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Clinical Journal of the American... May 2015Alterations in water homeostasis can disturb cell size and function. Although most cells can internally regulate cell volume in response to osmolar stress, neurons are... (Review)
Review
Alterations in water homeostasis can disturb cell size and function. Although most cells can internally regulate cell volume in response to osmolar stress, neurons are particularly at risk given a combination of complex cell function and space restriction within the calvarium. Thus, regulating water balance is fundamental to survival. Through specialized neuronal "osmoreceptors" that sense changes in plasma osmolality, vasopressin release and thirst are titrated in order to achieve water balance. Fine-tuning of water absorption occurs along the collecting duct, and depends on unique structural modifications of renal tubular epithelium that confer a wide range of water permeability. In this article, we review the mechanisms that ensure water homeostasis as well as the fundamentals of disorders of water balance.
Topics: Brain; Cell Size; Diabetes Insipidus; Homeostasis; Humans; Hyponatremia; Kidney Medulla; Kidney Tubules, Collecting; Osmotic Pressure; Sensory Receptor Cells; Thirst; Vasopressins; Water; Water-Electrolyte Balance
PubMed: 25078421
DOI: 10.2215/CJN.10741013 -
Nutrients Mar 2021During endurance exercise, two problems arise from disturbed fluid-electrolyte balance: dehydration and overhydration. The former involves water and sodium losses in... (Review)
Review
During endurance exercise, two problems arise from disturbed fluid-electrolyte balance: dehydration and overhydration. The former involves water and sodium losses in sweat and urine that are incompletely replaced, whereas the latter involves excessive consumption and retention of dilute fluids. When experienced at low levels, both dehydration and overhydration have minor or no performance effects and symptoms of illness, but when experienced at moderate-to-severe levels they degrade exercise performance and/or may lead to hydration-related illnesses including hyponatremia (low serum sodium concentration). Therefore, the present review article presents (a) relevant research observations and consensus statements of professional organizations, (b) 5 rehydration methods in which pre-race planning ranges from no advanced action to determination of sweat rate during a field simulation, and (c) 9 rehydration recommendations that are relevant to endurance activities. With this information, each athlete can select the rehydration method that best allows her/him to achieve a hydration middle ground between dehydration and overhydration, to optimize physical performance, and reduce the risk of illness.
Topics: Athletes; Dehydration; Endurance Training; Female; Fluid Therapy; Humans; Hyponatremia; Male; Physical Endurance; Sodium; Sweating; Water; Water-Electrolyte Imbalance
PubMed: 33803421
DOI: 10.3390/nu13030887 -
Cell Jan 2020The function of central appetite neurons is instructing animals to ingest specific nutrient factors that the body needs. Emerging evidence suggests that individual... (Review)
Review
The function of central appetite neurons is instructing animals to ingest specific nutrient factors that the body needs. Emerging evidence suggests that individual appetite circuits for major nutrients-water, sodium, and food-operate on unique driving and quenching mechanisms. This review focuses on two aspects of appetite regulation. First, we describe the temporal relationship between appetite neuron activity and consumption behaviors. Second, we summarize ingestion-related satiation signals that differentially quench individual appetite circuits. We further discuss how distinct appetite and satiation systems for each factor may contribute to nutrient homeostasis from the functional and evolutional perspectives.
Topics: Animals; Appetite; Appetite Regulation; Brain; Feeding Behavior; Homeostasis; Humans; Hunger; Nervous System Physiological Phenomena; Neurons; Satiation; Sodium; Thirst
PubMed: 31923398
DOI: 10.1016/j.cell.2019.11.040 -
Proceedings of the Japan Academy.... 2022Extracellular fluids, including blood, lymphatic fluid, and cerebrospinal fluid, are collectively called body fluids. The Na concentration ([Na]) in body fluids is... (Review)
Review
Extracellular fluids, including blood, lymphatic fluid, and cerebrospinal fluid, are collectively called body fluids. The Na concentration ([Na]) in body fluids is maintained at 135-145 mM and is broadly conserved among terrestrial animals. Homeostatic osmoregulation by Na is vital for life because severe hyper- or hypotonicity elicits irreversible organ damage and lethal neurological trauma. To achieve "body fluid homeostasis" or "Na homeostasis", the brain continuously monitors [Na] in body fluids and controls water/salt intake and water/salt excretion by the kidneys. These physiological functions are primarily regulated based on information on [Na] and relevant circulating hormones, such as angiotensin II, aldosterone, and vasopressin. In this review, we discuss sensing mechanisms for [Na] and hormones in the brain that control water/salt intake behaviors, together with the responsible sensors (receptors) and relevant neural pathways. We also describe mechanisms in the brain by which [Na] increases in body fluids activate the sympathetic neural activity leading to hypertension.
