Myocardial structure and functional alterations in a preclinical model of exertional heat stroke

Aim: Relatively little information is available about the effect of an acute exertional heat stroke (EHS) on myocardium structure and function. Herein, we used a survival male rat model of EHS to answer the question. Main methods: Adult male Wistar rats underwent forced treadmill running at a 36 degrees C room temperature and 50 % relative humidity until EHS onset, characterized by hyperthermia and collapse. All rats that were followed for 14 days survived. Injury severity scores of both gastrocnemius and myocardium were determined histologically. Following an EHS event, pathological echocardiography, skeletal muscle and myocardial damage scores and indicators, myocardial fibrosis, hypertrophy, and autophagy were elucidated. Key findings: Rats with EHS onset displayed skeletal muscle damage, elevated serum levels of skeletal muscle damage indicators (e.g., creatinine kinase, myoglobin, and potassium), and myocardial injury indicators (e.g., cardiac troponin I, creatinine kinase, and lactate dehydrogenase) returning to homeostasis within 3 days postEHS. However, EHS-induced myocardial damage, pathological echocardiography, myocardial fibrosis, hypertrophy, and deposited misfolded proteins lasted up to 14 days post-EHS at least. Significance: First, we provide evidence to confirm that despite the apparent return to homeostasis, underlying processes may still be ongoing after EHS onset. Second, we provide several key findings emphasizing the pathophysiology and risk factors of EHS, highlighting gaps in knowledge with the aim of stimulating future studies.