Metabolomic profiling identifies a novel mechanism for heat stroke‑related acute kidney injury

Heat stroke can induce a systemic inflammatory response, which may lead to multi‑organ dysfunction including acute kidney injury (AKI) and electrolyte disturbances. To investigate the pathogenesis of heat stroke (HS)‑related AKI, a mouse model of HS was induced by increasing the animal's core temperature to 41˚C. Blood samples obtained from the tail vein were used to measure plasma glucose and creatinine levels. Micro‑positron emission tomography‑computed tomography (micro‑PET/CT), H&E staining and transmission electron microscopy were conducted to examine metabolic and morphological changes in the mouse kidneys. Immunohistochemistry (IHC) and western blot analyses were performed to investigate the expression of apoptosis‑inducing factor mitochondria‑associated 2 (Aifm2), high‑mobility group box 1 (HMGB1) and receptor for advanced glycosylation end products (RAGE). Liquid chromatography‑mass spectrometry analysis was conducted to find differential metabolites and signaling pathways. The HS mouse model was built successfully, with significantly increased creatinine levels detected in the serum of HS mice compared with controls, whereas micro‑PET/CT revealed active metabolism in the whole body of HS mice. H&E and TUNEL staining revealed that the kidneys of HS mice exhibited signs of hemorrhage and apoptosis. IHC and western blotting demonstrated significant upregulation of Aifm2, HMGB1 and RAGE in response to HS. Finally, 136 differential metabolites were screened out, and enrichment of the 'biosynthesis of unsaturated fatty acids' pathway was detected. HS‑associated AKI is the renal manifestation of systemic inflammatory response syndrome, and may be triggered by the HMGB1/RAGE pathway. Metabolomics indicated increased adrenic acid, docosahexaenoic acid and eicosapentaenoic acid may serve as metabolic biomarkers for AKI in HS. The findings suggested that a correlation between the HMGB1/RAGE pathway and biosynthesis of unsaturated fatty acids may contribute to the progression of HS‑related AKI.

Prior viral illness increases heat stroke severity in mice

NEW FINDINGS

What is the central question of this study? We hypothesized that prior illness would increase the susceptibility to and severity of heat stroke (HS). What is the main finding and its importance? We provide the first experimental evidence, using a mouse model of HS, that recent viral illness increases the severity of HS. Our data indicate that this effect is not attributable to the exacerbation of hyperthermia but is a consequence of ongoing coagulation and systemic inflammatory reactions. Our data suggest that measurement of platelets, cytokines and chemokines before heat exposure might be indicative of susceptibility to HS, with coagulation and inflammation being potential targets for intervention that could improve recovery.

ABSTRACT

It is hypothesized that prior illness exacerbates heat stroke (HS) in otherwise healthy organisms by augmenting hyperthermia during heat exposure or deactivating cellular pathways that protect against organ injury. To test these hypotheses, we injected telemetered male C57BL/6J mice with lipopolysaccharide (LPS; 50 µg kg-1 i.p.) or polyinosinic:polycytidylic acid (PIC; 100 µg i.p.) as a bacterial or a viral mimic, respectively, with saline (SAL; equivalent volume) as a control. Mice recovered for 48 or 72 h before HS (maximal core temperature = 42.4°C). Platelet counts, cytokines, chemokines and organ injury were determined 48 or 72 h after injection (without heating) or at maximal core temperature and at 1 day of recovery from HS. In the absence of heat, PIC induced more robust signs of sickness and increased cytokines and chemokines (TNF-α, RANTES, IP-10 and MIP-1β) at 48 h, which was not observed with LPS (P < 0.05). Responses of both groups recovered by 72 h, although low platelet counts persisted after PIC (P < 0.05). Heat-induced hyperthermia was similar among mice injected with SAL, LPS and PIC; however, PIC-injected mice displayed more severe responses during recovery from HS, with reduced survival (48 h, 70 versus 100%; P < 0.05), deeper and longer post-HS hypothermia, greater reductions in platelets, elevated RANTES, IP-10, IL-6 and TNF-α and greater duodenal injury (P < 0.05). By 72 h, survival from HS was no longer reduced in PIC-injected mice, although hypothermia, the reduction in platelets and elevated cytokines persisted. Our data indicate that prior illness exacerbates the severity of HS in the absence of signs of illness at the time of heat exposure and suggest that this is attributable to persistent coagulation and inflammatory reactions that might be targets for intervention to improve recovery.

Biochemical recovery from exertional heat stroke follows a 16-day time course

BACKGROUND

The aim of this study was to characterize the time-resolved progression of clinical laboratory disturbances days-following an exertional heat stroke (EHS). Currently, normalization of organ injury clinical biomarker values is the primary indicator of EHS recovery. However, an archetypical biochemical recovery profile following EHS has not been established.

METHODS

We performed a retrospective analysis of EHS patient records in US military personnel from 2008-2014 using the Military Health System Data Repository (MDR). We focused on commonly reported clinical laboratory analytes measured on the day of injury and all proceeding follow-up visits.

RESULTS

Over the prescribed period, there were 2,529 EHS episodes treated at 250 unique treatment locations. Laboratory results, including a standardized set of blood, serum and urine assays, were analyzed from 0-340 days following the initial injury. Indicators of acute kidney injury, including serum electrolyte disturbances and abnormal urinalysis findings, were most prevalent on the day of the injury but normalized within 24-48hours (creatinine, blood urea nitrogen, and blood and protein in urine). Muscle damage and liver function-associated markers peaked 0-4 days after injury and persisted outside their respective reference ranges for 2-16 days (alanine aminotransferase, aspartate aminotransferase, creatine phosphokinase, myoglobin, prothrombin time).

CONCLUSION

Biochemical recovery from EHS spans a 16-day time course, and markers of end-organ damage exhibit distinct patterns over this period. This analysis underscores the prognostic value of each clinical laboratory analyte and will assist in evaluating EHS patient presentation, injury severity and physiological recovery.

[Predictive value of myoglobin and D-dimer on severe heat stroke: a clinical analysis of 38 patients with severe heat stroke]

OBJECTIVE

To explore the clinical characteristics and early sensitive indicators of severe heat stroke patients in order to predict the development of severe heat stroke in the early stage.

