Effects of combination treatment with dexamethasone and mannitol on neuronal damage and survival in experimental heat stroke

Heat stroke alters hippocampal and cerebellar transmitter metabonomics

BACKGROUND

The mechanisms underlying heat stroke (HS)-induced hippocampal injury remain unclear. This study aimed to evaluate the HS-induced metabonomics of hippocampal and cerebellar transmitters.

METHODS

The HS model was established with male Sprague-Dawley rats subjected to heat exposure of up to 42 °C at a humidity of (55.0±5.0)%. The hippocampal and cerebellar transmitters and metabolites of rats were tested via ultra-high-performance liquid chromatography-mass spectrometry (UPLC-MS/MS). The primary transmitters and metabolites were identified by principal component analysis (PCA) and orthogonal partial least square-discriminant analysis (OPLS-DA). The major metabolic pathways for HS were selected after enrichment. The brain injury was evaluated by histological tests.

RESULTS

HS induced hippocampal and cerebellar injuries in rats. HS upregulated the protein levels of hippocampal glutamate, glutamine, gamma-aminobutyric acid, L-tryptophan (Trp), 5-hydroxy-indoleacetic acid, and kynurenine; however, it downregulated asparagine, tryptamine, 5-hydroxytryptophan, melatonin, 3,4-dihydroxyphenylalanine (L-DOPA), and vanillylmandelic acid. HS also sharply elevated the protein levels of cerebellar methionine and Trp, and decreased the levels of serotonin, L-alanine, L-asparagine, L-aspartate, cysteine, norepinephrine, spermine, spermidine, and tyrosine. Hippocampal glutamate, monoamine transmitters, cerebellar aspartate acid, and catecholamine transmitters' metabolic pathways were identified as the main metablic pathways in HS.

CONCLUSION

The hippocampus and cerebellum were injured in rats with HS, possibly induced the disorder of hippocampal glutamate and serotonin metabolism, cerebellar aspartate acid and catecholamine transmitter metabolism, and related metabolic pathways.

The efficacy of steroids in reducing morbidity and mortality from extreme hyperthermia and heatstroke-A systematic review

Severe hyperthermia from classical or exertional heatstroke, or from drug ingestion or other noninfective pyrogens, is associated with a high mortality and morbidity. A systemic pro-inflammatory response occurs during heatstroke, characterized by elevated cytokines with endotoxemia from elevated lipopolysaccharide (LPS) levels. Corticosteroids reduce LPS and cytokine levels, suggesting that they may improve outcome. A systematic review searching Embase, MEDLINE, and PubMed from the earliest date available until September 2019 was conducted, according to the PRISMA guidelines, with five papers identified. In four studies, systemic steroids administered before or at the onset of heat stress improved mortality or reduced organ dysfunction. Survival time was greatest when steroid administration preceded heat stress. In one study, a nonsignificant increase in mortality was seen. A dose response was observed, with higher doses extending survival time. Animal studies suggest that steroids improve mortality and/or organ dysfunction after an episode of heat stress or extreme hyperthermia.

The pathophysiological basis and consequences of fever

There are numerous causes of a raised core temperature. A fever occurring in sepsis may be associated with a survival benefit. However, this is not the case for non-infective triggers. Where heat generation exceeds heat loss and the core temperature rises above that set by the hypothalamus, a combination of cellular, local, organ-specific, and systemic effects occurs and puts the individual at risk of both short-term and long-term dysfunction which, if severe or sustained, may lead to death. This narrative review is part of a series that will outline the pathophysiology of pyrogenic and non-pyrogenic fever, concentrating primarily on the pathophysiology of non-septic causes.

Dexamethasone improves heat stroke-induced multiorgan dysfunction and damage in rats

Dexamethasone (DXM) is known as an immunosuppressive drug used for inflammation control. In the present study, we attempted to examine whether DXM administration could attenuate the hypercoagulable state and the overproduction of pro-inflammatory cytokines, improve arterial hypotension, cerebral ischemia and damage, and vital organ failure in a rat model of heat stroke. The results indicated that all the rats suffering from heat stroke showed high serum levels of tumor necrosis factor-α (TNF-α) and interleukin-1β (IL-1β), accompanied with increased prothrombin time, activated partial thromboplastin time and D-D dimer, and decreased protein C. During the induction period of heat stroke, plasma levels of blood urea nitrogen (BUN), creatinine, glutamic oxaloacetic transaminase (SGOT), glutamic pyruvic transaminase (SGPT), and alkaline phosphatase (ALP), were consistently increased. High striatal levels of glycerol, glutamate, and lactate/pyruvate were simultaneously detected. On the contrary, the mean arterial pressure, plasma levels of interleukin-10 (IL-10), and local cerebral blood flow at the striatum were all decreased. Importantly, intravenous administration of DXM substantially ameliorated the circulatory dysfunction, systematic inflammation, hypercoagulable state, cerebral ischemia and damage during the induction period of heat stroke. These findings demonstrated that DXM may be an alternative therapy that can ameliorate heat stroke victims by attenuating activated coagulation, systemic inflammation, and vital organ ischemia/injury during heat stroke.

Heatstroke model for desert dry-heat environment and observed organ damage

BACKGROUND

Heatstroke is one of the most common clinical emergencies. Heatstroke that occurred in a dry-heat environment such as desert is usually more seriously effective and often leads to death. However, the report of the pathophysiologic mechanisms about heatstroke in dry-heat environment of desert has not been seen.

OBJECTIVES

Our objectives are to establish a rat model of heatstroke of dry-heat environment of desert, to assess the different degrees of damage of organ, and to preliminarily discuss the mechanism of heatstroke in dry-heat environment of desert.

METHODS

The first step, we have established a rat heatstroke model of dry heat environment of desert. The second step, we have accessed changes in morphology and blood indicators of heatstroke rats in dry-heat environment of desert.

RESULTS

The heatstroke rats have expressed the changing characteristics of mean arterial pressure, core temperature, and heart rate. The organ damage changed from mild to serious level, specifically in the morphology and blood enzymology parameters such as alanine aminotransferase, aspartate aminotransferase, creatinine, urea, uric acid, creatine kinase-MB, creatine kinase, and blood gas parameters such as base excess extracellular fluid and bicarbonate ions (HCO3-).

CONCLUSIONS

We have successfully established the rat heatstroke model of dry-heat environment of desert. We have identified heatstroke rats that presented changing characteristics on physiological indicators and varying degrees of organ damage, which are aggravated by the evolution of heatstroke in dry-heat environment of desert. We have preliminarily discussed the mechanism of heatstroke in dry-heat environment of desert.

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.