Tomelukast

We performed an in vivo evaluation of bronchodilation using a model of antigen-induced bronchoconstriction in anesthetized guinea pigs pretreated with indomethacin, pyrilamine and propranolol, and the results were compared with those for the histamine-induced response. Test drugs were administered intravenously when the antigen or histamine response reached its peak. Leukotriene (LT) D4 antagonists, FPL55712 and LY171883, gradually reduced the antigen-induced response, whereas the lipoxygenase inhibitor phenidone had no such effect. The bronchodilator theophylline rapidly reduced the antigen-induced response, and the adenylate cyclase activator forskolin had a similar effect. The following drugs also had no effect: nifedipine (calcium-channel antagonist), cromakalim (potassium-channel opener), amlexanox and disodium cromoglycate: DSCG (anti-allergic drugs), OKY-046 (thromboxane A2 synthetase inhibitor), and dapsone (anti-inflammatory drug). Theophylline, the beta-adrenoceptor agonist salbutamol and the histamine H1-blocker pyrilamine had only a small reversing effect on histamine-induced bronchoconstriction. These results suggest that antigen-, but not histamine-, induced bronchoconstriction in anesthetized guinea pigs is a useful in vivo model for evaluating the bronchodilating effect of anti-asthmatic drugs.

Peptido-leukotrienes (LTs) elicit myocardial depression in several mammalian species, and radioligand binding assays with 3H-LTC4 and 3H-LTD4 have provided evidence of putative receptor sites on guinea pig cardiac ventricular membranes (GPCVM). Our objective was to characterize specific binding of 3H-ICI 198,615, a potent and selective LTD4 antagonist, to the 155,000 X g pellet of GPCVM. 3H-ICI 198,615 (0.01-3.8 nM) showed high specific binding (85-90% of total), which was protein dependent, saturable (Bmax = 4914 +/- 706 fmol/mg protein, n = 3), of high affinity (Kd = 4.3 +/- 0.8 nM, n = 3) and without cooperativity. Equilibrium binding was achieved by 20 minutes and could be rapidly reversed by addition of excess unlabeled ICI 198,615 or FPL55712. Competition studies with 3H-ICI 198,615 against several LTD4 antagonists produced an order of potency: ICI 198,615 much greater than SKF102922 greater than FPL55712 greater than or equal to LY171883. Addition of divalent cations caused a concentration dependent decrease in specific binding apparently due to a reduction in affinity. Binding was not influenced by the guanine nucleotide analogs GTP gamma S and Gpp(NH)p, EDTA, or a multitude of diverse non-LT receptor agonists and antagonists. These data provide evidence supporting the existence of specific and high affinity binding sites for 3H-ICI 198,615 in GPCVM.