Regulation of Thirst and Vasopressin Release

New insights on diagnosis and treatment of AVP deficiency

Arginine vasopressin deficiency (AVP-D) is one of the main entities of the polyuria-polydipsia syndrome. Its correct diagnosis and differentiation from the other two causes - AVP resistance and primary polydipsia - is crucial as this determines the further management of these patients.Over the last years, several new diagnostic tests using copeptin, the stable surrogate marker of AVP, have been introduced. Among them, hypertonic saline stimulated copeptin was confirmed to reliably and safely improve the diagnostic accuracy to diagnose AVP-D. Due to its simplicity, arginine stimulated copeptin was put forward as alternative test procedure. Glucagon-stimulated copeptin also showed promising results, while the oral growth hormone secretagogue Macimorelin failed to provide a sufficient stimulus. Interestingly, an approach using machine learning techniques also showed promising results concerning diagnostic accuracy.Once AVP-D is diagnosed, further workup is needed to evaluate its etiology. This will partly define the further treatment and management. In general, treatment of AVP-D focuses on desmopressin substitution, with oral formulations currently showing the best tolerance and safety profile. However, in addition to desmopressin substitution, recent data also showed that psychopathological factors play an important role in managing AVP-D patients.

Cannabinoid receptor type 1 activation causes a water diuresis by inducing an acute central diabetes insipidus in mice

Cannabis and synthetic cannabinoid consumption are increasing worldwide. Cannabis contains numerous phytocannabinoids that act on the G protein-coupled cannabinoid receptor type 1 (CB1R) and cannabinoid receptor type 2 expressed throughout the body, including the kidney. Essentially every organ, including the kidney, produces endocannabinoids, which are endogenous ligands to these receptors. Cannabinoids acutely increase urine output in rodents and humans, thus potentially influencing total body water and electrolyte homeostasis. As the kidney collecting duct (CD) regulates total body water, acid/base, and electrolyte balance through specific functions of principal cells (PCs) and intercalated cells (ICs), we examined the cell-specific immunolocalization of CB1R in the mouse CD. Antibodies against either the C-terminus or N-terminus of CB1R consistently labeled aquaporin 2 (AQP2)-negative cells in the cortical and medullary CD and thus presumably ICs. Given the well-established role of ICs in urinary acidification, we used a clearance approach in mice that were acid loaded with 280 mM NH4Cl for 7 days and nonacid-loaded mice treated with the cannabinoid receptor agonist WIN55,212-2 (WIN) or a vehicle control. Although WIN had no effect on urinary acidification, these WIN-treated mice had less apical + subapical AQP2 expression in PCs compared with controls and developed acute diabetes insipidus associated with the excretion of large volumes of dilute urine. Mice maximally concentrated their urine when WIN and 1-desamino-8-d-arginine vasopressin [desmopressin (DDAVP)] were coadministered, consistent with central rather than nephrogenic diabetes insipidus. Although ICs express CB1R, the physiological role of CB1R in this cell type remains to be determined.NEW & NOTEWORTHY The CB1R agonist WIN55,212-2 induces central diabetes insipidus in mice. This research integrates existing knowledge regarding the diuretic effects of cannabinoids and the influence of CB1R on vasopressin secretion while adding new mechanistic insights about total body water homeostasis. Our findings provide a deeper understanding about the potential clinical impact of cannabinoids on human physiology and may help identify targets for novel therapeutics to treat water and electrolyte disorders such as hyponatremia and volume overload.

Arginine vasopressin deficiency: diagnosis, management and the relevance of oxytocin deficiency

Polyuria-polydipsia syndrome can be caused by central diabetes insipidus, nephrogenic diabetes insipidus or primary polydipsia. To avoid confusion with diabetes mellitus, the name 'central diabetes insipidus' was changed in 2022 to arginine vasopressin (AVP) deficiency and 'nephrogenic diabetes insipidus' was renamed as AVP resistance. To differentiate the three entities, various osmotic and non-osmotic copeptin-based stimulation tests have been introduced in the past decade. The hypertonic saline test plus plasma copeptin measurement emerged as the test with highest diagnostic accuracy, replacing the water deprivation test as the gold standard in differential diagnosis of the polyuria-polydipsia syndrome. The mainstay of treatment for AVP deficiency is AVP replacement with desmopressin, a synthetic analogue of AVP specific for AVP receptor 2 (AVPR2), which usually leads to rapid improvements in polyuria and polydipsia. The main adverse effect of desmopressin is dilutional hyponatraemia, which can be reduced by regularly performing the so-called desmopressin escape method. Evidence from the past few years suggests an additional oxytocin deficiency in patients with AVP deficiency. This potential deficiency should be further evaluated in future studies, including feasible provocation tests for clinical practice and interventional trials with oxytocin substitution.

Zonulin and copeptin relation to some metabolic markers in school-aged obese children

BACKGROUND

Using Zonulin and Copeptin as potential obesity markers in children, hasn't yet been focused.

AIM

To evaluate the association between serum levels of both Zonulin and Copeptin with the obesity markers, and to assess their role as metabolic disturbance predictors in obese children.

METHODS

A case-control study comprised 111 Egyptian children (45 males and 66 females); aged 6-10 years to avoid the effect of puberty (prepubertal). They were classified according to their body mass index (BMI) percentiles into: 72 obese (BMI ≥ 95th ), and 39 control ones (BMI > 15th - <85th ), based on the Egyptian Growth Charts for children and adolescents. Anthropometric parameters and blood pressure were measured, and body composition analysis, lipid profile, Zonulin, and Copeptin levels were assessed.

