Chin-Chen Wu

Systemic Administration of Lipopolysaccharide Induces Release of Nitric Oxide and Glutamate and c-fos Expression in the Nucleus Tractus Solitarii of Rats

There is increasing recognition that communication pathways exist between the immune system and brain, which allows bidirectional regulation of immune and brain responses to infection. The endotoxin lipopolysaccharide (LPS) has been reported to elicit release of cytokines and expression of inducible nitric oxide synthase (iNOS) in peripheral organs. Whereas LPS given systemically causes endotoxic shock, little is known about its central nervous system action, particularly the induction of iNOS. Nitric oxide (NO) and glutamate in the nucleus tractus solitarii (NTS) are important mediators of central cardiovascular regulation. We have previously demonstrated that intravenous injections of LPS increased the NO precursor L-arginine-induced depressor effect in the NTS. The present study investigated further the effects of LPS on the release of NO and glutamate in the NTS and the expression of c-fos, an immediate early response gene product, in neural substrates for central cardiovascular control. In vivo microdialysis coupled with chemiluminescence and electrochemical detection techniques were used to measure extracellular levels of NO and glutamate in the rat NTS. Immunohistochemistry was used for the examination of c-fos protein expression. We found that intravenous infusion of LPS (10 mg/kg) produced a biphasic depressor effect, with an early, sharp hypotension that partially recovered in 15 minutes and a secondary, more prolonged hypotension. In the NTS, a progressive increase of extracellular glutamate and NO levels occurred 3 and 4 hours after LPS was given, respectively. The effects of LPS on the induction of delayed hypotension and NO formation in the NTS were abolished by pretreatment with the iNOS inhibitor aminoguanidine. Finally, c-fos protein expression in the NTS and related structures for cardiovascular regulation was observed after LPS challenge. Taken together, these data suggest that an endotoxin given systemically can elicit delayed increases of glutamate release and iNOS-dependent NO production in the NTS and activate the central neural pathway for modulating cardiovascular function.

Incidence and factors predictive of acute renal failure in patients with advanced liver cirrhosis

BACKGROUND Acute renal failure (ARF) is a life-threatening entity that frequently complicates advanced liver disease. This study documents a number of factors that may predispose to or precipitate ARF and influence outcomes in patients with advanced liver disease. Comparisons are also made between subgroups of patients with viral and alcohol-induced liver cirrhosis in those with ARF. PATIENTS AND METHODS We conducted a retrospective chart review over one year of 127 consecutive hospital admissions in 82 patients who were diagnosed with advanced liver cirrhosis (Child-Pugh Class C) in a tertiary care center. A diagnosis of ARF was made in 29 admissions and another 98 admissions not complicated by ARF served as controls. This study evaluated different etiologies of ARF and developed a database which included clinical features, biochemical parameters, the etiology of cirrhosis, possible predisposing factors, and precipitating events. Version II of the Acute Physiology and Chronic Health Physiology Scoring system (APACHE II) was applied to predict short-term hospital mortality rates. RESULTS ARF occurred in 29 admissions over the one-year study period (23%). The mean age of these patients was 56.8 +/- 12.0 years, and 73% were men. The patients with ARF had significant hyponatremia and higher levels of serum bilirubin, aspartate aminotransferase (AST), alanine aminotransferase (ALT), and white cell counts on admission than the controls. Patients who developed ARF were more likely to have had infection, especially septicemia, and gastrointestinal (GI) bleeding. Mortality rate in the patients with ARF was much higher than in those patients without ARF (72% vs. 13%, p < 0.001). The patients with viral cirrhosis and ARF were found to have higher leukocyte counts, serum bilirubin levels, and more frequent incidence of infection, septicemia and GI bleeding compared to the patients with alcoholic liver cirrhosis and ARF. Those with viral hepatitis were also significantly older and had more frequent incidence of ascites, but had lower levels of gamma-glutamyl transpeptidase and less frequent incidence of encephalopathy. CONCLUSIONS The risk of ARF is significantly increased in patients with advanced liver cirrhosis presenting with marked hyperbilirubinemia, hyponatremia, elevated liver enzymes, infection, and GI bleeding. The presence of ARF leads to higher mortality rates in both viral and alcohol-induced liver cirrhosis.

