Action Of Arginine Vasopressin Research Articles

A better understanding of basic science may help our management of LUTS/LUTD in older persons with nocturnal polyuria and nocturia: ICI-RS 2024.

To discuss the role of autocrine/paracrine signaling of urothelial arginine vasopressin (AVP) on mammalian bladder capacities and micturition thresholds, impact of distension on water/urea reabsorption from the bladder, review of the literature to better characterize the central/peripheral effects of AVP, desmopressin (dAVP) toxicity, and urine biomarkers of nocturia. This review summarizes discussions during an International Consultation on Incontinence-Research Society2024 think tank with respect to the role of urothelial AVP in aged individuals with nocturnal polyuria, impact of solute and water reabsorption by the bladder on uninterrupted sleep, central effects of AVP, pharmacological basis of dAVP toxicity, and biomarkers in nocturia/lower urinary tract dysfunction(LUTD) with neurological diseases. Consensus recognized AVP function and pathways in thecentral nervous system(CNS), pre-proAVP localized using immunohistochemistry in bladder sections from adult/aged noncancerous human punch biopsies and rodent bladder sections is likely to accelerate the systemic uptake of water and urea from the bladder of anesthetized mice instilled with 3H-water and 14C-urea. Mechanisms for charged and uncharged solutes and water transport across the bladder, mechanism of dAVP toxicity, and utility of urine biomarkers in those with neurological diseases/nocturia were determined from literature reviews. Pre-proAVP is present in human/rodent bladders and may be involved in water reabsorption from bladder that prevents the sensation of fullness for uninterrupted sleep in healthy adults. The mechanism of action of AVP in the CNS was discussed, as was electrolyte/water transport across the bladder, the basis for dAVP toxicity, and feasibility of urine biomarkers to identify nocturia/LUTDwith neurological diseases.

Arginine vasopressin: Critical regulator of circadian homeostasis

Circadian rhythms optimally regulate numerous physiological processes in an organism and synchronize them with the external environment. The suprachiasmatic nucleus (SCN), the center of the circadian clock in mammals, is composed of multiple cell types that form a network that provides the basis for the remarkable stability of the circadian clock. Among the neuropeptides expressed in the SCN, arginine vasopressin (AVP) has attracted much attention because of its deep involvement in the function of circadian rhythms, as elucidated in particular by studies using genetically engineered mice. This review briefly summarizes the current knowledge on the peptidergic distribution and topographic neuronal organization in the SCN, the molecular mechanisms of the clock genes, and the relationship between the SCN and peripheral clocks. With respect to the physiological roles of AVP and AVP-expressing neurons, in addition to a sex-dependent action of AVP in the SCN, studies using AVP receptor knockout mice and mice genetically manipulated to alter the clock properties of AVP neurons are summarized here, highlighting its importance in maintaining circadian homeostasis and its potential as a target for therapeutic interventions.

Arginine vasopressin regulates the renal Na+-Cl- and Na+-K+-Cl- cotransporters through with-no-lysine kinase 4 and inhibitor 1 phosphorylation.

Vasopressin regulates water homeostasis via the V2 receptor in the kidney at least in part through protein kinase A (PKA) activation. Vasopressin, through an unknown pathway, upregulates the activity and phosphorylation of Na+-Cl- cotransporter (NCC) and Na+-K+-2Cl- cotransporter 2 (NKCC2) by Ste20-related proline/alanine-rich kinase (SPAK) and oxidative stress-responsive kinase 1 (OSR1), which are regulated by the with-no-lysine kinase (WNK) family. Phosphorylation of WNK4 at PKA consensus motifs may be involved. Inhibitor 1 (I1), a protein phosphatase 1 (PP1) inhibitor, may also play a role. In human embryonic kidney (HEK)-293 cells, we assessed the phosphorylation of WNK4, SPAK, NCC, or NKCC2 in response to forskolin or desmopressin. WNK4 and cotransporter phosphorylation were studied in desmopressin-infused WNK4-/- mice and in tubule suspensions. In HEK-293 cells, only wild-type WNK4 but not WNK1, WNK3, or a WNK4 mutant lacking PKA phosphorylation motifs could upregulate SPAK or cotransporter phosphorylation in response to forskolin or desmopressin. I1 transfection maximized SPAK phosphorylation in response to forskolin in the presence of WNK4 but not of mutant WNK4 lacking PP1 regulation. We observed direct PP1 regulation of NKCC2 dephosphorylation but not of NCC or SPAK in the absence of WNK4. WNK4-/- mice with desmopressin treatment did not increase SPAK/OSR1, NCC, or NKCC2 phosphorylation. In stimulated tubule suspensions from WNK4-/- mice, upregulation of pNKCC2 was reduced, whereas upregulation of SPAK phosphorylation was absent. These findings suggest that WNK4 is a central node in which kinase and phosphatase signaling converge to connect cAMP signaling to the SPAK/OSR1-NCC/NKCC2 pathway.NEW & NOTEWORTHY With-no-lysine kinases regulate the phosphorylation and activity of the Na+-Cl- and Na+-K+-2Cl- cotransporters. This pathway is modulated by arginine vasopressin (AVP). However, the link between AVP and WNK signaling remains unknown. Here, we show that AVP activates WNK4 through increased phosphorylation at putative protein kinase A-regulated sites and decreases its dephosphorylation by protein phosphatase 1. This work increases our understanding of the signaling pathways mediating AVP actions in the kidney.

