Recombinant human manganese superoxide dismutase attenuates early but not delayed skeletal muscle dysfunction following reperfusion injury.

OBJECTIVES: to assess the efficacy of recombinant human manganese superoxide dismutase (rhMnSOD) in prevention of early and late skeletal muscle ischaemia-reperfusion injury mediated by superoxide (O2-). Design : randomised controlled trial. MATERIALS: seventy-two Sprague-Dawley rats (250-350 g) randomised to receive either 7.5 mg/kg of rhMnSOD or saline. Four hours of ischaemia was induced in the cremaster muscle by dissecting free and clamping its vascular supply. Cremaster muscle contractile function was assessed following 90 minutes, 24, 48 hours and one week of reperfusion. Electrophysiological muscle function was assessed using electrical field stimulation in an organ bath system. RESULTS: muscle function in the untreated groups following ischaemia reperfusion was significantly reduced at 90 minutes, 24, 48 hours and one week of reperfusion (p <0.05). rhMnSOD significantly protected and maintained normal muscle function at 24 and 48 hours (p <0.001). However at one week of reperfusion there was a reduction in function of the treated muscle, such that there was no significant difference between treated and untreated muscle at this point in time. CONCLUSIONS: these data demonstrate that skeletal muscle dysfunction after ischaemia reperfusion injury is attenuated at 24 and 48 hrs of reperfusion by the superoxide scavenger rhMnSOD. This protective effect is not maintained after seven days of reperfusion.     

Diaphragmatic dysfunction secondary to experimental lower torso ischaemia-reperfusion injury is attenuated by thermal preconditioning

BACKGROUND: Preconditioning describes the process whereby tissue exposure to a subcritical stress confers protection from subsequent injuries. This study assessed diaphragmatic muscle function after lower torso ischaemia-reperfusion (IR) and the role of thermal preconditioning in attenuation of this injury. METHODS: Sprague-Dawley rats were randomized into three groups (24 per group): a control group, an IR group that had aortic cross-clamping for 1 h followed by reperfusion, and a third group that received thermal preconditioning 18 h before IR. Diaphragmatic function was assessed at 24 h, 48 h and 7 days. RESULTS: IR resulted in significant diaphragmatic twitch and tetanic dysfunction compared with control muscle. Thermal preconditioning significantly attenuated this injury (P < 0.05). Mean(s.e.m.) muscle twitch and tetanic forces in the IR group were 204.9(17.2) and 282.7(19.2) g respectively at 24 h. Corresponding twitch and tetanic forces in preconditioned muscle were 270.4(25.1) and 552.0(35.2) g. CONCLUSION: This study demonstrated that systemic IR injury produced a respiratory muscle mechanical dysfunction that was attenuated by thermal preconditioning, at 24 h, 48 h and 7 days. Preconditioning may have a role in clinical practice, particularly before elective surgery.     

Effects of systemic and regional taurine on skeletal muscle function following ischaemia-reperfusion injury.

INTRODUCTION: Tissues subjected to prolonged ischaemia are paradoxically further damaged when their perfusion is restored. The mechanisms underlying this ischaemia-reperfusion injury are complex, but oxidative attack is a central feature. Among the therapeutic agents used to attenuate ischaemia-reperfusion injury, endogenous agents such as taurine which form part of the native defence mechanism against oxidative damage are of particular interest. METHODS: Using a model of hindlimb ischaemia-reperfusion injury in the rat, taurine solution was administered either into the operated hindlimb, into the systemic circulation, or both. Contraction strengths of gastrocnemius biopsies from the operated and contralateral (control) hindlimbs of each animal were measured. RESULTS: Fast twitch strength was impaired significantly by ischaemia-reperfusion injury, and taurine injected into the operated limb conferred partial protection. A similar trend was observed for tetany, but protection by taurine was not statistically significant for tetanic contraction strength. CONCLUSION: Preservation of fast twitch strength following ischaemia-reperfusion injury by administration of taurine before ischaemia has clinical potential. However, delivery to the affected tissues during ischaemia presents technical difficulties.     