Therapeutic effects of melatonin on peritonitis-induced septic shock with multiple organ dysfunction syndrome in rats.

Abstract:  The pathogenesis of multiple organ dysfunction syndrome (MODS) in septic shock is complicated and not fully understood. Some studies show that an overproduction of nitric oxide (NO) leads to the refractory hypotension and multiple organ failure, while other studies suggest that free radicals, e.g. superoxide (O2−), contribute to the detrimental effect on vascular responsiveness and tissue/organ damage. Thus, this study was performed on the Wistar rat by using cecal ligation and puncture (CLP) to induce septic shock‐associated MODS. We evaluated the effect of an antioxidant melatonin in CLP‐induced septic rats and demonstrated that melatonin (3 mg/kg, i.v. at 3, 6, 12 hr after CLP) significantly (a) attenuated hyporeactivity to norepinephrine and delayed hypotension, (b) reduced plasma index of hepatic and renal dysfunction, (c) diminished plasma NO and interleukin‐1β (IL‐1β) concentrations as well as aortic O2− levels, (d) reduced marked infiltration of polymorphonuclear neutrophils (PMNs) in the lung and liver tissues, and (e) promoted the survival rate at 18 hr to twofold compared with the CLP alone group. The current study underlined the inhibition of plasma NO and IL‐1β as well as aortic O2− production and the reduction of PMN infiltration may lead to the amelioration of MODS, which may contribute to the beneficial effect of antioxidants (e.g. melatonin in this study) in conscious rats with peritonitis‐induced lethality. Thus, the antioxidant could be a novel agent for the treatment of septic animals or patients in the early stage.

Therapeutic effects of hypertonic saline on peritonitis-induced septic shock with multiple organ dysfunction syndrome in rats.

Objective:Significant mortality in patients with sepsis results from the development of multiple organ dysfunction syndrome. Small-volume resuscitation with 7.5% NaCl hypertonic saline has been proposed to restore physiologic hemodynamics in hemorrhagic shock. Therefore, we hypothesized that hypertonic saline resuscitation could alleviate the development of multiple organ dysfunction syndrome in sepsis induced by cecal ligation and puncture. Design:Randomized, prospective animal experiment. Setting:Academic research laboratory. Subjects:Male Wistar rats. Interventions:The animals were randomly allocated to one of four groups: 1) sham operation (0.9% NaCl, 4 mL/kg intravenously, at 3 hrs after laparotomy); 2) sham operation plus hypertonic saline (7.5% NaCl, 4 mL/kg intravenously, at 3 hrs after laparotomy); 3) cecal ligation and puncture (0.9% NaCl, 4 mL/kg intravenously, at 3 hrs after cecal ligation and puncture); and 4) cecal ligation and puncture plus hypertonic saline (7.5% NaCl, 4 mL/kg intravenously, at 3 hrs after cecal ligation and puncture). Measurements and Main Results:Cecal ligation and puncture for 18 hrs was associated with circulatory failure (i.e., hypotension and vascular hyporeactivity to norepinephrine), multiple organ dysfunction syndrome (examined by biochemical variables and histologic studies), and 18-hr mortality. Hypertonic saline not only ameliorated the deterioration of hemodynamic changes but also attenuated neutrophil infiltration in the lung and the liver of septic animals. Hypertonic saline increased the survival rate at 9 and 18 hrs compared with the cecal ligation and puncture group. Moreover, hypertonic saline reduced plasma nitric oxide and interleukin-1&bgr; and organ O2−· levels in rats that underwent cecal ligation and puncture. Conclusions:Hypertonic saline prevented circulatory failure, alleviated multiple organ dysfunction syndrome, and decreased the mortality rate in animals receiving cecal ligation and puncture. These beneficial effects of hypertonic saline may be attributed to reducing the plasma concentration of nitric oxide and interleukin-1&bgr; as well as the organ O2−· level and decreasing lung neutrophil infiltration and liver necrosis. Our study suggests that hypertonic saline could be a potential and inexpensive therapeutic agent in the early sepsis of animals or patients.

