Aggregation of platelets and inert particles induced by thrombin

|June 30, 1976

Summary

Thrombin triggers platelet aggregation through ADP release and fibrin polymerization. This study reveals fibrin

Area of Science:

Background:

Platelet aggregation is crucial for hemostasis and thrombosis.
Thrombin plays a key role in activating platelets and initiating blood coagulation.
The precise mechanisms underlying thrombin-induced platelet aggregation, particularly the role of fibrinogen-fibrin transformation, require further elucidation.

Purpose of the Study:

To investigate the role of fibrinogen-fibrin transformation in thrombin-induced platelet aggregation using aggregometer tracings.
To differentiate the contributions of platelet ADP release and fibrin polymerization to platelet aggregation.
To explore the interaction between thrombin-activated platelets and polymerizing fibrin.

Main Methods:

Washed platelet suspensions and inert particle suspensions were used.
Thrombin was added at concentrations of 0.25-2.0 U/ml.
Light transmission increase (LTI) and platelet aggregation were monitored using aggregometry and phase microscopy.
Inhibitors such as sodium sulfite, apyrase, and PGE1 were employed.
Experiments were conducted with and without fibrinogen.

Main Results:

Thrombin induced two waves of LTI in the presence of fibrinogen, accompanied by aggregate formation.
Without fibrinogen, thrombin caused rapid ADP release but failed to induce a second LTI wave.
The second LTI wave was linked to the interaction of thrombin-treated platelets or particles with polymerizing fibrin.
Inhibitors of fibrin polymerization (sodium sulfite, low pH) blocked the second LTI wave.
Apyrase and PGE1 affected the first LTI wave but not the second.

Conclusions:

Thrombin-induced platelet aggregation involves both ADP release (first phase) and interaction with polymerizing fibrin (second phase).
Fibrinogen-fibrin transformation is essential for the second phase of thrombin-induced platelet aggregation.
The blood coagulation system appears to directly participate in platelet aggregation mechanisms.

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