Serotonin release and phosphoinositide breakdown in thrombin-induced activation of human platelets

The release reaction and the metabolism of inositol lipids were studied in parallel in washed human platelets following the activation by low doses of thrombin. The breakdown of phosphatidylinositol 4,5-bisphosphate (PI-P2) was accompanied by the release of serotonin. These events preceded the breakdown of the other phosphoinositides and the release of alpha-granules and lysosome constituents, respectively. The secretion of serotonin probably is triggered by products of thrombin-induced activation of the phospholipase C directed against PI-P2.