Vasopressin Expressed in Hypothalamic CRF Neurons Causes Impaired Water Diuresis in Secondary Adrenal Insufficiency.

Patients with secondary adrenal insufficiency can present with impaired free water excretion and hyponatremia, which is due to the enhanced secretion of vasopressin (AVP) despite increased total body water. AVP is produced in magnocellular neurons in the paraventricular nucleus of the hypothalamus (PVH) and supraoptic nucleus and in parvocellular corticotropin-releasing factor (CRF) neurons in the PVH. This study aimed to elucidate whether magnocellular AVP neurons or parvocellular CRF neurons coexpressing AVP are responsible for the pathogenesis of hyponatremia in secondary adrenal insufficiency. The number of CRF neurons expressing copeptin, an AVP gene product, was significantly higher in adrenalectomized AVP-floxed mice (AVPfl/fl) than in sham-operated controls. Adrenalectomized AVPfl/fl mice supplemented with aldosterone showed impaired water diuresis under ad libitum access to water or after acute water loading. They became hyponatremic after acute water loading, and it was revealed under such conditions that aquaporin-2 (AQP2) protein levels were increased in the kidney. Furthermore, translocation of AQP2 to the apical membrane was markedly enhanced in renal collecting duct epithelial cells. Remarkably, all these abnormalities observed in the mouse model for secondary adrenal insufficiency were ameliorated in CRF-AVP-/- mice that lacked AVP in CRF neurons. Our study demonstrates that CRF neurons in the PVH are responsible for the pathogenesis of impaired water excretion in secondary adrenal insufficiency.

Hypoosmosis alters hepatocyte mitochondrial morphology and induces selective release of carbamoyl phosphate synthetase 1.

Carbamoyl phosphate synthetase 1 (CPS1) is the most abundant hepatocyte mitochondrial matrix protein. Hypoosmotic stress increases CPS1 release in isolated mouse hepatocytes without cell death. We hypothesized that increased CPS1 release during hypoosmosis is selective and associates with altered mitochondrial morphology. Both ex vivo and in vivo models were assessed. Mouse hepatocytes and livers were challenged with isotonic or hypoosmotic (35 mosM) buffer. Mice were injected intraperitoneally with water (10% body weight) with or without an antidiuretic. Mitochondrial and cytosolic fractions were isolated using differential centrifugation, then analyzed by immunoblotting to assess subcellular redistribution of four mitochondrial proteins: CPS1, ornithine transcarbamylase (OTC), pyrroline-5-carboxylate reductase 1 (PYCR1), and cytochrome c. Mitochondrial morphology alterations were examined using electron microscopy. Hypoosmotic treatment of whole livers or hepatocytes led to preferential or increased mitochondrial release, respectively, of CPS1 as compared with two mitochondrial matrix proteins (OTC/PYCR1) and with the intermembrane space protein, cytochrome c. Mitochondrial apoptosis-induced channel opening using staurosporine in hepatocytes led to preferential CPS1 and cytochrome c release. The CPS1-selective changes were accompanied by dramatic alterations in ultrastructural mitochondrial morphology. In mice, hypoosmosis/hyponatremia led to increased liver vascular congestion and increased CPS1 in bile but not blood, coupled with mitochondrial structural alterations. In contrast, isotonic increase of intravascular volume led to a decrease in mitochondrial size with limited change in bile CPS1 compared with hypoosmotic conditions and absence of the hypoosmosis-associated histological alterations. Taken together, hepatocyte CPS1 is selectively released in response to hypoosmosis/hyponatremia and provides a unique biomarker of mitochondrial injury.NEW & NOTEWORTHY Exposure of isolated mouse livers, primary cultured hepatocytes, or mice to hypoosmosis/hyponatremia conditions induces significant mitochondrial shape alterations accompanied by preferential release of the mitochondrial matrix protein CPS1, a urea cycle enzyme. In contrast, the intermembrane space protein, cytochrome c, and two other matrix proteins, including the urea cycle enzyme ornithine transcarbamylase, remain preferentially retained in mitochondria. Therefore, hepatocyte CPS1 manifests unique mitochondrial stress response compartmentalization and is a sensitive sensor of mitochondrial hypoosmotic/hyponatremic injury.

