In vitro inhibition of NO consumption by aspirin and in vivo inhibition following 150 mg oral aspirin/day in platelets from HF subjects. Platelets from HF subjects were examined for inhibition by aspirin in vitro (1 mM aspirin, 30 minutes, room temperature). NO consumption was determined as described in “Patients, materials, and methods.” (A) Cumulative data showing rates of NO consumption following in vitro aspirin (n = 4, mean ± SEM; *P < .005, Student unpaired t test). (B) Representative traces from one HF subject showing NO consumption by platelets (i) at baseline, (ii) following aspirin supplementation, (iii) after placebo, and (iv) after in vitro aspirin incubation, with 50 μM arachidonate added at arrow. (C) Cumulative data from the HF subject in B, showing the effect of aspirin in vivo or in vitro on platelet NO consumption rates (mean ± SEM, n = 3 separate determinations; *P < .002, Student unpaired t test). (D) Cumulative data showing the effect of supplementation with 150 mg aspirin/day on HF platelet NO consumption rates, compared with baseline, placebo, low-dose aspirin, and in vitro aspirin (mean ± SEM, n = 4 separate donors; *P < .05, Student unpaired t test). Note: baseline, placebo, 75 mg/day aspirin and in vitro rates are provided for comparison with 150 mg/day dose and are already shown in Figures 5B and 6A.