METHODS

Thirty-eight patients with severe heat stroke admitted to emergency department of Beijing Daxing District People's Hospital from July 30th to August 5th in 2018 were enrolled. There were 18 patients suffered from exertional heat stroke (EHS), and 12 patients suffered from classical heat stroke (CHS), and 8 patients with heat spasm and heat exhaustion were selected as control group. The gender, age, onset time, body temperature, heart rate (HR), lactic acid (Lac), platelet (PLT), alanine aminotransferase (ALT), alanine aminotransferase (AST), blood urea nitrogen (BUN), serum creatinine (SCr), serum sodium at admission of hospital, as well as positive rate of myoglobin (MYO) and D-dimer (the positive threshold of MYO and D-dimer was 107 μg/L and 600 μg/L respectively) were recorded and compared among the groups. Receiver operating characteristic (ROC) curve was plotted to analyze the prognostic value of MYO and D-dimer on heat stroke. The outcome of all patients was followed up, and the 28-day mortality between EHS and CHS patients was compared. The patient's body temperature was measured again after 4 hours of active cooling treatment (T_{4 h}), and the relationship between T_{4 h} and 28-day mortality was discussed.

RESULTS

The majority of severe heat stroke patients were male, especially in EHS patients. EHS patients were younger than CHS ones, and had shorter onset time, with significant differences among the groups. The body temperature and HR at admission in the EHS group and the CHS group were significantly higher than those in the control group [body temperature (centigrade): 41.34±0.67, 40.39±0.58 vs. 37.80±1.39; HR (bpm): 139.78±15.63, 113.08±17.70 vs. 92.00±15.89, all P < 0.05], PLT was significantly lowered (×10⁹/L: 164.94±73.80, 165.78±53.49 vs. 249.50±84.22, both P < 0.05), and the positive rates of MYO and D-dimer were also significantly increased [MYO positive rate: 100.0% (18/18), 100.0% (12/12) vs. 50.0% (4/8); D-dimer positive rate: 77.8% (14/18), 100.0% (12/12) vs. 12.5% (1/8), all P < 0.05]. ROC curve analysis showed that positive MYO and D-dimer at admission had certain diagnostic value for heat stroke, the area under ROC curve (AUC) was 0.750 and 0.871, the sensitivity was 50.0% and 87.5%, and the specificity was 100% and 86.7%, respectively. The 28-day mortality of the EHS group was significantly higher than that of the CHS group [44.4% (8/18) vs. 8.3% (1/12), P < 0.05]. Furthermore, the 28-day mortality of the patients with T_{4 h} ≥ 38 centigrade in the EHS group was significantly higher than those with T_{4 h} < 38 centigrade [70.0% (7/10) vs. 12.5% (1/8), P < 0.05].

CONCLUSIONS

The decreased PLT and the increased D-dimer in the early stage of heat stroke indicate that the damage of coagulation mechanism is prominent in patients with heat stroke. EHS patients have the characteristics of acute onset, severe condition, rapid progression and poor prognosis, and the 28-day mortality is significantly higher than that of CHS patients. MYO and D-dimer are sensitive indicators in early stage of heat stroke patients, which can be used as reference for early diagnosis of heat stroke.

Identification of whole blood mRNA and microRNA biomarkers of tissue damage and immune function resulting from amphetamine exposure or heat stroke in adult male rats

This work extends the understanding of how toxic exposures to amphetamine (AMPH) adversely affect the immune system and lead to tissue damage. Importantly, it determines which effects of AMPH are and are not due to pronounced hyperthermia. Whole blood messenger RNA (mRNA) and whole blood and serum microRNA (miRNA) transcripts were identified in adult male Sprague-Dawley rats after exposure to toxic AMPH under normothermic conditions, AMPH when it produces pronounced hyperthermia, or environmentally-induced hyperthermia (EIH). mRNA transcripts with large increases in fold-change in treated relative to control rats and very low expression in the control group were a rich source of organ-specific transcripts in blood. When severe hyperthermia was produced by either EIH or AMPH, significant increases in circulating organ-specific transcripts for liver (Alb, Fbg, F2), pancreas (Spink1), bronchi/lungs (F3, Cyp4b1), bone marrow (Np4, RatNP-3b), and kidney (Cesl1, Slc22a8) were observed. Liver damage was suggested also by increased miR-122 levels in the serum. Increases in muscle/heart-enriched transcripts were produced by AMPH even in the absence of hyperthermia. Expression increases in immune-related transcripts, particularly Cd14 and Vcan, indicate that AMPH can activate the innate immune system in the absence of hyperthermia. Most transcripts specific for T-cells decreased 50–70% after AMPH exposure or EIH, with the noted exception of Ccr5 and Chst12. This is probably due to T-cells leaving the circulation and down-regulation of these genes. Transcript changes specific for B-cells or B-lymphoblasts in the AMPH and EIH groups ranged widely from decreasing ≈ 40% (Cd19, Cd180) to increasing 30 to 100% (Tk1, Ahsa1) to increasing ≥500% (Stip1, Ackr3). The marked increases in Ccr2, Ccr5, Pld1, and Ackr3 produced by either AMPH or EIH observed in vivo provide further insight into the initial immune system alterations that result from methamphetamine and AMPH abuse and could modify risk for HIV and other viral infections.

Serum histones as biomarkers of the severity of heatstroke in dogs

Heatstroke is associated with systemic inflammatory response syndrome, leading to multiple organ dysfunction and death. Currently, there is no specific treatment decreasing hyperthermia-induced inflammatory/hemostatic derangements. Emerging studies indicate that histones leaking from damaged cells into the extracellular space are toxic, pro-inflammatory, and pro-thrombotic. We therefore hypothesize that serum histones (sHs) are elevated during heatstroke and are associated with the severity of the disease. Sixteen dogs with heatstroke and seven healthy controls were included in the study. Median serum histones (sHs) upon admission in dogs with heatstroke were significantly higher (P = 0.043) compared to that in seven controls (13.2 vs. 7.3 ng/mL, respectively). sHs level was significantly higher among non-survivors and among dogs with severe hemostatic derangement (P = 0.049, median 21.4 ng/mL vs. median 8.16 ng/mL and P = 0.038, 19.0 vs. 7.0 ng/mL, respectively). There were significant positive correlation between sHs and urea (r = 0.8, P = 0.02); total CO2 (r = 0.661, P = 0.05); CK (r = 0.678, P = 0.04); and prothrombin time (PT) 12 h post presentation (r = 0.888, P = 0.04). The significant positive correlation between sHs and other heatstroke severity biomarkers, and significant increase among severely affected dogs, implies its role in inflammation/oxidation/coagulation during heatstroke. sHs, unlike other prognostic and severity biomarkers in heatstroke, can be pharmacologically manipulated, offering a potential therapeutic target.

