Arachidonic acid distribution and release in human and rat blood platelets: importance of transacylases]

Human platelets release about 5 fold more arachidonate than rat platelets when they ar triggered with a high dose of thrombin. Total arachidonate content of the phospholipids was not significantly different between the two species. In contrast, phosphatidylcholine (PC) from human platelets exhibited twice more arachidonate than PC from rat platelet and opposite arachidonate contents were found in phosphatidylethanolamine. Moreover, rat platelet PC was very rich in disaturated species, primarily dipalmitoyl whereas high levels of oleate and linoleate were present in human platelets PC. The differences in the fatty acids content of the two species are the result of CoA-independent and CoA-dependent transacylase activities which are more efficient in rat than in human platelets and could account for the low level of arachidonate released from rat platelets.