QUANTITATIVE ASSESSMENT OF DEGENERATIVE CHANGES IN SOLEUS MUSCLE AFTER HINDLIMB SUSPENSION AND RECOVERY

The aim of this study was to quantify the degenerative and regenerativ e changes in rat soleus muscle resulting from 3-week hindlimb suspensi on at 45 degrees tilt (HS group, n = 8) and 4-week normal cage recover y (HS-R group, n = 7). Degenerative changes were quantified by microsc ope examination of muscle cross sections, and the myosin heavy chain ( MHC) composition of soleus muscles was studied by sodium dodecyl sulph ate polyacrylamide gel electrophoresis. At the end of 3-week hindlimb suspension, histological signs of muscle degenerative changes were det ected in soleus muscles. There was a significant variability in the pe rcentage of fibres referred to as degenerating (%dg) in individual ani mals in the I-IS group [%dg = 8.41 (SEM 0.5)%, range 4.66%-14.08%]. Mo reover. %dg varied significantly along the length of the soleus muscle . The percentage of fibres with internal nuclei was less than %dg in H S-soleus muscles [4.12 (SEM 0.3)%, range 1.24%-8.86%]. In 4-week recov ery rats, the greater part of the fibres that were not referred to as normal, retained central nuclei [15.8 (SEM 2.2)%, range 6.2%-21.1%]. A significant increase in the slow isoform of MHC was recorded in the H S-R rats, compared to muscles from age-matched rats (P < 0.01). These results would suggest that a cycle of myofibre degeneration-regenerati on occurred during HS and passive recovery, and that the increased acc umulation of slow MHC observed in soleus muscles after recovery from I -IS could be related to the prevalence of newly formed fibres.