Disorders of antidiuretic hormone secretion

[Consensus recommendations on the diagnosis and treatment of hyponatremia from the Austrian Society for Nephrology 2024]

Hyponatremia is a disorder of water homeostasis. Water balance is maintained by the collaboration of renal function and cerebral structures, which regulate thirst mechanisms and secretion of the antidiuretic hormone. Measurement of serum-osmolality, urine osmolality and urine-sodium concentration help to diagnose the different reasons for hyponatremia. Hyponatremia induces cerebral edema and might lead to severe neurological symptoms, which need acute therapy. Also, mild forms of hyponatremia should be treated causally, or at least symptomatically. An inadequate fast increase of the serum sodium level should be avoided, because it raises the risk of cerebral osmotic demyelination. Basic pathophysiological knowledge is necessary to identify the different reasons for hyponatremia which need different therapeutic procedures.

Consensus document on the management of hyponatraemia of the Acqua Group of the Spanish Society of Endocrinology and Nutrition

INTRODUCTION

Hyponatremia is the most prevalent electrolyte disorder in the outpatient and inpatient settings. Despite this frequency, hyponatremia, including severe hyponatremia, is frequently underestimated and inadequately treated, thus highlighting the need to produce consensus documents and clinical practice guidelines geared towards improving the diagnostic and therapeutic approach to it in a structured fashion.

MATERIAL AND METHODS

Members of the Acqua Group of the Spanish Society of Endocrinology and Nutrition (SEEN) met using a networking methodology over a period of 20 months (between October 2019 and August 2021) with the aim of discussing and developing an updated guideline for the management of hyponatraemia. A literature search of the available scientific evidence for each section presented in this document was performed.

RESULTS

A document with 8 sections was produced, which sets out to provide updated guidance on the most clinically relevant questions in the management of hyponatraemia. The management of severe hyponatraemia is based on the i.v. administration of a 3% hypertonic solution. For the management of chronic euvolemic hyponatraemia, algorithms for the initiation of treatment with the two pharmacological therapeutic options currently available in Spain are presented: urea and tolvaptan.

CONCLUSIONS

This document sets out to simplify the approach to and the treatment of hyponatraemia, making it easier to learn and thus improve the clinical approach to hyponatremia.

Aquaporins in Diabetes Insipidus

Disruption of water and electrolyte balance is frequently encountered in clinical medicine. Regulating water metabolism is critically important. Diabetes insipidus (DI) presented with excessive water loss from the kidney is a major disorder of water metabolism. To understanding the molecular and cellular mechanisms and pathophysiology of DI and rationales of clinical management of DI is important for both research and clinical practice. This chapter will first review various forms of DI focusing on central diabetes insipidus (CDI) and nephrogenic diabetes insipidus (NDI). This is followed by a discussion of regulatory mechanisms underlying CDI and NDI, with a focus on the regulatory axis of vasopressin, vasopressin receptor 2 (V2R) and the water channel molecule, aquaporin 2 (AQP2). The clinical manifestation, diagnosis, and management of various forms of DI will also be discussed with highlights of some of the latest therapeutic strategies that are developed from in vitro experiments and animal studies.

Clinical manifestations and associated factors in acquired hypoaldosteronism in endocrinological practice

INTRODUCTION

Hypoaldosteronism can be congenital or acquired, isolated or part of primary adrenal insufficiency, and caused by an aldosterone deficit, resistance, or a combination of both. Reduced mineralocorticoid action can induce a decrease in urine K+ and H+ excretion and an increase in urine Na+ excretion, leading to hyperkalemia, and/or hyponatremia, often combined with metabolic acidosis. We aimed to characterize the clinical manifestations of hypoaldosteronism, and their associated factors.

METHODS

Retrospective analysis of 112 episodes of hypoaldosteronism diagnosed in 86 adult patients from 2012-2019 by the Endocrinology and Nutrition Department of a tertiary hospital. The frequency of hyperkalemia, hypovolemic hyponatremia (HH) and metabolic acidosis (MA), and their associated factors were evaluated.

RESULTS

Patients had a median age of 77 [65 - 84], 55.4% were male. 94.6% cases showed hyperkalemia, 54.5% HH, and 60.3% MA. The mean serum K+ of all cases was 5.4 ± 0.5 mmol/L, Na+: 132.1 ± 6.3 mmol/L, HCO3: 22.6 ± 3.3 mmol/L. Hypoaldosteronism was isolated in the majority of cases: only 6/112 (5%) had primary adrenal insufficiency. Hypovolemia was associated with hyponatremia and a more florid clinical presentation. HH was associated with a combined presence of aldosterone-lowering and mineralocorticoid resistance factors. MA was associated with the presence of mineralocorticoid resistance factors.