Human umbilical cord blood-derived CD34+ cells cause attenuation of multiorgan dysfunction during experimental heatstroke

Multiorgan dysfunction ensuing from severe heatstroke includes hypotension, hepatic and renal failure, hypercoagulable state, activated inflammation, and cerebral ischemia and injury. We attempted to assess whether human umbilical cord blood-derived CD34+ cell therapy improves survival during experimental heatstroke by attenuating multiorgan dysfunction. Anesthetized rats, immediately after the onset of heatstroke, were divided into 2 major groups and given CD34- or CD34+ cells (1 x 10(5)-5 x 10(5)/mL/kg body weight) i.v. They were exposed to ambient temperature of 43 degrees C to induce heatstroke. Another group of rats were exposed to room temperature (26 degrees C) and used as normothermic controls. Hypotension, hepatic and renal failure (evidenced by increased serum urea nitrogen, creatinine, aspartate aminotransferase, alanine aminotransferase, and alkaline phosphatase levels in plasma), hypercoagulable state (evidenced by increased prothrombin time, activated partial thromboplastin time, and D-dimer, and decreased platelet count and protein C in plasma), activated inflammation (evidence by increased TNF-alpha levels in serum), and cerebral dysfunction (evidenced by intracranial hypertension, cerebral hypoperfusion and hypoxia, and cerebral ischemia and injury) were monitored. When the CD34- cell-treated or untreated rats underwent heat stress, their survival time values were found to be 19 to 23 min. Resuscitation with CD34+ cells significantly improved survival time (duration, 63-291 min). As compared with normothermic controls, all CD34- cell-treated heatstroke animals displayed hypotension, hepatic and renal failure, hypercoagulable state, activated inflammation, and cerebral ischemia and injury. However, CD34+ cell therapy significantly caused attenuation of all the above-mentioned heatstroke reactions. In addition, the levels of IL-10 in plasma and glial cell line-derived neurotrophic factors in brain were all significantly increased after CD34+ cell therapy during heatstroke. Our data indicate that CD34+ cell therapy may resuscitate persons who had a heatstroke by reducing multiorgan dysfunction or failure.

Resuscitation from experimental heatstroke by brain cooling therapy

We have used hypothermic retrograde jugular venous flush to cool the brain previously and to provide better resuscitation than peripheral cold saline infusion during heatstroke in the rat. The current study was performed to assess the effects of brain cooling further on production of reactive nitrogen species, reactive oxygen species, tumor necrosis factor-alpha, and interleukin-10 in both serum and brain during heatstroke. Rats, under general anaesthesia, were randomized into the following groups and given: (a) 36 degrees C or (b) 4 degrees C saline infusion in the external jugular vein immediately after onset of heatstroke. They were exposed to an ambient temperature of 43 degrees C for exactly 70 min to induce heatstroke. When the 36 degrees C saline-treated rats underwent heat stress, their survival time values were found to be 21-25 min. Immediately after the onset of heatstroke, resuscitation with an i.v. dose of 4 degrees C saline greatly improved survival (226-268 min). Compared with the normothermic controls, the 36 degrees C saline-treated heatstroke rats displayed higher levels of brain temperature, intracranial pressure, serum and hypothalamic nitric oxide metabolite, tumor necrosis factor-alpha and dihydroxybenzoic acid as well as hypothalamic inducible nitric oxide synthase immunoreactivity. In contrast, the values of mean arterial pressure, cerebral perfusion pressure, and hypothalamic levels of local blood flow, and partial pressure of oxygen were all significantly lower during heatstroke. The cerebrovascular dysfunction, the increased levels of nitric oxide metabolites, tumor necrosis factor-alpha, and dihydroxybenzoic acid in both the serum and the hypothalamus, and the increased levels of hypothalamic inducible nitric oxide synthase immunoreactivity occurred during heatstroke were significantly suppressed by brain cooling. Although the serum and hypothalamic interleukin-10 maintained at a negligible level before stress, they were significantly elevated by brain cooling during heatstroke. These findings suggest that brain cooling may resuscitate persons who had heatstroke by decreasing overproduction of reactive nitrogen species, tumor necrosis factor-alpha, reactive oxygen species and cerebrovascular dysfunction, but increasing production of interleukin-10.

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.

Activated protein C therapy in a rat heat stroke model

OBJECTIVE

To evaluate the therapeutic effects of activated protein C in an animal model of heat stroke.

DESIGN

Laboratory investigation.

SETTING

Chi-Mei Medical Center research laboratory.

SUBJECTS

Male Sprague-Dawley rats weighing 252-304 g.

INTERVENTIONS

Anesthetized animals were subjected to heat stress (40 degrees C) to induce heat stroke. A bolus injection of normal saline or recombinant human activated protein C (drotrecogin alfa, activated) was conducted via femoral catheters immediately after the onset of heat stroke. Blood sampling was done before initiation of heat stress and 0 and 40 mins after the onset of heat stroke.

MEASUREMENTS AND MAIN RESULTS

When the vehicle-treated rats underwent heat exposure, their survival time values were found to be 56-64 mins (n = 16). Resuscitation with activated protein C significantly and dose-dependently improved survival during heat stroke (108-246 mins for doses of 0.5-20 mg of activated protein C per kilogram of body weight) (n = 32). 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 by cellular ischemia and injury/dysfunction included increased plasma levels of blood urea nitrogen, creatinine, glutamic oxaloacetic transaminase, glutamic pyruvic transaminase, and alkaline phosphatase; increased striatal levels of glutamate, glycerol, and lactate/pyruvate ratio; and decreased striatal levels of partial pressure of oxygen and local cerebral blood flow, which were all observed during heat stroke. These heat stroke reactions were all significantly suppressed by resuscitation with activated protein C but not vehicle solution.

CONCLUSIONS

The results indicate that systemic delivery of human recombinant activated protein C at the time point of onset of heat stroke may improve survival by ameliorating systemic inflammation, hypercoagulable state, and tissue ischemia and injury in multiple organs.

Arginine metabolic pathways determine its therapeutic benefit in experimental heatstroke: role of Th1/Th2 cytokine balance

We have demonstrated that therapeutic administration of L-arginine (L-arg) (120 mg/kg) at +2 h of whole body hyperthermia (WBH) could rescue the mice from heatstroke-induced death. Studies were undertaken to elucidate the role of L-arg in the immunomodulation of the heat-stressed mice. Administration of L-arginine (L-arg), (120 mg/kg, i.p.), at +2 h of WBH, rescued the mice from heat-induced death and reduced the hypothermia. At +4 and +24 h of WBH, levels of IL-1beta, IFN-gamma, nitrite, TNF-alpha, IL-4, TGF-beta1, inducible form of nitric oxide synthase (iNOS), and corticosterone significantly increased compared to the sham group. The elevated levels of Th(1) cytokines, namely TNF-alpha, IL-1beta, IFN-gamma, nitrite, and iNOS, decreased significantly both at +4 and +24 h of WBH, following L-arg administration. However, L-arg administration did not reduce the increased levels of Th(2) cytokines, namely IL-4 and TGF-beta1, in WBH mice at +4 h of WBH. L-arg administration significantly increased the levels of Th(2) cytokines at +24 h of WBH, compared to the saline-treated WBH mice. L-arg administration significantly increased both the splenic and hepatic arginase activity at +4 and +24 h of WBH compared to the saline-treated WBH mice. L-NAME treatment at +2 h of WBH and anti-TGF-beta antibody treatment at 0 h of WBH significantly increased the mortality compared to the saline-treated WBH mice. Altered liver histopathology was attenuated following the administration of L-arg at +2 h of WBH. These results suggest that therapeutic administration of L-arg at appropriate concentration and time attenuates the acute inflammatory response, leading to the rescue of mice from heatstroke.

