REFLEX CONTROL OF ACTIVE CUTANEOUS VASODILATION BY SKIN TEMPERATURE IN HUMANS

The purpose of this study was to examine whether reflex effects of cha nges in whole body skin temperature (T-sk) on cutaneous vasculature ar e mediated through the vasoconstrictor or the active vasodilator arm o f the sympathetic nervous system. In six subjects, reflex responses in forearm skin blood flow (SkBF) to changes in T-sk were monitored by l aser-Doppler flowmetry. SkBF was monitored at a control site and at a 0.6-cm(2) site where bretylium (BT) had been iontophoretically applied to abolish sympathetic vasoconstrictor control. Reflex control of SkB F at BT-treated sites is solely through active vasodilator activity. A n index of cutaneous vascular conductance (CVC) was calculated from th e blood flow signal and mean arterial pressure, measured noninvasively . Data are expressed relative to maximum CVC (CVCmax) achieved by loca l warming of measurement sites to 42 degrees C at the end of each stud y. T-sk was controlled with a water-perfused suit covering the entire body except for the head and arms. Esophageal temperature (T-es) was m easured as an index of internal temperature. In part A (rest), raising T-sk at rest from 31.9 +/- 0.3 to 36.7 +/- 0.2 degrees C increased CV C at control sites from 3 +/- 0.2 to 5 +/- 0.6% of CVCmax CVC did not change at BT-treated sites, suggesting that at rest, with a normal int ernal temperature, reflex effects of raising T-sk on SkBF are mediated through vasoconstrictor withdrawal. In part B (exercise), exercise at a low T-sk increased T-es to 37.49 +/- 0.1 degrees C. Raising T-sk du ring exercise from 31.4 +/- 0.3 to 36.7 +/- 0.2 degrees C produced lar ge simultaneous increases in CVC at control (6 +/- 2 to 33 +/- 3% of C VCmax) and BT-treated sites (10 +/- 3 to 40 +/- 5% of CVCmax). There w as no net change in T-es during this period. Thus, at the elevated int ernal temperature of exercise, reflex cutaneous vascular effects of ra ising T-sk are largely mediated through the active vasodilator system. In conclusion, reflex effects of whole body T-sk can be mediated thro ugh either of the efferent systems controlling SkBF, depending on back ground internal temperature.