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Hypertension. 2007;49:e34
Published online before print March 26, 2007, doi: 10.1161/HYPERTENSIONAHA.107.089862
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(Hypertension. 2007;49:e34.)
© 2007 American Heart Association, Inc.


Letters to the Editor

Context Dependency of Serum and Urinary Lithium: Implications for Measurement of Proximal Sodium Reabsorption

Murielle Bochud

Community Prevention Unit, University Institute for Social and Preventive Medicine, Lausanne, Switzerland

Jan A. Staessen

Department of Cardiovascular Diseases, University of Leuven, Leuven, Belgium

Angela Woodiwiss; Gavin Norton

Cardiovascular Pathophysiology and Genomics Research Unit, University of the Witwatersrand, Johannesburg, South Africa

Marc Maillard; Michel Burnier

Nephrology Division, University Hospital of Lausanne, Lausanne, Switzerland

To the Editor:

As reported previously in this journal, the endogenous lithium clearance is a marker of proximal tubular sodium handling.1,2 To investigate the context dependency of the endogenous lithium clearance, we measured by electrothermal atomic absorption spectrophotometry the lithium concentrations in serum and in exactly timed urine samples in 745 whites (51.5% women) and 266 blacks (62.8%) who were recruited randomly from the population in Belgium1 and South Africa.3 Mean age (±SD) was 40.6±15.8 and 42.6±18.2 years, respectively. The average (±SD) concentration of lithium in tap water (1.37±0.56 versus 0.03±0.01 µmol/L) and the 24-hour urinary lithium excretion (8.2±5.6 versus 3.1±4.1 µmol per 24 hours) were higher and more dispersed in Belgium than in South Africa (P<0.0001 for differences in means and variances; Figure). These results strongly suggest that the environment, probably via the food chain,4 determines the dietary intake of lithium. By contrast, the serum lithium distributions (0.31±0.16 versus 0.32±0.21 µmol/L) were very similar in means (P=0.58) but not in variances (P<0.0001). These observations suggest that serum lithium is tightly regulated despite large variations in dietary intake. The rank correlations (±SE) between the lithium and creatinine clearances (0.44±0.04 versus 0.42±0.06; P=0.70 for between-country difference) and between the serum and urinary lithium concentrations (0.30±0.04 versus 0.22±0.06; P=0.26) were similar across countries. The latter observation suggests that the endogenous lithium clearance, whether expressed as clearance or as fractional excretion, remains a useful marker of proximal sodium reabsorption under various environmental conditions.


Figure 1
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Distributions of serum and urinary lithium. Outlier values were removed.


*    Acknowledgments
 
Sources of Funding

The study was financed in part by InGenious HyperCare (LSHM-CT-2006-037093), a grant of the European Union.

Disclosures

None.


*    References
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*References
 
1. Seidlerova J, Staessen JA, Maillard M, Nawrot T, Zhang H, Bochud M, Kuznetsova T, Richart T, Van Bortel LM, Struijker-Boudier HA, Manunta P, Burnier M, Fagard R, Filipovsky J. Association between arterial properties and renal sodium handling in a general population. Hypertension. 2006; 48: 609–615.[Abstract/Free Full Text]

2. Eap CB, Bochud M, Elston RC, Bovet P, Maillard M, Nussberger J, Schild L, Shamlaye C, Burnier M. CYP3A5 and ABCB1 genes influence blood pressure and response to treatment, and their effect is modified by salt. Hypertension. 2007; 49: 1007–1014.[Abstract/Free Full Text]

3. Shiburi CP, Staessen JA, Maseko M, Wojciechowska W, Thijs L, Van Bortel LM, Woodiwiss AJ, Norton GR. Reference values for SphygmoCor measurements in South Africans of African ancestry. Am J Hypertens. 2006; 19: 40–46.[CrossRef][Medline] [Order article via Infotrieve]

4. Schrauzer GN. Lithium: occurrence, dietary intakes, nutritional essentiality. J Am Coll Nutr. 2002; 21: 14–21.[Abstract/Free Full Text]





This Article
Right arrow Extract Freely available
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49/5/e34    most recent
HYPERTENSIONAHA.107.089862v1
Right arrow Alert me when this article is cited
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Google Scholar
Right arrow Articles by Bochud, M.
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