The effects of allopurinol in hepatic ischemia and reperfusion: experimental study in rats

BACKGROUND/AIMS: Some studies have shown that postischemic hepatic dysfunction is mainly due to oxygen free radicals that are generated by xanthine oxidase. The present study was undertaken to determine the effect of allopurinol, an inhibitor of xanthine oxidase, on oxidative stress, liver injury and histologic alterations induced by hepatic ischemia-reperfusion in rats. METHODS: One hundred and sixty Wistar rats were used and divided into three groups. Group 1: sham operation; group 2: 50 min of ischemia followed by 1 h of reperfusion, and group 3: pretreatment with allopurinol and 50 min of ischemia followed by 1 h of reperfusion. The effect of allopurinol was evaluated by plasma levels of alanine aminotransferase and aspartate aminotransferase, histopathologic studies, and lipid peroxidation measured by the thiobarbituric acid reactive substances method and chemiluminescence initiated by tert-butyl hydroperoxide technique. RESULTS: Ischemia followed by reperfusion promoted an increase in lipid peroxidation of the hepatic cells when compared to the sham-operated group (p<0.05). This increase was attenuated in the group treated with allopurinol (p< 0.05). Allopurinol also showed a protective effect on hepatocellular necrosis (p<0.05), and the plasma levels of liver enzymes returned earlier to the normal range in rats pretreated with allopurinol in comparison to those that did not receive the drug (p<0.05). CONCLUSIONS: Allopurinol exerted a protective effect on hepatic ischemia and reperfusion in rats. The administration of this drug prior to liver operations should be considered to be submitted to trials in humans.     

Free radicals and cardioplegia: allopurinol and oxypurinol reduce myocardial injury following ischemic arrest

Oxygen-derived free radicals generated by xanthine oxidase may represent a major cause of myocardial injury during ischemia and reperfusion. We have used the isolated working rat heart model of cardiopulmonary bypass and ischemic arrest to assess whether allopurinol or oxypurinol, which should prevent free radical formation through their ability to inhibit xanthine oxidase, can improve postischemic myocardial recovery when the drugs are administered either chronically (pretreatment) or acutely (as an addition to the cardioplegic or reperfusion solution). With normothermic ischemic arrest, both drugs, when given either chronically or acutely, significantly improved postischemic recovery of function. However, under hypothermic conditions, allopurinol conferred no protection when given either as pretreatment or during reperfusion, but it was effective when added to the cardioplegic solution. When administered under the appropriate conditions, both allopurinol and oxypurinol enhanced the protective effect afforded by the St. Thomas' Hospital cardioplegic solution, possibly by inhibiting xanthine oxidase activity and preventing the formation of oxygen-derived free radicals.     

Effects of Allopurinol on Ischemia and Reperfusion in Rabbit Livers

In this work, we evaluated the effects of allopurinol (ALO), an inhibitor of xanthine oxidase (XO), on hepatic lesions caused by ischemia/reperfusion (I/R) in the rabbit liver. Rabbits were pretreated with ALO (10 mg/kg IV) or saline solution 0.9% before the hepatic I/R procedure. The effects of ALO on hepatic injury were evaluated before and after I/R. A standard, warm hepatic I/R procedure caused profound acute liver injury, as indicated by elevated serum aspartate aminotransferase, alanine aminotransferase, and lactic dehydrogenase levels, as well as a high apoptotic cell count. All of these changes were reversed by the administration of ALO before the hepatic I/R procedure. In conclusion, ALO exerted protective effects on hepatic I/R lesions. This protective effect of ALO was probably associated with blocking the generation of superoxide anions during the hepatic I/R procedure by inhibiting XO activity.     