Effects of bile duct ligation on the inhibitory control of supraoptic vasopressin neurons.

Dilutional hyponatremia due to increased plasma arginine vasopressin (AVP) is associated with liver cirrhosis. However, plasma AVP remains elevated despite progressive hypoosmolality. This study investigated changes to inhibitory control of supraoptic nucleus (SON) AVP neurons during liver cirrhosis. Experiments were conducted with adult male Sprague-Dawley rats. Bile duct ligation was used as a model of chronic liver cirrhosis. An adeno-associated virus containing a construct with an AVP promoter and either green fluorescent protein (GFP) or a ratiometric chloride indicator, ClopHensorN, was bilaterally injected into the SON of rats. After 2 weeks, rats received either BDL or sham surgery, and liver cirrhosis was allowed to develop for 4 weeks. In vitro, loose patch recordings of action potentials were obtained from GFP-labeled and unlabeled SON neurons in response to a brief focal application of the GABAA agonist muscimol (100 µM). Changes to intracellular chloride ([Cl]i) following muscimol application were determined by changes to the fluorescence ratio of ClopHensorN. The contribution of cation chloride cotransporters NKCC1 and KCC2 to changes in intracellular chloride was investigated using their respective antagonists, bumetanide (BU, 10 µM) and VU0240551 (10 µM). Plasma osmolality and hematocrit were measured as a marker of dilutional hyponatremia. The results showed reduced or absent GABAA -mediated inhibition in a greater proportion of AVP neurons from BDL rats as compared to sham rats (100% inhibition in sham vs. 47% in BDL, p = .001). Muscimol application was associated with increased [Cl]i in most cells from BDL as compared to cells from sham rats (χ2 = 30.24, p < .001). NKCC1 contributed to the impaired inhibition observed in BDL rats (p < .001 BDL - BU vs. BDL + BU). The results show that impaired inhibition of SON AVP neurons and increased intracellular chloride contribute to the sustained dilutional hyponatremia in liver cirrhosis.

Aquaporins in Edema.

One of the most prevalent indications of water-electrolyte imbalance is edema. Aquaporins (AQPs) are a protein family that can function as water channels. Osmoregulation and body water homeostasis are dependent on the regulation of AQPs. Human kidneys contain nine AQPs, five of which have been demonstrated to have a role in body water balance: AQP1, AQP2, AQP3, AQP4, and AQP7. Water imbalance is connected with AQP dysfunction. Hyponatremia with elevated AQP levels can accompany edema, which can be caused by disorders with low effective circulating blood volume and systemic vasodilation, such as congestive heart failure (CHF), hepatic cirrhosis, or the syndrome of incorrect antidiuretic hormone secretion (SIADH). In CHF, upregulation of AQP2 expression and targeting is critical for water retention. AQP2 is also involved in aberrant water retention and the formation of ascites in cirrhosis of the liver. Furthermore, water retention and hyponatremia in SIADH are caused by increased expression of AQP2 in the collecting duct. Fluid restriction, demeclocycline, and vasopressin type-2 receptor antagonists are widely utilized to treat edema. The relationship between AQPs and edema is discussed in this chapter.

Hyponatremia elicits gene expression changes driving osteoclast differentiation and functions.

