Renal effects of the chronic inhibition of nitric oxide synthesis in cirrhotic rats with ascites

Previous studies have shown that acute inhibition of nitric oxide (NO) synthesis improves sodium and water excretion and increases blood pressure in cirrhotic rats with ascites, thus suggesting that NO is an important factor contributing to the arterial hypotension and sodium retention of liver cirrhosis. In the present work we have analyzed the renal effects derived from the chronic oral treatment (10 days) with aminoguanidine (AG, 100 mg/kg/day), a preferential inhibitor of inducible NO synthase (iNOS), or Nw-Nitro-L-Arginine Methyl Ester (L-NAME, 0.5 mg/kg/day), a nonselective inhibitor of NOS, in an experimental model of liver cirrhosis with ascites (carbon tetrachloride inhalation). Untreated cirrhotic rats showed lower mean arterial pressure (MAP), diuresis, natriuresis and glomerular filtration rate (GFR) and similar renal blood flow (RBF) compared with the untreated control rats. Chronic administration of AG did not modify significantly any parameter in cirrhotic and control animals. Conversely, long-term L-NAME administration to cirrhotic rats normalized MAP and significantly increased water and sodium excretion, whereas in control animals these parameters were not significantly modified. These results show that chronic NO synthesis inhibition with L-NAME, but not with aminoguanidine, improves renal perfusion pressure and increases the lower sodium and water excretion of cirrhotic rats with ascites. Thus, an enhanced production of NO is an important factor contributing to the renal sodium and water retention characteristic of liver cirrhosis.     

NCX-1000, a nitric oxide-releasing derivative of ursodeoxycholic acid, ameliorates portal hypertension and lowers norepinephrine-induced intrahepatic resistance in the isolated and perfused rat liver

BACKGROUND/AIMS: We studied whether acute administration of NCX-1000, a nitric oxide (NO)-releasing derivative of ursodeoxycholic acid (UDCA), to animals with established liver cirrhosis decreases intrahepatic resistance and modulates hepatic vascular hypereactivity to norepinephrine (NE). METHODS: Four-week bile duct ligated (BDL) cirrhotic and control, sham-operated, rats were treated orally with 28 mg/kg per day NCX-1000 or 15 mg/kg per day UDCA for 5 days. Isolated normal and cirrhotic livers were perfused with NE, from 10 nM to 30 microM, in a recirculating system. RESULTS: NCX-1000 administration to BDL cirrhotic rats decreased portal pressure (P<0.01) without affecting mean arterial pressure and heart rate. In the isolated perfused liver system, administration of NE resulted in a dose-dependent increase of intrahepatic resistance. Vasoconstriction caused by 30 microM NE was reduced by 60% in animals treated with NCX-1000 (P<0.001), while UDCA was uneffective. The same portal pressure lowering effect was documented in cirrhotic and sham operated rats. Administration of NCX-1000 to BDL and sham operated rats resulted in a similar increase of nitrite/nitrate and cGMP concentrations in the liver. CONCLUSIONS: By selectively delivering NO to the liver, NCX-1000 increases cGMP concentrations and effectively counteracts the effect of endogenous vasoconstrictors on the hepatic vascular tone.     

Effect of L—NAME on nitric oxide and gastrointestinal motility alterations in cirrhotic rats

