title: Effect of 7-nitroindazole on tolerance to morphine, U-50,488H and [D-Pen2, D-Pen5] enkephalin in mice.
abstract: The effects of 7-nitroindazole (7-NI), an inhibitor of the neuronal nitric oxide synthase (nNOS) which does not increase blood pressure, on tolerance to the antinociceptive activity of mu-(morphine), kappa-(U-50,488H) and delta-([D-Pen2, D-Pen5]enkephalin, DPDPE) opioid receptor agonists were determined in mice. Male Swiss-Webster mice were made tolerant by twice daily injections of morphine (20 mg/kg, s.c.), U-50,488H (25 mg/kg, i.p.) or DPDPE (20 micrograms/mouse, i.c.v.) for 4 days. When tested on day 5, tolerance to their antinociceptive activity was evidenced by decreased response in chronic drug treated mice in comparison to vehicle-injected mice. Concurrent administration of 7-NI (20, 40 or 80 mg/kg, i.p.) with DPDPE did not modify the development of tolerance to the antinociceptive action of DPDPE. However, 7-NI (40 or 80 mg/kg, i.p.) inhibited the development of tolerance to the antinociceptive activity of morphine and U-50,488H but the lower dose of 7-NI (20 mg/kg, i.p.) was not effective. Chronic administration of 7-NI by itself did not modify the acute response to morphine, U-50,488H or DPDPE. It is concluded that a specific inhibitor of nNOS can inhibit tolerance to the antinociceptive activity of mu- and kappa- but not of delta-opioid receptor agonists in mice.
authors.affiliation: Department of Pharmaceutics and Phamacodynamics (M/C 865), University of Illinois at Chicago 60612, USA. drhnb@uic.edu
authors.forename: H N
authors.initials: HN
authors.lastname: Bhargava
authors.forename: Y J
authors.initials: YJ
authors.lastname: Cao
authors.forename: G M
authors.initials: GM
authors.lastname: Zhao
mesh_terms: D019900:3,4-Dichloro-N-methyl-N-(2-(1-pyrrolidinyl)-cyclohexyl)-benzeneacetamide, (trans)-Isomer / Q000494:pharmacology*; D000701:Analgesics, Opioid / Q000494:pharmacology*; D000818:Animals; D004361:Drug Tolerance; D020881:Enkephalin, D-Penicillamine (2,5)-; D004745:Enkephalins / Q000494:pharmacology*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D007191:Indazoles / Q000494:pharmacology*; D008297:Male; D051379:Mice; D009020:Morphine / Q000494:pharmacology*; D019001:Nitric Oxide Synthase / Q000037:antagonists & inhibitors; D009619:Nociceptors / Q000187:drug effects; D017465:Receptors, Opioid, delta / Q000819:agonists; D017473:Receptors, Opioid, kappa / Q000819:agonists
chemical_list: D000701:Analgesics, Opioid; D004745:Enkephalins; D004791:Enzyme Inhibitors; D007191:Indazoles; D017465:Receptors, Opioid, delta; D017473:Receptors, Opioid, kappa; D019900:3,4-Dichloro-N-methyl-N-(2-(1-pyrrolidinyl)-cyclohexyl)-benzeneacetamide, (trans)-Isomer; D009020:Morphine; D020881:Enkephalin, D-Penicillamine (2,5)-; D019001:Nitric Oxide Synthase; C080122:7-nitroindazole