Studies on Alismatis rhizoma. I. Anti-allergic effects of methanol extract and six terpene components from Alismatis rhizoma (dried rhizome of Alisma orientale).

Methanol and aqueous extracts (TMe-ext and TAq-ext) from dried rhizomes of Alisma orientale have been screened for activity in experimental models of type I-IV allergies. In the type III allergic model, TMe-ext at oral doses of 50, 200 mg/kg showed an inhibitory effect on the direct passive Arthus reaction (DPAR) in rats, while TAq-ext did not. Four triterpenes (alisol A, alisol B, alisol A monoacetate and alisol B monoacetate) and two sesquiterpenes (alismol and alismoxide) isolated from TMe-ext also exhibited this inhibitory effect. In a type I allergic model, TMe-ext inhibited 48-h homologous passive cutaneous anaphylaxis (PCA) in rats. In a type II allergic model, it was found that TMe-ext inhibits reversed cutaneous anaphylaxis (RCA) in rats. Furthermore, in a type IV allergic model, TMe-ext had an inhibitory effect on the induction phase in picryl chloride-induced contact dermatitis (PC-CD) in mice. These results indicate that Alismatis Rhizoma not only inhibits antibody-mediated allergic reactions but also influences cell reactions and should be recognized as a material for the treatment of allergic reactions, and the anti-type III allergic components are partially attributable to the terpenes mentioned above.