title: The role of vasopressin on the effect of U-50,488 to block the development of morphine tolerance and physical dependence.
abstract: U-50,488, a selective kappa-opioid receptor agonist, has been reported to inhibit the development of antinociceptive tolerance to morphine in mice, rats and guinea pigs, but the mechanism involved in this action remains unknown. Since U-50,488 has been reported to suppress the plasma vasopressin level, we investigated the role of vasopressin with U-50,488 in the male Sprague Dawley rat in this study. Animals (230-270 g) were chronically treated with morphine (10 mg/kg, i.p.) twice a day for 6 days in order to induce tolerance to antinociceptive effect measured by tail-flick test. Withdrawal symptoms were precipitated by naloxone (10 mg/kg, i.p.) on day 7. U-50,488 (i.p.) or AVP (i.p. or i.c.v.) or U-50,488 and AVP was (were) coadministered with chronic morphine to investigate their effects on morphine tolerance and dependence. We found that coadministration of 8 mg/kg U-50,488 (i.p.) with morphine almost completely block morphine tolerance and partially block withdrawal symptoms. In contrast, coadministration of AVP (0.3 microgram/kg, i.p., or 0.01 microgram, i.c.v.) with morphine and U-50,488, the effects of U-50,488 to block morphine tolerance and dependence were reversed. In addition, treatment of AVP antagonist (dPTyr(Me)AVP, 0.5 microgram/kg, i.p. or 0.5 microgram, i.c.v.) has the similar effect as U-50,488 to block morphine tolerance. In summary, the effect of U-50,488 to block morphine tolerance and dependence may relate to its inhibitory effect on AVP release.
authors.affiliation: Department of Pharmacology, National Defense Medical Center, Taipei, Taiwan, R.O.C.
authors.forename: P L
authors.initials: PL
authors.lastname: Tao
authors.forename: W C
authors.initials: WC
authors.lastname: Liu
authors.forename: Y S
authors.initials: YS
authors.lastname: Tsuei
authors.forename: C Y
authors.initials: CY
authors.lastname: Cheng
mesh_terms: D019900:3,4-Dichloro-N-methyl-N-(2-(1-pyrrolidinyl)-cyclohexyl)-benzeneacetamide, (trans)-Isomer; D000700:Analgesics / Q000494:pharmacology*; D000818:Animals; D001127:Arginine Vasopressin / Q000008:administration & dosage / Q000494:pharmacology*; D004361:Drug Tolerance / Q000502:physiology; D007274:Injections, Intraperitoneal; D007276:Injections, Intraventricular; D008297:Male; D009020:Morphine / Q000494:pharmacology*; D009021:Morphine Dependence / Q000517:prevention & control*; D010147:Pain Measurement / Q000187:drug effects; D011759:Pyrrolidines / Q000494:pharmacology*; D051381:Rats; D017207:Rats, Sprague-Dawley
chemical_list: D000700:Analgesics; D011759:Pyrrolidines; D001127:Arginine Vasopressin; D019900:3,4-Dichloro-N-methyl-N-(2-(1-pyrrolidinyl)-cyclohexyl)-benzeneacetamide, (trans)-Isomer; D009020:Morphine