Vasopressin Release Research Articles

Arginine vasopressin deficiency (central diabetes insipidus) with partial empty sella: a case report

BackgroundArginine vasopressin deficiency (central diabetes insipidus) is defined as a reduction in the release of arginine vasopressin (AVP) resulting in a variable degree of polyuria. Partial empty sella refers to an enlarged sella turcica that is not completely filled by pituitary gland. It can be either primary or secondary and its manifestation ranges from asymptomatic cases to isolated posterior pituitary, isolated anterior pituitary or both anterior and posterior pituitary dysfunctions. Diabetes insipidus caused by a partially empty sella is rare.Case presentationThe patient, an 18-year-old Ethiopian woman who presented with long standing headache, increased urination, increased thirst, absence of menses and weight loss. Urine and serum osmolality was done and suggested diabetes insipidus. On further workup, brain magnetic resonant imaging was done and partially empty sella was diagnosed.ConclusionDiabetes insipidus secondary to partially empty sella is uncommon. In patients presenting with headache and anterior or posterior pituitary dysfunction, empty sella should be considered, whether partial or complete.

8431 Triphasic response of pituitary stalk post anoxic injury in a mechanically ventilated patient

Abstract Disclosure: P. Henriquez Feliz: None. H. Neizer: None. E. Alshdifat: None. F. Abdulkarim: None. T. Mazhude: None. T. Zahra: None. Introduction: A phenomenon may manifest wherein the pituitary undergoes a triphasic response following an inciting event. Phases include diabetes insipidus (DI) followed by Syndrome of inappropriate Antidiuretic Hormone (ADH), and finally a recurrence of DI. Research has established that this is a common complication to neurosurgical interventions but there are limited reports following anoxic brain injury. This case demonstrates a potential pituitary stalk injury after an anoxic brain injury. Case: Unknown 30 year old male found by EMS with pulseless electrical activity cardiac arrest likely from polysubstance use. Returned of spontaneous circulation after 30 minutes in the emergency department. Total downtime unknown. Managed by Intensive Care Unit. Scans were negative. Initial blood work showed eunatremia with a specific gravity (sg) 1.068 and serum osmolarity (Sosm) 311. Eventually, developed hypernatremia, 163 mmol/L, and a urine osmolarity (Uosm) of 428 mosm, raising concern for central DI (CDI). Responded to hypotonic fluids not requiring desmopressin at that time. On day 10, developed severe hyponatremia 113 mmol/L with a Uosm of 774, suggesting ADH mediated response or excessive free water intake. Sodium normalized after managed with fluid restriction. On day 16, patient developed hypernatremia, 178 mmol/L, and Uosm of 869 mosm. Suggestive of CDI recurrence. Treated with desmopressin and hydrocortisone. Discussion: Changes in water-electrolyte balances may occur after anoxic brain injury. The mechanism is believed to arise from axonal shock due to disruptions in vascular supply leading to unregulated release of ADH from degenerating posterior pituitary, causing oliguria and hyponatremia, and subsequent permanent DI from loss of neurons. These stages may last 5-7 days on initial phase, and the second phase can extend anywhere from 2-14 days. In this case, phases one and two lasted four and three days, respectively. It is important to acknowledge that timelines may vary based on management initiation and recognition of transition between stages. CDI treatment involves hypotonic fluids with desmopressin. Our patient was initially managed with free water due to low suspicion for CDI. During shift towards suspected second phase, Uosm increased, urine output and sodium dropped significantly. However, it is uncertain whether this was due to axonal injury causing SIADH or a consequence of hypotonic fluids causing increased response of ADH. As predicted during triphasic response, patient became oliguric with a net negative fluid balance of >10L and Uosm of 869. Therefore, desmopressin was started with good response. Further follow up was unattainable as neurological status deteriorated preceding to brain death. Most cases reported showed hypoattenuation lesion of posterior pituitary on MRI; MRI would have been required to determine if there was injury to the pituitary in this case. Presentation: 6/2/2024

