Effects of isorhamnetin on liver injury in heat stroke-affected rats under dry-heat environments via oxidative stress and inflammatory response.

Isorhamnetin is a natural flavonoid compound, rich in brass, alkaloids, and sterols with a high medicinal value. This study investigated the effects of isorhamnetin on liver injury and oxidative and inflammatory responses in heat-stroke-affected rats in a dry-heat environment. Fifty Sprague Dawley rats were randomly divided into five groups: normal temperature control (NC, saline), dry-heat control (DHC, saline), low-dose isorhamnetin-pretreated (L-AS, 25 mg/Kg), medium-dose isorhamnetin-pretreated (M-AS, 50 mg/Kg), and high-dose isorhamnetin-pretreated (H-AS, 100 mg/Kg) group. Saline was administered to the NC and DHC groups and corresponding concentrations of isorhamnetin were administered to the remaining three groups for 1 week. Blood and liver tissue were analyzed for oxidative stress and inflammation. The liver histopathological injury score, serum liver enzyme (alanine transaminase, aspartate transaminase, and lactate dehydrogenase), liver oxidative stress index (superoxide dismutase [SOD], catalase [CAT], and malondialdehyde), and inflammation index (tumor necrosis factor α [TNF-α], interleukin [IL]-1ß, IL-6, and lipopolysaccharides) were significantly higher in the DHC group than in the NC group (P < 0.05). These index values in the L-AS, M-AS, and H-AS groups were significantly lower than those in the DHC group (P < 0.05). The index values decreased significantly with an increase in the concentration of isorhamnetin (P < 0.05), while the index values of CAT and SOD showed the opposite tendency (P < 0.05). The expression of liver tissue nuclear factor kappa B (NF-κB), caspase-3, and heat shock protein (HSP-70) was higher in the DHC group than in the NC group (P < 0.05). Comparison between the isorhamnetin and DHC groups revealed that the expression of NF-кB and caspase-3 was decreased, while that of HSP-70 continued to increase (P < 0.05). The difference was significant for HSP-70 among all the isorhamnetin groups (P < 0.05); however, the NF-кB and caspase-3 values in the L-AS and H-AS groups did not differ. In summary, isorhamnetin has protective effects against liver injury in heat-stroke-affected rats. This protective effect may be related to its activities concerning antioxidative stress, anti-inflammatory response, inhibition of NF-кB and caspase-3 expression, and enhancement of HSP-70 expression.

Bovine Lactoferrin Alleviates Pulmonary Lipid Peroxidation and Inflammatory Damage in Heat Stroke Rats.

Lung injury occurring in the early stage of heat stroke (HS) leads to hypoxia and further aggravation of other organic damage. Lactoferrin (LF) is an iron binding protein with anti-inflammatory and antioxidant effects. This study focuses on the protection of preadministration of bovine lactoferrin (BLF) against lung injury in rats with HS. Sixty-four Sprague-Dawley male rats were divided into four groups randomly: control (CON)+phosphate-buffered saline (PBS) (n = 16), HS+PBS (n = 16), HS+low-dose BLF (LBLF) (n = 16), and HS+high-dose BLF (HBLF) (n = 16). CON+PBS and HS+PBS were preadministered 10 mL/kg PBS for 1 week. HS+LBLF and HS+HBLF were preadministered 100 and 200 mg/kg BLF for 1 week, respectively. The HS onset time and the survival rate were recorded, and bronchoalveolar lavage fluid was obtained to measure protein concentration. Lung was obtained for pathological analysis and wet/dry weight ratio measurement; later, the content of malondialdehyde (MDA), activity of myeloperoxidase (MPO), and superoxide dismutase (SOD) were measured in lung tissue homogenate. The results indicated that BLF preadministration could delay the HS onset time, enhance the survival rate, the levels of serum inflammatory cytokine and MDA content in HS+LBLF and HS+HBLF showed significant reduction compared with HS+PBS, while a significant elevation of SOD activity and reduction of MPO activity in HS+HBLF. Our results demonstrate that BLF preadministration could relieve lung injury in HS rats by enhancing thermal endurance, and alleviating serum inflammatory response and pulmonary oxidative stress damage.

The efficacy of antibiotics in reducing morbidity and mortality from heatstroke - A systematic review.

