Genomic and non-genomic effects of aldosterone on the individual variation of the sweat Na⁺ concentration during exercise in trained athletes

To clarify whether the resting background effects (genomic) or exercise-related action (non-genomic) of aldosterone (ALD) is primarily affected to an individual variation in the sweat Na⁺ concentration ([Na⁺]_sweat), we analyzed the cross-sectional relationship between [Na⁺]_sweat and the plasma ALD concentration during rest and exercise in a hot environment. Eleven college-aged male subjects with a mean maximal oxygen uptake of 48 (range 42–59) ml kg⁻¹ min⁻¹ performed three sessions of 20-min cycle exercise at two levels of intensity (40 or 60% \(\dot VO_{\rm 2max}\)) in a room maintained at 31°C. The chest sweat rate (SR_ch) and its containing Na⁺ were higher and individual differences in SR_ch and [Na⁺]_sweat were greater at 60% exercise than at 40% exercise. In each individual, the [Na⁺]_sweat increased significantly (P < 0.05) with the increase in the SR_ch. In all subjects, the mean [Na⁺]_sweat during exercise correlated negatively with the resting plasma ALD level at either percentage, but it did not correlate with the exercising ALD. These results suggest that individual variations in the increase of the [Na⁺]_sweat in response to a rise in the SR_ch may thus be more closely related to the resting ALD than to the exercising ALD. As a result, the genomic action of ALD may be affected more by the sweat Na⁺ variation than by the rapidly non-genomic action during exercise in humans.