Effects Of Endotoxemia Research Articles

Atividade antioxidante de macrófagos alveolares em ratos endotoxêmicos

Avaliou-se o efeito da endotoxemia sobre a atividade antioxidante de macrófagos alveolares em ratos da linhagem Wistar. Foram utilizados 24 ratos machos, com idade entre 90 e 120 dias, os quais foram divididos em dois grupos: controle e endotoxêmico. O grupo endotoxêmico foi submetido à injeção intraperitonial de lipopolissacarídio na dose de 1mg/kg de peso corporal. Após 24 h, coletou-se sangue para contagem total e diferencial de leucócitos; lavado broncoalveolar para contagem total e diferencial dos leucócitos e, a partir de macrófagos isolados deste lavado, foram realizadas as dosagens de superóxido e superóxido dismutase. A endotoxemia aumentou a contagem total de leucócitos e o número de neutrófilos no sangue periférico, no lavado broncoalveolar, e aumentou a produção de superóxido sem modificar a produção da superóxido dismutase. Esses resultados sugerem que a endotoxemia induz a uma resposta inflamatória no pulmão. Contudo, não altera a atividade antioxidante em ratos adultos. Tal fato potencializa a resposta contra agentes infecciosos pelo hospedeiro, mas também pode contribuir na patogênese de injúria pulmonar.

Effects of endotoxaemia and carbohydrate overload on glucose and insulin dynamics and the development of laminitis in horses

Insulin resistance (IR) is a risk factor for pasture-associated laminitis in equids and alimentary carbohydrate overload may trigger laminitis. Whether glucose metabolism responses to carbohydrate overload are more pronounced in insulin-resistant horses requires further study. Horses pretreated with endotoxin to alter insulin sensitivity differ significantly in their glucose and insulin responses to carbohydrate overload. Horses (n=24) were divided into 3 groups. A lipopolysaccharide (LPS; n=8) group that received endotoxin as an 8 h 7.5 ng/kg bwt/h i.v. continuous rate infusion, an oligofructose (OF; n=8) group that received an infusion of saline followed by 5 g/kg bwt OF via nasogastric intubation, and a LPS/OF (n=8) group that received LPS followed 16 h later by OF. Glucose and insulin dynamics were evaluated at -24 h and 48 h using the frequently sampled i.v. glucose tolerance test and minimal model analysis. Physical examinations and haematology were performed and the severity of laminitis assessed. Horses receiving LPS developed leucopenia and both LPS and OF induced clinical signs consistent with systemic inflammation. Insulin sensitivity significantly decreased (P < 0.001) over time, but responses did not differ significantly among groups. Time (P < 0.001) and treatment x time (P = 0.038) effects were detected for the acute insulin response to glucose, with mean values significantly increasing in LPS and LPS/OF groups, but not the OF group. Five horses in the LPS/OF group developed clinical laminitis compared with 0 and 2 horses in the LPS and OF groups, respectively. Endotoxaemia and carbohydrate overload reduce insulin sensitivity in horses. Endotoxin pretreatment does not affect the alterations in glucose metabolism induced by carbohydrate overload. Insulin sensitivity decreases after carbohydrate overload in horses, which may be relevant to the development of pasture-associated laminitis.

Effects of endotoxaemia on protein metabolism in rat fast-twitch skeletal muscle and myocardium.

BackgroundIt is unclear if the rat myocardium undergoes the same rapid reductions in protein content that are classically observed in fast-twitch skeletal muscle during endotoxaemia.Methodology/Principal FindingsTo investigate this further, and to determine if there is any divergence in the response of skeletal muscle and myocardium in the mechanisms that are thought to be largely responsible for eliciting changes in protein content, Sprague Dawley rats were implanted with vascular catheters and administered lipopolysaccharide (LPS; 150 µg kg−1 h−1) intravenously for 2 h, 6 h or 24 h (saline administered control animals were also included), after which the extensor digitorum longus (EDL) and myocardium were removed under terminal anaesthesia. The protein-to-DNA ratio, a marker of protein content, was significantly reduced in the EDL following 24 h LPS administration (23%; P<0.05), but was no different from controls in the myocardium. At the same time point, a significant increase in MAFbx/atrogin-1 and MuRF1 mRNA (3.7±0.7- and 19.5±1.9-fold increase vs. controls, respectively; P<0.05), in addition to protein levels of α1-3, 5–7 subunits of the 20S proteasome, were observed in EDL but not myocardium. In contrast, elevations in phosphorylation of p70 S6K residues Thr421/Ser424, and 4E-BP1 residues Thr37/Thr46 (P<0.05), consistent with an elevation in translation initiation, were seen exclusively in the myocardium of LPS-treated animals.Conclusions/SignificanceIn summary, these findings suggest that the myocardium does not undergo the same catabolic response as skeletal muscle during early endotoxaemia, partly due to the absence of transcriptional and signalling events in the myocardium typically associated with increased muscle proteolysis and the suppression of protein synthesis.

