3 FK888 inhibited the contraction of guinea-pig isolated ileum induced by SP in the presence of atropine and indomethacin (a NKI receptor bioassay) with a pA2 value of 9.29 (8.60-9.98).4 FK888 inhibited contractions of rat vas deferens by NKA (a NK2 receptor bioassay) and of rat portal vein by NKB (a NK3 receptor bioassay) at concentrations at least 10,000 times greater than that required to inhibit contractions of guinea-pig ileum. 5 FK888 also inhibited SP-induced airway oedema in guinea-pig after both intravenous and oral administration. 6 These data demonstrate that FK888 is a potent and selective NK, antagonist which is active both in vitro and in vivo.

1 We have discovered a novel tripeptide substance P (SP) antagonist, FR 113680 [N-[N`-(N-acetyl-L-

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