Inhibitory effects of methanol extracts of herbal medicines on substance P-induced itch-scratch response.

In a search for new anti-pruritic drugs we screened methanol extracts of 33 herbal medicines which have been used for cutaneous diseases for their antipruritic activity using substance P (SP) as a pruritogen in mice. When administered perorally 30 min before SP injection, methanol extracts of 6 of these herbal medicines, the root of Scrophularia ningpoensis Hemsl., the root of Patrinia villosa (Thunb.) Juss, the fruit of Forsythia suspenna Vahl, the rhizome of Cimicifuga dahurica (Turcz.) Maxim., the aerial part of Schizonepeta tenuifolia Briq. and the fruit of Cnidium monnieri (L.) Cuss, inhibited SP-induced itch-scratch response at a dose of 200 mg/kg with-out affecting locomotor activity. Dose dependence of these 6 extracts (50-500 mg/kg) was investigated and all of them inhibited SP-induced itch-scratch response, with extracts from Scrophularia ningpoensis, Schizonepeta tenuifolia and Cnidium monnieri showing particularly significant inhibition. The results suggest that these 6 methanol extracts have inhibitory activity against SP-induced itching.