Catalase inhibits ³²P-Ins 1,3,4 P3 (IP3) production. (A) Catalase (250 to 500 to 1,000 U/mL) inhibited³²P-Ins 1,3,4 P3 (IP3) production by collagen (50 μg/mL) but was ineffective if thrombin (1 U/mL) was used as an agonist. Data are expressed as the mean ± SEM of five separate experiments (*P < .05). (B) In ASA (100 μmol/L)-treated platelets, 250 U/mL catalase inhibited ³²P-Ins 1,3,4 P3 (IP3) production by collagen (50 μg/mL). Similar findings were obtained in samples added also with the ADP scavenger system CP/CPK. Data are expressed as the mean ± SEM of five separate experiments (*P < .05; **P < .01).