title: Possible regulatory role of dynorphin-(1-13) on narcotic-induced changes in naloxone efficacy.
abstract: Pretreatment of mice with a single injection of morphine, beta-endorphin, Leu-enkephalin, FK33824 or [D-Ala2-D-Leu5]enkephalin, for 3 h increased the ability of naloxone to antagonize the analgesic effects of morphine. However, dynorphin-(1-13) can only antagonize morphine, beta-endorphin or Leu-enkephalin induced increased naloxone efficacy but not FK33824 or [D-Ala2-D-Leu2]enkephalin. Dynorphin itself can also increase naloxone efficacy when treated alone. However, this effect can be prevented when animals are pretreated with dynorphin and naloxone together.
mesh_terms: D000698:Analgesia; D000700:Analgesics / Q000494:pharmacology*; D000818:Animals; D005405:D-Ala(2),MePhe(4),Met(0)-ol-enkephalin; D004361:Drug Tolerance; D004399:Dynorphins; D004723:Endorphins / Q000494:pharmacology*; D004744:Enkephalin, Methionine; D004745:Enkephalins / Q000494:pharmacology; D008297:Male; D051379:Mice; D009020:Morphine / Q000494:pharmacology*; D009270:Naloxone / Q000494:pharmacology*; D010446:Peptide Fragments / Q000494:pharmacology*; D011957:Receptors, Opioid / Q000187:drug effects; D001615:beta-Endorphin
chemical_list: D000700:Analgesics; D004723:Endorphins; D004745:Enkephalins; D010446:Peptide Fragments; D011957:Receptors, Opioid; D009270:Naloxone; D004744:Enkephalin, Methionine; D001615:beta-Endorphin; D005405:D-Ala(2),MePhe(4),Met(0)-ol-enkephalin; C026843:dynorphin (1-13); D004399:Dynorphins; D009020:Morphine