Nitric oxide production is enhanced in patients with heat stroke

Antimicrobial peptide cathelicidin LL-37 preserves intestinal barrier and organ function in rats with heat stroke

Global warming increases the incidence of heat stroke (HS) and HS causes the reduction of visceral blood flow during hyperthermia, leading to intestinal barrier disruption, microbial translocation, systemic inflammation and multiple organ failure. Cathelicidin LL-37 exhibits antimicrobial activities, helps innate immunity within the gut to maintain intestinal homeostasis, and augments intestinal wound healing and barrier function. Thus, we evaluated the effects and possible mechanisms of cathelicidin LL-37 on HS. Wistar rats were placed in a heating-chamber of 42 ̊C to induce HS. Changes in rectal temperature, hemodynamic parameters, and survival rate were measured during the experimental period. Blood samples and ilea were collected to analyze the effects of LL-37 on systemic inflammation, multiple organ dysfunction, and intestinal injury. Furthermore, LS174T and HT-29 cells were used to assess the underlying mechanisms. Our data showed cathelicidin LL-37 ameliorated the damage of intestinal cells induced by HS. Intestinal injury, systemic inflammation, and nitrosative stress (high nitric oxide level) caused by continuous hyperthermia were attenuated in HS rats treated with cathelicidin LL-37, and hence, improved multiple organ dysfunction, coagulopathy, and survival rate. These beneficial effects of cathelicidin LL-37 were attributed to the protection of intestinal goblet cells (by increasing transepithelial resistance, mucin-2 and Nrf2 expression) and the improvement of intestinal barrier function (less cyclooxygenase-2 expression and FITC-dextran translocation). Interestingly, high cathelicidin expression in the ileal samples of inflammatory bowel disease patients was associated with better clinical outcome. These results suggest that cathelicidin LL-37 could prevent heat stress-induced intestinal damage and heat-related illnesses.

Biomarkers of heatstroke-induced organ injury and repair

NEW FINDINGS

What is the topic of this review? The status and potential role of novel biological markers (biomarkers) that can help identify the patients at risk of organ injury or long-term complications following heatstroke. What advances does it highlight? Numerous biomarkers were identified related to many aspects of generalized heatstroke-induced cellular injury and tissue damage, and heatstroke-provoked cardiovascular, renal, cerebral, intestinal and skeletal muscle injury. No novel biomarkers were identified for liver or lung injury.

ABSTRACT

Classic and exertional heatstroke cause acute injury and damage across numerous organ systems. Moreover, heatstroke survivors may sustain long-term neurological, cardiovascular and renal complications with a persistent risk of death. In this context, biomarkers, defined as biological samples obtained from heatstroke patients, are needed to detect early organ injury, and predict outcomes to develop novel organ preservation therapeutic strategies. This narrative review provides preliminary insights that will guide the development and future utilization of these biomarkers. To this end, we have identified numerous biomarkers of widespread heatstroke-associated cellular injury, tissue damage and repair (extracellular heat shock proteins 72 and 60, high mobility group box protein 1, histone H3, and interleukin-1α), and other organ-specific biomarkers including those related to the cardiovascular system (cardiac troponin I, endothelium-derived factors, circulation endothelial cells, adhesion molecules, thrombomodulin and von Willebrand factor antigen), the kidneys (plasma and urinary neutrophil gelatinase-associated lipocalin), the intestines (intestinal fatty acid-binding protein 2), the brain (serum S100β and neuron-specific enolase) and skeletal muscle (creatine kinase, myoglobin). No specific biomarkers have been identified so far for liver or lung injury in heatstroke. Before translating the identified biomarkers into clinical practice, additional preclinical and clinical prospective studies are required to further understand their clinical utility, particularly for the biomarkers related to long-term post-heatstroke health outcomes.

Expert consensus on the diagnosis and treatment of heat stroke in China

Heat stroke (HS) is a fatal disease caused by thermal damage in the body, and it has a very high mortality rate. In 2015, the People's Liberation Army Professional Committee of Critical Care Medicine published the first expert consensus on HS in China, Expert consensus on standardized diagnosis and treatment for heat stroke. With an increased understanding of HS and new issues that emerged during the HS treatment in China in recent years, the 2015 consensus no longer meet the requirements for HS prevention and treatment. It is necessary to update the consensus to include the latest research evidence and establish a new consensus that has broader coverage, is more practical and is more in line with China's national conditions. This new expert consensus includes new concept of HS, recommendations for laboratory tests and auxiliary examinations, new understanding of diagnosis and differential diagnosis, On-site emergency treatment and In-hospital treatment, translocation of HS patients and prevention of HS.

