Differences in the effects of NK1‐receptor antagonists, (±)‐CP 96,345 and CP 99,994, on agonist‐induced responses in guinea‐pig trachea

1 The effects of the NK1‐receptor antagonists, (±)‐CP 96,345 and CP 99,994, on NK1‐agonist evoked contractions were compared in isolated rings of guinea‐pig tracheal smooth muscle. 2 (±)‐CP 96,345 and CP 99,994 were similarly effective in antagonizing responses evoked by septide, whereas CP 99,994 was more effective than (±)‐CP 96,345 in inhibiting responses evoked by [Sar9Met11(O2)] substance P. 3 These results suggest that responses to septide and [Sar9Met11(O2)] substance P may be operated via different populations of NK1‐receptors.