AIM: To invsstigare the effect of L-NAME on nitric oxide andgastriubtestubal motility alterations in cirrhotic ratsMETHODS: Rats with cirrhosis induced by carbontetrachloride were randomly divided into two groups, one( n= 13) receiving 0. 5 mg@ kg-1 per clay of NG-nitro-L-argininemethyl ester (L-NAME), a nitric oxide synthase inhibitor,for 10 days, whereas the other group ( n = 13) and control( n = 10) rats were administrated the same volume of 9 g@ L-1saline.Half gastric emptying time and 2 h residual rate weremeasured by SPECT, using 99m Tc-DTPA-labeled bariumsuifate as test meal. Gastrointestinal transition time wasrecorded simultaneously. Serum concentration of nitrcoxide (NO) was determined by the kinetic cadmiunreduction and colorimetric methods. ImmunohistochemicalSABC method was used to observe the expression anddistribution of three types of nitric oxide synthase (NOS)isoforms in the mt gastrointestinal tract. Western blot wasused to detect expression of gastrointestinal NOS isoforms.RESULTS: Half gastric emptying time and trans-gastrointestinal time were significantly prolonged( 124.0 ± 26.4min; 33.7± 8.9min;72.1 ± 15.3 min; P＜0.01), (12.4±0.5h; 9.5±0.3 h; 8.2±0.8 h; P＜0.01), 2h residual rate wasraised in cirrhotic rots than in controls and cirrhotic ratstreated with L-NAME(54.9± 7.6 % ,13.7 ± 3.2 %, 34.9± 10.3%, P＜ 0.01). Serum concentration of NO was significantlyincreased in cirrhotic rots than in the other groups (8.20 ± 2.48)μmol@L-1, (5.94± 1.07) μmol@L-1 ,and control (5.66± 1.60) tμmol@L-1, P＜ 0.01. NOS staining intensities which weremainly located in the gastrointestinal tissues were markedlylower in cirrhotic rats than in the controls and cirrhotic ratsafter treated with L- NAME.CONCLUSION: Gastrointestinal motility was remarkablyinhibited in cirrhotic rats, which could he alleviated by L-NAME. Nitric oxide may play an important role in theinhibition of gastrointestinal motility in cirrhotic rats.     

Cholestatic liver disease modulates susceptibility to ischemia/reperfusion-induced arrhythmia, but not necrosis and hemodynamic instability: the role of endogenous opioid peptides

BACKGROUND/AIMS: Acute cholestasis is associated with cardiovascular complications, which mainly manifest during stressful conditions. The goal of this study is to evaluate susceptibility of 7-day bile duct-ligated rats to ischemia/reperfusion-induced injury. METHODS: Sham-operated and cholestatic rats, treated with daily normal saline, L-NAME (a non-selective NO synthase inhibitor) naltrexone, or both L-NAME and naltrexone were subjected to 30 min of ischemia followed by 2 h of reperfusion. RESULTS: Cholestatic rats demonstrated significant bradycardia, hypotension (P < 0.01), and QT prolongation (P < 0.001). The incidence of premature ventricular contractions (P < 0.01), incidence and duration of ventricular tachycardia (P < 0.05), but not ventricular fibrillation, were significantly lower in cholestatic rats. There was no significant difference in hemodynamic instability and infarct size between the groups. L-NAME corrected QT prolongation in cholestatic rats (P < 0.05), with no effect on heart rate, blood pressure and arrhythmia. Naltrexone restored normal heart rate (P < 0.05), blood pressure (P < 0.05) and susceptibility to arrhythmia (P < 0.05) in cholestatic animals, with no significant effect on QT interval. L-NAME and naltrexone co-administration corrected bradycardia (P < 0.05), hypotension (P < 0.05), QT prolongation (P < 0.05) and abolished resistance of cholestatic rats against arrhythmia (P < 0.05). CONCLUSIONS: This study suggests that short-term cholestasis is associated with resistance against ischemia/reperfusion-induced arrhythmia, which depends on availability of endogenous opioids.     

The effect of N-nitro-L-arginine methyl ester on morphine-induced changes in the plasma corticosterone and testosterone levels in mice.

Effects of the nitric oxide synthase inhibitor, N-nitro-L-arginine methyl ester (L-NAME, 30 mg/kg i.p.), on morphine-induced changes in the plasma corticosterone and testosterone levels were studied in male mice. Acute morphine administration (15 and 30 mg/kg i.p.) enhanced the corticosterone level after 1 and 2 hr (at a dose of 30 mg/kg only). A 4-day treatment with increasing doses of morphine, from 15 to 50 mg/kg i.p., increased the plasma corticosterone concentration at 2 hr after the last injection. Single administration of L-NAME (30 mg/kg i.p.) had no effect on the corticosterone level, whereas its repeated injections (30 mg/kg i.p., twice a day for four days) elevated the hormone concentration at 2 hr after the last dose. Pretreatment of mice with L-NAME enhanced the stimulatory effects of both acute and repeated morphine administration on the corticosterone level. D-NAME (30 mg/kg i.p.), an inactive form of the nitric oxide synthase inhibitor, had no effect on the morphine-induced changes in the corticosterone level. Acute morphine administration had no effect on the plasma testosterone level after 1 or 2 hr, whereas repeated drug injections decreased the hormone concentration after 2 hr. Single or repeated L-NAME administration did not influence the testosterone level in either control or morphine-treated animals. The above results indicate that inhibition of nitric oxide synthase enhances the stimulatory effect of morphine on corticosterone secretion, but does not influence the inhibitory effect of repeated morphine on the plasma testosterone concentration in mice.     

