Time course of collagen-stimulated platelet releasate. Equal volumes of platelets (2.5 × 10⁸) were stimulated with collagen in the presence or absence of low-dose aspirin (20 μM) at different time points (30 seconds, 3 minutes, and 30 minutes). The aggregation response was plotted (mean ± SD of 3 independent experiments) using different donors (A). Platelet releasate from a single representative donor was visualized using coomassie-stained (4%-20%) acrylamide (B, upper panel). An immunoblot for thrombospondin was performed on these fractions (B, lower panel).