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.

PLATONIN, A CYANINE PHOTOSENSITIZING DYE, CAUSES ATTENUATION OF CIRCULATORY SHOCK, HYPERCOAGULABLE STATE, AND TISSUE ISCHEMIA DURING HEAT STROKE

The aim of this study was to investigate the therapeutic effect of platonin, a cyanine photosensitizing dye as well as an inhibitor of proinflammatory cytokines, in an animal model of heat stroke. Anesthetized rats, immediately after the onset of heat stroke, were divided into two major groups and given the following: normal saline (1 mL per kg body weight) intravenously, or platonin (12.5-50 microg/mL per kg body weight) intravenously. They were exposed to ambient temperature of 43 degrees C to induce heat stroke. Another group of rats was exposed to room temperature (26 degrees C) and used as normothermic controls. Their physiologic and biochemical parameters were continuously monitored. When the vehicle-treated rats underwent heat exposure, their survival time values were found to be 18 to 22 min. Resuscitation with intravenous doses of platonin, but not normal saline, immediately at the onset of heat stroke, significantly improved survival during heat stroke (41-147 min). All heat-stressed animals displayed systemic inflammation and activated coagulation, evidenced by increased tumor necrosis factor-alpha, prothrombin time, activated partial thromboplastin time, fibrinogen degradation products, 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 partial pressure of oxygen, local cerebral blood flow, glycerol, glutamate, and lactate/pyruvate were all elevated during heat stroke. The systemic inflammation, hypercoagulable state, and cerebral ischemia and injury during heat stroke were all significantly suppressed by platonin. The data demonstrate that platonin therapy may resuscitate heat stroke victims by reducing circulatory shock, systemic inflammation, hypercoagulable state, and tissue ischemia and injury.

Elevated serum beta-D-glucan level and depressed neutrophil phagocytosis in a heatstroke patient

Endotoxemia has been reported as a mechanism for the fatal sequela after heatstroke. Subsequent disseminated fungal infection in a heatstroke patient has been also described. Beta-D-glucan, a constituent of the fungal cell wall, is an early diagnostic measure for fungal infection. In a heatstroke case, we examined for the first time levels of serum beta-d-glucan and endotoxin. A 34-year-old man with a body temperature of 43.5 degrees C was admitted in a state of shock. Prior to the development of disseminated intravascular coagulopathy (DIC), a remarkable elevation of serum beta-D-glucan level to 116 pg/mL (normal level<6.0 pg/mL) was revealed on the first day of admission. However, serum endotoxin was not detected when using a method that excluded beta-D-glucan contamination from endotoxin measurement (normal level<1.0 pg/mL). This change of beta-D-glucan level was accompanied by a depressed neutrophil function, especially in phagocytosis of 34% (normal range 70-90%) but not in bacterocidal function (81% versus a normal range of 70-100%). After intensive care including continuous hemodiafiltration, the patient regained consciousness but remained ataxic due to cerebellar infarction, which might have resulted from DIC, and subsequent bilateral fungal oculitis were revealed 45 days after admission. This case report demonstrates the elevation of serum beta-D-glucan but normal endotoxin levels after heatstroke, which may prompt further study to re-examine the serum levels of endotoxin in such catastrophic insults.

Role of gastrointestinal permeability in exertional heatstroke

Reduced splanchnic blood flow and hyperthermia during exercise-heat stress can produce gastrointestinal barrier dysfunction and increased gastrointestinal permeability. This may allow endotoxin to enter the internal environment, causing local and systemic immune responses. These responses may be involved in the cause and outcome of exertional heatstroke. Countermeasures may reduce gastrointestinal permeability and possibly exertional heatstroke occurrence and outcome.

Exertional heat injury and gene expression changes: a DNA microarray analysis study

This study examined gene expression changes associated with exertional heat injury (EHI) in vivo and compared these changes to in vitro heat shock responses previously reported by our laboratory. Peripheral blood mononuclear cell (PBMC) RNA was obtained from four male Marine recruits (ages 17-19 yr) who presented with symptoms consistent with EHI, core temperatures ranging from 39.3 to 42.5°C, and elevations in serum enzymes such as creatine kinase. Controls were age- and gender-matched Marines from whom samples were obtained before and several days after an intense field-training exercise in the heat (“The Crucible”). Expression analysis was performed on Affymetrix arrays (containing ∼12,600 sequences) from pooled samples obtained at three times for EHI group (at presentation, 2-3 h after cooling, and 1-2 days later) and compared with control values (average signals from two chips representing pre- and post-Crucible samples). After post hoc filtering, the analysis identified 361 transcripts that had twofold or greater increases in expression at one or more of the time points assayed and 331 transcripts that had twofold or greater decreases in expression. The affected transcripts included sequences previously shown to be heat-shock responsive in PBMCs in vitro (including both heat shock proteins and non-heat shock proteins), a number of sequences whose changes in expression had not previously been noted as a result of in vitro heat shock in PBMCs (including several interferon-induced sequences), and several nonspecific stress response genes (including ubiquitin C and dual-specificity phosphatase-1). We conclude that EHI produces a broad stress response that is detectable in PBMCs and that heat stress per se can only account for some of the observed changes in transcript expression. The molecular evidence from these patients is thus consistent with the hypothesis that EHI can result from cumulative effects of multiple adverse interacting stimuli.

Role of circulating cytokines and chemokines in exertional heatstroke

OBJECTIVE

The interplay between inflammatory and anti-inflammatory cytokines, as well as chemokines, has not been well explored in exertional heatstroke.

DESIGN

Prospective, observational study.

PATIENTS

Seventeen military recruits who developed exertional heatstroke and 17 exertional controls who did not develop exertional heatstroke during the same training exercises.

SETTING

University teaching hospital.

