title: Naltrexone does not affect isoflurane minimum alveolar concentration in cats.
abstract: OBJECTIVE
  To test whether naltrexone, an opioid receptor antagonist, affects the minimum alveolar concentration (MAC) of isoflurane in cats, a species that is relatively resistant to the general anesthetic sparing effects of most opioids.
  
  
  METHODS
  Randomized, crossover, placebo-controlled, blinded experimental design.
  
  
  METHODS
  Six healthy adult cats weighing 4.9 ± 0.7 kg.
  
  
  METHODS
  The cats were studied twice. In the first study, baseline isoflurane MAC was measured in duplicate. The drug (saline control or 0.6 mg kg(-1)  naltrexone) was administered IV every 40-60 minutes, and isoflurane MAC was re-measured. In the second study, cats received the second drug treatment using identical methods 2 weeks later.
  
  
  RESULTS
  Isoflurane MAC was 2.03 ± 0.12% and was unchanged from baseline following saline or naltrexone administration.
  
  
  CONCLUSIONS
  Minimum alveolar concentration was unaffected by naltrexone. Because MAC in cats is unaffected by at least some mu-opioid agonists and antagonists, spinal neurons that are directly modulated by mu-opioid receptors in this species cannot be the neuroanatomic sites responsible for immobility from inhaled anesthetics.
authors.affiliation: Department of Surgical and Radiological Sciences, School of Veterinary Medicine, University of California, Davis, CA 95616, USA. rjbrosnan@ucdavis.edu
authors.forename: Robert J
authors.initials: RJ
authors.lastname: Brosnan
authors.forename: Bruno H
authors.initials: BH
authors.lastname: Pypendop
authors.forename: Chalon R
authors.initials: CR
authors.lastname: Majewski-Tiedeken
authors.forename: Yael
authors.initials: Y
authors.lastname: Shilo-Benjamini
authors.forename: Jan E
authors.initials: JE
authors.lastname: Ilkiw
mesh_terms: D000769:Anesthesia, Inhalation; D018685:Anesthetics, Inhalation / Q000008:administration & dosage / Q000493:pharmacokinetics*; D000818:Animals; D002415:Cats; D018592:Cross-Over Studies; D004347:Drug Interactions; D007530:Isoflurane / Q000008:administration & dosage / Q000493:pharmacokinetics*; D009271:Naltrexone / Q000008:administration & dosage / Q000493:pharmacokinetics*; D009292:Narcotic Antagonists / Q000008:administration & dosage / Q000493:pharmacokinetics*; D011650:Pulmonary Alveoli
chemical_list: D018685:Anesthetics, Inhalation; D009292:Narcotic Antagonists; D009271:Naltrexone; D007530:Isoflurane