Chronic Inhibition of Nitric Oxide Ameliorates Splanchnic Hyposensitivity to Glypressin in a Hemorrhage-transfused Rat Model of Portal Hypertension

Background: Vasopressin given during hemorrhage is less effective than when given during a stable state in experimental portal hypertension or patients with cirrhosis (the so-called hyposensitivity phenomenon). This study investigated whether chronic inhibition of nitric oxide (NO) synthesis by N^G-nitro-L-arginine methyl ester (L-NAME), a non-selective NO synthase inhibitor, could potentiate the portal-hypotensive effect of glypressin (a long-acting vasopressin analogue) in portal-hypertensive rats during acute bleeding status. Methods: Portal hypertension was induced by partial portal vein ligation (PVL). Rats were divided to receive either L-NAME (~25 mg/kg/day in tap water) or placebo (tap water) treatment orally from 2 days prior to until 14 days after the operation. At the end of treatment, L-NAME-and placebo-treated PVL rats were subdivided into without-bleeding and with-bleeding groups to assess the effects of glypressin (0.07 mg/kg) on systemic and portal hemodynamics. In rats with a hypotensive hemorrhage, 4.5 ml of blood was withdrawn and 50% of the withdrawn blood was reinfused before the administration of glypressin. Results: As compared with placebo-treated rats, chronic treatment with L-NAME in PVL rats significantly increased mean arterial pressure (P &lt; 0.001) without modulating portal pressure (P &gt; 0.05). In placebo-treated PVL rats, glypressin resulted in a less decrease in portal pressure in rats with bleeding than in those without bleeding (P &lt; 0.05). For PVL rats with bleeding, the portal-hypotensive effect of glypressin was significantly potentiated after chronic L-NAME treatment (P &lt; 0.05). Conclusions: Chronic inhibition of NO alleviates the splanchnic hyposensitivity to glypressin observed in bleeding PVL rats, suggesting the pathophysiological role of nitric oxide in mediating this splanchnic hyposensitivity.     

Magnesium deficiency in adult rats promotes the induction of ventricular tachycardia by the administration of epinephrine

Summary The effects of magnesium deficiency on epinephrine-induced ventricular tachyarrhythmia were investigated in adult rats. Forty-two adult Wistar rats were fed a magnesium-deficient diet while 30 rats were fed a standard diet for 20 days. The plasma magnesium concentration was lower in the magnesium-deficient rats (0.22 ± 0.01mmol/l) than in the control rats (0.76 ± 0.03 mmol/l,P < 0.001). Using a telemetry system, electrocardiograms and arterial blood pressure were recorded on a polygraph in an unrestrained condition. Epinephrine was infused intravenously starting at 5 µg/kg per minute. The QT interval was prolonged to 50 ± 1ms in the magnesium-deficient rats compared with 44 ± 1 ms in the control rats (P < 0.001). Before the administration of epinephrine, no ventricular tachyarrhythmias or seizures were found in either the control or the magnesium-deficient rats. The incidence of epinephrine-induced sustained ventricular tachycardia (VT) was higher in the magnesiumdeficient rats (86%) than in the control rats (43%,P < 0.01). However, this VT did not result in sudden death. Seizures always preceded death in both the magnesium-deficient and control rats while the arrhythmias observed immediately before death were mainly bradyarrhythmias. The present study in an adult rat magnesium-deficient model revealed that magnesium deficiency enhances the susceptibility to epinephrine-induced ventricular tachyarrhythmias.This study was supported in part by grants from the Salt Science Research Foundation (9131, 92045)     

Antiplatelet Agents Sarpogrelate and Cilostazol Affect Experimentally-induced Ventricular Arrhythmias and Mortality

