The time course and dose-dependency of plasma aPC concentration in the guinea pig thrombosis model during infusion of aPC (A) and of the zymogen FLIN-Q3 (B). Plasma concentration was determined using an immunocapture amidolytic assay for aPC. Compare the presence of activity during infusion with aPC (A) with the absence of aPC activity after 15 minutes of infusion with FLIN-Q3 (B) before thrombin generation and thrombus formation during the first period of thrombosis. Note the increase in aPC concentration during the second period of thrombus formation even though the FLIN-Q3 infusions (B) had been stopped for 15 minutes and compared with the absence of activity during this period after infusion with aPC (A).