Dipyridamole inhibits platelet aggregation induced by oxygen-derived free radicals

Pyrogallol (a generator of superoxide anions) caused 50% increase in platelet aggregation induced by 400 microM of arachidonic acid. Dipyridamole did not produce a statistically significant inhibition of arachidonic-acid induced platelet aggregation, but it caused 100% inhibition of pyrogallol-stimulated platelet aggregation. Ferrous salts (Fe2+) induced 34% platelet aggregation which was inhibited (79.6%) by a concentration of dipyridamole of 10 microM. Dipyridamole inhibited ferrous-induced lipid peroxidation with IC-50 values of 17.5 microM. When arachidonic acid was used as aggregating agent, the corresponding IC-50 value was 140.5 microM. These results indicate that dipyridamole prevented platelet activation induced by oxygen-derived free radicals.