Antiplatelet agents, sarpogrelate (SAR), a 5-hydroxy tryptamine 2A receptor antagonist and cilostazol (CIL), a phosphodiesterase-III inhibitor, were observed to be beneficial in attenuating cardiac remodeling and improving cardiac function in congestive heart failure due to myocardial infarction in rats; however, CIL increased ventricular tachycardia and mortality. In order to study the effects of these antiplatelet agents on arrhythmias, Sprague-Dawley rats were pretreated with either SAR or CIL (5 mg/kg/day) for 2 weeks and were then either injected cumulative doses of epinephrine (Epi) or subjected to coronary occlusion. Saline-treated animals served as controls. Electrocardiographic analysis revealed that SAR pretreatment decreased the incidence and severity of ventricular arrhythmias (time of onset of arrhythmias as well as the occurrence of premature ventricular contractions, salvos, tachycardia, and fibrillations), whereas CIL treatment augmented the incidence of cardiac arrhythmias due to both Epi and coronary occlusion. None of the drugs affected the corrected QT interval significantly. Furthermore, the levels of cyclic adenosine monophosphate (cAMP) in left ventricle were markedly higher in CIL-pretreated rats when compared to SAR-pretreated or control rats. It is suggested that an excessive level of cAMP may contribute to increase incidence of ventricular arrhythmias and mortality in animals pretreated with CIL, unlike the SAR-pretreated rats.     

Sympathomimetic infusion and cardiac repolarization: the normative effects of epinephrine and isoproterenol in healthy subjects

Introduction: Catecholamines are known to affect cardiac repolarization, and provocation with either isoproterenol or epinephrine has been proposed as a tool for uncovering latent repolarization abnormalities. This study systematically compares the effects of isoproterenol and epinephrine infusions on QT interval (QT), T waves and U waves in normal subjects.
Methods and Results: Twenty-four normal subjects (29 ± 8 years) were evaluated during graded infusions of up to 0.30 μg/kg/minute epinephrine and 5.0 μg/minute isoproterenol. Heart rates at peak doses were 81 ± 13 bpm at 0.28 ± 0.04 μg/kg/minute epinephrine and 104 ± 5 bpm at 2.4 μg/minute isoproterenol. The longest absolute QT increase was 4 ± 5 msec above baseline during isoproterenol (P < 0.001) and 12 ± 23 msec during epinephrine (P = 0.07), while the longest corrected QT interval (QTc) increase was 67 ± 28 msec (P < 0.0001) and 79 ± 40 msec (P < 0.0001) above baseline during isoproterenol and epinephrine, respectively (P = 0.12 for difference). There was a 2-fold increase in U-wave amplitude during each intervention (P < 0.001). The specificity of paradoxical QT prolongation (≥30 msec at 0.05 μg/kg/minute or ≥35 msec at 0.10 μg/kg/minute epinephrine) and an increase in QTc ≥600 msec at any dose epinephrine were 100%. However, the specificity of other proposed criteria that utilized QTc measurement (≥30 msec at 0.10 μg/kg/minute or ≥65 msec at any dose) was poor whether all leads or only lead II were assessed.
Conclusion: Both epinephrine and isoproterenol are associated with QTc prolongation and amplification of the U wave in normal subjects. The specificity of proposed criteria for epinephrine provocation in diagnosis of the long-QT syndrome is variable; however, paradoxical QT prolongation at low-dose epinephrine or a QTc ≥600 msec is highly specific.     

Simvastatin for rats with thioacetamide-induced liver failure and encephalopathy

Background and Aim:  Nitric oxide (NO) inhibition aggravates hepatic damage and encephalopathy and increases mortality in rats with thioacetamide (TAA)-induced acute liver failure. Statins enhance NO synthase expression beyond their lipid-lowering capability, but the impact on encephalopathy remains unexplored. The aim of this study was to assess the effects of simvastatin on rats with TAA-induced acute liver damage and hepatic encephalopathy.
Methods:  Sprague–Dawley rats received TAA (350 mg/kg/day) or normal saline (NS) by intraperitoneal injection for 3 consecutive days. Two days before injections, each group was divided into three subgroups, taking (i) distilled water; (ii) simvastatin (20 mg/kg/day); or (iii) simvastatin plus N ^G-nitro- l -arginine methyl ester (L-NAME, 25 mg/kg/day) by oral gavage for 5 days. On the fifth day, severity of encephalopathy was assessed and plasma levels of alanine aminotransferase (ALT), aspartate aminotransferase (AST), total bilirubin and ammonia were measured.
Results:  The TAA subgroups showed higher ALT, AST, bilirubin and ammonia levels and lower motor activity counts as compared with the NS subgroups. Among the TAA-treated subgroups, rats with simvastatin treatment exerted higher motor activity counts and survival rate ( P  = 0.043), and a trend of lower ALT, AST, bilirubin and ammonia levels than those receiving saline. All rats that underwent simvastatin plus L-NAME treatment died during or after TAA injections.
Conclusions:  Simvastatin improved encephalopathy and survival in TAA-administered rats. The beneficial effect was offset by L-NAME, suggesting the role of NO in liver damage and encephalopathy.     

