Increase In Osmolality Research Articles

Advances in aquaporin-2 trafficking mechanisms and their implications for treatment of water balance disorders.

In mammals, conservation of body water is critical for survival and is dependent on the kidneys' ability to minimize water loss in the urine during periods of water deprivation. The collecting duct water channel aquaporin-2 (AQP2) plays an essential role in this homeostatic response by facilitating water reabsorption along osmotic gradients. The ability to increase the levels of AQP2 in the apical plasma membrane following an increase in plasma osmolality is a rate-limiting step in water reabsorption, a process that is tightly regulated by the antidiuretic hormone arginine vasopressin (AVP). In this review, the focus is on the role of the carboxyl-terminus of AQP2 as a key regulatory point for AQP2 trafficking. We provide an overview of AQP2 structure, disease-causing mutations in the AQP2 carboxyl-terminus, the role of posttranslational modifications such as phosphorylation and ubiquitylation in the tail domain, and their implications for balanced trafficking of AQP2. Finally, we discuss how various modifications of the AQP2 tail facilitate selective protein-protein interactions that modulate the AQP2 trafficking mechanism.

MON-LB65 Lithium: The Culprit of Multiple Endocrinopathies

Background: Lithium, commonly used to treat various psychiatric disorders such as bipolar disorder, can cause acute toxicity that presents with nausea, vomiting and diarrhea. Lithium can also cause life-threatening endocrine abnormalities, including hypercalcemia, hypernatremia, and both hypo- and hyperthyroidism. Clinical Case: A 61-year old female with hypothyroidism, bipolar disorder, hyperparathyroidism with two-gland parathyroidectomy on lithium for over 30 years presented with altered mental status.Initial labs revealed elevated creatinine 1.92 mg/dL (0.8-2.00mg/dL) compared to baseline 0.82 mg/dL, sodium 154 mg/dL (135-147 mg/dL), Corrected calcium 11.7 mg/dL (8.5-10.5 mg/dL), PTH 96 pg/mL (15-65 pg/mL), and high lithium levels 1.45 mmol/L (0.60-1.20 mmol/L). Further studies showed hypotonic polyuria with no increase in urine osmolality after desmopressin, consistent with nephrogenic diabetes insipidus. Lithium was held and she was treated with aggressive intravenous hydration with dextrose 5% water.Hypercalcemia is thought to result from increased secretion of PTH due to an increased set point at which calcium suppresses PTH release; this often resolves once lithium is stopped. Lithium can also unmask previously unrecognized mild hyperparathyroidism, and/or raise serum PTH concentrations independent of calcium levels.1 The drug interferes with the kidneys’ ability to concentrate urine in the collecting tubules by desensitizing response to antidiuretic hormone, causing diabetes insipidus. The resulting volume depletion from excessive urinary water loss in turn lead to acute kidney injury and hypernatremia.2 Hypothyroidism results from lithium-inhibited synthesis and release of thyroid hormones and decreases iodine trapping. Conclusion: Although these are infrequent complications of lithium use, they remain pertinent clinical findings to consider due to their morbidity. In this case, our patient may have avoided multiple chronic electrolyte abnormalities leading to altered mental status if lithium toxicity had been recognized earlier.

Effect of salinity acclimation on osmoregulation, oxidative stress, and metabolic enzymes in the invasive Xenopus laevis.

Aquatic animals often display physiological adjustments to improve their biological performance and hydrosaline balance in saline environments. In addition to energetic costs associated with osmoregulation, oxidative stress, and the activation of the antioxidant system are common cellular responses to salt stress in many species, but the knowledge of osmoregulation-linked oxidative homeostasis in amphibians is scarce. Here we studied the biochemical responses and oxidative responses of Xenopus laevis females exposed for 40 days to two contrasting salinities: hypo-osmotic (150 mOsm·kg-1 ·H2 O NaCl, HYPO group) and hyper-osmotic environments (340 mOsm·kg-1 ·H2 O NaCl, HYPER group). We found an increase of plasma osmolality and plasma urea concentration in the animals incubated in the HYPER treatment. Increases in electrolyte concentration were paralleled with an increase of both citrate synthase and cytochrome c oxidase activities in liver and heart. Interestingly, HYPO group had higher catabolic activity of the skin and liver total antioxidant capacity (TAC), compared with animals from the HYPER group. Moreover, there was an inverse relationship between liver TAC and plasma osmolality; and with the metabolic enzymes from liver. These findings suggest that salinity induces changes in urea metabolism and specific activity of metabolic enzymes, which appears to be tissue-dependent in X. laevis. Contrary to our expectations, we also found a moderate change in the oxidative status as revealed by the increase in TAC activity in the animals acclimated to low salinity medium, but constancy in the lipid peroxidation of membranes.