Role of AQP1 in endotoxemia-induced acute kidney injury

The effect of endotoxemia (lipopolysaccharide, 2.5 mg/kg ip) was investigated in aquaporin (AQP) 1 knockout (KO) compared with wild-type (WT) mice. At baseline, KO mice exhibited higher water intake (WI) and urine output (UO). After endotoxemia, WI and UO remained higher in the KO than WT mice, and urine osmolality was lower. The higher serum osmolality in AQP1-KO mice during endotoxemia was associated with higher AQP2 (133 +/- 8 vs. 100 +/- 3%, P < 0.01), AQP3 (140 +/- 8 vs. 100 +/- 4%, P < 0.001) and Na(+)-K(+)-2Cl(-) cotransporter type 2 (NKCC2; 152 +/- 14 vs. 100 +/- 15%, P < 0.05) expression than that in WT mice. These responses during endotoxemia in the AQP1-KO mice compared with WT were associated with lower glomerular filtration rate (GFR) (69 +/- 8 vs. 96 +/- 8 ml/min, P < 0.05) and renal blood flow (0.77 +/- 0.1 vs. 1.01 +/- 0.1 ml/min, P < 0.01). Urinary sodium excretion and fractional sodium excretion were higher in KO compared with WT mice in endotoxemia and were accompanied by more severe tubular injury. With water repletion and comparable serum osmolalities, GFR was still lower in KO (57 +/- 13 vs. 120 +/- 6 ml/min, P < 0.01) compared with WT during endotoxemia. The abundance of AQP2 and AQP3 protein in KO mice was not different from WT mice; however, NKCC2, Na(+)/H(+) exchanger type 3, and fractional sodium excretion remained higher in KO compared with WT. Thus the polyuria in AQP1-KO mice does not protect against endotoxemia-induced acute kidney injury but rather absence of AQP1 predisposed to enhanced endotoximic renal injury.

Tissue Doppler imaging suggests an association between endotoxemia and impaired myocardial relaxation

Tissue Doppler imaging (TDI) is a novel technique that measures myocardial velocity. The peak early diastolic mitral annulus velocity (E') offers a relatively preload-insensitive measure of LV relaxation. There are scant data regarding its use in sepsis or endotoxemia. This study sought to determine the effect of endotoxemia upon TDI variables.

Effect of endotoxemia on skin antioxidant enzymes under experimental conditions

Intraperitoneal injection of bacterial lipopolysaccharide in a dose of 1 mg/kg was followed by prestimulation of whole blood leukocytes in rats. Activities of peroxide- and lipoperoxide-utilizing antioxidant enzymes glutathione peroxidase, glutathione S-transferase, and catalase increased 1 day after lipopolysaccharide administration, while the content of malonic dialdehyde in the skin remained unchanged.