RESULTS

The obese group showed a significantly higher value of Copeptin and a lower value of Zonulin than the control one Also, the obese group showed significant negative correlations between Zonulin and both anthropometric obesity markers and body composition, whereas Copeptin showed significant positive ones. Moreover, significant positive correlations were found between Copeptin and both body weight and fat distribution. Insignificant correlations were observed between both serum Zonulin and Copeptin levels and blood pressure and lipid profile.

CONCLUSION

Zonulin and Copeptin cannot be used as metabolic disturbance predictors, among Egyptian children, as they were insignificantly correlated with lipid profile or blood pressure.

Fluid management in children with volume depletion

Volume depletion is a common condition and a frequent cause of hospitalization in children. Proper assessment of the patient includes a detailed history and a thorough physical examination. Biochemical tests may be useful in selected cases. Understanding the pathophysiology of fluid balance is necessary for appropriate management. A clinical dehydration scale assessing more physical findings may help to determine dehydration severity. Most dehydrated children can be treated orally; however, intravenous therapy may be indicated in patients with severe volume depletion, in those who have failed oral therapy, or in children with altered consciousness or significant metabolic abnormalities. Proper management consists of restoring circulatory volume and electrolyte balance. In this paper, we review clinical aspects, diagnosis, and management of children with volume depletion.

Paediatric perspectives in the diagnosis of polyuria-polydipsia syndrome

The elucidation of the underlying cause of polyuria-polydipsia syndrome (PPS) is a challenging-especially in the differentiation of partial defects of arginine vasopressin (AVP) secretion or action from primary polydipsia. The water deprivation test has been utilized for many decades, and its application in the paediatric population has been applied using parameters predominantly established in adult cohorts. In more recent times, the development of automated commercial assays for copeptin, a surrogate marker for AVP, has represented a significant advancement in the diagnostic approach to PPS. Measurement of copeptin concentrations has major advantages and has essentially superseded measurement of AVP in diagnostic protocols for PPS. Additionally, stimulated-copeptin protocols utilizing hypertonic saline infusion, arginine, and glucagon have been investigated, and are promising. However, further studies are required in the population-incorporating the differences in physiological regulation of water homeostasis, and safety requirements-before there is widespread adoption into clinical practice.

Fasting increases circulating angiotensin levels and brain Agtr1a expression in male rats

In addition to being recognised for involvement in cardiovascular control and hydromineral balance, the renin-angiotensin system (RAS) has also been associated with the neuroendocrine control of energy balance. One of the main brain sites for angiotensin II (ANG II)/type 1 receptor (AT1 R) signalling is the subfornical organ (SFO), a circumventricular organ related to the control of autonomic functions, motivated behaviours and energy metabolism. Thus, we hypothesised that circulating ANG II may act on the SFO AT1 R receptors to integrate metabolic and hydromineral balance. We evaluated whether food deprivation can modulate systemic RAS activity and Agrt1a brain expression, and if ANG II/AT1 R signalling influences the hypothalamic expression of mRNAs encoding neuropeptides and food and water ingestion in fed and fasted Wistar rats. We found a significant increase in both ANG I and ANG II plasma levels after 24 and 48 h of fasting. Expression of Agrt1a mRNA in the SFO and paraventricular nucleus (PVN) also increased after food deprivation for 48 h. Treatment of fasted rats with low doses of losartan in drinking water attenuated the decrease in glycemia and meal-associated water intake without changing the expression in PVN or arcuate nucleus of mRNAs encoding selected neuropeptides related to energy homeostasis control. These findings point to a possible role of peripheral ANG II/SFO-AT1 R signalling in the control of refeeding-induced thirst. On the other hand, intracerebroventricular losartan treatment decreased food and water intake over dark time in fed but not in fasted rats.

Dysnatremia and subsequent sodium level changes following various intravenous treatments in infants with acute gastroenteritis

Acute gastroenteritis is one of the main causes of electrolyte imbalance in infants. We aimed to determine the frequency of and factors associated with dysnatremia at presentation and establish the ideal intravenous treatment scheme. The records of hospitalized infants aged 1-12 months with community-acquired acute gastroenteritis between January 2017 and March 2021 were retrospectively reviewed. Factors associated with dysnatremia at presentation were analyzed by multivariable logistic regression analysis. Subsequent sodium levels 4-24 h after intravenous fluid treatments, which were categorized into 2 groups, were determined in the subgroup of infants with normal sodium levels at presentation. A total of 347 infants with a median age of 8.0 (5.0-10.0) months were included. The frequency of dysnatremia at presentation was 14% (hyponatremia 12% and hypernatremia 2.0%). Severe dehydration was associated with dysnatremia at presentation (p = 0.048). Among 68 infants with normal sodium levels at presentation, the median sodium change was highest in the 5% dextrose in saline group, with changes of + 3 (0.5-5) and + 1 (- 2 to 2) mmol/L in infants who received 5% dextrose in saline and 5% dextrose in 1/3-1/2 saline, respectively (p = 0.001). Four out of 47 infants (8.5%) developed hyponatremia while receiving 5% dextrose in 1/3-1/2 saline. None of those who received 5% dextrose in saline developed subsequent dysnatremia.   Conclusion: The frequency of dysnatremia at presentation among infants with acute gastroenteritis was 14%. Severe dehydration was associated with dysnatremia at presentation, so electrolyte levels need to be assessed in these patients. The use of isotonic solution did not promote acquired dysnatremia. This study supports once more that current guidelines recommending isotonic solution for children, and, especially, infant rehydration, are important also for infants in Thailand. What is Known: • There were a wide variation in the incidence of dysnatremia at presentation in children with acute gastroenteritis in previous pediatric series. • The AAP guidelines recommend using isotonic solution in children with acute illness from 28 days to 18 years of age to prevent acquired hyponatremia. What is New: • The incidence of dysnatremia at presentation in infants with acute gastroenteritis was 14% (hyponatremia 12% and hypernatremia 2.0%). • The use of isotonic solution did not promote acquired dysnatremia in infants with acute gastroenteritis.

