Role of nitric oxide synthase on local sweat rate in older adults during intermittent exercise in the heat

Abstract

Studies suggest that nitric oxide (NO) has a role in sweating. Older adults have a lower production of and sensitivity to NO which may explain why older adults have lower local sweat rates (LSR) compared with their younger counterparts during exercise. We examined the role of NO synthase (NOS) on LSR during intermittent exercise in the heat. Ten young (Y) and ten older (O) participants completed 3 × 15 min of cycling (rate of metabolic heat production of 600 W) separated by 15 min recovery in the heat (35ºC, 30% RH). Intradermal microdialysis probes were inserted in the forearm and perfused with either 0.9% saline (CON) or 10 mM L‐NAME (a NOS inhibitor). LSR was measured directly over each membrane. LSR was similar between Y and O during the exercise bouts at the CON (average of the 3 exercise bouts: Y; 0.96 ± 0.20 vs. O; 0.87 ± 0.25 mg·min−1·cm−2 p=0.327) and the LNAME (Y: 0.74 ± 0.18 vs. O: 0.83 ± 0.27 mg·min−1·cm−2 p=0.327) sites. However, the relative contribution of NO to the sweating response was reduced in Y (CON: 0.96 ± 0.20 vs. L‐NAME: 0.74 ± 0.18 mg·min−1·cm−2, p=0.017), but not O (CON: 0.87 ± 0.25 vs. L‐NAME: 0.83 ± 0.27 mg·min−1·cm−2, p=0.965). We conclude that the exercise‐induced increase in sweating is influenced by NO in younger adults. However, it appears that the level of influence is blunted in older individuals during high intensity exercise in the heat.This research was funded by Natural Sciences and Engineering Research Council (RGPIN‐298159–2009, held by Dr. Kenny).