[Plasma norepinephrine variation with dietary sodium intake in normotensive subjects and patients with essential hypertension]

Sympathetic nervous system may play an important role in the pathogenesis of essential hypertension. The present study was undertaken to evaluate the interaction between sodium intake and sympathetic nervous activity in the patients with essential hypertension. Plasma and urinary catecholamines (CA) were measured in 38 hypertensive patients (WHO 1-2 stage) and 24 age-matched normal subjects on regular (urinary sodium excretion (UNaV): 133 +/- 8 mEq/day; mean +/- SEM), high (UNaV 317 +/- 90 mEq/day), and low (UNaV 67 +/- 28 mEq/day) sodium diets for each 5 days at random. CA were analyzed by THI methods after HPLC separation. Twenty-four hour urinary norepinephrine (NE), epinephrine (E), and electrolytes (Na+, K+) excretion on the 5th day of each regimen were determined. In the 6th day morning supine and 5 min upright plasma NE(PNE), plasma E (PE), and plasma renin activity were determined after blood pressure and pulse rate measurement. The results were also analyzed according to the difference between salt-sensitive and non-salt-sensitive type of hypertensive patients. Plasma NE was 1.1 +/- 0.4 p mol/ml (supine), 1.5 +/- 0.4 p mol/ml (upright) in normotensive subjects and 1.8 +/- 1.1 p mol/ml (supine), 2.5 +/- 1.1 p mol/ml (upright) in the patients with essential hypertension, 24 hr urinary NE excretion were 116 +/- 54 micrograms/day in normotensive subjects and 138 +/- 88 micrograms/day in the patients with essential hypertension on regular sodium intake. Mean plasma NE levels in patients with essential hypertension were always higher than those in normotensive subjects on any sodium diets. Plasma NE and urinary NE were significantly reduced by high sodium intake and increased by low sodium intake in both normotensive subjects and the patients with essential hypertension. Percentile decrease in PNE when the diet was changed from low sodium to high sodium was much greater in normotensive subjects than the patients with essential hypertension. These tendency was observed in both salt-sensitive and non-salt-sensitive hypertensive patients. However, PNE in non-salt-sensitive hypertensive subjects tended to be higher than those in salt-sensitive hypertensive subjects. These results suggest that abnormal relationship between sodium intake and sympathetic nervous system may play an important role in the pathogenesis of essential hypertension.