Dihydroetorphine is a mu-receptor-selective ligand

Abstract

The selectivity to opioid receptors of dihydroetorphine, a potent analgesic with only mild physical dependence, was investigated using radioligand binding assay and its analgesic activity in mice determined. The relative affinity ratio of dihydroetorphine to mu-, delta- and kappa- opioid receptors was 333:1:1. The analgesic effect of intracerebro-ventricular injection in mice could be antagonized by the mu-antagonist beta-funaltrexamine but could not be antagonized by delta- and kappa-selective antagonists naltrindole and norbinaltorphimine. We conclude that dihydroetorphine is a selective ligand for the mu-opioid receptor.