Hyponatremia, arginine vasopressin dysregulation, and vasopressin receptor antagonism

Avoidance of added salt for 6-12-month-old infants: A narrative review

Most nutrition guidelines recommend avoiding foods with added salt for infants aged 6-12 months. However, the reason for no added salt lacks enough and reliable evidence. We re-searched and re-studied the relevant evidence. We searched PubMed and the Cochrane database for English-language studies published from 1904 through 2021. We also searched the databases of the websites of different national institutions. Randomized clinical trials (RCTs), systematic reviews, observational studies, and dietary guidelines were included in this review. The kidneys of infants aged 6-12 months have adequate sodium excretion capacity. There is insufficient evidence that high salt (sodium) intake early in life might lead to hypertension or salty diet preference in adults. Infants aged 6-12 months might be at risk of low sodium intake of only 150-300 mg of sodium/day, which may not meet the body's needs, if their supplementary food is not adequately salted.

Efficacy and Safety of Isotonic and Hypotonic Intravenous Maintenance Fluids in Hospitalised Children: A Systematic Review and Meta-Analysis of Randomised Controlled Trials

Hyponatraemia is a known complication in hospitalised children receiving maintenance intravenous fluid. Several studies have been published to investigate the efficacy and safety of intravenous fluids in children. However, there is still an ongoing debate regarding the ideal solution to be used in the paediatric population. Therefore, the aim of this meta-analysis was to investigate the safety and efficacy of administering isotonic versus hypotonic intravenous maintenance fluid in hospitalised children. An extensive search was undertaken on PubMed, Web of Science, Scopus, ScienceDirect, Google Scholar and Cochrane Library on 28 December 2020. Only randomised controlled trials (RCTs) were included. We used the random-effects model for all analyses. Risk ratio (RR) and mean difference with 95% confidence intervals (CIs) were used for dichotomous and continuous outcomes, respectively. The quality of each study was assessed using the Joanna Briggs Institute critical appraisal tool for RCTs. This study is registered with PROSPERO (CRD42021229067). Twenty-two RCTs with a total of 3795 participants were included. The studies encompassed surgical and medical patients admitted to intensive care unit as well as to general wards. We found that hypotonic fluid significantly increases the risk of hyponatremia at both ≤24 h (RR 0.34; 95% CI: 0.26–0.43, p < 0.00001) and >24 h (RR 0.48; 95% CI: 0.36–0.64, p < 0.00001). Isotonic fluid increases the risk of hypernatraemia at ≤24 h (RR 2.15; 95% CI: 1.24–3.73, p = 0.006). The prevalence of hyponatraemia was also higher in the hypotonic group at both ≤24 h (5.7% vs. 23.3%) and >24 h (6.0% vs. 26.3%). There was no statistically significant difference in the risk of developing adverse outcomes between the two groups. Mean serum and urine sodium as well as serum osmolality/osmolarity was lower in the hypotonic group. Isotonic solution is protective against the development of hyponatraemia while hypotonic solution increases the risk of hyponatraemia.

The Biology of Vasopressin

Vasopressins are evolutionarily conserved peptide hormones. Mammalian vasopressin functions systemically as an antidiuretic and regulator of blood and cardiac flow essential for adapting to terrestrial environments. Moreover, vasopressin acts centrally as a neurohormone involved in social and parental behavior and stress response. Vasopressin synthesis in several cell types, storage in intracellular vesicles, and release in response to physiological stimuli are highly regulated and mediated by three distinct G protein coupled receptors. Other receptors may bind or cross-bind vasopressin. Vasopressin is regulated spatially and temporally through transcriptional and post-transcriptional mechanisms, sex, tissue, and cell-specific receptor expression. Anomalies of vasopressin signaling have been observed in polycystic kidney disease, chronic heart failure, and neuropsychiatric conditions. Growing knowledge of the central biological roles of vasopressin has enabled pharmacological advances to treat these conditions by targeting defective systemic or central pathways utilizing specific agonists and antagonists.