Allopurinol plus pentoxifilline in hepatic ischaemia/reperfusion injury

OBJECTIVES: Ischaemia/reperfusion injury of the liver is the major cause of liver dysfunction and cellular death in transplantation and in liver resection with hepatic pedicle clamping. Many agents are used to prevent this phenomenon, which occurs following interaction of different mediators during both ischaemia and reperfusion. In this study, we aimed to assess the effects of allopurinol, a xanthine oxidase inhibitor, and pentoxifilline, on liver ischaemia/reperfusion injury when used together and to compare these with the effects of using these agents singly. METHODS: Thirty-two rats were divided into four groups consisting of eight rats: Group C, control; Group P, pentoxifilline; Group A, allopurinol; and Group PA, pentoxifilline + allopurinol. Alanine aminotransferase (ALT), aspartate aminotransferase (AST), and lactate dehydrogenase (LDH) levels were measured before hepatic pedicle clamping, on the 45th minute of ischaemia and 15 and 45 minutes after reperfusion. Group P rats were injected with 50 mg/kg pentoxifilline, Group A rats 50 mg/kg allopurinol and Group PA rats were injected with both agents 15 minutes before hepatic pedicle clamping. RESULTS: Ischaemia/reperfusion injury was produced by hepatic pedicle clamping, as demonstrated by AST, ALT and LDH increase. Injury prevention occurred in Groups P, A and PA. No significantly different (better) prevention was provided by giving allopurinol plus pentoxifilline to the rats. Furthermore, no difference was observed between the allopurinol and pentoxifilline injected groups in terms of preventing ischaemia/reperfusion injury. CONCLUSIONS: Pretreatment with allopurinol or pentoxifilline resulted in significantly lower hepatic enzyme elevation than that in controls in the rat liver ischaemia/reperfusion model. Using both agents does not provide better protection than using either agent alone.     

Ischemic preconditioning: a defense mechanism against the reactive oxygen species generated after hepatic ischemia reperfusion

BACKGROUND: Preconditioning protects against both liver and lung damage after hepatic ischemia-reperfusion (I/R). Xanthine and xanthine oxidase (XOD) may contribute to the development of hepatic I/R. OBJECTIVE: To evaluate whether preconditioning could modulate the injurious effects of xanthine/XOD on the liver and lung after hepatic I/R. METHODS: Hepatic I/R or preconditioning previous to I/R was induced in rats. Xanthine and xanthine dehydrogenase/xanthine oxidase (XDH/XOD) in liver and plasma were measured. Hepatic injury and inflammatory response in the lung was evaluated. RESULTS: Preconditioning reduced xanthine accumulation and conversion of XDH to XOD in liver during sustained ischemia. This could reduce the generation of reactive oxygen species (ROS) from XOD, and therefore, attenuate hepatic I/R injury. Inhibition of XOD prevented postischemic ROS generation and hepatic injury. Administration of xanthine and XOD to preconditioned rats led to hepatic MDA and transaminase levels similar to those found after hepatic I/R. Preconditioning, resulting in low circulating levels of xanthine and XOD activity, reduced neutrophil accumulation, oxidative stress, and microvascular disorders seen in lung after hepatic I/R. Inhibition of XOD attenuated the inflammatory damage in lung after hepatic I/R. Administration of xanthine and XOD abolished the benefits of preconditioning on lung damage. CONCLUSIONS: Preconditioning, by blocking the xanthine/XOD pathway for ROS generation, would confer protection against the liver and lung injuries induced by hepatic I/R.     

Hemorrhagic shock-induced bacterial translocation is reduced by xanthine oxidase inhibition or inactivation

Experiments were performed to determine whether bacterial translocation (BT) after hemorrhagic shock is due to a reperfusion injury mediated by xanthine oxidase-derived oxidants. Rats were subjected to 30 minutes of shock (30 mm Hg) followed by reinfusion of shed blood. Twenty-four hours after hemorrhage and reinfusion, the mesenteric lymph node, liver, and spleen were harvested from each animal for bacterial culture, and the ileum and cecum were examined histologically. Sham-shocked (control) rats were instrumented, but blood was not withdrawn. The incidence of BT was higher in the shocked rats (61%) than in the sham-shocked animals (7%) (p less than 0.01). Allopurinol (50 mg/kg, administered orally), a competitive inhibitor of xanthine oxidase, reduced the incidence of shock-induced BT to 14% (p = 0.02). Similarly, rats fed a tungsten-supplemented molybdenum-free diet, which inactivates xanthine oxidase, reduced shock-induced BT to 10% (p = 0.02). The histologic damage cause by hemorrhagic shock was prevented by blocking xanthine oxidase activity. Thus hemorrhagic shock-induced bacterial translocation from the gut appears to be mediated by oxidants generated by activation of the xanthine oxidase system.     

