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JOURNAL
OF
SPORTS SCIENCE &
MEDICINE
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Research
article
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TIME COURSE CHANGE OF IGF1/AKT/MTOR/P70S6K PATHWAY ACTIVATION IN RAT GASTROCNEMIUS MUSCLE DURING REPEATED BOUTS OF ECCENTRIC EXERCISE |
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Eisuke Ochi1  ,
Naokata Ishii2 and Koichi Nakazato3 |
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1Laboratory of Health and Sports Sciences, Center for Liberal Arts, Meiji Gakuin University, 2Department of Life Sciences, Graduate School of Arts and Sciences, The University of Tokyo, 3Department of Exercise Physiology, Graduate School of Sport Science, Nippon Sport Science University, Japan |
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© Journal of Sports Science and Medicine (2010) 9, 170 - 175 |
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| ABSTRACT | |||
| The purpose of this study was to examine whether insulin-like
growth factor (IGF-1) and Akt/mTOR/p70S6K pathway activity is altered by
chronic eccentric exercise in rat medial gastrocnemius muscle. Male Wistar
rats (n = 24) were randomly assigned to 1 of the 2 groups: eccentric exercise
(ECC) group or sham-operated control (CON) group. Rats in the ECC group
were trained every second day for 10 days (5 sessions in total) or 20 days
(10 sessions in total). After either 5 or 10 exercise sessions, muscle specimens
were dissected and weighed. The mRNA expression of IGF-1 and its variant,
mechano growth factor (MGF), was evaluated using real time reverse transcriptase-polymerase
chain reaction (RT-PCR). Tissue concentrations of Akt (P), mTOR (P), and
p70S6K (P) were measured by using western blot analysis. The medial gastrocnemius
muscle mass of the ECC group did not show any significant difference after
5 exercise sessions, whereas the muscle mass increased significantly after
10 exercise sessions with a concomitant increase in the cross-sectional
area of muscle fibers (p < 0.05). The expression of IGF-1 mRNA and the
tissue concentrations of Akt (P) and p70S6K (P) after 10 exercise sessions
was significantly higher than those of the age-matched controls and the
rats that received 5 exercise sessions. The expression of MGF mRNA in both
ECC5S and ECC10S were significantly higher than that in each period-matched
control (p < 0.01). The tissue concentration of mTOR (P) after 10 sessions
showed a significant increase when compared with period-matched controls
(p < 0.01). These results suggest that activation of the IGF-1/Akt/mTOR/p70S6K
signaling pathway becomes dominant in the later phase of chronic exercise,
when significant muscular hypertrophy is observed. Key words: Signal pathway, skeletal muscle, eccentric contractions, hypertrophy. |
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