Use of microdialysis for in-vivo monitoring of hydroxyl free-radical generation in the rat

Attenuating heatstroke-induced acute lung inflammation, edema, and injury in rats by exercise preconditioning

BACKGROUND

This study aimed to ascertain whether heat-induced acute lung edema, inflammation, and ischemic damage can be affected by heat shock protein 70 (HSP-70)-mediated exercise preconditioning (EP) in rats.

METHODS

Wistar rats were assigned to one of the following four groups: the non-EP + nonheated group, the non-EP + heated group, the EP + heated group, and the EP + HSP-70 antibodies + heated group. EP groups of animals were subjected to a protocol of running on a treadmill for 30 minutes at 20 m/min, 30 minutes at 30 m/min, and 60 minutes at 30 m/min after 1, 2, and 3 weeks of training, respectively. Heated group of animals, under general anesthesia, were put in a folded heating pad of 43°C for 68 minutes. Then, the heated animals were allowed to recover at room temperature. HSP-70 antibodies were injected intravenously 24 hours before heat exposure.

RESULTS

As compared with the non heated + non-EP rats, the heated + non-EP rats had significantly higher scores of alveolar edema, neutrophil infiltration, and hemorrhage, acute pleurisy, and increased bronchoalveolar fluid levels of proinflammatory cytokines and ischemic and oxidative damage markers. EP, in addition to inducing overexpression of HSP-70 in lung tissues, significantly attenuated heat-induced acute pulmonary edema, inflammation, and ischemic and oxidative damage in the lungs. HSP-70 antibodies, in addition to reducing HSP-70 expression in the lungs, significantly attenuated the beneficial effects of EP in reducing acute lung inflammation and injury.

CONCLUSION

EP may attenuate the occurrence of pulmonary edema, inflammation, as well as ischemic and oxidative damage caused by heatstroke by up-regulating HSP-70 in the lungs.

Attenuating systemic inflammatory markers in simulated high-altitude exposure by heat shock protein 70-mediated hypobaric hypoxia preconditioning in rats

BACKGROUND/PURPOSE

The primary goal of this study was to test whether high-altitude exposure (HAE: 0.9% O(2) at 0.47 ATA for 24 hours) was capable of increasing the systemic inflammatory markers as well as the toxic organ injury indicators in rats, with a secondary goal to test whether preinduction of heat shock protein (HSP) 70 by hypobaric hypoxia preconditioning (HHP: 18.3% O(2) at 0.66 ATA for 5 h/day on 5 days consecutively for 2 weeks) attenuated the proposed increased serum levels of both the systemic inflammatory markers and the toxic organ injury indicators.

METHODS

Rats were assigned to: (1) non-HHP (21% O(2) at 1.0 ATA)+non-HAE (21% O(2) at 1.0 ATA) group; (2) non-HHP+HAE group; (3) HHP+non-HAE group; (4) HHP+HAE group; and (5) HHP+HSP70 antibodies (Ab)+HAE group. For the HSP70Ab group, a neutralizing HSP70Ab was injected intravenously at 24 hours prior to HAE. All the physiological and biochemical parameters were obtained at the end of HAE or the equivalent time period of non-HAE. Blood samples were obtained for determination of both the systemic inflammatory markers (e.g., serum tumor necrosis factor-α, interleukin-1β, E-selectin, intercellular adhesion molecule-1, and liver myeloperoxidase activity) and the toxic organ injury indicators (e.g., nitric oxide metabolites, 2,3-dihydroxybenzoic acid, and lactate dehydrogenase).

RESULTS

HHP, in addition to inducing overexpression of tissue HSP70, significantly attenuated the HAE-induced hypotension, bradycardia, hypoxia, acidosis, and increased tissue levels of both the systemic inflammatory markers and the toxic organ injury indicators. The beneficial effects of HHP in inducing tissue overexpression of HSP70 as well as in preventing the HAE-induced increased levels of the systemic inflammatory markers and the toxic organ injury indicators could be significantly reduced by HSP70Ab preconditioning.

CONCLUSION

These results suggest that HHP may downgrade both the systemic inflammatory markers and the toxic organ injury indicators in HAE by upregulating tissue HSP70.

