Heat acclimation induces peripheral modifications in cutaneous vascular function in humans

Abstract

The aim of this study was to explore heat acclimation effects on cutaneous vascular responses and sweat rate to local acetylcholine (Ach) infusions. Ach (1, 10, and 100mM) was infused in 12 cyclists via microdialysis before and after a period of heat acclimation. Eight subjects served as controls to eliminate training effects. Skin blood flow was monitored via laser‐Doppler flowmetry (LDF) and cutaneous vascular conductance (CVC) was calculated as LDF/MAP. Sweat rate was measured by resistance hygrometry. Maximal forearm blood flow (FBF) was obtained by heating the contralateral forearm in a water spray device and measured by Doppler ultrasound. Heat acclimation increased CVC to 1, 10, and 100 mM Ach (43.5 ± 3.4 vs. 52.6 ± 2.6 %CVCmax; 67.7 ± 3.4 vs. 78.0 ± 3.0 %CVCmax; 81.0 ± 3.8 vs. 88.5 ± 1.1 %CVCmax; all P < 0.05). Maximal FBF remained unchanged after heat acclimation (290.9 ± 12.7 vs. 269.9 ± 23.6 ml min−1). Heat acclimation also increased sweat rate to Ach doses (0.13 ± 0.02 vs. 0.18 ± 0.02 mg cm−2 min−1; 0.21 ± 0.03 vs. 0.31 ± 0.03 mg cm−2 min−1; 0.45 ± 0.05 vs. 0.67 ± 0.06 mg cm−2 min−1; all P < 0.05). No differences were found in the control group in any of the variables. Local adaptations within the skin microcirculation and sweat gland apparatus play major roles in the increased thermoregulatory responses induced by heat acclimation. Sponsored by the Eugene and Clarissa Evonuk Memorial Graduate Fellowship