Enkephalinase inhibition suppresses naloxone-induced jumping in morphine-dependent mice.

The effect of the enkephalinase inhibitor phosphoramidon on the withdrawal syndrome following acute and chronic morphine-induced physical dependence in mice, was investigated. Phosphoramidon administered intracerebroventricularly (50-200 micrograms) suppressed significantly the naloxone-precipitated withdrawal jumping and wet dog shakes while forelimb shakes were potentiated in both acute and chronic morphine-dependent mice. It is suggested that increased saturation of the opioid receptors by endogenous opioid peptides following enkephalinase inhibition, might suppress the severity of the withdrawal syndrome.