Hypobaric hypoxia preconditioning attenuates acute lung injury during high-altitude exposure in rats via up-regulating heat-shock protein 70

HHP (hypobaric hypoxia preconditioning) induces the overexpression of HSP70 (heat-shock protein 70), as well as tolerance to cerebral ischaemia. In the present study, we hypothesized that HHP would protect against HAE (high-altitude exposure)-induced acute lung injury and oedema via promoting the expression of HSP70 in lungs prior to the onset of HAE. At 2 weeks after the start of HHP, animals were exposed to a simulated HAE of 6000 m in a hypobaric chamber for 24 h. Immediately after being returned to ambient pressure, the non-HHP animals had higher scores of alveolar oedema, neutrophil infiltration and haemorrhage, acute pleurisy (e.g. increased exudate volume, increased numbers of polymorphonuclear cells and increased lung myeloperoxidase activity), increased pro-inflammatory cytokines [e.g. TNF-α (tumour necrosis factor-α), IL (interleukin)-1β and IL-6], and increased cellular ischaemia (i.e. glutamate and lactate/pyruvate ratio) and oxidative damage [glycerol, NOx (combined nitrate+nitrite) and 2,3-dihydroxybenzoic acid] markers in the BALF (bronchoalveolar fluid). HHP, in addition to inducing overexpression of HSP70 in the lungs, significantly attenuated HAE-induced pulmonary oedema, inflammation, and ischaemic and oxidative damage in the lungs. The beneficial effects of HHP in preventing the occurrence of HAE-induced pulmonary oedema, inflammation, and ischaemic and oxidative damage was reduced significantly by pretreatment with a neutralizing anti-HSP70 antibody. In conclusion, HHP may attenuate the occurrence of pulmonary oedema, inflammation, and ischaemic and oxidative damage caused by HAE in part via up-regulating HSP70 in the lungs.

Hyperbaric oxygenation alleviates MCAO-induced brain injury and reduces hydroxyl radical formation and glutamate release

The present study examined the effect of hyperbaric oxygen (HBO) on the formation of 2,3-dihydroxybenzoic acid (2,3-DHBA) and 2,5-dihydroxybenzoic acid (2,5-DHBA), the products of salicylate trapping of hydroxyl free radicals, and glutamate release in the striatum during acute ischemia and reperfusion. Non-HBO rats (n = 8) were subjected to 1-h ischemia. Study rats (n = 8) were treated with HBO at 2.8 ATA for 1 h during ischemia. Artificial CSF solution containing 5 mM sodium salicylate was perfused at 1 microl/min. Samples were continuously collected at 15 min intervals and the levels of 2,3-DHBA, 2,5-DHBA, and glutamate were analyzed. The lesion volume was determined by TTC stain. Occlusion of the middle cerebral artery induced a significant increase in the levels of 2,3-DHBA and 2,5-DHBA. A peak of approximately two and fourfold of baseline levels was reached at 45 min and was maintained at elevated levels during reperfusion. The level of glutamate increased approximately two times at 30 min during ischemia, continued to increase, and reached approximately three times baseline level during reperfusion. HBO significantly alleviated brain injury associated with decreased levels of 2,3-DHBA, 2,5-DHBA and glutamate. This study suggests that the decreased glutamate release and the reduced formation of hydroxyl free radicals might contribute to the neuroprotective effect of HBO.

Effect of xanthine oxidase-generated extracellular superoxide on skeletal muscle force generation

