Sodium restriction lowers high blood pressure through a decreased response of the renin system--direct evidence using saralasin.

Twenty-nine patients with essential hypertension were studied while on their normal diets, on the 5th day of a high sodium diet (around 350 mmol/day) and on the 5th day of a low sodium diet (10 mmol/day). The fall in mean arterial pressure on changing from the high sodium to the low sodium diet was 9.0 +/- 1.6 mmHg and the rise in the plasma renin activity in the same period was 2.52 +/- 0.41 ng/ml/h, these two variables being significantly correlated (r = -0.45; P less than 0.02). An infusion of saralasin was given on the 5th day of the low sodium diet. A highly significant negative correlation was found between the fall in blood pressure on sodium restriction and the change in blood pressure with saralasin (r = -0.52; P less than 0.005); this correlation was still significant when corrected for the severity of the hypertension (r = -0.41; P = 0.03) while it became non-significant if controlled for plasma renin activity on the low sodium diet (r = -033; NS). These results provide direct evidence that the fall in blood pressure which is seen on reducing sodium intake in many patients with essential hypertension is, at least in part, directly mediated by the reactivity of the renin angiotensin system.