Kappa opioid antagonist effects of the novel kappa antagonist 5′-guanidinonaltrindole (GNTI) in an assay of schedule-controlled behavior in rhesus monkeys

Stevens S. Negus, Nancy K. Mello, David C. Linsenmayer, R. Jones, Philip S. Portoghese

Research output: Contribution to journalArticlepeer-review

48 Scopus citations


Rationale: Opioid receptors are divided into three types: kappa, mu, and delta receptors. Receptor-selective antagonists are useful experimental tools for evaluation of opioid receptor-mediated processes. 5′-Guanidinonaltrindole (GNTI) was recently developed as a novel kappa-selective antagonist. Objectives: To evaluate the potency, time course, and selectivity of GNTI's opioid antagonist effects in rhesus monkeys in an assay of schedule-controlled responding. Methods: Five rhesus monkeys were trained to respond under a fixed ratio 30 schedule of food reinforcement. The rate-decreasing effects of the kappa agonists U50,488 and U69,593, the mu agonist morphine, and the delta agonist SNC80 were examined alone and after pretreatment with GNTI (0.1 and 1.0 mg/kg i.m.; 1 h to 14 days). Results: U50,488, U69,593, morphine, and SNC80 dose-dependently decreased response rates in this procedure. GNTI produced a dose- and time-dependent antagonism of the rate-decreasing effects of U50,488. The kappa antagonist effects of GNTI had a slow onset and a long duration of action, and peak antagonist effects were observed after 24 h. A higher dose of 3.2 mg/kg GNTI eliminated responding in one monkey and was not studied further. The antagonist effects of GNTI were kappa selective, because 1.0 mg/kg GNTI also antagonized the effects of U69,593, but not those of morphine or SNC80. Conclusions: These results suggest that GNTI is a potent and selective kappa antagonist with a slow onset and long duration of action in rhesus monkeys. Relative to the prototype kappa antagonist nor-binaltorphimine, GNTI may have some advantages as a tool for the study of kappa receptor-mediated processes.

Original languageEnglish (US)
Pages (from-to)412-419
Number of pages8
Issue number3-4
StatePublished - 2002

Bibliographical note

Funding Information:
Acknowledgements This work was supported by grants RO1-DA02519, RO1-DA11460, RO1-DA-01533, U19-DA11007, and K05-DA00101 from the National Institute on Drug Abuse. The authors would like to thank Kate Banks D.V.M. for veterinary assistance.


  • 5′-Guanidinonaltrindole
  • Kappa opioid receptor
  • Nor-binaltorphimine
  • Rhesus monkey


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