Hypothermia attenuates circulatory shock and cerebral ischemia in experimental heatstroke

We tested the hypothesis in a rat model that body cooling suppresses circulatory shock and cerebral ischemia in heatstroke. Animals under urethane anesthesia were exposed to water blanket temperature (Tblanket) of 42 degrees C until mean arterial pressure (MAP) and local cerebral blood flow (CBF) in the hippocampus began to decrease from their peak levels, which was arbitrarily defined as the onset of heatstroke. Control rats were exposed to 26 degrees C. Extracellular concentrations of glutamate, glycerol, lactate, and lactate/pyruvate in the hippocampus were assessed by microdialysis methods. Cooling was accomplished by decreasing Tblanket from 42 degrees C to 16 degrees C. The values of MAP and CBF after the onset of heat stroke in heatstroke rats received no cooling were all significantly lower than those in control rats. However, the neuronal damage score and extracellular levels of ischemia and damage markers in the hippocampus were greater. Cooling immediately after the onset of heatstroke reduced the heatstroke-induced circulatory shock, cerebral ischemia, neuronal damage, and surge of tissue ischemia and damage markers in the hippocampus, and resulted in prolongation of survival time. Delaying the onset of cooling reduced the therapeutic efficiency. The results suggest that body cooling attenuates circulatory shock and cerebral ischemia insults in heatstroke.     

Progressive exercise preconditioning protects against circulatory shock during experimental heatstroke

Heat shock protein (HSP) 72 expression protects against arterial hypotension in rat heatstroke. HSP72 can also be induced in multiple organs, including hearts from rats with endurance exercise. We validated the hypothesis that progressive exercise preconditioning may confer cardiovascular protection during heatstroke by inducing the overexpression of HSP72 in multiple organs. To deal with the matter, we assessed the effects of heatstroke on mean arterial pressure, heart rate, cardiac output, stroke volume, total peripheral vascular resistance, colonic temperature, blood gases, and serum or tissue levels of tumor necrosis factor-alpha (TNF-alpha) in urethane-anesthetized rats pretreated without or with progressive exercise training for 1, 2, or 3 weeks. In addition, HSP72 expression in multiple organs was determined in different groups of animals. Heatstroke was induced by exposing the rats to a high blanket temperature (43 degrees C); the moment at which mean arterial pressure decreased from the peak value was taken as the time of heatstroke onset. Previous exercise training for 3 weeks, but not 1 or 2 weeks, conferred significant protection against hyperthermia, arterial hypotension, decreased cardiac output, decreased stroke volume, decreased peripheral vascular resistance, and increased levels of serum or tissue TNF-alpha during heatstroke and correlated with overexpression of HSP72 in multiple organs, including heart, liver, and adrenal gland. However, 10 days after 3 weeks of progressive exercise training, when HSP72 expression in multiple organs returned to basal values, the beneficial effects exerted by 3 weeks of exercise training were no longer observed. These results strongly suggest that HSP72 preconditioning with progressive exercise training protects against hyperthermia, circulatory shock, and TNF-alpha overproduction during heatstroke.     

Ipsapirone and ketanserin protects against circulatory shock, intracranial hypertension, and cerebral ischemia during heatstroke

We assess the effects of ipsapirone (a 5-HT1A receptor agonist), ketanserin (a 5-HT2A receptor antagonist), (-)-pindolol (a 5-HT1A receptor antagonist), and DOI (a 5-HT2A receptor agonist) on heatstroke in a rat model. Animals, under urethane anesthesia, were exposed to high ambient temperature of 42 degrees C until mean arterial pressure and local cerebral blood flow in the striatum began to decrease, which was arbitrarily defined as the onset of heatstroke. Normothermic controls were exposed to room temperature of 24 degrees C. In rats treated with normal saline immediately before the initiation of heat stress, the values for survival time were found to be 21 to 25 min. Systemic administration of ipsapirone (10 mg/kg) or ketanserin (2 mg/kg) immediately before the initiation of heat stress significantly increased the survival time to new values of 92 to 104 min. Combined treatment with ipsapirone and ketanserin had additive effects (survival time of 156-194 min). In contrast, systemic administration of (-)-pindolol (2 mg/kg) or DOI (2 mg/kg) significantly decreased the survival time to new values of 2 to 3 min. In vehicle-treated heatstroke rats, the values for core temperature, intracranial pressure, and the extracellular levels of cellular ischemia (e.g., glutamate and lactate/pyruvate ratio) or damage (e.g., glycerol) markers and neuronal damage scores in striatum were significantly higher than those of normothermic controls. On the other hand, the values for mean arterial pressure, cerebral perfusion pressure, cerebral blood flow, and brain partial pressure of O2 were significantly lower than those of normothermic controls. The heatstroke-induced hyperthermia, arterial hypotension, intracranial hypertension, cerebral hypoperfusion and hypoxia, and increased levels of cellular ischemia and damage markers in striatum were all significantly attenuated by prior administration of ipsapirone or ketanserin. The present results strongly suggest that previous activation of 5-HT1A receptors or antagonism of 5-HT2A receptors protects against heatstroke by reducing circulatory shock and cerebral ischemia, whereas prior antagonism of 5-HT1A receptors or activation of 5-HT2A receptors exacerbates heatstroke.     

