BW373U86, a δ-opioid receptor agonist, reverses bradykinin-induced thermal allodynia in rhesus monkeys

The synthetic δ-opioid receptor agonist BW373U86 (0.18-0.56 mg/kg s.c.) was studied in rhesus monkeys with a warm-water, tail-withdrawal assay, designed to detect bradykinin (0.1 μg) and prostaglandin E₂ (5-15.8 μg)-induced thermal allodynia. BW373U86 dose-dependently reversed bradykinin allodynia, but was ineffective against prostaglandin E₂ allodynia. The BW373U86 dose-effect curve was shifted to the right by the δ-opioid receptor-selective antagonist naltrindole (1.0 mg/kg) but not by the μ-opioid receptor-selective antagonist quadazocine (0.1 mg/kg). The present findings add to the conditions in which δ-opioid receptor-mediated behavioral effects have been detected in primates, and suggest that δ-opioid agonists may be of therapeutic interest in the treatment of some types of hyperalgesic conditions.