TYB-2285 (1-30 mg/kg p.o.) inhibited ovalbumin (OA)- and dinitrophenyl-Ascaris (DNPAs)-induced passive cutaneous anaphylaxis (PCA) in a dose-dependent manner. 2. The ED50 of TYB-2285 and ketotifen fumarate on OA-induced PCA were 0.5 and 3.9 mg/kg, respectively. The ED50 of TYP-2285 and amlexanox on DNP-As-induced PCA were 3.5 and 0.9 mg/ kg, respectively. 3. TYB-2285 (3-30 mg/kg p.o.) inhibited histamine consumption at the PCA site. 4. Unlike cyproheptadine or amlexanox, TYB-2285 (30 mg/kg p.o.) did not inhibit histamine-, serotonin-, ascites-, 48/80-, or A23187-induced capillary permeability. It inhibited dextran-induced capillary permeability slightly. 5. These results demonstrate that TYB-2285 inhibits PCA by inhibiting histamine release, although it does not inhibit capillary permeability.
