Attenuation of urinary sodium excretion during cold-air exposure in trained athletes

To clarify whether an increase in urinary sodium (Na) excretion during cold -air exposure is attenuated in trained athletes, we analyzed the urinary an d hormonal responses to cold-air exposure at 15 degrees C in trained (TR, n =9) and untrained men (UT, n=9), During 15 degrees C exposure in the UT gro up, the urinary Na excretion (UNaV), fractional excretion of Na and urinary Na to K ratio (U-Na/K) increased significantly (p<0.01-0.05), but there we re no variations in creatinine clearance or the filtered Na load. In the TR group, however, no significant changes were demonstrated in these paramete rs. The amount of increase in plasma noradrenaline and of decrease in plasm a volume were greater, and the ADH and adrenaline responses were smaller in the TR group than those found in the UT group during 15 degrees C air expo sure. A significant positive correlation was demonstrated between the incre ase of UNaV and both the relative changes of U-Na/K and mean blood pressure . These results indicated that natriuresis during cold-air exposure was ind uced by the decrease in tubular reabsorption of Na, and that natriuresis wa s attenuated in trained athletes.