The cysteinyl-leukotrienes act at a single receptor (CysLT1) located on the airway muscle. Stimulation of this receptor induces airway muscle contraction. This response is blocked by a variety of antagonists (CysLT1-antag). In the smooth muscle of pulmonary veins another cysteinyl-leukotriene receptor (CysLT2) is present. Stimulation of this receptor produced a contraction which was not blocked by the antagonists known to be effective in airways. In addition, the endothelium contains two receptors; a (CysLT1) which is associated with contraction and is blocked by the antagonists as well as a second receptor (CysLT2) associated with relaxation. This latter receptor is also resistant to the antagonists which block the airway responses (Gorenne et al., Trends Pharmacol. Sci., 1996). Functional studies of leukotriene receptors in vascular tissues (Walch et al., Am. J. Respir. Crit. Care Med., 2000). International Union of Pharmacology XXXVII. Nomenclature for leukotriene and lipoxin receptors. Brink C, Dahlen SE, Drazen J, Evans JF, Hay DW, Nicosia S, Serhan CN, Shimizu T, Yokomizo T. Pharmacol Rev. 2003 Mar;55(1):195-227 (pdf).