Reflex control of the cutaneous circulation after acute and chronic local capsaicin.
To investigate whether local activity of capsaicin-sensitive sensory afferents in the skin has a modulatory role in the reflex cutaneous vasodilator response to hyperthermia in humans, experiments were conducted in two parts. First, low-dose topical capsaicin (0.025%) was administered acutely to stimulate local activity of these afferents. Second, we temporarily desensitized 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 using water-perfused suits and then by local warming to 42 degrees C for assessment of maximum cutaneous vascular conductance. Skin blood flow was measured by laser-Doppler flowmetry and divided by mean arterial pressure (Finapres) for assessment of cutaneous vascular conductance. Maximum vascular conductance was not influenced by either acute or chronic capsaicin treatment (P > 0.10). After acute capsaicin, baseline cutaneous vascular conductance was 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). Furthermore, neither acute (control: 112.74 +/- 36.83 vs. acute capsaicin: 96.92 +/- 28.92%max/ degrees C; P > 0.10) nor chronic (control: 142.45 +/- 61.89 vs. chronic capsaicin: 132.12 +/- 52.60%max/ degrees C; P > 0.10) capsaicin administration 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 hyperthermia.
Charkoudian
N
N
Laboratoire de Physiologie et d'Explorations Fonctionnelles Vasculaires Université d'Angers, 49045 Angers, France. charkoudian.nisha@mayo.edu
Fromy
B
B
Saumet
J L
JL
D000287:Administration, Topical; D000328:Adult; D001831:Body Temperature; D002211:Capsaicin / Q000008:administration & dosage / Q000494:pharmacology*; D004334:Drug Administration Schedule; D005260:Female; D006358:Hot Temperature; D006801:Humans; D008297:Male; D009824:Ointments; D012039:Regional Blood Flow / Q000187:drug effects / Q000502:physiology; D012867:Skin / Q000098:blood supply*; D014664:Vasodilation / Q000187:drug effects / Q000502:physiology*
D009824:Ointments; D002211:Capsaicin