biliary cirrhosis

BACKGROUND/AIMS

The increased susceptibility of the stomach to injury observed in portal hypertension may be related to a defect in the hyperemic response to luminal irritants. The aim of this study was to evaluate the components that mediate this hyperemic response in a rat model of cirrhosis and portal hypertensive gastropathy.

METHODS

Cirrhosis was induced by bile duct ligation, whereas controls underwent sham operation. Gastric blood flow responses to topical application of acid, capsaicin, nitrovasodilators, misoprostol, 8-bromo-cyclic guanosine monophosphate, and 8-bromo-cyclic adenosine monophosphate were measured by laser Doppler flowmetry using an ex vivo gastric chamber preparation. Calcitonin gene-related peptide immunoreactivity was used as an index of the anatomic integrity of the sensory afferent neurons of the stomach.

RESULTS

Blood flow responses to acid, capsaicin, nitrovasodilators, and 8-bromo-cyclic guanosine monophosphate were significantly depressed in cirrhotic rats, whereas they were augmented after topical application of misoprostol and 8-bromo-cyclic adenosine monophosphate. Calcitonin gene-related peptide immunoreactivity was similar in the stomachs of cirrhotic and control rats.

CONCLUSIONS

Gastric vasodilation after stimulation of sensory afferent neurons is impaired in cirrhotic rats despite the normal anatomic distribution of these nerves. This effect seemed to be related to a depressed response of the gastric microcirculation to cyclic guanosine monophosphate-dependent vasodilators. This alteration may contribute to the increased susceptibility to gastric ulceration in cirrhotics.