Prednisolone inhibits platelet aggregation. Human PRP was incubated with the reported glucocorticoid for 5 minutes before addition of 4 μm ADP, and platelet aggregation was monitored. (A) Prednisolone (PRED, 10 μM), but not dexamethasone (DEX, 10 μM), inhibited ADP-induced aggregation. Traces are representative of 6 distinct experiments. (B) Prednisolone and its nitro-derivative NCX-1015 are effective in inhibiting ADP-induced aggregation, whereas dexamethasone (Dex), hydrocortisone (Hydro), aldosterone (Aldo), and RU486 are inactive (all compounds tested at 10 μM). (C) Concentration response for prednisolone (added 5 minutes earlier) against 4 μM ADP- or 1 μM U46619-induced platelet aggregation. The effect of RU486 (10 μM; 5 minutes prior to prednisolone) is also shown, which blocks the inhibitory action of prednisolone on either stimulant. Inset: representative traces showing prednisolone's (10 μM) effect upon U46619-induced platelet aggregation. In all cases, data are mean ± SEM of 4 experiments with distinct platelet donors and performed in duplicate. ^*P < .05 versus control aggregation; #P < .05 versus respective prednisolone + buffer values.