Acute liver failure and hepatic encephalopathy in exertional heat stroke

A 31-year-old man was brought to Accident & Emergency after collapsing during a race. On presentation, the patient had a temperature of 41.7°C (rectal). External cooling was started immediately. The patient was intubated in view of a Glasgow Coma Scale of 7 and was transferred to theintensive therapy unit. Laboratory results revealed an acute kidney injury, rhabdomyolysis, disseminated intravascular coagulopathy and acute liver failure. The patient was encephalopathic, jaundiced and difficult to sedate. His liver function continued to deteriorate with alanine aminotransferase (ALT) levels reaching 9207 U/L. King's Hospital Liver Centre, London was contacted for a possible liver transplant, and they advised an infusion of N-acetylcysteine. The following day liver function tests improved; thus, transplantation was not performed. The patient failed multiple sedation holds and required a tracheostomy. He continued to spike a fever. Despite no source of sepsis being found, the patient remained on broad spectrum antibiotics to cover for any potential infective causes until day 27. After 15 days, the patient's encephalopathy gradually improved. He was weaned off the ventilator and underwent intense physiotherapy. The patient was discharged from hospital one month after admission.

Distinct functional responses to stressors of bone marrow derived dendritic cells from diverse inbred chicken lines

Differences in responses of chicken bone marrow derived dendritic cells (BMDC) to in vitro treatment with lipopolysaccharide (LPS), heat, and LPS + heat were identified. The Fayoumi is more disease resistant and heat tolerant than the Leghorn line. Nitric Oxide (NO) production, phagocytic ability, MHC II surface expression and mRNA expression were measured. NO was induced in BMDC from both lines in response to LPS and LPS + heat stimulation; Fayoumi produced more NO with LPS treatment. Fayoumi had higher phagocytic ability and MHC II surface expression. Gene expression for the heat-related genes BAG3, HSP25, HSPA2, and HSPH1 was strongly induced with heat and few differences existed between lines. Expression for the immune-related genes CCL4, CCL5, CD40, GM-CSF, IFN-γ, IL-10, IL-12β, IL-1β, IL-6, IL-8, and iNOS was highly induced in response to LPS and different between lines. This research contributes to the sparse knowledge of genetic differences in chicken BMDC biology and function.

Cerebral Vascular Control and Metabolism in Heat Stress

This review provides an in-depth update on the impact of heat stress on cerebrovascular functioning. The regulation of cerebral temperature, blood flow, and metabolism are discussed. We further provide an overview of vascular permeability, the neurocognitive changes, and the key clinical implications and pathologies known to confound cerebral functioning during hyperthermia. A reduction in cerebral blood flow (CBF), derived primarily from a respiratory-induced alkalosis, underscores the cerebrovascular changes to hyperthermia. Arterial pressures may also become compromised because of reduced peripheral resistance secondary to skin vasodilatation. Therefore, when hyperthermia is combined with conditions that increase cardiovascular strain, for example, orthostasis or dehydration, the inability to preserve cerebral perfusion pressure further reduces CBF. A reduced cerebral perfusion pressure is in turn the primary mechanism for impaired tolerance to orthostatic challenges. Any reduction in CBF attenuates the brain's convective heat loss, while the hyperthermic-induced increase in metabolic rate increases the cerebral heat gain. This paradoxical uncoupling of CBF to metabolism increases brain temperature, and potentiates a condition whereby cerebral oxygenation may be compromised. With levels of experimentally viable passive hyperthermia (up to 39.5-40.0 °C core temperature), the associated reduction in CBF (∼ 30%) and increase in cerebral metabolic demand (∼ 10%) is likely compensated by increases in cerebral oxygen extraction. However, severe increases in whole-body and brain temperature may increase blood-brain barrier permeability, potentially leading to cerebral vasogenic edema. The cerebrovascular challenges associated with hyperthermia are of paramount importance for populations with compromised thermoregulatory control--for example, spinal cord injury, elderly, and those with preexisting cardiovascular diseases.

Critical care at extremes of temperature: effects on patients, staff and equipment

Modern travel and military operations have led to a significant increase in the need to provide medical care in extreme climates. Presently, there are few data on what happens to the doctor, their drugs and equipment when exposed to these extremes. A review was undertaken to find out the effects of 'extreme heat or cold' on anaesthesia and critical care; in addition, subject matter experts were contacted directly. Both extreme heat and extreme cold can cause a marked physiological response in a critically ill patient and the doctor treating these patients may also suffer a decrement in both physical and mental functioning. Equipment can malfunction when exposed to extremes of temperature and should ideally be stored and operated in a climatically controlled environment. Many drugs have a narrow range of temperatures in which they remain useable though some have been shown to remain effective if exposed to extremes of temperature for a short period of time. All personnel embarking on an expedition to an extreme temperature zone should be of sufficient physical robustness and ideally should have a period of acclimatisation which may help mitigate against some of the physiological effects of exposure to extreme heat or extreme cold. Expedition planners should aim to provide climatic control for drugs and equipment and should have logistical plans for replenishment of drugs and medical evacuation of casualties.