Addition of nitric oxide donor S-nitroso-N-acetylcysteine to selective iNOS inhibitor 1400W further improves contractile function in reperfused skeletal muscle

This study examines the effects of combination therapy with the nitric oxide (NO) donor S-nitroso-N-acetylcysteine (SNAC) and the iNOS inhibitor N-(3-(aminomethyl)benzyl) acetamidine (1400W) on contractile function in reperfused rat skeletal muscle. The right extensor digitorum longus (EDL) muscles of 104 rats were subjected to 3 h of ischemia followed by reperfusion times of 3 h, 24 h, and 7 days. For each time period, rats were further divided into sham operation, control, 1400W only, and 1400W plus SNAC groups. In vitro muscle contractile functional testing was performed in an organ chamber with electrical stimulation. The results showed that twitch and isometric tetanic forces were significantly improved in the 1400W-alone group compared to controls for 24 h and 7 days, but not 3 h of reperfusion. However, all three time periods of reperfusion showed that combination treatment of 1400W + SNAC significantly improved muscle contractile force compared to both control and 1400W-only groups. This corresponded to the decreased tissue necrosis and inflammation seen with combination therapy histologically. Our results demonstrate that combination treatment of 1400W + SNAC promotes functional recovery in reperfused skeletal muscle, supporting that manipulation of NO levels with a NO donor and an iNOS inhibitor is more beneficial than either treatment in isolation.     

Recovery of neuromuscular function during reperfusion of the ischemic extremity: effect of mannitol and superoxide dismutase

The ability of mannitol and superoxide dismutase (SOD) to improve the recovery of peripheral nerve and skeletal muscle function and to influence metabolism during reperfusion after 4 hours of complete ischemia was investigated in an autoperfused canine hind-limb model. Study groups included control subjects (n = 7), subjects given 5000 units/kg of SOD intra-arterial bolus immediately before reperfusion and 10,000 units/kg infusion during first hour of reperfusion (n = 7), and subjects given 150 mg/kg isosmolar mannitol intra-arterial bolus before reperfusion and 1 gm/kg intravenous infusion during the first hour of reperfusion. Function was evaluated by determining isometric twitch and tetanic contractile force of paw dorsiflexion by stimulating the peroneal nerve or the anterior tibial muscle. Metabolic responses (oxygen consumption and lactate clearance) and blood flow were not influenced by either treatment protocol. However, mannitol significantly reduced muscle damage and significantly improved neuromuscular contractile function compared to control and SOD treatment regimens.     

Effects of dexamethasone on the contractile function of reperfused skeletal muscle

This study evaluated the effects of dexamethasone (DXM) on contractile function of reperfused extensor digitalis longus (EDL) muscles following 3-hour ischemia and 24-hour reperfusion. The rats were divided into four groups: normal muscle, ischemia with saline treatment, ischemia/reperfusion with saline treatment, and ischemia/reperfusion with DXM treatment groups. DXM (0.6 mg kg⁻¹) or saline (3.0 ml kg⁻¹) was administered at 3 hours prior to ischemia. Results showed that although contractile force in all three treated groups was significantly lower than that of normal EDL, the average isometric tetanic contractile force in the DXM-treated group was significantly greater than that in the saline-treated ischemia and ischemia/reperfusion groups. A significant difference was also seen at the peak force and at 5 seconds of the fatigue trains, and with a longer fatigue half-time (FT_1/2) in the DXM-treated group than in the other two groups. Histologically, edema, inflammation and necrosis of muscle fiber were less severe in the DXM-treated group than in the saline-treated group. The results indicate that pretreatment with DXM appears to attenuate, but does not completely reverse, the contractile function deficit of ischemic skeletal muscle during the first 24 hours of reperfusion. MICROSURGERY 17:313–320 1996 © 1997 Wiley-Liss, Inc.     

