Formation of lysophosphatidylcholine by human platelets in response to thrombin. Support for the phospholipase A2 pathway for the liberation of arachidonic acid.

Significant increases in lysophosphatidylcholine from a basal level of 4.2 +/- 0.36 nmol/mg of platelet protein to 6.4 +/- 0.46 nmol/mg of protein occur within 20 s after the addition of thrombin (5 units/ml) to washed human platelets. The increases are essentially complete by 1 min, at which time levels of 8.5 +/- 0.53 nmol of lysophosphatidylcholine/mg of platelet protein are reached. Decreases in phosphatidylcholine and also phosphatidylethanolamine occur within 20 s after stimulation of platelets by thrombin. These changes were detected by quantitative measurements of endogenous phospholipid phosphorus after extraction and thin layer chromatography of the platelet lipids. The concomitant increases in lysophosphatidylcholine and decreases in phosphatidylcholine, as well as the decreases in phosphatidylethanolamine, can only be explained by the stimulation of phospholipase A2 activity in platelets by thrombin.