8067 AVP Gene Mutation: A Rare Cause of Diabetes Insipidus

Abstract Disclosure: N. Navrange: None. M. Williams: None. P. Madhavan: None. Introduction: Arginine vasopressin deficiency (AVP-D), also known as neurohypophyseal or central diabetes insipidus (DI), is marked by a reduced secretion of arginine vasopressin (AVP), resulting in polyuria and polydipsia. AVP-D is a rare disorder, with a prevalence of 1 in 25,000. Typically, the disorder is acquired. However, in less than 5% of cases, it has a genetic etiology. The majority of mutations in the AVP gene are autosomal dominant. Normally, AVP encodes vasopressin, also known as antidiuretic hormone (ADH). It plays a key role in the reabsorption of water in the kidney, the regulation of blood pressure, and controlling the body’s osmotic balance. However, a mutation in this gene leads to a deficient release of ADH, leading to reduced reabsorption of water in the collecting duct and decreased ability to concentrate urine. This results in increased urine output and excessive thirst. The onset and severity of symptoms varies between individuals. Case Report: In this report, we discuss the case of a 40-year-old Caucasian female with familial neurohypophyseal diabetes insipidus. The patient presented to the clinic for follow-up care of DI and hyponatremia. She received her DI diagnosis before the age of 5 and has multiple family members with the condition including her maternal grandfather, mother, and 2 siblings. Additionally, she suspected one of her children was exhibiting excessive urination. Past medical history is also significant for seizure disorder, postpartum cardiomyopathy, Chiari malformation type I and remote history of substance abuse. Vitals were stable with blood pressure of 122/86 mmHg, heart rate of 93 bpm, body mass index of 31.8. Physical exam was unremarkable except for obesity. She is currently managed with DDAVP 0.05 mg twice daily. Previously, imaging was performed to rule out pituitary abnormalities. The patient was referred for genetic testing due to her family history and was found to have a previously described rare autosomal dominant mutation of the AVP protein. The single nucleotide polymorphism in exon 1 results in a missense mutation substituting an alanine nucleotide for threonine (c.55G>A). The patient was counseled to share these results with her children’s pediatrician, as they could benefit from testing for the mutation. Discussion: Our patient has a pathogenic variant in AVP, specifically a missense mutation from Alanine to Threonine at codon 19 of the AVP protein. This mutation is associated with autosomal dominant neurohypophyseal diabetes insipidus. This case provides an example of a rare cause of neurohypophyseal diabetes insipidus and emphasizes the necessity of obtaining detailed family history in patients who have DI and considering genetic testing for patients with suspicion for familial involvement. Presentation: 6/2/2024

O98 NEW APPROACHES TARGETING THE RENIN-ANGIOTENSIN SYSTEM: BRAIN ACE2 ACTIVATION FOLLOWING BRAIN AMINOPEPTIDASE A BLOCKADE BY FIRIBASTAT IN SALT-DEPENDENT HYPERTENSION

Background and Objective: In the brain, aminopeptidase A (APA), a membrane-bound zinc metalloprotease, generates angiotensin III from angiotensin II. Brain angiotensin III exerts a tonic stimulatory effect on the control of blood pressure (BP) in hypertensive rats and increases vasopressin release. Blocking brain angiotensin III formation by the APA inhibitor prodrug RB150/firibastat normalizes arterial BP in hypertensive deoxycorticosterone acetate (DOCA)-salt rats. Ang II and Ang III have similar affinities for AT1 receptors and blocking brain AngIII formation by RB150 decreases arterial BP without inducing Ang II accumulation. Methods: We therefore hypothesized that another metabolic pathway of brain angiotensin II, such as the conversion of angiotensin II into angiotensin 1-7 (Ang 1-7) by angiotensin-converting enzyme 2 (ACE2) might be activated following brain APA inhibition. To answer this question, we use surgical animal models that could allow us to monitor awake blood pressure responses to intracerebroventricular (icv) injections and measure enzymatic activity. Results: We found that the intracerebroventricular administration of RB150/firibastat in conscious DOCA-salt rats both inhibited brain APA activity and induced an increase in brain ACE2 activity. Then, we showed that the decreases in BP and vasopressin release resulting from brain APA inhibition with RB150/firibastat were reduced if ACE2 was concomitantly inhibited by MLN4760, a potent ACE2 inhibitor, or if the Mas receptor (MasR) was blocked by A779, a MasR antagonist. Conclusions: Our findings suggest that in the brain, the increase in ACE2 activity resulting from APA inhibition by RB150/firibastat treatment, subsequently increasing Ang 1-7 and activating the MasR while blocking angiotensin III formation, contributes to the antihypertensive effect and the decrease in vasopressin release induced by RB150/firibastat. RB150/firibastat treatment constitutes an interesting therapeutic approach to improve BP control in hypertensive patients by inducing in the brain renin-angiotensin system, hyperactivity of the beneficial ACE2/Ang 1-7/MasR axis while decreasing that of the deleterious APA/Ang II/Ang III/ATI receptor axis.

Circadian copeptin and oxytocin profiles in anorexia nervosa: Exploring the interplay with neurohypophysis opioid tone.

