THE EFFECT OF LOW AND HIGH SODIUM DIETS ON PLASMA ATRIAL-NATRIURETIC-FACTOR, THE RENIN-ALDOSTERONE SYSTEM AND BLOOD-PRESSURE IN SUBJECTS WITH ESSENTIAL-HYPERTENSION

OBJECTIVE Increasing dietary sodium intake increases blood pressure in some subjects with essential hypertension. Atrial natriuretic factor (ANF) has a potential role in modifying these changes. The purpose of this study was to observe the blood pressure and plasma ANF responses to low and high sodium diets in subjects with essential hypertension t o see if the plasma ANF and blood pressure responses were related. DES IGN An in-patient study of subjects taking their normal diet (day 1), a 12 mmol sodium diet for 6 days and a 250 mmol diet for 6 days. PATIE NTS Seven men with essential hypertension. MEASUREMENTS Continuous 24 hour urine collections were analysed for sodium excretion. Blood press ure was recorded at 0900, 1205 and 1700 h on days 1, 7 and 13. Blood w as taken at 0900 h (fasting supine overnight) and at 1200 h (after 2 h ours erect posture) on the above days for plasma ANF, plasma renin act ivity (PRA) and serum aldosterone. RESULTS Urinary sodium excretion wa s (mean+/-SEM) 11 +/- 1 mmol on day 5 of the low sodium diet, and 294 +/- 17 mmol during the fifth day of the high sodium diet. Plasma ANF ( supine and erect) was significantly lower (2.8 +/- 0.6, 1.6 +/- 0.2 pm ol/l) on the low sodium diet when compared to the high sodium diet (8. 6 +/- 2.4, 5.0 +/- 1.6 pmol/l (P<0.05)). Supine and erect PRA and seru m aldosterone were significantly higher on the low compared to the hig h sodium diet. Blood pressure responses were heterogeneous rather than bimodal. Mean arterial blood pressure was 107 +/- 3 mmHg on the low s odium diet and 111 +/- 4 mmHg on the high sodium diet (P<0.05). Change s of brood pressure did not correlate with the changes of plasma ANF. CONCLUSIONS Failure of plasma atrial natriuretic factor to rise with i ncreasing dietary sodium did not therefore determine the blood pressur e reponse to the change in dietary sodium. No link was established bet ween plasma atrial natriuretic factor response and sodium sensitivity.