Aging enhances pressure-induced arterial superoxide formation

Abstract

The purpose of this study was to investigate the mechanisms that regulate superoxide (O2•−) production as a function of an acute elevation of intravascular pressure and age. Mesenteric arteries isolated from young (6 mo) and aged (24 mo) male Fischer 344 rats were used. O2•− production in vessels in response to 80 (normal pressure, NP) and 180 (high pressure, HP) mmHg was determined by the superoxide dismutase-inhibitable nitroblue tetrazolium (NBT) reduction assay. In vessels exposed to NP, O2•− production was significantly higher in aged than in young vessels (32.7 ± 7.0 vs. 15.4 ± 2.4 nmol·mg−1·30 min−1). HP enhanced O2•− production in vessels of both groups, but the enhancement was significantly greater in aged than in young vessels (63.4 ± 6.7 vs. 32.7 ± 4.3 nmol·mg−1·30 min−1). Apocynin (100 μmol/l) attenuated HP-induced increases in O2•− production in both groups, whereas allopurinol (100 μmol/l) and Nω-nitro-l-arginine methyl ester (100 μmol/l) inhibited the response only in aged vessels. Confocal microscopy showed increases in O2•− in response to HP in endothelial and smooth muscle layers of both groups, with much greater fluorescent staining in aged than in young rats and in the endothelium than in smooth muscle cells. No significant changes in NAD(P)H oxidase gene and protein expressions were observed in vessels of the two groups. Upregulation of protein expression of xanthine oxidase was detected in aged vessels. We conclude that NAD(P)H oxidase contributes importantly to HP-induced enhanced O2•− production in vessels of both young and aged rats, whereas xanthine oxidase and nitric oxide synthase-dependent O2•− production also contribute to the enhancement in mesenteric arteries of aged rats.