Leukotriene D<sub>4</sub> (LTD<sub>4</sub>) is one of the leukotrienes. Its main function in the body is to induce the contraction of smooth muscle, resulting in bronchoconstriction and vasoconstriction. It also increases vascular permeability. LTD<sub>4</sub> is released by basophils. Other leukotrienes that function in a similar manner are leukotrienes C<sub>4</sub> and E<sub>4</sub>. Pharmacological agents that inhibit the function of these leukotrienes are leukotriene receptor antagonists (e.g., zafirlukast, montelukast) and are useful for asthmatic individuals.