Glycogen overload by postexercise insulin administration abolished the exercise-induced increase in GLUT4 protein |
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Authors: | Chia-Hau?Chou Yin-Lan?Tsai Chien-Wen?Hou Hsing-Hao?Lee Wei-Hsiang?Chang Tzi-Wen?Lin Tung-Hsiung?Hsu Yi-Jen?Huang Email author" target="_blank">Chia-Hua?KuoEmail author |
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Institution: | (1) Center for General Education, National Chi-Nan University, Nantou, Taiwan, ROC;(2) Department of Athletic Training, National College of Physical Education and Sports, Taoyuan, Taiwan, ROC;(3) Laboratory of Exercise Biochemistry, Taipei Physical Education College, 5 Dun-Hua N. Rd, Taipei, Taiwan 105, ROC;(4) Department of Physical Education, Soochow University, Taipei, Taiwan, ROC |
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Abstract: | Summary To elucidate the role of muscle glycogen storage on regulation of GLUT4 protein expression and whole-body glucose tolerance,
muscle glycogen level was manipulated by exercise and insulin administration. Sixty Sprague-Dawley rats were evenly separated
into three groups: control (CON), immediately after exercise (EX0), and 16 h after exercise (EX16). Rats from each group were
further divided into two groups: saline- and insulin-injected. The 2-day exercise protocol consisted of 2 bouts of 3-h swimming
with 45-min rest for each day, which effectively depleted glycogen in both red gastrocnemius (RG) and plantaris muscles. EX0
rats were sacrificed immediately after the last bout of exercise on second day. CON and EX16 rats were intubated with 1 g/kg
glucose solution following exercise and recovery for 16 h before muscle tissue collection. Insulin (0.5 μU/kg) or saline was
injected daily at the time when glucose was intubated. Insulin injection elevated muscle glycogen levels substantially in
both muscles above saline-injected group at CON and EX16. With previous day insulin injection, EX0 preserved greater amount
of postexercise glycogen above their saline-injected control. In the saline-injected rats, EX16 significantly increased GLUT4
protein level above CON, concurrent with muscle glycogen supercompensation. Insulin injection for EX16 rats significantly
enhanced muscle glycogen level above their saline-injected control, but the increases in muscle GLUT4 protein and whole-body
glucose tolerance were attenuated. In conclusion, the new finding of the study was that glycogen overload by postexercise
insulin administration significantly abolished the exercise-induced increases in GLUT4 protein and glucose tolerance. |
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Keywords: | athletes glucose tolerance glucose transporter glycogen supercompensation insulin sensitivity |
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