(+/-)-CP-96,345, a selective tachykinin NK1 receptor antagonist, has non-specific actions on neurotransmission.

1. The non-specific effects of the non-peptide tachykinin receptor antagonist (+/-)-CP-96,345, were assessed in several smooth muscle-nerve preparations. The preparations were the iris sphincter muscle of the rabbit and the taenia coli, vas deferens and seminal vesicle of the guinea-pig. 2. (+/-)-CP-96,345 concentration-dependently inhibited the electrically evoked, tachykinin-mediated contractile responses of the iris sphincter and the taenia coli. The pIC50 values were 5.4 +/- 0.2 (mean +/- s.e.mean) and 5.7 +/- 0.08 respectively. 3. (+/-)-CP-96,345 also inhibited non-tachykinin-mediated contractile responses to electrical stimulation of the iris sphincter, taenia coli, vas deferens and seminal vesicle. The pIC50 values were 4.3 +/- 0.02, 4.8 +/- 0.03, 4.7 +/- 0.02 and 4.4 +/- 0.05 respectively. These values differ significantly from the pIC50 values of the inhibition of the tachykinin-mediated response in the iris sphincter and taenia coli. 4. (+/-)-CP-96,345 was without effect on carbachol- and noradrenaline-evoked contractions of the iris sphincter but inhibited carbachol- and prostaglandin F2 alpha (PGF2 alpha)-evoked contractions of the taenia coli. 5. We suggest that (+/-)-CP-96,345, apart from its NK1 receptor blocking activity, induces non-specific suppression of neurotransmission, exerted at both pre- and post-junctional sites.