Growing evidence indicates that chronic hyponatremia represents a significant risk for bone loss, osteoporosis, and fractures in our aging population. Our prior studies on a rat model of the syndrome of inappropriate antidiuretic hormone secretion indicated that chronic hyponatremia causes osteoporosis by increasing osteoclastic bone resorption, thereby liberating stored sodium from bone. Moreover, studies in RAW264.7 pre-osteoclastic cells showed increased osteoclast formation and resorptive activity in response to low extracellular fluid sodium ion concentration (low [Na+]). These studies implicated a direct stimulatory effect of low [Na+] rather than the low osmolality on cultured osteoclastic cells. In the present cellular studies, we explored gene expression changes triggered by low [Na+] using RNA sequencing and gene ontology analysis. Results were confirmed by mouse whole genome microarray, and quantitative RT-PCR. Findings confirmed gene expression changes supporting osteoclast growth and differentiation through stimulation of receptor activator of nuclear factor kappa-B ligand (RANKL), and PI3K/Akt pathways, and revealed additional pathways. New findings on low [Na+]-induced upregulation of lysosomal genes, mitochondrial energy production, MMP-9 expression, and osteoclast motility have supported the significance of osteoclast transcriptomic responses. Functional assays demonstrated that RANL and low [Na+] independently enhance osteoclast functions. Understanding the molecular mechanisms of hyponatremia-induced osteoporosis provides the basis for future studies identifying sodium-sensing mechanisms in osteoclasts, and potentially other bone cells, and developing strategies for treatment of bone fragility in the vulnerable aging population most affected by both chronic hyponatremia and osteoporosis. ISSUE SECTIONS: Signaling Pathways; Parathyroid, Bone, and Mineral Metabolism.

Whole-brain metabolic pattern analysis in patients with anti-leucine-rich glioma-inactivated 1 (LGI1) encephalitis.

BACKGROUND AND PURPOSE: Faciobrachial dystonic seizures (FBDS) and hyponatremia are the distinct clinical features of autoimmune encephalitis (AE) caused by antibodies against leucine-rich glioma-inactivated 1 (LGI1). The present study aims to explore the pathophysiological patterns and neural mechanisms underlying these symptoms. METHODS: We included 30 patients with anti-LGI1 AE and 30 controls from a retrospective observational cohort. Whole-brain metabolic pattern analysis was performed to assess the pathological network of anti-LGI1 AE, as well as the symptom networks associated with FBDS. Logistic regression was applied to explore independent predictors of FBDS. Finally, we used a multiple regression model to investigate the hyponatremia-associated brain network and its effect on serum sodium levels. RESULTS: The pathological network of anti-LGI1 AE involved hypermetabolism in the cerebellum, subcortical structures and Rolandic area, as well as hypometabolism in the medial prefrontal cortex. The symptom network of FBDS included hypometabolism in the cerebellum and Rolandic area (pFDR <0.05). Hypometabolism in the cerebellum was an independent predictor of FBDS (p < 0.001). Hyponatremia-associated network highlighted a negative effect on the caudate nucleus, frontal and temporal white matter. The metabolism of the hypothalamus was negatively associated with (Pearson's R = -0.180, p = 0.342), while not the independent predictor for serum sodium level (path c' = -7.238, 95% confidence interval = -30.947 to 16.472). CONCLUSIONS: Our results provide insights into the whole-brain metabolic patterns of patients with anti-LGI1 AE, including the symptom network associated with FBDS and the hyponatremia-associated brain network. The findings help us to understand the neural mechanisms underlying anti-LGI1 AE and to evaluate the progress of this disease.

The Role of Na+/K+-ATPase in the Development of Hyponatrenemia under Conditions of Hypoxic Stress in Patients with SARS-CoV-2 Infection.

We studied laboratory parameters of patients with COVID-19 against the background of chronic pathologies (cardiovascular pathologies, obesity, type 2 diabetes melitus, and cardiovascular pathologies with allergy to statins). A decrease in pH and a shift in the electrolyte balance of blood plasma were revealed in all studied groups and were most pronounced in patients with cardiovascular pathologies with allergy to statin. It was found that low pH promotes destruction of lipid components of the erythrocyte membranes in patients with chronic pathologies, which was seen from a decrease in Na+/K+-ATPase activity and significant hyponatrenemia. In patients with cardiovascular pathologies and allergy to statins, erythrocyte membranes were most sensitive to a decrease in pH, while erythrocyte membranes of obese patients showed the greatest resistance to low pH and oxidative stress.

N-(4-acetamidophenyl)-5-acetylfuran-2-carboxamide as a novel orally available diuretic that targets urea transporters with improved PD and PK properties.

