Induction of Oxidative Stress by Glutathione Depletion Causes Severe Hypertension in Normal Rats
Several recent studies have shown that certain forms of genetic and acquired hypertension (HTN) are associated with oxidative stress and respond favorably to antioxidant therapy. We hypothesize that oxidative stress, per se, may cause HTN via (among other mechanisms) enhanced oxidation and inactivation of nitric oxide (NO). To test this hypothesis, Sprague-Dawley rats were subjected to oxidative stress by glutathione (GSH) depletion using GSH synthase inhibitor, buthionine sulfoximine (BSO, 30 mmol/L in drinking water), for two weeks. The control group was given drug-free drinking water. In parallel experiments, subgroups of animals were provided vitamin E-fortified chow and vitamin C-supplemented drinking water. Arterial blood pressure, urinary excretion of NO metabolites (NO2+NO3, NOx), and liver tissue GSH were measured. In addition, plasma, kidney, heart, liver and aorta were tested by Western blot analysis for nitrotyrosine, which is the footprint of NO inactivation by reactive oxygen species (ROS). The BSO-treated group showed a three-fold fall in hepatic tissue GSH content (0.99±0.3 vs 3.4±0.3 μmol/g wet tissue, P<0.001), a marked elevation in blood pressure (203±3 vs 120±2 mmHg, P<0.001) and a significant reduction in urinary excretion of NO metabolites, nitrate + nitrite (316±23 vs 595±29 μmol/g creatinine, P<0.01), suggesting depressed NO availability. This was associated with a significant accumulation in all tested tissues of nitrotyrosine (P<0.05 for all comparisons). Administration of vitamins E+C ameliorated HTN (156±4 mmHg, P<0.01), improved urinary NOx excretion (392±28 μmol/g creatinine, P<0.05) and mitigated nitrotyrosine accumulation (despite persistent GSH depletion) in the BSO-treated animals. However, vitamins E+C treatment had no effect on any of the above parameters in the control group (data not shown). In conclusion, GSH depletion resulted in perturbation of the NO system and severe HTN in normal animals. The effects of BSO were mitigated by concomitant antioxidant therapy despite GSH depletion, supporting the notion that oxidative stress was involved in the pathogenesis of HTN in this model.