Effect of endothelin blockade on pressure natriuresis in nitric oxide-deficient hypertensive rats

OBJECTIVE: Chronic inhibition of nitric oxide synthesis has been shown to cause arterial hypertension and an important blunting of the pressure diuresis and natriuresis response. The mechanisms mediating these abnormalities are not completely established. We therefore studied the effects of endothelin on these alterations. MATERIALS AND METHODS: Pressure diuretic and natriuretic relationships were evaluated in rats treated chronically (3 weeks) with the nitric oxide synthesis inhibitor N(omega)-nitro-L-arginine methyl ester (L-NAME; 40 mg/kg per day), alone or in combination with bosentan sodium salt (acute treatment: 10 mg/kg, intravenously; chronic treatment: 10 mg/kg per day). RESULTS: Chronic treatment with L-NAME significantly elevated mean arterial pressure (143.7 +/- 2.8 mmHg versus 102.8 +/- 1.6 in controls), reduced the glomerular filtration rate and renal blood flow and shifted the pressure diuretic and natriuretic responses to the right. Treatment with bosentan, either acute or chronically, did not attenuate the arterial hypertension of the L-NAME-treated rats but normalized the glomerular filtration rate and renal blood flow. In spite of the normalization of renal hemodynamics, the pressure diuretic and natriuretic responses of the bosentan-treated groups were not normalized, although chronic bosentan significantly improved the pressure natriuretic response. CONCLUSIONS: These results indicate that endothelin participates in the renal hemodynamic and excretory alterations that follow chronic inhibition of nitric oxide synthesis. However, the arterial hypertension is not mediated by endothelin activation.     

The hydroxyl radical scavengers dimethylsulfoxide and dimethylthiourea protect rats against thioacetamide-induced fulminant hepatic failure.

BACKGROUND/AIMS: Reactive oxygen species, proinflammatory cytokines, glutathione depletion and nitric oxide have all been implicated in the pathogenesis of fulminant hepatic failure. The aim of the present study was to examine the respective roles of these factors in the pathogenesis of thioacetamide-induced fulminant hepatic failure in rats. METHODS: Fulminant hepatic failure was induced by 3 consecutive intraperitoneal injections of thioacetamide (400 mg/kg) at 24-h intervals. Rats were pretreated with one of the following agents: the free radical scavengers dimethylsulfoxide (4 g/kg every 6 h) or dimethylthiourea (200 mg/kg every 12 h), the glutathione donor, N-acetylcysteine (130 or 200 mg/kg every 6 h), or the anti-tumor necrosis factor-alpha agents pentoxifylline (100 and 200 mg/kg) and soluble tumor necrosis factor receptor (100 or 1000 microg/rat). The nitric oxide synthase inhibitor N-mono-methyl arginine ester (L-NAME, 0.1 mg/ml) was administered in the drinking water, starting 7 days prior to thioacetamide administration. RESULTS: Serum levels of liver enzymes, blood ammonia and prothrombin time and the stage of hepatic encephalopathy were significantly improved in rats treated with dimethylsulfoxide or dimethylthiourea compared to the other treatment groups (p<0.001). Liver histology and the survival rate in these rats were not adversely affected by thioacetamide administration (p<0.001), while in all the other treatment groups those parameters were similar to control rats with fulminant hepatic failure. Furthermore, dimethylsulfoxide ameliorated liver damage and improved survival even when its administration was initiated 8 and 16 h after the first thioacetamide injection. The hepatic concentration of methanesulfinic acid, which is produced after direct interaction of dimethylsulfoxide with hydroxyl radicals, was increased five-fold in rats treated with thioacetamide+dimethylsulfoxide (p<0.001), suggesting a role for hydroxyl radical scavenging in the protection from fulminant hepatic failure in this model. In the group of thioacetamide-treated rats that were pretreated with L-NAME, liver enzymes, blood ammonia levels and the mortality rate were higher than in the control group, treated with thioacetamide only. CONCLUSIONS: In thioacetamide-induced fulminant hepatic failure, the hydroxyl radical scavengers dimethylsulfoxide and dimethylthiourea prevent liver injury. Neither N-acetylcysteine nor antagonists of tumor necrosis factor-alpha are protective in this rat model. Inhibition of nitric oxide formation aggravates liver damage and reduces the survival of rats with thioacetamide-induced liver damage.     