Severe hyperthermia, for example, classical heatstroke or exertional heatstroke from heatwaves or exercise respectively, or from drug ingestion or other non-infective pyrogens, is associated with a high mortality and morbidity, which may be chronic or permanent. Abolition of lipopolysaccharide, from gram-negative intestinal bacteria translocating into the systemic circulation via an intestinal wall rendered permeable from the hyperthermia, reduces the adverse effects, suggesting that antibiotics against the intestinal bacteria may have a similar effect. A systematic review searching Embase, MEDLINE and PubMed from the earliest date available until 2019 was conducted, according to PRISMA guidelines. Two papers were found which fit the criteria. In one, non-absorbable oral antibiotics were administered prior to the onset of heat stress, which reduced the cardiovascular dysfunction and rise in endotoxaemia, but animals succumbed at a lower temperature. In the second, non-absorbable oral antibiotics, in combination with a laxative and enema, given prior to the onset of heat stress, improved mortality; antibiotics administered after the heat stress did not, but the antibiotics used may have limited action against intestinal bacteria. Only two papers were found; both suggest an improvement in organ dysfunction or mortality after an episode of heat stress. No papers were found that investigate the sole use of antibiotics effective against intestinal bacteria given after the onset of heat stress, although biological plausibility suggest they warrant further research.

Proteomic identification of hippocalcin and its protective role in heatstroke-induced hypothalamic injury in mice.

Heatstroke is a devastating condition that is characterized by severe hyperthermia and central nervous system dysfunction. However, the mechanism of thermoregulatory center dysfunction of the hypothalamus in heatstroke is unclear. In this study, we established a heatstroke mouse model and a heat-stressed neuronal cellular model on the pheochromocytoma-12 (PC12) cell line. These models revealed that HS promoted obvious neuronal injury in the hypothalamus, with high pathological scores. In addition, PC12 cell apoptosis was evident by decreased cell viability, increased caspase-3 activity, and high apoptosis rates. Furthermore, 14 differentially expressed proteins in the hypothalamus were analyzed by fluorescence two-dimensional difference gel electrophoresis and identified by matrix-assisted laser desorption ionization time-of-flight mass spectrometry. Expression changes in hippocalcin (HPAC), a downregulated neuron-specific calcium-binding protein, were confirmed in the hypothalamus of the heatstroke mice and heat-stressed PC12 cells by immunochemistry and western blot. Moreover, HPAC overexpression and HPAC-targeted small interfering RNA experiments revealed that HPAC functioned as an antiapoptotic protein in heat-stressed PC12 cells and hypothalamic injury. Lastly, ulinastatin (UTI), a cell-protective drug that is clinically used to treat patients with heatstroke, was used in vitro and in vivo to confirm the role of HPAC; UTI inhibited heat stress (HS)-induced downregulation of HPAC expression, protected hypothalamic neurons and PC12 cells from HS-induced apoptosis and increased heat tolerance in the heatstroke animals. In summary, our study has uncovered and demonstrated the protective role of HPAC in heatstroke-induced hypothalamic injury in mice.

Microcirculatory Disorders and Protective Role of Xuebijing in Severe Heat Stroke.

This study was conducted to explore underlying mechanism of microcirculation dysfunction and protectiverole of Xuebijing in heat stroke. Forty rats were divided into: control, vehicle + heat stress (HS), superoxide dismutase (SOD) + HS, and Xuebijing + HS groups. Rats in heat stress groups were subjected to continuous heat stress in infant incubator 1 h after tail vein injection of the tested compound and spinotrapezius preparation. Velocity of blood flow through micro-vessels and vascular diameter were detected in real time. Another 27 rats were divided into: vehicle, SOD, and Xuebijing groups, then further divided into three subgroups each: control, Tcore = 38 °C, Tcore = 41 °C. Rats were sacrificed, and spinotrapezius single-cell suspensions were prepared for detecting SOD and reactive oxygen species (ROS). The results showed that heat stress decreased SOD activity, increased ROS levels, and reduced the blood flow rate. Xuebijing increased SOD activity, decreased ROS levels and exhibited a protective effect in terms of blood flow rate but was less protective than SOD. The survival time in Xuebijing + HS group was longer than that in vehicle group but shorter than that in SOD + HS group. The results suggested Xuebijing could decrease ROS levels and have protective effects in severe heat stroke.