CONCLUSIONS

Hypoaldosteronism in adult endocrinological clinical practice is primarily isolated, and acquired. It predisposes not only to the development of hyperkalemia and MA, but also to that of HH. Hypoaldosteronism must be considered in the differential diagnosis of HH with urinary sodium wasting.

Syndrome of Inappropriate Secretion of Antidiuretic Hormone Caused by Very Short-term Use of Proton Pump Inhibitor

Proton pump inhibitors (PPIs) are widely used medicines worldwide. However, a rare etiology of syndrome of inappropriate secretion of antidiuretic hormone (SIADH) related to PPI was recently reported. Therefore, the putative role of PPIs in SIADH cannot be underestimated. A 78-year-old Japanese woman was admitted to our hospital for treatment of left Bell's palsy. On admission, the patient was oriented with normal laboratory data, including a serum Na level of 135 mEq/L. Oral glucocorticoids and a proton pump inhibitor were initiated in combination with oral valaciclovir. Six days later, the patient's consciousness became impaired. Laboratory data showed a serum Na level of 103 mEq/L, a urine Na level of 64.8 mEq/L, a urine K level of 43.6 mEq/L, and a urine osmolality of 450 mOsm/kg H₂O. The patient met the criteria for SIADH. The initial treatment included water restriction and 3% hypertonic saline administration. The cessation of PPI significantly improved the urine diluting capacity and concomitantly increased serum Na, which indicated that the use of PPI had been responsible for the etiology of SIADH. The present case illustrates that physicians need to be aware of the uncommon adverse effects of PPI, such as SIADH.

Diabetes Insipidus

Disruption of water and electrolyte balance is frequently encountered in clinical medicine. Regulating water metabolism is critically important. Diabetes insipidus (DI) presented with excessive water loss from the kidney is a major disorder of water metabolism. To understand the molecular and cellular mechanisms and pathophysiology of DI and rationales of clinical management of DI is important for both research and clinical practice. This chapter will first review various forms of DI focusing on central diabetes insipidus (CDI) and nephrogenic diabetes insipidus (NDI ) . This is followed by a discussion of regulatory mechanisms underlying CDI and NDI , with a focus on the regulatory axis of vasopressin, vasopressin receptor 2 (V2R ) and the water channel molecule, aquaporin 2 (AQP2 ). The clinical manifestation, diagnosis and management of various forms of DI will also be discussed with highlights of some of the latest therapeutic strategies that are developed from in vitro experiments and animal studies.

Hyponatremia in psychiatric patients: update on evaluation and management

BACKGROUND

Hyponatremia (serum sodium concentration < 136 mEq/L) is a prevalent and potentially dangerous medical comorbidity in psychiatric patients.

METHODS

MEDLINE was used to identify peer-reviewed publications that described the role of arginine vasopressin (AVP) in the pathogenesis of hyponatremia, the presentation and treatment of hyponatremia in psychiatric patients, and promising new treatment options.

RESULTS

Polydipsia may lead to hyponatremia in patients with schizophrenia, which is mediated, in part, by a reduced osmotic threshold for the release of AVP and by a defect in the osmoregulation of thirst. Acute-onset hyponatremia may require emergent treatment with hypertonic (3%) saline, whereas chronic cases mandate gradual correction to minimize the risk of osmotic demyelination. The AVP-receptor antagonists, including conivaptan, tolvaptan, lixivaptan, and satavaptan, represent a therapeutic advance in the treatment of dilutional hyponatremia.

CONCLUSION

Based on the role of AVP in the development of hyponatremia, further studies are warranted to determine the efficacy of the AVP-receptor antagonists in psychiatric patients with hyponatremia.

Disorders of water and salt metabolism associated with pituitary disease

Disorders of water and sodium homeostasis are very common problems encountered in clinical medicine. Disorders of water metabolism are divided into hyperosmolar and hypoosmolar states, with hyperosmolar disorders characterized by a deficit of body water in relation to body solute and hypoosmolar disorders characterized by an excess of body water in relation to total body solute. This article briefly reviews the physiology of hyperosmolar and hypoosmolar syndromes, then focuses on a discussion of the pathophysiology, evaluation, and treatment of specific pre- and postoperative disorders of water metabolism in patients with pituitary lesions.

