The influence of sodium restriction on orthostatic sympathetic nervous activity

To evaluate the influence of low-salt diet on the sympathetic nervous system activity, the adaptation to upright posture in five normal subjects was studied during normal salt and 10mEq sodium and 60-mEq potassium diets. On assuming upright posture, there were similar rises in pulse rate and diastolic blood pressure (BP) but a decline in systolic BP, during both diets. A prompt rise in plasma norepinephrine level during low-sodium diet was greater than during normal diet. Orthostatic response of the plasma epinephrine level was small, although significant, but unaffected by the diets. During normal-sodium diet, plasma renin activity response was delayed, but a prompt and enhanced response was observed during low-sodium diet. These data suggest that sodium deprivation enhances the sympathetic nervous system activity and the orthostatic stimulation of renin release.