[Muscle atrophy in microgravity and during its simulation]

Summarized are the results of comparative analysis of morphological changes in rat's skeletal muscles after microgravity and its simulation. On completion of space flight, hindlimb muscles of rats exhibited atrophy developed in space microgravity in consequence of the lack of weight-bearing loads and changes solely in the slow anti-g muscles due to the hemodynamic disorders appearing after space flight. Immobilization combined with clinostatting cannot be a veridical laboratory model of microgravity, as horizontally positioned animals still possess weight and, besides, experience severe chronic stress of immobilization. Tail suspension with the head-end permanently down and the hind limbs out of use appeared the most demonstrative model of the space microgravity effects. With this model, the hindlimb muscles underwent changes identical to what had been observed in space flown animals. Data of the simulation studies suggest stabilization of muscle atrophy at a certain level and an earlier and stronger reaction to the hindlimb unloading in young rats as compared to old animals. Skeletal muscles in females and males responded to suspension similarly in spite of difference in the hormonal status.