Skeletal muscle contractions increase superoxide anion in skeletal muscle extracellular space. We tested the hypotheses that 1) after an isometric contraction protocol, xanthine oxidase (XO) activity is a source of superoxide anion in the extracellular space of skeletal muscle and 2) the increase in XO-derived extracellular superoxide anion during contractions affects skeletal muscle contractile function. Superoxide anion was monitored in the extracellular space of mouse gastrocnemius muscles by following the reduction of cytochrome c in muscle microdialysates. A 15-min protocol of nondamaging isometric contractions increased the reduction of cytochrome c in microdialysates, indicating an increase in superoxide anion. Mice treated with the XO inhibitor oxypurinol showed a smaller increase in superoxide anions in muscle microdialysates following contractions than in microdialysates from muscles of vehicle-treated mice. Intact extensor digitorum longus (EDL) and soleus muscles from mice were also incubated in vitro with oxypurinol or polyethylene glycol-tagged Cu,Zn-SOD. Oxypurinol decreased the maximum tetanic force produced by EDL and soleus muscles, and polyethylene glycol-tagged Cu,Zn-SOD decreased the maximum force production by the EDL muscles. Neither agent influenced the rate of decline in force production when EDL or soleus muscles were repeatedly electrically stimulated using a 5-min fatiguing protocol (stimulation at 40 Hz for 0.1 s every 5 s). Thus these studies indicate that XO activity contributes to the increased superoxide anion detected within the extracellular space of skeletal muscles during nondamaging contractile activity and that XO-derived superoxide anion or derivatives of this radical have a positive effect on muscle force generation during isometric contractions of mouse skeletal muscles.

Oxidative stress and ischemic injuries in heat stroke

When rats were exposed to high environmental temperature (e.g., 42 or 43 degrees C), hyperthermia, hypotension, and cerebral ischemia and damage occurred during heat stroke were associated with increased production of free radicals (specifically hydroxyl radicals and superoxide anions), higher lipid peroxidation, lower enzymatic antioxidant defenses, and higher enzymatic pro-oxidants in the brain of heat stroke-affected rats. Pretreatment with conventional hydroxyl radical scavengers (e.g., mannitol or alpha-tocopherol) prevented increased production of hydroxyl radicals, increased levels of lipid peroxidation, and ischemic neuronal damage in different brain structures attenuated with heat stroke and increased subsequent survival time. Heat shock preconditioning (a mild sublethal heat exposure for 15min) or regular, daily exercise for at least 3 weeks, in addition to inducing overproduction of heat shock protein 72 in multiple organs including brain, significantly attenuated the heat stroke-induced hyperthermia, hypotension, cerebral ischemia and damage, and overproduction of hydroxyl radicals and lipid peroxidation. The precise function of heat shock protein 72 are unknown, but there is considerable evidence that these proteins are essential for survival at both normal and elevated temperatures. They also play a critical role in the development of thermotolerance and protection from oxidative damage associated with cerebral ischemia and energy depletion during heat stroke. In addition, Shengmai San or magnolol (Chinese herbal medicines) or hypervolemic hemodilution (produced by intravenous infusion of 10% human albumin) is effective for prevention and repair of ischemic and oxidative damage in the brain during heat stroke. Thus, it appears that heat shock protein 72 preconditioning induced by prior heat shock or regular exercise training, as well as pretreatment with Shengmai San or magnolol is able to prevent the oxidative damage during heat stroke. On the other hand, hypervolemic hemodilution, Shengmai San, or magnolol is able to treat the oxidative damage after heat stroke onset.

Cardiac sympathetic neuroprotective effect of desipramine in tachycardia-induced cardiomyopathy

Cardiac sympathetic transmitter stores are reduced in the failing heart. In this study, we proposed to investigate whether the reduction of cardiac sympathetic neurotransmitters was associated with increased interstitial norepinephrine (NE) and reactive oxygen species in congestive heart failure (CHF), using a microdialysis technique and salicylate to detect ·OH generation. Rabbits with and without rapid ventricular pacing (340 beats/min) were randomized to receive desipramine (10 mg/day) or placebo for 8 wk. Rapid pacing produced left ventricular dilation and systolic dysfunction. The failing myocardium also showed reduced tissue contents of NE and tyrosine hydroxylase protein and activity. In contrast, myocardial interstitial NE was increased in CHF (0.89 ± 0.11 ng/ml) compared with the sham-operated animals (0.26 ± 0.03 ng/ml). In addition, cardiac oxidative stress was increased in CHF animals as measured by myocardial interstitial ·OH radical, tissue oxidized glutathione, and oxidized mitochondrial DNA. Desipramine treatment produced significant NE uptake inhibition as evidence by an exaggerated pressor response and a greater increase of myocardial interstitial NE in response to intravenous NE infusion but no significant effects on cardiac function or hemodynamics in sham-operated or CHF animals. However, desipramine treatment attenuated the reductions of tissue NE and tyrosine hydroxylase protein and activity in CHF. Desipramine also prevented the reduction of tyrosine hydroxylase produced by NE in PC12 cells. Thus the reduction of cardiac sympathetic neurotransmitters is related to the increased interstitial NE and tissue oxidative stress in CHF. Also, normal neuronal uptake of NE is required for NE or its oxidized metabolites to exert their neurotoxic effects.