Therapeutic treatment with ascorbate rescues mice from heat stroke-induced death by attenuating systemic inflammatory response and hypothalamic neuronal damage.

The impact of ascorbate on oxidative stress-related diseases is moderate because of its limited oral bioavailability and rapid clearance. However, recent evidence of the clinical benefit of parenteral vitamin C administration has emerged, especially in critical care. Heatstroke is defined as a form of excessive hyperthermia associated with a systemic inflammatory response that results in multiple organ dysfunctions in which central nervous system disorders such as delirium, convulsions, and coma are predominant. The thermoregulatory, immune, coagulation and tissue injury responses of heatstroke closely resemble those observed during sepsis and are likely mediated by similar cellular mechanisms. This study was performed by using the characteristic high lethality rate and sepsis-mimic systemic inflammatory response of a murine model of heat stroke to test our hypothesis that supra-physiological doses of ascorbate may have therapeutic use in critical care. We demonstrated that parenteral administration of ascorbate abrogated the lethality and thermoregulatory dysfunction in murine model of heat stroke by attenuating heat stroke-induced accelerated systemic inflammatory, coagulation responses and the resultant multiple organ injury, especially in hypothalamus. Overall, our findings support the hypothesis and notion that supra-physiological doses of ascorbate may have therapeutic use in critical care.

[Pretreatment with Xuebijing injection alleviates systemic inflammatory response induced by severe heat-stroke via ameliorating intestinal injury in rats].

OBJECTIVE: To observe the effect of Xuebijing injection pretreatment on systemic inflammatory response induced by severe heat-stroke, and to investigate the mechanism of alleviation of intestinal injury in rats. METHODS: Thirty-six healthy adult male Wistar rats with grade SPF were randomly assigned into three groups with randomized number method, namely sham group, severe heat-stroke model group, and Xuebijing pretreatment group ( XBJ group ), with 12 rats in each group. The animals were placed in a pre-warm chamber [ temperature ( 40±2 ) centigrade, humidity ( 65±5 )% ] in order to induce typical heat-stroke. The duration of heat-stress was 60 minutes, while the animals in sham group were exposed to ambient temperature of 25 centigrade. Arterial blood samples were collected at the beginning and the end of heat-stress, the concentrations of tumor necrosis factor-α( TNF-α), interleukins ( IL-1ß, IL-6 ), and lipopolysaccharide ( LPS ) in peripheral blood were determined by enzyme linked immunosorbent assay ( ELISA ). The intestinal tissues were harvested after heat-stress, and the pathological changes in intestine tissues were observed after hematoxylin-eosin ( HE ) staining and under optical microscope. The pathological injury scores were calculated. Immunohistochemistry was performed to determine inducible nitric oxide synthase ( iNOS ) expression in intestinal tissue. Apoptosis was determined by terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling ( TUNEL ) staining. Western Blot was used to measure the tight junction protein occludin expression. RESULTS: The concentrations of TNF-α, IL-1ß, IL-6 and LPS in blood of the rats after heat-stress in model group were significantly higher than those of sham group [ TNF-α ( µg/L ): 443.00±110.10 vs. 98.36±44.61, IL-1ß ( µg/L ): 436.37±163.64 vs.64.24±16.15, IL-6 ( µg/L ): 342.70±92.42 vs. 54.40±13.22, LPS ( µg/L ): 0.68±0.22 vs. 0.09±0.02, all P < 0.01 ], but the levels of these parameters in XBJ group were significantly lower than those of model group [ TNF-α ( µg/L ): 340.45±68.57 vs. 443.00±110.10, IL-1ß ( µg/L ): 191.33±82.78 vs. 436.37±163.64, IL-6 ( µg/L ): 192.21±37.89 vs. 342.70±92.42, LPS ( µg/L ): 0.43±0.17 vs. 0.68±0.22, all P < 0.01 ]. Infiltration of inflammatory cells, necrosis and hemorrhage in intestinal mucosa were found in the intestine of heat-stroke animals in model group. The pathological lesions in XBJ group were milder than those of model group, with a decreased pathological injury score compared with model group ( 2.10±1.15 vs. 3.20±0.67, P < 0.01 ). The expression of iNOS and apoptosis of cells in intestinal tissue in model group were increased compared with that of sham group, but they were significantly less marked in XBJ group compared with model group [ iNOS ( adjusted A value ): 0.32±0.15 vs. 0.74±0.17, apoptotic index: 0.23±0.08 vs. 0.56±0.07, both P < 0.01 ]. The order of expression for occludin protein from high to low was sham group, XBJ group and model group ( A value was 0.96±0.25, 0.62±0.20, 0.33±0.11, respectively ). Furthermore, there was significant difference in the expression of occludin protein between model group and both XBJ group and sham group ( both P < 0.01 ). CONCLUSIONS: Xuebijing injection alleviates inflammation and endotoxemia produced by severe heat-stroke in rats. The mechanism may be related to amelioration of oxidative injury, apoptosis, and dysfunction of tight junction protein occludin expression.