Thirst: neuroendocrine regulation in mammals

Animals can sense their changing internal needs and then generate specific physiological and behavioural responses in order to restore homeostasis. Water-saline homeostasis derives from balances of water and sodium intake and output (drinking and diuresis, salt appetite and natriuresis), maintaining an appropriate composition and volume of extracellular fluid. Thirst is the sensation which drives to seek and consume water, regulated in the central nervous system by both neural and chemical signals. Water and electrolyte homeostasis depends on finely tuned physiological mechanisms, mainly susceptible to plasma Na+ concentration and osmotic pressure, but also to blood volume and arterial pressure. Increases of osmotic pressure as slight as 1-2% are enough to induce thirst ("homeostatic" or cellular), by activation of specialized osmoreceptors in the circumventricular organs, outside the blood-brain barrier. Presystemic anticipatory signals (by oropharyngeal or gastrointestinal receptors) inhibit thirst when fluids are ingested, or stimulate thirst associated with food intake. Hypovolemia, arterial hypotension, Angiotensin II stimulate thirst ("hypovolemic thirst", "extracellular dehydration"). Hypervolemia, hypertension, Atrial Natriuretic Peptide inhibit thirst. Circadian rhythms of thirst are also detectable, driven by suprachiasmatic nucleus in the hypothalamus. Such homeostasis and other fundamental physiological functions (cardiocircolatory, thermoregulation, food intake) are highly interdependent.

Unraveling the roles of endoplasmic reticulum-associated degradation in metabolic disorders

Misfolded proteins retained in the endoplasmic reticulum cause many human diseases. ER-associated degradation (ERAD) is one of the protein quality and quantity control system located at ER, which is responsible for translocating the misfolded proteins or properly folded but excess proteins out of the ER for proteasomal degradation. Recent studies have revealed that mice with ERAD deficiency in specific cell types exhibit impaired metabolism homeostasis and metabolic diseases. Here, we highlight the ERAD physiological functions in metabolic disorders in a substrate-dependent and cell type-specific manner.

Natural Peptide Toxins as an Option for Renewed Treatment of Type 2 Vasopressin Receptor-Related Diseases

The type 2 vasopressin receptor (V2R) is expressed in the kidneys, and it is the keystone of water homeostasis. Under the control of the antidiuretic hormone vasopressin, the V2R ensures vital functions, and any disturbance has dramatic consequences. Despite decades of research to develop drugs capable of activating or blocking V2R function to meet real medical needs, only one agonist and one antagonist are virtually used today. These two drugs cover only a small portion of patients’ needs, leaving millions of patients without treatment. Natural peptide toxins known to act selectively and at low doses on their receptor target could offer new therapeutic options.

Vasopressin: a possible link between hypoxia and hypertension

Cardiovascular and respiratory diseases are frequently associated with transient and prolonged hypoxia, whereas hypoxia exerts pro-hypertensive effects, through stimulation of the sympathetic system and release of pressor endocrine factors. This review is focused on the role of arginine vasopressin (AVP) in dysregulation of the cardiovascular system during hypoxia associated with cardiovascular disorders. AVP is synthesized mainly in the neuroendocrine neurons of the hypothalamic paraventricular nucleus (PVN) and supraoptic nucleus (SON), which send axons to the posterior pituitary and various regions of the central nervous system (CNS). Vasopressinergic neurons are innervated by multiple neuronal projections releasing several neurotransmitters and other regulatory molecules. AVP interacts with V1a, V1b and V2 receptors that are present in the brain and peripheral organs, including the heart, vessels, lungs, and kidneys. Release of vasopressin is intensified during hypernatremia, hypovolemia, inflammation, stress, pain, and hypoxia which frequently occur in cardiovascular patients, and blood AVP concentration is markedly elevated in cardiovascular diseases associated with hypoxemia. There is evidence that hypoxia stimulates AVP release through stimulation of chemoreceptors. It is suggested that acting in the carotid bodies, AVP may fine-tune respiratory and hemodynamic responses to hypoxia and that this effect is intensified in hypertension. There is also evidence that during hypoxia, augmentation of pro-hypertensive effects of vasopressin may result from inappropriate interaction of this hormone with other compounds regulating the cardiovascular system (catecholamines, angiotensins, natriuretic peptides, steroids, nitric oxide). In conclusion, current literature indicates that abnormal mutual interactions between hypoxia and vasopressin may significantly contribute to pathogenesis of hypertension.

