DIHYDROETORPHINE IS A MU-RECEPTOR-SELECTIVE LIGAND

The selectivity to opioid receptors of dihydroetorphine, a potent anal gesic with only mild physical dependence, was investigated using radio ligand binding assay and its analgesic activity in mice determined. Th e relative affinity ratio of dihydroetorphine to mu-, delta- and kappa - opioid receptors was 333:1:1. The analgesic effect of intracerebro-v entricular 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 .