EICOSAPENTAENOIC ACID ENHANCES HEATSTROKE-IMPAIRED INTESTINAL EPITHELIAL BARRIER FUNCTION IN RATS.

OBJECTIVE: Dysfunction of the intestinal barrier plays an important role in the pathological process of heatstroke. Omega-3 (or n-3) polyunsaturated fatty acids, including eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), help protect the intestinal mucosal barrier. This study assessed if pretreating rats with EPA or DHA could alleviate heat stress-induced damage to the intestinal barrier caused by experimental heatstroke. METHODS: Male Wistar rats were pregavaged with either EPA, DHA, corn oil, or normal saline (all 1 g/kg) for 21 days before the heatstroke experiment (control rats were not exposed to heat). Experimental rats were exposed to an ambient temperature of 37°C and 60% humidity to induce heatstroke, and then they were allowed to recover at room temperature after rapid cooling. Survival time of rats was monitored after heatstroke. Horseradish peroxidase flux from the gut lumen and the level of plasma D-lactate were measured to analyze intestinal permeability at 6 h after heatstroke. Plasma endotoxin levels were determined using a limulus amoebocyte lysate assay. Expressions of the tight junction (TJ) proteins occludin and ZO-1 were analyzed by Western blot and localized by immunofluorescence microscopy. Tight junction protein morphology was observed by transmission electron microscopy. Fatty acids of ileal mucosa were analyzed using gas chromatography-mass selective detector. RESULTS: Eicosapentaenoic acid significantly increased survival time after heatstroke. Eicosapentaenoic acid significantly decreased intestinal permeability and plasma endotoxin levels. Eicosapentaenoic acid effectively attenuated the heatstroke-induced disruption of the intestinal structure and improved the histology score, whereas DHA was less effective, and corn oil was ineffective. Pretreatment with EPA also increased expression of occludin and ZO-1 to effectively prevent TJ disruption. Eicosapentaenoic acid pretreatment enriched itself in the membrane of intestinal cells. CONCLUSIONS: Our results indicate that EPA pretreatment is more effective than DHA pretreatment in attenuating heat-induced intestinal dysfunction and preventing TJ damage. Enhanced expression of TJ proteins that support the epithelial barrier integrity may be important for maintaining a functional intestinal barrier during heatstroke.

Xuebijing injection reduces organ injuries and improves survival by attenuating inflammatory responses and endothelial injury in heatstroke mice.