Brain cooling causes attenuation of cerebral oxidative stress, systemic inflammation, activated coagulation, and tissue ischemia/injury during heatstroke

The purpose of the present study was to assess the therapeutic effect of hypothermic retrograde jugular vein flush (HRJVF) on heatstroke. HRJVF was accomplished by infusion of 4 degrees C isotonic sodium chloride solution via the external jugular vein (1.7 mL/100 g of body weight over 5 min). Immediately after the onset of heatstroke, anesthetized rats were divided into 2 major groups and given the following: 36 degrees C or 4 degrees C isotonic sodium chloride solution, i.v. They were exposed to ambient temperature of 43 degrees C to induce heatstroke. Another group of rats was exposed to room temperature (24 degrees C) and used as normothermic controls. When the 36 degrees C saline-treated rats underwent heat exposure, their survival time values were found to be 23 to 28 min. Immediately after the onset of heatstroke, resuscitation with an i.v. dose of 4 degrees C saline significantly improved survival during heatstroke (208-252 min). All heat-stressed animals displayed systemic inflammation and activated coagulation, evidenced by increased tumor necrosis factor alpha, prothrombin time, activated partial thromboplastin time, and d-dimer, and decreased platelet count and protein C. Biochemical markers evidenced cellular ischemia and injury/dysfunction: plasma levels of blood urea nitrogen, creatinine, glutamic oxaloacetic transaminase, glutamic pyruvic transaminase, and alkaline phosphatase; and striatal levels of glycerol, glutamate, and lactate/pyruvate; dihydroxy benzoic acid, lipid peroxidation, oxidized-form glutathione reduced-form glutathione, dopamine, and serotonin were all elevated during heatstroke. Core and brain temperatures and intracranial pressure were also increased during heatstroke. In contrast, the values of mean arterial pressure, cerebral perfusion pressure, and striatal levels of local blood flow, partial pressure of oxygen, superoxide dismutase, catalase, glutathione peroxidase, and glutathions reductase activities were all significantly lower during heatstroke. The circulatory dysfunction, systemic inflammation, hypercoagulable state, and cerebral oxidative stress, ischemia, and damage during heatstroke were all significantly suppressed by HRJVF. These findings demonstrate that brain cooling caused by HRJVF therapy may resuscitate persons who had a stroke by attenuating cerebral oxidative stress, systemic inflammation, activated coagulation, and tissue ischemia/injury during heatstroke.     

Effects of geranyl-geranyl-acetone administration before heat shock preconditioning for conferring tolerance against ischemia-reperfusion injury in rat livers

The effect of geranyl-geranyl-acetone (GGA) administration before heat shock preconditioning on heat shock protein (HSP) 72 induction and on the acquisition of tolerance against ischemia-reperfusion Injury was studied in rat livers. Male Wistar rats were divided into four groups: a control group (group C); a GGA group (group G); a simple heat shock group (group VH); and a heat shock with GGA premedication group (group GH). Five-, 10-, and 15-minute periods of heat shock preconditioning at 42 degrees C were performed in groups VH and GH. Subgroups were determined according to the period of heat shock exposure. After a 48-hour recovery, rats in groups C, VH5, VH15, and GH5 received a 30-minute period of hepatic ischemia. Induction of HSP72, survival rates, and changes in biochemical and histologic parameters were compared among the groups. Five-minute heat shock preconditioning was not enough to Induce HSP72. However, livers in group GH5 expressed approximately the same amount of HSP72 as those in group VH15. The expression of HSP72 in group GH15 was stronger than that found in group VH15. The degree and location of HSP72 expression were not different between groups GH5 and VH15. Seven-day survival was significantly better in groups GH5 (16/16) and VH15 (15/16) than in group C (8/16) or VH5 (9/16). The recovery of adenosine triphosphate in liver tissue was faster, and the release of liver-related enzymes during reperfusion was lower in groups GH5 and VH15 than in group C or VH5. Administration of GGA before heat shock preconditioning augmented the induction of HSP72 by decreasing the threshold for triggering the stress response.     

