EFFECT OF INCREASED PHYSICAL-ACTIVITY ON GROWTH AND DIFFERENTIATION OF REGENERATING RAT SOLEUS MUSCLE

Our purpose was to determine the effect of physical exercise on growth and differentiation during regeneration of a slow-twitch muscle. Dege neration/regeneration of the left soleus muscles of Wistar female rats was induced by injection of a snake venom. Muscular differentiation w as studied by monitoring the sequential expression of the various myos in heavy chain isoforms (MHCs). Rats were assigned to one of two group s: cage sedentary (n = 14) or exercised (n = 16). The exercise program me began 1-day post-injection and the rats ran 1 h/day on a motorized treadmill. Then, 9 and 25 days after venom treatment, the soleus MHC p henotype as determined by immunohistology, electrophoresis and immunob lotting, was studied. At 25 days the expression of MHCs by regeneratin g soleus was not changed by the increased level of physical activity ( P > 0.05). Exercised and sedentary regenerating muscles contained simi lar numbers of type-I fibres (100% of total fibres), levels of MHC-1 ( 85.4 and 89.5% of total MHCs), MHC-2a and M/HC-2x/d and their fibres e xpressed MHC-1 (100% of total fibres) and MHC-2 (45-50%) in the same w ay. Moreover, the masses of regenerating and nonregenerating soleus we re significantly increased by physical exercise (P < 0.02). At 9 days no effect of muscular exercise was found. In conclusion, endurance exe rcise did not alter differentiation of regenerating soleus. Moreover r egenerating soleus can respond to increased physical activity by enhan cing its mass in the same way as mature muscle.