Drinking to death: Hyponatraemia induced by synthetic phenethylamines

Synthetic phenethylamines are widely abused drugs, comprising new psychoactive substances such as synthetic cathinones, but also well-known amphetamines such as methamphetamine and 3,4-methylenedioxymethamphetamine (MDMA, ecstasy). Cathinones and amphetamines share many toxicodynamic mechanisms. One of their potentially life-threatening consequences, particularly of MDMA, is serotonin-mediated hyponatraemia. Herein, we review the state of the art on phenethylamine-induced hyponatremia; discuss the mechanisms involved; and present the preventive and therapeutic measures. Hyponatraemia mediated by phenethylamines results from increased secretion of antidiuretic hormone (ADH) and consequent kidney water reabsorption, additionally involving diaphoresis and polydipsia. Data for MDMA suggest that acute hyponatraemia elicited by cathinones may also be a consequence of metabolic activation. The literature often reveals hyponatraemia-associated complications such as cerebral oedema, cerebellar tonsillar herniation and coma that may evolve to a fatal outcome, particularly in women. Ready availability of fluids and the recommendation to drink copiously at the rave scene to counteract hyperthermia, often precipitate water intoxication. Users should be advised about the importance of controlling fluid intake while using phenethylamines. At early signs of adverse effects, medical assistance should be promptly sought. Severe hyponatraemia (<130 mmol sodium/L plasma) may be corrected with hypertonic saline or suppression of fluid intake. Also, clinicians should be made aware of the hyponatraemic potential of these drugs and encouraged to report future cases of toxicity to increase knowledge on this potentially lethal outcome.

A Systematic Review of Biological Mechanisms of Fatigue in Chronic Illness

Fatigue, a commonly reported symptom, is defined as an overwhelming, debilitating, and sustained sense of exhaustion that decreases the ability to function and carry out daily activities. To date, cancer researchers have been in the forefront in investigating the possible biological mechanisms of fatigue, identifying inflammation, dysregulation of the hypothalamic-pituitary-adrenal (HPA) axis, and activation of the autonomic nervous system. The purpose of this systematic review is to describe fatigue and what is known about the biological mechanisms described in cancer in five chronic, noninfectious illnesses: heart failure, multiple sclerosis, chronic kidney disease, rheumatoid arthritis, and chronic obstructive pulmonary disease. We searched PubMed and EMBASE using fatigue as a major Medical subject headings (MeSH) heading with each individual disease added as a search term followed by each biological mechanism. We included only primary research articles published in English between 1996 and 2016 describing studies conducted in adult humans. We identified 26 relevant articles. While there is some evidence that the biological mechanisms causing fatigue in cancer are also associated with fatigue in other chronic illnesses, more research is needed to explore inflammation, the HPA axis, and the autonomic nervous system, and other mechanisms in relation to fatigue in a variety of chronic illnesses.

Leptospirosis in human: Biomarkers in host immune responses

Leptospirosis remains one of the most widespread zoonotic diseases caused by spirochetes of the genus Leptospira, which accounts for high morbidity and mortality globally. Leptospiral infections are often found in tropical and subtropical regions, with people exposed to contaminated environments or animal reservoirs are at high risk of getting the infection. Leptospirosis has a wide range of clinical manifestations with non-specific signs and symptoms and often misdiagnosed with other acute febrile illnesses at early stage of infection. Despite being one of the leading causes of zoonotic morbidity worldwide, there is still a gap between pathogenesis and human immune responses during leptospiral infection. It still remains obscure whether the severity of the infection is caused by the pathogenic properties of the Leptospira itself, or it is a consequence of imbalance host immune factors. Hence, in this review, we seek to summarize the past and present milestone findings on the biomarkers of host immune response aspects during human leptospiral infection, including cytokine and other immune mediators. A profound understanding of the interlink between virulence factors and host immune responses during human leptospirosis is imperative to identify potential biomarkers for diagnostic and prognostic applications as well as designing novel immunotherapeutic strategies in future.