Hydroxyethyl starch produces attenuation of circulatory shock and cerebral ischemia during heatstroke

We hypothesized that hydroxyethyl starch (HES), which maintains colloid osmotic pressure and potentially "seals" capillary leaks, would ameliorate circulatory shock and cerebral ischemia during heatstroke in a rat model. Animals under urethane anesthesia were exposed to high ambient temperature (Ta) of 42 degrees C until mean arterial pressure and local cerebral blood flow in the striatum began to decrease from peak level, which was arbitrarily defined as the onset of heatstroke. Control rats were exposed to 24 degrees C. In rats treated with 1 mL/kg, 11 mL/kg, or 22 mL/kg of normal saline (NS) immediately after the onset of heatstroke, the values for survival time (interval between the initiation of heatstroke and animal death) were found to be 21 +/- 2, 36 +/- 9, or 92 +/- 7 min, respectively. Intravenous administration of 11 mL/kg of HES (about 5 times the volume-expanding effect of 11 mL/kg of NS), but not 2 mL/kg of HES (about the same volume-expanding effect as 11 mL/kg NS), significantly increased the survival time from the control values of 36 +/- 9 min to new values of 181 +/- 13 min. In NS (11 mL/kg)-treated or HES (2 mL/kg)-treated rats after heatstroke onset, the values for mean arterial pressure, stroke volume, total peripheral resistance, cerebral blood flow, blood pH, Paco2, Pao2, and brain Po2 were significantly lower than those of rats kept at Ta 24 degrees C. In contrast, the values for colonic temperature and the extracellular concentrations of glutamate, glycerol, and lactate/pyruvate ratio obtained in striatum were significantly higher than those of controls. The heatstroke-induced arterial hypotension, decreased stroke volume and total peripheral resistance, decreased blood pH and Pao2, decreased brain Po2, and increased levels of striatal glutamate, glycerol, and lactate/pyruvate ratio in NS-treated rats were all attenuated significantly by increasing the volume expansion with 11 mL/kg of HES administered immediately at the onset of heatstroke. Our data suggest that HES therapy seems superior to NS treatment during heatstroke. The benefit of HES therapy during heatstroke might have something to do with volume expansion rather than capillary permeability.     

Effects of hypertonic (3%) saline in rats with circulatory shock and cerebral ischemia after heatstroke

Objective To evaluate the effects of hypertonic (3%) saline in heatstroke rats with circulatory shock, intracranial hypertension, and cerebral ischemia.Design and setting Urethane-anesthetized rats were exposed to a high ambient temperature of 42°C until mean arterial pressure and local cerebral blood flow (CBF) in the corpus striatum began to decrease from their peak levels, which was arbitrarily defined as the onset of heatstroke. Control rats were exposed to 24°C.Measurements and results Extracellular concentrations of glutamate and lactate/pyruvate ratio (cellular ischemia markers), and glycerol (a cellular injury marker) in the corpus striatum of rat brain were assessed by intracerebral microdialysis methods. Striatal PO₂, temperature, and local CBF were measured with a combined OxyLite PO₂, thermocouple, and OxyFlo LDF, respectively. The values of mean arterial pressure, cerebral perfusion pressure, and striatal CBF and PO₂ in rats treated with 0.9% NaCl solution after the onset of heatstroke were all significantly lower than those in normothermic controls. In contrast, the values of intracranial pressure, brain temperature, and extracellular concentrations of glutamate, glycerol, and lactate/pyruvate in the corpus striatum were greater. Intravenous infusion of hypertonic (3%) saline solution either "0" time before the start of heat exposure or right after the onset of heatstroke significantly attenuated the heatstroke-induced arterial hypotension, intracranial hypertension, decreased cerebral perfusion, and cerebral ischemia and damage and resulted in prolongation of survival time.Conclusions Our results strongly suggest that the experimental heatstroke syndromes can be effectively prevented and treated by hypertonic saline.An editorial regarding this article can be found in the same issue ()     

Oral glutamine enhances heat shock protein expression and improves survival following hyperthermia