BACKGROUND: The pathogenesis of heatstroke is a multi-factorial process involved with an interplay among subsequent inflammation, endothelial injury and coagulation disturbances, which makes pharmacological therapy of heatstroke a challenging problem. Xuebijing injection (XBJ), a traditional Chinese medicine used to sepsis, has been reported to suppress inflammatory responses and restore coagulation disturbances. However, little is known about the role of XBJ in heatstroke. METHODS: Mice were treated with indicated dose of XBJ before and/or after the induction of heatstroke. Serum inflammatory cytokines, tumor necrosis factor-α (TNF-α) and interleukin-6 (IL-6), and endothelial markers, von Willebrand Factor (vWF) and E-selectin, were measured by ELISA. Liver, kidney and heart profiles including alanine aminotransferase, aspartic aminotransferase, creatinine, blood urea nitrogen, and lactate dehydrogenase, were evaluated by UniCel DxC 800 Synchron Clinical Systems, and troponin was measured by ELISA. Coagulation profiles, including thrombin time, prothrombin time, activated partial thromboplastin time, international normalized ratio, and fibrinogen were examined by STA Compact® Hemostasis System. Jejunum injury was evaluated with H&E staining. Changes in mitochondrial structure in cardiac tissue were assesed by electron microscopy. RESULTS: Pretreatment with XBJ decreased serum pro-inflammatory cytokines including TNF-α and IL-6, as well as endothelial injury markers, vWF and E-selectin, in a dose-dependent manner in heatstroke mice. Similar protective effects were observed when XBJ was administered after, or both before and after heat insult. These protective effects lasted for over 12 h in mice receiving XBJ before and after heat insult. XBJ also improved survival rates in heatstroke mice, ameliorated liver, heart, and kidney injuries, including mitochondrial damage to the heart, and reduced coagulation disturbances. CONCLUSIONS: XBJ prevents organ injuries and improves survival in heatstroke mice by attenuating inflammatory responses and endothelial injury. XBJ may be a potentially useful in the prevention and treatment of heatstroke.

Protection of intestinal injury during heat stroke in mice by interleukin-6 pretreatment.

KEY POINTS: Heat stroke afflicts thousands of humans each year, worldwide. The immune system responds to hyperthermia exposure resulting in heat stroke by producing an array of immunological proteins, such as interleukin-6 (IL-6). However, the physiological functions of IL-6 and other cytokines in hyperthermia are poorly understood. We hypothesized that IL-6 plays a protective role in conditions of heat stroke. To test this, we gave small IL-6 supplements to mice prior to exposing them to hot environments sufficient to induce conditions of heat stroke. Pretreatment with IL-6 resulted in improved ability to withstand heat exposure in anaesthetized mice, it protected the intestine from injury, reducing the permeability of the intestinal barrier, and it attenuated the release of other cytokines involved in inflammation. The results support the hypothesis that IL-6 is a 'physiological stress hormone' that plays an important role in survival during acute life-threatening conditions such as heat stroke. ABSTRACT: The role of interleukin-6 (IL-6) in hyperthermia and heat stroke is poorly understood. Plasma IL-6 is elevated following hyperthermia in animals and humans, and IL-6 knockout mice are more intolerant of severe hyperthermia. We evaluated the effect of IL-6 supplementation on organ injury following severe hyperthermia exposure in anaesthetized mice. Two hours prior to hyperthermia, mice were treated with 0.6 µg intraperitoneal IL-6, or identical volumes of saline in controls. Mice were anaesthetized, gavaged with FITC-dextran for measures of gastrointestinal permeability, and exposed to incremental (0.5°C every 30 min) increases in temperature. Heating stopped when maximum core temperature (Tc) of 42.4°C was attained (Tc,max). The mice recovered at room temperature (≈22°C) for 30 or 120 min, at which time plasma and tissues were collected. IL-6-treated mice, on average, required ≈25 min longer to attain Tc,max . Injury and swelling of the villi in the duodenum was present in untreated mice after 30 min of recovery. These changes were blocked by IL-6 treatment. IL-6 also reduced gastrointestinal permeability, assayed by the accumulation of FITC-dextran in plasma. Plasma cytokines were also attenuated in IL-6-treated animals, including significant reductions in TNFα, MCP-1 (CXCL2), RANTES (CCL5) and KC (CCL5). The results demonstrate that IL-6 has a protective influence on the pattern of physiological responses to severe hyperthermia, suggesting that early endogenous expression of IL-6 may provide a protection from the development of organ damage and inflammation.

Xuebijing injection alleviates liver injury by inhibiting secretory function of Kupffer cells in heat stroke rats.

