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

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Abstract
To examine possible racial differences in the relationship between urinary Na excretion (UNaV) and blood pressure in whites and blacks and to characterize cardiovascular, renal and humoral responses, 14 normotensive men (7 white and 7 black) were studied at 6 levels of Na intake from 10-1500 meq/24 h. Systolic and diastolic pressure increased from 113 .+-. 2/69 .+-. 2 mm Hg (SEM [standard error of the mean]) at the 10 meq/24 h level of Na intake to 131 .+-. 4/85 .+-. 3 mm Hg at the 1500 meq/24 h level of Na intake (P < 0.001). Cardiac index increased concomitantly from 2.6 .+-. 0.1 to 3.6 .+-. 0.31/min per m2 (P < 0.001). Linear and quadratic regression analysis of the relationship of UNaV and blood pressure revealed that blacks had higher blood pressures with Na loading than whites. Na loading caused a significant kaliuresis that was greater in whites than blacks. Six subjects were restudied while receiving K replacement. Compared with initial responses, blood pressure was elevated to a lesser degree (P < 0.02) and a greater natriuresis appeared at a level 1500 meq/24 h of Na intake (P < 0.02). Apparently blacks have an intrinsic reduction in the ability to excrete Na compared with whites. The increases in blood pressure with acute Na loading are due to an increase in cardiac index. K balance appears to influence the responses in blood pressure that occur with k loading.