PT  - JOURNAL ARTICLE
AU  - Tulunay, F C
AU  - Jen, M F
AU  - Chang, J K
AU  - Loh, H H
AU  - Lee, N M
TI  - Possible regulatory role of dynorphin on morphine- and beta-endorphin-induced analgesia.
DP  - 1981 Nov 01
TA  - Journal of Pharmacology and Experimental Therapeutics
PG  - 296--298
VI  - 219
IP  - 2
4099  - http://jpet.aspetjournals.org/content/219/2/296.short
4100  - http://jpet.aspetjournals.org/content/219/2/296.full
SO  - J Pharmacol Exp Ther1981 Nov 01; 219
AB  - In previous studies, we observed that dynorphin- (1-13), but not dynorphin-(1-9), can significantly inhibit morphine- or beta-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-, beta-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 beta-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 beta-endorphin, but not that due to enkephalin. The action of peptides on morphine- or beta-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.