Increase in muscle IGF-I protein but not IGF-I mRNA after 5 days of endurance training in young rats

Alon Eliakim, Mark Moromisato, David Moromisato, J. O.Anne Brasel, Charles Roberts, Dan M. Cooper

Research output: Contribution to journalArticlepeer-review


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 and 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.

Original languageEnglish
Pages (from-to)R1557-R1561
JournalAmerican Journal of Physiology - Regulatory Integrative and Comparative Physiology
Issue number4 42-4
StatePublished - 1997
Externally publishedYes


  • Exercise
  • Gene expression
  • Growth factor


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