No pharmacologic agent has shown benefit in treating heatstroke. Previous data indicate that enhanced heat shock protein 70 (HSP-70) expression can improve survival postexperimental heatstroke. Glutamine (GLN) can enhance HSP-70 expression in other injury models. This study assessed if orally administered GLN could enhance tissue HSP expression and could improve survival following whole body hyperthermia. Intestinal permeability and plasma endotoxin were assayed to determine if enhanced HSP expression correlated with improved organ function. GLN (0.65 g/kg) or an iso-nitrogenous control (Travasol; T) was given to rats via gavage twice daily for 5 days pre-heatstroke. Hyperthermia was performed in anesthetized rats by heating animals to 42 degrees C (rectal temperature) for 30 min. HSP-70 analyzed via Western blot. Gut permeability was measured 6 and 24 h post-hyperthermia. Plasma endotoxin was measured 24 h post-hyperthermia. Survival was analyzed for 5 days post-hyperthermia. GLN administration enhanced gut and lung HSP-70 post-hyperthermia. GLN administration led to significantly enhanced gut heat shock factor 1 (HSF-1) activation before heatstroke and at 1 h postheat stress. GLN decreased gut permeability at 6 and 24 h post-hyperthermia versus T. Plasma endotoxin also decreased in GLN-treated rats 24 h post-hyperthermia. Oral GLN therapy significantly improved survival (P < 0.05). Our results indicate that oral GLN can enhance tissue HSP-70 and HSF-1 activation post-hyperthermia. These results also indicate that enhanced HSP-70 may have functional significance as GLN-treated animals had decreased gut permeability, plasma endotoxin, and improve survival following lethal hyperthermia. Enhanced expression of HSP-70 may be an important mechanism leading to enhanced survival via GLN. These data indicate that oral GLN may useful in prevention of mortality from heatstroke in at risk populations.     

The protective effect of hypervolemic hemodilution in experimental heatstroke

The authors tested the hypothesis in a rat model that hypervolemic hemodilution during heatstroke affected the mean arterial pressure (MAP), striatal dopamine (DA) release, and local cerebral blood flow and neuronal damage score in different brain structures. The heatstroke was induced by exposing the urethane-anesthetized rats to an ambient temperature of 42 degrees C. Hypervolemic hemodilution was produced by intravenous administration of 10% human albumin. Relative and absolute blood flow in the corpus striatum were determined using the laser Doppler flowmetry and the autoradiography diffusible tracer technique, respectively. The DA release in the striatum was estimated using the in vivo microdialysis technique. After onset of heatstroke, animals with hypervolemic state alone, produced by saline or heparinized blood injection, displayed higher values of DA release, as well as neuronal damage score in the striatum, hypothalamus, or cortex, but lower values of MAP and blood flow in the striatum, hypothalamus, or cortex compared to normothermic controls. However, the heatstroke-induced arterial hypotension, cerebral ischemia, increased striatal DA overload, and increased neuronal damage score were attenuated by induction of both hypervolemic and hemodilution state with 10% albumin either before or after the onset of heatstroke. In addition, constant infusions of a vasopressor agent phenylephrine (2 microg kg(-1) min(-1)) after the onset of heatstroke failed to maintain appropriate levels of MAP and resulted in no protection against heatstroke. Thus, it appears that the observed benefit of the 10% albumin is secondary to hemodilution and/or maintenance of MAP.     

Resuscitation from experimental heatstroke by hyperbaric oxygen therapy

OBJECTIVE: Heatstroke is characterized by hyperthermia, vasoplegic shock, and cerebral ischemia and hypoxia. Hyperbaric oxygen (HBO) has been shown to reduce brain ischemia and behavioral dysfunction during cerebral artery occlusion. The efficacy of HBO therapy for resuscitation from heatstroke remains to be determined in the laboratory. DESIGN: Anesthetized rats were randomized to several groups and administered: 1) no resuscitation (normobaric air) after onset of heatstroke, 2) HBO for 1 hr (100% oxygen at 253 kPa for 1 hr), 3) cyclic HBO intermitted by a 5-min air break for 1 hr of treatment (100% oxygen at 253 kPa), 4) hyperbaric air (air at 253 kPa for 1 hr), 5) normobaric hyperoxia (100% oxygen at 101 kPa for 1 hr), or 6) 8% HBO (hyperbaric 8% oxygen at 253 kPa for 1 hr). SETTING: Laboratory investigation. SUBJECTS: Sprague-Dawley rats (300- to 400-g males). INTERVENTIONS: Rats were exposed to an ambient temperature of 43 degrees C to induce heatstroke. Their colonic temperature; mean arterial pressure; heart rate; arterial blood levels of pH, Paco2, Pao2, So2%, and tumor necrosis factor-alpha; the cortical levels of ischemic and damage markers, and cortical neuronal damage scores were determined. The moment at which mean arterial pressure began to decrease from peak levels was arbitrarily taken as the onset of heatstroke. MAIN RESULTS: Survival time (interval between onset of heatstroke and animal death) was 19 +/- 1 (n = 10), 131 +/- 18 (n = 14), 159 +/- 28 (n = 13), 72 +/- 14 (n = 10), 68 +/- 12 (n = 10), and 45 +/- 11 (n = 10) mins, respectively, for normobaric air, HBO for 1 hr, cyclic HBO, hyperbaric air, normobaric hyperoxia, and 8% HBO groups. The heatstroke induced arterial hypotension and bradycardia, decreased arterial levels of pH, Pao2, and So2%, increased arterial levels of tumor necrosis factor-alpha, and increased values of cellular ischemia and damage markers. In addition, neuronal damage scores in the cortex were significantly reduced by HBO for 1 hr and cyclic HBO resuscitation. CONCLUSION: We successfully demonstrated that HBO and, to some extent, hyperbaric air, normobaric hyperoxia, or HBO 8% was found beneficial in resuscitating rats with experimental heatstroke. HBO effectively reduced heatstroke-induced arterial hypotension, hypoxia, plasma tumor necrosis factor-alpha overproduction, and cerebral ischemia and damage and improved survival.     