Ischemic and oxidative damage to the hypothalamus may be responsible for heat stroke

The hypothalamus may be involved in regulating homeostasis, motivation, and emotional behavior by controlling autonomic and endocrine activity. The hypothalamus communicates input from the thalamus to the pituitary gland, reticular activating substance, limbic system, and neocortex. This allows the output of pituitary hormones to respond to changes in autonomic nervous system activity. Environmental heat stress increases cutaneous blood flow and metabolism, and progressively decreases splanchnic blood flow. Severe heat exposure also decreases mean arterial pressure (MAP), increases intracranial pressure (ICP), and decreases cerebral perfusion pressure (CPP = MAP - ICP), all of which lead to cerebral ischemia and hypoxia. Compared with normothermic controls, rodents with heatstroke have higher hypothalamic values of cellular ischemia (e.g., glutamate and lactate-to-pyruvate ratio) and damage (e.g., glycerol) markers, pro-oxidant enzymes (e.g., lipid peroxidation and glutathione oxidation), proinflammatory cytokines (e.g., interleukin-1β and tumor necrosis factor-α), inducible nitric oxide synthase-dependent nitric oxide, and an indicator for the accumulation of polymorphonuclear leukocytes (e.g., myeloperoxidase activity), as well as neuronal damage (e.g., apoptosis, necrosis, and autophagy) after heatstroke. Hypothalamic values of antioxidant defenses (e.g., glutathione peroxidase and glutathione reductase), however, are lower. The ischemic, hypoxic, and oxidative damage to the hypothalamus during heatstroke may cause multiple organ dysfunction or failure through hypothalamic-pituitary-adrenal axis mechanisms. Finding the link between the signaling and heatstroke-induced hypothalamic oxidative and ischemic damage might allow us to clinically attenuate heatstroke. In particular, free radical scavengers, heat shock protein-70 inducers, hypervolemic hemodilution, inducible nitric oxide synthase inhibitors, progenitor stem cells, flutamide, estrogen, interleukin-1 receptor antagonists, glucocorticoid, activated protein C, and baicalin mitigate preclinical heatstroke levels.

Exertional Heat Stroke – The Athlete's Nemesis

Heat stroke represents the extreme end of a spectrum of heat-related illnesses. It can occur in endurance athletes. Its incidence is probably under-reported. Patients present confused, drowsy or comatose, with a raised core temperature, but often a falsely reassuring peripheral temperature. Treatment is centred on reducing the core temperature as rapidly as possible and appropriate supportive management. Even with prompt treatment, it is associated with multi-organ dysfunction and death. Patients are often misdiagnosed, or diagnosed late. This is probably exacerbated by a wide differential diagnosis, the need for a core temperature measurement to reach the diagnosis and clinicians being unfamiliar with the disease. The need for immediate recognition, and immediate treatment compounds the problem. Survivors may experience long-term neurological disability and may be at risk of a further episode. Patients should return to sport gradually and only when they feel well. Its epidemiology, pathophysiology and clinical management are reviewed.

Recombinant thrombomodulin prevents heatstroke by inhibition of high-mobility group box 1 protein in sera of rats

Heatstroke, a severe inflammatory response disease, is a medical emergency characterized by high body temperature. The protein C anticoagulant system inhibits inflammation resulting from various causes. Thrombomodulin (TM), a widely expressed glycoprotein originally identified in vascular endothelium, is an important cofactor in the protein C anticoagulant system. We tested the hypothesis that TM could prevent acute inflammation induced by heat stress in a rodent model. Male Wistar rats received a bolus of 1 mg x kg of body weight of TM or saline injected into the tail vein, followed by heat-stress treatment (exposure to 42°C for 30 min). Serum concentrations of cytokines (IL-1β, IL-6, and TNF-α), NO, and high-mobility group box 1 (HMGB1) protein were measured at various time points after treatment. We observed a decrease in the levels of cytokines and HMGB1 protein in sera of TM-treated animals over time. Inhibition of NO overproduction by recombinant TM was observed during heat stress-induced inflammation. Because of the decline in inflammatory marker levels, TM ameliorated injury to various organs in the rat model of heat stress-induced acute inflammation. As TM exhibited a strong anti-inflammatory effect in a rat model of acute inflammation induced by heat stress, TM represents a potential therapeutic for heatstroke prevention or management in patients.

Inhibition of acute lung inflammation and injury is a target of brain cooling after heatstroke injury

BACKGROUND

Although brain cooling has recently been reported as effective in improving the survival after heatstroke generation in rats, the mechanisms underlying the therapeutic effects of brain cooling are not fully elucidated. This study was conducted to test whether the acute lung inflammation and damage that might occur during heatstroke could be affected by brain cooling.

METHODS

Anesthetized rats were randomized into four groups as follows: (a) normothermic controls (n = 8); (b) heatstroke rats without saline delivery (n = 8); (c) heatstroke rats treated with 36°C saline via retrograde jugular vein (n = 8); and (d) heatstroke rats treated with 4°C saline via retrograde jugular vein (n = 8). Heatstroke was induced by putting the animals in a folded heating pad of 42°C for 68 minutes controlled by circulating hot water. The core temperatures of normothermic groups were maintained at about 36°C. The cardiovascular parameters and core temperatures were monitored for all experiments. Bronchoalveolar lavage (BAL) was done in the left lung 20 minutes after termination of heat stress for determination of cellular ischemia markers (e.g., glutamate, lactate-to-pyruvate ratio), proinflammatory cytokines (interleukin-1, tumor necrosis factor-alpha), and nitric oxide metabolites. Parts of the right lung were excised for meloperoxidase measurement, whereas the rest was collected for lung damage score assessments.

