Anatomic heterogeneity of vascular aging: role of nitric oxide and endothelin

Abstract

We investigated the effects of aging, a cardiovascular risk factor, on vascular function with regard to endothelial nitric oxide synthase (eNOS), superoxide dismutase (SOD), and endothelin (ET-1) in aorta and femoral artery of the rat. Concentration-response curves to acetylcholine, calcium ionophore A23187, norepinephrine, ET-1, big endothelin, sodium nitroprusside, and exogenous SOD were obtained. Expression of eNOS mRNA was analyzed by reverse-transcription polymerase chain reaction, SOD activity was assessed using a chemiluminescence-based cytochrome c assay, and ET-1 plasma concentrations were measured by radioimmunoassay. In aorta of old rats, relaxations to acetylcholine and calcium ionophore A23187, basal NO release, and expression of eNOS mRNA in aortic endothelial cells were reduced (P<.05). In femoral arteries, relaxations to acetylcholine were preserved, whereas basal release of NO was attenuated (P<.05). Aging selectively increased contractions to norepinephrine and functional endothelin converting enzyme activity and attenuated contractions to ET-1 in aortas but not femoral arteries. Vascular SOD activity was higher in the femoral artery (P<.05) and unaffected by aging. Plasma ET-1 levels increased and plasma SOD activity decreased with age (P<.05). Aging was associated with an anatomic heterogeneity of endothelial dysfunction, functional endothelin converting enzyme activity, and vascular SOD activity. Vascular function was impaired in the aorta but not the femoral artery, which may be related to lower eNOS mRNA expression and SOD activity. These data suggest differential regulation of the vascular aging process that may contribute to the anatomic heterogeneity of atherosclerosis.