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Glycogenesis in muscle and liver during exercise
1Department of Physiology, Dalhousie University, Halifax, Nova Scotia, Canada.
Journal of Applied Physiology (Bethesda, Md. : 1985)
|June 1, 1989
Summary
Muscle glycogen synthesis increases during exercise, particularly in certain muscles like the white gastrocnemius, even before significant glycogen depletion occurs. However, the soleus muscle shows an initial decrease in synthesis during exercise.
Area of Science:
- Exercise Physiology
- Skeletal Muscle Metabolism
- Biochemistry
Background:
- Muscle glycogen serves as a primary energy source during exercise.
- Understanding glycogen synthesis regulation during physical activity is crucial for optimizing performance and recovery.
- Previous research has focused on glycogen depletion, with less emphasis on synthesis rates during exercise.
Purpose of the Study:
- To investigate the hypothesis that glycogenesis (glycogen synthesis) increases in muscle during exercise before significant glycogen depletion.
- To compare rates of glycogen synthesis across different hindlimb muscles and the liver in rats during and after exercise.
- To examine the relationship between glycogen synthesis rates and existing glycogen concentrations in various tissues.
Main Methods:
- Rats performed exercise for 15 or 90 minutes at varying speeds.
- D-[5-3H]glucose was administered 10 minutes before exercise completion to trace glucose incorporation into glycogen.
- Glycogen concentrations and synthesis rates were measured in hindlimb muscles (soleus, plantaris, EDL, red and white gastrocnemius) and liver.
Main Results:
- Significant differences in basal glucose incorporation into glycogen were observed among resting muscles.
- After 90 minutes of exercise, glycogen synthesis increased significantly in plantaris, red gastrocnemius, white gastrocnemius, EDL, and liver compared to rest.
- The soleus muscle showed a decrease in glycogen synthesis at 15 minutes of exercise, returning to resting rates by 90 minutes; synthesis here was inversely related to glycogen levels.
Conclusions:
- Muscle glycogenesis can increase during exercise, supporting the hypothesis, with varying responses across different muscle types.
- The soleus muscle exhibits a unique response, with an initial decrease in synthesis during exercise, suggesting complex regulatory mechanisms.
- These findings highlight the dynamic nature of glycogen metabolism during exercise and the differential regulation of synthesis across various tissues.