Inhibition of the compartment syndrome by the ablation of free radical-mediated reperfusion injury

Skeletal muscle edema secondary to an increase in capillary permeability after reflow is an important cause of the compartment syndrome after acute arterial revascularization. The purpose of this study was to investigate the possible role of oxygen free radicals, generated at reperfusion, in the pathogenesis of the compartment syndrome secondary to acute arterial ischemia/reperfusion. A reproducible model of this syndrome was produced in anesthetized rabbits by femoral artery occlusion after surgical devascularization of collateral branches from the aorta to the popliteal artery. Increasing periods of ischemia from 6 to 12 hours, followed by 2 hours of reperfusion, were associated with corresponding increases in the anterior muscle compartment hydrostatic pressure and inversely proportional decreases in tibialis anterior muscle blood flow within that compartment as assessed by xenon 133 washout (n = 46) (r = -0.62, p less than 0.001). Anterior compartment pressure increased from 5 +/- 1 to 48 +/- 5 mm Hg (n = 46) (p less than 0.001) after 7 hours of total arterial ischemia and 2 hours of reperfusion. Ablation of free radicals generated from xanthine oxidase with either allopurinol (n = 8) or oxypurinol (n = 8), by scavenging the superoxide radical at reperfusion with superoxide dismutase (n = 8), or by blocking secondary hydroxyl radical formation with deferoxamine (n = 8) significantly ameliorated the rise in compartment pressure (p less than 0.05) in each case; it also significantly improved muscle perfusion in the superoxide dismutase-, allopurinol-, and deferoxamine-treated animals (p less than 0.05). These findings indicate that development of the compartment syndrome after acute arterial revascularization may be due, at least in part, to microvascular injury mediated by oxygen-derived free radicals generated from xanthine oxidase at reperfusion.     

The effect of allopurinol on focal cerebral ischaemia: an experimental study in rabbits

In this experimental study, the neuroprotective effect of the xanthine oxidase inhibitor allopurinol on focal cerebral ischaemia created by permanent middle cerebral artery occlusion (MCAO) was investigated. Using high performance liquid chromatography (HPLC), we measured hypoxanthine, xanthine, and uric acid (UA) levels in rabbit brains following focal cerebral ischaemia. Rabbits were randomly and blindly assigned into four groups of eight animals each. The control groups received 2% carboxymethylcellulose solution, while 10% allopurinol 150 mg/kg was given to the treatment group 1 h before ischaemia. Each group was subdivided into two groups which were sacrificed 4 h or 24 h after ischaemia, respectively. UA and xanthine values of the rabbits in the control groups were quite high at both times and highest after 24 h, particularly in the centre of the ischaemia. A significant decrease in UA and xanthine values was observed in rabbits that were given allopurinol (P<0.05). According to our results, it was concluded that allopurinol pretreatment protects neural tissue in the early period after arterial occlusion and prevents cerebral injury in the late period, especially in the perifocal area, possibly by preventing the formation of free radicals with xanthine oxidase inhibition. Received: 22 June 1998 / Accepted: 21 February 2000     

Allopurinol in Renal Ischemia

ABSTRACT

Allopurinol is a xanthine oxidase inhibitor and antioxidant free radical scavenger which facilitates the protection of ischemic organs in part via this mechanism of action. The accumulation of free radicals during ischemia and reperfusion is in great manner overcome by inhibitors of xanthine oxidase and by the development of endogenous antioxidants. The ischemic lesion generates a well-established inflammatory response with the subsequent production of inflammatory molecules characteristically present at the first stages of the injury. Inflammatory cytokines, chemokines, adhesion molecules, and other cellular and molecular compounds are consequently produced as the lesion sets in. Under these conditions, allopurinol diminishes the effect of inflammatory mediators during the ischemic inflammatory response. This study reviews the literature associated with allopurinol and renal ischemia making special emphasis on the best dose and time of administration of allopurinol regarding its protective effect. It also defines the most accepted mechanism of protection on ischemichally damaged kidneys.     

