Differential expression of stress proteins in rat myocardium after free wheel or treadmill run training

High intensity treadmill exercise increases the expression of a cardioprote ctive, inducible 72-kDa stress protein (SP72) in cardiac muscle. This inves tigation examined whether voluntary free wheel exercise training would be s ufficient to confer a similar response. Male Sprague-Dawley rats were rando mly assigned to either treadmill (TM-Tr) or free wheel (FW-Tr) training gro ups. By the end of the 8-wk training period, TM-Tr animals ran 1 h/day, 5 d ays/wk up a 10% grade, covering a distance of 8,282 m/wk. FW-Tr rats ran, o n average, 5,300 m/wk, with one-third of the animals covering distances sim ilar to those for the TM-Tr group. At the time of death, hearts of trained and caged sedentary control (Sed) animals were divided into left (LV) and r ight (RV) ventricles. Citrate synthase activity and the relative immunoblot contents of SP72, SP73 (the constitutive isoform of the SP70 family), and a 75-kDa mitochondrial chaperone (SP75) were subsequently determined. LV an d RV did not differ on any measure, and SP73, SP75, and citrate synthase we re not affected by training. Cardiac SP72 levels were elevated over fourfol d in both ventricles of TM-Tr compared with RV of FW-Sed rats. Despite the animals having run a similar total distance, cardiac SP72 content in FW-Tr rats was not different from that in Sed animals. These data indicate that v oluntary exercise training is insufficient to elicit an elevation of SP72 i n rat heart and suggest that exercise intensity may be a critical factor in evoking the cardioprotective SP72 response.