Urea transporters (UTs) have been identified as new targets for diuretics. Functional deletion of UTs led to urea-selective urinary concentrating defects with relative salt sparing. In our previous study, a UT inhibitor with a diarylamide scaffold, which is denoted as 11a, was demonstrated as the first orally available UT inhibitor. However, the oral bioavailability of 11a was only 4.38%, which obstructed its clinical application. In this work, by replacing the nitro group of 11a with an acetyl group, 25a was obtained. Compared with 11a, 25a showed a 10 times stronger inhibitory effect on UT-B (0.14 µM vs. 1.41 µM in rats, and 0.48 µM vs. 5.82 µM in mice) and a much higher inhibition rate on UT-A1. Moreover, the metabolic stability both in vitro and in vivo and the drug-like properties (permeability and solubility) of 25a were obviously improved compared with those of 11a. Moreover, the bioavailability of 25a was 15.18%, which was 3 times higher than that of 11a, thereby resulting in significant enhancement of the diuretic activities in rats and mice. 25a showed excellent potential for development as a promising clinical diuretic candidate for targeting UTs to treat diseases that require long-term usage of diuretics, such as hyponatremia.

Effect of hyponatremia normalization on osteoblast function in patients with SIAD.

OBJECTIVE: Hyponatremia is associated with an increased risk of bone fragility and fractures. Many studies suggest that hyponatremia stimulates osteoclast activation, whereas other studies rather reveal a possible role of acute hyponatremia in impairing osteoblast function. We aimed to assess whether and how correction of hyponatremia in hospitalized patients with the syndrome of inappropriate antidiuresis (SIAD) has an impact on bone metabolism. DESIGN AND METHODS: This was a predefined secondary analysis of 88 hospitalized patients with SIAD undergoing a randomized treatment with SGLT-2 inhibitors or placebo for 4 days. Biochemical markers of bone resorption (CTX) and bone formation (PINP) were collected in serum at baseline and after the intervention (day 5). Bone formation index (defined as PINP/CTX) and its difference between day 5 and baseline were calculated. Patients with steroid therapy (n = 6), fractures (n = 10), or whose data were missing (n = 4) were excluded from the analysis. RESULTS: Out of 68 patients, 27 (39.7%) were normonatremic at day 5. These patients showed an increase in serum PINP (P = 0.04), whereas persistent hyponatremic patients did not (P = 0.38), with a relevant difference between these two subgroups (P = 0.005). Serum CTX increased similarly in the two groups (P = 0.43). This produced a 47.9 points higher PINP/CTX difference between discharge and admission in normonatremic patients (95% CI: 17.0-78.7, P = 0.003) compared to patients with persistent hyponatremia, independent of age, sex, BMI, smoking habits, randomization arm, and baseline cortisol levels. CONCLUSIONS: Our predefined post hoc analysis shows that correction of hyponatremia in hospitalized patients with SIAD might have a positive impact on osteoblast function.

Effects of osmolality on the expression of brain aquaporins in AQP11-null mice.

Water transport in the brain is tightly controlled by blood-brain-barrier (BBB) composed of capillary endothelial cells expressing AQP1/AQP11 and glial foot processes expressing AQP4. Here we examined each AQP mRNA expression in acute hyponatremic and hypernatremic mouse models of wild type (WT) and AQP11 KO mice (KO). The expressions of AQP1, AQP4 and AQP11 mRNAs were quantified by real-time qRT-PCR analysis of whole brain RNA. Acute hyponatremia enhanced AQP4 expression without changing AQP1 expression in KO, whereas it did not change the expression of all AQPs in WT. On the other hand, acute hypernatremia increased AQP4 but decreased AQP1 expression by half in KO, whereas it decreased AQP1 and AQP11 by half without changing AQP4 expression in WT. Enhanced AQP4 expression by osmotic challenges with sodium in KO seems to be a compensation for the loss of AQP11. A stronger hypertonic stimulation with mannitol decreased all AQPs by 30-80% in WT. Since AQP4 plays an important role in the regulation of brain edema at BBB, the results suggest that AQP11 may also be involved in the osmotic regulation of the brain.

Distinguishing active pediatric COVID-19 pneumonia from MIS-C.

