In vivo evidence for the activation of a septide-sensitive tachykinin receptor in guinea pig bronchoconstriction.

Intravenous administration of the undecapeptide [Sar9]substance P (SP) sulfone (1.5 nmol/kg) and the hexapeptide [Glp6,Pro9]SP(6-11) (septide; 0.4 nmol/kg) produced a comparable (about 30-40% of maximal effect) increase of insufflation pressure (bronchospasm) in anesthetized guinea-pigs. The non peptide NK-1 receptor antagonist, (+/-)CP 96,345 and the peptide NK-1 receptor antagonist, GR 82,334 antagonized dose-dependently the response to both agonists. Both antagonists were more potent against septide than against [Sar9]SP sulfone (9 and 4 fold difference in ED50 for (+/-)CP 96,345 and GR 82,334, respectively). These findings indicate that a 'septide-sensitive' mechanism mediates bronchoconstriction in vivo and it influences the estimate of the potency of NK-1 receptor antagonists.