Effect of brazilin in potentiating or stimulating human platelet aggregation in washed platelets or platelet-rich plasma. Washed platelets (3.6 × 108/ml) were incubated with brazilin (1 to 50 μM), either with (A) or without (B) the addition of collagen (0.1 μg/ml) to trigger platelet aggregation. In additional experiments, washed platelets (3.6 × 108/ml) were preincubated with (C) ATP (50 μM) or (D) yohimbine (5 μM); this was followed by the addition of ADP (20 μM), brazilin (50 μM), or epinephrine (10 μM) to trigger platelet aggregation. (E) Furthermore, platelet-rich plasma was incubated with collagen (1 μg/ml) or brazilin (50 to 10 μM) to trigger platelet aggregation. Aggregation profiles (A to E) are representative examples of 4 similar experiments.