Published Online
on September 16, 2002

A more recent version of this article appeared on October 8, 2002

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Submitted on May 17, 2002
Revised on July 23, 2002
Accepted on July 23, 2002

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

Guido Grassi MD, Raffaella Dell'Oro MD, Gino Seravalle MD, Gerardo Foglia MD, Fosca Quarti Trevano MD, and Giuseppe Mancia MD^*

From Clinica Medica, Dipartimento di Medicina Clinica, Prevenzione e Biotecnologie Sanitarie, Università Milano-Bicocca, Centro Interuniversitario di Fisiologia Clinica e Ipertensione and Istituto Auxologico Italiano, Milan, Italy.

^* To whom correspondence should be addressed. E-mail: giuseppe.mancia{at}unimib.it.

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.

Key words: hypertension • sodium • nervous system, sympathetic • nervous system, autonomic • baroreceptors

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