THE BIOACTIVE PHOSPHOLIPID LYSOPHOSPHATIDIC ACID IS RELEASED FROM ACTIVATED PLATELETS

Lysophosphatidic acid (LPA) is a water-soluble phospholipid with hormo ne-like and growth-factor-like activities. LPA activates a putative G- protein-coupled receptor in responsive cells, but the natural source o f exogenous LPA is unknown. Here we show that LPA is present in mammal ian serum in an active form (bound to albumin) at concentrations of 1- 5 muM, but is not detectable in platelet-poor plasma, suggesting that LPA is produced during blood clotting. We find that thrombin activatio n of platelets prelabelled with [P-32]P(i) results in the rapid releas e of newly formed [P-32]LPA into the extracellular environment. We con clude that LPA is a novel platelet-derived lipid mediator that may pla y a role in inflammatory and proliferative responses to injury.