Abstract
THE prostaglandin (PG) endoperoxides, PGG2 and PGH2, are thought to have a function in human platelet aggregation, since they are formed during thrombin-induced aggregation1. They induce aggregation on addition to platelet-rich plasma (PRP), either directly or after conversion to thromboxane A2 (TXA2)2. TXA2 (half life ∼ 30 s) is formed in vitro by a microsomal enzyme which is insensitive to inhibition by aspirin-like drugs3,4. It is therefore distinct from the cyclo-oxygenase that converts arachidonic acid (AA) into PG endoperoxides. AA, after incorporation into membrane phospholipids, is liberated during thrombin-induced aggregation and is then almost completely metabolised5 by the cyclo-oxygenase and AA-lipoxygenase6. Therefore, we tested platelets of animals that were deprived of AA, and still observed aggregation with collagen, indicating that PG endoperoxides and TXA2 are not essential for aggregation.
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