OBJECTIVE: To evaluate the effects of Xuebijing (XBJ) injection in heat stroke (HS) rats and to investigate the mechanisms underlying these effects. METHODS: Sixty anesthetized rats were randomized into three groups and intravenously injected twice daily for 3 days with 4 mL XBJ (XBJ group) or phosphate buffered saine (HS and Sham groups) per kg body weight. HS was initiated in the HS and XBJ groups by placing rats in a simulated climate chamber (ambient temperature 400C, humidity 60% ). Rectal temperature, aterial pressure, and heart rate were monitored and recorded. Time to HS onset and survival were determined, and serum concentrations of tumor necrosis factor (TNF)-alpha interleukin (IL)-1beta, IL-6, alanine-aminotransferase (ALT), and aspartate-aminotransferase (AST) were measured. Hepatic tissue was harvested for pathological examination and electron microscopic examination. Kupffer cells (KCs) were separated from liver at HS initiation, and the concentrations of secreted TNF-a, IL-beta and IL-6 were measured. RESULTS: Time to HS onset and survival were significantly longer in the XBJ than in the HS group. Moreover, the concentrations of TNF-alpha, IL-1beta, IL-6, ALT and AST were lower and liver injury was milder in the XBJ than in the HS group. Heat-stress induced structural changes in KCs and hepatic cells were more severe in the HS than in the XBJ group and the concentrations of TNF-alpha, IL-beta and IL-6 secreted by KCs were lower in the XBJ than in the HS group. CONCLUSION: XBJ can alleviate HS-induced systemic inflammatory response syndrome and liver injury in rats, and improve outcomes. These protective effects may be due to the ability of XBJ to inhibit cytokine secretion by KCs.

Flutamide, an androgen receptor antagonist, improves heatstroke outcomes in mice.

Flutamide has been used as an adjunct for decreasing the mortality from subsequent sepsis. Heatstroke resembles septic shock in many aspects. We hypothesized that heat-induced multiple organ dysfunction syndromes and lethality could be reduced by flutamide therapy. In heatstroke groups, mice were exposed to whole body heating (41.2°C, for 1h) in a controlled-environment chamber. The heat-stressed mice were returned to normal room temperature (24°C) after whole body heating. Mice still alive on day 4 of WBH treatment were considered survivors. Physiological and biochemical parameters were monitored for 2.5h post-WBH. Heatstroke mice were subcutaneously treated with flutamide (12.5-50mg/kg body weight in 0.05 ml) or vehicle solution (0.05 ml/kg body weight) once daily for 3 consecutive days post-WBH. We evaluated the effect of flutamide in heatstroke mice and showed that flutamide significantly (i) attenuated hypothermia, (ii) reduced the number of apoptotic cells in the hypothalamus, the spleen, the liver, and the kidney, (iii) attenuated the plasma index of toxic oxidizing radicals (e.g., nitric oxide metabolites and hydroxyl radicals), (iv) diminished the plasma index of the organ injury index (e.g., lactate dehydrogenase), (v) attenuated plasma systemic inflammation response molecules (e.g., tumor necrosis factor-α and interleukin-6), (vi) reduced the index of infiltration of polymorphonuclear neutrophils in the lung (e.g., myeloperoxidase activity), and (vii) allowed three times the fractional survival compared with vehicle. Thus, flutamide appears to be a novel agent for the treatment of mice with heatstroke or patients in the early stage of heatstroke.

Protection in rats with heatstroke: hyperbaric oxygen vs activated protein C therapy.

The present study was attempted to evaluate the therapeutic effects of activated protein C and/or hyperbaric oxygen in an animal model of heatstroke. Sixty-eight minutes heat stress (43 degrees C) initiated, the anesthetized rats were randomized to several groups and administered: 1) no resuscitation (vehicle solution plus normabaric air, 2) intravenous activated protein C (1mg in 1ml of normal saline per kg of body weight), 3) hyperbaric oxygen (100% oxygen at 202kpa for 17min), and 4) intravenous activated protein C plus hyperbaric oxygen. Another group of rats exposed to room temperature (26 degrees C) was used as normothermic controls. Blood sampling was 0min, 70min, and 85min after heat stress initiated. When the vehicle-treated rats underwent heat exposure, their survival time values found were to be 19-25min. Resuscitation with activated protein C or hyperbaric oxygen significantly and equally improved survival during heatstroke (134-159min). As compared with those of activated protein C or hyperbaric oxygen alone, combined activated protein C and hyperbaric oxygen significantly had higher survival time values (277-347min). All vehicle-treated heatstroke animals displayed systemic response, hypercoagulable state, and hepatic and renal dysfunction. Combined activated protein C and hyperbaric oxygen therapy reduced these heatstroke reactions better than activated protein C or hyperbaric oxygen alone. The results indicate consequently, combined activated protein C and hyperbaric oxygen therapy heightens benefit in combating heatstroke reactions.