A possible mechanism of action of tetramethylpyrazine on vascular smooth muscle in rat aorta.

The vasodilatation of isolated rat aorta by tetramethylpyrazine (TMP) was studied by examining its effect on phenylephrine-induced contraction. We found no difference between the effects on intact and on endothelium-denuded preparations. The effect of TMP was similar to that of theophylline because propranolol did not block the vasodilatation. Also, there was a summation effect when the pyrazine was combined with theophylline. Furthermore, like that due to theophylline, the vasodilatation was accompanied by an increase in cyclic AMP. The pyrazine, as do other dilators, affected differently the two separate phases of the contractile response elicited with either phenylephrine or high potassium. The drug predominantly suppressed the phasic responses but both the phasic and tonic phases could be inhibited significantly if the concentration of the pyrazine was high enough. The present results suggest that intracellular accumulation of cyclic AMP and blockade of the release of calcium from internal stores may be important elements of the mechanism by which TMP reduces the development of tension in rat aortic smooth muscle.

Role of nitric oxide and K+-channels in vascular hyporeactivity induced by endotoxin.

Abstract This study was to investigate possible mechanisms associated with vascular hyporeactivity to vasoconstrictor agents in rats with endotoxaemia. Wistar-Kyoto rats were anaesthetised and injected with endotoxin [E. coli lipopolysaccharide (LPS); 10 mg/kg, i.v.] for 4 h. Pressor responses to noradrenaline (NA; 1 μg/kg, i.v.) were determined prior to and at every hour after LPS injection. After the in vivo experiment, rat thoracic aortas were excised and prepared as rings 3–4 mm in width. The endothelium was mechanically removed to evaluate K+-channel activity and the effects of nitric oxide (NO) on the vascular smooth muscle. Our results demonstrated that: (1) injection of LPS caused a significant fall in blood pressure and a severe vascular hyporeactivity to NA in the anaesthetised rat, (2) the relaxation induced by the K+-channel opener cromakalim was greater in rings obtained from endotoxaemic rats and this enhanced relaxation was partially inhibited by pretreatment of these rings with 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ), an inhibitor of the NO/cGMP pathway, (3) endotoxaemia for 4 h was also associated with a profound vascular hyporeactivity to NA ex vivo and this vascular hyporesponsiveness was partially inhibited by ODQ, tetraethylammonium (TEA, a non-selective inhibitor of K+-channels) and charybdotoxin [CTX, a selective inhibitor of large conductance calcium-activated K+ channels (BKCa)], but not by apamin, and (4) the combination of TEA or CTX with ODQ completely restored that vascular responsiveness to normal. These results suggest that activation of BKCa and overproduction of NO in the vascular smooth muscle simultaneously contribute to vascular hyporeactivity to vasoconstrictor agents in endotoxaemia.

Pentoxifylline improves circulatory failure and survival in murine models of endotoxaemia.