Effect of a NOS inhibitor, L-NMMA, on the contractile function of reperfused skeletal muscle

The authors investigated the effect of NG-monomethyl-L-arginine acetate (L-NMMA), a nitric oxide synthase (NOS) inhibitor, on the contractile function of skeletal muscle following ischemia/reperfusion (I/R) injury. The extensor digitorum longus (EDL) muscles of 50 rats were divided into seven groups. Contractile function in non-ischemic EDL did not change statistically significantly with L-NMMA infusion. I/R (1.5 hr I and 3 hr R) significantly decreased EDL contractile function, with an average maximal twitch force of 56 percent of the contralateral normal muscle force and isometric tetanic contractile forces between 47 and 84 percent at four different stimulation frequencies. Following L-NMMA administration at three different dosages, contractile function of I/R muscle decreased in a dose-dependent manner. The highest dosage of L-NMMA (10 micromol/min) reduced the average maximal twitch force to 15 percent and the isometric tetanic contractile forces to between 10 to 23 percent. Histologic evaluation revealed increased edema, neutrophil infiltration, and muscle-fiber necrosis in L-NMMA-infused EDL, compared to the controls. 1) Skeletal muscle contractile function was dose-dependently decreased with the administration of L-NMMA during I/R. 2) The concentrations of L-NMMA used in this study did not influence the function of non-ischemic EDL. These findings suggest that reduction of NO production during I/R is damaging to skeletal muscle function and would impair successful functional outcomes in microsurgical replantation.     

Early assessment of skeletal muscle damage after ischaemia-reperfusion injury using Tc-99m-glucarate

PURPOSE: After acute arterial obstruction of the lower extremity, muscle damage is the critical determinant for clinical outcome. The extent of muscle damage and limb viability are currently assessed by clinical examination, which is inaccurate. Tc-99m-pyrophosphate (PYP) has been applied for imaging ischaemia-reperfusion damage. More recently, a new imaging agent, Tc-99m-glucarate (GLUC), was introduced for delineating early myocardial infarction after ischaemia-reperfusion. The aim of this study was to determine if GLUC could delineate early skeletal muscle damage after ischaemia-reperfusion. Both tracers were used in a novel murine model of hindlimb ischaemia-reperfusion. METHODS: In anaesthetised mice, ischaemia of one hindlimb was maintained for 2, 3 and 4h using a tourniquet, followed by a reperfusion period of 1h. Additionally, reperfusion periods of 3, 24 and 96h were studied after 3h of ischaemia. PYP or GLUC was injected 45min before end of reperfusion. Concentrations of both agents were determined in blood, reperfused and contralateral muscle. Reperfused-to-contralateral muscle ratios were calculated. In separate experiments, muscle biopsies were obtained for histologic examination. RESULTS: Ischaemia and reperfusion damage was demonstrated histologically. Using scintigraphy GLUC depicted reperfusion significantly better than PYP. After 2, 3 and 4h of ischaemia, the reperfused-to-contralateral ratios for GLUC were 10.7+/-0.9, 8.9+/-0.9 and 8.6+/-1.1, as compared to 4.5+/-0.7, 4.9+/-0.4 and 4.5+/-0.4 for PYP (P<0.05 at all points). For longer periods of reperfusion, the ratios for GLUC decreased to similar levels as observed for PYP. CONCLUSION: The present study indicates that GLUC is a specific early marker of myocyte necrosis after ischaemia-reperfusion. GLUC may become an useful agent for clinical, early, non-invasive monitoring of skeletal muscle damage after ischaemia-reperfusion.     

Viability of hypothermic preserved muscle determined by gene expression levels.

We report a muscle viability index (MVI) that reflects mRNA degradation. The viability of hypothermically preserved (48C) rat skeletal muscle was evaluated using this MVI. To evaluate the hypothermic ischaemic insult of the muscle, 21 hind limbs of Fischer rats (three subgroups of seven limbs each) were hypothermically preserved for 1h, 3h and 6h, before harvesting the tibialis anterior muscle. To investigate reperfusion injury after hypothermic preservation, an additional 28 limbs were transplanted to recipient Fischer rats after hypothermic ischaemia for either 3h or 6h. The transplanted muscles were harvested on either day 3 or day 7 after transplantation. Seven fresh muscles were also harvested, and used as controls. In the 3h ischaemia group, the MVIs of both the hypothermic-ischaemia and the ischaemia-reperfusion subgroups were comparable to the controls. Likewise, there were no significant differences between the controls and the 6h hypothermic ischaemia and ischaemia-reperfusion subgroups. These results show that muscle viability is maintained with hypothermic preservation of up to 6h, and after reperfusion. Therefore, in clinical replantations the amputated extremity should be preserved under hypothermic conditions from the time of injury to the time of surgery.     