MEASUREMENTS AND MAIN RESULTS

The severity of exertional heatstroke was evaluated using a Simplified Acute Physiology Score. Plasma cytokines and chemokines were determined using enzyme-linked immunosorbent assay kits. Body temperatures were 41.2 +/- 1.2 degrees C and 37.6 +/- 0.8 degrees C in exertional heatstroke and exertional controls, respectively. Significantly, plasma cytokines including interleukin (IL)-1beta (3.1 +/- 1.6 vs. 1.2 +/- 0.8 pg/mL; p <.05), tumor necrosis factor alpha (4.9 +/- 4.1 vs. 1.2 +/- 2.4 pg/mL; p <.05), IL-6 (15.8 +/- 3.2 vs. 1.2 +/- 1.2 pg/mL; p <.01), interferon gamma (7.3 +/- 4.9 vs. 2.4 +/- 4.1 pg/mL; p <.01), IL-2 receptor (1568 +/- 643 vs. 610 +/- 214 pg/mL; p <.01), IL-4 (2.5 +/- 1.2 vs. 1.2 +/- 0.8 pg/mL; p <.05), and IL-10 (12.9 +/- 9.4 vs. 2.5 +/- 4.9 pg/mL; p <.01) and serum chemokines IL-8 (84.2 +/- 79.9 vs. 10.4 +/- 3.2 pg/mL; p <.01), monocyte chemoattractant protein 1 (959 +/- 589 vs. 158 +/- 217 pg/mL; p <.01), and RANTES (12464 +/- 10505 vs. 5570 +/- 2894 pg/mL; p <.01) were elevated in exertional heatstroke compared with exertional controls. Among cytokines, IL-6, interferon gamma, and IL-2 receptor were positively correlated with Simplified Acute Physiology Score (r =.573, p <.01; r =.625, p <.01; and r =.56, p <.05, respectively). Among chemokines, only serum monocyte chemoattractant protein 1 was positively correlated with Simplified Acute Physiology Score (r =.78, p <.001). There was no correlation between either cytokines or chemokines and body temperature.

CONCLUSIONS

Proinflammatory cytokines IL-1beta, tumor necrosis factor alpha, IL-6; T helper 1 cytokines INF-gamma and IL-2 receptor; and chemokines IL-8, monocyte chemoattractant protein 1, and RANTES are increased in patients with exertional heatstroke. T helper 2 cytokines may play a role as anti-inflammatory cytokines. IL-6, interferon gamma, IL-2 receptor, and monocyte chemoattractant protein 1 may serve as prognostic indicators of disease severity in exertional heatstroke.

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 degrees 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 degrees 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 PO(2), temperature, and local CBF were measured with a combined OxyLite PO(2), thermocouple, and OxyFlo LDF, respectively. The values of mean arterial pressure, cerebral perfusion pressure, and striatal CBF and PO(2) 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.

The effects of exertional heatstroke and exercise-heat acclimation on plasma beta-endorphin concentrations

INTRODUCTION

It has been suggested that a proopiomelanocortin peptide beta-endorphin may play an important role in temperature regulation and therefore have specific heat stroke response patterns.

METHODS

The purpose of this study was to examine the response patterns of plasma beta-endorphin at baseline, during a 7-d exercise-heat acclimation period (HA; 90 min x d(-1), 40 degrees C), and during a 6-h exercise-heat tolerance test (HTT; 6 h, 40 degrees C) performed before and after HA. Subjects were nine previously diagnosed heatstroke patients (P) and eight matched controls (C). No differences between the two groups were observed at rest, prior to HTT.

RESULTS

Plasma beta-endorphin concentration in P significantly increased above resting values at 2, 4, and 6 h of HTT and were significantly greater than C responses. During HA tests, a significantly higher beta-endorphin concentration was observed in P before exercise on day 1 and day 7, but not on day 4. A significant increase occurred after exercise in both groups, on all days of HA; no differences were observed between the groups on days 4 and 7.

DISCUSSION

These results demonstrate that the opioid peptide responses in individuals with recent exertional heatstroke were greater than control subjects during the initial 6-h HTT. Decreased physical training among P may have contributed to these results. However, 7 d of HA abolished these between-group differences by reducing the magnitude of beta-endorphin responses in P, indicative of an adaptation of pituitary function.

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.

Post-mortem urinary myoglobin levels with reference to the causes of death

To evaluate pathophysiological significance of post-mortem urinary myoglobin levels in determining the cause of death, we investigated 210 forensic autopsy cases, partially in comparison with serum levels. Post-mortem serum myoglobin levels were extraordinary high in most cases possibly due to post-mortem change. Urinary myoglobin levels did not correlate with the serum levels, showing possible post-mortem elevation in cases of a prolonged post-mortem period over 48h. A high (>1000 ng/ml), moderate (100-1000 ng/ml), slight (50-100 ng/ml) and not significant (<50 ng/ml) elevation of urinary myoglobin were observed in 26, 43, 31 and 110 cases, respectively. Half the highly elevated cases were those with a survival time over 24h. In cases of minor muscle injury such as head trauma, elevation of urinary myoglobin level was closely related to longer survival. In acute/subacute deaths with a post-mortem interval within 48h, a significant difference was observed in relation to the blood carboxyhemoglobin (COHb) levels of fire victims: myoglobinuria over 100 ng/ml was more frequently and markedly observed in cases with COHb below 60% than over 60%, suggesting muscle damage in fatal burns. Similar elevation was observed in heat stroke victims, and also in some cases of acute and subacute death from polytrauma, asphyxiation, drowning, electricity and spontaneous cerebral bleeding, but not in myocardial infarction. Thus, it was suggested that high post-mortem urinary myoglobin levels in acute and subacute death cases may be a possible indicator of antemortem massive skeletal muscle damage as well as exertional muscle hyperactivity or convulsive disorders associated with hypoxia.

[A study on relationship between plasma heat stress protein 70 and cytokine in patients with heat apoplexy]

OBJECTIVE

To study the change of levels of plasma heat stress protein 70 (HSP70) and cytokine and their interrelationship in pathogenicity of heat apoplexy.

METHODS

Plasma HSP70 was determined with Western blot, and plasma interleukin-2 (IL-2), soluble interleukin-2 receptor (sIL-2R) and interleukin-6 (IL-6) were determined with enzyme-linked immunosorbent assay (ELISA).

RESULTS

Plasma level of HSP70 was 4 211.2 +/- 1,286.2 (integral optical density) in average in the patients of heat apoplexy group, 4,137.8 +/- 1, 207.5 in those of severe heat apoplexy group, and 6,043.5 +/- 1,354.8 in control group, with very significant difference (P < 0.01). Plasma IL-2 level was (64.3 +/- 32.3) pg/ml and (200.0 +/- 50.0) pg/ml and sIL-2R (54.9 +/- 33.3) U/ml and (167.5 +/- 89.0) U/ml in the patients with heat apoplexy and in controls, respectively, with very significant difference. But, there was no significant difference in IL-6 between varied groups.