Topics: Animals; Body Fluids; Homeostasis; Hormones; Sodium; Sodium Chloride, Dietary; Water
PubMed: 35908954
DOI: 10.2183/pjab.98.016 -
Cureus Feb 2021Diabetes insipidus (DI) is an endocrine condition involving the posterior pituitary peptide hormone, antidiuretic hormone (ADH). ADH exerts its effects on the distal... (Review)
Review
Diabetes insipidus (DI) is an endocrine condition involving the posterior pituitary peptide hormone, antidiuretic hormone (ADH). ADH exerts its effects on the distal convoluted tubule and collecting duct of the nephron by upregulating aquaporin-2 channels (AQP2) on the cellular apical membrane surface. DI is marked by expelling excessive quantities of highly dilute urine, extreme thirst, and craving for cold water. The two main classifications of DI are central diabetes insipidus (CDI), characterized by a deficiency of the posterior pituitary gland to release ADH, and nephrogenic diabetes insipidus (NDI), characterized by the terminal distal convoluted tubule and collecting duct resistance to ADH. The two less common classifications include dipsogenic DI, characterized by excessive thirst due to a low osmotic threshold, and gestational DI, characterized by increased concentration of placental vasopressinase during pregnancy. Treatment of DI is dependent on the disease classification, but severe complications may arise if not tended to appropriately. The most important step in symptom management is maintaining fluid intake ahead of fluid loss with emphasis placed on preserving the quality of life. The most common treatment of CDI and gestational DI is the administration of synthetic ADH, desmopressin (DDAVP). Nephrogenic treatment, although more challenging, requires discontinuation of medications as well as maintaining a renal-friendly diet to prevent hypernatremia. Treatment of dipsogenic DI is mainly focused on behavioral therapy aimed at regulating water intake and/or administration of antipsychotic pharmaceutical therapy. Central and nephrogenic subtypes of DI share a paradoxical treatment in thiazide diuretics.
PubMed: 33786230
DOI: 10.7759/cureus.13523 -
Science (New York, N.Y.) Sep 2017Water deprivation produces a drive to seek and consume water. How neural activity creates this motivation remains poorly understood. We used activity-dependent genetic...
Water deprivation produces a drive to seek and consume water. How neural activity creates this motivation remains poorly understood. We used activity-dependent genetic labeling to characterize neurons activated by water deprivation in the hypothalamic median preoptic nucleus (MnPO). Single-cell transcriptional profiling revealed that dehydration-activated MnPO neurons consist of a single excitatory cell type. After optogenetic activation of these neurons, mice drank water and performed an operant lever-pressing task for water reward with rates that scaled with stimulation frequency. This stimulation was aversive, and instrumentally pausing stimulation could reinforce lever-pressing. Activity of these neurons gradually decreased over the course of an operant session. Thus, the activity of dehydration-activated MnPO neurons establishes a scalable, persistent, and aversive internal state that dynamically controls thirst-motivated behavior.
Topics: Animals; Cell Line; Dehydration; Drinking Behavior; Gene Expression Profiling; Mice; Motivation; Neurons; Optogenetics; Preoptic Area; Single-Cell Analysis; TNF Receptor-Associated Factor 2; Thirst
PubMed: 28912243
DOI: 10.1126/science.aan6747 -
Frontline Gastroenterology 2022A high-output stoma (HOS) or fistula is when small bowel output causes water, sodium and often magnesium depletion. This tends to occur when the output is >1.5...
