High salt intake enhances blood pressure increase during development of hypertension via oxidative stress in rostral ventrolateral medulla of spontaneously hypertensive rats

Abstract

High salt intake increases blood pressure (BP) in spontaneously hypertensive rats (SHR), and central neural mechanisms are suggested to be involved. Increased generation of reactive oxygen species (ROS) in the rostral ventrolateral medulla (RVLM) contributes to the neural mechanism of hypertension in SHR. We sought to examine whether high salt intake increases hypertension in SHR and whether the increased ROS in the RVLM contributes to this mechanism. Male SHR and Wistar-Kyoto rats (WKY) (6 weeks old) were fed a high-salt diet (8%: HS-S; HS-W) or a regular-salt diet (0.5%: RS-S; RS-W) for 6 weeks. Systolic BP was significantly higher in HS-S than in RS-S at 12 weeks of age (244±5 vs. 187±7 mmHg, n=8; p<0.05). Urinary norepinephrine excretion was significantly higher in HS-S than in RS-S. Thiobarbituric acid-reactive substances levels in the RVLM were significantly higher in HS-S than in RS-S (9.9±0.5 vs. 8.1±0.6 μmol/g wet wt, n=5; p<0.05). Microinjection of tempol or valsartan into the RVLM induced significantly greater BP reduction in HS-S than in RS-S. The increase in angiotensin II type 1 receptor (AT1R) expression and the increase in reduced nicotinamide-adenine dinucleotide phosphate (NAD(P)H) oxidase activity in the RVLM were significantly greater in HS-S than in RS-S. These findings indicate that high salt intake exacerbates BP elevation and sympathetic nervous system activity during the development of hypertension in SHR. These responses are mediated by increased ROS generation that is probably due to upregulation of AT1R/ NAD(P)H oxidase in the RVLM.