Irreversible opiate agonists and antagonists. II. Evidence against a bivalent mechanism of action for opiate azines and diacylhydrazones

Abstract

A series of opiate azines, including naloxonazine, naltrexonazine and oxymorphonazine, produce both a wash-resistant inhibition of 3H-opioid binding and prolonged actions in vivo. Opiate diacylhydrazones synthesized from succinic, adipyl and suberic dihydrazides possess similar actions against 3H-opioid binding. Competition studies measuring inhibition of binding in the presence of the compounds revealed little difference between standard, reversible opiates such as naloxone, oxymorphone and naltrexone and our two series of compounds, the diacylhydrazones and the azines. In these assays, the diacylhydrazones, the azines, oxymorphone, naloxone and naltrexone all inhibited 3H-opioid binding with very similar IC50 values, typically under 5 nM. At concentrations under 5 nM, the inhibition of all the compounds was reversible. At higher concentrations, however, much of the inhibition of the diacylhydrazones and azines was not freely reversible, in distinction to oxymorphone, naloxone and naltrexone. Washing after the incubation of membranes with the naloxone, naltrexone or oxymorphone (50 nM) returned binding to control levels. Despite the extensive washing, the diacylhydrazones, on the other hand, lowered binding by as much as 90%. Mu binding was most sensitive to wash-resistant binding. In general, the longer dihydrazide derivatives produced wash-resistant inhibition more effectively than either the shorter dihydrazide derivatives or the corresponding azines. The ability of these compounds to produce wash-resistant inhibition of binding probably did not result from a bivalent attachment of the ligand to two binding sites at once. Additional assymetric azines and diacylhydrazones unable to bind simultaneously to two sites still produced wash-resistant inhibition of binding.(ABSTRACT TRUNCATED AT 250 WORDS)