The chloride channel Bestrophin‐1 acts in the Malpighian tubule and hindgut of Drosophila melanogaster to maintain salt and water balance

ObjectiveThe Malpighian tubule and hindgut are iono‐ and osmoregulatory epithelia in insects. The tubule secretes KCl‐rich fluid, and ions and water are subsequently reabsorbed in the hindgut. We characterized the role of the chloride channel, Bestrophin‐1 (Best1), in the tubule and hindgut of Drosophila melanogaster.MethodsWe studied flies carrying a germline mutation in Best1, Best1c04106, as well as Best1c04106 flies with genomic rescue, and flies with tissue‐specific knockdown (quantified by qRT‐PCR) or rescue of Best1. Malpighian tubule ion flux was measured ex vivo, and immunostaining was performed using antibodies to HA‐tagged Bestrophin‐1. Flies were assayed for lethality on normal vs. 0.3 M‐supplemented NaCl (high‐salt) diet and after water restriction. Excretion was quantified by counting excretory drops. Hemolymph and excretory drop osmolality were measured using a vapor pressure osmometer. Water weight was determined by measuring flies’ weight before and after baking at 60 °C.ResultsBest1c04106 mutant Malpighian tubules had decreased fluid secretion and transepithelial ion flux that was rescued by expression of wild‐type Best1 in the K+‐secreting principal cell. Principal cell Best1 knockdown decreased transcript levels by 80% and decreased fluid secretion and ion flux. We previously showed that NKCC is required for principal cell K+ secretion. Here, we immunolocalized both Best1 and NKCC to the principal cell basolateral membrane. There was no further decrease in ion transport in Best1 knockdown tubules when NKCC was mutated, suggesting that Best1 allows Cl− entering through the NKCC to recycle across the basolateral membrane. Best1c04106 mutant flies also had increased lethality on high‐salt diet. Hemolymph osmolality increased in control flies fed high‐salt diet, but Best1c04106 mutants had decreased osmolality on both normal and high salt diet, and increased number and osmolality of excretory drops. As a consequence, Best1c04106 mutant flies were dehydrated and died when water restricted. The Best1c04106 mutant phenotypes were rescued by genomic rescue (which recapitulates normal Best1 expression throughout the body), or targeted rescue in the Malpighian tubule and hindgut.ConclusionBest1 is required for normal ion transport in the Drosophila Malpighian tubule, and in the tubule and hindgut for iono‐ and osmoregulation, where ion reabsorption through Best1 in high‐salt conditions allows an increase in hemolymph osmolality to prevent osmotic water loss and dehydration.Support or Funding InformationNIH DK110358

Effectiveness of Tolvaptan in the Treatment for Patients with Autosomal Dominant Polycystic Kidney Disease: A Meta-analysis.

