Abstract P214: Impact Of NADPH Oxidase 4 Knockout On Renal O 2 Consumption In Dahl Salt-sensitive Rats

Abstract

It has been generally thought that in normal Sprague-Dawley (SD) rats, a high salt diet has minimal impact on blood pressure and kidney function. However, as we have recently reported, the kidneys of SD rats fed a 4.0% NaCl diet (HS) exhibit enhanced O 2 consumption (VO 2 ) and marked changes in the metabolic pathways responsible for the generation of ATP and reactive oxygen species (ROS). In the current study, we examined the level of renal VO 2 in Dahl salt-sensitive (SS) rats and those in which the NADPH Oxidase 4 (NOX4) gene was globally knocked out (SS Nox4 -/- ). Male SS (n=9) and SS Nox4 -/- (n=10) rats were fed a 0.4% NaCl (LS) diet. At 7-8 weeks of age, the rats were implanted with a renal artery ultrasonic flow probe (Transonic) together with a femoral arterial catheter and a renal venous catheter. Renal blood flow (RBF) and mean arterial pressure (MAP) were measured continuously (24/7) and arterial (A) and renal venous (Vr) blood was sampled intermittently when rats were fed a LS and on days 7, 14, and 21 after switching to a HS diet. Blood O 2 content was immediately measured by a radiometer. The average 24-hour MAP of SS rats rose after switching to a HS diet from 122 ± 2 on the LS to 140 ± 2 on HS7, and to 164 ± 5 by HS21. In contrast, MAP in SS Nox4 -/- rats increased from 121 ± 2 mmHg at LS to 132 ± 1 mmHg at HS7 and 152 ± 3 mmHg at HS21 (p<0.05). RBF was not significantly changed but tended to progressively rise in both strains of rats with 24-hr flows averaging 7.8 ± 0.7 ml/min when fed LS and 8.9 ± 1.0 ml/min at HS21, and SS Nox4 -/- from 6.9 ± 0.7 to 8.2 ± 0.9. Normalized by changes of kidney weights obtained in another group of SS and SS Nox4 -/- rats, RBF was significantly reduced over the 3 weeks of the HS diet given the increase of kidney weights (SS LS 7.0 ± 0.6, HS7 5.7 ± 0.5, HS21 4.9 ± 0.6; SS Nox4 -/- LS 6.4 ± 0.7, HS7 6.2 ± 0.7, HS21 5.4 ± 0.7). Most importantly, the O 2 extraction ratio at LS was lower in SS Nox4 -/- (10.5 ± 1.0%) compared to SS (14.6 ± 1.0%) (p<0.05). When switched to the HS diet, this was further reduced in the SS Nox4 -/- rats reaching 7.6 ± 0.9% at HS21 (p<0.05), while it did not change significantly in SS (13.3 ± 1.4%) at HS21. We conclude that the elevated levels of renal O 2 consumption observed in SS rats are at least in part a consequence of increased oxidative stress associated with NOX4.