title: [Local analgesic effect of tramadol is not mediated by opioid receptors in early postoperative pain in rats].
abstract: OBJECTIVE
  Tramadol is known as a central acting analgesic drug, used for the treatment of moderate to severe pain. Local analgesic effect has been demonstrated, in part due to local anesthetic-like effect, but other mechanisms remain unclear. The role of peripheral opioid receptors in the local analgesic effect is not known. In this study, we examined role of peripheral opioid receptors in the local analgesic effect of tramadol in the plantar incision model.
  
  
  METHODS
  Young male Wistar rats were divided into seven groups: control, intraplantar tramadol, intravenous tramadol, intravenous naloxone-intraplantar tramadol, intraplantar naloxone-intraplantar tramadol, intravenous naloxone-intravenous tramadol, and intravenous naloxone. After receiving the assigned drugs (tramadol 5mg, naloxone 200μg or 0.9% NaCl), rats were submitted to plantar incision, and withdrawal thresholds after mechanical stimuli with von Frey filaments were assessed at baseline, 10, 15, 30, 45 and 60min after incision.
  
  
  RESULTS
  Plantar incision led to marked mechanical hyperalgesia during the whole period of observation in the control group, no mechanical hyperalgesia were observed in intraplantar tramadol group, intraplantar naloxone-intraplantar tramadol group and intravenous naloxone-intraplantar tramadol. In the intravenous tramadol group a late increase in withdrawal thresholds (after 45min) was observed, the intravenous naloxone-intravenous tramadol group and intravenous naloxone remained hyperalgesic during the whole period.
  
  
  CONCLUSIONS
  Tramadol presented an early local analgesic effect decreasing mechanical hyperalgesia induced by plantar incision. This analgesic effect was not mediated by peripheral opioid receptors.
authors.affiliation: Laboratório de Investigação Médica (LIM-08), Faculdade de Medicina da Universidade de São Paulo (USP), São Paulo, SP, Brasil.
authors.forename: Angela Maria
authors.initials: AM
authors.lastname: Sousa
authors.affiliation: Laboratório de Investigação Médica (LIM-08), Faculdade de Medicina da Universidade de São Paulo (USP), São Paulo, SP, Brasil. Electronic address: hazem.ashmawi@hc.fm.usp.br.
authors.forename: Hazem Adel
authors.initials: HA
authors.lastname: Ashmawi
keywords: Dor no pós‐operatório; Opioid receptors; Postoperative pain; Ratos Wistar; Receptores opioides; Tramadol; Wistar rats