Catalase inhibits collagen-induced platelet aggregation both in untreated and ASA-treated platelets. (A): (a) TC of collagen; (b, c, and d) TC collagen plus catalase (250, 500, and 1,000 U/mL respectively). (B): (a) same as in (A); (b) ASA (100 μmol/L)-treated platelets stimulated with TC collagen; (c) ASA-treated platelets stimulated by eightfold TC collagen; (d) same as in (c) plus catalase at 250 U/mL. Similar results have been obtained in five separate experiments. The threshold concentration (TC) in this experiment was 2 μg/mL.