Differences in response to sodium administration in normotensive white and black subjects

In order to examine possible differences in PRA, PA, and renal electrolyte excretion in normotensive black and white subjects, we studied 68 age-matched subjects: 19 white men, 19 black men, 15 white women, and 15 black women. PRA was measured before and after the infusion of 2 L of normal saline to evaluate suppression of the renin-aldosterone system. The excretion of sodium, potassium, and creatinine in response to the salt load was monitored for 24 hr. PRA and PA measurements were repeated after 2 hr of ambulation on the morning following salt loading. Dietary sodium was then restricted and oral furosemide (120 mg) was administered in order to assess PRA and PA responsiveness to sodium and volume depletion. White and black subjects had similar PRA and PA responses to normal saline and furosemide administration. Over a 24 hr period, black subjects excreted significantly less sodium and potassium following the salt load than did white subjects. The PRA values of black subjects 24 hr following the salt load were significantly suppressed as well. These observations suggest that there may be racial differences in renal sodium excretion reflected by decreased urinary sodium excretion and a relative suppression of PRA following a salt load in black persons.