Oxidative stress implies excess production or reduced metabolism of reactive oxygen species (ROS). A major ROS involved in vascular and renal homeostasis is superoxide. In this study excess superoxide is generated by chronic angiotensin II treatment via stimulation of oxidase enzymes, such as NADPH oxidase and by excessive oxygen, via mitochondria cytochrome c conversion. Superoxide reacts with nitric oxide (NO), thus reducing its biological activity. NO, a potent vasodilator regulates renal blood flow and glomerular filtration rate. We will study the roles of 5 proteins in the generation of key components that define the role of oxidative stress in the regulation of renal function. We will evaluate the roles of 5 key proteins by using mice with gene deletions in two series of physiological studies.
In Specific Aim 1, we will assess the impact of oxidative stress on the kidney's usage of oxygen and renal function after chronic angiotensin II treatment, in 5 separate strains of genetically altered mice. Genes for endothelial nitric oxide synthase (eNOS), neuronal NOS (nNOS), the p47/phox subu7nit of NAD(P)H oxidase, extracellular superoxide dismutase (EC-SOD) and dopamine-5 receptor (D5-R) will be studied. We will test the hypothesis that renal oxygen consumption relative to sodium transported is increased and renal tissue oxygen is decreased in mice during oxidative stress generated by angiotensin II. These effects are due to the lack of NO which is reduced by excess superoxide, generated by the combination of increased activity of NADPH oxidase and reduced antioxidant activity of EC-SOD and/or D5-R.
In Specific Aim 2, we will measure the NO responsiveness will be assessed by the single nephron GFR change during perfusion of the renal nephron with a NO donor. We will test the hypothesis that chronic oxidative stress in the renal cortex reduces NO responsiveness in the JGA.
In Specific Aim 3, we will test the effect of acute oxidative stress generated by hyperoxia on NO responsiveness in the juxtaglomerular apparatus, in similar experiments. Results from these studies should identify the role of oxidative stress and oxygenation on nitric oxide regulation of renal function.
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