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An assay for plasminogen activator inhibitor in human platelets is described. With this assay we find an average value of 6.8 X 10(-8) IU/platelet (S.D. = 3.0 X 10(-8); n = 20) in a healthy population. We characterized the PA-inhibitor from platelets and identified it as endothelial cell type plasminogen activator inhibitor, by its immunologic and functional properties. Besides the plasma pool of plasminogen activator inhibitor with a very high turnover rate, platelets constitute a second pool of plasminogen activator inhibitor in the circulation of the same order of magnitude. The two different pools of plasminogen activator inhibitor might have a different physiologic function.
Sprengers et al. (Wed,) studied this question.