Influence of platelet factor 4 on plasma APC levels in thrombin-infused cynomolgus monkeys. Plasma APC was measured by enzyme capture amidolytic assay before, during, and after a 10-minute infusion of 1 μg/kg/min human thrombin, represented by the black bar under the x-axis. For 2 minutes prior to initiation of the thrombin infusion, groups of 6 monkeys were infused with either 7.5 mg/kg PF4 (▪) or a vehicle buffer control (□). A single monkey was infused with PF4 without subsequent thrombin infusion (▴). Data shown are means ± SEM.