Sympathoexcitation by Oxidative Stress in the Brain Mediates Arterial Pressure Elevation in Salt-Sensitive Hypertension

Abstract

Central sympathoexcitation is involved in the pathogenesis of salt-sensitive hypertension. We have suggested that oxidative stress in the brain modulates the sympathetic regulation of arterial pressure. Thus, we investigated whether oxidative stress could mediate central sympathoexcitation in salt-sensitive hypertension. Five- to 6-week-old male Dahl salt-sensitive rats and salt-resistant rats were fed with a normal (0.3%) or high- (8%) salt diet for 4 weeks. In urethane-anesthetized and artificially ventilated rats, arterial pressure, renal sympathetic nerve activity, and heart rate decreased in a dose-dependent fashion, when 20 or 40 micromol of tempol, a membrane-permeable superoxide dismutase mimetic, was infused into the lateral cerebral ventricle. The same degree of reduction was noted in salt-sensitive and salt-resistant rats without salt loading. Salt loading significantly increased central tempol-induced reductions in arterial pressure (-29.1+/-4.8% versus -10.6+/-3.3% at 40 micromol; P<0.01), sympathetic nerve activity (-18.7+/-2.0% versus -7.1+/-1.8%; P<0.01), and heart rate (-10.7+/-2.8% versus -2.0+/-0.7%; P<0.05) in salt-sensitive rats but not in salt-resistant rats. Intracerebroventricular diphenyleneiodonium, a reduced nicotinamide-adenine dinucleotide phosphate oxidase inhibitor, also elicited significantly greater reduction in each parameter in salt-loaded salt-sensitive rats. Moreover, salt loading increased reduced nicotinamide-adenine dinucleotide phosphate-dependent superoxide production in the hypothalamus in salt-sensitive rats but not in salt-resistant rats. In addition, reduced nicotinamide-adenine dinucleotide phosphate oxidase subunits p22(phox), p47(phox), and gp91(phox) mRNA expression significantly increased in the hypothalamus of salt-loaded salt-sensitive rats. In conclusion, in salt-sensitive hypertension, increased oxidative stress in the brain, possibly via activation of reduced nicotinamide-adenine dinucleotide phosphate oxidase, may elevate arterial pressure through central sympathoexcitation.