Neurohypophysis (NH) function in eating disorders (ED) remains poorly elucidated. Studies on vasopressin and oxytocin display inconclusive findings regarding their levels and associations with psychological complications in ED. The profile of opioid tone, a crucial NH activity regulator, is also unknown. To characterise the circadian profile of NH hormones and NH opioid tone using positron emission tomography/MRI (PET/MRI) imaging in patients with ED compared to healthy controls. Twelve-point plasma circadian profiles of copeptin and oxytocin, alongside nutritional and psychological scores, were assessed in age-matched female participants: 13 patients with anorexia nervosa restrictive-type (ANR), 12 patients recovered from AN (ANrec), 14 patients with bulimia nervosa and 12 controls. Neurohypophysis PET/MRI [11C] diprenorphin binding potential (BPND) was evaluated in AN, ANrec and controls. Results revealed lower copeptin circadian levels in both ANR and ANrec compared to controls, with no oxytocin differences. Bulimia nervosa exhibited elevated copeptin and low oxytocin levels. [11C] diprenorphin pituitary binding was fully localised in NH. Anorexia nervosa restrictive-type displayed lower NH [11C] diprenorphin BPND (indicating higher opioid tone) and volume than controls. In ANR, copeptin inversely correlated with osmolarity. Neurohypophysis [11C] diprenorphin BPND did not correlated with copeptin or oxytocin. Copeptin demonstrated significant group differences, highlighting its potential diagnostic and prognostic value. Oxytocin levels exhibited conflicting results, questioning the reliability of peripheral blood assessment. Increased NH opioid tone in anorexia nervosa may influence the vasopressin or oxytocin release, suggesting potential therapeutic applications.

Arginine vasopressin activates serotonergic neurons in the dorsal raphe nucleus during neonatal development in vitro and in vivo

Birth stress is a risk factor for psychiatric disorders and associated with exaggerated release of the stress hormone arginine vasopressin (AVP) into circulation and in the brain. In perinatal hippocampus, AVP activates GABAergic interneurons which leads to suppression of spontaneous network events and suggests a protective function of AVP on cortical networks during birth. However, the role of AVP in developing subcortical networks is not known. Here we tested the effect of AVP on the dorsal raphe nucleus (DRN) 5-hydroxytryptamine (5-HT, serotonin) system in male and female neonatal rats, since early 5-HT homeostasis is critical for the development of cortical brain regions and emotional behaviors. We show that AVP is strongly excitatory in neonatal DRN: it increases excitatory synaptic inputs of 5-HT neurons via V1A receptors in vitro and promotes their action potential firing through a combination of its effect on glutamatergic synaptic transmission and a direct effect on the excitability of these neurons. Furthermore, we identified two major firing patterns of neonatal 5-HT neurons in vivo, tonic regular firing and low frequency oscillations of regular spike trains and confirmed that these neurons are also activated by AVP in vivo. Finally, we show that the sparse vasopressinergic innervation in neonatal DRN originates exclusively from cell groups in medial amygdala and bed nucleus of stria terminalis. Hyperactivation of the neonatal 5-HT system by AVP during birth stress may impact its own functional development and affect the maturation of cortical target regions, which may increase the risk for psychiatric conditions later on.

Sodium-Glucose Cotransporter 2 Inhibitor Combined with Conventional Diuretics Ameliorate Body Fluid Retention without Excessive Plasma Volume Reduction.

We previously reported that sodium-glucose cotransporter 2 (SGLT2) inhibitors exert sustained fluid homeostatic actions through compensatory increases in osmotic diuresis-induced vasopressin secretion and fluid intake. However, SGLT2 inhibitors alone do not produce durable amelioration of fluid retention. In this study, we examined the comparative effects of the SGLT2 inhibitor dapagliflozin (SGLT2i group, n = 53) and the combined use of dapagliflozin and conventional diuretics, including loop diuretics and/or thiazides (SGLT2i + diuretic group, n = 23), on serum copeptin, a stable, sensitive, and simple surrogate marker of vasopressin release and body fluid status. After six months of treatment, the change in copeptin was significantly lower in the SGLT2i + diuretic group than in the SGLT2i group (-1.4 ± 31.5% vs. 31.5 ± 56.3%, p = 0.0153). The change in the estimated plasma volume calculated using the Strauss formula was not significantly different between the two groups. Contrastingly, changes in interstitial fluid, extracellular water, intracellular water, and total body water were significantly lower in the SGLT2i + diuretic group than in the SGLT2i group. Changes in renin, aldosterone, and absolute epinephrine levels were not significantly different between the two groups. In conclusion, the combined use of the SGLT2 inhibitor dapagliflozin and conventional diuretics inhibited the increase in copeptin levels and remarkably ameliorated fluid retention without excessively reducing plasma volume and activating the renin-angiotensin-aldosterone and sympathetic nervous systems.

Tumor Necrosis Factor-alpha (TNFα) receptor type 1 (TNFR1) activation during severe inflammation; Can it be a therapeutic target in hypervolemic hyponatremia?

