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

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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 μg/ml) was obviously suppressed by tranilast (10-6-10-3 M). Tranilast (10-4 M) inhibited antigeninduced 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.