Importance of the Renin System in Determining Blood Pressure Fall With Salt Restriction in Black and White Hypertensives

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Abstract
—Seventy-one white and 33 black patients with essential hypertension were studied while on a high sodium intake of 350 mmol/d for 5 days and low sodium intake of 10 mmol/d for 5 days. The fall in blood pressure on changing from the high sodium to the low sodium diet was 17/6 mm Hg in whites and 22/10 mm Hg in blacks. Compared with whites, black patients had a 7-mm Hg greater fall ( P P =0.068) in diastolic blood pressure (adjusted for age and blood pressure on the normal diet) with similar changes in urinary sodium excretion. With sodium restriction, plasma renin activity rose from 0.65 to 3.03 ng · mL −1 · h −1 in whites, whereas in blacks it rose only from 0.3 to 1.28 ng · mL −1 · h −1 ( P P P <0.01). Significant inverse correlations were obtained for all patients between the fall in systolic blood pressure from the high to low salt diet and the rise in plasma renin activity and angiotensin II, as well as the absolute level on the low salt diet. These results demonstrate that the larger fall in blood pressure with a reduction in salt intake in blacks is due at least in part to a less responsive renin-angiotensin-aldosterone system in blacks.