IMPORTANCE: Active pediatric COVID-19 pneumonia and MIS-C are two disease processes requiring rapid diagnosis and different treatment protocols. OBJECTIVE: To distinguish active pediatric COVID-19 pneumonia and MIS-C using presenting signs and symptoms, patient characteristics, and laboratory values. DESIGN: Patients diagnosed and hospitalized with active COVID-19 pneumonia or MIS-C at Children's of Alabama Hospital in Birmingham, AL from April 1 through September 1, 2020 were identified retrospectively. Active COVID-19 and MIS-C cases were defined using diagnostic codes and verified for accuracy using current US Centers for Disease Control case definitions. All clinical notes were reviewed for documentation of COVID-19 pneumonia or MIS-C, and clinical notes and electronic medical records were reviewed for patient demographics, presenting signs and symptoms, prior exposure to or testing for the SARS-CoV-2 virus, laboratory data, imaging, treatment modalities and response to treatment. FINDINGS: 111 patients were identified, with 74 classified as mild COVID-19, 8 patients as moderate COVID-19, 8 patients as severe COVID-19, 10 as mild MIS-C and 11 as severe MIS-C. All groups had a male predominance, with Black and Hispanic patients overrepresented as compared to the demographics of Alabama. Most MIS-C patients were healthy at baseline, with most COVID-19 patients having at least one underlying illness. Fever, rash, conjunctivitis, and gastrointestinal symptoms were predominant in the MIS-C population whereas COVID-19 patients presented with predominantly respiratory symptoms. The two groups were similar in duration of symptomatic prodrome and exposure history to the SARS-CoV-2 virus, but MIS-C patients had a longer duration between presentation and exposure history. COVID-19 patients were more likely to have a positive SAR-CoV-2 PCR and to require respiratory support on admission. MIS-C patients had lower sodium levels, higher levels of C-reactive protein, erythrocyte sedimentation rate, d-dimer and procalcitonin. COVID-19 patients had higher lactate dehydrogenase levels on admission. MIS-C patients had coronary artery changes on echocardiography more often than COVID-19 patients. CONCLUSIONS AND RELEVANCE: This study is one of the first to directly compare COVID-19 and MIS-C in the pediatric population. The significant differences found between symptoms at presentation, demographics, and laboratory findings will aide health-care providers in distinguishing the two disease entities.

Different expressions of AQP1 and AQP4 in hyponatremic rat brain / Diferentes expresiones de AQP1 y AQP4 en cerebro de rata hiponatrémico

SUMMARY: The expression of aquaporin-1 (AQP1) in choroid plexus and aquaporin-4 (AQP4) in astrocyte of the hippocampal formation (HF) was studied in the rat to determine the role of AQP1 and AQP4 in the pathophysiology of systemic hyponatremia (SH). SH was induced by coadministration of dextrose solution intraperitoneally and through subcutaneous implantation of an osmotic minipump containing 8-deamino-arginin vasopressin (50ng/µl/h) for 24 and 48 h. Twenty- four and 48 h after the drug administration, there were significant reductions in Na+ concentration (111 ± 5 and 104 ± 2 mmol) and serum osmolarity (240 ± 13 and 221 ± 14 mOsm/L) as compared with control values (140 ± 4.7 mmol and 296 ± 5.2 mOsm/L), (p<0.01). The expression of AQP1 in the choroid plexus was increased three to five times from 24 h to 48 h after SH (329.86 ± 10.2 % and 531.5 ± 4.4 %, n=4, p<0.01). In contrast, AQP4 expression was significantly decreased up to 48 h after SH (36 ± 9 %, n=4, p<0.01). Quantitative immunoblotting revealed significant decreases of neuronal proteins in the HF after 24 to 48 h of SH. Therefore, we suggest that altered expression of AQP1 and AQP4 plays important role in the pathogenesis of systemic hyponatremia.