Autosomal Dominant Polycystic Kidney Disease (ADPKD) is a common chronic kidney disease that leads to End-Stage Renal Disease (ESRD). The key target of this therapy is to prevent the progression of kidney failure. Tolvaptan could slow kidney cyst growth and are proven highly effective. The aims of this analysis are to perform a systematic review, estimate and evaluate the efficacy and safety of tolvaptan in ADPKD patients. Randomized controlled trials of tolvaptan in ADPKD were identified in PubMed, Ovid, Web of Science and the Cochrane Library electronic database. The changes observed in kidney function, treatment efficiency and the incidence of adverse events between the tolvaptan and placebo groups were compared. Data were analyzed by the RevMan software. Eight trials, including 7 double-blinded randomised controlled trials and 1 quasi RCT involving 1,536 patients were extracted. Significant differences in the annual rate of change in the total kidney volume TKV at any stages of CKD (MD = -3.32, 95%CI =-4.57,-2.07, I2 =70%) and the glomerular filtration rate (MD = 1.4, 95%CI = 0.83,1.97, I2 =0%) were observed between the tolvaptan group and the placebo group. Subgroup analysis of patients in different CKD stages also showed the same conclusion. There was an increase in the urine osmolality, and 24-hour urine volume in patients receiving tolvaptan. Tolvaptan reduced the rate of serious hypertension and kidney pain events in ADPKD patients. At higher doses, it increased the rate of adverse events (liver injuries, thirst, pollakiuria, and nocturia). There was no significant risk of bias in the included studies. Tolvaptan has a beneficial effect on ADPKD, but is associated with an increase in adverse events at high doses when compared with the placebo. Further RCTs on tolvaptan may be required to support this conclusion.

Characterization of Oligofructose-Induced Acute Rumen Lactic Acidosis and the Appearance of Laminitis in Zebu Cattle.

Simple SummaryIn this paper we characterize oligofructose-induced acute rumen lactic acidosis in zebu cattle focusing on alterations of the experimental protocol concerning ruminal condition. Here we describe zebu cattle’s lack of adaptation to the oligofructose induction model for laminitis and we provide methodology of adaptation that allows the higher occurrence of laminitis with a lower degree of ruminal acidosis and better animal welfare. Additionally, we compare the animals that required and did not required supportive treatment, to try to understand which factors are related to susceptibility. The induction model promoted marked reduction in rumen pH, rumen anaerobiosis, carbon dioxide pressure, and an increase in rumen lactate, blood osmolarity, and cortisol concentration. The animals treated had lower values of rumen pH and marked dehydration, evidenced by the increase in globular volume and serum urea. The clinical condition caused by excess oligofructose is more severe than the classical sucrose induction model, but is efficient in producing laminitis.The objective of this study was to characterize oligofructose-induced acute rumen lactic acidosis and its consequences in zebu cattle. We used 29 Nellore heifers which were submitted to experimental induction of laminitis by oligofructose excess. During the induction period, the animals underwent clinical examination, including laminitis diagnosis (hoof pressure testing and locomotion score) and blood and ruminal fluid sampling every six hours (over the initial 24 h) and every 12 h (up to 72 h), after the highest dose. Almost half of the animals (48.1%) required treatment with bicarbonate and saline to correct metabolic acidosis and dehydration. Due to this treatment, the animals were analyzed in treated (n = 13) and non-treated (n = 14) groups. The induction model promoted marked reduction in rumen pH, rumen anaerobiosis, carbon dioxide pressure, and increase in rumen lactate, blood osmolarity, and cortisol concentration. The animals treated had lower values of rumen pH and marked dehydration, evidenced by the increase in globular volume and serum urea. The clinical condition caused by excess oligofructose is severe, with the differential of the appearance of ephemeral fever and respiratory compensation against systemic acidosis, in addition to the frequent appearance of laminitis.

Unique Organization of Actin Cytoskeleton in Magnocellular Vasopressin Neurons in Normal Conditions and in Response to Salt-Loading.

Magnocellular neurosecretory cells (MNCs) are intrinsically osmosensitive and can be activated by increases in blood osmolality, triggering the release of antidiuretic hormone vasopressin (VP) to promote water retention. Hence, the activity of magnocellular VP neurons is one of the key elements contributing to the regulation of body fluid homeostasis in healthy organisms. Chronic exposure to high dietary salt leads to excessive activation of VP neurons, thereby elevating levels of circulating VP, which can cause increases in blood pressure contributing to salt-dependent hypertension. However, the molecular basis underlying high-salt diet-induced hyperactivation of magnocellular VP neurons remains not fully understood. Previous studies suggest that magnocellular neurosecretory neurons contain a subcortical layer of actin filaments and pharmacological stabilization of this actin network potentiates osmotically-induced activation of magnocellular neurons. Using super-resolution imaging in situ, we investigated the organization of the actin cytoskeleton in rat MNCs under normal physiological conditions and after a chronic increase in blood osmolality following 7 d of salt-loading (SL). We found that, in addition to the subcortical layer of actin filaments, magnocellular VP neurons are endowed with a unique network of cytoplasmic actin filaments throughout their somata. Moreover, we revealed that the density of both subcortical and cytoplasmic actin networks in magnocellular VP neurons is dramatically increased following SL. These results suggest that increased osmo-responsiveness of VP neurons following chronic exposure to high dietary salt may be mediated by the modulation of unique actin networks in magnocellular VP neurons, possibly contributing to elevated blood pressure in this condition.

