Prostaglandins are synthesized from arachidonate(Lipoxygenase which catalyze the dioxygenation of polyunsaturated fatty acids) in the cell membrane by the action of phospholipase A2. Cyclooxygenase and lipoxygenase pathways, compete with one another to form prostaglandins(as well as thromboxane or leukotriene-leukotriene being a bronchial stimulator),
In the cyclooxygenase pathway, the prostaglandins D, E and F plus thromboxane and prostacyclin are made. Thromboxanes are made in platelets and cause constriction of vascular smooth muscle and platelet aggregation
Leukotrienes are made in leukocytes and macrophages via the lipoxygenase pathway. They are potent constrictors of the bronchial airways. They are also important in inflammation and hypersensitivity reactions as they increase vascular permeability.