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[Kinetics of merthiolate-induced aggregation of human platelets]
Abstract:
Incubation of human platelets (in the form of platelet rich plasma or washed platelet suspension) with sodium merthiolate (ethyl mercuric salicylate inhibiting the arachidonic acid incorporation into phospholipids) induces their irreversible aggregation, which is accompanied by TxB2 synthesis. The merthiolate-induced aggregation has a lag-period of 0.5-10 min, whose magnitude is inversely correlated with the merthiolate concentration. The concentration dependencies of the rate of the merthiolate-induced and arachidonate-induced aggregation are threshold ones; the Hill coefficients are more than 30. The merthiolate-induced aggregation occurs in two phases: a slow phase which is independent of the arachidonic acid cyclooxygenase metabolism and a fast phase which is fully blocked by indomethacin. This aggregation is inhibited by PGE1 and ajoene (an inhibitor of the fibrinogen interaction with the fibrinogen receptor, GPIIb/IIIa). Quantitative and qualitative analyses of the experimental data were performed, using a model which took account of: (a) increase in the concentration of free endogenous arachidonic acid resulting from the inhibition by merthiolate of the arachidonic acid re-incorporation into phospholipids, and (b) existence of a threshold intracellular arachidonic acid concentration needed for the irreversible aggregation of platelets.
Insights
Sodium merthiolate causes irreversible platelet aggregation by increasing free arachidonic acid levels. This process involves a threshold concentration and is inhibited by PGE1 and ajoene.
Area of Science:
- Biochemistry
- Hematology
- Pharmacology
Background:
- Platelet aggregation is a critical process in hemostasis and thrombosis.
- Arachidonic acid metabolism plays a key role in platelet activation.
- Sodium merthiolate is known to affect cellular processes.
Purpose of the Study:
- To investigate the mechanism of sodium merthiolate-induced platelet aggregation.
- To elucidate the role of arachidonic acid in this process.
- To identify potential inhibitors of merthiolate-induced platelet aggregation.
Main Methods:
- Incubation of human platelets (platelet rich plasma or washed suspensions) with sodium merthiolate.
- Measurement of platelet aggregation and thromboxane B2 (TxB2) synthesis.
- Analysis of concentration dependencies and lag-period kinetics.
- Inhibition studies using PGE1 and ajoene.
- Modeling of arachidonic acid metabolism and platelet aggregation.
Main Results:
- Sodium merthiolate induces irreversible platelet aggregation and TxB2 synthesis.
- Aggregation exhibits a concentration-dependent lag-period.
- Concentration dependencies for merthiolate- and arachidonate-induced aggregation show threshold kinetics (Hill coefficients > 30).
- Merthiolate-induced aggregation has a slow, cyclooxygenase-independent phase and a fast, indomethacin-sensitive phase.
- PGE1 and ajoene inhibit merthiolate-induced aggregation.
Conclusions:
- Merthiolate-induced platelet aggregation is mediated by an increase in free endogenous arachidonic acid due to inhibited re-incorporation into phospholipids.
- A threshold intracellular arachidonic acid concentration is necessary for irreversible platelet aggregation.
- Merthiolate serves as a tool to study platelet activation pathways involving arachidonic acid.