title: Inflammation enhances peripheral mu-opioid receptor-mediated analgesia, but not mu-opioid receptor transcription in dorsal root ganglia.
abstract: mu-Opioid receptor agonist [D-Ala2,NMe-Phe4,Gly5-ol]enkephalin (DAMGO)-induced peripheral analgesic effects occur early in hindpaws inoculated with Freund's complete adjuvant and increase in parallel to the development of inflammatory signs. Antagonism of these effects by beta-funaltrexamine, an irreversible mu-opioid receptor antagonist, suggests that the effective number of peripheral opioid receptors does not increase during early stages, but does so at later stages of the inflammation. As determined by a ribonuclease protection assay, mu-opioid receptor mRNA in dorsal root ganglia is abundant in untreated animals, but does not significantly increase following inflammation. Thus, peripheral analgesic efficacy of DAMGO is not correlated with transcription or number of mu-opioid receptors at early inflammatory stages. At later stages, however, the number of peripheral mu-opioid receptors appears to increase and may enhance opioid efficacy.
authors.affiliation: Division of Intramural Research, National Institute on Drug Abuse, Baltimore, MD 21224, USA.
authors.forename: M
authors.initials: M
authors.lastname: Schäfer
authors.forename: Y
authors.initials: Y
authors.lastname: Imai
authors.forename: G R
authors.initials: GR
authors.lastname: Uhl
authors.forename: C
authors.initials: C
authors.lastname: Stein
mesh_terms: D000595:Amino Acid Sequence; D000698:Analgesia; D000700:Analgesics / Q000494:pharmacology; D000818:Animals; D004305:Dose-Response Relationship, Drug; D020875:Enkephalin, Ala(2)-MePhe(4)-Gly(5)-; D004745:Enkephalins / Q000494:pharmacology; D005528:Foot / Q000473:pathology; D005727:Ganglia, Spinal / Q000201:enzymology / Q000378:metabolism*; D007249:Inflammation / Q000378:metabolism / Q000473:pathology / Q000503:physiopathology*; D008297:Male; D008969:Molecular Sequence Data; D009271:Naltrexone / Q000031:analogs & derivatives / Q000494:pharmacology; D009292:Narcotic Antagonists / Q000494:pharmacology; D010147:Pain Measurement / Q000187:drug effects; D012333:RNA, Messenger / Q000096:biosynthesis; D051381:Rats; D017208:Rats, Wistar; D017450:Receptors, Opioid, mu / Q000037:antagonists & inhibitors / Q000096:biosynthesis* / Q000502:physiology*; D012260:Ribonucleases / Q000378:metabolism
chemical_list: D000700:Analgesics; D004745:Enkephalins; D009292:Narcotic Antagonists; D012333:RNA, Messenger; D017450:Receptors, Opioid, mu; D020875:Enkephalin, Ala(2)-MePhe(4)-Gly(5)-; D009271:Naltrexone; C024524:beta-funaltrexamine; D012260:Ribonucleases