Increased oxidative stress in rats with chronic nitric oxide depletion:measurement of urinary 8-hydroxy-2′-deoxyguanosine excretion

Abstract

Urinary 8-hydroxy-2′-deoxyguanosine (8-OHdG) has been reported to serve as a sensitive biomarker of oxidative stress. We examined the effect of chronic blockade of nitric oxide (NO) on urinary excretion of 8-OHdG in rats. Two types of NO synthase inhibitor were used: N^G-nitro-L-arginine methyl ester (L-NAME) as a non-selective inhibitor and aminoguanidine (AG) as a selective inhibitor of the inducible isoform. Oral administration of L-NAME (20, 50 and 80 mg/dl of drinking water), but not AG (400 mg/dl), for 4 weeks induced systemic hypertension and a significant reduction in urinary excretion of NO₂^-/NO₃^-. Rats treated with L-NAME also showed a significant increase in urinary 8-OHdG excretion compared with the control animals. The effects of L-NAME (50 mg/dl) on blood pressure and urinary excretion of NO₂^-/NO₃^- and 8-OHdG were restored by a large dose of L-arginine (2.0 g/dl). Chronic AG administration did not significantly alter urinary 8-OHdG excretion. On combining all the data, there was a significant negative correlation between urinary NO₂^-/NO₃^- and 8-OHdG. These observations suggest the importance of constitutive NO synthase activity in the maintenance of oxidant buffering capacity in rats. Oral administration of L-NAME may serve as a model of hypertension due to chronic NO deficiency with increased oxidative stress.