RESUMEN: En este análisis se estudió la expresión de acuaporina-1 (AQP1) en plexo coroideo y acuaporina-4 (AQP4) en astrocitos de la formación hipocampal (FH) en ratas para determinar el papel de AQP1 y AQP4 en la fisiopatología de la hiponatremia sistémica (HS). La HS fue inducida mediante la coadministración de solución de dextrosa por vía intraperitoneal y mediante la implantación subcutánea de una minibomba osmótica que contenía vasopresina 8-desaminoarginina (50 ng /µ l / h) durante 24 y 48 h. Veinticuatro y 48 h después de la administración del fármaco, hubo reducciones significativas en la concentración de Na + (111 ± 5 y 104 ± 2 mmol) y la osmolaridad sérica (240 ± 13 y 221 ± 14 mOsm /µL) en comparación con los valores de control (140 ± 4,7 mmol y 296 ± 5,2 mOsm / L), (p <0,01). La expresión de AQP1 en el plexo coroideo se incrementó de tres a cinco veces de 24 a 48 h después de HS (329,86 ± 10,2 % y 531,5 ± 4,4 %, n = 4, p <0,01). Por el contrario, la expresión de AQP4 se redujo significativamente hasta 48 h después de HS (36 ± 9 %, n = 4, p <0,01). La inmunotransferencia cuantitativa reveló disminuciones significativas de proteínas neuronales en el FH después de 24 a 48 h de SH. Por lo tanto, sugerimos que la expresión alterada de AQP1 y AQP4 juega un papel importante en la patogénesis de la hiponatremia sistémica.

Is There a Relationship between COVID-19 and Hyponatremia?

Nowadays, humanity faces one of the most serious health crises, the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) pandemic. The severity of coronavirus disease 2019 (COVID-19) pandemic is related to the high rate of interhuman transmission of the virus, variability of clinical presentation, and the absence of specific therapeutic methods. COVID-19 can manifest with non-specific symptoms and signs, especially among the elderly. In some cases, the clinical manifestations of hyponatremia may be the first to appear. The pathophysiological mechanisms of hyponatremia among patients with COVID-19 are diverse, including syndrome of inappropriate antidiuretic hormone secretion (SIADH), digestive loss of sodium ions, reduced sodium ion intake or use of diuretic therapy. Hyponatremia may also be considered a negative prognostic factor in patients diagnosed with COVID-19. We need further studies to evaluate the etiology and therapeutic management of hyponatremia in patients with COVID-19.

Electrolyte imbalance in COVID-19 patients admitted to the Emergency Department: a case-control study.

In patients visiting the emergency department (ED), a potential association between electrolytes disturbance and coronavirus disease 2019 (COVID-19) has not been well studied. We aim to describe electrolyte disturbance and explore risk factors for COVID-19 infection in patients visiting the ED. We carried out a case-control study in three hospitals in France, including adult ED inpatients (≥ 18 years old). A total of 594 ED case patients in whom infection with COVID-19 was confirmed, were matched to 594 non-COVID-19 ED patients (controls) from the same period, according to sex and age. Hyponatremia was defined by a sodium of less than 135 mmol/L (reference range 135-145 mmol/L), hypokalemia by a potassium of less than 3.5 mmol/L (reference range 3.5-5.0 mmol/L), and hypochloremia by a chloride of less than 95 mmol/L (reference range 98-108 mmol/L). Among both case patients and controls, the median (IQR) age was 65 years (IQR 51-76), and 44% were women. Hyponatremia was more common among case patients than among controls, as was hypokalemia and hypochloremia. Based on the results of the multivariate logistic regression, hyponatremia, and hypokalemia were associated with COVID-19 among case patients overall, with an adjusted odds ratio of 1.89 [95% CI 1.24-2.89] for hyponatremia and 1.76 [95% CI 1.20-2.60] for hypokalemia. Hyponatremia and hypokalemia are independently associated with COVID-19 infection in adults visiting the ED, and could act as surrogate biomarkers for the emergency physician in suspected COVID-19 patients.

Pheochromocytoma crisis in a patient with newly diagnosed neurofibromatosis type 1.

Pheochromocytoma occasionally engenders catecholamine-induced hypertension crisis. Pheochromocytoma is clinically identified in 0.1%-5.7% of patients with neurofibromatosis type 1 (NF1), which is 10 times more frequently than in healthy individuals. This report describes a case of newly diagnosed NF1 presenting with pheochromocytoma crisis, with severe electrolyte depletion and deteriorating recurrent ventricular tachycardia storm. Characteristic skin lesions such as café-au-lait macules and neurofibromas contributed to the diagnosis of NF1 and pheochromocytoma. No recurrence of electrolyte depletion was found after the adrenalectomy. Primary care physicians must distinguish the characteristic skin lesions of NF1, such as café-au-lait macules and neurofibromas and recognise the risk for pheochromocytoma.

