Effect of non-peptide tachykinin NK 1 receptor antagonists on non-adrenergic, non-cholinergic neurogenic mucus secretion in ferret trachea

Abstract

We investigated, in ferret trachea in vitro, the binding characteristics and the inhibition of non-adrenergic, non-cholinergic (NANC) neural mucus secretion of four tachykinin receptor antagonists: the non-peptide tachykinin NK 1 receptor antagonists CGP 49823 ((2 R,4 S)-2-benzyl-1-(3,5-dimethylbenzoyl)-4-(quinolin-μ-ylmethyl amino) piperidine), CGP 55000 ((2 R,4 S)-2-benzyl-1-(3,5-bistrifluoromethyl-benzoyl)-4-(quinolinyl-methylamino)piperidine) and CP 99,994 ((+)-(2 S,3 S)-3-methoxybenzyl amino)-2-phenylpiperidine), and the peptide tachykinin NK 2 receptor antagonist MEN 10,627 (cyclo(Met-Asp-Trp-Phe-Dap-Leu)cyclo(2β–5β)). CGP 49823, CGP 55000 and CP 99,994 concentration-dependently displaced [ 125I]Bolton–Hunter substance P binding in tracheal membranes with Hill coefficients not different from unity and IC 50 values of 1.4, 1.7 and 1.3 nM, respectively. In contrast, MEN 10,627 displaced binding according to a two-site model, with IC 50s of 0.2 nM and 1.3 μM. Electrical stimulation of tracheal segments with adrenoceptor and cholinoceptor blockade increased output of the mucus marker 35SO 4 by 59% above baseline (representing the NANC neural secretory response). CGP 49823, CGP 55000 or CP 99,994 concentration-dependently inhibited NANC neural secretion with IC 50 values of 30, 8 and 120 nM, respectively. In contrast, MEN 10,627 (3 μM) did not inhibit secretion. The NK 1 antagonists, but not the NK 2 antagonist, inhibited [Sar 9]substance P-induced secretion, while none of the antagonists affected acetylcholine-induced secretion. We conclude that NANC neural secretion in ferret trachea in vitro is a useful test system for tachykinin NK 1 receptor antagonists with therapeutic potential in conditions of the airways in which tachykininergic mechanisms and mucus hypersecretion are implicated in pathophysiology, for example asthma and chronic bronchitis.