Effects of endotoxemia on splanchnic blood flow

目的 观察在内毒素血症状态下,肠系膜上动脉、肝动脉、门静脉血流以及肝动脉缓冲效应(hepatic arterial barffer response,HABR)的变化.方法24头雌性猪(21～35kg),随机分为二组.一组静脉持续注入大肠杆菌内毒素,为内毒素组(n=12);一组静脉注入生理盐水,为对照组(n=12).通过7F Swan-Ganz右心漂浮导管和超声流量探头监测心排出量(CO)、肺动脉楔压(Ppaw),记录肝动脉(Qha)、门静脉(Qpv)和肠系膜上动脉(Qmsa)血流.通过阻断门静脉血流的方法检测HABR,采用肝动脉血流的变化值(△Qha)/门静脉血流变化值(△Qpv)的方式表示HABR(△Qha/AQpv).结果静脉持续注射内毒素后,心率明显加快.内毒素组CO在1 h明显增加(与基础值比较P≤0.05),MAP和CO在6、8 h明显下降(与对照组比较差异显著,P≤0.01).在注射内毒素后,Qha由(0.05±0.03)ml/(kg·min)降至(0.01±0.01)ml/(kg·min)(P≤0.01),Qpv由(0.26±0.06)ml/(kg·min)降至(0.18±0.09)ml/(kg·min)(P≤0.05),Qmsa由(0.15±0.03)ml/(kg·min)降至(0.05±0.04)ml/(kg·min)(P≤0.01),△Qha/△Qpv由(0.16±0.12)降至(0.04±0.04)(P≤0.01).对照组未发生上述改变.结论在静脉持续注射内毒素的情况下,实验动物表现出由高血流动力学到低血流动力学的变化,同时内脏血流进行性减少;HABR功能减退,难以发挥维持肝血流量的作用。

Prevention of cardiovascular effects of endotoxaemia by monoclonal antibodies specific for core endotoxin.

Passive immunization with antibody to the core region of endotoxin (core lipopolysaccharide (LPS)) has been reported to reduce mortality in severe sepsis. A rat model of endotoxaemia that reproduces the hyperdynamic cardiovascular state seen in early sepsis was developed to test monoclonal antibodies specific for core LPS. A thermodilution technique of measuring cardiac output was adapted for use in rats. Twenty-five animals were anaesthetized and mechanically ventilated with monitoring of central venous pressure and mean arterial pressure. Fluid replacement was adjusted to maintain the central venous pressure. Controls (n = 10) and antibody-treated animals (n = 5) showed no significant change in cardiac output. Animals given 0.1 mg kg-1 R2 endotoxin over 1 h (n = 5) showed a significant rise in cardiac output of 65 per cent (P < 0.01). This was abolished in rats given both antibody and endotoxin (n = 5). This study provides evidence that a monoclonal antibody against core LPS abolishes the hyperdynamic state induced by endotoxin infusion.

Microdialysis: an innovative new tool to detect endotoxin tolerance

Metabolic changes in different organs in the critical state are often subtle and remain unrecognized with conventional hemodynamic and metabolic parameters. Since the development of the microdialysis technique, which mimics the passive function of a capillary blood vessel, it is now possible to examine the interstitial space of intact tissue. Preconditioning an animal with low doses of endotoxin has been shown to induce endotoxin hyperresponsiveness, the so-called 'endotoxin tolerance'. The exact pathophysiological mechanism involved has still not been fully elucidated. It appears to represent an essential mechanism to prevent unreasonable expansion of inflammatory or indiscriminate immune and metabolic responses before specific antibodies are developed. Up to this study, no data were available about the effect of endotoxaemia with and without endotoxin preconditioning regarding regional metabolic monitoring by the microdialysis technique.

Upregulation of renal inducible NO synthase and proximal tubule damage during human endotoxemia

