The effect of ADP, thrombin, or adrenaline on forskolin-stimulated cyclic AMP accumulation. Washed platelets prepared from normal (▪) or patient (□) blood were preincubated with 0.5 mM 3-isobutyl-1-methylxanthine (IBMX) for 10 minutes followed by an additional 10-minute incubation with 50 μM forskolin alone or with either ADP (10 μM), thrombin (0.2 U/mL), or adrenaline (10 μM). At the end of the final incubation, cAMP was extracted and the levels determined by immunoassay, as described in “Patient, materials, and methods.” Control values were obtained from forskolin-stimulated platelets and the results following agonist stimulation are expressed as percentages of these control values. Data values are mean ± SEM from triplicate determinations from 3 separate experiments.