Heat shock pretreatment may protect against heatstroke-induced circulatory shock and cerebral ischemia by reducing oxidative stress and energy depletion

The mechanisms underlying the protective effects of heat shock pretreatment on heatstroke remain unclear. Here we attempted to ascertain whether the possible occurrence of oxidative stress and energy depletion exhibited during heatstroke can be reduced by heat shock preconditioning. In the present study, colonic temperature, mean arterial pressure, heart rate, striatal levels of heat shock protein 72 (HSP72), local Po2, brain temperature, cerebral blood flow, cellular ischemia and damage markers, dihydroxybenzoic acid (DHBA), lipid peroxidation, glutathione, glutathione peroxidase and reductase activities, and ATP were assayed in normothermic control rats and in heatstroke rats with or without preconditioning 16 or 96 h before initiation of heatstroke. Heatstroke was induced by exposing the anesthetized rats to a high ambient temperature (Ta = 43 degrees C) until the moment at which MAP decreased from its peak level. Sublethal heat shock pretreatment 16 h before initiation of heatstroke, in addition to increasing striatal HSP72 levels, conferred significant protection against heatstroke-induced arterial hypotension, striatal ischemia and damage, increment of hydroxyl radical formation, lipid peroxidation, glutathione oxidation, and decrement of glutathione peroxidase activity and ATP. However, at 96 h after heat shock, when striatal HSP72 expression returned to basal levels, the above responses that occurred during onset of heatstroke were indistinguishable between the two groups. These results suggest that heat shock pretreatment induces HSP72 overexpression in striatum and confers protection against heatstroke-induced striatal ischemia and damage by reducing oxidative stress and energy depletion.

Chinese Herbal Medicine, Shengmai San, Is Effective for Improving Circulatory Shock and Oxidative Damage in the Brain During Heatstroke

The aim of this study was to investigate the effect of Shengmai San (SMS), a traditional Chinese herbal medicine, on heatstroke-induced circulatory shock and oxidative damage in the brain in rats. Anesthetized rats were exposed to a high ambient temperature (43 degrees C) to induce heatstroke. After the onset of heatstroke, the values of mean arterial pressure, cerebral perfusion pressure, cerebral blood flow, and brain partial pressure of O(2) were all significantly lower than those in normothermic controls. However, the values of intracranial pressure, brain and colonic temperatures, and brain levels of free radicals, lipid peroxidation, and cellular ischemia and damage markers were all greater in heatstroke rats compared with those of normothermic controls. Pretreatment or post-treatment with SMS significantly reduced the hypotension, intracranial hypertension, cerebral hypoperfusion and hypoxia and increased levels of ischemia and damage markers in the brain during heatstroke. The protective effects exerted by SMS pretreatment is superior to those of SMS post-treatment. The results demonstrate that SMS is effective for prevention and repair of circulatory shock and ischemic and oxidative damage in the brain during heatstroke.

Release of reactive oxygen and nitrogen species from contracting skeletal muscle cells

A number of studies have indicated that exercise is associated with an increased oxidative stress in skeletal muscle tissue, but the nature of the increased oxidants and sites of their generation have not been clarified. The generation of extracellular reactive oxygen and nitrogen species has been studied in myotubes derived from an immortalized muscle cell line (H-2k(b) cells) that were stimulated to contract by electrical stimulation in culture. Cells were stimulated to contract with differing frequencies of electrical stimulation. Both induced release of superoxide anion and nitric oxide into the extracellular medium and caused an increase in extracellular hydroxyl radical activity. Increasing frequency of stimulation increased the nitric oxide generation and hydroxyl radical activity, but had no significant effect on the superoxide released. Additions of inhibitors of putative generating pathways indicated that contraction-induced NO release was primarily from neuronal NO synthase enzymes and that the superoxide released is likely to be generated by a plasma membrane-located, flavoprotein oxidoreductase system. The data also indicate that peroxynitrite is generated in the extracellular fluid of muscle during contractile activity.

