Increased concentration of the fast-acting plasminogen activator inhibitor in plasma associated with familial venous thrombosis.

We have earlier demonstrated that in a family with a tendency to recurrent venous thrombosis the release of tissue plasminogen activator (t-PA) activity in blood after stimulation was abnormally low. This observation could be related either to an impaired release of t-PA into the blood stream or to a masking of the released t-PA by a high concentration of PA inhibitor(s). In order to distinguish between these two possibilities the family was reinvestigated using various newer techniques, including an ELISA for t-PA, an assay for quantitation of the fast-acting PA inhibitor and SDS polyacrylamide gel electrophoresis followed by fibrin-enzymography. Hereby the family members were demonstrated to have a high concentration in plasma of the PA inhibitor. After stimulation the release of t-PA into the blood was normal, the t-PA activity, however, was immediately inactivated by complex formation with the fast-acting PA inhibitor.