肝缺血再灌注致大鼠脑损伤时诱导型一氧化氮合酶表达的变化

目的 评价肝缺血再灌注致大鼠脑损伤时诱导型一氧化氮合酶(iNOS)表达的变化.方法 健康雄性Wistar大鼠32只,体重240～280 g,随机分为假手术组(S组,n=8)和肝缺血再灌注组(IR组,n=24).S组仅开腹分离肝动脉、门静脉和胆管,游离脾静脉,40 min后切脾,关腹;IR组通过夹闭肝动脉、门静脉和胆管建立大鼠脾静脉-股静脉转流下全肝缺血再灌注模型,全肝缺血40 min后再灌注,同时切脾.S组断头处死大鼠,IR组分别于再灌注3、6、24 h时断头处死8只大鼠,取脑组织,采用硝酸还原酶法测定一氧化氮(NO)含量,黄嘌呤氧化酶法测定超氧化物歧化酶(SOD)活性,硫代巴比妥酸比色法测定丙二醛(MDA)含量,Western blot法检测硝化酪氨酸(NT)表达,RT-PCR法检测iNOS mRNA表达.结果 与S组比较,IR组再灌注6、24 h时脑组织NO及MDA的含量升高,NT及iNOS mRNA的表达上调,再灌注6 h时SOD活性降低(P<0.05或0.01);与再灌注3 h时比较,再灌注6、24 h时IR组脑组织NO及MDA的含量升高,SOD活性降低(P<0.05).结论 肝缺血再灌注时大鼠脑组织iNOS表达上调,产生大量NO,生成OONO-,导致脑损伤.     

The role of alpha-tocopherol and allopurinol in lipid peroxidation and mitochondrial respiration in the ischemic rat liver

In the present study, the effects of alpha-tocopherol and allopurinol in liver ischemia and reperfusion injury on lipid peroxidation and mitochondrial respiratory function were investigated in rats. Ischemia was induced in the left and median liver lobes clamping the vessels for 90 minutes. After declamping reperfusion was continued for 60 minutes. Liver tissue was taken before and 90 minutes after ischemia and 60 minutes after reperfusion to measure lipid peroxides and mitochondrial respiratory function. In one group of rats alpha-tocopherol (10mg/kg) was given intraperitoneally for three consecutive days preoperatively and in the other group allopurinol (50mg/kg) was given intravenously 10 minutes before ischemia. alpha-Tocopherol caused inhibition of increase in lipid peroxides at reperfusion and improvement in lowering of mitochondrial respiratory function. This improvement was less than previously reported, probably due to not only reperfusion injury but also ischemic injury. Allopurinol, on the other hand, caused neither such inhibition nor such improvement, suggesting the other source of oxygen-derived free radicals than xanthine oxidase system.     

The effect of xanthine oxidase inhibitor on hindlimb ischemia-induced thromboxane A2 release

Our previous studies demonstrated that the bilateral hindlimb ischemia/reperfusion stimulates thromboxane A2 (TXA2) production. The present study tests the role of xanthine oxidase-derived oxygen free radicals in mediating this event. In twelve anesthetized dogs, the abdominal aorta and the inferior vena cava were clamped for 150 min, declamped and reperfused for 30 min. Two groups were studied: untreated control group and pretreated group with xanthine oxidase inhibitor, allopurinol 100 mg.kg-1 orally 24 hr before clamping plus 25 mg.kg-1 intravenously 15 min before clamping. In the control group, plasma TXB2 levels increased markedly after reperfusion. On the other hand, prior treatment with allopurinol attenuated the increase in plasma TXB2 levels at 30 min after reperfusion. This model revealed partial ischemia, because the femoral arterial blood flow was approximately 15% of baseline during clamping. However, the present study suggests that ischemia/reperfusion stimulates TXA2 production, which may be partly affected by hypoxanthine-xanthine oxidase-derived oxygen free radicals and may be an important mechanism responsible for reperfusion injury.     