Renal water transport in health and disease

Saving body water by optimal reabsorption of water filtered by the kidney leading to excretion of urine with concentrations of solutes largely above that of plasma allowed vertebrate species to leave the aquatic environment to live on solid ground. Filtered water is reabsorbed for 70% and 20% by proximal tubules and thin descending limbs of Henle, respectively. These two nephron segments express the water channel aquaporin-1 located along both apical and basolateral membranes. In the proximal tubule, the paracellular pathway accounts for at least 30% of water reabsorption, and the tight-junction core protein claudin-2 plays a key role in this permeability. The ascending limb of Henle and the distal convoluted tubule are impermeant to water and are responsible for urine dilution. The water balance is adjusted along the collecting system, i.e. connecting tubule and the collecting duct, under the control of arginine-vasopressin (AVP). AVP is synthesized by the hypothalamus and released in response to an increase in extracellular osmolality or stimulation of baroreceptors by decreased blood pressure. In response to AVP, aquaporin-2 water channels stored in subapical intracellular vesicles are translocated to the apical plasma membrane and raise the water permeability of the collecting system. The basolateral step of water reabsorption is mediated by aquaporin-3 and -4, which are constitutively expressed. Drugs targeting water transport include classical diuretics, which primarily inhibit sodium transport; the new class of SGLT2 inhibitors, which promotes osmotic diuresis and the non-peptidic antagonists of the V2 receptor, which are pure aquaretic drugs. Disturbed water balance includes diabetes insipidus and hyponatremias. Diabetes insipidus is characterized by polyuria and polydipsia. It is either related to a deficit in AVP secretion called central diabetes insipidus that can be treated by AVP analogs or to a peripheral defect in AVP response called nephrogenic diabetes insipidus. Diabetes insipidus can be either of genetic origin or acquired. Hyponatremia is a common disorder most often related to free water excess relying on overstimulated or inappropriate AVP secretion. The assessment of blood volume is key for the diagnosis and treatment of hyponatremia, which can be classified as hypo-, eu-, or hypervolemic.

Effects of carbohydrate use on preoperative thirst: a randomized clinical trial

OBJECTIVES

to evaluate the effectiveness of carbohydrate popsicles, carbohydrate solution, and usual care (fasting) on the intensity and discomfort of preoperative thirst.

METHODS

a randomized clinical trial with 60 preoperative patients aged between 18 and 60 years, randomized into three groups: control (fasting), carbohydrate solution (100 ml), and carbohydrate popsicle (100 ml). The outcomes were thirst intensity and discomfort.

RESULTS

there was a difference between groups for final thirst intensity (p = 0.01) and final thirst discomfort (p = 0.001). The effect size for both the Solution Group and the Popsicle Group was robust: 0.99 and 1.14, respectively.

CONCLUSIONS

the groups that received the carbohydrate fasting abbreviation showed a reduction in thirst discomfort compared to the control group. The carbohydrate popsicle proved more effective in reducing the intensity of thirst. NCT: 3.209.283.

Renal transcriptome profiles in mice reveal the need for sufficient water intake irrespective of the drinking water type

This study sought to characterize the impact of long-term dehydration in terms of physiological and biochemical parameters, as well as renal transcriptomes. Furthermore, we assessed whether consumption of specific types of water elicit more beneficial effects on these health parameters. To this end, C57BL/6 mice were either provided water for 15 min/day over 2 and 4 weeks (water restricted; RES), or ad libitum access to distilled (CON), tap, spring, or purified water. Results show that water restriction decreases urine output and hematocrit levels while increasing brain vasopressin mRNA levels in RES mice compared to control mice (CON). Meanwhile, blood urea nitrogen and creatinine levels were higher in the RES group compared to the CON group. Kidney transcriptome analysis further identified kidney damage as the most significant biological process modulated by dehydration. Mechanistically, prolonged dehydration induces kidney damage by suppressing the NRF2-signaling pathway, which targets the cytoprotective defense system. However, type of drinking water does not appear to impact physiological or blood biochemical parameters, nor the renal transcriptome profile, suggesting that sufficient water consumption is critical, irrespective of the water type. Importantly, these findings also inform practical action for environmental sustainability by providing a theoretical basis for reducing bottled water consumption.

Evidence for a Prehypertensive Water Dysregulation Affecting the Development of Hypertension: Results of Very Early Treatment of Vasopressin V1 and V2 Antagonism in Spontaneously Hypertensive Rats

In addition to long-term regulation of blood pressure (BP), in the kidney resides the initial trigger for hypertension development due to an altered capacity to excrete sodium and water. Betaine is one of the major organic osmolytes, and its betaine/gamma-aminobutyric acid transporter (BGT-1) expression in the renal medulla relates to interstitial tonicity and urinary osmolality and volume. This study investigated altered water and sodium balance as well as changes in antidiuretic hormone (ADH) activity in female spontaneously hypertensive (SHR) and normotensive Wistar Kyoto (WKY) rats from their 3–5 weeks of age (prehypertensive phase) to SHR’s 28–30 weeks of age (established hypertension-organ damage). Young prehypertensive SHRs showed a reduced daily urine output, an elevated urine osmolarity, and higher immunostaining of tubule BGT-1, alpha-1-Na-K ATPase in the outer medulla vs. age-matched WKY. ADH circulating levels were not different between young prehypertensive SHR and WKY, but the urine aquaporin2 (AQP2)/creatinine ratio and labeling of AQP2 in the collecting duct were increased. At 28–30 weeks, hypertensive SHR with moderate renal failure did not show any difference in urinary osmolarity, urine AQP2/creatinine ratio, tubule BGT-1, and alpha-1-Na-K ATPase as compared with WKY. These results suggest an increased sensitivity to ADH in prehypertensive female SHR. On this basis, a second series of experiments were set to study the role of ADH V1 and V2 receptors in the development of hypertension, and a group of female prehypertensive SHRs were treated from the 25th to 49th day of age with either V1 (OPC21268) or V2 (OPC 41061) receptor antagonists to evaluate the BP time course. OPC 41061-treated SHRs had a delayed development of hypertension for 5 weeks without effect in OPC 21268-treated SHRs. In prehypertensive female SHR, an increased renal ADH sensitivity is crucial for the development of hypertension by favoring a positive water balance. Early treatment with selective V2 antagonism delays future hypertension development in young SHRs.

