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The effect of limb immobilization on muscle wasting and recovery of young and old rats was studied. Limb immobilization caused rapid and pronounced muscle weight loss, which was overcome efficiently in the muscles of young animals. However, muscles of old animals did not recover as well, indicating that muscle turnover (degradation and synthesis of proteins) is slower in old muscles than in young ones. The mechanisms of muscle wasting due to immobilization may involve two stages, the fast phase employing calciumdependent proteolysis and the slower phase recruiting the lysosomal and ubiquitin-proteosome systems. The slow phase most probably involves the penetration of white cells between the muscle fibers and involves the secretion of cytokines that mediate a cascade of intracellular events, which culminates in muscle protein degradation. Thus, it was shown in our study and in other similar reports that through the influence of TNF-α α α α and an increase in oxidative stress, there is marked activation of transcription factor NF-κ κ κ κB, which in turn induces many proteins to carry the signals that eventually result in protein breakdown. Because protein turnover was shown to slow down with age, it will be of great interest to study these events in aging muscles and to try to ascertain the specific events that make protein breakdown in aged muscles different from that in young ones.

We immobilised the right hindlimbs of six-month-old female Wistar rats for four weeks using a biplanar external fixation bridging the knee. The untreated left limbs served as a control group. An additional group of rats was allowed to recover for four weeks after removal of the frame. Immobilisation caused reduction in the wet weights of approximately 50% in the gastrocnemius, quadriceps, soleus and plantaris muscles; this was not restored completely after remobilisation. There was an increase in the activity of acid phosphatase of approximately 85% in the gastrocnemius and quadriceps muscles whereas that of creatine phosphokinase was reduced by about 40%. These values returned to nearly normal after remobilisation. Histological and ultrastructural examination showed a marked myopathy of the gastrocnemius muscle after immobilisation although the morphology was largely restored after remobilisation. We conclude that after four weeks of remobilisation, hind-limb muscles do not return to preimmobilisation weights, although biochemical activities and ultrastructural appearance are largely restored.

We immobilised the right hindlimbs of six-month-old female Wistar rats for four weeks using a biplanar external fixation bridging the knee. The untreated left limbs served as a control group. An additional group of rats was allowed to recover for four weeks after removal of the frame. Immobilisation caused reduction in the wet weights of approximately 50% in the gastrocnemius, quadriceps, soleus and plantaris muscles; this was not restored completely after remobilisation. There was an increase in the activity of acid phosphatase of approximately 85% in the gastrocnemius and quadriceps muscles whereas that of creatine phosphokinase was reduced by about 40%. These values returned to nearly normal after remobilisation. Histological and ultrastructural examination showed a marked myopathy of the gastrocnemius muscle after immobilisation although the morphology was largely restored after remobilisation. We conclude that after four weeks of remobilisation, hind-limb muscles do not return to preimmobilisation weights, although biochemical activities and ultrastructural appearance are largely restored.