Exercise pretraining protects against heatstroke-induced cerebral ischemia in rats

Yu-Wen Chen ¹, Sheng-Hsien Chen ¹, Willy Chou ², Yi-Ming Lo ², Ching-Hsia Hung ^3* and Mao-Tsun Lin ¹

¹ Department of Medical Research, Chi Mei Medical Center, Taiwan
² Department of Rehabilitation Medicine, Chi Mei Medical Center, Taiwan
³ Department of Physical Therapy, National Cheng Kung University, Taiwan

^* To whom correspondence should be addressed. E-mail: chhung{at}mail.ncku.edu.tw.

Accepted 27 April 2007

Abstract

Background: In the rat brain, heatstroke-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 heatstroke-induced cerebral ischemia and injury.

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

Results: Three weeks of progressive exercise pretreatment induced HSP72 preconditioning in the brain and conferred significant protection against heatstroke-induced hyperthermia, arterial hypotension, cerebral ischemia and neuronal damage; it also prolonged animal survival.

Conclusions: Exercise for 3 weeks can improve heat tolerance as well as attenuate heatstroke-induced cerebral ischemia in rats. The maintenance of appropriate levels of MAP and CBF in the rat brain may be related to the overexpression of HSP72.

Key Words: brain damage, exercise training, heat shock protein 72, heat stress, hyperthermia

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