title: Endogenous opioid peptides contribute to antinociceptive potency of intrathecal [Dmt1]DALDA.
abstract: [Dmt(1)]DALDA (H-Dmt-d-Arg-Phe-Lys-NH(2); Dmt = 2',6'-dimethyltyrosine) is a dermorphin analog that shows high affinity and selectivity for the mu opioid receptor. The intrathecal potency of [Dmt(1)]DALDA far exceeded its affinity at mu receptors and suggests that other mechanisms must be involved in its action in the spinal cord. The affinity and selectivity of [Dmt(1)]DALDA was determined using cell membranes expressing cloned human mu, delta, and kappa opioid receptors. Competitive displacement binding with [(3)H][Dmt(1)]DALDA, [(3)H]DPDPE (H-Tyr-d-Pen-Gly-Phe-d-Pen), and [(3)H]U69,593 [(5alpha,7alpha,8beta)-(+)-N-methyl-N-(7-[1-pyrrolidinyl]-1-oxaspiro[4.5]dec-8-yl)-benzeneacetamide] revealed K(i) of 156 +/- 26 pM for mu opioid receptor (MOR), 1.67 +/- 0.04 microM for delta opioid receptor (DOR), and K(i) of 4.4 +/- 1.7 nM for kappa opioid receptor (KOR), respectively. [Dmt(1)]DALDA increased guanosine 5'-O-(3-[(35)S]thiotriphosphate) binding in MOR, DOR, and KOR membranes, with EC(50) being 17 (8.8-33) nM, 2 (1.2-3.2) microM, and 124 (15-1000) nM, respectively. Intrathecal [Dmt(1)]DALDA inhibited the tail-flick response in mice with ED(50) = 1.22 (0.59-2.34) pmol. Intrathecal administration of an antiserum against dynorphin A(1-17) or [Met(5)]enkephalin significantly attenuated the response to i.t. [Dmt(1)]DALDA, resulting in ED(50) of 6.2 (3.6-12.6) pmol and 6.6 (3.5-19.6) pmol, respectively. Neither antisera had any effect on the response to i.t. morphine. Intracerebroventricular (i.c.v.) [Dmt(1)]DALDA was not affected by previous i.c.v. administration of anti-Dyn or anti-ME. Pretreatment with norbinaltorphimine or naltriben also attenuated the antinociceptive response to i.t., but not i.c.v., [Dmt(1)]DALDA. These data suggest that i.t. [Dmt(1)]DALDA causes the release of dynorphin and [Met(5)]enkephalin-like substances that act at kappa and delta receptors, respectively, to contribute to the extraordinary potency of [Dmt(1)]DALDA.
authors.affiliation: Department of Pharmacology, Joan and Sanford I. Weill Medical College of Cornell University, 1300 York Avenue, New York, NY 10021, USA. hhszeto@med.cornell.edu
authors.forename: Hazel H
authors.initials: HH
authors.lastname: Szeto
authors.forename: Yi
authors.initials: Y
authors.lastname: Soong
authors.forename: Dunli
authors.initials: D
authors.lastname: Wu
authors.forename: XuanXuan
authors.initials: X
authors.lastname: Qian
authors.forename: Guo-Min
authors.initials: GM
authors.lastname: Zhao
mesh_terms: D000701:Analgesics, Opioid / Q000008:administration & dosage / Q000494:pharmacology*; D000818:Animals; D019138:Antibodies, Blocking / Q000494:pharmacology; D003001:Cloning, Molecular; D004399:Dynorphins / Q000037:antagonists & inhibitors / Q000276:immunology / Q000502:physiology; D004723:Endorphins / Q000502:physiology*; D004744:Enkephalin, Methionine / Q000037:antagonists & inhibitors / Q000276:immunology / Q000502:physiology; D016244:Guanosine 5'-O-(3-Thiotriphosphate) / Q000378:metabolism; D006358:Hot Temperature; D007276:Injections, Intraventricular; D007278:Injections, Spinal; D008297:Male; D051379:Mice; D009270:Naloxone / Q000031:analogs & derivatives* / Q000494:pharmacology; D009271:Naltrexone / Q000031:analogs & derivatives* / Q000494:pharmacology; D009292:Narcotic Antagonists / Q000494:pharmacology; D009842:Oligopeptides / Q000008:administration & dosage / Q000494:pharmacology*; D010147:Pain Measurement / Q000187:drug effects; D011869:Radioligand Assay; D011930:Reaction Time; D017465:Receptors, Opioid, delta / Q000187:drug effects; D017473:Receptors, Opioid, kappa / Q000187:drug effects; D017450:Receptors, Opioid, mu / Q000187:drug effects
chemical_list: C424424:2',6'-dimethyltyrosyl-arginyl-phenylalanyl-lysinamide; D000701:Analgesics, Opioid; D019138:Antibodies, Blocking; D004723:Endorphins; D009292:Narcotic Antagonists; D009842:Oligopeptides; D017465:Receptors, Opioid, delta; D017473:Receptors, Opioid, kappa; D017450:Receptors, Opioid, mu; D009270:Naloxone; C051844:norbinaltorphimine; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D004744:Enkephalin, Methionine; D009271:Naltrexone; D004399:Dynorphins; C034643:naloxonazine