| Popis: |
Interferences of plasmin inhibitors are a main drawback in the functional assay of PAI in plasma. To overcome them, an acidification step, prior to residual tPA assay has been frequently used.A simple chromogenic method, based on the inhibition of purified tPA by plasma prediluted in PAI-depleted plasma, is described. The residual tPA was subsequently measured in the presence of fibrinogen fragments used as Stimulator, plasminogen and chromogenic substrate (CBS 30.41). The assay can discriminate between PAI and plasmin inhibitors since the concentration of these proteins remains constant because brought in excess by the PAI-depleted plasma. Parallel dose-response curve were obtained when PAI-depleted plasma was used instead of buffer, for the preparation of the reference curve and for the dilution of samples. The residual tPA activity measured was directly proportional to the PAI activity of the sample using a single concentration of tPA. Samples containing 0 to 30 IU/ml of PAI could be measured using a 1:40 dilution.Values for 27 normal volunteers at rest were 5.1 IU/ml (range : 0 to 11.8 IU/ml). PAI activity was decreased in afternoon samples (4.6 IU/ml) compared to those of the morning (5.8 IU/ml). After stasis, when a concomitant release of tPA was observed, the values obtained (3.1 IU/ml) were significantly lower than the values obtained before (4.1 IU/ml).The activity measured is probably related to PAI-1 (endothelial ceil type PAI), but PAI-2 related activity (placental PAI) can be also estimated since pregnancy plasma showed high levels of inhibitor (mean : 15.1 IU/ml, range : 9.5 to 28.1 IU/rni).The present method is simple and rapid to perform. It can be routinely used in the screening of various thrombotic disorders. |
