Output of NaCl by Sweat Glands and Kidneys in Relation to Dehydration and to Salt Depletion

Acute changes in arginine vasopressin, sweat, urine and serum sodium concentrations in exercising humans: does a coordinated homeostatic relationship exist?

“…20 Sweat sodium concentration is neither constant over time nor identical over different regions of the body, 21 with significant intersubject and intrasubject variability 1 supporting a plausible role for sweat glands in fluid and electrolyte balance. Although the activation, 1 12 22 anatomy 1 19 and function 1 23 of the sweat glands are morphologically and functionally distinct from those of the renal tubules, similar responses to perturbations in both salt intake [23][24][25] and plasma chloride concentration (as a surrogate for NaCl) 26 suggest that they may perform similar and complementary functions in the acute regulation of serum [Na + ] and plasma osmolality. AVP may affect sweat rate and composition via two possible mechanisms: (1) vasoconstriction of cutaneous blood flow (via AVP V 1A receptors) or (2) water reabsorption (via AVP V 2 receptors).…”

Physiology of sweat gland function: The roles of sweating and sweat composition in human health

“…shorter duration (≤3 days) of Na manipulation has minimal or no impact [134,195,242,244,245] Dietary intake of other minerals (Ca, Fe, Zn, Cu) and vitamins (ascorbic acid, thiamine)…”

“…Acute/ Chronic No effect on sweat mineral or vitamin concentrations [230,231,[248][249][250] Fluid intake Acute Water ingestion results in a reflex (oropharyngeal) transient increase in RSR, especially when in a hypohydrated state [360,361]; no effect on sweat Na, K, Cl, and lactate concentrations [361] Dehydration Acute Reduced WBSR and RSR attributed to hyperosmolality-induced increase in threshold for sweat onset and to a lesser extent by a hypovolemia-induced decrease in sweat sensitivity (see Figure 3) [42,[76][77][78]80,82]; equivocal effects on sweat [Na] and [Cl] [134,153,[190][191][192][193][194][195]; no effect on sweat [K] [190] Alcohol Acute No effect on sweating rate [331,332]; sweat ethanol concentration increases with ethanol ingestion and rises linearly with increases in blood alcohol concentration [334,335] Exercise Intensity Acute Increase in WBSR and RSR with increases in exercise intensity [104,362] as metabolic heat production is directly proportional to energy expenditure [201,203]; sweat [Na] and [Cl] increase with increases in exercise intensity because the relative rate of Na and Cl reabsorption is flow dependent [39,159], minimal or no effect on sweat [K] [159], inverse relation between sweating rate and sweat lactate [162] and ammonia concentrations [6,…”

“…These confounding factors likely explain the discrepancy in results across studies measuring sweat composition and changes in hydration status. Dehydration has been associated with increased [134,153,190], decreased [191,192], or no change [193][194][195] in sweat [Na] and [Cl]. Sweat [K] and pH are also poor indicators of hydration status [190].…”

“…Indeed, most studies have shown that several days to weeks of dietary Na manipulation are associated with changes in sweat [Na] [45,224,225,235,236,[239][240][241]. Other studies, usually of shorter duration (up to 3 days) [195,242] or with relatively small changes in daily Na ingestion [243,244] have reported no or minimal effect of dietary Na on sweat [Na] or the rate of Na excretion. The relation between acute (i.e.…”