In the kidney, the free radical nitric oxide (NO) participates in several vital processes, although excessive NO production, through inducible NO synthase (iNOS), can be cytotoxic. iNOS is predominantly, but only weakly, expressed in renal proximal tubules. Animal experiments demonstrate that an induction in iNOS expression occurs during systemic inflammation. In humans, renal effects of endotoxemia are unknown. The objective of the present study was to investigate the pathophysiological role of iNOS induction in renal proximal tubules during experimental endotoxemia in humans. A bolus injection of 2 ng/kg lipopolysaccharide of Escheria Coli (0113) was administered to eight healthy volunteers (four male/four female, age 24 ± 3 years), and 11 volunteers (five male/six female, age 22 ± 2 years) received the vehicle only (controls). At different time points, arterial blood in urine was collected and analyzed for nitrates/nitrites, the stable metabolites of NO. The amount of iNOS mRNA was determined by quantitative real-time RT-PCR from isolated cells of the urine. The urinary excretion of both glutathione-S-transferase-α (GST-α, present only in proximal tubular cells) and glutathione-S-transferase-π (GST-π, confined to distal tubular cells) were measured as well. Administration of endotoxin resulted in the expected increase of proinflammatory cytokines (TNF-α from < 0.015 to 856 ± 158 pg/ml, P = 0.002), accompanied by fever (maximum temperature 38.7 ± 0.3°C, P < 0.0001), flu-like symptoms and cardiovascular changes (heart rate from 63 ± 3 bpm at baseline to 91 ± 3 bpm at t = 5 hours, P < 0.0001; and mean arterial pressure from 96 ± 3 mmHg to 79 ± 4 mmHg, P < 0.0001). All changes were significantly different from the control group. Blood samples did not show a significant change in NO metabolites following the administration of endotoxin. Twelve hours after endotoxin administration, the urinary level of NO metabolites doubled (P < 0.05), whereas no significant change was observed in the control group. This effect was associated with an increase in iNOS mRNA measured 24 hours after endotoxin administration. Urinary excretion of GST-α increased from 0.7 ± 0.3 μmol/hour to 3.1 ± 1.3 μmol/hour at t = 12 hours (P < 0.01), whereas GST-π remained unchanged (from 0.2 ± 0.04 to 0.4 ± 0.13 μmol/hour). In controls, no difference in both GST-α and GST-π excretion was observed. Our results indicate that systemic inflammation induced by endotoxin in humans results in upregulation of renal iNOS, associated with proximal tubule injury.

Endotoxemia inhibits intestinal adaptation in a rat model of short bowel syndrome.

Sepsis is commonly associated with or complicates short bowel syndrome (SBS). The purpose of the present study was to investigate the effects of endotoxemia on intestinal adaptation in a rat model of SBS. Male Sprague-Dawley rats were divided into three experimental groups: Sham rats underwent bowel transection and re-anastomosis, SBS rats underwent 75% small bowel resection, and SBS-LPS rats underwent bowel resection and were given lipopolysaccharide. Bowel weight, organ weights, and parameters of intestinal adaptation (bowel and mucosal weights, mucosal DNA and protein, villus height, and crypt depth) were determined on day 15 following operation. The results of this study demonstrate that SBS rats showed a significant increase (vs. Sham) in jejunal and ileal bowel and mucosal weight, mucosal DNA and protein, villus height, and crypt depth. SBS-LPS animals demonstrated lower (vs. SBS rats) final body weight (215 +/- 7 vs. 287 +/- 10 g, P < 0.05), overall weight in duodenum (98+/- 2 vs. 119 +/-5 mg/cm, P < 0.05) and jejunum (144 +/- 9 vs. 189 +/- 16 mg/cm, P < 0.05), mucosal weight in jejunum (54 +/- 5 vs. 69 +/- 5 mg/cm, P < 0.05) and ileum (31 +/- 2 vs. 37 +/- 3 mg/cm, P < 0.05), mucosal DNA in jejunum (89 +/- 11 vs. 120 +/- 11 microg/cm, P < 0.05) and ileum (46 +/- 6 vs. 61 +/- 4 microg/cm, P < 0.05), jejunal crypt depth (152 +/- 19 vs. 189 +/- 12 microm, P < 0.05), and ileal villus height (405 +/- 63 vs. 515 +/- 30 pm, P < 0.05). In addition, the SBS group had no late (second week) mortality, whereas the SBS-LPS group had an 17% late mortality rate. In conclusion, in a rat model of SBS-LPS, endotoxemia appears to inhibit structural intestinal adaptation and increase mortality.

Reactive oxygen species and endotoxic shock: effect of dimethylthiourea.

