PT  - JOURNAL ARTICLE
AU  - Tamara Hew-Butler
AU  - Kevin Weisz
TI  - The Hydration Sweet Spot: Importance of Aquaporins
AID  - 10.29074/ascls.29.3.186
DP  - 2016 Jul 01
TA  - American Society for Clinical Laboratory Science
PG  - 186--193
VI  - 29
IP  - 3
4099  - http://hwmaint.clsjournal.ascls.org/content/29/3/186.short
4100  - http://hwmaint.clsjournal.ascls.org/content/29/3/186.full
SO  - Clin Lab Sci2016 Jul 01; 29
AB  - Recognize the regulated variables of water balance (osmolality and volume)Describe the short-term regulation of water balanceExplain long-term adaptations to chronic dehydration and overhydrationRecognize the limitations and advantages for using body weight and urine color to determine hydration statusIn both hyponatremia and hypernatremia, the sodium value (numerator) appears the most deranged. However, it is the changes in water content (denominator) that is most responsible for the pathophysiology, morbidity and mortality associated with dysnatremia. Therefore, fluid homeostasis involves both short-term and long-term water regulation at the molecular level to accommodate simultaneous and continuous changes in both fluid intake and output. Behavioral manipulation of long-term renal adaptations appear counter-intuitive in healthy individuals (i.e. water-loading induces dehydration – not water retention - in athletes seeking to “weigh-in light”), but do offer protection against behavioral (polydipsia) and environmental (dehydration) extremes. This mini-review summarizes both the short-term and long-term renal response to water intake, from the molecular perspective of the aquaporin-2 water channel. Then, four frequently asked questions will be addressed from this perspective: 1) What are the clinical consequences of drinking too much and 2) What are the clinical consequences of drinking too little? 3) How do we measure hydration? And 4) How much water do we need? We will close with practical advice on how humans should best maintain normal blood sodium concentrations (normonatremia, with preferential cellular size) from the perspective of thirst, vasopressin and small - but powerful - armies of aquaporin channels.ABBREVIATIONS: [Na+] – sodium concentration, ADH - anti-diuretic hormone, AVP – arginine vasopressin, AQP – aquaporin, AQP2 – aquaporin-2 water channel, V2R – vasopressin 2 receptors, SIADH - syndrome of anti-diuretic hormone secretion, UOsm - urine osmolality, USG – urine specific gravity,