Serum osmolality, cerebrospinal fluid specific gravity and overt hepatic encephalopathy severity in patients with liver failure

Hepatic encephalopathy (HE) is a leading contributor to morbidity in liver disease. While hyperammonaemia plays a key role, the mechanisms of cerebral toxicity are unclear. We hypothesized that serum hyperosmolality contributes to HE during acute (ALF) and acute-on-chronic liver failure (ACLF) through mechanisms that affect the water and solute composition of the cerebral environment. We performed a retrospective analysis of serum osmolality, cerebral spinal fluid (CSF) solute density (specific gravity, determined from computed tomography attenuation) and clinical HE severity (Glasgow Coma Score [GCS]) at the time of intensive care admission in a prospectively identified cohort of liver failure patients with overt HE. Seventy-three patients (39 ALF and 34 ACLF) were included, of whom 28 (38%) were comatose. Serum osmolality (303.9±15.4mOsm/kg) was elevated despite normal serum sodium (136.6±6.3mEq/L). Increased osmolality was independently associated with more severe encephalopathy (ordinal adjusted OR 0.26 [95% CI 0.22, 0.31] for higher GCS per standard deviation increase in osmolality) and lower CSF-specific gravity (linear adjusted β=-0.039 [95% CI -0.069, -0.009] Hounsfield unit per 1mOsm/kg). In the context of related research, these data suggest that hyperosmolality increases brain exposure to metabolic toxins by blood-brain barrier alteration and may be a unique therapeutic target.

Advances in the Management of Perioperative Patients' Thirst.

In response to an increase in osmolarity or a decrease in plasma volume, surgical patients often experience thirst during the perioperative period. Thirst causes intense discomfort for patients, but perioperative nurses and health care providers have received minimal direction on how to address this concern. This article presents evidence related to the advances in the management of patients' thirst and discusses clinical strategies that perioperative personnel can safely implement for their patients during the preoperative and postoperative periods. The Thirst Study and Research Group at Londrina State University, Brazil, developed the Thirst Management Model to provide a standardized method for perioperative personnel. Four pillars comprise this model: identification of thirst, measurement of thirst, safety assessment for the management of thirst, and application of relief strategies. This evidence-based model should assist perioperative nurses with translating knowledge and scientific evidence into clinical practice to provide safe patient care.

Phase inversion-based nanoemulsions of medium chain triglyceride as potential drug delivery system for parenteral applications.

Lipid nanoemulsions are attractive drug delivery systems for lipophilic drugs. To produce nanoemulsions with droplets of very small diameter (<100 nm), we investigated thermotropic phase transitions as an alternative to the standard procedure of high-pressure homogenization. Employing shock dilution with ice-cold water during the phase inversion gives the opportunity to produce nanoemulsions without any use of potentially toxic organic solvents. The systematic investigation of the relation of the three involved components surfactant, aqueous phase and lipid phase showed that depending on the ratio of surfactant to lipid the emulsions contained particles of diameters between 16 and 175 nm with narrow polydispersity index distributions and uncharged surfaces. Nanoemulsions with particles of 50 and 100 nm in diameter showed very little toxicity to fibroblast cells in vitro. An unusual, exponential-like nonlinear increase in osmolality was observed with increasing concentration of the nonionic surfactant Kolliphor HS 15. The experimental results indicate, that nanoemulsions with particles of small and tunable size can be easily formed without homogenization by thermal cycling.

Effects of salt loading on the organisation of microtubules in rat magnocellular vasopressin neurones.