Ischemic preconditioning of skeletal muscle: duration of late-phase protection

BACKGROUND: The time course of the late phase of ischemic preconditioning (IPC) was determined in latissimus dorsi muscle (LDM) flaps using viability and function as the endpoints. MATERIALS AND METHODS: LDM flaps from Sprague-Dawley rats were allocated into 6 groups. LDMs were preconditioned with 2 30-minute periods of ischemia separated by 10 minutes of reperfusion and subjected to a 4-hour ischemic insult after 24, 48, 72, and 96 hours from IPC. LDMs were evaluated for percent necrosis and muscle contractile function and compared with controls. RESULTS: The late phase of IPC provides significant protection against necrosis up to 72 hours. Conversely, when the end point used was muscle contractile function, the protection only lasted 48 hours. CONCLUSION: The time course of late-phase protection in skeletal muscle is 2-3 days. Late phase IPC appears to protect muscle flaps during the most critical time period following elevation.     

Up-regulation of MMP-2 and MMP-9 leads to degradation of type IV collagen during skeletal muscle reperfusion injury; protection by the MMP inhibitor, doxycycline.

OBJECTIVES: to determine the role of matrix metalloproteinases, MMP-2 and MMP-9, in reperfusion injury following skeletal muscle ischaemia and whether inhibition of MMPs by doxycycline protects against tissue damage. METHODS: rats were anaesthetised and a tourniquet applied to the proximal thigh to occlude blood flow. Four hours of ischaemia was followed by reperfusion for 0, 4, 24 or 72 h. Two further groups received doxycycline for 7 days prior to bilateral ischaemia and 24 h reperfusion. Skeletal muscle from both limbs, kidneys and lungs were harvested for zymography and immunohistochemical staining for type IV collagen. RESULTS: upregulation of MMP-2 and MMP-9 was detected by zymography in the ischaemic leg and lung but not in the kidney. Quantitative immunohistochemical analysis showed marked degradation of type IV collagen in reperfused muscle, lung and kidney. Doxycycline-treated rats showed significant preservation of type IV collagen in skeletal muscle and a trend towards preservation in kidney and lung. CONCLUSIONS: MMP-2 and MMP-9 are strongly upregulated in skeletal muscle ischaemia/reperfusion injury and are also upregulated in remote organs, leading to degradation of basement membranes. Inhibition of MMP activity may therefore be potentially therapeutically useful in reducing the severity of reperfusion injury.     

Activated protein C attenuates skeletal muscle ischaemia reperfusion injury.

Aims: Pharmacological modulation of skeletal muscle reperfusion injury after an ischaemic insult may improve limb salvage rates and prevent the associated systemic sequelae. Activated Protein C (APC) is an endogenous anti-coagulant with anti-inflammatory properties that has been extensively studied in the setting of sepsis. The purpose of our study was to evaluate the effects of APC on skeletal muscle ischaemia reperfusion injury. Methods: Adult male Sprague Dawley rats (n = 24) were randomised into three groups: control group, I/R group treated with normal saline and I/R group treated with APC. Bilateral hind-limb ischaemia was induced by rubber band application proximal to the level of the greater trochanters for two hours. Treatment groups received either normal saline or APC prior to tourniquet release. Following twelve hours reperfusion, the tibialis anterior was dissected and muscle function assessed electrophysiologically by electrical field stimulation. The animals were then sacrificed and skeletal muscle harvested for evaluation. Skeletal muscle injury was assessed based on myeloperoxidase content as a measure of neutrophil infiltration and wet to dry ratio as a measure of oedema formation. Histological analysis was also performed on the muscle. Results: APC significantly attenuated skeletal muscle reperfusion injury as shown by reduced myeloperoxidase content, wet to dry ratio and electrical properties of skeletal muscle (Table). These findings were supported by our histological findings. Statistical significance was determined using variance analysis. Conclusion: Activated Protein C may have a protective role in the setting of skeletal muscle ischaemia reperfusion injury.     

