Blood platelets and vascular endothelium generate prostaglandin derivatives with opposing effects: cyclic endoperoxides and thromboxane A2 (TXA2) aggregate platelets, whereas prostaglandin I2 (PGI2, prostacyclin) inhibits aggregation. Since aspirin inhibits the synthesis and effects of all these metabolites of arachidonic acid, the rationale for clinical use of this drug in thrombosis prevention trials is questionable. Treatment schedules would have to be calibrated to inhibit proaggregating platelet prostaglandins and TXA2 without affecting protective vascular prostaglandins (PGI2). This important clinical information cannot easily be obtained from studies in man. The present study indicates that normal rat platelets are more sensitive to aspirin (ID50=3̇6 mg/kg) than arterial tissues (ID50=25̇0 mg/kg) and are almost as sensitive as venous tissues (ID50=2̇3 mg/kg). Platelet prostaglandin production was monitored through the measurement of malondialdehyde (MDA) output and standard stimulation with thrombin. PGI2-like activity released from the abdominal aorta and inferior vena cava was determined as platelet aggregation inhibitory potency and characterized by standard criteria. The inhibitory effect of aspirin (at doses of 10 and 50 mg/kg) on platelet MDA production lasted much longer in platelets (96-120 h) than in venous (24-72 h) or arterial tissue (less than 24 h). The findings suggest that in rats the (potentially antithrombotic) effect of aspirin on platelet prostaglandin and TXA2 generation may be distinguished, though not completely, from the (potentially prothormbotic) effect on vascular PGI2 on the basis of duration of inhibition more than on the sensitivity of the target cells to the drug. The different capacities of anucleated platelets and of nucleated vascular endothelial cells to overcome aspirin inhibition could be exploited for more rational clinical use of this drug.
|Number of pages||7|
|Journal||British Journal of Haematology|
|Publication status||Published - 1979|
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