The effects of endotoxemia on the cardiac function and contractility, oxygen radical production by polymorphonuclear leukocytes (PMNL-CL), cardiac antioxidant reserve (LV-CL), antioxidant enzymes (superoxide dismutase [SOD], catalase, glutathione peroxidase [GSH-P(X)]) and malondialdehyde (MDA); and plasma creatine kinase (CK) and lactate in the absence or presence of dimethylthiourea (DMTU), an antioxidant, in anesthetized dogs were studied. Dogs were assigned to three groups: group 1, control; group II, endotoxin (ET) (5 mg/kg body wt intravenously), and group III, ET + DMTU (500 mg/kg intravenously). ET produced decreases in the cardiac function and contractility, antioxidant reserve, antioxidant enzymes; and increases in PMNL-CL, cardiac MDA, plasma CK, and lactate. Pretreatment with DMTU attenuated the ET-induced cardiac dysfunction and changes in the cardiac MDA, antioxidant reserve, and antioxidant enzymes, PMNL-CL, and plasma CK and lactate levels. These results suggest that reactive oxygen species may be involved in the deterioration of cardiac function and contractility, and cellular injury during endotoxic shock and that antioxidants may be of value in the treatment of endotoxic shock.

Induction of the stress response increases interleukin-6 production in the intestinal mucosa of endotoxaemic mice

Previous studies suggest that production of interleukin-6 (IL-6) is increased in the intestinal mucosa during sepsis and endotoxaemia. We tested the hypothesis that mucosal IL-6 production during endotoxaemia is increased further by the heat-shock (stress) response. The stress response was induced in mice by hyperthermia (rectal temperature of 42 degrees C for 3 min) or by intraperitoneal injection of sodium arsenite (10 mg/kg). At 2 h after induction of the stress response, groups of mice were injected subcutaneously with endotoxin (10 mg/kg) or sterile saline. IL-6 mRNA and protein levels in the jejunal mucosa were determined by an RNase protection assay and an ELISA respectively, and levels of hsp72 (heat-shock protein of 72 kDa) were determined by Western blot analysis. Hyperthermia and sodium arsenite increased hsp72 levels in the intestinal mucosa. IL-6 concentrations were increased in the jejunal mucosa of endotoxaemic mice, and this effect of endotoxaemia was potentiated by the stress response. Mucosal IL-6 mRNA levels were increased in endotoxaemic mice, and were increased further by the stress response. Thus it is concluded that mucosal IL-6 production during endotoxaemia may be further stimulated by the stress response. Increased IL-6 levels in the intestinal mucosa may be a potential mechanism by which the stress response exerts a protective effect during sepsis and endotoxaemia.

Room F, 10/17/2000 9: 00 AM - 11: 00 AM (PS) The Effects of Endotoxemia on the Function, Oxygenation, and Energetics of Skeletal Muscle at Rest and Exercise

<b>Room F, 10/17/2000 9: 00 AM - 11: 00 AM (PS) The Effects of Endotoxemia on the Function, Oxygenation, and Energetics of Skeletal Muscle at Rest and Exercise</b>

Thrombin and leukocyte recruitment in endotoxemia.

Because thrombin has been implicated in sepsis, it has been proposed that antithrombin III (AT III) is beneficial due to its anticoagulatory and antiadhesive effects. Using intravital microscopy, we visualized leukocyte-endothelium interactions in postcapillary venules of the feline mesentery exposed to lipopolysaccharide (LPS). At a concentration of AT III that blocks leukocyte adhesion in postischemic mesentery, we found no role for thrombin in LPS-induced rolling, adhesion and emigration, or microvascular dysfunction. Furthermore, AT III did not attenuate leukocyte-endothelial interactions after tumor necrosis factor-alpha superfusion of the mesentery. In contrast, fucoidan, a selectin inhibitor, prevented almost all LPS-induced rolling and reduced adhesion, emigration, and microvascular dysfunction. In a model of endotoxemia, leukocyte recruitment into mesentery or lungs was unaffected by AT III. Finally, in a human cell system that mimics the flow conditions in vivo, human neutrophils rolled, adhered, and emigrated similar to the feline postcapillary microvessels, and AT III had no effect on leukocyte recruitment induced by LPS. If AT III has beneficial effects in endotoxemia, it is not due to a direct effect upon leukocyte rolling, adhesion, or emigration in postcapillary venules in vivo.

Antithrombin reduces leukocyte adhesion during chronic endotoxemia by modulation of the cyclooxygenase pathway.

