[Ultrastructural changes in elements of skeletal muscle tissue during late ontogeny in the rat].

The mm. tibialis anterior, soleus and gastrocnemius have been studied electron microscopically in mature and old rats. In the skeletal muscle tissue of the old rats there are present unchanged, atrophied, degeneratively changed and hypertrophic muscle fibers. During the developmental course of the age changes the relationships between the energy-forming, protein-synthesizing and contractile structures are disturbed. Simultaneously with the distrophic and atrophic processes, compensatory-adaptive rearrangements of the ultrastructures develop in the fibers; they are directed to support the functional activity of the skeletal muscles. The ultramicroscopical changes of the histohematic barrier probably make one of the pathogenetic mechanisms presenting the base of the age changes in the skeletal muscle tissue.