Anti-leukotriene effects of WY-50,295 tromethamine in isolated guinea pig pulmonary tissues.

The abilities of WY-50,295 tromethamine, a 5-lipoxygenase inhibitor, to inhibit antigen-induced leukotriene (LT) release from guinea pig lung fragments, and to prevent LTD4 or antigen-induced contraction of isolated guinea pig tracheal muscle were compared with the activities of zileuton and MK-886 (two selective 5-lipoxygenase inhibitors), and LY171883 (a LTD4 receptor antagonist). In fragmented guinea pig lung, WY-50,295 tromethamine inhibited antigen-induced LT release with an IC50 of 0.63 microM, and was 4.6- and 5.2-fold more potent than zileuton and MK-886, respectively. WY-50,295 tromethamine differed from these 5-lipoxygenase inhibitors, however, in that WY-50,295 tromethamine competitively antagonized LTD4-induced tracheal contractions (pA2 = 6.06) at concentrations that inhibited LT release. LY171883 was an effective LTD4 receptor antagonist (pA2 = 6.96), that only inhibited antigen-induced LT release at higher concentrations (IC50 = 7.9 microM). WY-50,295 tromethamine almost completely inhibited antigen-induced leukotriene-dependent tracheal contractions, whereas high concentrations of zileuton, MK-886, or LY171883 produced only partial inhibition. This partial inhibition was likely to result from 'breakthrough' 5-lipoxygenase activity, because combinations of zileuton plus MK-886 or zileuton plus LY171883, were more effective than zileuton, MK-886, or LY171883 alone. The greater efficacy of WY-50,295 tromethamine in the antigen-challenged guinea pig trachea is likely to result from its combined abilities to prevent LT biosynthesis and block LTD4 receptors.