Pentoxifylline, a methylxanthine derivative, has been widely used to improve erythrocyte deformability and capillary blood circulation in patients with claudication and cerebrovascular disorders as well as in animals with sepsis. Here, we investigate the effects of pentoxifylline on the hypotension, vascular hyporeactivity to noradrenaline, release of tumour necrosis factor-alpha (TNF-alpha) and nitric oxide (NO), and inducible NO synthase protein expression in a rat model of circulatory shock induced by bacterial endotoxin (Escherichia coli lipopolysaccharide). In addition, we have evaluated the effect of pentoxifylline on the 36-h survival rate in a murine model of endotoxaemia. Male Wistar-Kyoto rats were anaesthetised and instrumented for the measurement of mean arterial pressure and heart rate. Injection of lipopolysaccharide (10 mg/kg, i.v.) resulted in a significant fall in mean arterial pressure and an increase of heart rate. In contrast, animals pretreated with pentoxifylline (3 mg/kg, i.v., at 30 min prior to lipopolysaccharide) maintained a significantly higher mean arterial pressure but showed no effect on the tachycardia when compared to rats given only lipopolysaccharide (lipopolysaccharide-rats). The pressor effect of noradrenaline (1 microg/kg, i.v.) was also significantly reduced after the treatment of rats with lipopolysaccharide. Similarly, rings of thoracic aorta obtained from lipopolysaccharide-rats showed a significant reduction in the contractile responses elicited by noradrenaline (1 microM). Pretreatment of lipopolysaccharide-rats with pentoxifylline partially, but significantly, prevented this lipopolysaccharide-induced hyporeactivity to noradrenaline in vivo and ex vivo. The injection of lipopolysaccharide resulted in bell-shape changes in plasma TNF-alpha level which reached a peak at 60 min, whereas the effect of lipopolysaccharide on the plasma level of nitrate (an indicator of NO formation) was increased in a time-dependent manner. This increase of both TNF-alpha and nitrate levels induced by lipopolysaccharide was significantly reduced in lipopolysaccharide-rats pretreated with pentoxifylline. Endotoxaemia for 240 min caused a significantly increased protein expression of inducible NO synthase in the lung. In lipopolysaccharide-rats pretreated with pentoxifylline, inducible NO synthase protein expression in lung homogenates was attenuated by 48 +/- 5%. Treatment of conscious mice with a high dose of endotoxin (60 mg/kg, i.p.) resulted in a survival rate of only 10% at 36 h (n = 20). However, therapeutic application of pentoxifylline (3 mg/kg, i.p. at 0, 6, 15 and 24 h after lipopolysaccharide) increased the 36-h survival to 35% (n = 20). Thus, pentoxifylline protects against circulatory failure and improves survival in rodents with severe endotoxaemia. These effects may be due to inhibition of the release of TNF-alpha and of the induction of inducible NO synthase.

Terbutaline prevents circulatory failure and mitigates mortality in rodents with endotoxemia.

Septic shock is characterized by a decrease in systemic vascular resistance. Nevertheless, regional increases in vascular resistance can occur that may predispose mammals to organ dysfunction, including the acute respiratory distress syndrome. In the host infected by endotoxin (lipopolysaccharide, LPS), the expression and release of proinflammatory tumor necrosis factor-alpha (TNFalpha) rapidly increases, and this cytokine production is regulated by agents elevating cyclic AMP. In this report, we present evidence that terbutaline, a beta2-agonist, inhibits TNFalpha production and enhances interleukin-10 (IL-10) release in the anesthetized rat treated with LPS. In addition, an overproduction of nitric oxide (NO, examined by its metabolites nitrite/nitrate) by inducible NO synthase (iNOS, examined by western blot analysis) is attenuated by pretreatment of LPS rats with terbutaline. Overall, pretreatment of rats with terbutaline attenuates the delayed hypotension and prevents vascular hyporeactivity to norepinephrine. In addition, pretreatment of mice with terbutaline also improves the survival in a model of severe endotoxemia. The infiltration of polymorphonuclear neutrophils into organs (e.g., lung and liver) from the surviving LPS mice treated with terbutaline was reduced almost to that seen in the normal controls. These findings suggest that the inhibition of TNFalpha and NO (via iNOS) production as well as the increment of IL-10 production contribute to the beneficial effect of terbutaline in animals with endotoxic shock.

