Abstract
The aim of our study was to determine if habitual endurance training can influence the relative contribution of nitric oxide synthase (NOS) and cyclooxygenase (COX) in the regulation of sweating during a passive heat stress in young adults. Ten trained athletes and nine untrained counterparts were passively heated until oral temperature (as estimated by sublingual temperature, Tor) increased by 1.5°C above baseline resting. Forearm sweat rate (ventilated capsule) was measured at three skin sites continuously perfused with either lactated Ringer's solution (Control), 10 mmol/L NG‐nitro‐L‐arginine methyl ester (L‐NAME, non‐selective NOS inhibitor), or 10 mmol/L ketorolac (Ketorolac, non‐selective COX inhibitor) via intradermal microdialysis. Sweat rate was averaged for each 0.3°C increase in Tor. Sweat rate at the L‐NAME site was lower than Control following a 0.9 and 1.2°C increase in Tor in both groups (all P ≤ 0.05). Relative to the Control site, NOS‐inhibition reduced sweating similarly between the groups (P = 0.51). Sweat rate at the Ketorolac site was not different from the Control at any levels of Tor in both groups (P > 0.05). Nevertheless, a greater sweat rate was measured at the end of heating in the trained as compared to the untrained individuals (P ≤ 0.05). We show that NOS contributes similarly to sweating in both trained and untrained individuals during a passive heat stress. Further, no effect of COX on sweating was measured for either group. The greater sweat production observed in endurance‐trained athletes is likely mediated by factors other than NOS‐ and COX‐dependent mechanisms.
Highlights
It is well-established that endurance trained individuals show an enhanced sweat production relative to their untrained counterparts during a passive (Amano et al.2013; Tokizawa et al 2016) or exercise-induced (Piwonka et al 1965; Yamazaki et al 1994; Ichinose-Kuwahara et al 2010) heat stresses
This is the first study to evaluate the relative contribution of nitric oxide synthase (NOS) and COX in the regulation of the sweating in endurance-trained athletes during a passive heat stress
We showed that NOS inhibition attenuated sweat rate relative to the continuously perfused with either lactated Ringer’s solution (Control) site in both untrained and endurance-trained individuals following Tor increments of 0.9 and 1.2°C above resting levels
Summary
It is well-established that endurance trained individuals show an enhanced sweat production relative to their untrained counterparts during a passive (Amano et al.2013; Tokizawa et al 2016) or exercise-induced (Piwonka et al 1965; Yamazaki et al 1994; Ichinose-Kuwahara et al 2010) heat stresses. To date the mechanisms governing the elevated sweating response in endurancetrained athletes remains unclear. It is possible, that the greater sweat production may in part be due to the hypertrophy of eccrine sweat glands A growing body of evidence has shown that nitric oxide (NO) (Lee and Mack 2006; Welch et al 2009; Fujii et al 2014b, 2015, 2016b; Stapleton et al 2014; Louie et al 2016) and cyclooxygenase (COX) (Sato 2001; Fujii et al 2014b) mediates the regulation of sweating and may play a role in governing the endurance-training induced elevation in sweating
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