NOCICEPTIN, AN ENDOGENOUS LIGAND FOR THE ORL1 RECEPTOR, HAS VASODILATOR ACTIVITY IN THE HINDQUARTERS VASCULAR BED OF THE RAT

The heptadecapeptide nociceptin, also known as Orphanin FQ, is a newly discovered endogenous ligand for the G-protein coupled, opioid-like r eceptor ORL1. In the present study, responses to intra-arterial inject ions of nociceptin were investigated in the hindquarters vascular bed of the rat. Under constant-flow conditions nociceptin induced dose-dep endent decreases in hindquarters perfusion pressure when injected in d oses of 1-30 nmol into the hindquarters perfusion circuit. The decreas es in hindquarters perfusion pressure were rapid in onset and pressure returned to control values over a 3-6 min period. In terms of relativ e vasodilator activity, nociceptin was approximately equipotent to the nitric: oxide donor, DEA/NO, and 30-fold less potent than adrenomedul lin. These data demonstrate that nociceptin has significant vasodilato r activity in the hindquarters vascular bed of the rat. (C) 1997 Elsev ier Science Inc.