Systems Biology of the Vasopressin V2 Receptor: New Tools for Discovery of Molecular Actions of a GPCR

Systems biology can be defined as the study of a biological process in which all of the relevant components are investigated together in parallel to discover the mechanism. Although the approach is not new, it has come to the forefront as a result of genome sequencing projects completed in the first few years of the current century. It has elements of large-scale data acquisition (chiefly next-generation sequencing-based methods and protein mass spectrometry) and large-scale data analysis (big data integration and Bayesian modeling). Here we discuss these methodologies and show how they can be applied to understand the downstream effects of GPCR signaling, specifically looking at how the neurohypophyseal peptide hormone vasopressin, working through the V2 receptor and PKA activation, regulates the water channel aquaporin-2. The emerging picture provides a detailedframework for understanding the molecular mechanisms involved in water balance disorders, pointing the way to improved treatment of both polyuric disorders and water-retention disorders causing dilutional hyponatremia.

Efeitos da utilização do carboidrato sobre a sede no pré-operatório: ensaio clínico randomizado

RESUMO Objetivos: avaliar a efetividade do picolé de carboidrato, solução de carboidrato e cuidado usual (jejum) sobre a intensidade e desconforto da sede no pré-operatório. Métodos: ensaio clínico randomizado, com 60 pacientes no pré-operatório, idade entre 18 e 60 anos, aleatorizados em três grupos: controle (jejum); solução de carboidrato (100 ml); picolé de carboidrato (100 ml). Os desfechos foram a intensidade e o desconforto da sede. Resultados: houve diferença entre os grupos quanto à intensidade final da sede (p = 0,01) e ao desconforto final da sede (p = 0,001). O tamanho do efeito tanto para o Grupo Solução quanto para o Grupo Picolé foi forte: 0,99 e 1,14, respectivamente. Conclusões: os grupos que receberam a abreviação do jejum com carboidrato apresentaram redução no desconforto da sede quando comparados ao grupo-controle. O picolé de carboidrato mostrou-se mais efetivo na redução da intensidade da sede. NCT: 3.209.283

Early Diagnosis and Antibiotic Treatment Combined with Multicomponent Hemodynamic Support for Addressing a Severe Case of Lemierre's Syndrome

A 20-year-old man was admitted to the intensive care unit for septic shock due to Lemierre’s syndrome. It is a rare syndrome that manifests as an upper respiratory infection, although systemic involvement, severe coagulopathy, and multi-organ failure can dangerously complicate the clinical picture. In this syndrome, sepsis-related neuroendocrine dysregulation and microcirculation impairment can have a rapid deleterious progression. Consequently, proper diagnosis, early source control, and appropriate antibiotics administration are mandatory to improve the prognosis. The intensive treatment is aimed at limiting organ damage through hemodynamic optimization. Remarkably, in septic shock due to Lemierre’s syndrome, hemodynamic optimization can be achieved through the synergic effect of norepinephrine, argipressin, and hydrocortisone.

Vasopressin and Breathing: Review of Evidence for Respiratory Effects of the Antidiuretic Hormone

Vasopressin (AVP) is a key neurohormone involved in the regulation of body functions. Due to its urine-concentrating effect in the kidneys, it is often referred to as antidiuretic hormone. Besides its antidiuretic renal effects, AVP is a potent neurohormone involved in the regulation of arterial blood pressure, sympathetic activity, baroreflex sensitivity, glucose homeostasis, release of glucocorticoids and catecholamines, stress response, anxiety, memory, and behavior. Vasopressin is synthesized in the paraventricular (PVN) and supraoptic nuclei (SON) of the hypothalamus and released into the circulation from the posterior lobe of the pituitary gland together with a C-terminal fragment of pro-vasopressin, known as copeptin. Additionally, vasopressinergic neurons project from the hypothalamus to the brainstem nuclei. Increased release of AVP into the circulation and elevated levels of its surrogate marker copeptin are found in pulmonary diseases, arterial hypertension, heart failure, obstructive sleep apnoea, severe infections, COVID-19 due to SARS-CoV-2 infection, and brain injuries. All these conditions are usually accompanied by respiratory disturbances. The main stimuli that trigger AVP release include hyperosmolality, hypovolemia, hypotension, hypoxia, hypoglycemia, strenuous exercise, and angiotensin II (Ang II) and the same stimuli are known to affect pulmonary ventilation. In this light, we hypothesize that increased AVP release and changes in ventilation are not coincidental, but that the neurohormone contributes to the regulation of the respiratory system by fine-tuning of breathing in order to restore homeostasis. We discuss evidence in support of this presumption. Specifically, vasopressinergic neurons innervate the brainstem nuclei involved in the control of respiration. Moreover, vasopressin V1a receptors (V1aRs) are expressed on neurons in the respiratory centers of the brainstem, in the circumventricular organs (CVOs) that lack a blood-brain barrier, and on the chemosensitive type I cells in the carotid bodies. Finally, peripheral and central administrations of AVP or antagonists of V1aRs increase/decrease phrenic nerve activity and pulmonary ventilation in a site-specific manner. Altogether, the findings discussed in this review strongly argue for the hypothesis that vasopressin affects ventilation both as a blood-borne neurohormone and as a neurotransmitter within the central nervous system.

