Cutaneous adrenergic nerve blockade attenuates sweating response during incremental exercise in habitually trained and untrained men

Abstract

Human eccrine sweat glands are governed by adrenergic nerves and noradrenergic agonists can elicit sweating. However, it remained unknown whether this neural adrenergic mechanism functionally contributes to sweat production during exercise. To clarify the mechanisms of adrenergic sweat production during exercise associated with habitual exercise training, this study examined 1) whether a blockade of cutaneous noradrenaline release from adrenergic nerve terminals attenuates sweating response during incremental exercise, and 2) whether the neural adrenergic sweating, if any, would be greater in habitually trained individuals relative to untrained counterparts. Nine habitually trained and 10 untrained males (VO2max: 57.6±5.1 and 38.9±6.7 ml kg−1 min−1, respectively, P < 0.05) performed incremental semi‐recumbent cycling (20W min−1) until exhaustion. Sweat rates (ventilated capsule) were measured at two bilateral forearm skin sites that were transdermally administered via iontophoresis with either 10 mM bretylium tosylate (BT, an inhibitor of noradrenaline release from sympathetic adrenergic nerve terminals) or saline (Control). Ninety min after the iontophoresis, foot cold water immersion was performed for 2 min to verify bretylium tosylate abolishes adrenergic cutaneous vasoconstriction associated with cold stress. Sweat rate was evaluated as a function of relative (percentage of maximum workload) exercise intensities. Trained individuals exhibited higher sweat production compared with untrained counterparts at exercise intensity of ≥70% relative workload (all P < 0.05). In trained individuals, sweat rate at the BT site was attenuated compared to the Control at relative exercise intensities of 70% (0.12±0.16 vs. 0.24±0.22 ml cm−2 min−1), 80% (0.32±0.25 vs. 0.48±0.28ml cm−2 min−1), 90% (0.48±0.29 vs. 0.66±0.29 ml cm−2 min−1), and 100% (0.60±0.29 vs. 0.77±0.29ml cm−2 min−1), respectively (all P < 0.05). Similarly, sweat rate measured in untrained group was reduced at BT vs. Control site at relative exercise intensities of 80% (0.04±0.08 vs. 0.10±0.09 ml cm−2 min−1), 90% (0.12±0.14 vs. 0.20±0.14 ml cm−2 min−1), and 100% (0.22±0.17 vs. 0.30±0.19 ml cm−2 min−1), respectively (all P < 0.05). BT‐induced reduction in sweat rate was greater in trained than in untrained individuals during exercise at the intensities of 70% (−0.12±0.11 vs. 0.00±0.03 ml cm−2 min−1), 80% (−0.16±0.12 vs. −0.06±0.10 ml cm−2 min−1), and 90% (−0.18±0.14 vs. −0.08±0.14 ml cm−2 min−1), respectively (all P < 0.05). To the best of our knowledge, this is the first study demonstrating noradrenaline release from sympathetic adrenergic nerve terminal does modulate sweating during high intensity exercise (i.e., >70% maximum) with habitually trained males exhibiting greater adrenergic sweating in comparison to untrained counterparts.Support or Funding InformationThis study was supported by a Grant‐in‐Aid for Scientific Research (no. 16K16521) from the Japan Society for the Promotion of Science from the Ministry of Education, Culture, Sports, Science, and Technology of Japan.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.