The purpose of this study was to determine the effect of heat stress on denervation-induced muscle dysfunction. Sixteen male Lewis rats (8 wk old) were assigned to randomly to a control (C), control with heat stress (CH), denervation (D), or denervation with heat stress (DH) group. Hindlimb of animals in the CH and DH groups were exposed to heated water at 42°C for 50 min. Twenty-four hours after heat stress, both D and DH groups were subjected to bilateral denervation of sciatic nerve. After 2 days of denervation, extensor digitorum longus (EDL) and soleus muscles were removed and analyzed for force production and the levels of heat shock protein (Hsp). Compared with C group, the twitch and tetanic force per crosssectional area were markedly decreased in the EDL and soleus muscle from both the D and DH groups. There was no difference in the specific force production between D and DH animals. The relative content of Hsp72 in the EDL muscle was markedly elevated in both the CH and DH groups, while the levels of Hsp25 and α B-crystallin were increased in both the D and DH groups. In contrast, the expression levels of these Hsps in the soleus muscle were not different between the groups. These data suggest that upregulation of Hsp72 by prior heat stress may not ameliorate denervation-induced muscle dysfunction, at least in fast-twitch skeletal muscle.

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