<prompt> Which of the following is an inhibitor of platelet aggregation?Leukotriene A4ProstacyclinThromboxane A2Protaglandin H2  <response>: Endothelial Cells Synthesize Prostacyclin Other Compounds That Affect Clotting ThrombosisThe endothelial cells in the walls of blood vessels make impoant contributions to the overall regulation of hemostasis and thrombosis.these cells synthesize the prostanoid prostacyclin PGI2, a potent inhibitor of platelet aggregation.Prostacyclin acts by stimulating the activity of adenylyl cyclase in the surface membranes of platelets its G protein-coupled receptor.The resulting increase of intraplatelet cAMP opposes the increase in the level of intracellular Ca2 produced by IP3 and thus inhibits platelet activation.Reference: Harper biochemistry30th edition page no 720 