Recovery of muscles of old rats after hindlimb immobilisation by external fixation is impaired compared with those of young rats

The right hindlimbs of 24-month-old female Wistar rats were immobilised for 4 weeks using external fixation of the knee joint. In a further group, after the external fixation was removed, the rats were allowed to remobilise for an additional 4 weeks. Hindlimb immobilisation for 4 weeks caused a 32-42% reduction in wet weights of the hindlimb muscles of the rats as compared to those of the contralateral non-immobilised legs. After 4 weeks of remobilisation the hindlimb muscles had not returned to the "control" weights. Biochemical changes in the gastrocnemius muscle resulting from the external fixation showed greatly elevated acid phosphatase activities (33.2%) and markedly reduced creatine phosphokinase activities (17.2%), which did not recover to preimmobilisation values after 4 weeks of remobilisation. Light and transmission electron microscopy showed that remobilisation for 4 weeks (after external fixation) resulted in only partial morphological restoration of the damage to the muscles in these aged rats. A comparison of similar hindlimb external fixation and remobilisation in young (6 months old) rats showed that remobilisation caused a substantial recovery in biochemical parameters in both age groups, with the muscles of the young group (but not the old group) often reaching almost complete recovery accompanied by morphological restoration. We conclude that the net gain in the recovery period of biochemical and morphological parameters is significantly greater in the young rats compared to the old rats indicating that muscle metabolism and capacity for recovery from disuse atrophy is impaired with ageing. (C) 2001 Elsevier Science Inc. All rights reserved.