Hcy amplifies platelet aggregation and degranulation in vitro. Washed platelets harvested from C57BL/6J mice were incubated with or without Hcy (100 μM) for 10 minutes and then stimulated with the indicated concentrations of ADP (A), collagen (B), U46619 (C), and thrombin (D) at 37°C, with constant stirring (1200 rpm). Then, platelet aggregation was monitored with a turbidimetric aggregometer. (E-F) ATP secretion was measured in the presence of luciferin/luciferase reagent. The traces in the figures are representative of at least 3 independent experiments. (G-H) Flow cytometric analysis of P-selectin exposure in platelets with or without Hcy stimulation in the presence of thrombin (0.01 U/mL) (G) or collagen (1.5 μg/mL) (H). MFI, mean fluorescence intensity. (I-J) TXB2 production in control and Hcy-treated platelets stimulated with thrombin (0.01 U/mL) (I) or collagen (1.5 μg/mL) (J) was analyzed by enzyme-linked immunosorbent assay. All data are expressed as the mean ± SEM (n = 3-5). *P < .05 compared with ctrl; #P < .05 compared with thrombin or collagen.