Glutathione depletion impairs transcriptional activation of heat shock genes in primary cultures of guinea pig gastric mucosal cells.

When primary cultures of guinea pig gastric mucosal cells were exposed to heat (43 degree C), ethanol, hydrogen peroxide (H2O2), or diamide, heat shock proteins (HSP90, HSP70, HSP60, and HSC73) were rapidly synthesized. The extent of each HSP induction varied with the type of stress. Ethanol, H2O2, and diamide increased the syntheses of several other undefined proteins besides the HSPs. However, none of these proteins were induced by exposure to heat or the reagents, when intracellular glutathione was depleted to <10% of the control level by pretreatment with DL-buthionine-[S,R]-sulfoximine. Gel mobility shift assay using a synthetic oligonucleotide coding HSP70 heat shock element showed that glutathione depletion inhibited the heat- and the reagent-initiated activation of the heat shock factor 1 (HSF1) and did not promote the expression of HSP70 mRNA. Immunoblot analysis with antiserum against HSF1 demonstrated that the steady-state level of HSF1 was not changed in glutathione-depleted cells, but glutathione depletion inhibited the nuclear translocation of HSF1 after exposure to heat stress. These results suggest that intracellular glutathione may support early and important biochemical events in the acquisition by gastric mucosal cells of an adaptive response to irritants.     

Geranylgeranylacetone attenuates septic diaphragm dysfunction by induction of heat shock protein 70

OBJECTIVE: The purposes of the present study were to evaluate the induction of heat shock protein (HSP) 70 expression in the diaphragm by geranylgeranylacetone (GGA) administration and to determine the effect of HSP70 induction on diaphragm contractility measured in vitro and the production of oxygen-derived free radicals during experimental septic peritonitis. DESIGN: Prospective laboratory study. SETTING: University laboratory. SUBJECTS: One-hundred sixty male Wistar rats. INTERVENTIONS: In experiment 1, rats received GGA intragastrically, and time-dependent induction of HSP70 expression in the diaphragm was determined at 0, 12, 24, and 36 hrs after GGA administration. To evaluate dose-dependent inhibition of GGA-induced HSP70 expression by quercetin, rats were pretreated with progressive doses of quercetin before GGA administration. In experiment 2, rats received gum arabic solution (vehicle), 100, 200, or 400 mg/kg of GGA. In experiment 3, rats were pretreated with quercetin or glycerol before GGA or vehicle administration. Intra-abdominal sepsis was induced by cecal ligation and perforation (CLP) under inhalation anesthesia after GGA or vehicle administration in experiments 2 and 3. MEASUREMENTS AND MAIN RESULTS: Western blot analysis using diaphragm homogenates obtained from normal rats showed that HSP70 expression peaked at 24 or 36 hrs after GGA administration and that pretreatment with >10 mg/kg of quercetin blocked the induction of HSP70 expression by GGA. CLP induced diaphragmatic dysfunction and increased diaphragmatic malondialdehyde concentrations and superoxide dismutase and glutathione peroxidase activities. GGA attenuated CLP-induced diaphragm dysfunction and increased malondialdehyde concentrations in a dose-dependent manner but did not affect superoxide dismutase and glutathione peroxidase activities after CLP. Diaphragm dysfunction and increased diaphragmatic malondialdehyde concentrations after CLP were maintained on quercetin pretreatment despite GGA administration. CONCLUSIONS: GGA induces HSP70 expression in the diaphragm, and this induction attenuates septic diaphragm impairment by inhibiting the production of oxygen-derived free radicals.     

