Overexpression of Inducible Nitric Oxide Synthase in Rostral Ventrolateral Medulla Causes Hypertension and Sympathoexcitation via an Increase in Oxidative Stress

Abstract

Abstract-The present study examined the role of inducible nitric oxide synthase (iNOS) in the rostral ventrolateral medulla (RVLM) of the brain stem, where the vasomotor center is located, in the control of blood pressure and sympathetic nerve activity. Adenovirus vectors encoding iNOS (AdiNOS) or ␤-galactosidase (Ad␤gal) were transfected into the RVLM in Wistar-Kyoto (WKY) rats. Blood pressure and heart rate were monitored using a radiotelemetry system. iNOS expression in the RVLM was confirmed by immunohistochemical staining or Western blot analysis. Mean arterial pressure significantly increased from day 6 to day 11 after AdiNOS transfection, but did not change after Ad␤gal transfection. Urinary norepinephrine excretion was significantly higher in AdiNOS-transfected rats than in Ad␤gal-transfected rats. Microinjection of aminoguanidine or S-methylisothiourea, iNOS inhibitors, or tempol, an antioxidant, significantly attenuated the pressor response evoked by iNOS gene transfer. The levels of thiobarbituric acid-reactive substances, a marker of oxidative stress, were significantly greater in AdiNOS-transfected rats than in Ad␤gal-transfected rats. Dihydroethidium fluorescence in the RVLM was increased in AdiNOS-transfected rats. In addition, nitrotyrosine-positive cells were observed in the RVLM only in AdiNOS-transfected rats. Intracisternal infusion of tempol significantly attenuated the pressor response and the increase in the levels of thiobarbituric acid-reactive substances induced by AdiNOS transfection. These results suggest that overexpression of iNOS in the RVLM increases blood pressure via activation of the sympathetic nervous system, which is mediated by an increase in oxidative stress. Key Words: nitric oxide synthase Ⅲ blood pressure Ⅲ sympathetic nervous system Ⅲ oxidative stress Ⅲ gene transfer N itric oxide (NO) in the central nervous system (CNS), including the brain stem and hypothalamus, plays an important role in the regulation of blood pressure via the sympathetic nervous system. [1][2][3][4][5][6][7] In general, NO in the CNS inhibits sympathetic nerve activity, thereby reducing blood pressure. [2][3][4] The rostral ventrolateral medulla (RVLM) in the brain stem contains sympathetic premotor neurons responsible for maintaining the tonic excitation of sympathetic preganglionic neurons involved in cardiovascular regulation. 8 -10 The functional integrity of the RVLM is essential for the maintenance of basal vasomotor tone, and RVLM abnormalities might be related to the pathophysiology of hypertension 11-14 and heart failure. 15,16 Recently, we developed a technique for adenovirusmediated endothelial NO synthase (eNOS) gene transfer into the RVLM 11,14,[17][18][19] or the nucleus tractus solitarii (NTS) 20,21 in vivo. An increase in NO production in the RVLM induced by eNOS overexpression decreases blood pressure and heart rate (HR) by inhibiting the sympathetic nervous system. 11,14,19 In that series of studies, we used eNOS instead of neuronal NO synthase (nNOS), which is normally abundant...

Redox Control of Renal Function and Hypertension

“…The antioxidant adrenomedullin was shown to inhibit SNS-induced hypertension in salt-loaded mice (74). Overexpression of inducible NO synthase in the rostral ventrolateral medulla causes hypertension and sympathoexcitation via an increase in oxidative stress (161). Increased ROS in the rostral ventrolateral medulla contribute to neural mechanisms of hypertension in stroke-prone SHRs (163).…”

Olmesartan reduces oxidative stress in the brain of stroke-prone spontaneously hypertensive rats assessed by an in vivo ESR method

“…Urinary NE concentration was measured by high-performance liquid chromatography to calculate urinary NE excretion as a marker of sympathetic nervous system activity. 13,14,16 NADPH oxidase activity Nicotinamide adenine dinucleotide phosphate (NADPH) oxidase activity was evaluated using lucigenin chemiluminescence as described elsewhere, 25 in membrane fraction proteins. Briefly, a deeply anesthetized rat (sodium pentobarbital, 75 mg kg À1 , intraperitoneal) was perfused transcardially with 200 ml chilled saline.…”

“…[6][7][8][9][10] Oxidative stress in the brain increases blood pressure through activation of the sympathetic nervous system. [11][12][13][14] The major source of reactive oxygen species (ROS) is nicotinamide adenine dinucleotide phosphate (NAD(P)H) oxidase, 12,15,16 which is activated by AT1 receptor stimulation. AT1 receptor expression levels in the brain, such as in the RVLM, are upregulated in hypertensive animal models compared with normotensive controls.…”

Effect of high-fat diet feeding on hypothalamic redox signaling and central blood pressure regulation

“…11 On the other hand, overexpression of inducible NO synthase (iNOS) in the rostral ventrolateral medulla increases oxidative stress and elevates SNS activity. 12 As obesity affects both redox signaling and NO synthesis throughout the body, [13][14][15] there is a possibility that oxidative stress and reduced bioavailability of NO in cardiovascular regulatory nuclei mediate, at least in part, sympathoexcitation and blood pressure elevation in response to obesity.…”