Hyponatremia is a life-threatening situation in severe inflammatory disorders. Managing this disorder is seriously hampered because its underlying pathophysiology has remained elusive. An increase in tumor necrosis factor-alpha (TNFα) during systemic inflammation may be involved in this hyponatremic mechanism as it is known that circulating TNFα exerts potent natriuresis via its action on receptor type 1 (TNFR1). Systemic inflammation also induces non-osmotic release of Antidiuretic Hormone (ADH), commonly known as ‘Syndrome of Inappropriate ADH’ (SIADH), that would cause water retention to increase in Extracellular Fluid Volume (ECV). Thus, the inflammation-induced TNFR1 activation and sodium loss coupled with SIADH-induced increases in ECV, would lead to the serious condition of hypervolemic hyponatremia. In this brief review, some experimental evidence will be provided that indicates TNFR1 activation during the inflammatory process can be targeted therapeutically to prevent such critical conditions of hypervolemic hyponatremia. The importance of these co-morbidities also extends to several other clinical scenarios of hyponatremia observed in patients with heart failure, liver disease, and renal disease. Besides the pathophysiological insights, the recognition of the propensity for both antidiuresis and natriuresis during inflammation is critically important in selecting the appropriate intravenous fluid regimens in patients with this disorder such as in the coronavirus disease of 2019 (COVID-19).

Central Inhibition of Antidiuretic Hormone by the Kappa Opioid Receptor Agonist Nalfurafine Prevents and Reverses Loop Diuretic Resistance

PURPOSE: Diuretic resistance is a failure to achieve a therapeutically desired increase in the renal excretion of sodium and water and reduction in edema despite a full dose of a loop diuretic. High levels of antidiuretic hormone (ADH) have been associated with reduced urine output in heart failure patients. However, ADH’s contribution to the development of diuretic resistance is not known. Assuming that ADH may be released in response to the diuresis produced by loop diuretics, we tested the premise that co-treatment of rats with nalfurafine, a centrally acting kappa opioid (KOR) agonist that inhibits the release of ADH would prevent and/or reverse diuretic resistance to the loop diuretic furosemide. METHODS: Changes in 5-hr urine output (metabolic cages; no water access during collection), urinary Na/K excretion, and osmolality were measured in male Sprague-Dawley rats administered twice-daily i.p. injections (9:00am, 2:00pm; n=6/group) for 11 days with 1) furosemide only (F, 10mg/kg, i.p.; days 1-11), 2) furosemide + nalfurafine (F+N, 10ug/kg, i.p.; days 1-11) or 3) F (days 1-5) followed by F+N (days 6-11). 5-hr urine collection was measured in between the morning and afternoon drug injections and rats were returned to home cages. Control 5-hr urine samples (saline, i.p.) were collected 2 days prior to beginning drug treatments. SUMMARY: Initial treatment (day 1) of rats with F alone and F+N markedly increased urine output. However, over days 6-10, urine output was significantly reduced (diuretic resistance) in rats that continued to receive F alone. Daily co-treatment of F+N beginning day 1 maintained a marked 5-hrdiuresis for all 11 days. Further, delaying addition of nalfurafine co-administration with F until day 6 reversed established diuretic resistance as noted by a marked increase in diuresis over days 6-10 with F+N cotreatment. Initial treatment (day 1) of rats with furosemide also produced a marked natriuresis and kaliuresis. However, on subsequent days (2-11) there was a significant decrease in the renal excretion of sodium and potassium that remained lower in all 3 treatment groups. In contrast, nalfurafine co-treatment beginning either day 1 (Group 2) or day 6 (Group 3) increased free-water clearance as compared to furosemide alone (Group 1). CONCLUSIONS: These results demonstrate that co-administration of the KOR agonist nalfurafine prevented and reversed diuretic resistance to furosemide without worsening electrolyte excretion. Further, these findings support the premise that in response to fluid loss caused by repeated loop diuretic administration, a compensatory release and renal action of ADH plays an important role in mediating loop diuretic resistance. NIH P30GM106392 (DK) LSUHSC REP243 (DK). This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Investigating the role of local acidosis in hypothalamic vasopressin cell excitation during hypoxia

The supraoptic nucleus (SON) of the hypothalamus plays a key role in the regulation of fluid homeostasis through the synthesis and release of vasopressin (VP). In this population, VP release can occur at both dendritic and axonal sites, allowing for both localized and distal effects such as renal water retention and vasoconstriction. Recent work from our laboratory demonstrated an inverse neurovascular coupling (iNVC) response in which VP cell activation by acute salt loading resulted in dendritic release of VP, leading to localized vasoconstriction and hypoxia. Additionally, we demonstrated that the hypoxic milieu in turn potentiates VP cell activity and increases firing, suggesting that these mechanism constitutes a positive feedback loop that optimized VP activation in order to cope with the homeostatic challenge (Roy et al., Cell Reports 2021). Still, the biophysical mechanism by which the iNVC-hypoxia elicits increased firing in VP neurons has not yet been explored. We hypothesized that hypoxia-induced acidosis, via activation of acid sensitive ion channels (ASICs) (which are present in SON VP neurons; Ohbuchi et al in 2010) is a key mechanism contributing to VP cell excitation in the iNVC positive feedback loop. We investigated this with whole cell patch clamp electrophysiology using eGFP-VP transgenic rats. We recorded from identified SON VP cells and measured deflections in voltage as bath pH was changed from 7.25 to 6.3 (10 mins). Bath solution was either HCL-buffered artificial cerebrospinal fluid (aCSF) aerated with 95% O2/5% CO2 or HEPES-buffered solution (HBS). We observed an excitatory response to the decreases in pH in most SON VP cells recorded (68.75%, n = 11/16). These responses were reversible and, in many cases, repeatable following a second stimulation. To examine cell-type specificity, ongoing studies are focusing on comparing these responses to those obtained from oxytocin cells. Further, we plan to repeat these experiments in the presence of the ASIC-blocker amiloride and determine whether the hypoxia-induced excitatory effect during iNVC is indeed dependent on ASIC-channels. Together, our results support our hypothesis that tissue acidosis (likely via activation of ASIC-channels) contributes to the excitatory feedback loop evoked during salt-induced iNVC in VP neurons. This abstract was supported by the National Heart Lung and Blood Institute of the National Institutes of Health [R01 HL162575-01 (J.E.S.)]. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

