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Glucose turnover in 48-hour-fasted running rats
The American Journal of Physiology
|March 1, 1987
Summary
Exercise causes hyperglycemia in fed rats, unlike fasted states. Glucose production during exercise depends on glycogen stores, with fasted rats showing better glucose balance.
Area of Science:
- Exercise Physiology
- Metabolic Regulation
- Endocrinology
Background:
- Existing research on fasted humans and dogs suggests euglycemia during exercise, with glucose production (Ra) regulated by feedback.
- This contrasts with observations in fed rats, where hyperglycemia develops during physical activity.
Purpose of the Study:
- To investigate the impact of feeding status on glucose metabolism and production during exercise in rats.
- To compare glucose kinetics in fed, food-restricted, and fasted rats during a standardized exercise bout.
Main Methods:
- Comparison of fed (C), overnight food-restricted (FR), and 48-hour-fasted (F) rats.
- Infusion of [3-3H]- and [U-14C] glucose during treadmill running (21 m/min, 0% grade).
- Measurement of blood glucose, glucose production (Ra), glucose disappearance, glycogen stores, glycogenolysis, lactate production, and gluconeogenesis.
Main Results:
- Fed rats exhibited the largest increase in glucose production (Ra) and plasma glucose during exercise.
- Fasted rats showed the least increase in Ra, with production closely matching glucose disappearance.
- Liver and muscle glycogen stores and exercise glycogenolysis were highest in fed rats and lowest in fasted rats.
Conclusions:
- In rats, exercise-induced changes in glucose production and plasma concentration are significantly influenced by the size of liver and muscle glycogen stores.
- Glucose production better matches increased clearance in fasted states compared to fed states during exercise.
- Feedforward mechanisms likely stimulate glucose production, with feedback mechanisms becoming relevant when plasma glucose levels decrease.
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