To investigate whether local activity of capsaicin-sensitive sensory affere
nts in the skin has a modulatory role in the reflex cutaneous vasodilator r
esponse to hyperthermia in humans, experiments were conducted in two parts.
First, low-dose topical capsaicin (0.025%) was administered acutely to sti
mulate local activity of these afferents. Second, we temporarily desensitiz
ed these nerves in a small area of skin using chronic capsaicin treatment (
0.075% for 7 days). Each intervention was followed by whole body heating us
ing water-perfused suits and then by local warming to 42 degreesC for asses
sment of maximum cutaneous vascular conductance. Skin blood flow was measur
ed by laser-Doppler flowmetry and divided by mean arterial pressure (Finapr
es) for assessment of cutaneous vascular conductance. Maximum vascular cond
uctance was not influenced by either acute or chronic capsaicin treatment (
P > 0.10). After acute capsaicin, baseline cutaneous vascular conductance w
as elevated above that at control sites (25.34 +/- 6.25 vs. 10.57 +/- 2.42%
max; P < 0.05). However, internal temperature thresholds for vasodilation
were not affected by either acute or chronic capsaicin (P > 0.10). Furtherm
ore, neither acute (control: 112.74 +/- 36.83 vs. acute capsaicin: 96.92 +/
- 28.92% max/degreesC; P > 0.10) nor chronic (control: 142.45 +/- 61.89 vs.
chronic capsaicin: 132.12 +/- 52.60% max/degreesC; P > 0.10) capsaicin adm
inistration influenced the sensitivity of the reflex cutaneous vasodilator
response. We conclude that local activity of capsaicin-sensitive afferents
in the skin does not modify reflex cutaneous vasodilation during hypertherm
ia.