Abstract
We previously reported that heat-shock protein (HSP) 70 content decreased in the soleus muscle atrophied by unloading and that such a decrease was inhibited by isometric resistance exercise (IRE) during unloaded condition. The present study was designed to investigate age-associated effect of IRE on preservation of muscle mass and HSP70 expression. Fischer-344 female rats (4-, 10-, and 20-month old) were assigned to either of control or hindlimb-unloaded (HU) group. Rats of HU group had their hindlimbs suspended for 3 weeks with or without IRE. IRE (stationary support on a flat wire mesh with 60~80 degree incline) was done for 30 min a day, 6 days a week, with an additional load of 30% body mass to the tail during HU period. Maximum force and myofibrillar protein content, and HSP70 were measured in the soleus muscle. Maximum force and myofibrillar protein content decreased significantly with HU and the degree of these decreases was greater with ageing. IRE inhibits these decreases by HU, but the inhibitory effect of IRE became lesser with advancing age. HSP70 content decreased by HU irrespective of age. IRE prevented decreases in HSP70 content and inhibitory effect of IRE became greater with aging. These findings demonstrate that preventive effect of IRE on muscle atrophy is associated with HSP70 expression but this interrelation is disturbed with aging. [Jpn J Physiol 54 Suppl:S239 (2004)]