Magnocellular vasopressin (VP) neurones are activated by increases in blood osmolality, leading to the secretion of VP into the circulation to promote water retention in the kidney, thus constituting a key mechanism for the regulation of body fluid homeostasis. However, chronic high salt intake can lead to excessive activation of VP neurones and increased circulating levels of VP, contributing to an elevation in blood pressure. Multiple extrinsic factors, such as synaptic inputs and glial cells, modulate the activity of VP neurones. Moreover, magnocellular neurones are intrinsically osmosensitive, and are activated by hypertonicity in the absence of neighbouring cells or synaptic contacts. Hypertonicity triggers cell shrinking, leading to the activation of VP neurones. This cell-autonomous activation is mediated by a scaffold of dense somatic microtubules, uniquely present in VP magnocellular neurones. Treating isolated magnocellular neurones with drugs modulating microtubule stability modifies the sensitivity of neuronal activation in response to acute hypertonic stimuli. However, whether the microtubule network is altered in conditions associated with enhanced neuronal activation and increased VP release, such as chronic high salt intake, remains unknown. We examined the organisation of microtubules in VP neurones of the supraoptic and paraventricular hypothalamic nuclei (SON and PVN, respectively) of rats subjected to salt-loading (drinking 2% NaCl for 7days). Using super-resolution imaging, we found that the density of microtubules in magnocellular VP neurones from the SON and PVN was significantly increased, whereas the density and organisation of microtubules remain unchanged in other hypothalamic neurones, as well as in neurones from other brain areas (e.g., hippocampus, cortex). We propose that the increase in microtubule density in magnocellular VP neurones in salt-loading promotes their enhanced activation, possibly contributing to elevated blood pressure in this condition.

Multibiomarker approach to fipronil exposure in the fish Dicentrarchus labrax under two temperature regimes

Fipronil is a phenylpyrazole insecticide widely used to control pests in agriculture even though evidence of harmful side effects in non-target species has been reported. A comprehensive study on the effects of dietary administration of Regent®800WG (80 % fipronil) in European sea bass juveniles was carried out under two temperature regimes: a) natural conditions, and b) 3 °C above the natural temperature (an increase predicted for the NW Mediterranean by the end of this century). Fipronil was added to the fish food (10 mg fipronil /Kg feed) and the effects were studied at several time points including right before administration, 7 and 14 days after daily fipronil feed and one-week after the insecticide withdrawal from the diet (depuration period). A wide array of physiological and metabolic biomarkers including feeding rate, general condition indices, plasma and epidermal mucus metabolites, immune response, osmoregulation, detoxification and oxidative-stress markers and digestive enzymes were assessed. General linear models and principal component analyses indicated that regardless of water temperature, fipronil resulted in a significant alteration of several of the above listed biomarkers. Among them, glucose and lactate levels increased in plasma and decreased in epidermal mucus as indicators of a stress response. Similarly, a depletion in catalase activity and higher lipid peroxidation in liver of fipronil-exposed fish were also indicative of an oxidative-stress condition. Fipronil induced a time dependent inhibition of Cytochrome P450-related activities and an increase of phase II glutathione-S-transferase. Moreover, fipronil administration was able to reduce the hypo-osmoregulatory capability as shown by the increase of plasmatic osmolality and altered several digestive enzymes including trypsin, lipase, alpha amylase and maltase. Finally, analyses in bile and muscle confirmed the rapid clearance of fipronil but the persistence of the metabolite fipronil-sulfone in bile even after the 7-day depuration period. Altogether, the results reveal a notable impact of this compound on the physiological condition of the European sea bass. The results should be considered in future environmental risk assessment studies since fipronil could be hazardous to fish species, particularly those inhabiting estuarine ecosystems exposed to the discharge of agriculture runoffs where this pesticide is mainly used.

Osmotic regulation of UT-B urea transporters in the RT4 human urothelial cell line.

