Influence of antioxidant depletion on nitrergic relaxation in the pig gastric fundus.
1. The hypothesis that endogenous tissue antioxidants might explain the inability of the superoxide generators 6-anilino-5,8-quinolinedione (LY83583) and hydroquinone (HQ) and of the NO-scavengers hydroxocobalamin (HC) and 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (c-PTIO) to affect nitrergic neurotransmission in the porcine gastric fundus was tested by selective pharmacological depletion of respectively Cu/Zn superoxide dismutase (Cu/Zn SOD) and reduced glutathione (GSH) in circular smooth muscle preparations. 2. Diethyldithiocarbamate (DETCA; 3x10(-3) M), which almost completely abolished tissue Cu/Zn SOD activity, had no effect per se on nitrergic relaxations induced by either electrical field stimulation (EFS; 4 Hz, 10 s) or exogenous nitric oxide (NO; 10(-5) M). In these DETCA-treated tissues however, electrically-induced nitrergic relaxations became sensitive to inhibition by LY83583 (10(-5) M) or HC (10(-4) M), but not by HQ (10(-4) M) or c-PTIO (10(-4) M); only for the combination of DETCA plus LY83583, this inhibition was partially reversed by exogenous Cu/Zn SOD (1000 u ml(-1)). 3. Immunohistochemical analysis of porcine gastric fundus revealed a 100% colocalization of Cu/Zn SOD and neuronal nitric oxide synthase (nNOS) in the intrinsic neurons of the myenteric plexus. 4. Buthionine sulphoximine (BSO; 10(-3) M) in the absence or presence of LY83583 (10(-5) M) or HC (10(-4) M) did not alter nitrergic relaxations, although it reduced per se the tissue GSH content to 62% of control. 5. Pharmacological depletion studies, corroborated by immunohistochemical data, thus suggest a role for Cu/Zn SOD but not for GSH in nitrergic neurotransmission in the porcine gastric fundus.
Colpaert
E E
EE
Heymans Institute of Pharmacology, Ghent University Medical School, De Pintelaan 185, B-9000 Ghent, Belgium.
Timmermans
J-P
JP
Lefebvre
R A
RA
D000634:Aminoquinolines / Q000494:pharmacology; D000818:Animals; D001565:Benzoates / Q000494:pharmacology; D019328:Buthionine Sulfoximine / Q000494:pharmacology; D002330:Carmustine / Q000494:pharmacology; D002614:Chelating Agents / Q000494:pharmacology; D004050:Ditiocarb / Q000494:pharmacology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D004976:Ethacrynic Acid / Q000494:pharmacology; D005748:Gastric Fundus / Q000378:metabolism / Q000502:physiology*; D005978:Glutathione / Q000172:deficiency / Q000378:metabolism*; D006879:Hydroxocobalamin / Q000494:pharmacology; D007093:Imidazoles / Q000494:pharmacology; D007150:Immunohistochemistry; D066298:In Vitro Techniques; D009569:Nitric Oxide / Q000502:physiology*; D019001:Nitric Oxide Synthase / Q000378:metabolism; D052248:Nitric Oxide Synthase Type I; D013482:Superoxide Dismutase / Q000096:biosynthesis / Q000172:deficiency / Q000378:metabolism*; D013552:Swine; D013869:Thiolester Hydrolases / Q000378:metabolism; D043222:Ubiquitin Thiolesterase; D014664:Vasodilation / Q000187:drug effects / Q000502:physiology*
D000634:Aminoquinolines; D001565:Benzoates; D002614:Chelating Agents; D004791:Enzyme Inhibitors; D007093:Imidazoles; C079393:1,3-dihydroxy-4,4,5,5-tetramethyl-2-(4-carboxyphenyl)tetrahydroimidazole; D009569:Nitric Oxide; D019328:Buthionine Sulfoximine; C041715:6-anilino-5,8-quinolinedione; D004050:Ditiocarb; D019001:Nitric Oxide Synthase; D052248:Nitric Oxide Synthase Type I; D013482:Superoxide Dismutase; D013869:Thiolester Hydrolases; D043222:Ubiquitin Thiolesterase; D005978:Glutathione; D004976:Ethacrynic Acid; D006879:Hydroxocobalamin; D002330:Carmustine