Inhibition of tachykinin release from peripheral endings of sensory nerves by nociceptin, a novel opioid peptide.

The novel heptadecapeptide opioid, nociceptin, produced a concentration-dependent (EC50 28 nM) suppression of the inotropic response of the guinea-pig isolated renal pelvis to electrical stimulation, a response mediated by release of tachykinins from sensory nerves. Nociceptin did not affect the response to neurokinin A, indicating a prejunctional site of action on tachykininergic nerves. The effect of nociceptin was unchanged in the presence of the mu, delta and kappa opioid receptor antagonists, naloxone, naltrindole and nor-binaltorphimine.