Vasopressin-receptor antagonist therapy in patients with hyponatraemia

Hyponatraemia often complicates the treatment of underlying conditions in patients who are seriously ill. Arginine vasopressin receptor antagonists block the action of arginine vasopressin and correct sodium and water imbalance in patients with euvolaemic or hypervolaemic hyponatraemia.

Response of interleukin-1beta in the magnocellular system to salt-loading

Drinking 2% NaCl decreases interleukin (IL)-1beta in the neural lobe and enhances IL-1 Type 1 receptor expression in magnocellular neurones and pituicytes. To quantify cytokine depletion from the neural lobe during progressive salt loading and determine whether the changes are reversible and correspond with stores of vasopressin (VP) or oxytocin (OT), rats were given water on day 0 and then 2% NaCl to drink for 2, 5, 8 or 5 days followed by 5 days of water (rehydration). Control rats drinking only water were pair-fed amounts eaten by 5-day salt-loaded animals. Animals were decapitated on day 8, the neural lobe frozen and plasma hormones analysed by radioimmunoassay (OT, VP) or enzyme-linked immunosorbent assay (IL-1beta). IL-1beta, VP and OT in homogenates of the neural lobe were quantified by immunocapillary electrophoresis with laser-induced fluorescence detection. Differences were determined by ANOVA, Tukey's t-test, Dunnett's procedure, Fisher's least significant difference and linear regression analysis. In response to salt-loading, rats lost body weight similar to pair-fed controls, drank progressively more 2% NaCl and excreted greater urine volumes. Plasma VP increased at days 2 and 8 of salt-loading, whereas osmolality, OT and cytokine were enhanced after 8 days with IL-1beta remaining elevated after rehydration. In the neural lobe, all three peptides decreased progressively with increasing duration of salt-loading (IL-1beta, r2 = 0.98; OT, r2 = 0.94; VP, r2 = 0.93), beginning on day 2 (IL-1beta; VP) or 5 (OT), with only VP replenished by rehydration. IL-1beta declined more closely (P < 0.0001; ANOVA interaction analysis) with OT (r2 = 0.96) than VP (r2 = 0.86), indicative of corelease from the neural lobe during chronic dehydration. Local effects of IL-1beta on magnocellular terminals, pituicytes and microglia in the neural lobe with activation of forebrain osmoregulatory structures by circulating cytokine may sustain neurosecretion of OT and VP during prolonged salt-loading.

Vasopressin antagonists: role in the management of hyponatremia

Hyponatremia is a common electrolyte disorder associated with potentially serious or life-threatening consequences. Serum osmolality and sodium concentration [Na+] are regulated by thirst, the hormone arginine vasopressin (AVP), and renal water and sodium handling. Hyponatremia is frequently caused by dysregulation of AVP, which accompanies disorders of water retention, such as congestive heart failure (CHF) and the syndrome of inappropriate secretion of antidiuretic hormone (SIADH). Clinical trials with AVP receptor antagonists have confirmed the important role of AVP in the pathophysiology of hyponatremia and suggest these agents are efficacious in treating hyponatremia associated with SIADH, cirrhosis, and CHF. Acting directly at AVP receptors in the renal tubules, these agents promote aquaresis - the electrolyte-sparing excretion of free water - in patients with hyponatremia. In clinical trials, AVP receptor antagonists have been shown to increase the serum [Na+] and urine output while decreasing urine osmolality.

Vasopressin excess and hyponatremia

Hyponatremia is a common electrolyte disorder that frequently is overlooked and undertreated. Although the pathophysiological process of hyponatremia is complex, arginine vasopressin (AVP) is a common etiologic factor. Excess AVP release by osmotic or nonosmotic stimuli or both can lead to sodium and water imbalance. Conventional treatment options for hyponatremia, including water restriction and administration of sodium chloride with or without loop diuretics, do not directly address the underlying water retention induced by excess AVP in many cases. Clinical trials showed that AVP-receptor antagonists, including lixivaptan, tolvaptan, and conivaptan, produce aquaresis, the electrolyte-sparing excretion of free water, to correct serum sodium concentration. We review results from recent clinical trials involving AVP-receptor antagonists in the treatment of hyponatremia associated with AVP excess.