Extracellular norepinephrine reduces neuronal uptake of norepinephrine by oxidative stress in PC12 cells

Cardiac norepinephrine (NE) uptake activity is reduced in congestive heart failure. Our studies in intact animals suggest that this effect on the cardiac sympathetic nerve endings is caused by oxidative stress and/or NE toxic metabolites derived from NE. In this study, we investigated the direct effects of NE on neuronal NE uptake activity and NE transporter (NET), using undifferentiated PC12 cells. Cells were incubated with NE (1–500 μM) either alone or in combination of Cu2+ sulfate (1 μM), which promotes free radical formation by Fenton reaction for 24 h. NE uptake activity was measured using [3H]NE. Cell viability was determined with the use of Trypan blue exclusion and 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-tetrazolium bromide assay, and cellular oxidative stress by dichlorodihydrofluorescein fluorescence and the GSH/GSSG ratio. Cell viability was reduced by NE >100 μM. At lower doses, NE produced oxidative stress and a dose-dependent reduction of NE uptake activity without affecting cell viability significantly. Cu2+, which has no direct effect on NE uptake activity, potentiated oxidative stress and reduction of NE uptake activity produced by NE. This decrease of NE uptake activity was associated with reductions of NE uptake binding sites and NET protein expression by using the radioligand assay and Western blot analysis, but no changes in NET gene expression. In addition, the free-radical scavenger mannitol, and antioxidant enzymes superoxide dismutase and catalase, reduced oxidative stress and attenuated the reductions of NE uptake activity and NET protein produced by NE/Cu. Thus our results support a functional role of oxidative stress in mediating the neuronal NE uptake reducing effect of NE and that this effect of NE on NET is a posttranscriptional event.

Role of mitochondrial superoxide dismutase in contraction-induced generation of reactive oxygen species in skeletal muscle extracellular space

Contractions of skeletal muscles produce increases in concentrations of superoxide anions and activity of hydroxyl radicals in the extracellular space. The sources of these reactive oxygen species are not clear. We tested the hypothesis that, after a demanding isometric contraction protocol, the major source of superoxide and hydroxyl radical activity in the extracellular space of muscles is mitochondrial generation of superoxide anions and that, with a reduction in MnSOD activity, concentration of superoxide anions in the extracellular space is unchanged but concentration of hydroxyl radicals is decreased. For gastrocnemius muscles from adult (6–8 mo old) wild-type ( Sod2+/+) mice and knockout mice heterozygous for the MnSOD gene ( Sod2+/-), concentrations of superoxide anions and hydroxyl radical activity were measured in the extracellular space by microdialysis. A 15-min protocol of 180 isometric contractions induced a rapid, equivalent increase in reduction of cytochrome c as an index of superoxide anion concentrations in the extracellular space of Sod2+/+and Sod2+/-mice, whereas hydroxyl radical activity measured by formation of 2,3-dihydroxybenzoate from salicylate increased only in the extracellular space of muscles of Sod2+/+mice. The lack of a difference in increase in superoxide anion concentration in the extracellular space of Sod2+/+and Sod2+/-mice after the contraction protocol supported the hypothesis that superoxide anions were not directly derived from mitochondria. In contrast, the data obtained suggest that the increase in hydroxyl radical concentration in the extracellular space of muscles from wild-type mice after the contraction protocol most likely results from degradation of hydrogen peroxide generated by MnSOD activity.

