Opioid mydriasis: Cross-tolerance between morphine and enkephalins

M. Ben-Am, A. D. Korczyn

Research output: Contribution to journalArticlepeer-review


The occurrence of cross-tolerance between morphine and met-enkephalin, and between morphine and DADL (D-Ala-D-Leu-enkephalin) in causing mydriasis in mice was studied. Morphine-tolerant mice treated with met-enkephalin or DADL intracerebroventricularly (ICV) showed marked reduction of the pupillary effect of the endopioids. Maximal mydriasis in tolerant animals was only about 30% for met-enkephalin and 50% for DADL, compared to levels in nontolerant animals. These results are among the first to demonstrate cross-tolerance between morphine and enkephalins in intact animals and may suggest involvement of multiple opiate receptor systems in producing mydriasis.

Original languageEnglish
Pages (from-to)278-282
Number of pages5
Issue number5
StatePublished - 1986


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