Xanthine:acceptor oxidoreductase activities in ischemic rat skin flaps

Xanthine:acceptor oxidoreductase activities were assayed in free skin flaps following prolonged preservation. In normal rat skin, xanthine dehydrogenase transfers electrons to NAD+ and accounts for 73% of total oxidoreductase activity, and xanthine oxidase transfers electrons to molecular oxygen and accounts for the remaining 27%. Xanthine oxidase activity increased significantly in skin flaps during ischemia: approximately 30 and 100% increases after 6 and 24 hr of ischemia, respectively. Allopurinol inhibited xanthine oxidoreductase activity: free skin flaps obtained from allopurinol-treated animals exhibited a low level of xanthine oxidoreductase activity throughout the period of preservation. Systemic allopurinol significantly improved the survival rate from 32 to 75% of free flaps transferred after 24 hr of preservation at room temperature. These observations suggest that the xanthine oxidase system is a major source of oxygen free radicals following ischemia/reperfusion in skin. The increase in xanthine oxidase is attributable to the conversion of xanthine dehydrogenase to oxidase, a conversion which involves sulfhydryl oxidation in skin flaps.     

Xanthine oxidase inhibition attenuates ischemic-reperfusion lung injury

Ischemic-reperfusion lung injury is a factor potentially limiting the usefulness of distant organ procurement for heart-lung transplantation. Toxic oxygen metabolites are considered a major etiologic factor in reperfusion injury. Although oxygen-free radicals may be generated by many mechanisms, we investigated the role of xanthine oxidase in this injury process by using lodoxamide, a xanthine oxidase inhibitor, to inhibit ischemic-reperfusion injury in an isolated rat lung model. Isolated rat lungs were perfused with physiologic salt solution (PSS) osmotically stabilized with Ficoll until circulating blood elements were nondetectable in the pulmonary venous effluent. Lungs were rendered ischemic by interrupting ventilation and perfusion for 2 hr at 37 degrees C. After the ischemic interval, the lungs were reperfused with whole blood and lung injury was determined by measuring the accumulation of 125I-bovine serum albumin in lung parenchyma and alveolar lavage fluid as well as by gravimetric measurements. Lung effluent was collected immediately pre- and postischemia for analysis of uric acid by high-pressure liquid chromatography. Lodoxamide (1 mM) caused significant attenuation of postischemic lung injury. Uric acid levels in the lung effluent confirmed inhibition of xanthine oxidase. Protection from injury was not complete, however, implying that additional mechanisms may contribute to ischemic-reperfusion injury in the lung.     

Ablation of free radical-mediated reperfusion injury for the salvage of kidneys taken from non-heartbeating donors. A quantitative evaluation of the proportion of injury caused by reperfusion following periods of warm, cold, and combined warm and cold ischemia

Postischemic renal failure is a severe problem following cadaveric renal transplantation, especially if the kidney has been harvested from a non-heartbeating donor, and thereby subjected to periods of both warm and cold ischemia. It is well established that a substantial component of postischemic injury is produced by oxygen-derived free radicals generated from xanthine oxidase at reperfusion. However, the clinical potential of free radical ablative therapy is dependent upon the proportion of the total injury caused by this reperfusion mechanism, compared with the proportion resulting from ischemic injury per se. Therefore, we quantitatively evaluated these proportions in porcine kidneys subjected to various periods of warm (renal artery occlusion in situ), cold (harvest, cold preservation, and allotransplantation), and combined warm and cold ischemia. Experiments were paired, one kidney treated with either superoxide dismutase (SOD) or allopurinol for free radical ablation, the contralateral kidney serving as a control. Creatinine clearance (Ccr) was measured separately for each kidney 48 hr after reperfusion. After 1 and 2 hr of warm ischemia, Ccr dropped to 50% and 36% of normal, respectively. This was improved to 110% and 55% when SOD was given into the renal artery at reperfusion. Similarly, after 24 and 48 hr of cold ischemia, kidney function was significantly improved from 30% and 18% to 72% and 47% of normal, respectively, when allopurinol was added to the preservation solution. SOD used at harvest and again at reperfusion was particularly effective following combined warm and cold ischemia, in a situation mimicking the harvest of cadaver kidneys from a non-heartbeating donor. These findings suggest that the ablation of free radical-mediated reperfusion injury may improve posttransplant renal function sufficiently to allow expansion of the cadaveric donor pool to include non-heartbeating donors.     

