Effect of a new dual neurokinin antagonist on airway smooth muscle in situ.

The effect of FK224 (N-(N2-[N-¿N-(N-2,3-didehydro-N-methyl-N-[N-3- (2-pentylphenyl)-propionyl¿-L-threonyl]tyrosyl-L-leucynyl)-D -phenylalanyl¿-L-allothreonyl]-L-asparaginyl)-L-serine-v-lacto ne, CAS 125787-94-2) on isometric contraction of canine tracheal smooth muscle in situ was studied. Contraction was induced by administration of substance P, neurokinin A, and neurokinin B intra-arterially into the tracheal circulation in five mongrel dogs. FK224 inhibited substance P- and neurokinin A-induced contraction in a dose-dependent manner, but it did not inhibit neurokinin B-induced contraction significantly. These data suggest that FK224 is a dual antagonist of both neurokinin 1 and neurokinin 2 receptors, with a similar potency in in vivo experiments.