Relative deficiency of nitric oxide-dependent vasodilation in salt-hypertensive Dahl rats: the possible role of superoxide anions

OBJECTIVE: The contribution of major vasoactive systems (renin-angiotensin system, sympathetic nervous system and nitric oxide) to blood pressure maintenance and the possible involvement of superoxide anions in the reduced efficiency of nitric oxide (NO)-dependent vasodilation to counterbalance sympathetic vasoconstriction were studied in salt-hypertensive Dahl rats. DESIGN AND METHODS: We used Dahl salt-sensitive (SS/Jr) and salt-resistant (SR/Jr) female rats kept on a low-salt (0.3% NaCl) or high-salt diet (8% NaCl) for 6 weeks since weaning. Mean arterial pressure (MAP) was measured in conscious animals subjected to acute consecutive blockade of the renin-angiotensin system (RAS) [captopril, 10 mg/kg intravenously (i.v.)], the sympathetic nervous system (SNS) (pentolinium, 5 mg/kg i.v.) and NO synthase (Nomega-nitro-L-arginine methyl ester (L-NAME), 30 mg/kg i.v.). Before the consecutive blockade of vasoactive systems one-half of the animals in each experimental group was pre-treated with a stable membrane-permeable mimetic of superoxide dismutase (tempol, 25 mg/kg i.v.) which functions as a superoxide scavenger. RESULTS: Compared to normotensive SR/Jr animals, salt-hypertensive SS/Jr rats were characterized by an enhanced blood pressure (BP) fall after ganglionic blockade (-104 +/- 8 versus -62 +/- 5 mm Hg, P < 0.001) and by higher residual blood pressure recorded after the blockade of both RAS and SNS (70 +/- 3 versus 43 +/- 3 mmHg, P < 0.01), but there was only a borderline elevation of their BP response to acute NO synthase inhibition (67 +/- 6 versus 49 +/- 4 mmHg, P < 0.05). The acute tempol pre-treatment elicited the most pronounced reduction of basal BP (-13 +/- 1 mmHg, P < 0.001) in the salt-hypertensive SS/Jr group in which the BP rise after L-NAME administration was augmented by about 50%. On the contrary, tempol pre-treatment did not affect norepinephrine- or angiotensin II-dependent vasoconstriction. CONCLUSIONS: The NO system is not able to counterbalance effectively the hyperactivity of the sympathetic nervous system in salt-hypertensive Dahl rats. The predominance of sympathetic vasoconstriction over NO-dependent vasodilation could be explained partially by enhanced NO inactivation due to augmented superoxide anion formation in hypertensive animals.     

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

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

Effects of antihypertensive therapy on factors mediating endothelium-dependent relaxation in rats treated chronically with L-NAME

