title: Analgesic effect of endomorphin-1.
abstract: OBJECTIVE
  To study the analgesic effect of endomorphin-1 (EM-1).
  
  
  METHODS
  The experiment was performed in rats and mice to study the analgesic effect of intraperitoneal (ip) injection of EM-1 with tail stimulation-vocalization test, writhing test, adjuvant arthritis, and neuropathic pain model and to compare it with the analgesic effects produced by intracerebroventricular (icv) and intrathecal (it) administrations.
  
  
  RESULTS
  1) EM-1 raised the pain threshold dose-dependently in tail stimulation-vocalization test in rats and inhibited the writhing responses induced by ip acetic acid in mice. EM-1 also decreased the hyperalgesia in both adjuvant arthritis and neuropathic pain model. 2) The analgesic effect induced by central (icv and it) administration of EM-1 was faster and more powerful than that induced by peripheral (ip) administration. 3) The analgesic effect of EM-1 was reversed by naloxone (opioid receptor antagonist), as well as by cyprodime (mu-opioid receptor selective antagonist). Repeated administrations of EM-1 induced tolerance.
  
  
  CONCLUSIONS
  EM-1 had a definite analgesic effect and the analgesic effect of EM-1 was mediated by central mu-opioid receptor.
authors.affiliation: Department of Physiology, School of Medicine, Showa University, Tokyo 142, Japan.
authors.forename: Z H
authors.initials: ZH
authors.lastname: Li
authors.forename: L D
authors.initials: LD
authors.lastname: Shan
authors.forename: X H
authors.initials: XH
authors.lastname: Jiang
authors.forename: S Y
authors.initials: SY
authors.lastname: Guo
authors.forename: G D
authors.initials: GD
authors.lastname: Yu
authors.forename: T
authors.initials: T
authors.lastname: Hisamitsu
authors.forename: Q Z
authors.initials: QZ
authors.lastname: Yin
mesh_terms: D000701:Analgesics, Opioid / Q000494:pharmacology* / Q000627:therapeutic use; D000818:Animals; D001169:Arthritis, Experimental / Q000150:complications / Q000503:physiopathology; D004361:Drug Tolerance; D008297:Male; D051379:Mice; D009619:Nociceptors / Q000187:drug effects*; D009842:Oligopeptides / Q000494:pharmacology* / Q000627:therapeutic use; D010146:Pain / Q000188:drug therapy* / Q000209:etiology; D010147:Pain Measurement; D017288:Pain Threshold / Q000187:drug effects; D051381:Rats; D017450:Receptors, Opioid, mu / Q000037:antagonists & inhibitors / Q000378:metabolism
chemical_list: D000701:Analgesics, Opioid; D009842:Oligopeptides; D017450:Receptors, Opioid, mu; C105293:endomorphin 1