Inhibitory effect of stearidonic acid (18:4 n-3) on platelet aggregation and arachidonate oxygenation

The effect of stearidonic acid (18:4 n-3) present in fish and some plant oils, such as black currant seed oil, was studied on human platelets. When added to platelets simultaneously with collagen, arachidonic acid or endoperoxide mimetic U46619, 18:4 n-3 appeared as a weak inhibitor of platelet aggregation. In addition, 18:4 n-3 did not alter the metabolism of exogenous arachidonic acid. In contrast, when preincubated with platelets after precoating onto albumin, 18:4 n-3 inhibited platelet aggregation induced by thrombin, collagen, arachidonic acid or U46619, and was as potent as eicosapentaenoic acid (20:5 n-3) tested under similar conditions. Stearidonic acid also altered the endogenous arachidonate oxygenation stimulated by low doses of thrombin, but to a significantly lesser extent than did 20:5 n-3. It seems therefore that, in addition to competing with endogenous arachidonate metabolism, 18:4n-3 may affect platelet aggregation by another mechanism.