Gefitinib induced severe hyponatremia: A case report.

INTRODUCTION: Evolution of targeted molecular therapies has greatly improved patient survival in cancer. Gefitinib is an oral, reversible, epidermal growth factor receptor inhibitor used in advance non-small cell lung cancer. Skin rashes and diarrhea are common adverse effects associated with gefitinib. However, electrolytes disorders are rarely reported with gefitinib, particularly hyponatremia. CASE REPORT: We describe a 65-year-old male with metastatic non-small cell lung cancer treated with gefitinib for the last three weeks. He presented to our hospital with complaints of acute onset drowsiness. On evaluation of drowsiness, patient was diagnosed with severe hyponatremia.Management and outcome: After ruling out other common causes of hyponatremia, gefitinib was attributed as a cause of hyponatremia. Gefitinib was immediately stopped and IV hypertonic saline (3% sodium chloride) was started due to severe symptomatic hyponatremia. After seven days of cessation of gefitinib, he became asymptomatic with normalisation of serum sodium levels. DISCUSSION: Hyponatremia in cancer patients is associated with poor prognosis and prolonged hospital stay. Possibility of gefitinib-induced hyponatremia should be considered in order to achieve early diagnosis and prevent significant mortality in cancer patients.

Sex Differences in the Regulation of Vasopressin and Oxytocin Secretion in Bile Duct-Ligated Rats.

INTRODUCTION: Hyponatremia due to elevated arginine vasopressin (AVP) secretion increases mortality in liver failure patients. No previous studies have addressed sex differences in hyponatremia in liver failure animal models. OBJECTIVE: This study addressed this gap in our understanding of the potential sex differences in hyponatremia associated with increased AVP secretion. METHODS: This study tested the role of sex in the development of hyponatremia using adult male, female, and ovariectomized (OVX) female bile duct-ligated (BDL) rats. RESULTS: All BDL rats had significantly increased liver to body weight ratios compared to sham controls. Male BDL rats had hyponatremia with significant increases in plasma copeptin and FosB expression in supraoptic AVP neurons compared to male shams (all p < 0.05; 5-7). Female BDL rats did not become hyponatremic or demonstrate increased supraoptic AVP neuron activation and copeptin secretion compared to female shams. Plasma oxytocin was significantly higher in female BDL rats compared to female sham (p < 0.05; 6-10). This increase was not observed in male BDL rats. Ovariectomy significantly decreased plasma estradiol in sham rats compared to intact female sham (p < 0.05; 6-10). However, circulating estradiol was significantly elevated in OVX BDL rats compared to the OVX and female shams (p < 0.05; 6-10). Adrenal estradiol, testosterone, and dehydroepiandrosterone (DHEA) were measured to identify a possible source of circulating estradiol in OVX BDL rats. The OVX BDL rats had significantly increased adrenal estradiol along with significantly decreased adrenal testosterone and DHEA compared to OVX shams (all p < 0.05; 6-7). Plasma osmolality, hematocrit, copeptin, and AVP neuron activation were not significantly different between OVX BDL and OVX shams. Plasma oxytocin was significantly higher in OVX BDL rats compared to OVX sham. CONCLUSIONS: Our results show that unlike male BDL rats, female and OVX BDL rats did not develop hyponatremia, supraoptic AVP neuron activation, or increased copeptin secretion compared to female shams. Adrenal estradiol might have compensated for the lack of ovarian estrogens in OVX BDL rats.

Vasopressin escape and memory impairment in a model of chronic syndrome of inappropriate secretion of antidiuretic hormone in mice.

