EFFECT OF THIOL MODULATORS AND CU ZN SUPEROXIDE-DISMUTASE INHIBITION ON NITRERGIC RELAXATIONS IN THE RAT GASTRIC FUNDUS/

1 The effects of superoxide anion generators before and after treatmen t with inhibitors of Cu/Zn superoxide dismutase (Cu/Zn SOD) and the ef fects of thiol-modulating agents were investigated on nitrergic relaxa tions to electrical stimulation of non-adrenergic non-cholinergic (NAN C) nerves of the rat gastric fundus and on relaxations to authentic ni tric oxide (NO) and nitroglycerin. 2 The superoxide anion generators, pyrogallol (30 mu M) and duroquinone (30-60 mu M), significantly inhib ited the relaxations to NO (0.03-3 mu M) but not nitrergic relaxations to NANC nerve stimulation (0.5-8 Hz) or those to ATP (10 mu M). Treat ment of the rat gastric fundus with the inhibitors of Cu/Zn SOD, dieth yldithiocarbamate (DETC, 1 mM for 2 h) or triethylenetetramine (TETA, 100 mu M for 2 h) had no effect on the relaxations to NANC nerve stimu lation (1-8 Hz), NO (0.03-3 mu M) Of on those to ATP (10 mu M). 3 Afte r treatment of the rat gastric fundus with DETC (1 mM) but not after t reatment with TETA (100 mu M), pyrogallol (30 mu M) and duroquinone (3 0-60 mu M) significantly inhibited the nitrergic relaxations to electr ical stimulation (0.5-8 Hz) and those to NO (0.03-3 mu M). This inhibi tory effect of pyrogallol and duroquinone was prevented by addition of exogenous SOD (250 units ml(-1)). Pyrogallol but not duroquinone also inhibited the NO-independent relaxations to ATP (10 mu M). 4 The thio l modulators, buthionine sulphoximine (1 mM for 2 h) and ethacrynic ac id (30 mu M for 2 h), significantly inhibited the relaxations to nitro glycerin (0.03-3 mu M) but had no effect on the nitrergic relaxations to electrical stimulation (0.5-8 Hz) or on those to NO (0.03-10 mu M) and ATP (10 mu M). The thiol modulators, sulphobromophthalein (100 mu M for 2 h) and diamide (30-100 mu M for 2 h) did not affect the relaxa tions to nitroglycerin, or those to NANC nerve stimulation and NO, 5 I n summary, thiol modulators significantly inhibited the thiol-dependen t relaxations to nitroglycerin but not those to NANC nerve stimulation or NO. Relaxations to nitrergic stimulation were decreased by superox ide anion generators only after inhibition of Cu/Zn SOD. These results suggest that the nitrergic NANC neurotransmitter in the rat gastric f undus is not a nitrosothiol but more likely free NO, which is protecte d from breakdown by tissue SOD.