OBJECTIVES: To evaluate the relative participation of endothelium-derived factors mediating relaxation in response to acetylcholine in isolated mesenteric vascular beds from rats treated chronically with N(G)-nitro-L-arginine methylester (L-NAME); and to compare the consequences of prolonged treatment with either an angiotensin converting enzyme inhibitor or a calcium channel blocker on the components of acetylcholine-induced relaxation in this vascular preparation. MATERIALS AND METHODS: Male Sprague- Dawley rats were treated for 8 weeks with L-NAME (40 mg/kg per day), quinapril (10 mg/kg per day), diltiazem (100 mg/kg per day), L-NAME + quinapril and L-NAME + diltiazem. Systolic blood pressure was estimated by a tail-cuff plethysmograph. Relaxing responses to acetylcholine (10(-12) to 10(-8) mol) in mesenteric vascular beds precontracted with phenylephrine (10(-5) mol/l) were studied in the presence and absence of L-NAME (10(-5) mol/l), L-NAME + indomethacin (10(-5) mol/l) or L-NAME + indomethacin + potassium chloride (6 x 10(-5) mol/l). The area under the dose- response curve was used to calculate the approximate participation of nitric oxide, prostaglandins or endothelium-derived hyperpolarizing factor in the acetylcholine-induced relaxation. RESULTS: Chronic administration of L-NAME increased blood pressure levels and vascular responsiveness to phenylephrine. Treatments with either quinapril or diltiazem reduced blood pressure levels and attenuated the increased response to phenylephrine. Relaxing responses to acetylcholine were similar in all groups, independently of the treatment received. The calculated participation of endothelium-derived hyperpolarizing factor in the acetylcholine-induced relaxation was higher than that of nitric oxide and prostaglandins in all groups, but was higher in L-NAME-treated than in untreated rats. In contrast, the participation of both nitric oxide and prostaglandins was higher in control than in L-NAME-treated rats. Quinapril increased the participation of prostaglandins in L-NAME-treated rats. Diltiazem increased the participation of nitric oxide in L-NAME-treated rats. CONCLUSIONS: The administration of L-NAME in Sprague-Dawley rats increased the production of endothelium-derived hyperpolarizing factor as a compensatory mechanism to maintain acetylcholine-induced relaxation. Antihypertensive therapy with either quinapril or diltiazem produced a selective redistribution of the endothelial factors mediating acetylcholine-induced relaxation.     

Pravastatin reduces myocardial lesions induced by acute inhibition of nitric oxide biosynthesis in normocholesterolemic rats.

Pravastatin is useful in restoring endothelium-dependent relaxation in hypercholesterolemic animals. A single intravenous bolus injection of N(omega)-nitro-L-arginine methyl ester (L-NAME), a non-specific inhibitor of NO synthase, causes myocardial necrosis and reduces coronary flow in rats. Since rats do not develop hypercholesterolemia and atherosclerosis, we have tested the hypothesis that pravastatin protects the heart from myocardial lesions induced by L-NAME in the absence of alterations in cholesterol levels and plaque formation. Male Wistar rats fed standard chow were divided into four groups: CONTROL (n=14) - rats that received tap water alone for 18 days; L-NAME (n=14) -- rats that received L-NAME (15 mg/kg, i.v.) on the 14th day of the study; PRAVASTATIN (n=11) -- rats that received pravastatin (6 mg/kg/day) in their drinking water for 18 days; PRAVASTATIN+L-NAME (n=12) -- rats that received pravastatin (6 mg/kg/day) and L-NAME (15 mg/kg, i.v.) as indicated in the preceding groups. At the end of 18 days, the rats were sacrificed and the hearts removed for stereological analysis by light microscopy. Plasma nitrate/nitrite and thromboxane B(2) concentrations were determined immediately before and after L-NAME administration. Pravastatin prevented the ischemic lesions induced by the acute inhibition of NO biosynthesis (the area of myocardial lesions in the L-NAME group was greater than in the Pravastatin+L-NAME group: 101.6 microm(2) vs. 1.2 microm(2), respectively; P<0.0001) and markedly increased the plasma nitrate/nitrate concentrations, even before L-NAME administration. There were no significant changes in the plasma thromboxane B(2) concentrations.     

Prolonged QT Interval in Cirrhosis: Twisting Time?

