Axon reflex flare evoked by nicotine in human skin.

(1) The purpose of the present study is to investigate whether or not the vasodilatation evoked by intradermal (I.D.) injection of nicotine is mediated through axon reflex mechanism, and to examine the involvement of histamine receptors or capsaicin-sensitive C-fibers in nicotine-induced vasodilator response, using a band method and a laser Doppler technique. (2) The vasodilator response, whether it was caused by nicotine or histamine, developed as quickly on the uninjected side as on the injected side of the band, while the wheal reaction was elicited only by histamine and was localized in the injection side of the band. (3) Pretreatment with either a local anesthetic (lidocaine) or 1% capasaicin markedly reduced the nicotine- and histamine-induced blood flow responses, whereas pretreatment with antihistaminergic agent (diphenhydramine) showed inhibitory effect to the blood flow response only to histamine. (4) These data suggest that two types of chemical receptors, i.e. the nicotinic and the histamine-sensitive receptors, exist in capsaicin-sensitive C-fibers to elicit axon reflex vasodilatation in human skin.