α-cell Gq signaling is critical for maintaining euglycemia

Glucagon, a hormone released from pancreatic α cells, plays a key role in maintaining euglycemia. New insights into the signaling pathways that control glucagon secretion may stimulate the development of novel therapeutic agents. In this study, we investigated the potential regulation of α cell function by G proteins of the G_q family. The use of a chemogenetic strategy allowed us to selectively activate G_q signaling in mouse α cells in vitro and in vivo. Acute stimulation of α cell G_q signaling led to elevated plasma glucagon levels, accompanied by increased insulin release and improved glucose tolerance. Moreover, chronic activation of this pathway greatly improved glucose tolerance in obese mice. We also identified an endogenous G_q-coupled receptor (vasopressin 1b receptor; V1bR) that was enriched in mouse and human α cells. Agonist-induced activation of the V1bR strongly stimulated glucagon release in a G_q-dependent fashion. In vivo studies indicated that V1bR-mediated glucagon release played a key role in the counterregulatory hyperglucagonemia under hypoglycemic and glucopenic conditions. These data indicate that α cell G_q signaling represents an important regulator of glucagon secretion, resulting in multiple beneficial metabolic effects. Thus, drugs that target α cell–enriched G_q-coupled receptors may prove useful to restore euglycemia in various pathophysiological conditions.

Presynaptic inputs to vasopressin neurons in the hypothalamic supraoptic nucleus and paraventricular nucleus in mice

Arginine vasopressin (AVP) neurons in the hypothalamic supraoptic nucleus (SON) and paraventricular nucleus (PVN) are involved in important physiological behaviors, such as controling osmotic stability and thermoregulation. However, the presynaptic input patterns governing AVP neurons have remained poorly understood due to their heterogeneity, as well as intermingling of AVP neurons with other neurons both in the SON and PVN. In the present study, we employed a retrograde modified rabies-virus system to reveal the brain areas that provide specific inputs to AVP neurons in the SON and PVN. We found that AVP neurons of the SON and PVN received similar input patterns from multiple areas of the brain, particularly massive afferent inputs from the diencephalon and other brain regions of the limbic system; however, PVN^AVP neurons received relatively broader and denser inputs compared to SON^AVP neurons. Additionally, SON^AVP neurons received more projections from the median preoptic nucleus and organum vasculosum of the lamina terminalis (a circumventricular organ), compared to PVN^AVP neurons, while PVN^AVP neurons received more afferent inputs from the bed nucleus of stria terminalis and dorsomedial nucleus of the hypothalamus, both of which are thermoregulatory nuclei, compared to those of SON^AVP neurons. In addition, both SON^AVP and PVN^AVP neurons received direct afferent projections from the bilateral suprachiasmatic nucleus, which is the master regulator of circadian rhythms and is concomitantly responsible for fluctuations in AVP levels. Taken together, our present results provide a comprehensive understanding of the specific afferent framework of AVP neurons both in the SON and PVN, and lay the foundation for further dissecting the diverse roles of SON^AVP and PVN^AVP neurons.

New Animal Data on Osmotic and Hypovolemic Thirst

INTRODUCTION

The group of Yuki Oka, working at Caltech, recently discovered unique populations of neurons in the mouse brain that separately drive osmotic thirst and hypovolemic thirst [<xref ref-type="bibr" rid="ref1">1</xref>]. After eating salty chips, the concentration of salts and minerals in blood becomes elevated which induces a state called osmotic thirst. On the other hand, after exercising and losing water and some electrolytes, a different thirst called hypovolemic thirst occurs since extracellular fluid volume is reduced. Two brain regions have already been defined to be important in drinking behaviors in animals, the subfornical organ and the organum vasculosum of the lamina terminalis.

METHODS

With a technique called single-cell RNA-seq, single cells were found to be involved in specific behavior states, that is, either drinking pure water and avoiding salty water, osmotic thirst, or, appetite for mineral-rich liquids for hypovolemic thirst (Fig. 1).

DISCUSSION/CONCLUSION

Thirst is therefore a multimodal, many ways, 2 or more, of doing things, sensation, activated by 2 different stimuli, osmotic and hypovolemic. Multimodal means having, or using, a variety of modes, or methods to do something. Multimodal teaching is a style in which students learn material through a number of different sensory modalities. For example, a teacher will create a lesson in which students learn through auditory and visual methods. For thirst, the 2 circumventricular sensory group of neurons, that is, the subfornical organ and organum vasculosum of the lamina terminalis, are able to perceive 2 modes of thirst. Other peripheral sensory systems are also characterized by multimodal sensations like taste and olfaction. The fungiform papilla of the anterior tongue involved in water and salt tasting is also described as a complex multimodal sensory organ for taste, tactile, and temperature modalities [<xref ref-type="bibr" rid="ref2">2</xref>]. The instantaneous and simultaneous sensations of taste, touch, and temperature when solid or liquid stimuli contact the tongue tip are necessary for eating and drinking. Oka and his team [<xref ref-type="bibr" rid="ref3">3</xref>] also found that the tongue has a taste for water: applying deionized water to mouse tongues caused specific taste nerves to fire owing to a change in the pH of the saliva as it was diluted by the water. Water is detected only by acid-sensing taste receptor cells (type III cells). The appetitive sodium responses are mediated through the sodium-selective ENaC pathway (type III cells), whereas the rejection of high salt results from the recruitment of the sour- and bitter-taste-sensing pathways (type II cells) [<xref ref-type="bibr" rid="ref4">4</xref>]. It is therefore inferred that our brain senses internal states by using similar strategies.

