Response of heat shock protein 72 to repeated bouts of hyperthermia in rat skeletal muscle.

We investigated the effects of repeated hyperthermic bouts on the heat shock response of heat shock protein (HSP) 72 in skeletal muscle. Rats were assigned to control and hyperthermia groups which were exposed to heated water at 42 °C. The hyperthermia group was further divided into sub-groups: a single bout (H30) or four bouts of hyperthermia for 30 min (H30x4). There was an increase in HSP72 protein content of the H30 groups in both extensor digitorum longus (EDL) and soleus muscles. Moreover, HSP72 protein expression in H30x4 group was significantly higher than in H30 group in both EDL and soleus muscles. The HSP72 mRNA was markedly increased from control levels in the H30 and H30x4 group in both types of muscles. However, HSP72 mRNA of the H30x4 group was lower than that of the H30 group in soleus muscles. Heat shock response of HSP72 is activated even after repeated bouts of hyperthermia, with a differential regulation between muscle types.