[A morphological study of skeletal muscles of rats flown aboard the space laboratory SLS-2]

M. soleus and m. gastrocnemius in rats flown aboard SLS-2 during 14 days have been studied histologically and electron-microscopically. It is found that the stay in a weightless environment causes muscular atrophy which is more pronounced in m. soleus. In rats killed on Day 13 of the flight and in five hours post-flight the morphological picture of the muscles was similar although in rats killed postflight the number of dystrophic changed fibers was greater. The availability of the active satellite cells, myoblasts and muscular tubes was indicative of a preserved regenerative capacity of the muscles. After a lapse of 14 days of readaptation to terrestrial gravity the size of muscular fibers in the rats of flight group has reached the level of control animals although the contractile apparatus of m. soleus did not restore completely. In the rats of this group m. soleus had the foci of small newly forming muscular fibers evidently appeared at the sites of fiber destruction as a result of hemodynamic disorders accompanying the transition from microgravity to terrestrial gravitation. Total number and number of functioning capillaries in the rats of flight groups did not change.