Ethnic differences in proximal and distal tubular sodium reabsorption are heritable in black and white populations.
BACKGROUND
Segmental handling of sodium along the proximal and distal nephron might be heritable and different between black and white participants.


METHODS
We randomly recruited 95 nuclear families of black South African ancestry and 103 nuclear families of white Belgian ancestry. We measured the (FENa) and estimated the fractional renal sodium reabsorption in the proximal (RNaprox) and distal (RNadist) tubules from the clearances of endogenous lithium and creatinine. In multivariable analyses, we studied the relation of RNaprox and RNadist with FENa and estimated the heritability (h) of RNaprox and RNadist.


RESULTS
Independent of urinary sodium excretion, South Africans (n = 240) had higher RNaprox (unadjusted median, 93.9% vs. 81.0%; P < 0.001) than Belgians (n = 737), but lower RNadist (91.2% vs. 95.1%; P < 0.001). The slope of RNaprox on FENa was steeper in Belgians than in South Africans (-5.40 +/- 0.58 vs. -0.78 +/- 0.58 units; P < 0.001), whereas the opposite was true for the slope of RNadist on FENa (-3.84 +/- 0.19 vs. -13.71 +/- 1.30 units; P < 0.001). h of RNaprox and RNadist was high and significant (P < 0.001) in both countries. h was higher in South Africans than in Belgians for RNaprox (0.82 vs. 0.56; P < 0.001), but was similar for RNadist (0.68 vs. 0.50; P = 0.17). Of the filtered sodium load, black participants reabsorb more than white participants in the proximal nephron and less postproximally.


CONCLUSIONS
Segmental sodium reabsorption along the nephron is highly heritable, but the capacity for regulation in the proximal and postproximal tubules differs between whites and blacks.
Bochud
Murielle
M
Community Prevention Unit, University Institute of Social and Preventive Medicine, University of Lausanne, Lausanne, Switzerland.
Staessen
Jan A
JA
Maillard
Marc
M
Mazeko
Muzi J
MJ
Kuznetsova
Tatiana
T
Woodiwiss
Angela
A
Richart
Tom
T
Norton
Gavin
G
Thijs
Lutgarde
L
Elston
Robert
R
Burnier
Michel
M
D000042:Absorption; D000328:Adult; D001530:Belgium; D044383:Black People / Q000235:genetics*; D003404:Creatinine / Q000097:blood / Q000493:pharmacokinetics / Q000652:urine; D005260:Female; D005828:Genetics, Population; D006801:Humans; D007686:Kidney Tubules, Distal / Q000502:physiology; D007687:Kidney Tubules, Proximal / Q000502:physiology; D008094:Lithium / Q000097:blood / Q000493:pharmacokinetics / Q000652:urine; D008297:Male; D008657:Metabolic Clearance Rate; D008875:Middle Aged; D009399:Nephrons / Q000187:drug effects / Q000502:physiology*; D009679:Nuclear Family / Q000208:ethnology; D012964:Sodium / Q000097:blood / Q000378:metabolism* / Q000652:urine; D013019:South Africa; D044465:White People / Q000235:genetics*
D008094:Lithium; D012964:Sodium; D003404:Creatinine