title: Free radical formation during ketamine anesthesia in rats: a cautionary note.
abstract: Ketamine is a useful anesthetic agent with good analgesic properties; however, when ketamine was used to anesthetize rats for spin trapping studies of alcohol-induced free radicals, liver extracts contained a strong electron paramagnetic resonance (EPR) signal of a novel radical. The same EPR signal was observed in liver extracts when rats which had not received alcohol were anesthetized with ketamine. When ketamine was added to liver microsomes and NADPH, a nitroxide radical derived from ketamine could be detected in organic extracts. When the spin trapping agent POBN was also added, microsomes produced both a ketamine nitroxide radical and a spin adduct. Similar results were obtained during ketamine oxidation by hydrogen peroxide in a tungstate-catalyzed reaction, or in a Fenton reaction system. The data suggest that the secondary amine group of ketamine can be oxidized to a stable nitroxide which produces an EPR spectrum in the absence of a spin trapping agent. The POBN spin adduct detected may be from a carbon-centered radical in the cyclohexanone ring of ketamine. Because several types of radicals can be formed from ketamine, this agent may not be appropriate as an anesthetic for many types of in vivo spin trapping experiments.
authors.affiliation: Department of Pharmacology and Toxicology, College of Pharmacy, University of Oklahoma Health Sciences Center, Oklahoma City 73190, USA. lester-reinke@uokhsc.edu
authors.forename: L A
authors.initials: LA
authors.lastname: Reinke
authors.forename: Y
authors.initials: Y
authors.lastname: Kotake
authors.forename: D R
authors.initials: DR
authors.lastname: Moore
authors.forename: A A
authors.initials: AA
authors.lastname: Nanji
mesh_terms: D000768:Anesthesia, General / Q000009:adverse effects*; D000818:Animals; D004578:Electron Spin Resonance Spectroscopy; D005609:Free Radicals / Q000378:metabolism; D007649:Ketamine / Q000009:adverse effects* / Q000378:metabolism*; D008297:Male; D008862:Microsomes, Liver / Q000378:metabolism; D009589:Nitrogen Oxides / Q000378:metabolism; D011725:Pyridines; D051381:Rats; D017207:Rats, Sprague-Dawley; D019097:Spin Trapping
chemical_list: D005609:Free Radicals; D009589:Nitrogen Oxides; D011725:Pyridines; C043438:alpha-(4-pyridyl-1-oxide)-N-tert-butylnitrone; D007649:Ketamine