title: Cross-tolerance between analgesia produced by xylazine and selective opioid receptor subtype treatments.
abstract: Opioid receptor agonists produce analgesia through multiple systems activated by stimulation of mu(1), mu(2), delta(1), delta(2) and kappa(1) opioid receptors. Morphine analgesia is modulated by stimulation of alpha(2) adrenoceptors. To understand how multiple opioid analgesic systems interact with alpha(2)-adrenoceptor systems, analgesic cross-tolerance between the alpha(2) adrenoceptor agonist xylazine and opioid receptor agonists was studied using the mouse tail-flick assay. Mice received either xylazine (20 mg/kg, s.c.) or saline (1 ml/kg) for five days. On day six, mice received a dose of s.c. xylazine, i.c.v. [D-Ala(2),MePhe(4),Gly(ol)(5)]enkephalin (DAMGO), i.t. Tyr-Pro-Trp-Gly-NH(2) (Tyr-W-MIF-1), i.c.v. or i.t. [D-Pen(2),D-Pen(5)]enkephalin (DPDPE), i.t. [D-Ala(2)]deltorphin II (deltorphin II), or s.c. trans-(+/-)-3, 4-dichloro-N-methyl-N-[2-(1-pyrrolidinyl-cyclohexyl] benzeneacetamide (U50,488). Xylazine tolerant mice required 4. 57-fold more xylazine to elicit the same response as saline treated animals and showed a 2.55-fold shift in i.c.v. DAMGO and a 3.37-fold shift in i.c.v. DPDPE antinociception. No cross-tolerance was seen with i.c.v. deltorphin II, i.t.Tyr-W-MIF-1, i.t. DPDPE, i.t. Tyr-W-MIF-1 or s.c. U50,488. These results implicate alpha(2) adrenoceptor systems in the modulation of supraspinal mu(1), and delta(1) opioid analgesic circuitry and raise the possibility that mu(2), delta(2) or kappa(1) opioid receptor agonists may be alternated with alpha(2) adrenoceptor agonists to minimize tolerance or treat opioid-tolerant patients.
authors.affiliation: Department of Pharmacology, Alcohol and Drug Abuse Center, Louisiana State University Health Sciences Center, 1901 Perdido Street, New Orleans, LA, USA.
authors.forename: T D
authors.initials: TD
authors.lastname: Ware
authors.forename: D
authors.initials: D
authors.lastname: Paul
mesh_terms: D019900:3,4-Dichloro-N-methyl-N-(2-(1-pyrrolidinyl)-cyclohexyl)-benzeneacetamide, (trans)-Isomer / Q000494:pharmacology; D000316:Adrenergic alpha-Agonists / Q000494:pharmacology*; D000698:Analgesia; D000701:Analgesics, Opioid / Q000494:pharmacology*; D000818:Animals; D004305:Dose-Response Relationship, Drug; D004361:Drug Tolerance; D020875:Enkephalin, Ala(2)-MePhe(4)-Gly(5)- / Q000494:pharmacology; D020881:Enkephalin, D-Penicillamine (2,5)- / Q000494:pharmacology; D008297:Male; D051379:Mice; D009842:Oligopeptides / Q000494:pharmacology; D018341:Receptors, Adrenergic, alpha-2 / Q000187:drug effects* / Q000502:physiology; D014991:Xylazine / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D015016:Yohimbine / Q000494:pharmacology
chemical_list: D000316:Adrenergic alpha-Agonists; D000701:Analgesics, Opioid; D009842:Oligopeptides; D018341:Receptors, Adrenergic, alpha-2; D020875:Enkephalin, Ala(2)-MePhe(4)-Gly(5)-; C060209:deltorphin II, Ala(2)-; D014991:Xylazine; D015016:Yohimbine; D019900:3,4-Dichloro-N-methyl-N-(2-(1-pyrrolidinyl)-cyclohexyl)-benzeneacetamide, (trans)-Isomer; D020881:Enkephalin, D-Penicillamine (2,5)-