Long double-stranded RNA-mediated RNA interference as a tool to achieve site-specific silencing of hypothalamic neuropeptides

RNA interference (RNAi) has become a popular tool to silence gene expression in a variety of in vitro and in vivo systems. However, it has met with limited success in inhibiting gene expression in adult mammals. Here we demonstrate that long double-stranded RNA (dsRNA) can be used to create a "site-specific", transient knockdown of genes in a fashion that is phenotypically akin to genetically manipulated organisms. Corticotropin-releasing factor (CRF) and arginine vasopressin (AVP) that regulate a variety of physiological processes including the hypothalamic-pituitary-adrenal axis (HPA axis), energy and water homeostasis were used as model systems. Stereotaxic injections of dsRNA against CRF and AVP in the PVN specifically abolished the expression of these genes in the PVN leaving expression in other loci intact. Control dsRNA did not affect CRF or AVP expression in any brain region, suggesting that dsRNA did not shut down global protein synthesis. ANOVA showed significant main effects of silencing of CRF on dampening of the stress-activated release of adrenocorticotrophin hormone (ACTH) (F(2,7)=4.87; p<0.047). Silencing of AVP resulted in increased water consumption, increased urine output and decreased urine osmolality as compared to control dsRNA-treated rats. Furthermore, dsRNA had no obvious deleterious effects on body weight or food consumption, variables considered essential in ruling out adverse physiologic effects in animal models. Thus, using long dsRNA, we were able to ascertain site-specific roles of CRF and AVP in adult rats without any developmental compensation and in a wild-type background.

Disorders of body water homeostasis

Disorders of body fluids are among the most commonly encountered problems in the practice of clinical medicine. This is in large part because many different disease states can potentially disrupt the finely balanced mechanisms that control the intake and output of water and solute. It therefore behoves clinicians treating such patients to have a good understanding of the pathophysiology, the differential diagnosis and the management of these disorders. Because body water is the primary determinant of the osmolality of the extracellular fluid, disorders of body water homeostasis can be divided into hypo-osmolar disorders, in which there is an excess of body water relative to body solute, and hyperosmolar disorders, in which there is a deficiency of body water relative to body solute. The classical hyperosmolar disorder is diabetes insipidus (DI), and the classical hypo-osmolar disorder is the syndrome of inappropriate antidiuretic hormone secretion (SIADH). This chapter first reviews the regulatory mechanisms underlying water and sodium metabolism, the two major determinants of body fluid homeostasis. The major disorders of water metabolism causing hyperosmolality and hypo-osmolality, DI and SIADH, are then discussed in detail, including the pathogenesis, differential diagnosis and treatment of these disorders.

Evaluation and management of hypo-osmolality in hospitalized patients

Hyponatremia is the most common electrolyte disorder encountered in the clinical setting. Abnormalities of the mechanisms that maintain normal water and sodium metabolism are often present in hospitalized patients, including defects in renal water excretion. All of the current therapeutic approaches in patients with the syndrome of inappropriate antidiuretic hormone secretion and other forms of vasopressin-induced hyponatremia have significant limitations. Studies in animal models and humans have demonstrated that antagonists of the AVP V2 receptor in the kidney are effective in correcting hyponatremia. These new agents have been termed "aquaretics" because of their ability to induce a free water diuresis without the natriuresis or kaliuresis characteristic of diuretic drugs. When approved for clinical use, selective V2, and possibly also combined V1 + V2 receptor antagonists will be helpful in therapy.

Management of disorders of water metabolism in patients with pituitary tumors

Disorders of body fluids, notably central diabetes insipidus (CDI) and the syndrome of inappropriate antidiuretic hormone secretion (SIADH), are relatively uncommon as a presenting symptom of sellar and suprasellar masses, but quite common following surgical resection of such lesions. It therefore behooves clinicians treating such patients to have a good understanding of the pathophysiology, the differential diagnosis and the management of these disorders. This review discusses some general issues concerning the pathogenesis, differential diagnosis, clinical manifestations and therapy of hyperosmolar and hypoosmolar syndromes, including CDI and SIADH, and then more specifically addresses the evaluation and treatment of pre- and postoperative disorders of water metabolism in patients with pituitary adenomas.

