Effects of olopatadine hydrochloride on the cutaneous vascular hyperpermeability and the scratching behavior induced by poly-L-arginine in rats

Intradermal injections of poly-L-arginine induce cutaneous vascular hyperpe rmeability and scratching behavior in rats. Recently, we elucidated that th e plasma extravasation involved both histamine and substance P, while the s cratching behavior involved substance P, but not histamine. This study exam ined the effects of olopatadine hydrochloride (olopatadine), an antiallergi c drug with histamine H-1-antagonistic action, on the poly-L-arginine-induc ed responses. Olopatadine (1 mg/kg, p.o.) significantly inhibited both the plasma extravasation and the scratching behavior, suggesting that its inhib itory effects are mediated by the suppression of neuropeptidergic action as well as histaminic action. Olopatadine seems to be a novel-type drug for t he treatment of dermatitis.