Individual variations in nitric oxide synthase‐dependent sweating in young and older males during exercise in the heat: role of aerobic power

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 N(G)‐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.