RESULTS

When compared with those of normothermic controls, untreated or 36°C saline-treated heatstroke rats had higher values of BAL fluid levels of cellular ischemia markers, proinflammatory cytokines, nitric oxide metabolites, lung meroperoxidase activity, lung damage score, and neutrophil infiltration. Brain cooling causes by 4°C saline infusion significantly reduced the heat-induced increased BAL levels of cellular ischemia markers, proinflammatory cytokines, and nitric oxide metabolites, and reduced lung damage score and neutrophil infiltration.

CONCLUSIONS

These experimental data indicate that acute lung inflammation and damage is a target of brain cooling after heatstroke injury.

Role of nitric oxide in young patients with vasovagal syncope

AIMS

Nitric oxide (NO) formed in the vascular endothelium produces, among other effects, a strong vasodilation. In order to evaluate the possible role of NO in hypotension induced by head-up tilt test (HUT), we measured plasma levels of its metabolites, nitrites and nitrates (NOx), during the test.

METHODS AND RESULTS

Twelve patients with vasovagal syncope and positive HUT [HUT(+)] (mean age: 23+/-5 years) and 13 healthy volunteers with negative HUT (controls) (mean age: 24+/-5 years) were included. Venous blood samples were obtained during the baseline stage for biochemical measurements. Plasma values of NOx were obtained under baseline conditions (T0), at the end of the HUT (T1), and 15 min after the end of the HUT (T2). The baseline biochemical values as well as haemodynamic parameters were similar in HUT(+) patients and controls. NOx plasma values (in micromol/L) were as follows [HUT(+) vs. controls]: T0: 5.7+/-1.6 vs. 8.8+/-4.7 (P=0.05), T1: 6.1+/-3.2 vs. 8.5+/-3.6 (P=NS), and T2: 6.1+/-3 vs. 10.2+/-8.9 (P=NS). The NOx levels were directly correlated with the insulin levels (Spearman's R=0.53, P=0.008).

CONCLUSION

Baseline plasma levels of NOx were significantly lower in HUT(+) patients than in controls. However, since the expected increase in NOx values during HUT-induced syncope was not observed, the possible role of NO in vasovagal hypotension is uncertain.

High-dose antithrombin III prevents heat stroke by attenuating systemic inflammation in rats

OBJECTIVE

Systemic inflammatory mediators, including the high mobility group box 1 (HMGB1) protein, play important roles in the development of various inflammatory conditions. Although anticoagulants, such as antithrombin III (AT III), inhibit inflammation resulting from various causes, their anti-inflammatory mechanism of action is not well understood. Nevertheless, as heat stroke is a severe inflammatory response disease, we hypothesized that AT III would inhibit inflammation and prevent heat stress-induced acute heat stroke.

METHODS

Male Wistar rats received a bolus injection of saline or 250 U of AT III per kg of body weight into the tail vein, followed by heat stress (exposure to 42 degrees C for 30 min). Levels of cytokines (interleukin-1 beta, interleukin-6, and TNF-alpha), NOx, and HMGB1 were measured in serum and tissue at regular intervals for 6 h after the heat stress induction.

RESULTS

Levels of cytokines, NOx, and HMGB1 in serum decreased over time in AT III-treated rats. AT III pretreatment also reduced NOx levels during heat stress-induced inflammation. As a result, AT III pretreatment improved survival in a rat model of heat stress-induced acute inflammation.

CONCLUSIONS

Our data suggest that AT III pretreatment inhibited the secretion of cytokines, NOx, and HMGB1, and prevented heat stress-induced acute inflammation.

Attenuation of acute lung inflammation and injury by whole body cooling in a rat heatstroke model

Whole body cooling is the current therapy of choice for heatstroke because the therapeutic agents are not available. In this study, we assessed the effects of whole body cooling on several indices of acute lung inflammation and injury which might occur during heatstroke. Anesthetized rats were randomized into the following groups and given (a) no treatment or (b) whole body cooling immediately after onset of heatstroke. As compared with the normothermic controls, the untreated heatstroke rats had higher levels of pleural exudates volume and polymorphonuclear cell numbers, lung myloperoxidase activity and inducible nitric oxide synthase expression, histologic lung injury score, and bronchoalveolar proinflammatory cytokines and glutamate, and PaCO2. In contrast, the values of mean arterial pressure, heart rate, PaO2, pH, and blood HCO3(-) were all significantly lower during heatstroke. The acute lung inflammation and injury and electrolyte imbalance that occurred during heatstroke were significantly reduced by whole body cooling. In conclusion, we identified heat-induced acute lung inflammation and injury and electrolyte imbalance could be ameliorated by whole body cooling.

Exercise pretraining protects against cerebral ischaemia induced by heat stroke in rats

BACKGROUND

In the rat brain, heat-stroke-induced damage to cerebral neurons is attenuated through heat-shock-induced overexpression of heat-shock protein 72 (HSP72).