Facilitative UT‐B urea transporters play important physiological roles in numerous tissues, including the urino‐genital tract. Previous studies have shown that urothelial UT‐B transporters are crucial to bladder function in a variety of mammalian species. Using the RT4 bladder urothelial cell line, this study investigated the potential osmotic regulation of human UT‐B transporters. Initial end‐point PCR experiments confirmed expression of both UT‐B1 and UT‐B2 transcripts in RT4 cells. Western blotting analysis revealed glycosylated UT‐B protein to be highly abundant and immunolocalization experiments showed it was predominantly located on the plasma membrane. Further PCR experiments suggested that a 48 hr, NaCl‐induced raise in external osmolality increased expression of UT‐B transcripts. Importantly, these NaCl‐induced changes also significantly increased UT‐B protein abundance (p < .01, n = 7, ANOVA), whereas mannitol‐induced changes in external osmolality had no effect (NS, n = 4, ANOVA). Finally, similar increases in both UT‐B RNA expression and protein abundance were observed with urea‐induced changes to external osmolality (p < .05, n = 4, ANOVA). In conclusion, these findings strongly suggest that increases in external osmolality, via either NaCl or urea, can regulate human urothelial UT‐B transporters.

Possible factors influencing post-ejaculatory changes of the osmolality of human semen in vitro.

The human ejaculate is made up of secretions from the different accessory sex glands that empty in sequence at ejaculation. However, the different secretions only mix completely in vitro when the entire ejaculate is collected in a container and handled in the laboratory. At ejaculation, proteins from the seminal vesicles form a gel in the ejaculate and semen cannot be properly analysed and processed until the gel is liquefied. During and after liquefaction, there is continuous enzymatic activities and an ongoing increase in osmolality. The aim of this study was to investigate possible factors that influence the increase in semen osmolality in vitro. Osmolality was measured by freezing-point depression. Prostatic secretion was measured as zinc concentration. The presence of spermatozoa neither influenced the actual measurement of semen osmolality, nor the increase in osmolality. Enzymatic inhibitors reduced the increase in osmolality, and semen dilution prevented any increase in semen osmolality. However, the increase in osmolality covaried with the seminal zinc concentration, indicating that the observed increase was related to factors of prostatic origin. A simple and convenient procedure to reduce the risk for osmotic challenges for spermatozoa during handling for assisted reproductive technologies might be early dilution of semen.

The effect of lid hygiene on the tear film and ocular surface, and the prevalence of Demodex blepharitis in university students

AimTo evaluate the effect blepharitis lid cleansers have on the tear film and ocular surface, and to examine the prevalence of Demodex folliculorum in a young population. MethodsForty-eight university students completed a randomised, controlled, investigator-masked, eight-week clinical trial. Three eyelid hygiene products were investigated: blepharitis eyelid cleanser (OCuSOFT® Lid Scrub® PLUS foam), diluted baby shampoo (10% Johnson’s® No More Tears ®) and a tea-tree based face wash (dr.organic®). Cooled boiled water was used as a control. Subjects attended for four visits: baseline, two weeks, four weeks and eight weeks. At each visit, subjective symptoms, non-invasive tear break up time, ocular surface staining and Demodex folliculorum investigation were assessed to evaluate any positive or negative effect on the tear film and ocular surface. Osmolarity was also measured at baseline and week eight only. ResultsThe overall prevalence of Demodex folliculorum found at baseline was 15%. Subjective symptoms improved in all groups, including control. There was no significant difference in mean osmolarity between the groups or within each group after eight weeks. There was a significant increase in osmolarity inter-eye variability in the baby shampoo group (5.5 ± 5.4 vs 15.2 ± 9.5; p = 0.03). There was no significant change in non-invasive tear break up time or ocular surface staining demonstrated after eight weeks of eyelid hygiene. ConclusionA low prevalence of Demodex folliculorum can be found in a young population. All blepharitis lid cleansers used demonstrated subjective improvement in symptoms, with no negative effects on tear break-up time or ocular surface staining. The blepharitis eyelid cleanser and tea-tree based face wash revealed no adverse effect on mean osmolarity or inter-eye variability. Similarly, baby shampoo did not cause a significant increase in mean osmolarity, however, a significant increase in inter-eye variability was found; suggesting a possible increase in ocular surface inflammation.

