BBB seminar: Jens Titze
Increased salt consumption induces body water conservation and decreases fluid intake
Division of Clinical Pharmacology, Vanderbilt University Medical Center, Nashville, TN, USA, and Cardiovascular and Metabolic Disorders Program, Duke-NUS Medical School, Singapore
Renal excretion of dietary Na+ under high-salt conditions occurs by a natriuretic principle. The assumption is that high salt intake triggers thirst and thereby increases fluid intake, which expands the extracellular fluid volume. Successful renal excretion of excess salt conversely increases the urine volume by osmotic diuresis and thereby corrects the extracellular volume. According to the established concept, high salt intake increases fluid intake. Subsequent renal elimination of surplus dietary salt is used to excrete the parallel surplus water load and reduce the expanded extracellular volume back to normal. We have studied the physiological role of the renal concentration mechanism during high salt intake, which is characterized by excretion of surplus dietary salt and antiparallel water movement for renal water conservation while the salt osmolytes are excreted. We have shown that urea metabolism plays an important role in extracellular volume control by maintaining the renal concentration mechanism during high salt intake. The physiological response of water conservation process during salt excretion can be summarized as natriuretic-ureotelic regulation for endogenous free water accrual within the renal urine concentration process to prevent body water loss. In addition, salt can induce a glucocorticoid-driven catabolic state with increased urea osmolyte and metabolic water generation. This natriuretic-ureotelic, water-conserving principle relies on metabolism-driven extracellular volume control and is regulated by concerted liver, muscle, and renal actions. Disease states with a predisposition to extracellular volume contraction therefore may be characterized by increased energy uptake, catabolic exploitation of endogenous nitrogen and energy fuels, and reprioritization of energy expenditure in favor of alternative osmolyte production for body water conservation.
Chairperson: Helge Wiig, Department of Biomedicine