Influence of antioxidant depletion on nitrergic relaxation in the pig gastric fundus

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. Diethyldithiocarbamate (DETCA; 3×10 −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 ). 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. 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. 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.British Journal of Pharmacology (2002) 135 , 917–926; doi: 10.1038/sj.bjp.0704553