Vitamin E Alleviates Renal Injury, but Not Hypertension, during Chronic Nitric Oxide Synthase Inhibition in Rats

Abstract

ABSTRACT. Chronic nitric oxide (NO) synthase inhibition in rats causes hypertension, renal vascular injury, and proteinuria. NO deficiency increases superoxide (O2−) activity, but the effects of antioxidant treatment on renal injury have not been studied in this model. Exposure of rats toNω-nitro-l-arginine (l-NNA) for 4 d markedly decreased NO-dependent relaxation in aortic rings and increased glomerular and renal interstitial monocyte influx, but renal O2−activity was not increased. After 7 d, BP and proteinuria were significantly increased. After 21 d ofl-NNA treatment, rats displayed severe hypertension, decreased GFR, marked proteinuria, glomerular ischemia, renal vascular and tubulointerstitial injury, and complete loss of NO-dependent relaxation. Renal O2−activity was markedly increased [lucigenin-enhanced chemiluminescence (LEC), 279 ± 71versus50 ± 7 counts/10 mg,P< 0.01; electron paramagnetic resonance spectroscopy, 0.57 ± 0.05versus0.34 ± 0.04 U/10 mg,P< 0.05]. Apocynin, a specific inhibitor of NADPH oxidase, and diphenyleneiodonium, an inhibitor of flavin-containing enzymes, completely inhibited LEC signalsin vitro, whereas allopurinol had no effect, indicating that NAD(P)H oxidase plays a major role in superoxide production in the kidney. Endothelial function remained impaired during cotreatment with α-tocopherol and there was no effect on hypertension or tubulointerstitial injury, but glomerular ischemia, decreases in GFR, and renal vascular injury were prevented and proteinuria was ameliorated. Renal LEC signals were intermediate between control andl-NNA-alone values (181 ± 84 counts/10 mg). Chronic NO synthase inhibition in rats results in marked increases in renal cortical O2−activity, mediated by flavin-dependent oxidases. The absence of early increases in renal O2−activity, in the presence of endothelial dysfunction and macrophage influx, indicates that increased renal O2−activity is neither attributable to NO deficiencyper senor solely related to macrophage influx. The improvement of glomerular function and amelioration of renal vasculitis and proteinuria with vitamin E cotreatment indicate that oxidants are involved in the pathogenesis of renal injury in this model. However, markedly impaired endothelial function and unabated hypertension persist with vitamin E treatment and seem to be directly attributable to NO deficiency.