This Article Free upon publication Full Text Full Text (PDF) All Versions of this Article: 53/4/715    most recent HYPERTENSIONAHA.108.121665v1 Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Request Permissions Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Weder, A. B. Articles by Sachdeva, A. Search for Related Content PubMed PubMed Citation Articles by Weder, A. B. Articles by Sachdeva, A. Related Collections Clinical Studies Other etiology

(Hypertension. 2009;53:715.)
© 2009 American Heart Association, Inc.

Original Articles

Whites Excrete a Water Load More Rapidly Than Blacks

From the Division of Cardiovascular Medicine (A.B.W., L.G.), Department of Internal Medicine, University of Michigan, Ann Arbor; and the University of California, Los Angeles (A.S.).

Correspondence to Alan B. Weder, 24 Frank Lloyd Wright Dr, Lobby M, Division of Cardiovascular Medicine, Department of Internal Medicine, University of Michigan, Ann Arbor, MI 48106. E-mail aweder{at}umich.edu

A recent report demonstrated a racial difference in response to furosemide compatible with increased ion reabsorption in the thick ascending limb of the loop of Henle in blacks. Urinary dilution is another function of the loop-diuretic–sensitive Na,K,2Cl cotransporter in the thick ascending limb, and racial differences in urinary diluting capacity have not been reported previously. We assessed diluting segment (cortical thick ascending limb and distal convoluted tubule) function in black and white normotensives in 2 studies using a water-loading approach. In both studies, we found that whites excreted a water load more rapidly than blacks. In the first study, the final free water clearance rates (mean±SD) were 7.3±4.7 mL/min in whites (n=17, 7 females and 10 males) and 3.8±3.6 mL/min in blacks (n=14, 9 females and 5 males; P<0.03). In the second study, final free water clearance rates were 8.3±2.6 mL/min in whites (n=17, 8 females and 9 males) and 6.4±1.8 mL/min in blacks (n=11, 8 females and 3 males; P<0.01). We found no evidence of a racial difference in renal proximal tubular fluid reabsorption as assessed by renal endogenous lithium clearance or in plasma vasopressin level that could explain the difference in free water excretion. We conclude that our observations are most consistent with a lower capacity of ion reabsorption in the renal diluting segment in blacks. Slower excretion of an acute water load may have been an advantage during natural selection of humans living in arid, hot climates.

Key Words: kidney • water • race • renal tubule • ion • vasopressin