FLUID, IONIC AND HORMONAL CHANGES INDUCED BY HIGH-SALT INTAKE IN SALT-SENSITIVE AND SALT-RESISTANT HYPERTENSIVE PATIENTS

1. The aim of the study was to detect differences between salt-sensiti ve and salt-resistant hypertensive patients in the response of the ren in-aldosterone axis, plasma noradrenaline and atrial natriuretic pepti de to high salt intake. 2. Fifty essential hypertensive patients follo wed 2 weeks of a standard diet with 20 mmol of NaCl daily, supplemente d by placebo tablets for the first 7 days and by NaCl tablets for the last 7 days, in a single-blind fashion, Salt sensitivity was defined a s a significant rise (P<0.05) in 24 h mean blood pressure obtained by ambulatory blood pressure monitoring from the low- to the high-salt pe riod, Biochemical and hormonal measurements were performed on the last day of both periods. 3. Twenty-two (44%) patients fulfilled criteria of salt-sensitive hypertension, whereas the remaining 28 (56%) were co nsidered salt-resistant, High salt intake promoted a significant decre ase (P<0.05) in plasma creatinine, potassium, glucose, cholesterol, lo w-density lipoprotein-cholesterol, triacylglycerols, uric acid and pla sma renin activity, and a significant increase in plasma atrial natriu retic peptide and 24 h urinary calcium excretion, The direction of the se changes did not differ between salt-sensitive and salt-resistant pa tients, Salt-resistant hypertensive patients exhibited a significant d ecrease in plasma aldosterone induced by high salt intake (from 446+/- 35 to 226+/-35 pmol/l; P<0.001), whereas this parameter was not signif icantly modified in salt-sensitive patients (from 485+/-76 to 364+/-83 pmol/l; P not significant), Salt-sensitive patients showed an increas e in plasma noradrenaline after high salt intake (from 1.15+/-0.11 to 156+/-014 nmol/l; P<0.05), whereas salt-resistant patients presented a decrease in this parameter (from 1.48 +/- 0.08 to 1.12+/-0.08 nmol/l; P<0.05). The change in plasma noradrenaline was directly correlated w ith the change in mean blood pressure induced by high salt intake (r-0 .479; P=0.003). 4. We conclude that the increase in blood pressure ind uced by high salt intake in salt-sensitive patients is associated with a stimulation of the sympathetic nervous system and a blunted decreas e in plasma aldosterane. Conversely, changes in renal function, electr olyte excretion and plasma concentrations of atrial natriuretic peptid e induced by high salt intake seem to be similar in both salt-sensitiv e and salt-resistant patients.