This paper describes the evaluation of LY170680 (5-less than 3-[2(R) (carboxyethylthio)-(S)-hydroxypentadeca 3(E)5(Z)-dienyl]phenyl greater than 1H tetrazole, as an antagonist of the cysteinyl leukotrienes C4, D4, E4, in a variety of in vitro and in vivo models. 2. In vitro, LY170680 was a potent, selective, and competitive antagonist of LTD4, and LTE4. It produced a concentration-dependent rightward displacement of the concentration-response curves elicited by either LTD4 or LTE4 on both the guinea-pig ileal and tracheal preparation. The pA2 values for LY170680 were estimated to be 8.1 +/- 0.2 (n = 8) and 8.1 +/- 0.1 (n = 6) on trachea, and 8.7 +/- 0.1 (n = 12) and 9.0 +/- 0.3 (n = 6) on ileum for both LTD4 and LTE4 respectively. The slopes of the Schild plots in these studies were all close to unity. 3. LY170680 was shown to be a modest antagonist of the LTC4-induced responses on guinea-pig ileum (pA2 7.0 +/- 0.2 n = 5), but had no discernable effects against contractions induced by histamine, prostaglandin E2 (PGE2), PGF2 alpha or acetylcholine. The compound also reduced the LTC4-induced responses on trachea, but in a non competitive manner. 4. Intravenous LY170680 reduced in a dose-dependent manner (ED50 3.8 mg kg-1, 60 min pretreatment) the fall in compliance in the anaesthetized guinea-pig, and the rise in total pulmonary resistance (TPR) (ED50 2.0 mg kg-1, 30 min pretreatment) in the artificially ventilated guinea-pig, produced by intraveous LTD4. 5. LY170680 (5mgkg-1, i.v.) was also effective in reducing the increase in TPR to intravenous antigen in sensitized animals pretreated with mepyramine, indomethacin and propranolol. 6. The compound was only moderately effective (ED5o 40mgkg-1 p.o.) in preventing the rise in TPR induced by intravenous LTD4, when given orally. 7. Inhaled LY170680 was particularly effective in preventing the increase in TPR produced by an exposure to aerosolised LTD4. An estimated 1-2 pg of LY170680 delivered to the airways by nebuliser 1 hour beforehand, produced a 6 fold lateral displacement to the right of the dose-response curve to LTD4. 8. Studies in conscious animals indicated that inhaled LY170680 produced a dose-dependent reduction in the increased volume of gas, trapped in the lung following exposure to aerosolised LTD4. Duration studies also indicated that an estimated inhaled dose of 10 g LY170680 significantly reduced the LTD4-induced' increase in trapped lung gas volume for at least 4 h. Inhaled LY170680 also reduced LTC4-induced increase in gas trapping in a manner similar to LTD4. However, histamine-induced gas trapping was unaffected.
