Abstract
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 language | English |
|---|---|
| Pages (from-to) | 278-282 |
| Number of pages | 5 |
| Journal | Pharmacology |
| Volume | 32 |
| Issue number | 5 |
| DOIs | |
| State | Published - 1986 |