N-acetylcysteine Protects Striated Muscle in a Model of Compartment Syndrome

Background

To avoid ischemic necrosis, compartment syndrome is a surgical emergency treated with decompression once identified. A potentially lethal, oxidant-driven reperfusion injury occurs after decompression. N-acetylcysteine is an antioxidant with the potential to attenuate the reperfusion injury.

Questions/purposes

We asked whether N-acetylcysteine could preserve striated muscle contractility and modify neutrophil infiltration and activation after simulated compartment syndrome release.

Materials and Methods

Fifty-seven rats were randomized to control, simulated compartment syndrome, and simulated compartment syndrome plus N-acetylcysteine groups. We isolated the rodent cremaster muscle on its neurovascular pedicle and placed it in a pressure chamber. Chamber pressure was elevated above critical closing pressure for 3 hours to simulate compartment syndrome. Experiments were concluded at three times: 1 hour, 24 hours, and 7 days after decompression of compartment syndrome. We assessed twitch and tetanic contractile function and tissue myeloperoxidase activity. Ten additional rats were randomized to control and N-acetylcysteine administration after which neutrophil respiratory burst activity was assessed.

Results

The simulated compartment syndrome decreased muscle contractility and increased muscle tissue myeloperoxidase activity compared with controls. Treatment with N-acetylcysteine preserved twitch and tetanic contractility. N-acetylcysteine did not alter neutrophil infiltration (myeloperoxidase activity) acutely but did reduce infiltration at 24 hours, even when given after decompression. N-acetylcysteine reduced neutrophil respiratory burst activity.

Conclusion

N-acetylcysteine administration before or after simulated compartment syndrome preserved striated muscle contractility, apparently by attenuating neutrophil activation and the resultant oxidant injury.

Clinical Relevance

Our data suggest a potential role for N-acetylcysteine in the attenuation of muscle injury after release of compartment syndrome and possibly in the prophylaxis of compartment syndrome.     

缺血预处理改善骨骼肌功能的研究

目的：探讨缺血预处理法改善缺血骨骼肌功能的临床价值。方法：用ＳＤ大鼠１２只，以右后肢为动物实验模型。分为缺血组（对照组，鼠６只），即缺血４小时后再灌注１小时的方法；缺血预处理组（实验组，鼠６只），缺血过程同对照组，但在缺血前预先经过２次缺血５分钟、再灌注１０分钟的处理。实验时，分别于缺血前、缺血１、４小时及再灌注１小时时，测定两组实验侧肢体腓肠肌最大肌张力的变化。实验结束后分别测量血ＭＤＡ、ＣＰＫ及大鼠右后肢９９ｍＴｃ亚甲基二磷酸计数。结果：实验组最大肌张力的变化（缺血４小时、再灌注１小时时）较对照组有明显改善；血ＭＤＡ、ＣＰＫ及肌肉９９ｍＴｃ亚甲基二磷酸较对照组显著降低。结论：缺血预处理不仅能改善骨骼肌的缺血耐受性，而且能有效地改善骨骼肌的功能     

Ischemia/reperfusion injury of skeletal muscle: plasma taurine as a measure of tissue damage

