We have reported that pharmacological doses of oral nitrite increase circulating nitric oxide (NO) and exert hypotensive effects in N -nitro-L-arginine methyl ester (L-NAME)-induced hypertensive rats. In this study, we examined the effect of a chronic dietary dose of nitrite on the hypertension and renal damage induced by chronic L-NAME administration in rats. The animals were administered tap water containing L-NAME (1 g/l) or L-NAME ϩ nitrite (low dose: 0.1 mg/l, medium dose: 1 mg/l, high dose: 10 mg/l) for 8 wk. We evaluated blood NO levels as hemoglobin-NO adducts (ironnitrosyl-hemoglobin), using an electron paramagnetic resonance method. Chronic administration of L-NAME for 8 wk induced hypertension and renal injury and reduced the blood iron-nitrosyl-hemoglobin level (control 38.8 Ϯ 8.9 vs. L-NAME 6.0 Ϯ 3.1 arbitrary units). Coadministration of a low dose of nitrite with L-NAME did not change the reduced iron-nitrosyl-hemoglobin signal and did not improve the L-NAMEinduced renal injury. The blood iron-nitrosyl-hemoglobin signals of the medium dose and high dose of nitrite were significantly higher than that of L-NAME alone. Chronic administration of a medium dose of nitrite attenuated L-NAME-induced renal histological changes and proteinuria. A high dose of nitrite also attenuated L-NAME-induced renal injury. These findings suggest that dietary doses of nitrite that protect the kidney are associated with significant increase in iron-nitrosyl-hemoglobin levels. We conclude that dietary nitrite-derived NO generation may serve as a backup system when the nitric oxide synthase/L-arginine-dependent NO generation system is compromised.vegetables; N -nitro-L-arginine methyl ester; kidney NITRIC OXIDE (NO) is a gaseous signaling molecule and exerts a variety of biological actions under physiological and pathophysiological conditions, such as regulation of the cardiovascular, inflammation, immune, and neuronal systems. NO also has numerous important functions in the kidney, such as the regulation of renal hemodynamics and glomerular microcirculation, the regulation of salt balance, the blunting of tubuloglomerular feedback, and the modulation of renal sympathetic nerve activity (18,26). Chronic blockade of nitric oxide synthases (NOSs) with N -nitro-L-arginine methyl ester (L-NAME) in rats results in severe hypertension and progressive kidney damage (3, 11). On the other hand, NO production seems to be low in chronic kidney disease (CKD) patients, and NO deficiency may play a role in CKD progression (5, 32). Treatment strategies to maintain the circulating NO level in healthy young people may be useful in preventing or slowing the progression of renal diseases.It is believed that NO is synthesized from L-arginine, NADPH, tetrahydrobiopterin, and the molecular oxygen catalyzed by NOSs in endothelial and other cells. The biological activity of NO is terminated by oxidation into nitrite and nitrate. Therefore, nitrite and nitrate in the blood are recognized as waste forms of NO. However, this dogma is now being challe...