Possible regulatory role of dynorphin on morphine- and β-endorphin-induced analgesia

F. C. Tulunay, M. F. Jen, J. K. Chang, H. H. Loh, N. M. Lee

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147 Scopus citations

Abstract

In previous studies, we observed that dynorphin- (1-13), but not dynorphin-(1-9), can significantly inhibit morphine- or β-endorphin-induced analgesia despite not having any appreciable analgesic activity itself. Dynorphin-(1-13) showed no inhibitory effect on Sandoz FK33824-induced analgesia. In the present study, we examined the effect of dynorphin on morphine-, β-endorphin-, D-ala2-D-leu5-enkephalin- or Sandoz FK33824-induced analgesia in both naive, morphine-tolerant and morphine-dependent mice. It was found that although dynorphin may inhibit morphine- or β-endorphin-induced analgesia in naive animals, the peptide is not effective in inhibiting D-ala2-D-leu5-enkephalin- or Sandoz FK33824-induced analgesia. Dynorphin is also effective in blocking spontaneous withdrawal jumping in morphine-dependent animals. It is suggested that dynorphin-(1-13) may play a modulatory role in regulating analgesia due to morphine or β-endorphin, but not that due to enkephalin. The action of peptides on morphine- or β-endorphin-induced analgesia in the naive state is different from that of the tolerant state, suggesting that dynorphin may be involved in the development of morphine tolerance and physical dependence.

Original languageEnglish (US)
Pages (from-to)296-298
Number of pages3
JournalJournal of Pharmacology and Experimental Therapeutics
Volume219
Issue number2
StatePublished - 1981

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