Arachidonic acid metabolism in platelets stored for 5 days

(C-14)-Arachidonic acid [(C-14)-AA] metabolism was studied in platelet concentrates (PCs) stored for 5 d. There was a gradual decrease in uptake of radioactivity from day 0 to 3 (P less than 0.01). On day 0, distribution of radioactivity in platelet phospholipids (PLs), and formation of phosphatidic acid, HETE and cyclooxygenase products, when platelets were exposed to thrombin (5 U/ml), were similar to that reported for fresh platelets. On day 3 there was a change in the distribution of (C-14)-AA in platelet PLs which consisted of an increase in the percentage of radioactivity bound to phosphatidylserine, from 5.3 +/- 0.9% on day 0 to 8.8 +/- 1.5% on day 3 (P less than 0.001), and a decrease in (C-14)-AA in phosphatidylinositol (PI), from 12.4 +/- 1.5% on day 0, to 7.9 +/- 0.9% on day 3 (P less than 0.001). Phosphatidic acid generated by thrombin-stimulated platelets on day 0, comprised 2.6 +/- 0.5% of total radioactivity, but dropped to 1.4 +/- 0.3% on day 3 (P less than 0.001), and 0.9 +/- 0.2% on day 5 (P less than 0.01). These values showed a good correlation with the percentage of (C-14)-AA released from PI on the same days (r = 0.9). On day 0, 13.4 +/- 4.4% of platelet radioactivity was released from phosphatidylcholine by thrombin, but this amount was reduced to 6.8 +/- 3.4% on day 5 (P less than 0.05). Generation of radioactive 12-hydroxy-5,8,10,14-eicosatetraynoic acid (HETE) also dropped from 7.2 +/- 2.9 on day 0, to 2.1 +/- 1 on day 5 (P less than 0.01). We could not detect changes in cyclooxygenase metabolites. In conclusion, we suggest that various enzymatic pathways implicated in AA metabolism by platelets are impaired by storage.