title: Ephedrine blocks rat sciatic nerve in vivo and sodium channels in vitro.
abstract: BACKGROUND
  The sympathomimetic drug ephedrine has been used intrathecally as the sole local anesthetic for labor and delivery. Because ephedrine may be a useful adjuvant to local anesthetics, the authors investigated the local anesthetic properties of ephedrine in a rat sciatic nerve block model and the underlying mechanism in cultured cells stably expressing Na channels.
  
  
  METHODS
  After approval of the animal protocol, the sciatic nerves of anesthetized rats were exposed by lateral incision of the thighs, 0.2 ml ephedrine at 0.25, 1, 2.5, or 5% and/or bupivacaine at 0.125% was injected, and the wound was closed. Motor and sensory/nociceptive functions were evaluated by the force achieved by pushing against a balance and the reaction to pinch, respectively. The whole cell configuration of the patch clamp technique was used to record Na currents from human embryonal kidney cells stably transfected with Nav1.4 channels.
  
  
  RESULTS
  The nociception blockade was significantly longer than the motor blockade at test doses of 2.5 and 5% of ephedrine, or when 1% ephedrine was combined with 0.125% bupivacaine (analysis of variance with repeated measures, P < 0.001, n = 8/group). In vitro, the 50% inhibitory concentrations of ephedrine at -150 and -60 mV were 1,043 +/- 70 and 473 +/- 13 mum, respectively. High-frequency stimulation revealed a use-dependent block of 18%, similar to most local anesthetics.
  
  
  CONCLUSIONS
  Because ephedrine's properties are at least partly due to Na channel blockade, detailed histopathologic investigations are justified to determine the potential of ephedrine as an adjuvant to clinically used local anesthetics.
authors.affiliation: Department of Anesthesiology, Mackay Memorial Hospital, Taipei, Taiwan.
authors.forename: Yu-Chun
authors.initials: YC
authors.lastname: Hung
authors.forename: Yi-Chuan
authors.initials: YC
authors.lastname: Kau
authors.forename: Anthony M
authors.initials: AM
authors.lastname: Zizza
authors.forename: Thomas
authors.initials: T
authors.lastname: Edrich
authors.forename: David
authors.initials: D
authors.lastname: Zurakowski
authors.forename: Robert R
authors.initials: RR
authors.lastname: Myers
authors.forename: Ging Kuo
authors.initials: GK
authors.lastname: Wang
authors.forename: Peter
authors.initials: P
authors.lastname: Gerner
mesh_terms: D000316:Adrenergic alpha-Agonists / Q000008:administration & dosage / Q000494:pharmacology*; D000818:Animals; D001522:Behavior, Animal / Q000187:drug effects; D002478:Cells, Cultured; D004305:Dose-Response Relationship, Drug; D004809:Ephedrine / Q000008:administration & dosage / Q000494:pharmacology*; D005260:Female; D007267:Injections; D008564:Membrane Potentials / Q000187:drug effects; D009046:Motor Neurons / Q000187:drug effects; D009407:Nerve Block; D009475:Neurons, Afferent / Q000187:drug effects; D010147:Pain Measurement / Q000187:drug effects; D018408:Patch-Clamp Techniques; D010902:Pituitary Gland / Q000166:cytology / Q000187:drug effects; D051381:Rats; D017207:Rats, Sprague-Dawley; D012018:Reflex / Q000187:drug effects; D012584:Sciatic Nerve / Q000187:drug effects*; D026941:Sodium Channel Blockers
chemical_list: D000316:Adrenergic alpha-Agonists; D026941:Sodium Channel Blockers; D004809:Ephedrine