OBJECTIVE

To ascertain whether progressive exercise preconditioning induces HSP72 expression in the rat brain and prevents heat-stroke-induced cerebral ischaemia and injury.

METHODS

Male Wistar rats were randomly assigned to either a sedentary group or an exercise group. Those in the exercise group progressively ran on a treadmill 5 days/week, for 30-60 min/day at an intensity of 20-30 m/min for 3 weeks. The effects of heat stroke on mean arterial pressure, cerebral blood flow, brain ischaemia markers (glutamate, lactate/pyruvate ratio and nitric oxide), a cerebral injury marker (glycerol) and brain neuronal damage score in the preconditioned animals were compared with effects in unexercised controls. Heat stroke was induced by exposing urethane-anaesthetised animals to a temperature of 43 degrees C for 55 min, which caused the body temperature to reach 42 degrees C.

RESULTS

Three weeks of progressive exercise pretreatment induced HSP72 preconditioning in the brain and conferred significant protection against heat-stroke-induced hyperthermia, arterial hypotension, cerebral ischaemia and neuronal damage; it also prolonged survival.

CONCLUSIONS

Exercise for 3 weeks can improve heat tolerance as well as attenuate heat-stroke-induced cerebral ischaemia in rats. The maintenance of mean arterial pressure and cerebral blood flow at appropriate levels in the rat brain may be related to overexpression of HSP72.

Inhibition of neuronal nitric oxide synthase causes attenuation of cerebrovascular dysfunction in experimental heatstroke

The present study was performed to assess the prophylactic effect of 7-nitroindazole (7-NI), an inhibitor of neuronal nitric oxide synthase (nNOS), in an animal model of heatstroke. Anesthetized rats, immediately before the start of heat stress, were divided into two major groups and given the following: vehicle solution (1 mL per kg body weight) or 7-NI (5-20mg/mL per kg body weight) intraperitoneally. They were exposed to ambient temperature of 43 degrees C to induce heatstroke. Another group of rats were exposed to room temperature (24 degrees C) and used as normothermic controls. Their physiologic and biochemical parameters were continuously monitored. When the vehicle-pretreated rats underwent heat stress, their survival time values were found to be 21-25 min. Pretreatment with intraperitoneal doses of 7-NI significantly improved survival during heatstroke (55-164 min). As compared to those of normothermic controls, all vehicle-pretreated heatstroke animals displayed higher levels of core temperature, intracranial pressure, nitric oxide metabolite (NO(2)(-)), glutamate, glycerol, lactate/pyruvate ratio, neuronal damage score and nNOS expression in the hypothalamus, and tumor necrosis factor-alpha (TNF-alpha) in the serum. In contrast, all vehicle-pretreated heatstroke animals had lower levels of mean arterial pressure, cerebral perfusion pressure, cerebral blood flow, and brain PO(2). Administration of 7-NI before the start of heat exposure significantly reduced the hyperthermia, intracranial hypertension, nNOS-dependent NO(2)(-), glutamate, glycerol, lactate/pyruvate ratio, and neuronal damage score in the hypothalamus, as well as overproduction of TNF-alpha in the serum that occurred during heatstroke. The data show that reduction of nNOS-dependent NO(2)(-) with 7-NI causes attenuation of cerebrovascular dysfunction, hyperthermia, and TNF-alpha overproduction during heatstroke in the rat.

The flavonoid baicalin protects against cerebrovascular dysfunction and brain inflammation in experimental heatstroke

The present study was performed to assess the prophylactic effect of baicalin, a flavonoid compound, in an animal model of heatstroke. Anesthetized rats, immediately before the start of heat stress, were divided into two major groups and given the following: vehicle solution (1mL per kg body weight) or baicalin (10-40mg per kg body weight) intravenously. They were exposed to ambient temperature of 43 degrees C to induce heatstroke. Another group of rats was exposed to room temperature (24 degrees C) and used as normothermic controls. Their physiologic and biochemical parameters were continuously monitored. When the vehicle-pretreated rats underwent heat stress, their survival time values were found to be 20-28min. Pretreatment with intravenous doses of baicalin significantly improved survival during heatstroke (65-248min). As compared to those of normothermic controls, all vehicle-pretreated heatstroke animals displayed higher levels of core temperature, intracranial pressure, and nitric oxide metabolite (NO(2)(-)), glutamate, glycerol, lactate/pyruvate ratio, and dihydroxybenzoic acid (DHBA) in hypothalamus. In addition, both serum and hypothalamic levels of interleukin-1beta (IL-1beta) and tumor necrosis factor-alpha (TNF-alpha) as well as plasma levels of creatinine, serum urea nitrogen, glutamic oxaloacetic transaminase, glutamic pyruvic transaminase and alkaline phosphatase were elevated after heatstroke onset. In contrast, all vehicle-pretreated heatstroke animals had lower levels of mean arterial pressure, cerebral perfusion pressure, cerebral blood flow, and brain PO(2). Administration of baicalin before the start of heat exposure significantly reduced the hyperthermia, intracranial hypertension, and the increased levels of NO(2)(-), glutamate, glycerol, lactate/pyruvate ratio, and DHBA in the hypothalamus that occurred during heatstroke. The heatstroke-induced increased levels of IL-1beta and TNF-alpha in both the serum and hypothalamus, and renal and hepatic dysfunction were suppressed by baicalin pretreatment. In contrast, both the serum and hypothalamic levels of IL-10 were significantly elevated by baicalin during heatstroke. We successfully demonstrated that baicalin can be used as a prophylactic agent for heatstroke. In particular, baicalin may protect against cerebrovascular dysfunction and brain inflammation in heatstroke.