Oral administration of geranylgeranylacetone improves survival rate in a rat endotoxin shock model: administration timing and heat shock protein 70 induction

The present study was performed to determine whether oral pretreatment with geranylgeranylacetone (GGA) inhibits proinflammatory cytokine liberation and nitric oxide (NO) production in lipopolysaccharide (LPS)-treated rats and protects rats against death from LPS-induced endotoxin shock, and whether such protection by GGA is related to heat shock protein (HSP) 70 induction in multiple organs of rats. GGA (200 mg/kg) was given orally to rats. LPS (20 mg/kg) was administered intraperitoneally 4, 8, 16, or 24 h after GGA administration. The survival of rats was monitored over 24 h after LPS administration. GGA treatment at 8 or 16 h before LPS dramatically improved the survival rate of LPS-treated rats. Plasma levels of proinflammatory cytokines (tumor necrosis factor-alpha and interleukin-6) and NO 6 h after LPS administration in these GGA-pretreated rats were less than one-half of those in rats treated with LPS alone. A GGA challenge 8 or 16 h before LPS administration enhanced HSP70 expression in rat organs after LPS. Treatment with GGA 8 h before LPS minimized hepatic and renal damage. Furthermore, the protective effect of GGA on mortality in LPS-treated rats was inhibited with quercetin, known as an HSP70 inhibitor. These results suggest that oral administration of GGA at an optimal time before LPS injection induces and enhances HSP70 expression in several organs, inhibits proinflammatory cytokine and NO production, and prevents organ damage, resulting in an improved survival rate.     

Effect of hypervolaemic haemodilution on cerebral glutamate, glycerol, lactate and free radicals in heatstroke rats

In the present study, we attempted to assess the mechanisms underlying the neuroprotective effect of hypervolaemic haemodilution in rat heatstroke. In anaesthetized rats treated with normal saline (NS) immediately after the onset of heatstroke induced by T (a) (ambient temperature) of 42 degrees C for 88 min, followed by T (a) of 24 degrees C for 12 min, the values for MAP (mean arterial pressure), ICP (intracranial pressure), CPP (cerebral perfusion pressure), CBF (cerebral blood blow), brain P O(2) (partial pressure of O(2)) and striatal glutamate, glycerol, lactate/pyruvate ratio, hydroxyl radicals and neuronal damage score were 42+/-3 mmHg, 33+/-3 mmHg, 9+/-3 mmHg, 109+/-20 BPU (blood perfusion units), 6+/-1 mmHg, 51+/-7 micromol/l, 24+/-3 micromol/l, 124+/-32, 694+/-22% of baseline and 2.25+/-0.05 respectively. In animals treated with 10% albumin immediately after the onset of heatstroke ( T (a) of 42 degrees C for 88 min), the values for MAP, ICP, CPP, CBF, brain P O(2) and striatal glutamate, glycerol, lactate/pyruvate ratio, hydroxyl radicals and neuronal damage score were 64+/-6 mmHg, 10+/-2 mmHg, 54+/-5 mmHg, 452+/-75 BPU, 15+/-2 mmHg, 3+/-2 micromol/l, 4+/-2 micromol/l, 7+/-3, 119+/-7% of baseline and 0.38+/-0.05 respectively. Apparently, the heatstroke-induced arterial hypotension, intracranial hypertension, cerebral hypoperfusion, cerebral ischaemia, brain hypoxia, increased levels of striatal glutamate, glycerol, lactate/pyruvate ratio and hydroxyl radicals, and increased striatal neuronal damage score values were all attenuated significantly by the induction of hypervolaemic haemodilution in rats immediately at the onset of heatstroke. These results demonstrate that the neuroprotective effect of hypervolaemic haemodilution is associated with a decrease in the elevation of glutamate, glycerol, lactate and free radicals in brain exposed to experimental heatstroke-induced cerebral ischaemia/hypoxia injury.     