L-arginine causes amelioration of cerebrovascular dysfunction and brain inflammation during experimental heatstroke.

Cerebrovascular dysfunction ensuing from severe heatstroke includes intracranial hypertension, cerebral hypoperfusion, and brain inflammation. We attempted to assess whether L-arginine improves survival during experimental heatstroke by attenuating these reactions. Anesthetized rats, 70 min after the start of heat stress (43 degrees C), were divided into two major groups and given the following: vehicle solution (1 mL/kg body weight) or L-arginine (50-250 mg/kg body weight) intravenously. Another group of rats was exposed to room temperature (24 degrees C) and used as normothermic controls. Their physiological and biochemical parameters were continuously monitored. When the vehicle-treated rats underwent heat stress, their survival time values were found to be 20 to 26 min. Treatment with i.v. doses of L-arginine significantly improved the survival rate during heatstroke (54-245 min). As compared with those of normothermic controls, all vehicle-treated heatstroke animals displayed higher levels of core temperature, intracranial pressure, and NO metabolite, glutamate, glycerol, lactate-pyruvate ratio, and dihydroxybenzoic acid in hypothalamus. In addition, hypothalamic levels of IL-1beta and TNF-alpha were elevated after heatstroke onset. In contrast, all vehicle-treated heatstroke animals had lower levels of MAP, cerebral perfusion pressure, cerebral blood flow, and brain partial pressure of oxygen. Administration of L-arginine immediately after the onset of heatstroke significantly reduced the intracranial hypertension and the increased levels of NO metabolite, glutamate, glycerol, lactate-pyruvate ratio, and dihydroxybenzoic acid in the hypothalamus that occurred during heatstroke. The heatstroke-induced increased levels of IL-1beta and TNF-alpha in the hypothalamus were suppressed by L-arginine treatment. In contrast, the hypothalamic levels of IL-10 were significantly elevated by L-arginine during heatstroke. The results suggest that L-arginine may cause attenuation of heatstroke by reducing cerebrovascular dysfunction and brain inflammation.

Glucocorticoids do not protect against the lethal effects of experimental heatstroke in baboons.

The mortality and neurological morbidity in heatstroke have been attributed to the host's inflammatory responses to heat stress, suggesting that anti-inflammatory therapy may improve outcome. We tested the hypothesis that a high dose of dexamethasone protects baboons against the lethal effects of heatstroke. Ten anesthetized baboons (Papio hamadryas) were assigned randomly to dexamethasone (n = 5) or control group (n = 5). Dexamethasone (2 mg/kg i.v.) was administered in four divided doses every 6 h starting immediately before heat stress and continuing during cooling. All animals were heat-stressed in a prewarmed neonatal incubator at 44 degrees C to 47 degrees C until systolic blood pressure fell less than 90 mmHg and then cooled passively at the ambient temperature. Mortality and neurological morbidity were noted, and biochemical markers of tissue injury/organ dysfunction were determined. Circulating interleukin (IL) 6 and complement components (C3 and C4) were measured sequentially. All heat-stressed animals had systemic inflammation indicated by increased plasma IL-6 and decreased C3 and C4 levels. Dexamethasone attenuated the complement system activation and maintained a higher plasma concentration of IL-6, with a significant augmentation of arterial blood pressure. Dexamethasone did not prevent the occurrence of severe heatstroke but unexpectedly aggravated significantly the tissue injury and multiorgan system dysfunction. Two animals (40%) in the control group and one in the steroid group survived (P > 0.05). Dexamethasone failed to protect the baboons from the lethal effects of heatstroke. These results do not support clinical testing of corticosteroids as beneficial in preventive or therapeutic strategies for the treatment of heatstroke in humans.

Cerebrovascular dysfunction is an attractive target for therapy in heat stroke.

