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 receptor ORL1. In the present study, responses to intra-arterial injections of nociceptin were investigated in the hindquarters vascular bed of the rat. Under constant-flow conditions nociceptin induced dose-dependent decreases in hindquarters perfusion pressure when injected in doses of 1-30 nmol into the hindquarters perfusion circuit. The decreases in hindquarters perfusion pressure were rapid in onset and pressure returned to control values over a 3-6 min period. In terms of relative vasodilator activity, nociceptin was approximately equipotent to the nitric oxide donor, DEA/NO, and 30-fold less potent than adrenomedullin. These data demonstrate that nociceptin has significant vasodilator activity in the hindquarters vascular bed of the rat.