Effects of volume expansion and contraction in normotensive whites, blacks, and subjects of different ages.

We studied the blood pressure, natriuretic, kaliuretic and humoral responses of 347 normal subjects after volume expansion and volume contraction to examine possible differences among whites, blacks and subjects of different ages. According to outpatient 24-hour urine collections, blacks excreted less sodium and potassium than whites. After similar states of sodium intake were achieved among all subjects, 2 liters normal saline were given i.v. Blacks and subjects greater than or equal to 40 years excreted less sodium than whites or subjects less than 40 years, over a 24-hour period. In addition, blacks excreted less potassium. The delay in sodium excretion occurred during the first 12 hours after the salt load. Blacks had a greater suppression of plasma renin activity than whites 24 hours after saline. Blacks also had higher blood pressures than whites after saline administration; their pressure remained elevated until furosemide was given. Furosemide, 120 mg over 24 hours, evoked greater natriuresis, but less kaliuresis in blacks than in whites. The greater prevalence of hypertension in both blacks and older subjects may be related to relatively blunted natriuretic responses when these groups engage in the high sodium-low potassium intake characteristic of our society.