Plasminogen inhibits platelet aggregation but not their activation in serum.

A: The activating effect of serum on platelets is counteracted with hirudin but not with plasminogen. Platelet activation was determined by detecting exposure of the activation marker P-selectin of platelet surfaces using flow cytometry. Shown are representative histograms of an assay performed three times. B: Inhibition of platelet aggregation in serum by addition of plasminogen and hirudin. Complete aggregation was set to 100% light transmission. Shown are mean values ± SD of an assay performed three times. For the time points marked with the line segment, absorbance values for samples incubated or not with plasminogen were compared (*, P