Muscle regeneration during hindlimb unloading results in a reduction in muscle size after reloading.
The hindlimb-unloading model was used to study the ability of muscle injured in a weightless environment to recover after reloading. Satellite cell mitotic activity and DNA unit size were determined in injured and intact soleus muscles from hindlimb-unloaded and age-matched weight-bearing rats at the conclusion of 28 days of hindlimb unloading, 2 wk after reloading, and 9 wk after reloading. The body weights of hindlimb-unloaded rats were significantly (P < 0.05) less than those of weight-bearing rats at the conclusion of hindlimb unloading, but they were the same (P > 0.05) as those of weight-bearing rats 2 and 9 wk after reloading. The soleus muscle weight, soleus muscle weight-to-body weight ratio, myofiber diameter, number of nuclei per millimeter, and DNA unit size were significantly (P < 0.05) smaller for the injured soleus muscles from hindlimb-unloaded rats than for the soleus muscles from weight-bearing rats at each recovery time. Satellite cell mitotic activity was significantly (P < 0.05) higher in the injured soleus muscles from hindlimb-unloaded rats than from weight-bearing rats 2 wk after reloading, but it was the same (P > 0.05) as in the injured soleus muscles from weight-bearing rats 9 wk after reloading. The injured soleus muscles from hindlimb-unloaded rats failed to achieve weight-bearing muscle size 9 wk after reloading, because incomplete compensation for the decrease in myonuclear accretion and DNA unit size expansion occurred during the unloading period.
Mozdziak
P E
PE
Department of Poultry Science, North Carolina State University, Raleigh, North Carolina 27695, USA. pemozdzi@unity.ncsu.edu
Pulvermacher
P M
PM
Schultz
E
E
D000818:Animals; D002467:Cell Nucleus / Q000648:ultrastructure; D004247:DNA / Q000235:genetics; D019417:Hindlimb Suspension; D008297:Male; D008938:Mitosis; D024510:Muscle Development; D018482:Muscle, Skeletal / Q000033:anatomy & histology* / Q000166:cytology / Q000254:growth & development / Q000502:physiology*; D009929:Organ Size; D051381:Rats; D017207:Rats, Sprague-Dawley; D012038:Regeneration / Q000502:physiology*
D004247:DNA