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.

The role of autacoids and the autonomic nervous system in cardiovascular responses to radio-frequency energy heating

Among the potential effects of exposure to high levels of radio-frequency energy (RFE) (which includes microwaves), an increase in body temperature is the primary consequence. Release of autacoids and activity of the autonomic nervous system may influence (or be directly responsible for) some of the physiological changes that occur in conjunction with this hyperthermia. The main focus of this review is the interaction of autacoids and the autonomic nervous system with cardiovascular changes during heating. Differences between environmental and RFE-induced heating (such as rate of temperature change and degree of skin vs. core heating) may be important when considering these effects. Antihistamines exhibited no beneficial effect on circulatory collapse during RFE-induced heating. The serotonergic blocker methysergide decreased survival time in rats during terminal RFE exposure, despite no effects on heart rate (HR) or blood pressure. Although blockade of platelet-activating factor resulted in lower HR before RFE exposure, there was a lack of effect on the subsequent increase in HR during heating. Nitric oxide did not contribute to the hypotension that occurs due to rapid heating by RFE exposure. There have been either no or very limited studies of effects of prostaglandins, bradykinin, or angiotensin on RFE-induced heating responses. beta-Adrenoceptor antagonism with propranolol resulted in significantly decreased survival times and lower final colonic temperatures during RFE exposure. A lack of effects of nadolol on survival time and temperature, coupled with its poor ability to traverse the blood-brain barrier, suggests that central beta-adrenergic stimulation rather than peripheral stimulation may alter thermoregulation. Effects of the autonomic nervous system (as studied by adrenoceptor blockade) on potassium changes during heating have not been fully investigated. Such changes could be important in animals' responses to RFE and other modalities of heating, and should be studied in future.

Endocrine markers of severity and prognosis in critical illness

The cellular processes that unfold in critical illness involve a variety of circulating substances, that may provide clinically relevant insight into the severity and outcome. Among hormonal markers, cortisol, several thyroid-related substances, as well as natriuretic peptides are discussed in this review. Glucose and lipids constitute metabolic markers, the identification and treatment of the former has been of particular importance. Among immune markers, both proinflammatory and anti-inflammatory cytokines, such as interleukin-6, contribute essential prognostic information. Finally, the complement and coagulation pathways also provide unique insight into this complex and heterogeneous process.

THERAPEUTIC TREATMENT WITH L-ARGININE RESCUES MICE FROM HEAT STROKE-INDUCED DEATH: PHYSIOLOGICAL AND MOLECULAR MECHANISMS

Heat stroke-induced death is a major killer worldwide. Mice were subjected to acute heat stress by exposing them to whole-body hyperthermia (WBH) treatment and were used as a model to study heat stroke. Administration of L-arginine (L-arg, 120 mg/kg, i.p) 2 h after the cessation of WBH rescued the mice from heat-induced death and reduced the hypothermia. Heat shock protein 70 levels in the liver were increased significantly in heat-stressed mice administered L-arg compared with the heat-stressed group. WBH induced apoptosis, as indicated by DNA fragmentation, and increased levels of p53 and caspase-3 activity, which were significantly reduced by the administration of L-arg. The levels of inducible nitric oxide synthase in the liver, nitrite, and inflammatory cytokines like interleukin 1beta and tumor necrosis factor-alpha in the serum increased in WBH-treated mice. The levels of the above markers of heat stress significantly decreased in L-arg-treated mice. Kinin-B1 receptor (kinin-B1R) in cardiac tissue that is upregulated in heat stressed mice was significantly lower in L-arg-administered mice. These data suggest the potential use of L-arg, a nonessential amino acid that is used as an enteral diet supplement, to treat heat stroke-related injury when administered at the appropriate dose and time.

Construction of a whole-cell gene reporter for the fluorescent bioassay of nitrate

The development of a whole-cell fluorescence-based biosensor for nitrate is reported. The sensor is Escherichia coli transformed with a plasmid (pPNARGFP) in which the promoter and regulatory regions of the membrane-bound nitrate reductase narGHJI operon (Pnar) are fused to a gfp gene encoding green fluorescent protein (GFP). Pnar-gfp activity was measured at a range of nitrate concentrations using whole-cell GFP fluorescence. The bioassay conditions have been optimized so that the fluorescence intensity is proportional to the extracellular nitrate concentration. The developed bioassay has established that E. coli (pPNARGFP) can be used for the quantitative determination of nitrate in environmental waters without interference from other electron acceptors, e.g., nitrite, dimethyl sulfoxide, trimethylamine-N-oxide and fumerate, and azide, an inhibitor of redox-active proteins.