Magnocellular hypothalamic system and its interaction with the hypothalamo-pituitary-adrenal axis

The hypothalamo-neurohypophyseal system plays a key role in maintaining homeostasis and in regulation of numerous adaptive reactions, e.g., endocrine stress response. Nonapeptides vasopressin and oxytocin are the major hormones of this system. They are synthesized by magnocellular neurons of the paraventricular and supraoptic hypothalamic nuclei. Magnocellular vasopressin is known to be one of the main physiological regulators of water-electrolyte balance. Its importance for control of the hypothalamo-pituitary-adrenal axis has been widely described. Magnocellular oxytocin is secreted predominantly during lactation and parturition. The complex actions of oxytocin within the brain include control of reproductive behavior and its involvement in central stress response to different stimuli. It's neuroendocrine basis is activation of the hypothalamo-pituitary-adrenal axis: corticotropin-releasing hormone is synthesized in parvocellular neurons of the paraventricular hypothalamic nuclei. The transitory coexpression of vasopressin in these cells upon stress has been described. Glucocorticoids, the end products of the hypothalamo-pituitary-adrenal axis have both central and peripheral actions. Their availability to target tissues is mainly dependent on systemic levels of corticosteroid-binding globulin. Intrinsic expression of this protein in different brain regions in neurons and glial cells has been recently demonstrated. Regulation of the hypothalamo-pituitary-adrenal axis and hypothalamo-neurohypophyseal system is highly complex. The role of both systems in the pathogenesis of various chronic ailments in humans has extensively been studied. Their disturbed functioning seems to be linked to various psychiatric, autoimmune and cardiovascular pathologies.

The burden of illness in patients with hyponatraemia in Sweden: a population-based registry study

BACKGROUND

Hyponatraemia (HN; serum sodium level < 135 mmol/l) is the most common electrolyte disturbance seen in clinical practice, and is associated with varying spectrum of symptoms. Syndrome of inappropriate antidiuretic hormone secretion (SIADH) is the most common aetiology in hospitalised patients, and can be caused by several different underlying conditions.

AIMS

The objectives of this study were to retrospectively examine the baseline characteristics, clinical outcomes and hospital resource utilisation of patients with HN and/or SIADH in Sweden over a 10-year period from 2001 to 2011. Additional analysis was performed on subpopulations of patients with hip fracture, pneumonia and small cell lung cancer (SCLC) to see if trends in outcomes were consistent across a broad range of aetiologies commonly associated with the condition.

METHODS

Patient information was taken from the Swedish National Patient Registry, the Swedish Cancer Registry, the Swedish Cause of Death Register and the Swedish Prescribed Drug Register. A total of 34,537 patients (4.38%) were identified with HN and/or SIADH, with the incidence and prevalence rising over the 10-year study period.

RESULTS

Of the 34,537 patients identified, 841 had hip fracture, 2635 had pneumonia and 106 had SCLC. Compared with matched control patients, those with HN and/or SIADH had a longer length of hospital stay, a higher re-admission rate and a shorter time to re-admission.

CONCLUSIONS

This study showed that HN and/or SIADH negatively impact patient outcomes and healthcare resources related to hospital stay irrespective of the underlying cause. The impact of HN is not confined to the initial hospitalisation, as re-admission rates are also affected.

Hyponatraemia at hospital admission is a predictor of overall mortality

BACKGROUND

Hyponatraemia is a prognostic marker of increased mortality and morbidity in selected groups of hospitalised patients. The aim of the present study was to examine the prevalence and prognostic significance of hyponatraemia at hospital admission in an unselected population with a broad spectrum of medical and surgical diagnoses.

METHODS

Consecutive patients >40 years of age admitted to a general district hospital in Greater Copenhagen between 1 April 1998 and 31 March 1999. Median follow-up time was 5.16 years (range 0-4372 days). Plasma sodium measurements were available in 2960 patients, and hyponatraemia defined as P-Na(+) <137 mmol/L at hospital admission was present in 1105 (37.3 %) patients.