1. The aim of the present review is to summarize clinical observations and results of animal models that advance the knowledge of the attenuation of cerebrovascular dysfunction in the setting of heat stroke. It is a narrative review of selected published literature from Medline over the period 1959-2005. 2. All heat-stressed rodents, even under general anaesthesia, have hyperthermia, systemic inflammation, hypercoagulable state, arterial hypotension and tissue ischaemia and injury in multiple organs. These findings demonstrate that rodent heat stroke models can nearly mirror the full spectrum of human heat stroke. Experimental heat stroke fulfills the empirical triad used for the diagnosis of classical human heat stroke, namely hyperthermia, central nervous system alterations and a history of heat stress. 3. These physiological dysfunctions and survival during heat stroke can be improved by whole-body or brain cooling therapy adopted immediately after the onset of heat stroke. 4. However, in the absence of body or brain cooling, these heat stroke reactions can still be reduced by the following measures: (i) fluid replacement with 3% NaCl solution, 10% human albumin or hydroxyethyl starch; (ii) intravenous delivery of anti-inflammatory drugs, free radical scavengers or interleukin-1 receptor antagonists; (iii) hyperbaric oxygen therapy; or (iv) transplantation of human umbilical cord blood cells. 5. In addition, before initiation of heat stress, prior manipulations with one of the following measures was found to be able to protect against heat stroke reactions: (i) systemic delivery of alpha-tocopherol, mannitol, inducible nitric oxide synthase inhibitors, mu-opioid receptor antagonists, endothelin ETA receptor antagonists, serotoninergic nerve depletors or receptor antagonists, or glutamate receptor antagonists; or (ii) heat shock protein 72 preconditioning. 6. There is compelling evidence that cerebrovascular dysfunction is an attractive target for therapy in heat stroke.

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.

Dantrolene and recovery from heat stroke.

Several authors have shown that dantrolene may be effective in the treatment of heat stroke patients. However, the scant data available are still controversial. The aim of this investigation was to establish an animal experimental model for studying the efficacy of this drug both as a prophylactic agent and as a means of hastening the cooling process after heat stroke. Male albino rats were divided into five groups: Sedentary controls (SC), Sedentary+dantrolene (S+D), Exercise controls (EC), and Exercise+dantrolene (E+D, E+D1). The drug (140 mg x kg(-1) body weight) was administered i.v. either prior to subjection to heat stress (40 degrees C) (S+D, E+D) or upon development of heat stroke syndrome (E+D1). In the S+D group, dantrolene administered prior to heat stress (HS) delayed the development of heat stroke by 70%, although colonic temperature (Tc) at the onset of heat stroke was similar to that in group SC (43.0 +/- 0.1 degrees C and 43.2 +/- 0.4 degrees C for S+D and SC, respectively). In E+D animals, dantrolene shortened exercise endurance in the heat by 17.5%, but concomitantly hindered severe Tc rise (40.9 +/- 0.2 degrees C and 40.0 +/- 0.2 degrees C for EC and E+D, respectively). Administration of dantrolene on the development of heat stroke appeared to improve cooling in the exercise group (0.25 degrees C x min(-1) and 0.18 degrees C x min(-1), for the first 1 5 min of cooling, for E+D1 and EC, respectively). The results suggest that dantrolene is effective as a prophylactic agent in sedentary animals only. It also might have application on development of heat stroke. It is hypothesized that the observed rapid cooling is associated with dantrolene's effect on muscle contraction, thus leading to attenuated heat production and peripheral vascular relaxation.

Interleukin-1 receptor antagonist increases survival in rat heatstroke by reducing hypothalamic serotonin release.

During onset of heatstroke, rats displayed higher values of hypothalamic serotonin release and score f hypothalamic neuronal damage, and lower values of mean arterial pressure and hypothalamic blood flow compared with normothermic control rats. In another group in which interleukin-1 receptor antagonist (IL-1 ra; 200 micrograms/kg, i.v.) was injected 30 or 60 min after the start of heat exposure, the augmented hypothalamic serotonin release, diminished hypothalamic blood flow, arterial hypotension and hypothalamic neuronal damage during heatstroke were reduced as compared to the saline control group. The survival time (interval between onset of heatstroke and death) of the heatstroke rats was prolonged by treatment with IL-1 ra. The data indicate that IL-1 ra increases survival during rat heatstroke by reducing hypothalamic serotonin release.