Interrelations of vasoconstrictor sympathetic outflow to skin and core temperature during unilateral sole heating in humans

The purpose of the present study was to clarify how skin sympathetic nerve activity (SSNA) influences the core temperature during local heating of the unilateral sole of the foot for 60 min. We recorded SSNA microneurographically from the tibial or peroneal nerve simultaneously with skin blood flow, sweat rate at heated and non-heated sites, with tympanic temperature (T_ty) as the core temperature. Sole heating began to suppress vasoconstrictive SSNA (vasoconstrictor) after 3.4±1.1 min, decrease T_ty after 7.4±2.0 min, activate vasoconstrictor after 33.4±2.2 min, and increase T_ty after 45.5±2.7 min. Regarding the interaction between vasoconstrictor and T_ty during sole heating, we found the following: (1) the capability to suppress vasoconstrictors (decrease rate) showed positive correlations with the time delay from vasoconstrictor suppression to the T_ty decrease (r=0.752, p<0.05), and with the T_ty decrease rate (r=0.795, p<0.05), (2) the T_ty decrease rate was inversely related to the capability to activate vasoconstrictors (increase rate) (r=-0.836, p<0.05), and (3) the capability to activate vasoconstrictors was inversely related to the time delay from vasoconstrictor activation to the T_ty increase (r=-0.856, p<0.05) and showed a positive correlation with the T_ty increase rate (r=0.819, p<0.05). These significant correlations indicate that the capability to control vasoconstrictors to the skin is one of the determinant factors maintaining core temperature in human thermoregulatory function. In conclusion, human thermoregulatory function is largely dependent on the suppression and activation capability of vasoconstrictors.