RESULTS

One-year mortality was higher for hyponatraemic patients than for normonatraemic patients: 27.5% versus 17.7%. Moreover, hyponatraemia was an independent predictor of short and long-term all-cause mortality after 1 year and after the entire observation period respectively: hazard ratio (HR) 1.6 (95 % confidence interval (CI) 1.4-1.9, P < 0.0001) and HR 1.4 (95 % CI 1.3-1.6, P < 0.0001). Patients with hyponatraemia had longer hospitalisations than patients with normonatraemia: 7.6 (±0.38) days vs 5.6 (±0.21) days, P < 0.001. There was no interaction between hyponatraemia at admission and any admission diagnoses (P > 0.05 for all interaction analyses).

CONCLUSION

Hyponatraemia is associated with increased all-cause mortality and longer admission length independently of diagnosis and clinical variables.

Correlation between changes in bodyweight and changes in ascites volume in liver cirrhosis patients with hepatic edema in short-term diuretic therapy

AIM

Although it is an important treatment challenge to treat ascites with diuretic therapy, no objective markers have been established to assess improvement of ascites. However, change in bodyweight has been used as a marker of change in ascites volume. Thus, we evaluated the relationship between changes in bodyweight and changes in ascites volume in liver cirrhosis patients with ascites.

METHODS

We calculated ascites volume in patients using the simple 5-point method by conventional computed tomography and conducted a correlation analysis between changes in bodyweight and changes in ascites volume as a part of our double-blind phase 3 trial of tolvaptan.

RESULT

Change in bodyweight (x-axis) was correlated with change in ascites volume (y-axis) in all included patients (r = 0.52). A strong correlation were observed between the changes in patients without lower limb edema (r = 0.61). These correlations between the changes were expressed by the following linear regression equations: y = -0.102 + 0.206x or y = -0.033 + 0.292x, respectively. Proportions of change in ascites volume to change in bodyweight were estimated to be nearly 30%. Therefore, bodyweight reduction was confirmed to lead to improvement in ascites.

CONCLUSION

Change in bodyweight can be an objective marker to assess improvement of hepatic edema in the short-term diuretic therapy in everyday clinical practice. Decrease in ascites volume was estimated to account for nearly 30% of bodyweight reduction.

Efficacy and safety of a 14-day administration of tolvaptan in the treatment of patients with ascites in hepatic oedema

OBJECTIVE

To investigate the efficacy and safety of 14 days' orally administered tolvaptan as adjunctive treatment for hepatic oedema in Japanese liver cirrhosis patients with insufficient response to conventional diuretics, with the option to increase dose in those who did not respond initially.

METHODS

This multicentre, single-arm, phase 3 study allocated patients with liver cirrhosis and persistent ascites to 7-day treatment with 7.5 mg/day tolvaptan followed by an additional 7 days' treatment. Responders at day 7 (achieving ≥ 1 kg body-weight reduction) continued on 7.5 mg/day tolvaptan; nonresponders (<1 kg body-weight reduction) received 15 mg/day tolvaptan. Conventional diuretic treatment continued throughout. The primary endpoint was change in body weight from baseline, as a marker of ascites volume.

RESULTS

A total of 51 patients received 7.5 mg/day tolvaptan for 7 days, which caused a significant reduction in mean body weight (55% response rate). During the second 7-day treatment period, 30 patients received 7.5 mg/day tolvaptan and 13 patients received tolvaptan 15 mg/day: response rates were 43% and 23%, respectively. Two serious adverse events were observed. Serum sodium was within normal range.

CONCLUSIONS

Tolvaptan therapy for 14 days (with possible dose increase as necessary), in combination with conventional diuretics, effectively reduced body weight in patients with hepatic oedema.