Distribution of plasma copeptin levels and influence of obesity in children and adolescents

In recent years, a more stable AVP surrogate, called copeptin, has been used as an adjuvant diagnostic tool for dysnatremia in adults and appears to be promising even in the pediatric age. The aim of this study is to present the distribution of plasma copeptin in a large pediatric cohort and to observe the influence of fluid consumption and obesity on its values. A cohort of 128 children and adolescents was divided into two groups on the basis of nocturnal deprivation (group A) or free access to oral fluids in the 6-8 h before blood collection (group B). At all distribution percentiles, copeptin levels were higher (p < 0.0001) in group A, as were plasma sodium levels and osmolality (p = 0.02 and p = 0.008, respectively). The influence of BMI on copeptin levels was investigated by dividing the cohort into nonobese (group C) and obese children and adolescents (group D). Copeptin levels were higher in group D (p = 0.04).Conclusion: The measurement of copeptin could represent a useful tool for the diagnostic pathway of dysnatremic conditions, but its interpretation should take into consideration the state of hydration. Furthermore, it could also be a promising marker for obesity and metabolic syndrome, although this hypothesis needs further studies to be confirmed. What is Known: • Copeptin use as a diagnostic tool in AVP-related disorders, such as diabetes insipidus or syndrome of inappropriate secretion of antidiuretic hormone, is well established in adults • In pediatric age, few studies are available, but the preliminary data, including our previous study, seems to be promising. What is New: • In this study, we represent the distribution of copeptin levels in a pediatric cohort and show the significant influence of fluid ingestion on its plasma levels. • Also BMI seems to be a significant variable on copeptin levels and may be used as an obesity marker in pediatric age.

Adipsic diabetes insipidus

Adipsic diabetes insipidus (ADI) is a rare but devastating disorder of water balance with significant associated morbidity and mortality. Most patients develop the disease as a result of hypothalamic destruction from a variety of underlying etiologies. Damage to osmolar-responsive neuroreceptors, primarily within the supraoptic and paraventricular nuclei, results in impaired production and release of arginine vasopressin (AVP). Important regulating circuits of thirst sense and drive are regionally colocalized with AVP centers and therefore are also injured. Patients with central diabetes insipidus with impaired thirst response, defined as ADI, suffer from wide swings of plasma osmolality resulting in repeated hospitalization, numerous associated comorbidities, and significant mortality. Treatment recommendations are based largely on expert advice from case series owing to the rarity of disease prevalence. Acute disease management focuses on fixed dosing of antidiuretic hormone analogues and calculated prescriptions of obligate daily water intake. Long-term care requires patient/family education, frequent reassessment of clinical and biochemical parameters, as well as screening and treatment of comorbidities.

Cellular, Molecular, and Physiological Adaptations of Hibernation: The Solution to Environmental Challenges

Thriving in times of resource scarcity requires an incredible flexibility of behavioral, physiological, cellular, and molecular functions that must change within a relatively short time. Hibernation is a collection of physiological strategies that allows animals to inhabit inhospitable environments, where they experience extreme thermal challenges and scarcity of food and water. Many different kinds of animals employ hibernation, and there is a spectrum of hibernation phenotypes. Here, we focus on obligatory mammalian hibernators to identify the unique challenges they face and the adaptations that allow hibernators to overcome them. This includes the cellular and molecular strategies used to combat low environmental and body temperatures and lack of food and water. We discuss metabolic, neuronal, and hormonal cues that regulate hibernation and how they are thought to be coordinated by internal clocks. Last, we touch on questions that are left to be addressed in the field of hibernation research. Studies from the last century and more recent work reveal that hibernation is not simply a passive reduction in body temperature and vital parameters but rather an active process seasonally regulated at the molecular, cellular, and organismal levels.

Primary polydipsia: Update

In primary polydipsia pathologically high levels of water intake physiologically lower arginine vasopressin (AVP) secretion, and in this way mirror the secondary polydipsia in diabetes insipidus in which pathologically low levels of AVP (or renal responsiveness to AVP) physiologically increase water intake. Primary polydipsia covers several disorders whose clinical features and significance, risk factors, pathophysiology and treatment are reviewed here. While groupings may appear somewhat arbitrary, they are associated with distinct alterations in physiologic parameters of water balance. The polydipsia is typically unrelated to homeostatic regulation of water intake, but instead reflects non-homeostatic influences. Recent technological advances, summarized here, have disentangled functional neurocircuits underlying both homeostatic and non-homeostatic physiologic influences, which provides an opportunity to better define the mechanisms of the disorders. We summarize this recent literature, highlighting hypothalamic circuitry that appears most clearly positioned to contribute to primary polydipsia. The life-threatening water imbalance in psychotic disorders is caused by an anterior hippocampal induced stress-diathesis that can be reproduced in animal models, and involves phylogenetically preserved pathways that appear likely to include one or more of these circuits. Ongoing translational neuroscience studies in these animal models may potentially localize reversible pathological changes which contribute to both the water imbalance and psychotic disorder.

