<prompt> Thromboxane is produced by?PlateletsLeukocytesVessel wallRBCs  <response>: Ans. a Platelets. Ref. Robbin, Pathology, 6th ed., 70, 71; Harpers biochemistry 27th ed. Table 50-3 Platelets contain the enzyme thromboxane synthetase and hence TXA2, is major product in these cells.Thromboxane A2 TxA2, a potent platelet-aggregating agent and vasoconstrictor, is itself unstable and rapidly converted to its inactive form TxB2. TXA, acts in cyclooxygenase pathway of inflammation.Inflammatory actions of eicosanoids: MetaboliteActions1TXA2 LTC4, D4, E4Vasoconstriction2PGI2 PGE1 PGE2 PGD2Vasodilatation3LTC4 D4, and E4Increased vascular permeability4LTB4 HETE, lipoxinChemotaxis, leukocyte adhesion5Chemokine eotaxinRecruitment of EosinophilsMolecules Synthesized by Endothelial Cells - Role in the Regulation of Thrombosis and Fibrinolysis.MoleculeActionADPase an ectoenzymeDegrades ADP an aggregating agent of platelets to AMP PiNitric oxide NOInhibits platelet adhesion and aggregation by elevating levels of cGMPHeparan sulfate a glycosaminoglycanAnticoagulant; combines with antithrombin to inhibit thrombinProstacyclin PGI2 a prostaglandinInhibits platelet aggregation by increasing levels of cAMP MoleculeActionThrombomodulin a glycoproteinBinds protein C, which is then cleaved by thrombin to yield activated protein C; in combination with protein S degrades factors Va and Villa, limiting their actions.Tissue plasminogen activatort-PA, a proteaseActivates plasminogen to plasmin, which digests fibrin; the action of t-PA is opposed by plasminogen activator inhibitor-1 PA 1 -1 