BACKGROUND: Cell membrane rupture by oxygen-derived free radicals is a systematic feature of ischemia/reperfusion (I/R) injury. High taurine concentration gradients in skeletal muscle prompted us to evaluate whether plasma taurine levels (pTau) are a useful marker of I/R injury after different periods of ischemia. METHODS: Rabbits were randomly assigned to either 1 or 2.5 hours of hind-limb ischemia followed by 2 hours of reperfusion (groups IR1 [n = 12] and IR2.5 [n = 13], respectively). Corresponding sham groups (SHAM1 [n = 8] and SHAM2.5 [n = 9]) were used as controls. Analyzed parameters included histomorphometry and electron microscopy of skeletal muscle biopsies, pTau, and plasma level of malondialdehyde. Skeletal muscle function was assessed 3 weeks after I/R injury. RESULTS: No significant morphologic changes were detectable at the end of ischemia. After reperfusion, mild interstitial edema with intact muscle cell membranes developed in IR1 group; pTau was not increased. IR2.5 group, by contrast, showed severe interstitial edema formation (interfiber area increased by 112%, P <.005), microvascular constriction (microvessel area decreased by 33%, P <.0005), and damage to the muscle cell membranes that was confirmed by the increased plasma malondialdehyde. pTau was higher than in the SHAM2.5 group (P <.0005). Pronounced cell damage in IR2.5 group resulted in impaired muscle function (maximal tetanic tension was reduced 2 times, P <.005) but not in IR1 group. CONCLUSION: Skeletal muscle tolerates 1 h/2 h but not 2.5 h/2 h of I/R, the latter resulting in interstitial edema formation, microvascular constriction, and a late muscle dysfunction. Cell membrane rupture through stimulated lipid peroxidation promotes leakage of intracellular taurine, leading to increased pTau after reperfusion and may be considered as prognostically unfavorable in terms of organ function reversibility. In the rabbit model, pTau seems to be a sensitive marker of I/R injury to skeletal muscle.     

The impact of intestinal ischaemia-reperfusion on caerulein-induced oedematous experimental pancreatitis

BACKGROUND: Intestinal ischaemia is a feature of severe acute pancreatitis. It is not known whether intestinal ischaemia and reperfusion contributes to the progression from mild to severe pancreatitis. AIM: The aim of this study was to examine the impact of intestinal ischaemia-reperfusion on caerulein-induced oedematous experimental pancreatitis. METHOD: Male Wistar rats (n = 48) were randomised to 6 experimental groups: controls (CO), saline infusion (S), saline infusion and intestinal ischaemia-reperfusion (SIR), caerulein infusion (C), caerulein and sham operation (CS), and caerulein infusion with intestinal ischaemia reperfusion (CIR). Caerulein was infused over 6 h to induce mild oedematous pancreatitis. Clamping the superior mesenteric artery for 10 min induced mild intestinal ischaemia. The reperfusion time was 24 h. The primary end point was histology of the pancreas at 24 h. RESULTS: There was no significant difference in histologic severity of pancreatitis at 24 h (Kruskal-Wallis, p = 0.37). CONCLUSION: The severity of acute oedematous pancreatitis was not increased by 10 min of intestinal ischaemia followed by 24 h of reperfusion.     

The separate and combined influence of antioxidant and anti-inflammatory drugs on the liver during ischaemia-reperfusion of the superior mesenteric artery: An experimental study

Aim-Background

To investigate the influence of N-acetyl-cysteine (NAC) and Atorvastatin, separately and combined, on the liver of rats after inducing ischaemia-reperfusion of the superior mesenteric artery.

Methods

Forty male rats aged 2½ months and weighing 220–250gr were randomly assigned to 5 groups of 8 rats. The rats in the first group were considered as controls. The second group was subjected to ischaemia of the superior mesenteric artery for 45 minutes, followed by reperfusion of the superior mesenteric artery for 3 hours, without any drug administration. In the third group, a single dose of Atorvastatin (10mg/kg) was administered 24 hours before the phase of ischaemia. The fourth group received a single dose of N-acetyl-cysteine (160mg/kg) 24 hours before the phase of ischaemia. The fifth group was given both drugs simultaneously 24 hours before the phase of ischaemia. Three hours after reperfusion of the superior mesenteric artery, the liver was surgically removed and prepared for histological examination.

Results

The histological examination of liver tissue samples revealed diffuse necrosis of hepatocytes in the group without any drug administration prior to ischaemia-reperfusion. The groups of animals that were treated with NAC or Atorvastatin or the combination of both drugs showed quite a different histological picture with focal necrosis of hepatocytes and less degenerative lesions.

Conclusions

This study shows that pretreatment with NAC, Atorvastatin and their combination protects the liver from injury induced by intestinal ischaemia-reperfusion. This is ascribed to the antioxidant and anti-inflammatory effect of the above-mentioned drugs.     

