title: Balancing wobbles in the body sodium.
abstract: Sodium balance is achieved within a matter of days and everything that enters should come out; sodium stores are of questionable relevance and sodium accumulation is accompanied by weight gain. Careful balance studies oftentimes conflicted with this view, and long-term studies suggested that total body sodium (TBNa) fluctuates independent of intake or body weight. We recently performed the opposite experiment in that we fixed sodium intake for weeks at three levels of sodium intake and collected all urine made. We found weekly (circaseptan) patterns in sodium excretion that were inversely related to aldosterone and directly related to cortisol. TBNa was not dependent on sodium intake, but instead exhibited far longer (greater than or equal to monthly) infradian rhythms independent of extracellular water, body weight or blood pressure. To discern the mechanisms further, we delved into sodium magnetic resonance imaging (Na-MRI) to identify sodium storage clinically. We found that sodium stores are greater in men than in women, increase with age and are higher in hypertensive than normotensive persons. We have suggestive evidence that these sodium stores can be mobilized, also in dialysis patients. The observations are in accordance with our findings that immune cells regulate a hypertonic interface in the skin interstitium that could serve as a protective barrier. Returning to our balance studies, we found that due to biological variability in 24-h sodium excretion, collecting urine for a day could not separate 12, 9 or 6 g/day sodium intakes with the precision of tossing a coin. Every other daily urine sampling correctly classified a 3-g difference in salt intake less than half the time, making the gold standard 24-h urine collection of little value in predicting salt intake. We suggest that wobbles in expected outcomes can lead to novel clinical insights even with respect to banal salt questions.
authors.affiliation: Interdisciplinary Center for Clinical Research and Department for Nephrology and Hypertension, Nikolaus-Fiebiger Center for Molecular Medicine, Friedrich-Alexander-University, Erlangen-Nürnberg, Germany Division of Clinical Pharmacology, Vanderbilt University School of Medicine, Nashville, TN, USA.
authors.forename: Jens
authors.initials: J
authors.lastname: Titze
authors.affiliation: Interdisciplinary Center for Clinical Research and Department for Nephrology and Hypertension, Nikolaus-Fiebiger Center for Molecular Medicine, Friedrich-Alexander-University, Erlangen-Nürnberg, Germany Experimental and Clinical Research Center, an institutional cooperation between the Charité Medical Faculty and the Max-Delbrück Center for Molecular Medicine, Berlin, Germany.
authors.forename: Natalia
authors.initials: N
authors.lastname: Rakova
authors.affiliation: Interdisciplinary Center for Clinical Research and Department for Nephrology and Hypertension, Nikolaus-Fiebiger Center for Molecular Medicine, Friedrich-Alexander-University, Erlangen-Nürnberg, Germany.
authors.forename: Christoph
authors.initials: C
authors.lastname: Kopp
authors.affiliation: Interdisciplinary Center for Clinical Research and Department for Nephrology and Hypertension, Nikolaus-Fiebiger Center for Molecular Medicine, Friedrich-Alexander-University, Erlangen-Nürnberg, Germany.
authors.forename: Anke
authors.initials: A
authors.lastname: Dahlmann
authors.affiliation: Institute of Clinical Microbiology and Hygiene, Universitätsklinikum Regensburg and Universität Regensburg, Regensburg, Germany.
authors.forename: Jonathan
authors.initials: J
authors.lastname: Jantsch
authors.affiliation: Division of Clinical Pharmacology, Vanderbilt University School of Medicine, Nashville, TN, USA Experimental and Clinical Research Center, an institutional cooperation between the Charité Medical Faculty and the Max-Delbrück Center for Molecular Medicine, Berlin, Germany.
authors.forename: Friedrich C
authors.initials: FC
authors.lastname: Luft
mesh_terms: D000818:Animals; D006801:Humans; D012965:Sodium Chloride / Q000008:administration & dosage / Q000378:metabolism*; D014882:Water-Electrolyte Balance
chemical_list: D012965:Sodium Chloride
keywords: hemodialysis; hypertension; magnetic resonance imaging; salt; sodium