CONCLUSIONS

The above-mentioned results suggest that establishment of heat acclimatization correlates to the interaction of network of neuroendocrine-cytokine-HSP, in which decrease in plasma IL-2 was one of the important factors causing reduction of HSP70 expression. Balance of network regulation was broken by pathological factors, finally resulting in heat apoplexy.

Efficacy of blood purification therapy for heat stroke presenting rapid progress of multiple organ dysfunction syndrome: a comparison of five cases

Five patients were admitted to our hospital because of classical heat stroke during the heat waves which attacked our country in the summers 1994 and 1995. The clinical and laboratory findings of all patients suggested the rapid progress of multiple organ dysfunction syndrome (MODS). Blood purification (BP) therapy, in addition to conventional treatment, was performed in three of the patients. Despite their disastrous general condition, all completely recovered or recovered sufficiently to be transferred to a rehabilitation hospital. Two additional patients were treated with conventional treatment only and both died in 1-3 days after admission. Clinical characteristics and laboratory findings on admission showed no differences between the cases receiving BP therapy and those not receiving BP therapy. These findings suggest that, in heat stroke patients, additional BP therapy may provide a better prognosis than conventional therapy only. These beneficial effects of BP may have been due mainly to the removal of proinflammatory cytokines related to heat stroke.

Nitric oxide production is enhanced in patients with heat stroke

OBJECTIVE

To determine whether nitric oxide (NO) production is increased in heat stroke (HS) patients.

DESIGN

A prospective analysis of nitrite and nitrate (NO2*/NO3) levels in ten HS patients was performed at the HS center in Makkah, Saudi Arabia.

METHODS

Plasma (NO2*/NO3) levels were determined spectrophotometrically before cooling (0 time), and at 6, 12, and 24 h post-cooling.

RESULTS

The mean level of NO in the ten HS victims before cooling was significantly higher than in eight control patients (35.6+/-37.0 vs. 3.0+/-4.2 micromol/l; p<0.01). The levels were higher in non-survivors than in survivors. NO also correlated positively with the Acute Physiology and Chronic Health Evaluation II score (r = 0.72, p<0.018). There was no correlation between the NO level before cooling and blood pressure, rectal temperature, or cooling time.

CONCLUSION

HS is associated with excessive NO production, the magnitude of which is proportional to the severity of illness. NO may be an important mediator and integral part of the pathophysiological processes resulting in HS and may be a central factor linking the neurological and cardiovascular abnormalities observed in HS.

Severe heat stroke associated with high plasma levels of plasminogen activator inhibitor 1

In a 38-year-old man, severe heat stroke caused disseminated intravascular coagulation (DIC) associated with significantly elevated plasma plasminogen activator inhibitor 1 levels. Investigation of the effects of hyperthermia on coagulation and fibrinolysis showed, in apparent conflict with previous reports, a time lag between the initial hypercoagulable and hyperfibrinolytic response (within 24 hr) and hypofibrinolysis shown by a disproportionate increase of PAI-1 (after 24 h), which possibly occurs in correspondence with the recovery of vascular endothelial integrity. The patient was discharged without sequelae although computed tomography (CT) scans indicated the likelihood of venous infarction or posterior inferior cerebellar artery area infarction secondary to DIC.

Involvement of interleukin-1 receptor mechanisms in development of arterial hypotension in rat heatstroke

Rats, under urethan anesthesia, were exposed to a high ambient temperature (42 degrees C) to induce heatstroke and to assess the hemodynamic changes associated with heatstroke. Compared with normothermic controls, rats with heatstroke showed higher values of colonic temperature, heart rate, and plasma levels of interleukin (IL)-1 but lower values of R wave amplitude, P-R and Q-T intervals, systolic wave amplitude, diastolic and dicrotic wave duration, mean arterial pressure, stroke volume, and cardiac output. Animals injected intravenously with an IL-1-receptor antagonist at the time of heatstroke induction were protected from some of the cardiovascular effects of heatstroke, such as depressed ventricular depolarization, decreased stroke volume, decreased cardiac output, and arterial hypotension. The hemodynamic changes associated with heatstroke could be mimicked by IL-1beta administration. Other cardiovascular parameters such as total peripheral vascular resistance were unaffected by heatstroke induction or IL-1beta treatment. The results indicate that a selective decline in stroke volume or ventricular depolarization resulting from increased plasma levels of IL-1 may be an important mechanism signaling arterial hypotension or circulatory failure in rat heatstroke.

Concentrations of soluble tumor necrosis factor and interleukin-6 receptors in heatstroke and heatstress

OBJECTIVE

Increased proinflammatory cytokine concentrations have been implicated in the pathogenesis of heatstroke. Soluble cytokine receptors can modulate circulating cytokine activities. We examined the possible role of soluble tumor necrosis factor receptors (sTNFR 60, sTNFR 80) and interleukin-6 receptor (sIL-6R) in heatstroke by determining their concentrations before and after cooling, as well as in heatstressed controls.

DESIGN

Prospective controlled study.

SETTING

Heatstroke Center, Makkah, Saudi Arabia (1993 pilgrimage).

PATIENTS

Twenty-five consecutive heatstroke patients before and after cooling, 14 heatstressed controls (HSC), and 13 normal controls (NC).

MEASUREMENTS AND MAIN RESULTS

Concentrations of sTNFR 60, sTNFR 80, and sIL-6R, as well as their ligands, were measured using commercially available enzyme-linked immunosorbent assay kits. Mean sTNFR 60 concentration was increased in heatstroke (p <.0001, vs. NC; p < .0001, vs. HSC) and in HSC (p = .004, vs. NC). Mean sTNFR 80 concentration was increased in heatstroke and decreased in HSC (p = .01, heatstroke vs. HSC). Mean sIL-6R concentration was decreased in heatstroke and increased in HSC (p = .04, heatstroke vs. NC; p = .001, heatstroke vs. HSC). IL-6 was undetectable in NC and mean IL-6 concentration was more increased in heatstroke than in HSC (p = .001). Rectal temperature and creatinine concentrations correlated significantly with sTNFR 60, sTNFR 80, sIL-6R, and IL-6 concentrations. After cooling, mean concentrations of sIL-6R and sTNFR 80 increased significantly, whereas the mean sTNFR 60 concentration did not change. Residual neurologic deficits were associated with higher precooling IL-6 (p = .002) and postcooling sTNFRs (p < .0001) concentrations.

CONCLUSIONS

Significant changes in cytokine receptor concentrations are associated with heatstress. In heatstroke, the changes are more pronounced, and for some cytokine receptors, the changes are in the opposite direction (compared with changes in heatstress). Concentrations of IL-6 and sTNFRs correlate with hyperthermia and outcome. Cooling did not normalize sTNFR concentrations, suggesting failure to control the inflammatory response.

