Short- and long-term swimming exercise training increases myocardial insulin-like growth factor-I gene expression.
OBJECTIVES. We investigated the effect of short- and long-term swimming exercise, with or without insulin-like growth factor (IGF)-I administration, on the expression of myocardial IGFs and contractile proteins.


METHODS
Sprague-Dawley male rats (n=36) were subjected to swimming exercise for 2 or 6 weeks. IGF-I (0.5mg/rat) was administered continuously for 1 week, using alzet osmotic pumps. Control groups remained sedentary. IGF-I, IGF-I receptor (IGF-IR), IGF-II, skeletal alpha-actin (sk-actin), and beta myosin heavy chain (beta MHC) mRNAs were measured using Northern blot analysis and RT-PCR.


RESULTS
A significant 2-fold increase in myocardial IGF-I mRNA was found after 2 and 6 weeks of swimming in both IGF-I treated and untreated rats (p<0.001). IGF-IR mRNA was significantly (p<0.05) increased after 6 weeks of training only in the IGF-I treated animals. IGF-II mRNA remained unchanged at all time points. While beta MHC mRNA was significantly decreased (p=0.003) at 2 and 6 weeks, sk-actin mRNA remained unchanged.


CONCLUSIONS
Short- and long-term swimming exercise training increase myocardial expression of IGF-I mRNA. Exogenous administration of IGF-I, during the first week of the exercise session, did not produce any effect on myocardial IGF-I but was associated with increased IGF-IR signal after the long-term exercise training. These data suggest a relationship between IGF-I expression and cardiac adaptation to exercise training.
Scheinowitz
M
M
The Neufeld Cardiac Research Institute, Sheba Medical Center and Department of Biomedical Engineering, Tel-Aviv University, Tel-Hashomer 52621, Israel. mickeys@post.tau.ac.il
Kessler-Icekson
G
G
Freimann
S
S
Zimmermann
R
R
Schaper
W
W
Golomb
E
E
Savion
N
N
Eldar
M
M
D000199:Actins / Q000235:genetics / Q000378:metabolism; D000818:Animals; D015152:Blotting, Northern; D017931:DNA Primers / Q000737:chemistry; D005786:Gene Expression Regulation; D006321:Heart; D007334:Insulin-Like Growth Factor I / Q000008:administration & dosage / Q000235:genetics*; D007335:Insulin-Like Growth Factor II / Q000235:genetics / Q000378:metabolism; D008297:Male; D018482:Muscle, Skeletal / Q000378:metabolism; D009132:Muscles / Q000378:metabolism; D009206:Myocardium / Q000378:metabolism*; D018995:Myosin Heavy Chains / Q000235:genetics / Q000378:metabolism; D010805:Physical Conditioning, Animal; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D017526:Receptor, IGF Type 1 / Q000235:genetics / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013550:Swimming
D000199:Actins; D017931:DNA Primers; D012333:RNA, Messenger; D007334:Insulin-Like Growth Factor I; D007335:Insulin-Like Growth Factor II; D017526:Receptor, IGF Type 1; D018995:Myosin Heavy Chains