WNK1 is a central osmolality sensor for arginine vasopressin release and acts through the OSR1/SPAK kinase cascade

Background: Maintaining internal osmolality constancy and water homeostasis is essential for life. The circumventricular organs (CVOs) of the brain, including the organum vasculosum of the lamina terminalis (OVLT) and subfornical organ (SFO), lack a blood-brain barrier. Neurons in OVLT and SFO detect increases in serum osmolality that stimulate the production of vasopressin (AVP) in paraventricular nuclei (PVN) to be released in the posterior pituitary. We have recently reported that WNK1 in sensory neurons in CVOs functions as an osmolality sensor for AVP release (Jin et al., JCI, 2023). WNK1 activates Kv3.1 to increase action potential, traveling down to PVN to increase AVP synthesis for release from the posterior pituitary. Here, we propose that OSR1/SPAK acts as the downstream kinase for WNK1 in regulating AVP release. We further investigated the regulation of vasopressin release by the WNK1-OSR1/SPAK cascade in response to extracellular hyperosmolality. Methods: Cre recombinase-carrying retrograde AAV virus was stereotaxically injected into PVN nuclei from normal mice and SPAK-null mice with a homozygous OSR1-floxed allele (SAPK−/−;OSR1flox/flox). Metabolic cage studies were performed on mice. Urine output, water intake, serum osmolality, serum AVP, and copeptin levels were measured. K+ currents were measured from the OVLT neurons by whole-cell patch clamp. Results: Increased osmolality, either by water restriction or mannitol injection, activated OSR1/SPAK in OVLT, as evident by increased serine-373 phospho-SPAK and serine-325 phospho-OSR. Like the WNK1 deletion, the double deletion of OSR/SPAK in OVLT caused polyuria with decreased urine osmolality that persisted in water restriction. Circulating levels of AVP and copeptin were increased by water restriction in control mice. In contrast, water restriction failed to increase the levels in OSR/SPAK-deletion mice. Knockdown of the Kv3.1 channel in OVLT by shRNA showed the central diabetes insipidus (DI) phenotype as well. Hypertonicity increased K+ currents and WNKs inhibitor prevented the increase in OVLT neurons. Conclusions: Mice with neuronal-specific OSR1/SPAK deletion have water homeostasis defects consistent with partial central DI; Evidence supporting that OSR1/SPAK acts downstream of WNK1 to regulate AVP release; WNK1-OSR1/SPAK activates Kv3.1 to increase firing frequency of neurons projecting from CVOs to PVN. Our findings reveal that an intracellular protein acts as a sensor for extracellular tonicity and provide fresh insights into the mechanisms by which the body maintains osmolality constancy. Future studies will investigate how OSR1/SPAK regulates Kv3.1 channels. NIDDK. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Lysine Acetylation of Aquaporin-3 in Renal Principal Cell Mediates Water Homeostasis

