Leukotrienes are produced from ?

Leukotrienes (LTs) - They are produced from arachidonic acid. LT B4 is produced in neutrophils; it is the most potent chemotactic agent (factor attracting cells to the inflammatory site). The number 4 denotes that there are 4 double bonds in the structure. The 12-lipo-oxygenase in platelets produces 12-HETE (hydroxy eicosa tetra-enoic acid) and 15-lipo-oxygenase in eosinophils produce 15-HETE. The slow reacting substance of anaphylaxis (SRS-A) contains LTC4, LTD4 and LTE4 . They cause smooth muscle contraction, constrict the bronchioles, increase capillary permeability, activate leukocytes and produce vasoconstriction. SRS is the mediator of hypersensitivity reactions such as asthma. REF : DM VASUDEVAN TEXTBOOK OF BIOCHEMISTRY, SIXTH EDITION, PG.NO., 165.