Heat-shock preconditioning reduces oxidative protein denaturation and ameliorates liver injury by carbon tetrachloride in rats

Membrane lipids and cytosolic proteins are major targets of oxidative injury. This study examined the effect of heat-shock preconditioning associated with the induction of heat-shock protein 72 on liver injury, from the aspect of lipid peroxidation and protein denaturation after carbon tetrachloride (CCl4) administration in rats — one of the representative oxidative injuries. Male Wistar rats were divided into two groups, group HS (preconditioned by heat exposure) and group C (not preconditioned). Expression of HSP72 in the liver tissue was confirmed by Western blot analysis. After a 48-h recovery period, all rats were given CCl₄ intragastrically. Liver damage was assessed by measuring serum liver-related enzyme levels and adenine nucleotide concentration in the liver tissue. Lipid peroxidation and protein denaturation were evaluated by measuring tiobarbituric acid reactive substances (TBARS) and by immunohistochemical staining of 4-hydroxy-2-nonenal(HNE)-modified proteins in the liver. Survival rates of the rats after CCl₄ administration were also compared. Expression of HSP72 was clearly detected in group HS, but not in group C. Heat-shock preconditioning significantly improved the survival rate, suppressed the increase in liver-related enzyme levels and maintained adenosine triphosphate levels (P<0.01 each). HNE-modified proteins — denatured proteins by free radical attack — were significantly less stained in group HS than in group C (P<0.05). However, TBARS levels did not differ between groups. Because heat-shock preconditioning did not alter TBARS levels but reduced HNE-modified proteins in association with the expression of HSP72, it is suggested that HSP72 did not prevent lipid peroxidation but decreased the lipid peroxidation-induced denaturation of proteins. This seemed to be a mechanism of heat-shock preconditioning to ameliorate oxidative liver injury.     

缺血预处理模型大鼠心肌组织小分子热休克蛋白的表达冰

背景：小分子热休克蛋白,尤其是热休克蛋白27和a-B晶体蛋白高表达量对于心肌组织缺血再灌注的保护作用已比较明确。但是在老龄大鼠中小分子热休克蛋白是否仍具有这种保护作用迄今仍无报道。目的：观察热休克蛋白27和a-B晶体蛋白在青年及老年大鼠心肌缺血预处理时表达的变化。方法：24月龄老龄大鼠及两三月龄青年大鼠在体心脏经缺皿5min、再灌注5min（反复3次）预处理后,于0,5,15,45,60min取左心室缺血的前壁与非缺血的后壁心肌组织分别匀浆,分离上清及沉淀蛋白,用WesternBlot检测热休克蛋白27和a-B晶体蛋白在预处理不同时间可溶性蛋白及不溶性蛋白含量的改变;采用RT-PCR方法观察缺血预处理对青年及老龄大鼠热休克蛋白27和a-B晶体蛋白mRNA在不同时间点表达的改变情况,采用免疫荧光观察缺血预处理后不同时间点热休克蛋白27和CI-B晶体蛋白的移位情况。结果与结论：老龄大鼠在缺血预处理后热休克蛋白27和a-B晶体蛋白表达量增加,表明老龄大鼠仍具有正常的基因转录及蛋白合成的能力;与青年大鼠比较,老龄大鼠缺血预处理后小分子热休克蛋白移位能力降低,从而减弱了与各相应蛋白结合的能力,限制其保护作用的发挥。提示老年大鼠心肌组织中小分子热休克蛋白丧失移位能力,可能是老年大鼠缺血预处理保护作用减弱的重要原因之一。     

HSP70在鼠背轴型皮管IPC后的保护作用的实验研究

目的：揭示IPC后皮瓣中延迟相HSP70表达的动态变化,提出其规律及保护作用的最佳时间。方法：采用大鼠背部轴型皮管,制成活体原位IPC模型,检测皮管存活率,组织细胞超微结构,HSP70测定及统计学分析。结果：IPC组和IPC后延迟48h断蒂组与对照组相比分别提高了皮瓣存活面积1.26倍和1.57倍;IPC后48h组细胞合成功能旺盛,有大量的蛋白质合成并贮存;IPC后48、72h组HSP70均较对照组升高,并且其表达以48h较为明显。结论：IPC对鼠背轴型皮管具有保护作用,而对延迟断 蒂组保护作用更佳,以48h为最佳时间点。HSP70可能发挥着重要的作用。     

Reduction of hepatic microcirculatory failure caused by normothermic ischemia/reperfusion-induced injury by means of heat shock preconditioning

