Abstract
We evaluated the association between aerobic power (defined by peak oxygen consumption; VO 2peak) and the contribution of nitric oxide synthase (NOS) to the sweating response in young and older individuals during exercise in the heat. Data from 44 young (24 ± 1 years) and 48 older (61 ± 2 years) males with mean VO 2peak of 47.8 ± 2.4 (range, 28.0–62.3) and 39.1 ± 2.3 (range, 26.4–55.7) mLO 2 kg−1 min−1, respectively, were compiled from our prior studies. Participants performed two 15‐ to 30‐min bouts of exercise at a fixed rate of metabolic heat production of 400 or 500 W, each separated by 15–20 min recovery in the heat (35°C, relative humidity of 20%). Forearm sweat rate (ventilated capsule technique) was measured at two skin sites that were continuously and simultaneously administered with lactated Ringers solution (Control) or 10 mmol/L NG‐nitro‐L‐arginine methyl ester (L‐NAME, nonselective NOS inhibitor) via intradermal microdialysis. Sweat rate during the final 5 min of each exercise bout was lower with L‐NAME compared to the Control in both groups (all P < 0.05). The magnitude of the attenuation in sweat rate induced by L‐NAME compared to the Control was not correlated with VO 2peak (all P ≥ 0.46) while this attenuation was negatively correlated with the sweat rate at the Control in both groups and in both exercise bouts (all P < 0.01, R ≤ −0.43). These results suggest that NOS‐dependent sweating is not associated with aerobic power per se, while it becomes evident in individuals who produce larger sweat rates during exercise irrespective of age.
Highlights
In humans, the evaporation of sweat is the major avenue of heat loss during exercise and exposure to hot ambient environments
To the best of our knowledge, this is the first study to evaluate the association between aerobic power and the contribution of nitric oxide synthase (NOS) to the sweating response during exercise in the heat
The contribution of NOS to the sweating response (i.e., NOSdependent sweating) during exercise was not correlated with aerobic power, in both the young and older adults
Summary
The evaporation of sweat is the major avenue of heat loss during exercise and exposure to hot ambient environments. Recent reports suggest that inter-individual variation in NOS-dependent sweating exists in both young (Fujii et al 2016) and older (Fujii et al 2015) adults While many factors such as age (Kenney and Munce 2003; Inoue et al 2004; Larose et al 2013; Stapleton et al 2014a, 2015) and aerobic power (Greenleaf et al 1972; Buono and Sjoholm 1988; Yamazaki et al 1994; Yoshida et al 1997; Ichinose-Kuwahara et al 2010; Amano et al 2013) could influence sweat rate during exercise, the mechanisms underlying the inter-individual variation in NOS-dependent sweating have not been fully investigated
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