Exercise Effects on Circadian Rhythmicity of Urine Osmolality and Diuresis in Rats

Sportsmen have to maintain hydration monitoring for health, but biomarkers are transient during the process of dehydration and rehydration. The aim of this study was to examine the circadian rhythmicity of urine osmolality and diuresis in rats at 4 h intervals, and to determine whether training exercise resulted in changes in this rhythmicity. Rats were trained progressively on a running wheel over four days. Two urine group samples were taken from each animal; the first was taken before the start of the training program and the second was taken at the completion of the last running trial. We found a characteristic circadian rhythmicity in diuresis and in urine osmolality, which was the same for pre- and postexercise patterns. However, post- exercise urine osmolality values were greater than pre-exercise values when the exercise intensity was of sufficient intensity to reduce urine production. The urine osmolality was elevated during the approximately 4 h period after termination of the exercise, and remained high up to 16 h after the termination of exercise, after which osmolality started to normalize. Thus, this study suggests that the urinary measures described herein represent a noninvasive and easy-to-use tool for the characterization of 24 h hydration status.