Partial and full agonism in endomorphin derivatives: Comparison by null and operational model

András Z. Rónai*, Mahmoud Al-Khrasani, Sándor Benyhe, Imre Lengyel, László Kocsis, György Orosz, Géza Tóth, Erzsébet Kató, László Tóthfalusi

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

17 Citations (Scopus)


The partial μ-opioid receptor pool inactivation strategy in isolated mouse vas deferens was used to determine partial agonism of endomorphins and their analogs (endomorphin-1-ol, 2′,6′-dimethyltyrosine (Dmt)-endomorphin-1, endomorphin-2-ol and (d-Met2)-endomorphin-2) using morphine, normorphine, morphiceptin, (d-Ala2,MePhe4,Gly5-ol)-enkephalin (DAMGO) and its amide (DAMGA) as reference opioid agonists. Agonist affinities (KA) and efficacies were assessed both by the "null" and the "operational" method. The KA values determined by the two methods correlated significantly with each other and also with the displacing potencies against 3H-naloxone in the receptor binding assay in the presence of Na+. DAMGO and DAMGA were full agonist prototypes, morphine, endomorphin-1, endomorphin-1-ol, Dmt-endomorphin-1, endomorphin-2-ol and (d-Met2)-endomorphin-2 were found by both methods to be partial agonists whereas the parameters for normorphine, morphiceptin and endomorphin-2 were intermediate.

Original languageEnglish
Pages (from-to)1507-1513
Number of pages7
Issue number6
Publication statusPublished - Jun 2006
Externally publishedYes


  • β-Funaltrexamine
  • Endomorphin derivatives
  • Mouse vas deferens
  • Null and operational model
  • Partial agonism
  • Residual receptor fraction

ASJC Scopus subject areas

  • Biochemistry
  • Physiology
  • Endocrinology
  • Cellular and Molecular Neuroscience

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