[Vasopressin receptor antagonists: the vaptans]

The non-peptide vasopressin antagonists (VPA), called vaptans, were developed in the 1990s to antagonize both the pressor and antidiuretic effects of vasopressin. There are three subtypes of VPA receptors: V1a, V1b and V2. V1a receptors are widely distributed in the body, mainly the blood vessels and myocardium. The V1b receptors are located mainly in the anterior pituitary gland and play a role in ACTH release. V2 receptors are located in the collecting tubular renal cells. Both V1a and V1b receptors act through the intracellular phosphoinositol signalling pathway, Ca(++) being the second messenger. V2 receptors work through AMPc generation, which promotes aquaporin 2 (AQP2) trafficking and allows water to enter the cell. The vaptans act competitively at the AVP receptor. The most important are mozavaptan, lixivaptan, satavaptan and tolvaptan, all of which are selective V2 antagonists and are administered through the oral route. In contrast, conivaptan is a dual V1 and V2 antagonist administered through the endovenous route. The main characteristics of vaptans are their effect on free water elimination without affecting electrolyte excretion. There are several studies on the effects of these drugs in hypervolemic hyponatremia (heart failure, hepatic cirrhosis) as well as in normovolemic hyponatremia (inappropriate secretion of ADH [SIADH]). Current studies show that the vaptans are effective and well tolerated, although knowledge of these drugs remains limited. There are no studies of the use of vaptans in severe hyponatremia. Osmotic demyelination syndrome due to excessively rapid correction of hyponatremia has not been described.

Electrolytes in the aging

The elderly population in the United States continues to grow and is expected to double by 2050. With aging, there are degenerative changes in many organs and the kidney is no exception. After 40 years of age, there is an increase in cortical glomerulosclerosis and a decline in both glomerular filtration rate and renal plasma flow. These changes may be associated with an inability to excrete a concentrated or a dilute urine, ammonium, sodium, or potassium. Hypernatremia and hyponatremia are the most common electrolyte abnormalities found in the elderly and both are associated with a high mortality. Under normal conditions, the elderly are able to maintain water and electrolyte balance, but this may be jeopardized by an illness, a decline in cognitive ability, and with certain medications. Therefore, it is important to be aware of the potential electrolyte abnormalities in the elderly that can arise under these various conditions to prevent adverse outcomes.

Conivaptan: Evidence supporting its therapeutic use in hyponatremia

INTRODUCTION

The available treatment options for euvolemic and hypervolemic hyponatremia are limited, and consist mainly of fluid restriction, diuresis, or hypertonic solutions. Most of these therapies are neither well tolerated nor totally effective, and many are associated with significant adverse effects. Vasopressin receptor antagonists, also known as vaptans, are a new class of agents that now offer an additional treatment option for hyponatremic patients. Conivaptan hydrochloride, a competitive antagonist of vasopressin V1a and V2 receptors, is the first agent in this class to be approved for treatment of euvolemic and hypervolemic hyponatremia in hospitalized patients.

AIMS

This review critically assesses the evidence that support the use of conivaptan for the treatment of patients with euvolemic and hypervolemic hyponatremia.

EVIDENCE REVIEW CONCLUSION

Conivaptan is effective in raising serum sodium levels in a predictable and safe fashion in euvolemic and hypervolemic hyponatremic patients. Conivaptan provides the first molecularly targeted approach for correcting hyponatremia in hospitalized patients.

Pharmacologic management of the cardiorenal syndrome in heart failure

Cardiorenal syndrome describes the impairment of renal function and associated diuretic resistance in patients with heart failure and clinically manifest volume overload. The pathophysiology of this syndrome is poorly understood, but appears to be caused by impairment of tubuloglomerular feedback, neurohormonal activation, and other factors and therapies used in the management of heart failure. Early diagnosis of the cardiorenal syndrome by way of markers of renal injury and function is critical for timely interventions that may attenuate progression. Many novel therapies have been evaluated in the cardiorenal syndrome setting, including agents that block key local factors (eg, adenosine A(I) receptor antagonists), improve diuresis, aquaresis, and natriuresis, and augment natural vasodilator mechanisms to improve renal perfusion. Furthermore, device-based approaches such as ultrafiltration may also play an important therapeutic role.

