A group of leukotrienes; (LTC4; LTD4; and LTE4) that is the major mediator of bronchoconstriction; hypersensitivity; and other allergic reactions. Earlier studies described a "slow-reacting substance of anaphylaxis" released from lung by cobra venom or after anaphylactic shock. The relationship between srs-a leukotrienes was established by UV which showed the presence of the conjugated triene. (From Merck Index, 11th ed)