Capsaicin-sensitive nerves and the cutaneous allergy reaction in man. Possible involvement of sensory neuropeptides in the flare reaction.

The effects of local capsaicin pretreatment on the cutaneous triple response reaction induced by allergen exposure or anti-IgE were studied in man. Acute exposure of the human skin to capsaicin caused a burning sensation and a clearcut flare reaction but no wheal response. Upon repeated administration these local reactions to capsaicin disappeared. The flare component and the subjective itching sensation of the cutaneous allergy reaction to rat antigen in sensitized persons or anti-IgE in non-allergic persons were then markedly reduced. Two weeks after capsaicin pretreatment the flare response to allergen was not significantly changed compared to the control reaction, suggesting a reversible effect of capsaicin treatment. The wheal component of the allergy or anti-IgE reaction was, however, not influenced by capsaicin pretreatment, indicating that the wheal and flare components are caused by different mechanisms. It is concluded that capsaicin sensitive sensory nerves are of importance for the human cutaneous triple response reaction induced by allergen exposure. Thus, secondary release of mediators, such as CGRP or tachykinins from sensory nerve branches, may contribute to the flare component of this reaction. Furthermore the itching sensation seems to be dependent to a large extent on capsaicin-sensitive nerves. However, sensory nerves seem to have less importance for the wheal reaction, i.e. the protein extravasation response.