Salt sensitivity in blacks. Salt intake and natriuretic substances.

Accumulating evidence suggests that hypertension in blacks is manifested in part by impaired renal excretion of salt. Consequently, this study was performed to determine if hypertensive and normotensive black subjects differ in their ability to generate known natriuretic substances. Fourteen normotensive and 11 hypertensive blacks were maintained on constant metabolic diets containing either 40 or 180 mmol of salt per day for 14 days each. During the last 4 days of each salt intake period, urine was collected for measurement of sodium, dopamine, and norepinephrine. On the last day of each 14-day dietary period, blood pressures were measured, blood was collected for measurement of plasma atrial natriuretic factor (ANF) and aldosterone, and urine was collected over 2 hours for measurement of prostaglandin E2 (PGE2). Both the normotensive and the hypertensive groups manifested salt sensitivity; their mean arterial pressure rose by 7 +/- 0.2 and 6 +/- 0.2%, respectively, when salt intake was increased from 40 to 180 mmol/day. The hypertensive group exhibited decreased (p less than 0.05) dopamine excretion as compared with the normotensive group for both dietary salt intakes. Plasma ANF levels increased (p less than 0.05) in the hypertensive group, but not in the normotensive group, with increasing dietary salt. Plasma aldosterone and urinary norepinephrine and PGE2 were comparable in the two groups for both dietary salt intakes. These data suggest that salt sensitivity is not unique to hypertensive blacks but occurs in normotensive blacks as well. Decreased renal production of dopamine may be a pathogenic factor in the development and maintenance of hypertension in blacks.