Cross tolerance between morphine and beta-endorphin in the in vivo vasodilating effect in the hamster cheek pouch.
The relative potencies of the in vivo vasodilating effect on the arterioles of the hamster cheek pouch of morphine and beta-endorphin decreased significantly after chronic morphine injection, indicating the existence of tolerance to morphine and cross tolerance between morphine and beta-endorphin. The apparent pA2 values of both morphine-naloxone and beta-endorphin-naloxone in morphine treated hamsters also decreased significantly. The results indicate that in this preparation there is a simultaneous reduction in the affinity of the opiate receptors to both agonists as well as antagonist associated with the development of tolerance or cross tolerance.
D000818:Animals; D001160:Arterioles / Q000187:drug effects; D002610:Cheek; D006224:Cricetinae; D004347:Drug Interactions; D004723:Endorphins / Q000494:pharmacology*; D008297:Male; D008647:Mesocricetus; D009020:Morphine / Q000494:pharmacology*; D009132:Muscles / Q000098:blood supply*; D014664:Vasodilation / Q000187:drug effects*; D001615:beta-Endorphin
D004723:Endorphins; D001615:beta-Endorphin; D009020:Morphine