Receptor binding, antagonist, and withdrawal precipitating properties of opiate antagonists

Rita J. Valentino, Jonathan L. Katz, Fedor Medzihradsky, James H. Woods

Research output: Contribution to journalArticle

68 Scopus citations

Abstract

A number of opiate antagonists and the dextro isomers of some of these drugs were studied for antagonism of acute opiate effects on ilea isolated from opiate-naive guinea pigs, precipitation of a withdrawal contraction of ilea isolated from morphine-dependent guinea pigs, precipitation of withdrawal in morphine-dependent rhesus monkeys and stereospecific displacement of 3H-etorphine binding to rat-brain membranes. With the exception of d-naloxone, all of the compounds displaced 3H-etorphine. With the exception of d-naloxone, nalorphine, and quaternary nalorphine, all of the antagonists caused a contraction of ilea isolated from morphine-dependent guinea pigs. Moreover, the IC 50 values of the compounds for displacing 3H-etorphine binding were well correlated with both their Ke values for antagonism in the ileum (r = 0.95) and with their EC 50 values for precipitating a contraction in this preparation (r = 0.92). Generally, the concentration of antagonist necessary to precipitate half maximal contracture was 30-fold greater than the Ke value of the antagonist. Most of the opiate antagonists also precipitated withdrawal when administered to morphine-dependent rhesus monkeys and their in vivo potencies were well correlated with their in vitro potencies in ileum (with Ke: r = 0.95; with EC 50: r = 0.99) and in displacing 3H-etorphine (r = 0.95). The quaternary derivative of naltrexone, however, was an effective opiate antagonist only in vitro, and was ineffective in precipitating withdrawal in morphine-dependent rhesus monkeys. These results suggest that the receptor sites labeled by 3H-etorphine are the same as those involved in antagonism of acute opiate actions and in precipitation of withdrawal.

Original languageEnglish (US)
Pages (from-to)2887-2896
Number of pages10
JournalLife Sciences
Volume32
Issue number25
DOIs
StatePublished - Jun 20 1983
Externally publishedYes

ASJC Scopus subject areas

  • Biochemistry, Genetics and Molecular Biology(all)
  • Pharmacology, Toxicology and Pharmaceutics(all)

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