Antithrombin (AT) is known as the most important natural inhibitor of thrombin activity and has been shown to improve distinct clinical parameters during the course of septic (endotoxin)-induced multiple organ dysfunction. We hypothesized that AT acts by inhibiting leukocyte activation and microvascular injury via the promotion of endothelial release of PGI(2), and therefore, we studied the effects of AT on leukocyte/endothelial cell interaction and microvascular perfusion during endotoxemia. In a skinfold preparation of Syrian hamsters, severe endotoxemia was induced by repeated administration of endotoxin intravenously [lipopolysaccharide (LPS), Escherichia coli, 2 mg/kg] at 0 and 48 h. AT (250 IU/kg) was administered intravenously at 0, 24, and 48 h (n = 6, AT group). In control animals (n = 5, control), LPS was given without AT supplementation. By intravital fluorescence microscopy, leukocyte-endothelial cell interaction and functional capillary density (FCD; measure of capillary perfusion) were analyzed during a 72-h period after the first LPS injection. AT significantly attenuated LPS-induced arteriolar and venular leukocyte adherence after both the first and the second LPS injection [P < 0.01, measures analysis of variance (MANOVA)]. In parallel, AT was effective in preventing LPS-induced depression of FCD after the first and the second LPS administration (P < 0.05, MANOVA). By pretreatment with the cyclooxygenase inhibitor indomethacin (n = 6), effects of AT on leukocyte adherence and FCD were found completely abolished. Thus our study indicates that AT exerts its beneficial effects in endotoxemia by reducing leukocyte-endothelial cell interaction and microvascular perfusion failure probably via liberation of prostacyclin from endothelial cells.

Effect of alanyl-glutamine on leucine and protein metabolism in endotoxemic rats.

Branched-chain amino acids (BCAA; valine, leucine, and isoleucine) have a regulatory effect on protein metabolism and are the main donor for synthesis of alanine and glutamine in the skeletal muscle. This study was performed to investigate whether exogenous alanine or glutamine would affect leucine and protein metabolism in intact and endotoxemic rats. Rats were injected with endotoxin of Salmonella enteritidis or saline. Thirty minutes later, the effects of endotoxemia and L-alanyl-L-glutamine (AG) on leucine and protein metabolism were evaluated using a primed constant infusion of [1-14C]leucine, endotoxin, and AG (200 mg/mL) solution or an infusion of [1-14C]leucine without endotoxin or AG. The specificity of the effect of exogenous alanine and glutamine was evaluated by a single infusion of alanine, glutamine, and glycine in a separate study. Endotoxin treatment induced more negative net protein balance caused mainly by an increase in whole-body proteolysis. Protein synthesis increased in kidneys, colon, and spleen, while a decrease was observed in skeletal muscle. The impressive effects of AG were the decrease in plasma branched-chain amino acid (BCAA) levels, decrease in leucine oxidized fraction, and improvement of protein balance associated with a decrease in whole-body proteolysis. Similar changes in leucine and protein metabolism were induced by infusion of alanine or glutamine but not by infusion of glycine. IV administration of alanine or glutamine improves protein balance and decreases leucine oxidized fraction in postabsorptive state and in endotoxemia. Decreased proteolysis is the main cause of decreased plasma BCAA levels after AG treatment.

Kinetics of tumour necrosis factor α and interleukin 10 in rats with endotoxaemia and obstructive jaundice-induced anergy

Abstract Background Obstructive jaundice leads to a significant increase in septic complications. In addition, endotoxaemia may cause a secondary insult. The effects of endotoxaemia and obstructive jaundice-induced anergy on the kinetics of two early mediators of the response to sepsis, tumour necrosis factor (TNF) α and interleukin (IL) 10, were investigated. Methods Wistar rats had either bile duct ligation (BDL) or sham operation. After 2 weeks, anergy was confirmed by a delayed-type hypersensitivity response in rats that had undergone BDL. All rats were challenged with Escherichia coli lipopolysaccharide (LPS) 20 mg kg−1 or saline. After 90 and 180 min, rats were killed and blood samples were obtained for TNF-α and IL-10 measurement. Results There was no intragroup difference after saline challenge. LPS injection significantly increased both TNF-α and IL-10 levels in all groups compared with all saline injection groups. LPS injection following BDL led to significantly higher TNF-α levels and lower IL-10 levels at 90 min compared with those after sham operation (P &amp;lt; 0·05). There were no differences between TNF-α and IL-10 levels at 180 min following LPS challenge in rats that had undergone BDL. Conclusion BDL primes for an increase in TNF-α levels to a subsequent LPS challenge. However, the IL-10 increase following an LPS challenge is suppressed by BDL. These results suggest that BDL primes for a more vigorous inflammatory response to LPS challenge.