Protective effects of alpha-tocopherol and mannitol in both circulatory shock and cerebral ischaemia injury in rat heatstroke

1. There is evidence that hydroxyl radicals are accumulated and oxidative stress is produced in multiple organs, including the brain, of rats with heat stroke. Herein, we investigated the effect on heat stroke-induced circulatory shock and cerebral ischaemic injury of two free radical scavengers, namely mannitol and alpha-tocopherol. 2. Urethane-anaesthetized rats were exposed to heat stress (ambient temperature 42 degrees C) to induce heat stroke. Control rats were exposed to 24 degrees C. Mean arterial pressure and cerebral blood flow after the onset of heat stroke were significantly lower in heat stroke rats than in control rats. However, cerebral free radicals, lipid peroxidation and the neuronal damage score were greater in heat stroke rats compared with control rats. Similarly, plasma cytokines, including tumour necrosis factor-alpha, interleukin (IL)-1beta and IL-6, were significantly higher in heat stroke rats compared with their normothermic controls. 3. Pretreatment with alpha-tocopherol (20 mg/kg, i.v.) or mannitol (10%, i.v.) 30 min before the onset of heat exposure significantly attenuated heat stroke-induced arterial hypotension, cerebral ischaemia and neuronal damage, the increased free radical formation and lipid peroxidation in the brain and the increased plasma levels of cytokines. Pretreatment with alpha-tocopherol or mannitol resulted in a prolongation of survival time in heat stroke. 4. These results demonstrate that although pretreatment with alpha-tocopherol and mannitol does not prevent the heat stroke syndrome entirely, an attenuation of the syndrome is observed.

Magnolol protects against cerebral ischaemic injury of rat heatstroke

1. Free radicals mediate cerebral ischaemic injury associated with heatstroke. Magnolol, an active component of Magnolia officinalis, is 1000-fold more potent than alpha-tocopherol in inhibiting lipid peroxidation in rat mitochondria. The aim of the present study was to ascertain whether magnolol attenuated cerebral ischaemic injury and free radical formation associated with heatstroke. 2. Urethane-anaesthetized rats were exposed to heat stress (ambient temperature 42 degrees C) to induce heatstroke. Controlled rats were exposed to 24 degrees C. Mean arterial pressure, cerebral perfusion pressure and cerebral blood flow after the onset of heatstroke were all significantly lower than in control rats. However, colonic temperature, intracranial pressure, heart rate, cerebral free radicals, lipid peroxidation and the neuronal damage score were greater after the onset of heatstroke. 3. Magnolol (20 or 40 mg/kg, i.v.) significantly attenuated the heatstroke-induced hyperthermia, arterial hypotension, intracranial hypertension, cerebral ischaemia and neuronal damage and increased free radical formation and lipid peroxidation in the brain. The extracellular concentrations of ischaemic (e.g. glutamate and lactate/pyruvate ratio) and damage (e.g. glycerol) markers in the corpus striatum were increased after the onset of heatstroke. Magnolol significantly attenuated the increase in striatal ischaemia and damage markers associated with heatstroke. 4. Thus, it appears that magnolol has impressive effects against heatstroke reactions.

Hydroxyl radical in living systems and its separation methods

It has recently been shown that hydroxyl radicals are generated under physiological and pathological conditions and that they seem to be closely linked to various models of pathology putatively implying oxidative stress. It is now recognized that the hydroxyl radical is well-regulated to help maintain homeostasis on the cellular level in normal, healthy tissues. Conversely, it is also known that virtually every disease state involves free radicals, particularly the most reactive hydroxyl radical. However, when hydroxyl radicals are generated in excess or the cellular antioxidant defense is deficient, they can stimulate free radical chain reactions by interacting with proteins, lipids, and nucleic acids causing cellular damage and even diseases. Therefore, a confident analytical approach is needed to ascertain the importance of hydroxyl radicals in biological systems. In this paper, we provide information on hydroxyl radical trapping and detection methods, including liquid chromatography with electrochemical detection and mass spectrometry, gas chromatography with mass spectrometry, capillary electrophoresis, electron spin resonance and chemiluminescence. In addition, the relationships between diseases and the hydroxyl radical in living systems, as well as novel separation methods for the hydroxyl radical are discussed in this paper.

Oxidative stress in rats with heatstroke-induced cerebral ischemia

BACKGROUND AND PURPOSE

Heatstroke is associated with cerebral ischemia as well as increased levels of interleukin-1beta, dopamine, and glutamate in the brain. These factors are known to increase free radical production. This study attempted to ascertain whether an excessive accumulation of cytotoxic free radicals in the brain and oxidative stress can occur during heatstroke.