Skeletal Muscle Ischaemia-reperfusion Injury: Further Characterisation of a Rodent Model

BACKGROUND: Postischaemic damage in skeletal muscle may be reflected in changes to microvascular blood flow, vascular permeability, and subsequent tissue viability. Previous preclinical studies have not addressed all these parameters, and have not used periods of ischaemia and reperfusion relevant to the clinical setting. This study aimed to develop an animal model hindlimb ischaemia-reperfusion to simulate acute lower limb ischaemia. METHODS: A rodent model of hindlimb tourniquet-induced ischaemia-reperfusion was employed. Gastrocnemius muscle blood flow (GMBF; radio-labelled microspheres), oedema (GMO; using a wet:dry ratio method) and viability (GMV; histochemistry and computerised planimetry) were quantified. RESULTS: 6 h ischaemia per seresulted in neither muscle oedema nor loss of viability, but these changes were apparent following 4 h reperfusion. Early reperfusion at 10 min demonstrated low reflow, with GMBF improving at 120 min before declining sharply at 240 min. CONCLUSION: Prolonged hindlimb ischaemia followed by reperfusion in this rodent model caused significant reductions in gastrocnemius muscle blood flow, associated with muscle oedema and necrosis. These three parameters have not been previously reported together in the same model. This reproducible model could be used in the evaluation of potential therapeutic intervention strategies aimed at ameliorating skeletal muscle reperfusion injury.     

Inhibition of iNOS with 1400W improves contractile function and alters nos gene and protein expression in reperfused skeletal muscle

This study examined the effects of 1400W, an inhibitor of inducible nitric oxide (iNOS), on contractile function and iNOS expression in reperfused skeletal muscle. The right extensor digitorum longus (EDL) muscle of 104 rats underwent a sham operation or 3-h ischemia followed by 3-h or 24-h reperfusion (I/R). Rats received 3 mg/kg 1400W, 10 mg/kg 1400W, or water subcutaneously. Results showed that EDL contractile function in both 1400W-treated groups significantly outperformed the controls at 24-h but not at 3-h reperfusion. Although iNOS expression increased in all three I/R groups during reperfusion, a significantly smaller increase was found in 1400W-treated muscles after 3-h reperfusion, and more dramatically so after 24-h reperfusion. Our results indicate that inhibition of iNOS preserved the contractile function in reperfused skeletal muscle, perhaps via downregulating iNOS expression. Protection by 1400W at 24-h reperfusion suggests that the role of iNOS in exaggerating reperfusion injury is more prominent in the later stages of injury.     

Skeletal muscle blood flow after prolonged tourniquet ischaemia and reperfusion with and without intervening reoxygenation: an experimental study in rats using laser Doppler perfusion imaging.

The total, safe, time available for operating during tourniquet ischaemia is thought to be prolonged by short, intervening episodes of reperfusion. However, animal experiments have suggested that this may cause a reduction of the postischaemic reperfusion injury. The purpose of the present study was to investigate the effect on final postischaemic reperfusion of intermittent, short periods of reperfusion compared with that of prolonged, continuous tourniquet ischaemia. A rat tourniquet model of total limb ischaemia and laser Doppler imaging to measure postischaemic microvascular perfusion in skeletal muscle was used in a total of 25 anaesthetised rats. Four were non-ischaemic controls. In 21 rats one hind leg was made totally ischaemic by a tourniquet. Fourteen were exposed to uninterrupted periods of either 1.5 hours or three hours, and seven to interrupted total ischaemia of three hours, with a 20 minutes reperfusion interval after 1.5 hours of ischaemia. The postischaemic blood flow was monitored 20 minutes after release of the tourniquet. Postischaemic skeletal muscle blood flow was significantly reduced after three hours of continuous ischaemia compared with the group that had an intervening short period of reoxygenation. The postischaemic reperfusion after three hours of ischaemia with a short reperfusion interval was not reduced after ischaemia compared with either that in controls or to that in the group exposed to only 1.5 hours of tourniquet ischaemia. These findings support the clinical practice of using intervening periods of reperfusion to prolong the total tourniquet time that can safely be used. There were no adverse effects on postischaemic reperfusion from intermittent reoxygenation.