P: 72 Hyponatremia Correction in Cirrhosis May Increase the Speed of Complex Information Processing

BACKGROUND: Hyponatremia is frequent in patients with advanced cirrhosis and ascites. A decrease in plasma osmolality exacerbates astrocyte swelling and through this mechanism may worsen cognitive function. Our objective was to determine whether, in patients with cirrhosis and ascites, an increase in plasma sodium (spontaneous or induced by an aquaretic) leads to an improvement in cognitive function. METHODS: 250 patients with liver cirrhosis and ascites were included in two double-blind, randomised, multicentre clinical studies of satavaptan (a vasopressin V2 antagonist). Patients were included after a "wash-out period" (one week on controlled sodium intake and spironolactone 100 mg/d) and received either placebo (n = 61) or satavaptan (n = 189) at three different doses (5, 12.5, 25 mg/d). Patients completed the trail-making test (TMT) at baseline and at 5–7 and 14–28 days of follow-up. The TMT (scored in seconds) assesses speed of information processing and is considered a test of simple (part A) and complex attention (part B). Improvement of hyponatraemia was defined as an increase in plasma sodium &gt;5 mmol/l or to a value &gt;135 mmol/l. RESULTS: At inclusion into the studies, patients with normonatremia exhibited better results on the TMT-A and TMT-B that could not be explained by differences on age. This group also exhibited better parameters of liver function (Table 1). Improvement of hyponatremia was associated with shortening on the time needed to complete TMT-B: −20 s vs −6.5 s (P = 0.02), but not TMT-A: −10 s vs −5 s (P = 0.16). Increase in serum osmolality was also associated with better TMT-B scores (P &lt; 0.001 at Day 5-7 and P = 0.033 at Day 14–28), but this was not shown for TMT-A. Liver function parameters remained stable in both groups of patients. Improvement of hyponatremia at Day 5 was most commonly seen in patients that received satavaptan (59.7%, n = 82) than in those treated with placebo (18.5%, n = 28). Median changes in TMT scores with satavaptan (all doses pooled) compared to placebo were: TMT-A −10 s vs 0 s (P = 0.08) and TMT-B −20 s vs −7.5 s (P = 0.12). CONCLUSIONS: Improvement of hyponatremia in cirrhosis was associated with an increase in the speed of complex information processing. Improvement of hyponatremia was achieved more frequently with satavaptan treatment, which showed a trend towards better results on cognitive function.

Osmolyte Depletion and Thirst Suppression Allow Hibernators to Survive for Months without Water.

Thirteen-lined ground squirrels (Ictidomys tridecemlineatus) are obligatory hibernators who can survive over 6months of the year in underground burrows or laboratory hibernaculum without access to food or water [1]. Hibernation consists of prolonged periods of torpor, lasting up to 18days, which are characterized by low body temperature and suppressed metabolism. This torpidity is interspersed with short periods of interbout arousal, lasting up to 48 h, during which squirrels temporarily return to an active-like state and lose small amounts of water to urination and evaporation [2]. Water is also lost during torpor due to a positive vapor pressure difference created by the slightly higher temperature of the body compared to its surroundings [2, 3]. Here, we investigate the physiological mechanism of survival during prolonged water loss and deprivation throughout hibernation. By measuring hydration status during hibernation, we show that squirrels remain hydrated during torpor by depleting osmolytes from the extracellular fluid. During brief periods of arousal, serum osmolality and antidiuretic hormone levels are restored, but thirst remains suppressed. This decoupling of thirst and diuresis enables water retention by the kidney while suppressing the drive to leave the safety of the underground burrow in search of water. An acute increase in serum osmolality reinstates water-seeking behavior, demonstrating preservation of the physiological thirst circuit during hibernation. Better mechanistic understanding of internal osmolyte regulation and thirst suppression could translate to advancements in human medicine and long-term manned spaceflight. VIDEO ABSTRACT.

