Transformations of exogenous arachidonic acid in human platelets in the presence of oleic- and eicosapentaenoic acids.

Effects of various concentrations (12.5-50 microM) of eicosapentaenoic acid (EPA) on the metabolism of exogenous arachidonic acid (AA) in washed human platelets were examined under two different incubation conditions. First platelets were pretreated with EPA before exposing them to labelled AA. In the second incubation platelets were exposed to a mixture of EPA (12.5 and 25 microM) and labelled AA. At all concentrations EPA reduced thromboxane B2 (TxB2) formation, and at 25 and 50 microM this fatty acid reduced also prostaglandins (PGE2, PGF2 alpha). A reduced formation of PGs and TxB2 was confirmed by a decreased formation of PG-endoperoxides. While in EPA treated platelets less CO-(TxB2, HHT, PGs) and lipoxygenase (HETE) products were formed at 25 and 50 microM, more HETE seemed to be generated at lower EPA concentration (12.5 microM). Oleic acid reduced TxB2 formation at high concentration (100 microM). EPA showed a dose-dependent inhibition of platelet aggregation induced by arachidonate, epinephrine and collagen; it was most effective against AA-induced aggregation.