The kidneys function to maintain water homeostasis. High plasma osmolality activates the release of the antidiuretic hormone vasopressin (AVP), which acts on the kidneys through its receptor AVPR2 on the principal cell (PC) to increase apical aquaporin-2 (AQP2) and basolateral AQP3 abundance for enhanced water reabsorption. However, unlike AQP2, the regulation mechanism(s) of AQP3 is unclear. We previously identified a novel AQP3 post-translational modification: acetylation of lysine 282 (K282), which we hypothesize to positively regulate PC water permeability. We developed mouse models of acetylated AQP3 by mutating K282 to glutamine (K282Q; Q mutant) and deacetylated AQP3 by mutating K282 to arginine (K282R; R mutant), on C57BL/6J background to determine the functional consequences of lysine acetylated AQP3. Male and female mice (10-15 weeks old) received a standard chow diet and free access to water. We first investigated the responses to endogenous AVPR2 activation by subjecting the mice to 18-hr overnight water deprivation and compared to mice with ad libitum water access (ad lib). All dehydrated mice (males WT 3087 ± 291 mOsm/kg, n = 8; Q 3688 ± 113 mOsm/kg, n = 6; R 3447 ± 171 mOsm/kg, n = 11; females WT 3393 ± 266 mOsm/kg, n = 8; Q 3586 ± 206 mOsm/kg, n = 9; R 3749 ± 126 mOsm/kg, n = 10) had higher urine osmolality than ad lib mice (males WT 2409 ± 165 mOsm/kg, n = 8; Q 2428 ± 316 mOsm/kg, n = 7; R 1960 ± 196 mOsm/kg, n = 7; females WT 2281 ± 96 mOsm/kg, n = 8; Q 1935 ± 190 mOsm/kg, n = 11; R 2279 ± 249, n = 7, two-way ANOVA p[treatment] <0.0001 for both sexes). However, there were no significant differences among the genotypes in both sexes [two-way ANOVA p[sex] > 0.05). For plasma osmolality, all dehydrated mice in both sexes (males WT 332 ± 2 mOsm/kg, n = 10; Q 324 ± 2 mOsm/kg, n = 8; R 323 ± 2 mOsm/kg n = 11; females WT 316 ± 3 mOsm/kg, n =10; Q 320 ± 2 mOsm/kg, n = 10; R 308 ± 3 mOsm/kg, n = 11) had higher values than ad lib mice (males WT 314 ± 3 mOsm/kg, n = 10; Q 309 ± 1 mOsm/kg, n = 9; R 313 ± 3 mOsm/kg n = 10; females WT 312 ± 2 mOsm/kg, n =11; Q 305 ± 2 mOsm/kg, n = 11; R 301 ± 4 mOsm/kg, n = 10, 2-way ANOVA p[treatment] < 0.0001 for males and = 0.0006 for females). Female R mutants had lower plasma osmolality than WTs and Q in both ad lib and dehydrated groups (2-way ANOVA p[genotype] = 0.0045). In males, compared to WTs, Q and R mutants had similar plasma osmolality in the ad lib but lower in dehydrated group (2-way ANOVA p[genotype] = 0.0359). This suggests that deacetylated AQP3 may result in a reset osmostat, although this remains to be explored further. We next compared the responses of WT and Q mutants to 4-hour exogenous AVPR2 activation by dDAVP (10 ng, i.p). Q females exhibited lower plasma osmolality than WT females (286 ± 4 vs. 305 ± 2 mOsm/kg, n = 11 for both, Student’s t-test p = 0.0005) suggesting lysine acetylation of AQP3 leads to acute enhancement of water permeability. However, there were no significant differences between Q and WT males (300 ± 5 (n = 7) vs. 303 ± 2 mOsm/kg (n = 8), Student’s t-test p > 0.05). Therefore, we conclude that lysine acetylation of AQP3 contributes to renal PC water permeability and this may be sex-dependent. Thus, acetylated AQP3 is a novel mechanism to maintain water homeostasis. R01DK128001. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Characterisation of a Novel Osmosensitive Pathway from the Supraoptic Nucleus to the Median Preoptic Nucleus

The Supraoptic Nucleus (SON) is well regarded for the neuroendocrine release of vasopressin and oxytocin through the posterior pituitary gland. Evidence also exists for extra-pituitary efferent projections of SON neurons, mainly collaterals to the lateral hypothalamus and central amygdala. The objective of this study was to examine the existence of a central SON projection to the median preoptic nucleus (MnPO) of the hypothalamus. Microinjections of the retrograde tracer Cholera Toxin B Subunit (CTb) into the MnPO of male Wistar rats (n = 3) retrogradely labelled SON neurons. Fluorescence immunohistochemistry revealed equal involvement of vasopressin (AVP) and oxytocin (OXT) — producing SON neurons (n = 107 AVP+/CTb+, n = 110 OXT+/ CTb+, n = 417 total CTb+ neurons). This major collateral projection was also examined in an animal model of Polycystic Kidney Disease, the Lewis Polycystic Kidney (LPK) rat (n = 3 animals; n = 104 AVP+/CTb+, n = 41 OXT+/CTb+, n = 372 total CTb+ neurons) and its healthy Lewis control (n = 3 animals; n = 115 AVP+/CTb+, n = 100 OXT+/CTb+, n = 430 total CTb+ neurons). Although the function of this projection is currently unclear, preliminary data in a subset of LPKs shows these SON neurons with MnPO collateral projections are activated by osmotic stressors (e.g., hypertonic saline). In summary, we report a major collateral projection from the SON to MnPO that is activated by osmotic stress. Given the well-known role of the MnPO in drinking behaviour, we suggest this SON-MnPO circuit may be involved in the coordination of fluid regulation and drinking behaviour. This project was funded by Macquarie University. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Mitochondria Regulate Spatiotemporal Ca2+ Dynamics Between Cellular Compartments Affecting the Intrinsic Excitability of Vasopressin Neurons

