[Phe1psi(CH2-NH)Gly2]nociceptin-(1-13)-NH2 acts as an agonist of the orphanin FQ/nociceptin receptor in vivo

Eur J Pharmacol. 1998 Sep 11;357(1):R1-3. doi: 10.1016/s0014-2999(98)00567-6.


The orphanin FQ/nociceptin (OFQ/N) derivative peptide, [Phe1psi(CH2-NH)Gly2] nociceptin-(1-13)-NH2 (Phe(psi)), has been claimed to be both an antagonist and an agonist of the orphan opioid receptor (ORL1) in different in vitro assays. We now report the dose-dependent inhibition of morphine analgesia by Phe(psi) in mice, an effect parallel to that of OFQ/N. Further, the anti-opioid actions of OFQ/N are not blocked by Phe(psi). Thus, Phe(psi) acts as an ORL1 receptor agonist, not an antagonist, in vivo.

Publication types

  • Comparative Study
  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Analgesia
  • Animals
  • Drug Interactions
  • Female
  • Injections, Intraperitoneal
  • Injections, Intraventricular
  • Male
  • Mice
  • Morphine / antagonists & inhibitors*
  • Narcotic Antagonists / pharmacology*
  • Opioid Peptides / pharmacology*
  • Peptide Fragments / pharmacology*
  • Receptors, Opioid / agonists*


  • Narcotic Antagonists
  • Opioid Peptides
  • Peptide Fragments
  • Receptors, Opioid
  • nociceptin (1-13)-NH2, Phe(1)-psi(CH2-NH)-Gly(2)-
  • Morphine
  • nociceptin
  • nociceptin receptor