A quantitative evaluation of the inhibition of platelet aggregation by low molecular weight degradation products of fibrinogen.

Abstract

Summary. The inhibitory effect of low molecular weight degradation products of fibrinogen (peptides) on in vitro platelet aggregation has been studied quantitatively. In our test system (0.3 μm ADP at 25°C) only concentrations higher than 0.65 mg/ml showed significant inhibitory activity. The higher concentrations of peptides also inhibited platelet aggregation induced by adrenaline, collagen and thrombin. Ultrafiltrates of plasma from patients receiving streptokinase showed no increase in inhibition of platelet aggregation as compared with pretreatment samples. This supports the idea that the peptides produced by streptokinase‐induced fibrinogcnolysis exert a quantitatively weak effect. Peptides produced by digestion of serum with trypsin showed inhibitory activity similar to that of the peptides produced by digestion of fibrinogen with plasmin, indicating that the inhibitory effect is unspccific as far as the protein source and the acting enzyme are concerned. Some specificity may exist, however, related to size and/or charge of the peptides, as suggested by the present experiments. These data do not support the view that the low molecular weight degradation products of fibrinogen significantly impair platelet aggregation in the fibrinolytic states.