title: Reversal by beta-funaltrexamine of the antinociceptive effect of opioid agonists in the rat.
abstract: The effect of the irreversible opioid receptor antagonist, beta-funaltrexamine (beta-FNA), on antinociception produced by mu- and kappa-receptor agonists was studied in the rat. beta-FNA, 20 to 80 mg kg-1, s.c., given 24 h before testing, produced a dose-related antagonism of the effects of morphine in the paw pressure, hotplate and tail-flick tests. Following the 80 mg kg-1 dose, the degree of antagonism of morphine was stable for up to 48 h after dosing, but was reduced by 5 days and had disappeared by 8 days. In the paw pressure test, beta-FNA, 40 mg kg-1, s.c., antagonized the effects of fentanyl, buprenorphine, tifluadom, ethylketocyclazocine and proxorphan; it was without effect against the highly selective kappa-agonist, U-50,488. In light of these results, the possible opioid receptor selectivities of both the agonists and beta-FNA are reassessed.
mesh_terms: D019900:3,4-Dichloro-N-methyl-N-(2-(1-pyrrolidinyl)-cyclohexyl)-benzeneacetamide, (trans)-Isomer; D000818:Animals; D001569:Benzodiazepines / Q000037:antagonists & inhibitors; D002047:Buprenorphine / Q000037:antagonists & inhibitors; D003496:Cyclazocine / Q000031:analogs & derivatives / Q000037:antagonists & inhibitors; D016314:Ethylketocyclazocine; D005283:Fentanyl / Q000037:antagonists & inhibitors; D008297:Male; D009271:Naltrexone / Q000031:analogs & derivatives* / Q000494:pharmacology; D010146:Pain; D011759:Pyrrolidines / Q000494:pharmacology; D051381:Rats; D011957:Receptors, Opioid / Q000378:metabolism; D017473:Receptors, Opioid, kappa; D017450:Receptors, Opioid, mu
chemical_list: D011759:Pyrrolidines; D011957:Receptors, Opioid; D017473:Receptors, Opioid, kappa; D017450:Receptors, Opioid, mu; D001569:Benzodiazepines; D002047:Buprenorphine; D016314:Ethylketocyclazocine; D009271:Naltrexone; D019900:3,4-Dichloro-N-methyl-N-(2-(1-pyrrolidinyl)-cyclohexyl)-benzeneacetamide, (trans)-Isomer; C024524:beta-funaltrexamine; D003496:Cyclazocine; C035470:tifluadom; D005283:Fentanyl