RESUMO
BACKGROUND: Nettles, of the plant family Urticae, cause nonimmunologic contact urticaria by stinging hairs. Light application of the leaf or stem to the skin results in the rapid development of a short-lived stinging sensation accompanied by wheal formation and itching. The types of chemical mediators causing the stinging sensation and wheal have not yet been clarified. OBJECTIVE: To investigate stinging and urticating substances causing contact urticaria when the skin is in contact with nettle(Urtica thunbergiana). METHODS: Twenty two volunteers were used for the clinical portion of this investigation. The time to wheal development and the evanescent time of pain and wheal were measured after pricking the forearm skin with nettle trichomes, following the administration of antihistamine, antiserotonin or corticosteroid, respectively or a combination of two, either with or without the application of substance P antagonist(capsaicin cream, 0.025%). Nettle extracts were prepared from dry stems and leaves of Urtica thunbergiana. Histamine, serotonin and substance P(SP) contents of nettle extracts were measured by gas chromatographic mass spectroscopy. RESULTS: After puncture of the skin by trichome of nettle, a stinging sensation developed within a few seconds but disappeared faster at the site where capsaicin cream had been applied than at the nonapplied skin site(p<0.05). The development and evanescent time of wheal were not significantly correlated with the application of capsaicin cream. The evanescent time of pain after pricking the skin with trichome following the administration of antiserotonin was significantly shortened at the nonapplied skin site. Pain disappeared more rapidly at the capsaicin applied site following the administration of antihistamine or antiserotonin than at the nonapplied sites(p<0.05), but not following prednisolone administration. Wheal development was delayed significantly at both the capsaicin applied and nonapplied sites after antihistamine administration(p<0.05). Histamine was detected only in the nettle extract. SP and serotonin were not detected because of their insolubility in solvents. CONCLUSION: These results suggest that wheal-and-flare reaction to nettle stings is due primarily to the histamine and partly to the serotonin and SP introduced by the nettle. SP may be mainly involved and partially involved by serotonin in stinging pain.