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Kinetics of merthiolate-induced aggregation of human platelets
P V Vrzheshch1, A V Tatarintsev, E V Orlova
1Bio-Rad Laboratories T.O. BioChemMack, Moscow, Russia.
Abstract:
Incubation of human platelet-rich plasma (PRP) or washed platelets with merthiolate (MT; sodium ethylmercurithiosalicylate; an inhibitor of lysophosphatide: arachidonoyl transferase) leads to irreversible platelet aggregation which is parallelled by an increase in thromboxane A2 synthesis. MT-induced aggregation is preceded by a pronounced lag-period (0.5-10 min). Duration of the latter is inversely related to the concentration of MT ([MT]). Platelet responses to MT are similar to those triggered by arachidonate (AA) in that the relationships of the aggregation rates both to [MT] and [AA] are threshold and exhibit characteristic super-high values of the apparent Hill coefficients (h > 30). A typical MT-induced response can be subdivided in two sequential phases: i) cyclooxygenase-independent slow aggregation, and ii) indomethacin-abrogated rapid aggregation. MT-induced responses are blocked by PGE1 or ajoene (which inhibits binding of fibrinogen to its cell surface receptor, GPIIb/IIIa). The obtained data are interpreted both quantitatively and qualitatively in terms of a model assuming the existence of: i) a relationship between the rate of MT-inhibitable AA incorporation into phospholipids and the concentration of intracellular free AA, [AA]i; ii) a certain threshold value of [AA]i essential for triggering the second phase of the aggregation.
Insights
Merthiolate (MT) induces irreversible platelet aggregation and thromboxane A2 synthesis in human platelets. This response, involving arachidonic acid (AA) and occurring in two phases, can be blocked by PGE1 or ajoene.
Area of Science:
- Biochemistry
- Hematology
- Pharmacology
Background:
- Platelet aggregation is crucial for hemostasis and thrombosis.
- Thromboxane A2 (TXA2) is a key mediator of platelet activation.
- Merthiolate (MT) is known to affect platelet function.
Purpose of the Study:
- To investigate the mechanism of MT-induced platelet aggregation.
- To elucidate the role of arachidonic acid (AA) and TXA2 in MT-induced responses.
- To characterize the phases of MT-mediated platelet activation.
Main Methods:
- Incubation of human platelet-rich plasma (PRP) and washed platelets with MT.
- Measurement of platelet aggregation rates and TXA2 synthesis.
- Analysis of dose-response relationships and Hill coefficients.
- Assessment of the effects of indomethacin, PGE1, and ajoene.
Main Results:
- MT induced irreversible platelet aggregation and increased TXA2 synthesis.
- MT-induced aggregation showed a lag phase inversely proportional to MT concentration.
- Responses to MT and AA exhibited threshold kinetics with high Hill coefficients.
- MT-induced aggregation occurred in two phases: cyclooxygenase-independent and indomethacin-abrogated.
- PGE1 and ajoene blocked MT-induced platelet responses.
Conclusions:
- MT triggers platelet aggregation via a mechanism involving AA incorporation into phospholipids.
- A threshold concentration of intracellular AA is necessary for the rapid aggregation phase.
- MT-induced platelet activation is a complex process with distinct sequential phases.