Study of the mechanism of inhibitory action of tranilast on chemical mediator release

We investigated the mechanism of inhibitory action of tranilast on chemical mediator release by antigen-antibody reactions. Tranilast (10(-5)-10(-3) M) inhibited antigen (DNP-Ascaris)-induced histamine release from sensitized purified rat mast cells (PMC), but did not show an obvious influence on intracellular cyclic AMP. 45Ca uptake into PMC induced by antigen (300 micrograms/ml) was obviously suppressed by tranilast (10(-6)-10(-3) M). Tranilast (10(-4) M) inhibited antigen-induced histamine release from and 45Ca uptake into PMC independently of the presence or absence of glucose in the medium. On the other hand, 2-deoxyglucose (10(-2) M) markedly inhibited both responses in the absence but not in the presence of glucose. Tranilast slightly inhibited Ca-induced contraction of guinea pig taenia coli, but had no influence on aggregation of rabbit platelets. Verapamil (10(-6)-10(-4) M) had no effect on antigen-induced histamine release, but it markedly suppressed Ca-induced contraction and platelet aggregation. From these results, we suggest that the mechanism of inhibitory action of tranilast on the release of antigen-induced chemical mediator from mast cells involves the suppression of Ca uptake, but that its mode of action is apparently different from those of 2-deoxyglucose and verapamil.