Dihydroetorphine is a μ-Receptor-selective Ligand

Abstract

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 μ-, δ- and κ- opioid receptors was 333:1:1. The analgesic effect of intracerebro-ventricular injection in mice could be antagonized by the μ-antagonist β-funaltrexamine but could not be antagonized by δ- and κ-selective antagonists naltrindole and nor-binaltorphimine. We conclude that dihydroetorphine is a selective ligand for the μ-opioid receptor.