CONTROL OF SKIN BLOOD-FLOW BY WHOLE-BODY AND LOCAL SKIN COOLING IN EXERCISING HUMANS

We examined the independent roles of whole body skin temperature (T-sk ) and tissue temperature (local temperature, T-loc) in the control of skin blood flow (SBF) during cooling and the roles of the vasoconstric tor (VC) and active vasodilator (AVD) systems in mediating these effec ts. SBF was monitored by laser-Doppler flowmetry (LDF) at untreated si tes and sites with local VC blockade by pretreat ment with bretylium ( BT). Seven subjects underwent four sessions of moderate bicycle exerci se (20-30 min duration) at neutral T-sk and T-loc (34 degrees C), neut ral T-sk and cool T-loc (27 degrees C), low T-sk (28 degrees C) and ne utral T-loc, and low T-sk and T-loc. Cutaneous vascular conductance (C VC; LDF/mean arterial pressure) was expressed relative to the maximum. Cool T-sk increased the threshold level of internal temperature at wh ich CVC began to rise equally at BT-treated and untreated sites (P < 0 .05). The rate of increase in CVC relative to internal temperature was reduced by local cooling. BT pretreatment partially reversed this eff ect (P < 0.05). Thus a cool environment results in reflex inhibition o f the onset of AVD activity by cool T-sk and a reduced rate of increas e in CVC due, in part, to norepinephrine release stimulated by cool T- loc.