Sex-dependent differences in water homeostasis in wild-type and V-ATPase B1-subunit deficient mice

Men tend to dehydrate more than women after prolonged exercise, possibly due to lower water intake and higher perspiration rate. Women are prone to exercise-associated hyponatremia, primarily attributed to the higher water consumption causing hypervolemia. Since aquaporin-2 (AQP2) water channels in the kidney collecting duct (CD) principal cells (PCs) are involved in maintaining water balance, we investigated their role in sex-dependent water homeostasis in wild-type (WT) C57BL/6 mice. Because CD intercalated cells (ICs) may also be involved in water balance, we also assessed the urine concentrating ability of V-ATPase B1 subunit-deficient (Atp6v1b1-/-) mice. Upon 12-hour water deprivation, urine osmolality increased by 59% in WT female mice and by only 28% in males. This difference was abolished in Atp6v1b1-/- mice, in which dehydration induced a ~30% increase in urine osmolarity in both sexes. AQP2 levels were highest in WT females; female Atp6v1b1-/- mice had substantially lower AQP2 expression than WT females, comparable to the low AQP2 levels seen in both Atp6v1b1-/- and WT males. After dehydration, AQP2 relocates towards the PC apical pole, especially in the inner stripe and inner medulla, and to a greater extent in WT females than in WT males. This apparent sex-dependent concentrating advantage was absent in Atp6v1b1-/- females, whose reduced AQP2 apical relocation was similar to WT males. Accordingly, female mice concentrate urine better than males upon dehydration due to increased AQP2 expression and mobilization. Moreover, our data support the involvement of ICs in water homeostasis, at least partly mediated by V-ATPase, in a sex-dependent manner.

Effect of hyperglycaemic conditions on the response of human periodontal ligament fibroblasts to mechanical stretching.

The aim of the present study was to investigate the impact of high glucose concentration on the response of human periodontal ligament fibroblasts (PDLFs) to cyclic tensile strain. Human PDLFs were incubated under normal or high glucose conditions, and then were subjected to cyclic tensile stretching (8 per cent extension, 1 Hz). Gene expression was determined by quantitative real-time polymerase chain reaction. Intracellular reactive oxygen species (ROS) were determined by the 2',7'-dichlorofluorescein-diacetate assay, activation of mitogen-activated protein kinase (MAPK) was monitored by western analysis and osteoblastic differentiation was estimated with Alizarin Red-S staining. Cyclic tensile stretching of PDLF leads to an immediate activation of extracellular signal-regulated kinase (ERK) and c-Jun N-terminal kinase (JNK), as well as to the increased expression of the transcription factor c-fos, known to regulate many osteogenesis-related genes. At later time points, the alkaline phosphatase and osteopontin genes were also upregulated. Hyperglycaemic conditions inhibited these effects. High glucose conditions were unable to increase ROS levels, but they increased the medium's osmolality. Finally, increase of osmolality mimics the inhibitory effect of hyperglycaemia on MAPK activation, c-fos and osteoblast-specific gene markers' upregulation, as well as osteogenic differentiation capacity. Our findings indicate that under high glucose conditions, human PDLFs fail to adequately respond to mechanical deformation, while their strain-elicited osteoblast differentiation ability is deteriorated. The aforementioned effects are most probably mediated by the increased osmolality under hyperglycaemic conditions.

CHRONIC NITRIC OXIDE SYNTHASE INHIBITION INCREASES RENAL VASOPRESSIN EFFECTS IN NORMOTENSIVE RAT

Objective: Nitric oxide is an important modulator of vascular tone but also of the sodium and water balance. These phenomena appear to be of particular relevance in the control of blood pressure and the development of arterial hypertension. Design and method: We evaluated in 4 week-old Wistar Kyoto normotensive rats the effects of chronic inhibition of nitric oxide synthase through NG-nitro-L-arginine methyl ester (L-NAME, 7.5 mg / kg / day per 4 weeks) on water and sodium balance. Results: The dose of L-NAME administered orally for 4 weeks did not generate a significant increase in blood pressure (116 ± 10 vs 112 ± 8). The volume of diuresis was reduced, associated with an increase in urine osmolarity in the group treated with L-NAME. Natriuresis levels were not significantly different between L-NAME treated and untreated rats. Urinary aquaporin2/creatinine ratio was significantly elevated in L-NAME group of rat (p < 0.05). Plasma and urinary metabolites of nitric oxide (NOx) were reduced in L-NAME treated rats as compared to untreated. Conclusions: These results support that nitric oxide synthase inhibition, at subpressor doses, determine a positive water balance by increasing tubular effect of vasopressin that lead to higher tubular water channel (aquaporin2) expression, and subsequently to the shedding in the urine.