AbstractThe effect of tranilast, an inhibitor for IgE-mediated mediator release from mast cells, on plasma extravasation induced by the intradermal injection of substance P in rats was examined. Tranilast (100 mg/kg, intraperitoneally) decreased plasma extravasation induced by substance P (10−-7-−10−-5M). Tranilast decreased plasma extravasation induced by the amino-terminal peptide substance P1–9(10−-6-−10−-4m), which is active for rat mast cells, but not by the carboxy-terminal peptide substance P6–11 (10−-6-−10−-4M), which is inactive for the mast cells. Therefore, tranilast prevents substance P-induced plasma extravasation most likely by inhibiting mast cell degranulation.