Heat-stress enhances proliferative potential in rat soleus muscle

The effects of heat-stress on proliferative potential in vivo were studied in rat skeletal muscle. Male Wistar rats (7-weeks-old) were divided into two groups: control (n=24) and heat-stressed (n=24). Rats in the experimental group were exposed to environmental heat-stress (41 degrees C for 60 min) in a heat chamber without anesthesia. The soleus muscles were dissected 1, 7, and 14 days after the heat exposure. The wet and dry weights of soleus muscle relative to body weight in the heat-stressed group were significantly higher than controls 7 days after the exposure (10.1% and 17.5%, respectively, p <0.05). The distribution of 5-bromo-2'-deoxyuridine and proliferating cell nuclear antigen-positive nuclei, that are the indicators for the cell proliferation, were increased by 2.2 and 5.1 times, respectively 1 day after heating (p <0.05). The expressions of heat shock protein 72 (58.0%) and phosphorylated p70S6 kinase (52.3%) were increased 1 day following heat exposure (p <0.05). These results suggest that heat-stress could promote the cell proliferation and induce muscular hypertrophy.