Effect of training and growth hormone suppression on insulin-like growth factor I mRNA in young rats.
The growth hormone (GH)-insulin-like growth factor I (IGF-I) axis plays a role in the adaptation to exercise training, but IGF-I gene expression in response to exercise training and GH suppression has not been studied. Twenty female rates underwent a 4-wk treadmill training program begun in the prepubertal period (day 14 of life). In 10 of the training rats, GH production was suppressed by anti-GH-releasing hormone antibodies (GH suppressed). IGF-I mRNA and protein levels were measured in liver and hindlimb skeletal muscle. GH suppression reduced IGF-I mRNA expression in the liver to a much greater extent than in the muscle. In the GH control rats, training induced significant increases in hepatic exon 1-derived IGF-I mRNA (mean increase 30%; P < 0.05) and muscle exon 2-derived mRNA (mean increase 35%; P < 0.05). In the GH-suppressed rats, only muscle exon 1-derived transcripts were significantly increased by training (55%; P < 0.05) and this was associated with a significant increase in muscle IGF-I protein levels (P < 0.05). We speculate that the anabolic response to training may involve both GH-dependent increases in IGF-I mRNA in the liver and GH-independent increases in the muscle.
Zanconato
S
S
Department of Pediatrics, Harbor-University of California Los Angeles Medical Center, Torrance 90509.
Moromisato
D Y
DY
Moromisato
M Y
MY
Woods
J
J
Brasel
J A
JA
Leroith
D
D
Roberts
C T
CT
Cooper
D M
DM
D000199:Actins / Q000378:metabolism; D000818:Animals; D001345:Autoradiography; D005260:Female; D015870:Gene Expression; D013006:Growth Hormone / Q000037:antagonists & inhibitors*; D007334:Insulin-Like Growth Factor I / Q000096:biosynthesis*; D008099:Liver / Q000378:metabolism; D009124:Muscle Proteins / Q000378:metabolism; D009132:Muscles / Q000378:metabolism; D009693:Nucleic Acid Hybridization; D010805:Physical Conditioning, Animal; D012333:RNA, Messenger / Q000096:biosynthesis*; D051381:Rats; D017207:Rats, Sprague-Dawley; D012260:Ribonucleases / Q000378:metabolism
D000199:Actins; D009124:Muscle Proteins; D012333:RNA, Messenger; D007334:Insulin-Like Growth Factor I; D013006:Growth Hormone; D012260:Ribonucleases