Short- and Long-Term Neuroadrenergic Effects of Moderate Dietary Sodium Restriction in Essential Hypertension

Abstract

Background— In essential hypertension, marked restrictions in dietary sodium intake cause in the short-term period an increase in muscle sympathetic nerve traffic (MSNA) and a baroreflex impairment. The present study was set out to assess on a long-term basis the neuroadrenergic and reflex effects of moderate sodium restriction. Methods and Results— In 11 untreated mild to moderate essential hypertensive patients (age 42.0±2.6 years, mean±SEM), we measured beat-to-beat blood pressure (Finapres), heart rate (ECG), and MSNA (microneurography) at rest and during stepwise intravenous infusions of phenylephrine and nitroprusside. Measurements were performed at regular sodium intake, after 1 and 8 weeks of low-sodium diet (80 mmol NaCl/d), and repeated again at regular sodium intake. After 1 week, urinary sodium excretion was markedly reduced. This was accompanied by a slight blood pressure reduction, no heart rate change, and a significant increase in plasma renin activity, aldosterone, and MSNA (+23.0±4.6% P <0.05). Whereas baroreflex heart-rate control was unchanged, baroreflex modulation of MSNA was reduced by 46.8±5.1% ( P <0.01). At the end of the 8-week low-sodium diet, the neurohumoral and baroreflex responses were similar to the ones observed after 1 week of the dietary intervention. All changes disappeared when regular sodium diet was restored. Conclusions— Thus, a moderate dietary sodium restriction triggers a sympathetic activation and a baroreflex impairment. Maintenance of low-sodium diet for several weeks does not attenuate these adverse adrenergic and reflex effects.