Cardiovascular and humoral responses to extremes of sodium intake in normal black and white men

Abstract

To examine possible racial differences in the relationship between urinary sodium excretion (U(na)V) and blood pressure in whites and blacks, and to characterize cardiovascular, renal and humoral responses, the authors studied 14 normotensive men (seven white and seven black) at six levels of sodium intake from 10-1500 mEq/24 hr. Systolic and diastolic pressure increased from 113 ± 2/69 ± 2 mm Hg (SEM) at the 10 mEq/24 hr level of sodium intake to 131 ± 4/85 ± 3 mm Hg at the 1500 mEq/24 hr level of sodium intake (p <0.001). Cardiac index increased concomitantly from 2.6 ± 0.1 to 3.6 ± 0.3 l/min/m2 (p<0.001). Linear and quadratic regression analysis of the relationship of U(na)V and blood pressure revealed that blacks had higher blood pressures with sodium loading than whites. Sodium loading caused a significant kaliuresis that was greater in whites than blacks. Six subjects were restudied while receiving potassium replacement. Compared with initial responses, blood pressure was elevated to a lesser degree (p<0.02) and a greater natriuresis appeared at a level of 1500 mEq/24 hr of sodium intake (p<0.02). The data suggest that blacks have an intrinsic reduction in the ability to excrete sodium compared with whites. The increases in blood pressure with acute sodium loading can be attributed to an increase in cardiac index. Potassium balance appears to influence the responses in blood pressure that occur with sodium loading.