Failure of naloxone to antagonize metoclopramide induced prolactin rise

Seven subjects aged 21--54 years were investigated. Serum PRL and DBH were estimated before and at 30, 60, 90 and 120 min after the administration of 20 mg clopropamide. The same parameters were estimated a second time when 0.4 mg naloxone was associated. PRL level increased and DBH decreased in all the patients in both investigations and no significant differences between the two occasions were detected. It is suggested that probably the two substances do not act on identical receptors.