Calcium (Ca2+) is a critical secondary messenger in all neurons that coordinates important mechanisms of cell physiology. In vasopressin (VP) neurons of supraoptic nucleus (SON) it’s required for somatodendritic release of VP and the slow afterhyperpolarization (sAHP), both of which coordinate neuronal output and thus control stimulus-secretion coupling. Recently, our lab demonstrated that VP sAHPs require endoplasmic reticulum (ER) Ca2+ for activation and that mitochondrial Ca2+ buffering shapes the spatiotemporal trajectory. We also have recent data demonstrating electrotonic segregation between cell compartments. Given the Ca2+ dependence of somatodendritic release and sAHPs, delineation of somatodendritic release from axonal release, and the decoupling of somatic and dendritic electrontonic properties, we hypothesized that calcium dynamics also may be compartmentally segregated as well. Utilizing patch clamp electrophysiology, live calcium imaging, and focal UV uncaging, we probed the spatiotemporal trajectory of rapidly evoked Ca2+ responses in VP neuron somas and dendrites with corresponding membrane potential. UV Ca2+ uncaging at the soma evokes a membrane sAHP and robust increase in cytosolic Ca2+ that propagates into the dendrites. Conversely, Ca2+ uncaged in dendrites propagates bidirectionally from the UV flash but does not penetrate the soma; no membrane hyperpolarization was observed under these conditions. Disabling mitochondrial Ca2+ buffering with Ru360 in the pipette amplifies Ca2+ signasl and sAHPs in somas and dendrites; Ca2+ uncaging in dendrites penetrates soma and can evoke sAHPs under these circumstances. Together, these results suggest that under normal conditions, Ca2+ movement between compartments in VP neurons is unidirectional (soma to dendrite), and that sAHP channels require somatic Ca2+ increases. Moreover, Ca2+ uptake by mitochondria is a critical mechanism that tightly controls the magnitude and progagation of dendritic Ca2+ signals between dendritic and somatic compartments, thus playing an important role in regulating intrinsic mechanisms and ultimately, their neuronal output. NIH K99HL168434 (M.K.K.); R01 HL162575-01 (J.E.S.). This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

A case of hyponatraemia cured by delivery

Hyponatraemia is the most common electrolyte abnormality in pregnancy. In severe cases, it can result in significant maternal and fetal morbidity and mortality. The prevalence of hyponatraemia in pregnancy has been estimated to be 0.27%, with the major causes being hyperemesis gravidarum in the first half and preeclampsia in the latter half of pregnancy. Pregnancy-specific causes of the syndrome of inappropriate antidiuretic hormone release include preeclampsia, prolonged labour, caesarean section, postpartum haemorrhage, cortisol deficiency and oxytocin. Excess water intake can also lead to hyponatraemia during labour, a period of excess antidiuretic hormone secretion. A case of idiopathic severe hyponatraemia with biochemistry consistent with inappropriate antidiuretic hormone secretion progressing during the third trimester with rapid spontaneous resolution post-partum is presented.

Brain sodium sensing for regulation of thirst, salt appetite, and blood pressure.

The brain possesses intricate mechanisms for monitoring sodium (Na) levels in body fluids. During prolonged dehydration, the brain detects variations in body fluids and produces sensations of thirst and aversions to salty tastes. At the core of these processes Nax , the brain's Na sensor, exists. Specialized neural nuclei, namely the subfornical organ (SFO) and organum vasculosum of the lamina terminalis (OVLT), which lack the blood-brain barrier, play pivotal roles. Within the glia enveloping the neurons in these regions, Nax collaborates with Na+ /K+ -ATPase and glycolytic enzymes to drive glycolysis in response to elevated Na levels. Lactate released from these glia cells activates nearby inhibitory neurons. The SFO hosts distinct types of angiotensin II-sensitive neurons encoding thirst and salt appetite, respectively. During dehydration, Nax -activated inhibitory neurons suppress salt-appetite neuron's activity, whereas salt deficiency reduces thirst neuron's activity through cholecystokinin. Prolonged dehydration increases the Na sensitivity of Nax via increased endothelin expression in the SFO. So far, patients with essential hypernatremia have been reported to lose thirst and antidiuretic hormone release due to Nax -targeting autoantibodies. Inflammation in the SFO underlies the symptoms. Furthermore, Nax activation in the OVLT, driven by Na retention, stimulates the sympathetic nervous system via acid-sensing ion channels, contributing to a blood pressure elevation.

