LTD4 is one of the constituents of slow-reacting substance of anaphylaxis (SRS-A) produced by the metabolism of LTC4 by γ-glutamyl transpeptidase. It is the first CysLT metabolite of LTC4. Like LTC4, LTD4-induced bronchoconstriction and enhanced vascular permeability contribute to the pathogenesis of asthma and acute hypersensitivity. LTD4 is equipotent to LTC4 in its biological activities, except that LTD4 is nearly 100-fold more effective in the contraction of peripheral airway smooth muscle.