Effect of classic heatstroke on serum procalcitonin

OBJECTIVE

Procalcitonin, the precursor peptide of calcitonin, has been shown to be a serum marker of the severity and mortality of several systemic inflammatory response syndromes. This study addressed the correlation of serum procalcitonin with the course of classic (nonexertional) heatstroke.

DESIGN

Serum samples were collected prospectively every 6 hrs for 24 hrs.

SETTING

Heatstroke treatment unit, Makkah, Saudi Arabia.

PATIENTS

A total of 25 patients were admitted during the annual Hajj pilgrimage in 1994. Ten patients evaluated in the same treatment center with minor illnesses and without pyrexia served as controls.

INTERVENTIONS

Patients were cooled according to an established evaporation method.

MEASUREMENTS AND MAIN RESULTS

Standard critical care parameters including continuous rectal temperature. A rapid immunochemical assay for serum procalcitonin was utilized. The mean serum procalcitonin was elevated 20-fold on admission in patients with heatstroke compared with controls (p < .011). The procalcitonin concentration subsequently increased to a plateau by 6 hrs and remained increased at 24 hrs, compared with the admission level (p < .0001). In this study, 77% of the patients with heatstroke survived. A subgroup analysis demonstrated that the patients who survived had a significantly higher procalcitonin concentration than those patients who died of heatstroke; a procalcitonin concentration of >0.5 ng/mL (>0.15 nmol/L) at 6 hrs predicted survival (p = .02).

CONCLUSION

Classic heatstroke is associated with increased concentrations of serum procalcitonin, particularly among survivors. Further studies are required to elucidate the source and action(s) of procalcitonin as well as its relationship to cytokine activation.

Blood lactate threshold and type II fibre predominance in patients with exertional heatstroke

OBJECTIVES

Severe damage to skeletal muscle is usually seen in patients with exertional heatstroke. Thirty seven young military recruits with exertional heatstroke in Taiwan from 1992 to 1995 were studied to evaluate changes in muscle pathology and blood lactate with exercise.

METHODS

A biopsy sample of the vastus lateralis was taken from recruits within 10 days of the initial presentation. Results were compared with those from 15 controls matched for age and sex. During the recovery period, 90-150 days after exertional heatstroke, 29 patients participated in a constant work load test on the treadmill to assess their blood lactate threshold, and a second biopsy sample was taken. Each biopsy was examined histologically for pathology, distribution of fibre types, and fibre diameter.

RESULTS

Twenty four of the 37 patients with exertional heatstroke developed rhabdomyolysis and 18 of these had type II fibre predominance in their muscle biopsy. The patients with type II fibre predominance had a higher tendency to develop rhabdomyolysis (chi 2 = 6.84, P < 0.01). The time required to reach a blood lactate threshold during a constant treadmill work load after recovery was significantly shorter in the patients with exertional heatstroke who had type II fibre predominance (P < 0.01). There was a positive correlation between the highest value of blood lactate and the percentage of type II fibres in all tested subjects (r = 0.82, P < 0.01).

CONCLUSION

Patients with type II fibre predominance are more susceptible to exertional heatstroke and tend to have a higher blood lactate concentration and a shorter time to reach blood lactate threshold under a treadmill load test.

Activation of coagulation and fibrinolysis in heatstroke

Hemorrhagic diathesis and widespread microthrombosis are common in heatstroke. To assess the early stages of coagulopathy in heatstroke, thrombin-antithrombin III (TAT), fibrin monomers, plasmin-alpha 2-antiplasmin (PAP), plasminogen and D-Dimer were measured in 16 heatstroke patients (means +/- SE rectal temperature 42.3 +/- 0.2 degrees C) pre- and postcooling and compared with 8 heatstressed and 23 normal controls. Comparing heatstroke patients with normal controls, TAT, fibrin monomers, PAP and D-Dimer were elevated to (median (range)) 16.5 (4-1000) versus 3.5 (2-7.2) micrograms/l p < 0.001, 16 (4-113) versus 2 (2-9) nM p < 0.001; 3300 (1000-36500) versus 255 (136-462) micrograms/l p < 0.001 and 0.72 (0.22-64.8) versus 0.15 (0.05-0.25) microgram/ml p < 0.01 respectively. Plasminogen decreased to 81% (34-106); PAP, TAT and D-Dimer correlated significantly with hyperthermia (r = 0.577, p = 0.02; r = 0.635, p = 0.01; r = 0.76, p = 0.003). Postcooling PAP decreased to 545 (260-850) micrograms/l p < 0.005, TAT 10 (6-70) micrograms/l, and fibrin monomers 22 (18-86) nM remained unchanged. Heatstressed controls showed mild but significant increase in all markers. Activation of coagulation and fibrinolysis occurs early and is profound and sustained in heatstroke. Cooling seems to attenuate the activation of fibrinolysis only, however, this requires confirmation in a larger study population.

Recurrent liver involvement in heatstroke

We report the case of a young patient who presented two self-limited episodes of acute jaundice that developed immediately following a long distance run. Zone 3 necrosis was the most prominent histologic change of the liver during the second episode. The diagnosis of heatstroke with liver damage was based on the exclusion of known causes of acute hepatitis, the histopathologic changes and the circumstances preceding the onset of liver disease. This seems to be the first case of severe and recurrent liver impairment due to heatstroke.

Evidence for endothelial cell activation/injury in heatstroke

OBJECTIVES

We treated the hypothesis that heatstroke is associated with endothelial cell activation/injury and examined the possibility that the markers of endothelial cell activation/injury may be associated with its severity and complications such as disseminated intravascular coagulation, lung injury, and renal dysfunction.

DESIGN

Prospective analyses.

SETTING

Heatstroke Center in Makkah, Saudi Arabia.

PATIENTS

Twenty-two adult patients with heatstroke.

INTERVENTIONS

The plasma concentration of endothelin, circulating intercellular adhesion molecule-1 (ICAM-1), and von Willebrand factor-antigen values were measured, respectively, by radioimmunoassay, enzyme-linked immunosorbent assay, and rocket electroimmunoassay, in heatstroke patients on admission (precooling) and after complete cooling (postcooling), and in ten normal control patients.