The Relationship of Cortisol Levels and Sleep Quality in Acute Ischemic Stroke Patients: A Literature Review

Hormonal factors are one of several elements that contribute to the process by which patients with acute ischemic stroke experience poor sleep quality. The hypothalamic-pituitary-adrenal (HPA) axis is responsible for producing the hormone cortisol. When the hypothalamus is activated, it releases vasopressin and Corticotropin Releasing Hormone (CRH), both of which influence Adrenocorticotropic Hormone (ACTH). This hormone triggers release of cortisol and other glucocorticoids by the adrenal glands. The HPA axis becomes engaged during an acute disease. Cortisol levels will rise as a result of HPA axis activation. Specifically, injury to the frontal or medial temporal lobes of the brain, as well as inflammation, or a lack of regulation of the HPA axis, can lead to this medical condition. Cortisol levels might remain elevated for up to seven days following the start of a stroke. An increase in cortisol levels is connected to an highly risk of stroke severity, length of hospital stay, and mortality in stroke patients. It is also an early warning sign of deteriorating sleep quality in patients with acute ischemic stroke.

Neural control of fluid homeostasis is engaged below 10°C in hibernation.

Thirteen-lined ground squirrels (Ictidomys tridecemlineatus) hibernate for several months each winter without access to water,1 but the mechanisms that maintain fluid homeostasis during hibernation are poorly understood. In torpor, when body temperature (TB) reaches 4°C, squirrels decrease metabolism, slow heart rate, and reduce plasma levels of the antidiuretic hormones arginine vasopressin (AVP) and oxytocin (OXT).1 Squirrels spontaneously undergo interbout arousal (IBA) every 2weeks, temporarily recovering an active-like metabolism and a TB of 37°C for up to 48 h.1,2 Despite the low levels of AVP and OXT during torpor, profound increases in blood pressure and heart rate during the torpor-IBA transition are not associated with massive fluid loss, suggesting the existence of a mechanism that protects against diuresis at a low TB. Here, we demonstrate that the antidiuretic hormone release pathway is activated by hypothalamic supraoptic nucleus (SON) neurons early in the torpor-arousal transition. SON neuron activity, dense-core vesicle release from the posterior pituitary, and plasma hormone levels all begin to increase before TB reaches 10°C. Invivo fiber photometry of SON neurons from hibernating squirrels, together with RNA sequencing and c-FOS immunohistochemistry, confirms that SON is electrically, transcriptionally, and translationally active to monitor blood osmolality throughout the dynamic torpor-arousal transition. Our work emphasizes the importance of the antidiuretic pathway during the torpor-arousal transition and reveals that the neurophysiological mechanism that coordinates the hormonal response to retain fluid is active at an extremely low TB, which is prohibitive for these processes in non-hibernators.

Diabetes Insipidus: Types, Diagnosis and Management

Diabetes insipidus (DI) is an acquired or hereditary water imbalance disorder characterized by polydipsia and polyuria. It is a condition that involves the excretion of dilute urine in large volumes. The illness can strike at any age, with males and females have identical rates of occurrence of the disease. The two main mechanisms responsible for diabetes insipidus are either insufficient release or production of ADH (antidiuretic hormone) from the hypothalamus (central diabetes insipidus) or ADH resistance in which the kidneys are unable to respond to ADH (nephrogenic diabetes insipidus). Another form of DI is transient diabetes insipidus commonly known as gestational diabetes insipidus that occurs in the second/third trimester of pregnancy due to increased levels of placental vasopressinase that occurs progressively during pregnancy and increases metabolic clearance of vasopressin. The fourth type of DI is primary polydipsia, characterized by elevated levels of water intake that physiologically lower vasopressin and may be psychogenic, iatrogenic or dipsogenic. Signs and symptoms of DI often include water electrolyte-imbalance, excessive or severe thirst, frequent and excessive urination, fatigue, dehydration, and weight loss. Diabetes insipidus (DI) should be distinguished from primary polydipsia, and whether it is caused by a central, nephrogenic, or gestational cause. This distinction is critical since incorrect treatment can result in serious repercussions. Diagnosis of DI includes measurement of plasma sodium and osmolality, baseline copeptin, hypertonic saline stimulation and arginine stimulation test. The treatment for DI includes the use of drugs such as desmopressin, thiazide diuretics, indomethacin and amiloride.

Management of Low Sodium in AMU

Hyponatremia is a common finding in acutely ill patients and is defined as serum sodium (Na) level less than 135 mEq/L which is due to a relative excess of water in relation to serum sodium. Reasons for hyponatremia are increase in water intake (hypotonic intravenous fluid therapy or primary polydipsia) or impaired water excretion due to renal failure or increase release of antidiuretic hormone. Optimum management depends on the duration and severity of hyponatremia and involves close monitoring and accurate fluid balance assessment. We will discuss in this article the basics of management, pitfalls to avoid in Hyponatremia and recommended approach based on literature review when reviewing a patient with Hyponatremia, firstly to enquire about the duration of Hyponatremia to differentiate acute from chronic as the threshold for treatment is different, following duration is assessment of severity (clinically by symptoms and signs as well as biochemistry) as severity will affect the management. Following duration and severity the acute physician should assess the volume status of the patient to hypovolemic, euvolemic or hypervolemic Hyponatremia which aids in reaching the possible cause of Hyponatremia and the right treatment.