Pre-treatment with topical capsaicin is known to induce neuropeptide depletion from sensory nerve endings and it is a useful pharmacological tool to evaluate the contribution of these nerves to skin injury and inflammation. To investigate the relative contribution of sensory neural stimulation to the action of bradykinin and histamine, a randomized, double-blind study has been undertaken evaluating the effect of topical capsaicin pre-treatment on the responses to intradermal injections of both agonists in 12 healthy volunteers. Capsaicin pre-treatment caused significant inhibition of the immediate mean flare responses (95% CI) to both bradykinin (from 51.5 [39.7–63.3] mm2 to 16.2 [8.0–24.5] mm2) (P < 0.01) and histamine (from 108.4 [80.4–136.4] mm2 to 52.3 [37.1–67.1] mm2) (P < 0.01). Topical capsaicin elicited a significant inhibition of the weal response induced by histamine, the mean weal area being reduced from 14.8 (12.6–17.0) mm2 to 12.1 (10.1–14.1) mm2 (P < 0.05). In addition, the effect of topical capsaicin was to completely inhibit the bradykinin induced weal response compared to control, the mean weal area (95% CI) being reduced from 13.4(11.4–15.4) mm2 to 8.2 (5.3–11.0) mm2 (P < 0.01). Our findings show that repealed topical application with capsaicin led to a significant reduction of the skin responses to intradermal injections with both agonists, and particularly with bradykinin. The weal responsiveness to bradykinin may entirely follow neuropeptide release from sensory nerves within the skin and the same applies to the flare response, although this is not completely inhibited by topical application with capsaicin.
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