Pathogenesis of malaria and clinically similar conditions

There is now wide acceptance of the concept that the similarity between many acute infectious diseases, be they viral, bacterial, or parasitic in origin, is caused by the overproduction of inflammatory cytokines initiated when the organism interacts with the innate immune system. This is also true of certain noninfectious states, such as the tissue injury syndromes. This review discusses the historical origins of these ideas, which began with tumor necrosis factor (TNF) and spread from their origins in malaria research to other fields. As well the more established proinflammatory mediators, such as TNF, interleukin-1, and lymphotoxin, the roles of nitric oxide and carbon monoxide, which are chiefly inhibitory, are discussed. The established and potential roles of two more recently recognized contributors, overactivity of the enzyme poly(ADP-ribose) polymerase 1 (PARP-1) and the escape of high-mobility-group box 1 (HMGB1) protein from its normal location into the circulation, are also put in context. The pathogenesis of the disease caused by falciparum malaria is then considered in the light of what has been learned about the roles of these mediators in these other diseases, as well as in malaria itself.

Nitric Oxide Synthetic Capacity in Relation to Dialysate Temperature

BACKGROUND

During hemodialysis, vascular reactivity is impaired, which can be corrected by lowering dialysate temperature. It has also been shown that nitric oxide (NO) is related to intradialytic hypotension. As NO synthesis may be temperature-dependent, this study addressed the influence of dialysate temperature on the NO synthetic capacity of plasma.

METHODS

NO synthetic capacity was studied during hemodialysis with a dialysate temperature of 37.5 degrees C (dialysis-37.5 degrees C) and programmed extracorporeal blood cooling (cool dialysis; Blood Temperature Monitor; Fresenius C) in 12 stable patients. NO synthetic capacity was assessed ex vivo by [3H]L-citrulline formation from [3H]L-arginine in cultured endothelial cells after incubation with plasma samples obtained during the respective sessions.

RESULTS

Core temperature decreased (-0.32 +/- 0.10 degrees C) and energy transfer rate was significantly lower (-27.5 +/- 2.8 W; p < 0.05) during cool dialysis compared to dialysis-37.5 degrees C (0.19 +/- 0.06 degrees C and -0.8 +/- 1.2 W respectively; p < 0.05). Systolic blood pressure decreased during dialysis-37.5 degrees C (-19 +/- 4 mm Hg; p < 0.05), but not during cool dialysis (-6 +/- 5 mm Hg). NO synthetic capacity increased during dialysis-37.5 degrees C (55.5 +/- 9.3 to 73.5 +/- 10.2 pmol/10(5) cells; p < 0.05), in contrast to cool dialysis (67.3 +/- 11.1 to 66.2 +/- 10.8 pmol/10(5) cells).

CONCLUSION

The stimulatory effect of uremic plasma on endothelial NO synthesis was augmented during dialysis-37.5 degrees C but not during cool dialysis.

Aminoguanidine Protects Against Intracranial Hypertension and Cerebral Ischemic Injury in Experimental Heatstroke

The aim of the present study was to ascertain whether aminoguanidine attenuated intracranial hypertension and cerebral ischemic injury in experimental heatstroke. Urethane-anesthetized rats were exposed to heat stress (ambient temperature of 43 degrees C) to induce heatstroke. Control rats were exposed to 24 degrees C. Mean arterial pressure, cerebral perfusion pressure, and cerebral blood flow after the onset of heatstroke were all significantly lower than in control rats. However, colonic temperature, intracranial pressure, heart rate, cerebral inducible nitric oxide synthase (iNOS)-dependent NO, and neuronal damage score were greater after the onset of heatstroke. Aminoguanidine (30 micromol/kg, i.v.; 30 min before the start of heat exposure) pretreatment significantly attenuated the heatstroke-induced hyperthermia, arterial hypotension, intracranial hypertension, cerebral ischemia and neuronal damage, and increased iNOS-dependent NO formation in the brain. The extracellular concentrations of ischemic (e.g., glutamate and lactate/pyruvate ratio) and damage (e.g., glycerol) markers in the hypothalamus were also increased after the onset of heatstroke. Aminoguanidine pretreatment significantly attenuated the increase in hypothalamic ischemia and damage markers associated with heatstroke. Delaying onset of aminoguanidine administration (i.e., 0 or 30 min after the start of heat exposure) reduced the preventive efficiency on heatstroke-induced hyperthermia, arterial hypotension, intracranial hypertension, cerebral ischemia, and increased iNOS-dependent NO formation in brain. These results suggest that aminoguanidine protects against heatstroke-induced intracranial hypertension and cerebral ischemic injury by inhibition of cerebral iNOS-dependent NO production.