Recently, chronic hyponatremia, even mild, has shown to be associated with poor quality of life and high mortality. The mechanism by which hyponatremia contributes to those symptoms, however, remains to be elucidated. Syndrome of inappropriate secretion of antidiuretic hormone (SIADH) is a primary cause of hyponatremia. Appropriate animal models are crucial for investigating the pathophysiology of SIADH. A rat model of SIADH has been generally used and mouse models have been rarely used. In this study, we developed a mouse model of chronic SIADH in which stable and sustained hyponatremia occurred after 3-week continuous infusion of the vasopressin V2 receptor agonist 1-desamino-8-D-arginine vasopressin (dDAVP) and liquid diet feeding to produce chronic water loading. Weight gain in chronic SIADH mice at week 2 and 3 after starting dDAVP injection was similar to that of control mice, suggesting that the animals adapted to chronic hyponatremia and grew up normally. AQP2 expression in the kidney, which reflects the renal action of vasopressin, was decreased in dDAVP-infused water-loaded mice as compared with control mice that received the same dDAVP infusion but were fed pelleted chow. These results suggest that "vasopressin escape" occurred, which is an important process for limiting potentially fatal severe hyponatremia. Behavioral analyses using the contextual and cued fear conditioning test and T-maze test demonstrated cognitive impairment, especially working memory impairment, in chronic SIADH mice, which was partially restored after correcting hyponatremia. Our results suggest that vasopressin escape occurred in chronic SIADH mice and that chronic hyponatremia contributed to their memory impairment.

Open-label, multicenter, dose-titration study to determine the efficacy and safety of tolvaptan in Japanese patients with hyponatremia secondary to syndrome of inappropriate secretion of antidiuretic hormone.

The purpose of this study was to determine the efficacy and safety of tolvaptan in Japanese patients with hyponatremia secondary to syndrome of inappropriate secretion of antidiuretic hormone (SIADH). This multicenter, open-label, dose-escalation, phase III study enrolled Japanese patients (20-85 years old) with hyponatremia secondary to SIADH who were unresponsive to fluid restriction. Oral tolvaptan was administered for up to 30 days, initially at 7.5 mg/day, but escalated daily as necessary, based on the serum sodium concentration and safety, over the first 10 days until the optimal maintenance dose was determined for each patient (maximum 60 mg/day). The primary endpoint was the proportion of patients with normalized serum sodium concentration on the day after the final tolvaptan dose. Secondary endpoints included the mean change in serum sodium concentration from baseline on the day after the final dose. Sixteen patients (male, 81.3%; mean ± standard deviation age 71.9 ± 6.1 years) received tolvaptan treatment and 11 patients completed the study with one patient re-administered tolvaptan in the treatment period. Serum sodium concentrations normalized in 13 of 16 (81.3%) patients on the day after the final tolvaptan dose. The mean change in serum sodium concentration from baseline on the day after the final dose was 11.0 ± 4.3 mEq/L. Adverse events considered related to tolvaptan (10 [62.5%] patients) were generally of mild to moderate severity. Oral tolvaptan corrects hyponatremia in Japanese patients with SIADH with a similar efficacy and safety profile as that noted in non-Japanese patients.

Hyponatremia in Cirrhosis: An Update.

Hyponatremia is frequently seen in patients with ascites secondary to advanced cirrhosis and portal hypertension. Although not apparent in the early stages of cirrhosis, the progression of cirrhosis and portal hypertension leads to splanchnic vasodilation, and this leads to the activation of compensatory mechanisms such as renin-angiotensin-aldosterone system (RAAS), sympathetic nervous system, and antidiuretic hormone (ADH) to ameliorate low circulatory volume. The net effect is the avid retention of sodium and water to compensate for the low effective circulatory volume, resulting in the development of ascites. These compensatory mechanisms lead to impairment of the kidneys to eliminate solute-free water in decompensated cirrhosis. Nonosmotic secretion of antidiuretic hormone (ADH), also known as arginine vasopressin, further worsens excess water retention and thereby hyponatremia. The management of hyponatremia in this setting is a challenge as conventional therapies for hyponatremia including fluid restriction and correction of hypokalemia are frequently inefficacious. In this review, we discuss the pathophysiology, complications, and various treatment modalities, including albumin infusion, selective vasopressin receptor antagonists, or hypertonic saline for patients with severe hyponatremia and those awaiting liver transplantation.