A high-output stoma (HOS) or fistula is when small bowel output causes water, sodium and often magnesium depletion. This tends to occur when the output is >1.5 -2.0 L/24 hours though varies according to the amount of food/drink taken orally. An HOS occurs in up to 31% of small bowel stomas. A high-output enterocutaneous fistula may, if from the proximal small bowel, behave in the same way and its fluid management will be the same as for an HOS. The clinical assessment consists of excluding causes other than a short bowel and treating them (especially partial or intermittent obstruction). A contrast follow through study gives an approximate measurement of residual small intestinal length (if not known from surgery) and may show the quality of the remaining small bowel. If HOS is due to a short bowel, the first step is to rehydrate the patient so stopping severe thirst. When thirst has resolved and renal function returned to normal, oral hypotonic fluid is restricted and a glucose-saline solution is sipped. Medication to slow transit (loperamide often in high dose) or to reduce secretions (omeprazole for gastric acid) may be helpful. Subcutaneous fluid (usually saline with added magnesium) may be given before intravenous fluids though can take 10-12 hours to infuse. Generally parenteral support is needed when less than 100 cm of functioning jejunum remains. If there is defunctioned bowel in situ, consideration should be given to bringing it back into continuity.
PubMed: 35300464
DOI: 10.1136/flgastro-2018-101108 -
Journal of the International Society of... Oct 2020Despite a substantial body of research, no clear best practice guidelines exist for the assessment of hydration in athletes. Body water is stored in and shifted between... (Review)
Review
BACKGROUND
Despite a substantial body of research, no clear best practice guidelines exist for the assessment of hydration in athletes. Body water is stored in and shifted between different sites throughout the body complicating hydration assessment. This review seeks to highlight the unique strengths and limitations of various hydration assessment methods described in the literature as well as providing best practice guidelines.
MAIN BODY
There is a plethora of methods that range in validity and reliability, including complicated and invasive methods (i.e. neutron activation analysis and stable isotope dilution), to moderately invasive blood, urine and salivary variables, progressing to non-invasive metrics such as tear osmolality, body mass, bioimpedance analysis, and sensation of thirst. Any single assessment of hydration status is problematic. Instead, the recommended approach is to use a combination, which have complementary strengths, which increase accuracy and validity. If methods such as salivary variables, urine colour, vital signs and sensation of thirst are utilised in isolation, great care must be taken due to their lack of sensitivity, reliability and/or accuracy. Detailed assessments such as neutron activation and stable isotope dilution analysis are highly accurate but expensive, with significant time delays due to data analysis providing little potential for immediate action. While alternative variables such as hormonal and electrolyte concentration, bioimpedance and tear osmolality require further research to determine their validity and reliability before inclusion into any test battery.
CONCLUSION
To improve best practice additional comprehensive research is required to further the scientific understanding of evaluating hydration status.
Topics: Absorptiometry, Photon; Blood Physiological Phenomena; Body Mass Index; Body Water; Dehydration; Drinking; Electric Impedance; Hematocrit; Hormones; Humans; Neutron Activation Analysis; Osmolar Concentration; Saliva; Serum; Sodium; Sports; Tears; Thirst; Urinalysis; Vital Signs
PubMed: 33126891
DOI: 10.1186/s12970-020-00381-6 -
Nature Dec 2020Fluid intake is an essential innate behaviour that is mainly caused by two distinct types of thirst. Increased blood osmolality induces osmotic thirst that drives...
Fluid intake is an essential innate behaviour that is mainly caused by two distinct types of thirst. Increased blood osmolality induces osmotic thirst that drives animals to consume pure water. Conversely, the loss of body fluid induces hypovolaemic thirst, in which animals seek both water and minerals (salts) to recover blood volume. Circumventricular organs in the lamina terminalis are critical sites for sensing both types of thirst-inducing stimulus. However, how different thirst modalities are encoded in the brain remains unknown. Here we employed stimulus-to-cell-type mapping using single-cell RNA sequencing to identify the cellular substrates that underlie distinct types of thirst. These studies revealed diverse types of excitatory and inhibitory neuron in each circumventricular organ structure. We show that unique combinations of these neuron types are activated under osmotic and hypovolaemic stresses. These results elucidate the cellular logic that underlies distinct thirst modalities. Furthermore, optogenetic gain of function in thirst-modality-specific cell types recapitulated water-specific and non-specific fluid appetite caused by the two distinct dipsogenic stimuli. Together, these results show that thirst is a multimodal physiological state, and that different thirst states are mediated by specific neuron types in the mammalian brain.
Topics: Animals; Base Sequence; Drinking; Female; Hypovolemia; Male; Mice; Mice, Inbred C57BL; Models, Animal; Neurons; Organum Vasculosum; Osmotic Pressure; Single-Cell Analysis; Subfornical Organ; Thirst; Water Deprivation
PubMed: 33057193
DOI: 10.1038/s41586-020-2821-8