title: Increase in muscle IGF-I protein but not IGF-I mRNA after 5 days of endurance training in young rats.
abstract: Five days of treadmill training in rats leads to increased muscle size and running time. This was used to examine the effect of exercise on circulating insulin-like growth factor I [IGF-I; radioimmunoassay (RIA)], local muscle (hindlimb) IGF-I (by RIA), and muscle IGF-I mRNA (by ribonuclease protection assay). Eight-week-old female Sprague-Dawley rats were divided into three groups: control (n = 10); single-exercise test (n = 10), untrained but with one maximal exercise test at the end of the study; and training (n = 16), trained for 5 days and one maximal exercise test on day 6. There were no differences among the groups with respect to circulating IGF-I. Muscle IGF-I protein in trained rats (4.2 +/- 1.5 ng/g of muscle tissue) was significantly greater than both control (0.27 +/- 0.1 ng/g) and single-exercise test (0.62 +/- 0.19 ng/g, P < 0.05 by analysis of variance). There was no difference among the groups in IGF-I mRNA gene expression. These data suggest that there is an early, marked, local muscle increase in IGF-I protein in response to exercise. This increase, however, may not be related to increased muscle IGF-I gene expression. Moreover, the IGF-I response was probably local in nature since it was not matched by any increase in circulating IGF-I.
authors.affiliation: Department of Research, Connecticut Children's Medical Center, University of Connecticut Health Center, Hartford 06106, USA.
authors.forename: A
authors.initials: A
authors.lastname: Eliakim
authors.forename: M
authors.initials: M
authors.lastname: Moromisato
authors.forename: D
authors.initials: D
authors.lastname: Moromisato
authors.forename: J A
authors.initials: JA
authors.lastname: Brasel
authors.forename: C
authors.initials: C
authors.lastname: Roberts
authors.forename: D M
authors.initials: DM
authors.lastname: Cooper
mesh_terms: D000818:Animals; D005260:Female; D013006:Growth Hormone / Q000097:blood; D007334:Insulin-Like Growth Factor I / Q000235:genetics* / Q000378:metabolism*; D018482:Muscle, Skeletal / Q000378:metabolism*; D010805:Physical Conditioning, Animal; D010807:Physical Endurance; D012333:RNA, Messenger / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D013997:Time Factors
chemical_list: D012333:RNA, Messenger; D007334:Insulin-Like Growth Factor I; D013006:Growth Hormone