Effects of melagatran, a novel direct thrombin inhibitor, during experimental septic shock

Sepsis and endotoxaemia initiate the generation of thrombin, which is responsible for the conversion of fibrinogen to fibrin, platelet aggregation and acts as an inflammatory mediator affecting numerous types of cells, including myocardial, smooth muscle and endothelial cells. Human Gram-negative septic shock, frequently seen in intensive care units, is a condition with high mortality. This condition can be replicated in the endotoxaemic pig. As many of the toxic effects of sepsis are due to thrombin generation, it was of interest to study, using this porcine experimental septic shock model, whether inhibition of thrombin could alleviate the effects of endotoxaemia. For this purpose melagatran, a direct synthetic thrombin inhibitor with a molecular weight of 429 Da, was employed. Melagatran does not significantly interact with any other enzymes in the coagulation cascade or fibrinolytic enzymes aside from thrombin. Furthermore, melagatran does not require endogenous co-factors such as antithrombin or heparin co-Factor II for its antithrombin effect, which is important, as these inhibitors are often consumed in septic patients. We have shown that melagatran exerts a beneficial effect on renal function, as evaluated by plasma creatinine and urinary output, during experimental septic shock. These effects were most pronounced during the later phase of the experimental period, after the infusion of melagatran had been discontinued. Prevention of intrarenal coagulation may be attributable to this finding. In addition, melagatran had beneficial effects on systemic haemodynamics (left ventricular stroke work index, pulmonary capillary wedge pressure and systemic vascular resistance index) in endotoxaemic pigs. This result may be explained by the ability of melagatran to inhibit thrombin, thereby counteracting thrombin’s cellular effects. Thus, it can be seen, using this experimental model of septic shock, that melagatran may help to alleviate some of the damaging effects of endotoxaemia, although more research is required to test this further.

Impaired vascular sensitivity to nitric oxide in the coronary microvasculature after endotoxaemia

1. The effects of endotoxaemia on coronary vasodilator responses to bradykinin (BK), sodium nitroprusside (SNP) and nicardipine were investigated in the rat isolated heart perfused at constant flow ex vivo. 2. Dose-dependent reductions in coronary perfusion pressure reaching a maximum of 56+/-3 and 57+/-5 mmHg were observed for BK and SNP respectively. The BK response was biphasic, consisting of a rapid dilator response that was insensitive to N(G)nitro-L-arginine methyl ester (L-NAME, 0.1 mM) and a second slower component whose duration was attenuated by L-NAME. 3. Hearts obtained from rats treated with endotoxin (2.5 mg kg(-1), i.p.) for 2 or 6 h had increased basal coronary perfusion pressure and reduced vasodilator responses to BK or SNP. Dilator responses to nicardipine were not affected by endotoxin treatment. In vitro perfusion of hearts from endotoxin-treated rats with L-NAME (0.1 mM) restored SNP responses to control values. 4. Treatment with dexamethasone (1 mg kg(-1)), 1 h before endotoxin did not alter the endotoxin-induced impairment of dilator responses to BK or SNP. 5. These results show that coronary microvascular responses are altered following endotoxin exposure. Endotoxin results in increased coronary microvascular tone despite induction of NO synthase and inhibits the dilator response to BK and SNP, vasodilators that act via the release of NO. Responses to SNP in endotoxin-treated hearts were restored to control values in the presence of L-NAME suggesting that enhanced endogenous NO synthesis might saturate guanylate cyclase resulting in reduced response to NO donors. The reduced response to vasodilators and increased coronary resistance might be important in determining the response of the coronary circulation to systemic inflammation and infection.