INTERACTION BETWEEN SUPEROXIDE ANION AND NITRIC-OXIDE IN THE REGULATION OF VASCULAR ENDOTHELIAL FUNCTION

1 Nitric oxide (NO)-mediated, endothelium-dependent vasodilator functi on in rat aortic smooth muscle was investigated in an in vitro model o f endogenous vascular superoxide anion stress, generated by pretreatme nt with the Cu/Zn superoxide dismutase (SOD, EC 1.15.1.1) inhibitor, d iethyldithiocarbamate (DETCA). 2 Contraction to noradrenaline (NA, 1 n M-1 mu M) in endothelium-intact vessels was augmented after a 30 min p retreatment with DETCA (10 mM) followed by 30 min washout. This effect was abolished by N-G-nitro-L-arginine methyl ester (L-NAME, 0.3 mM) a nd removal of the endothelium and partially reversed by exogenous Cu/Z n SOD (200 u ml(-1)). 3 Endothelium- and basal NO-dependent vasorelaxa tion to the phosphodiesterase (PDE) type V inhibitor ONO-1505 ylamino] -2-(1H-imidazol-1-yl)-6-methoxyquinazoline methanesulphonate) (0.1-10 mu M) was inhibited after DETCA (10 mM) pretreatment. In addition, the ability of L-NAME (0.3 mM) to enhance established contractile tone wa s effectively absent. 4 In contrast, DETCA pretreatment did not signif icantly affect vasorelaxation to acetylcholine (ACh, 1 nM-3 mu M) or S -nitroso-N-acetyl penicillamine (SNAP, 0.03-30 mu M). However, L-NAME (0.3 mM) unmasked an inhibitory effect of DETCA pretreatment on vasore laxation to SNAP in endothelium-intact vessels while markedly potentia ting vasorelaxation to SNAP in control tissue. 5 L-NAME (0.3 mM)- and exogenous catalase (200 u ml(-1))-sensitive vasorelaxation to exogenou s Cu/Zn SOD (200 u ml(-1)) was greater after DETCA (10 mM) pretreatmen t in endothelium-intact aortic rings. This difference was abolished by catalase (200 u ml(-1)). 6 In conclusion, tissue Cu/Zn SOD inhibition elicited a selective lesion in basal endothelial function in rat isol ated aortic smooth muscle, consistent with the inactivation of basal N O by superoxide anion. The resulting leftward shift in nitrovasodilato r reactivity, due to the loss of the tonic depression by basal NO, is likely to mask the inhibitory effect of superoxide anion on agonist-st imulated endothelial function and nitrovasodilator-derived NO, thereby accounting for the differential pattern of endothelial dysfunction af ter DETCA pretreatment.