Altered central TRPV4 expression and lipid raft association related to inappropriate vasopressin secretion in cirrhotic rats

Inappropriate vasopressin (AVP) release causes dilutional hyponatremia in many pathophysiological states such as cirrhosis. The central molecular mechanisms that mediate inappropriate AVP release are unknown. We tested the hypothesis that changes in the expression or trafficking of TRPV4 in the central nervous system may contribute to inappropriate AVP release in the bile duct ligation (BDL) model of cirrhosis in the rat. Four weeks after surgery, BDL rats demonstrated significantly increased plasma vasopressin and plasma renin activity (PRA), hypervolemia, and decreased plasma osmolality. These effects were blocked by providing BDL rats with 2% saline to drink for 15 days. TRPV4 protein expression was significantly increased in brain punches from BDL rats containing the supraoptic nucleus (SON) of the hypothalamus (100% +/- 11 to 157% +/- 4.8), and this effect was blocked in BDL rats given saline. Immunohistochemistry demonstrated a significant increase in TRPV4-positive cells and the percentage of AVP neurons that also were TRPV4-positive in the SON of BDL rats. In the hypothalamus of BDL rats, TRPV4 lipid raft association increased compared with sham (from 100% +/- 2.1 to 326.1% +/- 16). This effect was significantly attenuated in BDL rats given 2% saline to drink (174% +/- 11). In the brain stem, TRPV4 lipid raft association was reduced by BDL and inversely related to plasma AVP and PRA. We speculate that changes in TRPV4 expression and compartmentalization within lipid rafts could contribute to a feed-forward mechanism related to AVP release in cirrhosis.

Pathoetiological model of delirium: a comprehensive understanding of the neurobiology of delirium and an evidence-based approach to prevention and treatment

Delirium is the most common complication found in the general hospital setting. Yet, we know relatively little about its actual pathophysiology. This article contains a summary of what we know to date and how different proposed intrinsic and external factors may work together or by themselves to elicit the cascade of neurochemical events that leads to the development delirium. Given how devastating delirium can be, it is imperative that we better understand the causes and underlying pathophysiology. Elaborating a pathoetiology-based cohesive model to better grasp the basic mechanisms that mediate this syndrome will serve clinicians well in aspiring to find ways to correct these cascades, instituting rational treatment modalities, and developing effective preventive techniques.

[Etiology, diagnostics and therapy of hyponatremias]

Etiopathogenesis, diagnostics and therapy of hyponatremias are summarized for clinicians. Hyponatremia is the most common electrolyte abnormality. Mild to moderate hyponatremia and severe hyponatremia are found in 15-30% and 1-4% of hospitalized patients, respectively. Pathophysiologically, hyponatremias are classified into two groups: hyponatremia due to non-osmotic hypersecretion of vasopressin (hypovolemic, hypervolemic, euvolemic) and hyponatremia of non-hypervasopressinemic origin (pseudohyponatremia, water intoxication, cerebral salt wasting syndrome). Patients with mild hyponatremia are almost always asymptomatic. Severe hyponatremia is usually associated with central nervous system symptoms and can be life-threatening. Diagnostic evaluation of patients with hyponatremia is directed toward identifying the extracellular fluid volume status, the neurological symptoms and signs, the severity and duration of hyponatremia, the rate at which hyponatremia developed. The first step to determine the probable cause of hyponatremia is the differentiation of the hypervasopressinemic and non-hypervasopressinemic hyponatremias with measurement of plasma osmolality, glucose, lipids and proteins. For further differential diagnosis of hyponatremia, the determination of urine osmolality, the clinical assessment of extracellular fluid volume status and the measurement of urine sodium concentration provide important information. The most important representative of euvolemic hyponatremias is SIADH. The diagnosis of SIADH is based on the exclusion of other hyponatremic conditions; low plasma osmolality (<275 mosmol/kg) and inappropriate urine concentration (urine osmolality >100 mosmol/kg) are of pathognomic value. Acute (<48 hrs) severe hyponatremia (<120 mmol/l) necessitates emergency care with rapid restoration of normal osmotic milieu (1 mmol/l/hr increase rate of serum sodium). Patients with chronic symptomatic hyponatremia have a high risk of osmotic demyelination syndrome in brain if rapid correction of the plasma sodium occurs (maximal rate of correction of serum sodium should be 0.5 mmol/l/hr or less). The conventional treatments for chronic asymptomatic hyponatremia (except hypovolemic patients) include water restriction and/or the use of demeclocycline or lithium or furosemide and salt supplementation. Vasopressin receptor antagonists have opened a new forthcoming therapeutic era. V2 receptor antagonists, such as lixivaptan, tolvaptan, satavaptan and the V2+V1A receptor antagonist conivaptan promote the electrolyte-sparing excretion of free water and lead to increased serum sodium.

