title: Naloxone and its quaternary derivative, naloxone methiodide, have differing affinities for mu, delta, and kappa opioid receptors in mouse brain homogenates.
abstract: Naloxone and naloxone methiodide both act on opioid receptors but naloxone methiodide has limited access to the brain. Naloxone methiodide has been shown to have a lower affinity for opioid receptors than naloxone in the rat and guinea pig but has not been tested in the mouse. We aimed to investigate this by using [3H]DAMGO, [3H]DPDPE and [3H]U-69,593 to compare the ability of naloxone and naloxone methiodide to displace binding to mu, delta and kappa opioid receptors in mouse brain homogenates. Significant binding was observed for each receptor type and the binding affinity for naloxone versus naloxone methiodide was found to be 15:1 for mu, 6:1 for kappa and 330:1 for delta receptors. Therefore, naloxone methiodide does have a lower affinity for opioid receptors than naloxone in mouse brain tissue, which must be taken into consideration in experimental designs.
authors.affiliation: Department of Clinical and Experimental Pharmacology, 5th Floor, Medical School North, University of Adelaide, South Australia 5005, Adelaide, Australia. tanya.lewanowitsch@adelaid.edu.au
authors.forename: Tanya
authors.initials: T
authors.lastname: Lewanowitsch
authors.forename: Rodney James
authors.initials: RJ
authors.lastname: Irvine
mesh_terms: D000701:Analgesics, Opioid / Q000494:pharmacology; D000818:Animals; D044482:Benzeneacetamides; D001921:Brain / Q000187:drug effects* / Q000378:metabolism*; D020875:Enkephalin, Ala(2)-MePhe(4)-Gly(5)- / Q000494:pharmacology; D020881:Enkephalin, D-Penicillamine (2,5)- / Q000494:pharmacology; D008297:Male; D051379:Mice; D009270:Naloxone / Q000031:analogs & derivatives* / Q000378:metabolism / Q000494:pharmacology*; D009292:Narcotic Antagonists / Q000378:metabolism / Q000494:pharmacology*; D011759:Pyrrolidines / Q000494:pharmacology; D000644:Quaternary Ammonium Compounds; D017465:Receptors, Opioid, delta / Q000819:agonists / Q000378:metabolism*; D017473:Receptors, Opioid, kappa / Q000819:agonists / Q000378:metabolism*; D017450:Receptors, Opioid, mu / Q000819:agonists / Q000378:metabolism*; D014316:Tritium
chemical_list: D000701:Analgesics, Opioid; D044482:Benzeneacetamides; D009292:Narcotic Antagonists; D011759:Pyrrolidines; D000644:Quaternary Ammonium Compounds; D017465:Receptors, Opioid, delta; D017473:Receptors, Opioid, kappa; D017450:Receptors, Opioid, mu; D014316:Tritium; D020875:Enkephalin, Ala(2)-MePhe(4)-Gly(5)-; D009270:Naloxone; C041269:N-methylnaloxone; D020881:Enkephalin, D-Penicillamine (2,5)-; C045444:U 69593