Sodium kinetics in white and black normotensive subjects: possible relevance to salt-sensitive hypertension

The hypothesis that sodium (Na) kinetics are not a first order process was tested. Twelve normotensive white and 12 normotensive black men were given 10, 200, and 400 mmol/d Na as the chloride salt for 7 days in random order. All urine made was collected. No effect of Na intake on blood pressure was identified in either whites or blacks. The half-life (T1/2) with decreasing Na intake to 10 mmol/d was 1.08 days in whites and 1.65 days in blacks (p = not significant [NS]). With increasing Na intake, T1/2 increased in both whites and blacks; at the 400 mmol/d intake, the T1/2 for whites was 2.88 days and for blacks was 5.81 days (p < 0.05). At that intake, whites accumulated 385 +/- 153 mmol compared with 909 +/- 153 mmol for blacks (p < 0.05). The data showed that T1/2 increases with increasing Na intake and is, therefore, dose-dependent or "zero" order. The effect of dose is more prominent in blacks than in whites; blacks accumulate more Na with increasing Na intake than whites. These data may have relevance for the pathogenesis of salt-sensitive hypertension in blacks.