The primary localization of free radical generation after anoxia/reoxygenation in isolated endothelial cells

While free radical-mediated reperfusion injury is clearly important in a variety of disparate organs, the particular cellular source of these radicals is unclear. To address this question, we subjected relatively pure (92% +/- 3% by factor VIII immunoassay) cultures of rat pulmonary artery endothelial cells to 0 to 45 minutes of anoxia (95% N2, 5% CO2), followed by reoxygenation (95% air, 5% CO2), to simulate ischemia/reperfusion. Cell injury was assayed after reoxygenation by the release of previously incorporated 51chromium and/or lactate dehydrogenase, and viability was determined by means of trypan blue exclusion. These three end points correlated closely. Without anoxia, the cells remained viable, with minimal evidence of injury for the entire experimental period, while 45 minutes of hypoxia followed by 30 minutes of reoxygenation produced substantial evidence of cell injury in 71% +/- 6% of the cells. This injury was reduced to 21% +/- 2% by treatment with the highly specific free radical scavengers superoxide dismutase and catalase together, either before anoxia or after anoxia, but just before reoxygenation. Similar protection was provided by xanthine oxidase inhibition with allopurinol. The injury was mimicked (without anoxia) by the exogenous generation of superoxide radicals with xanthine and xanthine oxidase. These experiments establish the essential components of free radical generation at reperfusion to be localized within the isolated endothelial cell in the absence of neutrophils or parenchymal cells.     

Effects of selective cyclooxygenase inhibitors on ischemia/reperfusion-induced hepatic microcirculatory dysfunction in mice

We examined the effects of selective cyclooxygenase (COX) inhibition on hepatic warm ischemia/reperfusion (I/R) injury in mice. A selective COX-1 inhibitor, SC-560, selective COX-2 inhibitors, NS-398 and celecoxib, and indomethacin were administered 30 min before ischemia. Four hours after reperfusion, an in vivo microscopic study showed that I/R caused significant accumulation of leukocytes adhering to the hepatic microvessels and nonperfused sinusoids. Levels of plasma alanine transaminase (ALT) and tumor necrosis factor (TNF)-alpha also showed increases. SC-560, NS-398, celecoxib and indomethacin significantly reduced hepatic responses to I/R including microcirculatory dysfunction and release of ALT and TNF-alpha. Moreover, the effects of the thromboxane (TX) A(2) (TXA(2)) synthase inhibitor OKY-046 and the TXA(2) receptor antagonist S-1452 on hepatic responses to I/R exhibited results similar to those obtained with COX inhibitors. These results suggest that COX-1 and COX-2 contribute to I/R-induced hepatic microvascular and hepatocellular injury partly through TNF-alpha production, and that TXs derived from COX are partly responsible for I/R-induced liver injury.     

Xanthine oxidase: its role in the no-reflow phenomenon.

