Growth hormone, IGF-I, and exercise effects on non-weight-bearing fast muscles of hypophysectomized rats.
The effects of growth hormone (GH) or insulin-like growth factor I (IGF-I) with or without exercise (ladder climbing) in countering the effects of unweighting on fast muscles of hypophysectomized rats during 10 days of hindlimb suspension were determined. Compared with untreated suspended rats, muscle weights were 16-29% larger in GH-treated and 5-15% larger in IGF-I-treated suspended rats. Exercise alone had no effect on muscle weights. Compared with ambulatory control, the medial gastrocnemius weight in suspended, exercised rats was larger after GH treatment and maintained with IGF-I treatment. The combination of GH or IGF-I plus exercise in suspended rats resulted in an increase in size of each predominant fiber type, i.e., types I, I + IIa and IIa + IIx, in the medial gastrocnemius compared with untreated suspended rats. Normal ambulation or exercise during suspension increased the proportion of fibers expressing embryonic myosin heavy chain in hypophysectomized rats. The phenotype of the medial gastrocnemius was minimally affected by GH, IGF-I, and/or exercise. These results show that there is an IGF-I, as well as a GH, and exercise interactive effect in maintaining medial gastrocnemius fiber size in suspended hypophysectomized rats.
Grossman
E J
EJ
Life Science Division, National Aeronautics and Space Administration-Ames Research Center, Moffett Field 94035, USA.
Grindeland
R E
RE
Roy
R R
RR
Talmadge
R J
RJ
Evans
J
J
Edgerton
V R
VR
D000818:Animals; D001835:Body Weight / Q000502:physiology; D013006:Growth Hormone / Q000097:blood*; D006132:Growth Plate / Q000648:ultrastructure; D019417:Hindlimb Suspension; D007016:Hypophysectomy; D007150:Immunohistochemistry; D007334:Insulin-Like Growth Factor I / Q000378:metabolism*; D008297:Male; D018656:Muscle Fibers, Fast-Twitch / Q000378:metabolism / Q000502:physiology* / Q000648:ultrastructure; D009124:Muscle Proteins / Q000378:metabolism; D018482:Muscle, Skeletal / Q000378:metabolism / Q000502:physiology* / Q000648:ultrastructure; D018995:Myosin Heavy Chains / Q000378:metabolism; D009929:Organ Size / Q000502:physiology; D005082:Physical Exertion / Q000502:physiology*; D051381:Rats; D013977:Tibia / Q000254:growth & development
D009124:Muscle Proteins; D007334:Insulin-Like Growth Factor I; D013006:Growth Hormone; D018995:Myosin Heavy Chains