MEASUREMENTS AND MAIN RESULTS

Precooling heatstroke patients (rectal temperature 40.9 +/- 1.1 [SD] degrees C) had increased circulating concentrations of endothelin, c-ICAM-1, and von Willebrand factor-antigen in 100%, 80%, and 77% of patients to 126.4 +/- 11.2 pmol/L, 523.1 +/- 154.4 ng/mL, and 3.85 +/- 2.3 U/mL, respectively (control values: 13.7 +/- 4.2 pmol/L [p < .001]; 247.4 +/- 68.2 ng/ml [p < .001]; and < 1.5 U/mL, respectively). There was a significant (r2 = .68, p < .01) correlation between circulating ICAM-1 and endothelin concentrations. Plasma endothelin concentration correlated negatively with temperature (r2 = .35, p < .05). Mean endothelin concentration was similar in patients with or without renal dysfunction, and mean von Willebrand factor-antigen concentration was similar in patients with or without lung injury or disseminated intravascular coagulation. There were no significant correlations between circulating ICAM-1, endothelin, or von Willebrand factor-antigen concentration and the Simplified Acute Physiology core. After cooling, mean circulating ICAM-1 and endothelin concentrations decreased significantly to 400 +/- 109 ng/mL and 93 +/- 38.5 pmol/L, respectively, whereas the mean von Willebrand factor-antigen concentration increased to 5.55 +/- 2.18 U/mL (p > .05).

CONCLUSIONS

Our findings of increased circulating concentrations of circulating ICAM-1, endothelin, and von Willebrand factor-antigen are consistent with the hypothesis that heatstroke is associated with endothelial cell activation/injury. Whether the endothelial cell activation/injury is implicated in the pathophysiology of this disorder merits further studies.

Thermal regulatory dysfunction of growth hormone in classical heat stroke

Growth hormone (GH) secretion associated with classical (non-exertional) heat stroke (HS) was evaluated in 26 HS victims and 10 control (non heat-exhausted) subjects during the annual Hajj in Makkah, Saudi Arabia. On admission to the HS treatment unit, the GH level was 1.54 +/- 0.14 ng/ml (approximately 3.5-fold higher in the HS victims compared to controls; p = 0.005). The GH levels subsequently declined by 78% by 24 h. The categorized GH response was significantly associated with survival for those subjects with a GH level of < 5.53 ng/ml by 6 h (chi-squared test; p = 0.06). In those patients who died (N = 6), there was a continued increase in GH levels from the time of admission, which peaked at 6 h. In those patients who survived, the GH levels peaked at the time of admission and declined rapidly thereafter. There was a direct correlation of age and GH level upon admission (p = 0.02), as well as to peak GH (p = 0.041). However, there was no relationship of GH level to either body core temperature or the cooling time. In summary, HS induced significant GH secretion. The degree of GH response was not related to the body core temperature and was more pronounced in older individuals and in those that died. Although patients with GH deficiency and HS are characterized by anhidrosis/hypohidrosis, there does not appear to be dysfunction of GH response to heat stress-associated HS. In contrast, a vigorous GH response at 6 h suggested a worse outcome.

Changes in thyroid hormone metabolism in exertional heat stroke with or without acute renal failure

The effects of exertional heat stroke (ExHS), with or without acute renal failure (ARF), on thyroid hormone metabolism were investigated. Eighteen ExHS patients were recruited and divided into two groups based on the presence or absence of ARF. Eleven age-matched healthy subjects served as a control group. Serum values of T3, T4, TSH, free T4 (FT4), rT3, and sulfated T3 (T3S) were measured in these groups during the acute and recovery stages of ExHS. Serum T3, T4, and FT4 levels were reduced, with reciprocal increases in rT3 and T3S levels as the severity of ExHS increased. The following mean levels of thyroid hormones were found (controls vs. ExHS without ARF vs. with ARF): T3, 1514 vs. 1164 vs. 393 pmol/L (P < 0.05 each); T4, 97 vs. 79 vs. 49 nmol/L (P = NS and P < 0.05, respectively); FT4, 20.5 vs. 19.5 vs. 19.0 pmol/L (P = NS each); rT3, 371 vs. 617 vs. 805 pmol/L (P < 0.05 and P = NS, respectively); and T3S, 30.1 vs. 34.2 vs. 71.1 pmol/L (P = NS and P < 0.05, respectively). The serum TSH levels were not significantly different among the three groups. Significantly negative correlations were found between serum creatinine and T3 (r = -0.75; P < 0.001) and T4 levels (r = -0.65; P < 0.001), whereas no relationship was noted between serum creatinine and rT3 values (r = 0.11; P < 0.05). In contrast, a correlation was observed between serum glutamic pyruvic transaminase and rT3 (r = 0.45; P < 0.01). Thyroid function tests returned to normal after patients recovered. In conclusion, our results show that patients suffering from ExHS, with or without ARF, displayed altered serum thyroid function in proportion to the severity of their condition. No significant changes in serum levels of rT3 were observed between the two groups, whereas a positive relationship was observed between serum rT3 and serum glutamic pyruvic transaminase values, suggesting that the changes in serum rT3 levels were more dependent on extrarenal illness than on renal disease per se. The moderate increase in serum T3S levels found in patients suffering from both ExHS and ARF may represent a decrease in tissue 5'-monodeiodinase activity as found in other nonthyroidal illnesses. A return of serum thyroid function tests to normal values after recovery from ExHS suggests that the low T3 state may play a protective role to prevent undesirable catabolic effects. Replacement therapy is thus not recommended.

Circulating angiotensin-converting enzyme, von Willebrand factor antigen and thrombomodulin in exertional heat stroke

1. Military recruits frequently succumb to exertional heat stroke during intensive training. Since widespread endothelial injury is often associated with exertional heat stroke, the relationship between changes in three circulating endothelial cell markers (angiotensin-converting enzyme, von Willebrand factor antigen and thrombomodulin) and exertional heat stroke was studied. 2. Twelve recruits who had succumbed to exertional heat stroke during basic physical training (5000 m running) were included in the study. Another 10 age-matched healthy subjects who had gone through the same physical training regimen were selected as controls. 3. Blood was withdrawn on admission and on discharge for analyses of angiotensin-converting enzyme, von Willebrand factor antigen and thrombomodulin. Other physiological parameters and biochemical analyses reflecting renal and liver functions were also recorded. 4. Our results indicated that these subjects with exertional heat stroke exhibited impaired liver function as revealed by the significant elevation of both serum glutamic oxaloacetic transaminase (P < 0.05) and serum glutamic pyruvic transaminase (P < 0.05) as compared with normal healthy control subjects. Unfortunately, these values remained mostly somewhat elevated on discharge, although serum glutamic oxaloacetic transaminase was reduced dramatically. Indices of kidney functions, including creatinine clearance and uric acid and phosphorus secretion, were not significantly different from those observed in healthy controls. 5. Circulating angiotensin-converting enzyme activities in exertional heat stroke patients on admission were significantly lower than in normal subjects (10.68 +/- 2.15 versus 21.21 +/- 3.18 nmol hippuric acid min-1 ml-1, P < 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)