Approximately 30% to 70% of patients with cirrhosis have QT interval prolongation. In patients without cirrhosis, QT prolongation is associated with an increased risk of ventricular arrhythmias, such as torsade de pointes (TdP). In cirrhotic patients, there is likely a significant association between the corrected QT (QTc) interval and the severity of liver disease, and possibly with increased mortality. We present a stepwise overview of the pathophysiology and management of acquired long QT syndrome in cirrhosis. The QT interval is mainly determined by ventricular repolarization. To compare the QT interval in time it should be corrected for heart rate (QTc), preferably by the Fridericia method. A QTc interval >450 ms in males and >470 ms in females is considered prolonged. The pathophysiological mechanism remains incompletely understood, but may include metabolic, autonomic or hormonal imbalances, cirrhotic heart failure and/or genetic predisposition. Additional external risk factors for QTc prolongation include medication (I_Kr blockade and altered cytochrome P450 activity), bradycardia, electrolyte abnormalities, underlying cardiomyopathy and acute illness. In patients with cirrhosis, multiple hits and cardiac-hepatic interactions are often required to sufficiently erode the repolarization reserve before long QT syndrome and TdP can occur. While some risk factors are unavoidable, overall risk can be mitigated by electrocardiogram monitoring and avoiding drug interactions and electrolyte and acid-base disturbances. In cirrhotic patients with prolonged QTc interval, a joint effort by cardiologists and hepatologists may be useful and significantly improve the clinical course and outcome.     

Chronic administration of aminoguanidine reduces vascular nitric oxide production and attenuates liver damage in bile duct-ligated rats.

BACKGROUND: Nitric oxide (NO) has been implicated in the pathogenesis of liver cirrhosis. This study investigated the activity of nitric oxide synthase (NOS) in cirrhosis induced by bile duct-ligation (BDL) with NOS inhibitors. METHOD: Three days after operation, rats were randomized to receive aminoguanidine (AG, 25 mg/kg/day) or L-N(G)-nitro-L-arginine methyl ester (L-NAME, 10 mg/kg/day) for 21 days. RESULTS: Vascular NO production, which was increased in BDL cirrhotic rats, was reduced by 75% with AG but not L-NAME chronic administration. AG treatment attenuated liver damage, while L-NAME aggravated it. AG significantly suppressed inducible NOS (iNOS) expression in aorta of BDL rats at both mRNA and protein level, but much less efficient in reducing it in liver. In contrast, endothelial NOS (eNOS) expression was not markedly affected. Calcium-independent NOS activity, which was dramatically increased in aorta of BDL rats, was abolished by AG treatment. In liver, however, both calcium-dependent and -independent NOS activity were increased by AG treatment. CONCLUSION: Chronic administration of AG could reduce systemic NO levels as well as suppress iNOS expression and activity in aorta of BDL rats. It also improved liver function, possibly because of its ability to increase hepatic NOS activity, and to correct the systemic hemodynamic disorders by decreasing vascular NO production.     

Chronic inhibition of nitric oxide ameliorates splanchnic hyposensitivity to glypressin in a hemorrhage-transfused rat model of portal hypertension

BACKGROUND: Vasopressin given during hemorrhage is less effective than when given during a stable state in experimental portal hypertension or patients with cirrhosis (the so-called hyposensitivity phenomenon). This study investigated whether chronic inhibition of nitric oxide (NO) synthesis by NG-nitro-L-arginine methyl ester (L-NAME), a non-selective NO synthase inhibitor, could potentiate the portal-hypotensive effect of glypressin (a long-acting vasopressin analogue) in portal-hypertensive rats during acute bleeding status. METHODS: Portal hypertension was induced by partial portal vein ligation (PVL). Rats were divided to receive either L-NAME (approximately 25 mg/kg/day in tap water) or placebo (tap water) treatment orally from 2 days prior to until 14 days after the operation. At the end of treatment, L-NAME-and placebo-treated PVL rats were subdivided into without-bleeding and with-bleeding groups to assess the effects of glypressin (0.07 mg/kg) on systemic and portal hemodynamics. In rats with a hypotensive hemorrhage, 4.5 ml of blood was withdrawn and 50% of the withdrawn blood was reinfused before the administration of glypressin. RESULTS: As compared with placebo-treated rats, chronic treatment with L-NAME in PVL rats significantly increased mean arterial pressure (P < 0.001) without modulating portal pressure (P > 0.05). In placebo-treated PVL rats, glypressin resulted in a less decrease in portal pressure in rats with bleeding than in those without bleeding (P < 0.05). For PVL rats with bleeding, the portal-hypotensive effect of glypressin was significantly potentiated after chronic L-NAME treatment (P < 0.05). CONCLUSIONS: Chronic inhibition of NO alleviates the splanchnic hyposensitivity to glypressin observed in bleeding PVL rats, suggesting the pathophysiological role of nitric oxide in mediating this splanchnic hyposensitivity.