The influence of topical capsaicin on the local thermal control of skin blood flow in humans

To test whether heat-sensitive receptors participate in the cutaneous vascu lar responses to direct heating, we monitored skin blood flow (SkBF; laser Doppler flowmetry) where the sensation of heat was induced either by local warming (T-Loc; Peltier cooling/heating unit) or by both direct warming and chemical stimulation of heat-sensitive nociceptors (capsaicin). In part I, topical capsaicin (0.075 or 0.025%) was applied to 12 cm(2) of skin 1 h be fore stepwise local warming of untreated and capsaicin-treated forearm skin . Pretreatment with 0.075% capsaicin cream shifted the SkBF/T-Loc relations hip to lower temperatures by an average of 6 +/-0.8 degreesC (P<0.05). In p art II, we used a combination of topical capsaicin (0.025%) and local warmi ng to evoke thermal sensation at one site and only local warming to evoke t hermal sensation at a separate site. Cutaneous vasomotor responses were com pared when the temperatures at these two sites were perceived to be the sam e. SkBF differed significantly between capsaicin and control sites when com pared on the basis of actual temperatures, but that difference became insig nificant when compared on the basis of the perceived temperatures. These da ta suggest heat-sensitive nociceptors are important in the cutaneous vasodi lator response to local skin warming.