Naltrexone attenuates plasma nitric oxide release following acute heat stress

Previous studies have shown that naltrexone attenuates morbidity and mortality in heat stress by inhibiting endogenous opioids. In this study, we hypothesized that naltrexone can decrease heat stress by attenuating nitric oxide release. Male Sprague-Dawley rats were pretreated with naltrexone or normal saline, and exposed to 45 degrees C for 25 min; controls were exposed to 25 degrees C. Colonic temperatures were recorded and plasma samples from an in-dwelling i.v. cannula were analyzed for nitrate/nitrite levels. Following heat stress, peak colonic temperature was significantly diminished (P < 0.05) in naltrexone-treated rats compared to saline-treated rats. Plasma nitrate/nitrite levels were significantly lower (P < 0.05) in naltrexone-treated rats compared to saline-treated rats. These findings suggest that naltrexone is able to attenuate the rise in plasma nitric oxide levels commonly observed after heat stress.

Humoral markers of severity and prognosis of critical illness

Despite the considerable advances made in understanding the pathophysiology of systemic inflammation during critical illness, clinical progress has been elusive as it remains a very deadly condition. Cortisol and thyroid hormone levels can be as predictive of outcome as the commonly used severity parameters (i.e. APACHE). Indeed, levels of endocrine humoral substances such as arachidonic acids, nitric oxide, endothelin, calcitonin precursors, leptin and adenosine correlate with the severity and outcome of critical illness. Furthermore, calcitonin precursors represent a potentially new hormokine paradigm, being transcriptionally activated in all cells in response to infection. The cytokines are immune markers that often correlate with severity and outcome, but their release is transient. In contrast, the so-called acute phase proteins, such as C-reactive protein and serum amyloid A, are highly sensitive to inflammatory activity and can be important markers of severity and outcome. Leukocyte esterase, adhesion molecules, platelet activating factor and activated protein C are additional humoral immune markers; the replacement of the latter has been shown to be a promising therapeutic option. Natriuretic peptides are neurocrine humoral markers that have important cardiovascular implications. The level of macrophage migrating inhibitory factor, released by the pituitary, is elevated in sepsis and counteracts glucocorticoid action. Cellular markers to severe stress include the enhanced expression of protective substances in the form of heat shock proteins. High mobility group-1 is a DNA-binding protein and a late mediator of the inflammatory response. Apoptotic markers such as the soluble fas ligand are also elevated in inflammation. In summary, during critical illness, the endocrine, immune and nervous systems elaborate a multitude of humoral markers, the roles of which merit further scrutiny in order to improve therapeutic outcome.

Nitric oxide does not contribute to the hypotension of heatstroke

The purpose of this study was to determine whether nitric oxide (NO) contributes to the hypotensive state induced by prolonged environmental heat (EH) stress. Ketamine-anesthetized rats were instrumented for the measurement of arterial blood pressure, electrocardiogram, and temperature at four sites. Rats were exposed to EH (ambient temperature, 40 +/- 1 degrees C) until mean arterial blood pressure (MAP) decreased to 75 mmHg, which was arbitrarily defined as the induction of heatstroke. In addition to cardiovascular and temperature measurements, the time required to reach this MAP end point and the subsequent survival time were measured. In three separate experimental series, the competitive NO synthesis inhibitor N(omega)-nitro-L-arginine methyl ester (L-NAME) was administered (0, 10, or 100 mg/kg) either before, during (30 min after initiation of EH), or immediately after EH. L-NAME administered at any of these times transiently increased MAP. L-NAME infusion either before or during EH did not alter the EH time required to decrease MAP to 75 mmHg, but L-NAME pretreatment did decrease the colonic temperature at which this MAP end point was reached. L-NAME infusion before or after EH did not affect subsequent survival time, but L-NAME administered during EH significantly decreased survival time. The administration of L-NAME at any time point, therefore, did not prove beneficial in either preventing or reversing heatstroke. Taken together, these data suggest that NO does not mediate the hypotension associated with heatstroke.

Calor, exercício físico e hipertermia:

Semelhante às catástrofes provocadas pela natureza como terremotos e inundações, as ondas de calor geradas pelo aquecimento global também provocam muitas mortes. Em novembro passado, durante a terceira etapa de uma competição de Montain Bike dentro do Parque Nacional da Serra da Capivara (PI), uma competidora sentiuse mal, vindo a falecer após percorrer parte do trajeto sob sol forte a uma temperatura de aproximadamente 42°C. acredita-se que a causa tenha sido hipertermia. A hipertermia é o aumento da temperatura corporal por falência dos mecanismos de dissipação do calor, para se contrapor à febre onde há falência da regulação hipotalâmica. São cinco as formas de manifestação clínica: edema, cãibras, síncope, exaustão e hipertermia. Parece haver alguma relação entre hipertermia maligna e hipertermia por esforço. Apesar do grande número de mortes pouco se ouve falar sobre os riscos da hipertermia por exposição ao calor e menos ainda sobre a manifestação dos sintomas. Foram analisados os estudos que investigaram os fenômenos associados às doenças induzidas por calor e suas conseqüências no organismo. Para a localização dos artigos, foi criada uma estratégia de busca em bases de dados na Internet por meio de .palavras-chave., onde se estabeleceu a relação entre hipertermia e exercício.