Study on anti-Oketsu activity of rhubarb II. Anti-allergic effects of stilbene components from Rhei undulati Rhizoma (dried rhizome of Rheum undulatum cultivated in Korea).

Methanol extract (RM-ext) obtained from the dried rhizome of Rheum undulatum was screened for activity in experimental models of type I allergy. RM-ext exhibited the inhibition on 48-h homologous passive cutaneous anaphylaxis (PCA) in rats and an antigen-induced histamine release from rat peritoneal mast cells. Among nine stilbenes isolated from RM-ext, seven inhibited the histamine release. Rhapontigenin (compound 1), piceatannol (2) and piceatannol 3'-beta-D-glycoside (6) with oral administration showed the inhibition on PCA. Compounds 1 and 2 exhibited the inhibitory effect on sheep red blood cell-induced delayed-type hyper sensitivity (SRBC-DTH) of type IV allergic model. These results indicated that the rhizome of Rheum undulatum inhibits the allergic reactions and that these inhibitory effects may be partially attributable to the stilbenes mentioned above.