The effects of receptor selective opioid peptides on morphine-induced analgesia.
Utilizing the mouse tail-flick assay, four opioid peptides, which have been reported to be selective for either mu- or delta-opioid receptors, were examined for their analgesic potency and for their ability to modify morphine-induced analgesia. [D-Ala2,D-Leu5]enkephalin and [D-Ser2,Thr6]leucine-enkephalin, putative delta-receptor selective peptides, produced a potent analgesic response and at subanalgesic doses potentiated morphine-induced analgesia. Morphiceptin and [D-Ala2,Pro5]enkephalinamide, putative mu-receptor selective peptides, were similarly found to produce analgesia. However, in contrast to the delta-receptor selective peptides, three mu-receptor selective peptides were unable to alter the potency of morphine. Thus, it would appear that the potentiation of morphine analgesia is a unique property of delta-receptor selective peptides.
D000698:Analgesia; D000818:Animals; D004357:Drug Synergism; D004723:Endorphins / Q000494:pharmacology*; D008297:Male; D051379:Mice; D008815:Mice, Inbred Strains; D009020:Morphine / Q000494:pharmacology*; D011957:Receptors, Opioid / Q000187:drug effects* / Q000502:physiology
D004723:Endorphins; D011957:Receptors, Opioid; D009020:Morphine