Individual differences in biological regulation: Predicting vulnerability to drug addiction, obesity, and other dysregulatory disorders

Physiological regulation is so fundamental to survival that natural selection has greatly favored the evolution of robust regulatory systems that use both reactive and preemptive responses to mitigate the disruptive impact of biological and environmental challenges on physiological function. In good health, robust regulatory systems provide little insight into the typically hidden complex array of sensor-effector interactions that accomplish successful regulation. Numerous health disorders have been traced to defective regulatory mechanisms, and generations of scientists have worked to discover ways to correct these defects and restore normal physiological function. Despite progress, numerous chronic health disorders remain resistant to treatment, and indeed for some disorders the incidence is increasing. We propose that an individual's susceptibility to acquire certain persistent dysregulatory disorders can be traced to interindividual variation in how that individual's regulatory system responds to challenges. Preexisting reliable individual differences among regulatory systems are typically unrecognized until appropriate regulatory challenges (e.g., exposure to a drug of abuse) lead to dysregulation (e.g., drug addiction). Specific characteristics of an individual's regulatory responsiveness may include etiological factors that participate in the acquisition, escalation and maintenance of health disorders characterized by dysregulation. By appropriately challenging a healthy individual's regulatory systems to identify its underlying characteristics, it is possible to ascertain whether an individual has an elevated risk for acquiring a dysregulated health condition and thereby enable strategies designed to prevent, rather than treat, the condition. This model is applied to drug addiction, and in addition we relate this approach to other dysregulated conditions such as obesity. (PsycInfo Database Record (c) 2020 APA, all rights reserved).

Antidiuretic Hormone and Serum Osmolarity Physiology and Related Outcomes: What Is Old, What Is New, and What Is Unknown?

CONTEXT

Although the physiology of sodium, water, and arginine vasopressin (AVP), also known as antidiuretic hormone, has long been known, accumulating data suggest that this system operates as a more complex network than previously thought.

EVIDENCE ACQUISITION

English-language basic science and clinical studies of AVP and osmolarity on the development of kidney and cardiovascular disease and overall outcomes.

EVIDENCE SYNTHESIS

Apart from osmoreceptors and hypovolemia, AVP secretion is modified by novel factors such as tongue acid-sensing taste receptor cells and brain median preoptic nucleus neurons. Moreover, pharyngeal, esophageal, and/or gastric sensors and gut microbiota modulate AVP secretion. Evidence is accumulating that increased osmolarity, AVP, copeptin, and dehydration are all associated with worse outcomes in chronic disease states such as chronic kidney disease (CKD), diabetes, and heart failure. On the basis of these pathophysiological relationships, an AVP receptor 2 blocker is now licensed for CKD related to polycystic kidney disease.

CONCLUSION

From a therapeutic perspective, fluid intake may be associated with increased AVP secretion if it is driven by loss of urine concentration capacity or with suppressed AVP if it is driven by voluntary fluid intake. In the current review, we summarize the literature on the relationship between elevated osmolarity, AVP, copeptin, and dehydration with renal and cardiovascular outcomes and underlying classical and novel pathophysiologic pathways. We also review recent unexpected and contrasting findings regarding AVP physiology in an attempt to explain and understand some of these relationships.

Menthol chewing gum on preoperative thirst management: randomized clinical trial

Objective

to evaluate the effectiveness of menthol chewing gum, in the relief of the intensity and discomfort of the surgical patient’s thirst in the preoperative period.

Method

a randomized controlled trial, with 102 patients in the preoperative period, randomized in a control group, with usual care, and an experimental group, which received menthol gum, which was the study treatment variable. The primary clinical outcome was the variation in thirst intensity, evaluated by the Numeral Verbal Scale, and the secondary, the variation of the discomfort of thirst, evaluated by the Perioperative Thirst Discomfort Scale. Mann-Whitney test was used to compare measures between groups. The significance level adopted was of 0.05.

Results

menthol chewing gum significantly reduced the intensity (p <0.001), with Cohen’s medium-effect d, and thirst discomfort (p <0.001), with a large-effect Cohen’s d.

Conclusion

menthol chewing gum was effective in reducing the intensity and discomfort of preoperative thirst. The strategy proved to be an innovative, feasible and safe option in the use for the surgical patient, in the management of the preoperative thirst, in elective surgeries. NCT: 03200197.

Adipsic Diabetes Insipidus-The Challenging Combination of Polyuria and Adipsia: A Case Report and Review of Literature

Adipsic Diabetes Insipidus is a rare hypothalamic disorder characterized by a loss of thirst in response to hypernatraemia accompanied by diabetes insipidus. These occur secondary to a congregation of defects in the homeostatic mechanisms of water balance. A 27-year old Chinese female presented with Adipsic Diabetes Insipidus after cerebral arteriovenous malformation (AVM) surgery. Initial diagnosis and management was extremely challenging. Long term management required a careful interplay between low dose vasopressin analog treatment and fluids. Detailed charts of medication and sodium balance are described in the case presentation. We performed a literature search of similarly reported cases and describe the possible pathogenesis, etiology, clinical presentation, acute and chronic management, and prognosis.