Transient sublethal hyperthermia and the recovery from this exposure to heat (heat shock preconditioning) provides a cytoprotective effect on oxidative insults through an intracellular protective response, heat shock response. The impact of heat shock preconditioning on hepatic microvascular failure, which is a causative determinant of ischemia/reperfusion-induced injury of the liver, was investigated by using intravital fluorescence microscopy. In Sprague-Dawley rats, normothermic ischemia was induced by totally clamping the hepatoduodenal ligament for 20 min, followed by 120 min of reperfusion. Heat shock preconditioning was performed by whole-body hyperthermia (42 degrees C for 15 min) and subsequent 48 h recovery. In accordance with the prominent induction of heat shock protein 70 in the liver tissue, the postischemic decrease in sinusoidal perfusion rate and sinusoidal diameter, and the postischemic increase in the number of stagnant leukocytes in sinusoids and adherent leukocytes in postsinusoidal venules were significantly attenuated in the heat shock-treated animals. Furthermore, liver enzyme release (glutamate pyruvate transaminase and alpha-glutathione S-transferase) was significantly reduced and postischemic deterioration of bile production was attenuated. The 7-day survival rate after 20-minute ischemia was significantly improved from 50% to 80% (heat shock-nontreated group vs. heat shock-treated group, P < 0.05). These results indicate that heat shock preconditioning attenuates ischemia/reperfusion-induced hepatic injury by preventing postischemic microvascular disturbances, and that its protective effect is circumstantially associated with the concomitant induction of heat shock protein 70.     

Resuscitation from experimental heatstroke by estrogen therapy

OBJECTIVE: We investigated the effect of estrogen therapy on inflammatory responses, cardiovascular functions, and survival in a rat model of heatstroke. DESIGN: Controlled, prospective study. SETTING: Hospital medical research laboratory. SUBJECTS: Sprague-Dawley rats (280-312 g of body weight, males and females). INTERVENTIONS: Four major groups of anesthetized rats were designated for experiments: a) vehicle-treated male rats; b) vehicle- or premarin-treated estrus female rats; c) vehicle- or premarin-treated ovariectomized rats; and d) vehicle- or premarin-treated leuprolide-treated rats. All animals were exposed to heat stress (ambient temperature 43 degrees C for 70 mins) and then allowed to recover at room temperature (24 degrees C). Their survival time (interval between the onset of heatstroke and animal death) and physiologic and biochemical variables were monitored. Vehicle (normal saline 1 mL/kg of body weight, intravenously) or premarin (1 mg/mL/kg of body weight, intravenously) was administered 70 mins after initiation of heat stress. Ovariectomy or leuprolide (100 mug/kg/day, subcutaneously) injection was conducted 4 wks before the start of heat stress experiments. Another group of rats were exposed to 24 degrees C and used as normothermic controls. MEASUREMENTS AND MAIN RESULTS: Compared with the estrus female rats, the ovariectomized rats, the leuprolide-treated rats, and male rats all had lower levels of plasma estradiol and lower survival time values. However, after an intravenous dose of premarin, both the plasma estradiol and survival time values were significantly increased. Compared with the normothermic controls, the vehicle-treated male and ovariectomized rats all displayed higher levels of serum tumor necrosis factor-alpha, which could be suppressed by premarin therapy. In contrast, the serum levels of IL-10 in these groups were significantly elevated by premarin during heatstroke. Furthermore, the heatstroke-induced hyperthermia, arterial hypotension, intracranial hypertension, and cerebral hypoperfusion, hypoxia, and ischemia were significantly attenuated by premarin therapy in ovariectomized rats. CONCLUSIONS: We successfully demonstrated that estrogen replacement may improve survival during heatstroke by ameliorating inflammatory responses and cardiovascular dysfunction.     

HSP70对缺血预处理诱导大鼠海马缺血耐受的作用

目的探讨脑缺血时的组织学变化及热休克蛋白70（HSP70）在缺血预处理诱导的脑缺血耐受中的作用。方法取成年雄性SD大鼠48只，随机分为6组，A组：假手术对照组，手术后7d处死取脑；B组：全脑缺血3min，7d后处死取脑；C组：全脑缺血6min，2d后处死取脑；D组：全脑缺血6min，7d后处死取脑；E组：3min缺血预处理后3d，再缺血6min，2d后处死取脑；F组：3min缺血预处理后3d，再缺血6min，7d后处死取脑。行苏木精-伊红染色观察各组大鼠海马CA1区存活神经元密度，免疫组化染色方法观察大鼠海马CA1区HSP70染色强度，并作相关分析。结果光镜下A、B组大鼠海马CA1区神经元未见明显缺血性损伤，D组神经元大量坏死，C、E、F组神经元部分坏死，A组与C组、D组，D组与F组比较，差异有显著性（F=19．6，q=4．766～12．447，P〈0．01）。免疫组化染色显示，未经预处理的A、C、D组大鼠海马CA1区未见HSP70表达，预处理的E、F组大鼠在整个海马区均可见HSP70表达，C组与E组、D组与F组间差异有显著性（F=210．8，q=8．277～32．133，P〈0．01）。结论在脑缺血耐受中，缺血预处理对第二次致死性缺血表现出保护作用。在这个过程中，HSP70基因的表达上调发挥了重要的保护作用。