Enhanced renal Na+ reabsorption by carbohydrate in beverages during restitution from thermal and exercise-induced dehydration in men

Kamijo YI, Ikegawa S, Okada Y, Masuki S, Okazaki K, Uchida K, Sakurai M, Nose H
American Journal of Physiology - Regulatory, Integrative and Comparative Physiology 2012; 303: R824-R833

Purpose:
We studied whether the carbohydrates in an ion supply drink accelerated the fluid retention during the recovery from dehydration following exercise. In addition, we examined whether this was caused by an enhanced renal sodium reabsorption due to insulin secretion.

Methods:
Seven healthy young male subjects performed three cross-over designed trials using ion supply drinks A, B and C that had carbohydrate concentrations of 6.5 g/dl, 3.3 g/dl and 0.0 g/dl, respectively, and electrolyte concentrations of 49 mg/dl [Na+] and 20 mg/dl [K+]. After dehydration by 2.3% of the body weight due to cycle ergometer exercise in a hot environment (ambient temperature 36.0℃, relative humidity 30%), the subjects drank the same amount of beverage as the body weight loss within 30 min, then blood and urine samples were collected every 30 min.

Results:
A significant difference in the plasma volume recovery was observed between ion supply drinks A or B and ion supply drink C until 75 min after exercise, and between ion supply drink A and ion supply drinks B or C at 135 min, and between ion supply drink A and ion supply drink B at 165 min. A significant difference in the rate of renal sodium reabsorption was observed between subjects who received ion supply drink A and ion supply drink C from 15 to 105 min after exercise and between ion supply B and ion supply drink C at 45 and 75 min after exercise.

Conclusion:
The carbohydrates in an ion supply drink could accelerate the recovery of the plasma volume by stimulating insulin secretion and augmenting the renal sodium reabsorption.

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