Effect of a novel antiallergic drug, pemirolast, on activation of rat peritoneal mast cells: inhibition of exocytotic response and membrane phospholipid turnover

The effects of a potent antiallergic drug, pemirolast (TBX), on activation of signal-transducing Phospholipase C and A2, were examined in rat peritoneal mast cells. TBX at concentrations between 10(-7) and 10(-5) g/ml effectively inhibited degranulation in response to both antigen and compound 48/80. At the same concentrations the drug markedly suppressed the formation of 1,2-diacylglycerol and phosphatidic acid, and the decrease in phosphatidylinositol, suggesting the prevention of Phospholipase C activation. The blockade of Phospholipase A2 was suggested by the decrease in agonists-induced arachidonic acid liberation. These results indicate that TBX may exert its inhibitory effects on mast cells, at least in part, by preventing the activation of signal-transducing phospholipases.