METHODS

Urethane-anesthetized rats underwent instrumentation for the measurement of mean arterial pressure, cerebral blood flow, neuronal damage score, and colonic temperature. Rats were exposed to heat stress (ambient temperature, 42 degrees C) until mean arterial pressure and cerebral blood flow began to decrease from their peak levels, which was arbitrarily defined as the onset of heatstroke. Controlled rats were exposed to 24 degrees C. Concentrations of dihydroxybenzoic acid, lipid peroxidation, rate of O2*- generation, superoxide dismutase, and catalase activity of the brain or other vital organs were assessed during heatstroke.

RESULTS

The values of mean arterial pressure and cerebral blood flow after heatstroke onset were all significantly lower than those in control rats. However, the values of colonic temperature, dihydroxybenzoic acid levels in the striatum, and neuronal damage score were greater. The extent of lipid peroxidation in the brain and the rate of O2*- generation in the brain, liver, and heart were all greater in rats after heatstroke onset. In contrast, the values of total superoxide dismutase in the brain, liver, and heart and the catalase activity in the brain were lower.

CONCLUSIONS

Taken together, these results indicate that hydroxyl radicals mediate cerebral ischemic injury associated with heatstroke.

Measurement of free radical production by in vivo microdialysis during ischemia/reperfusion injury to skeletal muscle

Microdialysis techniques have been used to detect hydroxyl radical and superoxide release into the interstitial space of anaesthetized rat anterior tibialis muscles during a period of prolonged (4 h) limb ischemia and subsequent reperfusion. Data indicate that reperfusion of the ischemic skeletal muscle was associated with a large increase in hydroxyl radical activity in the interstitial space, which may contribute to the significant oxidation of muscle glutathione, protein thiols, and lipids also seen in this model. No evidence for release of superoxide into the interstitial space was found during reperfusion, although this was observed during electrically stimulated contractile activity of the rat limb muscle. These data imply that therapeutic approaches aimed at reduction of hydroxyl radical generation in the interstitial fluid are more likely to be beneficial in reduction of skeletal muscle reperfusion injury than approaches designed to scavenge superoxide radicals.

Contractile activity-induced oxidative stress: cellular origin and adaptive responses

Previous studies have reported that oxidizing free radical species are generated during exercise, and there has been considerable interest in the potential effects of these on exercising tissues. We hypothesized that contracting skeletal muscle was a major source of oxidizing free radical species and that untrained skeletal muscle would adapt to the oxidative stress of a single short period of contractile activity by upregulation of the activity of cytoprotective proteins in the absence of overt cellular damage. Fifteen minutes of aerobic contractile activity was found to induce a rapid release of superoxide anions from mouse skeletal muscle in vivo, and studies with contracting cultured skeletal muscle myotubes confirmed that this was due to release from myocytes rather than other cell types present within muscle tissue in vivo. This increased oxidant production caused a rapid, transient reduction in muscle protein thiol content, followed by increases in the activities of superoxide dismutase and catalase and in content of heat shock proteins. These changes occurred in the absence of overt damage to the muscle cells.

Experimental and theoretical microdialysis studies of in situ metabolism

Microdialysis sampling was performed to monitor localized metabolism in vivo and in vitro. A mathematical model that accounts for analyte mass transport during microdialysis sampling was used to predict metabolite concentrations in the microdialysis probe during localized metabolism experiments. The model predicts that metabolite concentrations obtained in the microdialysis probe are a function of different experimental parameters including membrane length, perfusion fluid flow rate, and sample diffusive and kinetic properties. Different microdialysis experimental parameters including membrane length and perfusion fluid flow rate were varied to affect substrate extraction efficiency (E(d)), or loss to the sample matrix, in vivo and in vitro. Local hepatic metabolism was studied in vivo in male Sprague-Dawley rats by infusing acetaminophen through the microdialysis probe. Acetaminophen sulfate concentrations increased linearly with respect to acetaminophen E(d) in contrast to modeling predictions. Xanthine oxidase was used as an in vitro model of localized metabolism. In vitro experimental results partially matched modeling predictions for 10-mm probes. These results suggest that monitoring local metabolism using microdialysis sampling is feasible. It is important to consider system parameters such as dialysis flow rate, membrane length, and sample properties because these factors will affect analyte concentrations obtained during local metabolism experiments.