Physiology and pathophysiology of the vasopressinergic system

Arginine vasopressin, a hypothalamic peptide hormone, has multiple physiological functions, including body water regulation, control of blood pressure and effects on body temperature, insulin release, corticotropin release, memory and social behaviour. These functions are achieved via at least three specific G-protein-coupled vasopressin receptors. Development of specific vasopressin receptor antagonists in recent years is helping to elucidate the precise actions of vasopressin at each of these receptor types. The complex signalling and messenger processes which take place after receptor stimulation are now more clearly understood. Vasopressin dysregulation can occur in various disease processes, and a better understanding of the mechanisms underlying physiological synthesis, release and regulation of vasopressin will help in the development of therapies to treat these conditions.

Hyponatremia in heart failure

Hyponatremia is the most common electrolyte abnormality found in hospitalized patients with heart failure. It may occur in patients who have hypovolemic, hypervolemic, or euvolemic state. It is usually not corrected by available therapies. It is a major predictor of prognosis, and correction of hyponatremia can be effectively accomplished by vasopressin antagonists. However, it still remains to be seen whether the normalization of serum sodium with vasopressin antagonists will also lead to an improved long-term prognosis.

The role of the arginine vasopressin Avp1b receptor in the acute neuroendocrine action of antidepressants

In times of stress the hypothalamic-pituitary-adrenal (HPA) axis is activated and releases two neurohormones, corticotropin-releasing hormone (Crh) and arginine vasopressin (Avp), to synergistically stimulate the secretion of adrenocorticotropin hormone (ACTH) from the anterior pituitary, culminating in a rise in circulating glucocorticoids. Avp mediates its actions at the Avp V1b receptor (Avpr1b) present on pituitary corticotropes. Dysregulation of the stress response is associated with the pathophysiology of depression and a major treatment involves increasing the availability of monamines at the synaptic cleft. Acute administration of selective serotonin reuptake inhibitors (SSRI) and tricyclic antidepressants (TCA) has previously been shown to activate the HPA axis. The present study was undertaken to evaluate the involvement of the Avpr1b in the HPA axis response to acute SC administration of an SSRI (fluoxetine 10mg/kg) and a TCA (desipramine 10mg/kg). We measured plasma ACTH and corticosterone (CORT) levels and neuropeptide mRNA expression in the hypothalamic paraventricular nucleus (PVN) of Avpr1b knockout (KO) mice and wild-type controls. Fluoxetine and desipramine administration significantly attenuated plasma ACTH and CORT levels in male and female Avpr1b KO mice when compared to their wild-type counterparts. Avp, oxytocin (Oxt) and Crh mRNA expression in the PVN did not change in fluoxetine-treated male Avpr1b KO or wild-type mice. In contrast, fluoxetine treatment increased PVN Avp mRNA levels in female Avpr1b wild type but not KO animals. PVN Oxt mRNA levels increased in fluoxetine-treated female mice of both genotypes. The data suggests that the Avpr1b is required to drive the HPA axis response to acute antidepressant treatment and provides further evidence of a sexual dichotomy in the regulation of PVN Avp/Oxt gene expression following antidepressant administration.

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.