This study was designed to probe the hypothesis that oxygen-derived free radicals are involved in initiation of the no-reflow phenomenon. We developed a reproducible model of no reflow in the rat hind limb. Laser Doppler studies confirmed that the hind limbs perfused well after 2 or 4 hours of ischemia, but perfusion ceased in the first 10 minutes after 6 hours of ischemia. Venous blood samples and biopsy specimens of skin and muscle were taken after 2 and 4 hours of ischemia to study tissue injury. Blood samples were evaluated for xanthine oxidase (XO), xanthine dehydrogenase, and creatine phosphokinase (CPK) activities. Conjugated dienes and iodine 125-labeled albumin extravasation were quantified in tissue samples. Groups of animals were treated with inhibitors of XO (allopurinol), antioxidant enzymes (superoxide dismutase plus catalase), and free radical scavengers (dimethyl sulfoxide and dimethyl thiourea) to assess the roles of free radicals in ischemia-reperfusion injury in the hind limbs. After 4 hours of ischemia followed by reperfusion, plasma XO activity rose threefold over preischemia levels (p less than 0.05). Xanthine dehydrogenase activity did not change; conjugated diene levels in muscle rose twofold; CPK levels rose sixfold, and 125I albumin extravasation rose twofold (p less than 0.05). Pretreatment with the XO inhibitor allopurinol reduced XO activity to negligible levels and significantly attenuated conjugated diene levels, CPK levels, and albumin extravasation. Albumin extravasation was also significantly attenuated by pretreating animals with superoxide dismutase together with catalase, dimethyl thiourea, and dimethyl sulfoxide. In all animals pretreated with allopurinol or superoxide dismutase and catalase, reperfusion persisted after 6 hours of ischemia. These data suggest that, in ischemia followed by reperfusion, tissue injury is related to oxygen products derived from XO activity.     

Genetic susceptibility to mucosal damage leads to bacterial translocation in a murine burn model

Since genetic factors may be important in host resistance to infections after thermal injury, we screened the susceptibility of three mouse strains (CD-1, Balb/c, and C57/bl) to thermally induced bacterial translocation from the GI tract. Bacteria translocated to the MLNs of Balb/c but not the CD-1 or C57/bl mice receiving 25% body burns. The increased incidence of bacterial translocation in the burned Balb/c mice appeared to be due to a burn-induced gut mucosal injury, since the intestinal mucosa of the Balb/c but not the CD-1 or C57/bl mice was damaged 24 hr after the thermal injury. The mucosal injury appears to be mediated, at least in part, by xanthine oxidase-generated oxygen-free radicals, since inhibition of xanthine oxidase activity with allopurinol, or inactivation of xanthine oxidase activity by a molybdenum-free tungsten diet, prevented the mucosal injury and reduced the extent of bacterial translocation.     

Repetitive brief ischemia: intermittent reperfusion during ischemia ameliorates the extent of injury in the perfused kidney

Acute renal failure commonly follows reduced renal perfusion or ischemia. Reperfusion is essential for recovery but can itself cause functional and structural injury to the kidney. The separate contributions of ischemia and of reperfusion were examined in the isolated perfused rat kidney. Three groups were studied: brief (5 min) ischemia, 20 min ischemia, and repetitive brief ischemia (4 periods of 5 min) with repetitive intervening reperfusion of 5 min. A control group had no intervention, the three ischemia groups were given a baseline perfusion of 30 min before intervention and all groups were perfused for a total of 80 min. In addition, the effects of exogenous *NO from sodium nitroprusside and xanthine oxidase inhibition by allopurinol were assessed in the repetitive brief ischemia-reperfusion model. Brief ischemia produced minimal morphological injury with near normal functional recovery. Repetitive brief ischemia-reperfusion caused less functional and morphological injury than an equivalent single period of ischemia (20 min) suggesting that intermittent reperfusion is less injurious than ischemia alone over the time course of study. Pretreatment with allopurinol improved renal function after repetitive brief ischemia-reperfusion compared with the allopurinol-untreated repetitive brief ischemia-reperfusion group. Similarly, sodium nitroprusside reduced renal vascular resistance but did not improve the glomerular filtration rate or sodium reabsorption in the repetitive brief ischemia-reperfusion model. Thus, these studies show that the duration of uninterrupted ischemia is more critical than reperfusion in determining the extent of renal ischemia-reperfusion injury and that allopurinol, in particular, counteracts the oxidative stress of reperfusion.