Abnormal Activation Of Potassium Channels In Aortic Smooth Muscle Of Rats With Peritonitis-induced Septic Shock

This study was conducted to examine the role of membrane hyperpolarization in mediating vascular hyporeactivity induced by cecal ligation and puncture (CLP) in endothelial-denuded strips of rat thoracic aorta ex vivo. The CLP for 18 h elicited a significant fall of blood pressure and a severe vascular hyporeactivity to norepinephrine as seen in severe sepsis. At the end of the in vivo experiments, thoracic aortas were removed from both CLP-treated and control rats. After removal of the endothelium, aortic segments were mounted in myographs for the recording of isometric tension and smooth muscle membrane potential. The membrane potential recording showed that a hyperpolarization was observed in the CLP-treated rats when compared with the control rats. This hyperpolarization was reversed by iberiotoxin (a large-conductance Ca2+-activated K+ channel blocker), 4-aminopyridine (a voltage-dependent K+ channel blocker), barium (an inward rectifier K+ channels blocker), N-(1-adamantyl)-N&vprime;-cyclohexyl-4-morpholinecarboxamidine hydrochloride (a pore-forming blocker of adenosine triphosphate (ATP)-sensitive K+ channels [KATP]), or methylene blue (a nonspecific guanylyl cyclase [GC] inhibitor). However, this hyperpolarization was not significantly affected by apamin (a small-conductance Ca2+-activated K+ channel blocker), glibenclamide (a sulfonylurea blocker of KATP), N&ohgr;-nitro-l-arginine methyl ester (a NOS inhibitor), or 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (an NO-sensitive GC inhibitor). In addition, the basal tension of the tissues obtained from CLP rats was increased simultaneously, whereas membrane potential was reversed. In contrast, none of these inhibitors had significant effects on the membrane potential or the basal tension in control tissues. Thus, we provide electrophysiological and functional evidence demonstrating that an abnormal activation of K+ channels in vascular smooth muscle in animals with septic shock induced by CLP. Our observations suggest that the activation of large conductance Ca2+-activated K+ channels, voltage-dependent K+ channels, inward rectifier K+ channels, and KATP channels, but not small conductance Ca2+-activated K+ channels, contributes to CLP-induced vascular hyporeactivity. Furthermore, the hyperpolarization in septic shock induced by CLP is likely via non-NO-sensitive GC pathway.

Nitric oxide contributes to abnormal vascular calcium regulation and reactivity induced by peritonitis-associated septic shock in rats

Calcium plays an important role in determining vascular smooth muscle tone. Norepinephrine (NE)-induced vascular contraction contains two components: 1) Ca2+ release from the sarcoplasmic reticulum as the fast phase and 2) Ca2+ influx via a voltage-dependent calcium channel as the slow phase. This study used functional isometric tension recording to evaluate mediators contributing to abnormal NE-induced Ca2+ handling and reactivity in isolated thoracic aortas from septic rats. Sepsis was induced by cecal ligation and puncture (CLP), and thoracic aortas were removed at 18 h after CLP. Our results showed that rats that received CLP for 18 h manifested severe hypotension and vascular hyporeactivity to NE in vivo. This vascular hyporecativity to NE was also observed in the aorta obtained from CLP-induced sepsis rat. Both the fast and slow phases of NE-induced contraction were reduced in aortas from sepsis rats. To clarify what possible mediators contribute to the abnormal Ca2+ handling in aortas from sepsis animals, inhibitors of Ca2+ channel and release were used. Inhibition by 2-aminoethoxy-diphenyl borane, ryanodine, and cyclopiazonic acid of the NE-induced contraction in Ca2+-free solution was greater in the aorta from sepsis rats and inhibitions of cyclopiazonic acid and ryanodine, but not of 2-aminoethoxy-diphenyl borane, were attenuated by NOS inhibitor N&ohgr;-nitro-l-arginine methyl ester. In addition, the attenuation of NE-induced contraction by nifedipine in the aorta was also greater in the CLP group. Our results suggest that abnormal NE-induced Ca2+ handling associated with vascular hyporeactivity in the CLP-induced sepsis is caused by a major decrease in sarcoplasmic reticulum function and a minor impairment of voltage-dependent Ca2+ channels on membrane to Ca2+ handling, at least, in the aorta, and this could be attributed to an overproduction of NO in sepsis.