Relationship Between Arachidonic Acid Content Of Blood Platelets And Their TXA₂-Propduction Upon Stimulation

There is good evidence that the potency of activated platelets to produce thromboxane A₂ (TxA₂) is of primary importance in the regulation of arterial thrombus formation. Therefore it is useful to know the factors that determine platelet TxA₂-production. In order to investigate the importance of the platelet arachidonic acid (AA) content in this respect, 6 groups of 24 rats were fed various diets which were likely to induce different platelet AA-contents. After 15 weeks of feeding, platelet rich plasma (PRP) of 4 rats were pooled. In one part of each PRP pool aggregation was triggered with four doses of collagen. After 5 minutes the aggregated PRP was processed for measuring the HHT, produced by the activated platelets, (CG/MS) which is considered a measure for the TxA₂ produced. The other part of the PRP was used for measuring the fatty acid composition (GLC) of the 5 major phospholipid (PL) classes (separated by two-dimensional TLC). The various diets did not cause major changes in platelet total PL content and PL class distribution. Highly significant changes in the fatty acid compositions of platelet PL classes were observed. A striking positive correlation was found between the lyso-lecithin and the AA-con- tent of blood platelets, which suggests a functional interaction between these two parameters. There was also a highly significant, positive correlation between the AA-content of platelet PL and the TxA₂-production by these platelets. Platelets of sunflowerseed oil fed animals did not fit this relationship because their TxA₂-production is too high in relation to their AA-content. The relationships are essentially similar for total PL and the various PL classes and do not change when taking into account the presence of other long chain polyunsaturated fatty acids, known to compete with AA for the cyclo oxygenase enzyme system. From this study it is apparent that the platelet AA-content is an important determinant of TxA₂ formation.