Regulatory effects of brazilin in hydroxyl radical formation and the occlusion time required for thrombus formation in the mesenteric venules of mice. (A) For the electron spin resonance (ESR) study, washed platelets were incubated with (a) Tyrode’s solution only (resting group), or platelets were incubated with (b) the solvent control (0.5% DMSO), (c) collagen (1 μg/ml), (d) brazilin (25 μM), or (e) brazilin (50 μM) to trigger hydroxyl radical formation. Asterisk (*) indicates the formation of hydroxyl radical. (B) Mice were administered either brazilin (2 and 4 mg/kg) or isovolumetric 0.5% DMSO (ctl; solvent control). Thereafter, mesenteric venules were selected for irradiation to induce microthrombus formation. The bar graphs (A) present the means ± S.E.M. of the occlusion time (s) for inducing platelet plug formation (n=5). *p < 0.05 compared with the individual solvent control.