THE EFFECT OF THE NK2 TACHYKININ RECEPTOR ANTAGONIST SR-48968 (SAREDUTANT) ON NEUROKININ-A INDUCED BRONCHOCONSTRICTION IN ASTHMATICS

Inhalation of neurokinin (NK) A causes bronchoconstriction in patients with asthma. The NKA-induced bronchoconstriction in isolated human ai rways is mediated via the NK2 receptor and inhibited by SR 48968, a po tent and specific nonpeptide tachykinin NK2 receptor antagonist. In th e present study, the effect of orally administered SR 48968 on NKA-ind uced bronchoconstriction was examined in 12 mild asthmatics, On the sc reening day and during the study periods, increasing concentrations of NKA (3.3x10(-9) to 1.0x10(-6) mol.mL(-1)) were inhaled, until the for ced expiratory volume in one second (FEV1) and specific airway conduct ance (sGaw) decreased by at least 20 and 50%, respectively. During the study periods, 100 mg SR 48968 or matched placebo was ingested in a d ouble-blind, randomized, crossover fashion and NKA provocation was per formed at 1.5 and 24 h after dosing. At 15 h, the mean (SEM) log10 pro vocative concentration of NKA causing a 20% fall in FEV1 (PC20 FEV1) w as -6.25 (0.20) after SR 48968 and -6.75 (0.17) after placebo (p=0,05) ; the mean log10 provocative concentration of NKA causing a 35% fall i n sGaw (PC35 sGaw) was -7.02 (0.28) after SR 48968 and -7.64 (0.19) af ter placebo (p=0,05),At 24 h, the mean log10 PC20 FEV1 was -6.21 (0.17 ) after SR 48968 and -6.65 (0,11) after placebo (p=0,05); the mean log 10 PC35 sGaw was -6.85 (0.23) after SR 48968 and -7.17 (0.15) after pl acebo (nonsignificant).As PC20 FEV1 and/or PC35 sGaw were not reached in up to 4 patients per SR 48968 group, the differences between SR 489 68 and placebo were underestimated. In conclusion, oral treatment with 100 mg SR 48968 caused a significant inhibition of neurokinin A-induc ed bronchoconstriction in asthmatics, This finding constitutes the fir st evidence of inhibition of sensory neuropeptide-induced bronchoconst riction by a selective tachykinin receptor antagonist in humans.