In vivo 'enkephalinase' inhibition by acetorphan in human plasma and CSF

Thiorphan, the potent inhibitor of 'enkephalinase', has shown some analgesic properties in experimental animals and in man. The possibility that the intravenous infusion of acetorphan, a prodrug of thiorphan (26 micrograms/kg per min for 60 min), can inhibit plasma and cerebrospinal fluid (CSF) enkephalinase in man in vivo was investigated. A decrease of approximately 65% in enzyme activity was observed in both plasma and CSF. Acetorphan did not induce any significant variation of plasma angiotensin-converting enzyme activity.