Maintenance of myonuclear domain size in rat soleus after overload and growth hormone/IGF-I treatment.
The purpose of this study was to determine the effects of functional overload (FO) combined with growth hormone/insulin-like growth factor I (GH/IGF-I) administration on myonuclear number and domain size in rat soleus muscle fibers. Adult female rats underwent bilateral ablation of the plantaris and gastrocnemius muscles and, after 7 days of recovery, were injected three times daily for 14 days with GH/IGF-I (1 mg/kg each; FO + GH/IGF-I group) or saline vehicle (FO group). Intact rats receiving saline vehicle served as controls (Con group). Muscle wet weight was 32% greater in the FO than in the Con group: 162 +/- 8 vs. 123 +/- 16 mg. Muscle weight in the FO + GH/IGF-I group (196 +/- 14 mg) was 59 and 21% larger than in the Con and FO groups, respectively. Mean soleus fiber cross-sectional area of the FO + GH/IGF-I group (2,826 +/- 445 microm2) was increased compared with the Con (2,044 +/- 108 microm2) and FO (2,267 +/- 301 microm2) groups. The difference in fiber size between the FO and Con groups was not significant. Mean myonuclear number increased in FO (187 +/- 15 myonuclei/mm) and FO + GH/IGF-I (217 +/- 23 myonuclei/mm) rats compared with Con (155 +/- 12 myonuclei/mm) rats, although the difference between FO and FO + GH/IGF-I animals was not significant. The mean cytoplasmic volume per myonucleus (myonuclear domain) was similar across groups. These results demonstrate that the larger mean muscle weight and fiber cross-sectional area occurred when FO was combined with GH/IGF-I administration and that myonuclear number increased concomitantly with fiber volume. Thus there appears to be some mechanism(s) that maintains the myonuclear domain when a fiber hypertrophies.
McCall
G E
GE
Department of Physiological Science, California 94080, USA.
Allen
D L
DL
Linderman
J K
JK
Grindeland
R E
RE
Roy
R R
RR
Mukku
V R
VR
Edgerton
V R
VR
D000818:Animals; D002452:Cell Count; D002467:Cell Nucleus / Q000187:drug effects / Q000648:ultrastructure; D005260:Female; D013006:Growth Hormone / Q000494:pharmacology*; D007334:Insulin-Like Growth Factor I / Q000494:pharmacology*; D018485:Muscle Fibers, Skeletal / Q000187:drug effects / Q000502:physiology / Q000648:ultrastructure; D018482:Muscle, Skeletal / Q000187:drug effects / Q000502:physiology* / Q000648:ultrastructure; D009929:Organ Size / Q000187:drug effects; D005082:Physical Exertion / Q000502:physiology*; D051381:Rats; D017207:Rats, Sprague-Dawley
D007334:Insulin-Like Growth Factor I; D013006:Growth Hormone