DETERMINATION OF PLASMINOGEN-ACTIVATOR INHIBITOR IN HUMAN PLASMA AND BLOOD-PLATELETS AND ITS CLINICAL RELEVANCE

The authors present a method for the determination of plasminogen activator inhibitor (PAI-1) activity in human platelets using snap-freezing and thawing techniques. By this method we found a mean PAI value of 7.5 × 10-8 AU/platelet (SD 1.3 × 10-8; n = 5) in healthy young volunteers. By subtraction of plasma from serum the PAI activity showed only a slightly lower value strongly pointing to platelets as the (main) source accounting for this difference. Absence of correlation between plasma and platelet PAI activity and apparently constant platelet PAI activity during the day, in contrast to changing plasma PAI (and t-PA) activity, leads to the conclusion that plasma PAI is not derived from platelet PAI activity and is independent of such activity. This method of platelet PAI activity determination is, in our opinion, easy to perform and reproducible. Furthermore, it facilitates the study of platelet PAI in relation to disease states, without the distortions caused by drugs or thrombopathies which can be a major disadvantage of aggregation techniques. © 1990.