Expression of heat shock protein 72 in atrophied rat skeletal muscles

Changes in the expression of heat shock protein 72 (HSP72) in response to a trophic-inducing perturbations of muscle involving chronic mechanical unloa ding and denervation were determined. Adult male Wistar rats were assigned randomly to a sedentary cage control (CON), hind limb unloading (HU, via ta il suspension), HU Plus tenotomy (HU + TEN), HU plus denervation (HU + DEN) , or HU + TEN + DEN group. Tenotomy and DEN involved cutting the Achilles t endon and removing a segment of the sciatic nerve, respectively. After 5 da ys, HSP72 levels in the soleus of the HU + DEN and HU + TEN + DEN groups we re 42 (P < 0.05) and 53% (P < 0.01) less than CON, respectively. Soleus wei ght decreased in both groups. neat shock protein 72 levels in the plantaris of the HU + TEN, HU + DEN, and HU + TEN + DEN groups were 31, 25, and 30% lower than CON, respectively(P < 0.05). Plantaris weight decreased in the H U + DEN and HU + TEN + DEN, but not in the HU + TEN group. Hind limb unload ing alone had little effect on the HSP72 level in either muscle. Reduced le vels of HSP72 were associated with a decreased soleus (r = 0.62, P < 0.01) and plantaris (r = 0.78, P < 0.001) weight. These results indicate that the levels of HSP72 in both a slow and a fast rat plantarflexor are responsive to a chronic decrease in the levels of loading and/or activation and sugge st that the neuromuscular activity level and the presence of innervation of a muscle are important factors that induce HSP72 expression.