1. The prostanoids are oxygenated derivatives of C20 fatty acids, mainly arachidonic acid, generated by the cyclooxygenase pathway. There are two important classes of prostanoids: the prostaglandins and the thromboxanes. Prostanoids are not stored. They are synthesised de novo and are released in response to a stimulus.59 Vascular endothelial cells release prostanoids, especially prostacyclin, when properly stimulated by agents such as histamine or thrombin. Prostacyclin was first detected in the vascular wall by Moncada et al in 1977.60 Since then its biological activity as a vasodilator and a potent inhibitor of platelet activation has been described. As LSEC differ both morphologically, for example, fenestration clustered in sieve plates and functionally, for example, expression of Fc receptors,61 from endothelial cells of other sources, data concerning prostanoids release by vascular endothelial cells from large vessels cannot be readily applied to the liver