Osmoregulation in water-deprived rats drinking hypertonic saline: effect of area postrema lesions

Rats drank rapidly when 0.3 M NaCl was the only drinking fluid available after overnight water deprivation, consuming approximately 200 ml/24 h. Although such large intakes of this hypertonic solution initially elevated plasma osmolality, excretion of comparable volumes of urine more concentrated than 300 meq Na(+)/l ultimately appears to restore plasma osmolality to normal levels. Rats drank approximately 100 ml of 0.5 M NaCl after overnight water deprivation, but urine Na(+) concentration (U(Na)) did not increase sufficiently to achieve osmoregulation. When an injected salt load exacerbated the initial dehydration caused by water deprivation, rats increased U(Na) to void the injected load and did not significantly alter 24-h intake of 0.3 or 0.5 M NaCl. Rats with lesions of area postrema had much higher saline intakes and lower U(Na) than did intact control rats; nonetheless, they appeared to osmoregulate well while drinking 0.3 M NaCl but not while drinking 0.5 M NaCl. Detailed analyses of drinking behavior by intact rats suggest that individual bouts were terminated by some rapid postabsorptive consequence of the ingested NaCl load that inhibited further NaCl intake, not by a fixed intake volume or number of licks that temporarily satiated thirst.

Acute myeloid leukaemia with trilineage myelodysplasia complicated by masked diabetes insipidus

We describe a rare case of acute myeloid leukaemia with trilineage myelodysplasia complicated by central diabetes insipidus. In the present case, diabetes insipidus was masked by corticosteroid deficiency due to hypopituitarism and clinical symptoms presented after administering methylprednisolone. Although the remission of leukaemia was not achieved by chemotherapy, excessive urinary output was well-controlled by nasal administration of 1-desamino-8-D-arginine vasopressin (DDAVP) during the course.

An assessment of posterior pituitary function in patients with Sheehan's syndrome

Antidiuretic hormone (ADH) function was assessed in a group of 16 patients with Sheehan's syndrome and 17 controls. All patients were on adequate cortisone and thyroxine replacement therapy before testing. During the dehydration test the patients revealed an impairment of ADH function. The maximum urine osmolalities and the urine-plasma osmolality ratios were significantly lower in the patients with Sheehan's syndrome compared to controls (maximum urine osmolalities 633 +/- 38 (SEM) and 873 +/- 29 (SEM) mOsm/kg, respectively, P less than 0.001; urine-plasma osmolality ratios 2.15 +/- 0.14 (SEM) and 3.01 +/- 0.10 (SEM), respectively, P less than 0.001). Plasma osmolalities were significantly higher in the patients (296.1 +/- 1.2 (SEM) and 290 +/- 0.9 (SEM), respectively, P less than 0.001). The patients took a longer period to achieve these maximum urine osmolalities. Three of the patients with Sheehan's syndrome were diagnosed as having diabetes insipidus since their maximum urine osmolalities were below 600 mOsm/kg and following desmopressin all three had an increment in urine osmolality which exceeded 9%. In addition these three patients had a maximum urine-plasma osmolality ratio below 1.9. Thus, it appears the patients with Sheehan's syndrome have an impairment of ADH function which manifests in some as diabetes insipidus.

Recurrent pregnancy-induced polyuria and thirst due to hypothalamic diabetes insipidus: an investigation into possible mechanisms responsible for polyuria

A young patient developed hypothalamic diabetes insipidus due to histiocytosis in infancy and was satisfactorily treated with Pitressin. As a teenager she no longer had thirst or polyuria after treatment was stopped. These symptoms only returned during her two pregnancies. When non-pregnant her urine output was 1.7-2.0 1/24 h, basal plasma osmolality 288-290 mOsm/kg, and during pregnancy 24 h urine volume was 4.5-5.21, plasma osmolality 278-280 mOsm/kg. Studies on osmoregulation of thirst and AVP release, and on renal sensitivity to the V2 agonist desmopressin and endogenous vasopressin were performed in pregnant and non-pregnant states. She had no circulating antibodies to AVP, and the effect of pregnancy-associated vasopressinase was eliminated. Results showed lowered basal plasma osmolality and osmolar thirst threshold in pregnancy but no failure of the renal concentrating mechanism. Plasma AVP concentrations after osmotic stimulation were lower in pregnancy. We propose that she developed thirst and polyuria during pregnancy because of lowering of her osmolar thirst threshold to plasma osmolalities which caused her to drink sufficient quantities of fluid to further reduce AVP secretion. We cannot exclude, however, the possibility that there was increased clearance of circulating AVP.