Novel plasmin inhibitors released from bovine platelets during aggregation

Area of Science:

• Biochemistry
• Hematology
• Molecular Biology

Background:

• Antifibrinolytic activity is crucial for hemostasis and thrombosis.
• Platelets are known to play a role in regulating blood coagulation and fibrinolysis.

Purpose of the Study:

• To investigate the source and nature of antifibrinolytic activity observed during platelet aggregation.
• To identify and characterize specific inhibitors of plasmin released from platelets.

Main Methods:

• Platelet aggregation was induced using thrombin, ADP, and 5-hydroxytryptamine.
• Antifibrinolytic activity in the platelet suspension medium was measured.
• Protease inhibition assays were performed to determine inhibitor specificity.
• Activity staining and molecular weight determination were used to identify inhibitors.

Main Results:

• Antifibrinolytic activity was detected in platelet-rich medium during aggregation.
• Platelet inhibitors specifically targeted plasmin, not other proteases like urokinase, thrombin, or trypsin.
• Approximately 10(8) platelets released enough inhibitor to neutralize one casein unit of plasmin activity during thrombin-induced aggregation.
• Two distinct plasmin inhibitors with molecular weights of 25,000 and 17,000 were identified.

Conclusions:

• Platelets contain and release specific inhibitors of plasmin.
• These platelet-derived plasmin inhibitors contribute to antifibrinolytic activity.
• The identified inhibitors likely play a physiological role in thrombus formation by modulating fibrinolysis.