Single-nucleus RNA and ATAC sequencing reveals marked changes and sex differences in the kidney collecting duct principal cell in response to mild dehydration

The kidney principal cells in the connecting tubule (CNTPCs) and collecting duct (CDPCs) function to fine-tune water reabsorption and concentrate the urine upon activation of arginine vasopressin (AVP) receptor-2. Our study aimed to determine the kidney single-nucleus transcriptome and DNA accessibility in response to dehydration, a potent physiological stimulus for AVP secretion. We hypothesized that dehydrated male and female mice would have different responses in the PCs.Male and female C57BL/6J mice at 11 weeks old were subjected to either ad libitum (ad lib) or 9hr of dehydration (n = 1 per group) with samples taken at midnight. 10X Genomics Chromium Next GEM Single Cell Multiome ATAC+Gene Expression Kit was used. The fastq files were processed using CellRanger ARC pipeline and downstream analyses completed with the R packages Seurat and Signac. Gene set enrichment analyses were performed with ToppGene Suite.A total of 22,821 nuclei (median fragments per nucleus = 12,961 ± 336) were sequenced and 34 clusters identified with 586 and 129 nuclei annotated as CDPC and CNTPC, respectively. We found more DEGs in CDPC than in CNTPC (106 vs. 13). The common top 5 most highly expressed genes in both CDPC and CNTPC in the dehydrated state compared to ad lib were Grem2, Pde10a, Pappa, Fam129a, Scg5 (adjusted P values < 0.01). Grem2 encodes a cytokine known to antagonize the bone morphogenic protein family (log2FC adlib/dehydrated for CDPC = -2.18 and CNTPC -1.96). Pde10a is a gene related to cAMP-mediated signaling (log2FC for CDPC = -2.17 and CNTPC -2.02). Pappa encodes a metalloproteinase (log2FC for CDPC = -1.36 and CNTPC -1.24). Fam129a encodes a protein that regulates protein phosphorylation (log2FC for CDPC = -1.17 and CNTPC -1.20). Finally, Scg5 encodes a chaperone protein that regulates pituitary hormone secretion (log2FC for CDPC = -0.84 and CNTPC -0.92). As expected, Aqp2 and Aqp3 were significantly higher in CDPCs from the dehydrated male and female mice. When stratifying by sex, we found more DEGs in female CDPCs than in males (79 vs. 54, χ2 p = 2.68E-8), but in CNTPC there were less in females than in males (1 vs 14, Fisher’s Exact p = 0.016). Pathway analyses determined that in dehydrated male DEGs that were highly expressed were enriched in circulatory system development and response to cAMP signaling pathways. In dehydrated female highly expressed DEGs were enriched in pathways related to renal development. Overall, chromatin analysis showed that changes in gene expression were not driven by changes in accessibility of chromatin.In conclusion, these findings suggest that CDPCs are more responsive to dehydration and that although there are common DEGs in dehydrated male and female mice, unique genes are enriched in different biological processes. NIDDK 1R01DK128001 This is the full abstract presented at the American Physiology Summit 2023 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.

Exercise-Induced Adrenocorticotropic Hormone Response Is Cooperatively Regulated by Hypothalamic Arginine Vasopressin and Corticotrophin-Releasing Hormone

Introduction: Exercise becomes a stress when performed at an intensity above the lactate threshold (LT) because at that point the plasma adrenocorticotropic hormone (ACTH), a marker of stress response, increases. It is possible that the exercise-induced ACTH response is regulated at least by arginine vasopressin (AVP) and possibly by corticotropin-releasing hormone (CRH), but this remains unclear. To clarify the involvement of these factors, it is useful to intervene pharmacologically in the regulatory mechanisms, with a physiologically acceptable exercise model. Methods: We used a special stress model of treadmill running (aerobic exercise) for male Wistar rats, which mimic the human physiological response, where plasma ACTH levels increase at just above the LT for 30 min. Animals were administered the AVP V_1b receptor antagonist SSR149415 (SSR) and/or the CRH type 1 receptor antagonist CP154526 (CP) intraperitoneally before the exercise, which allowed the monitoring of exercise-induced ACTH response. Immunohistochemical evaluation of activated AVP and CRH neurons with exercise was performed for the animals’ hypothalami. Results: A single injection of either antagonist, SSR or CP, resulted in inhibited ACTH levels after exercise stress. Moreover, the combined injection of SSR and CP strongly suppressed ACTH secretion during treadmill running to a greater extent than each alone. The running-exercise-induced activation of both AVP and CRH neurons in the hypothalamus was also confirmed. Conclusion: These results lead us to hypothesize that AVP and CRH are cooperatively involved in exercise-induced ACTH response just above the LT. This may also reflect the stress response with moderate-intensity exercise in humans.

OR30. Effect of hyponatremia in heart failure patients at discharge on 30-day readmission rate: a single-centre study

Abstract Background and Aims Hyponatremia is often observed in patients with heart failure. The proposed pathophysiology of hyponatremia in heart failure is due to increase of arginine vasopressin activity that elevates renal water reabsorption, thereby diluting sodium content in plasma. Hyponatremia has been identified as a factor that worsens heart failure patients' prognosis, including cardiovascular morbidity and mortality. Thus, this study was conducted to investigate the impact of hyponatremia in heart failure patients on rehospitalisation within thirty days. Methods and Results This is a single-centre prospective cohort study. A total of 205 acute decompensated heart failure patients admitted to National Cardiovascular Center Harapan Kita from July 2018 to March 2019 were included into the study. The study population was then divided into two groups based on predischarge sodium level. In this study, hyponatremia was defined as serum sodium level less than 135 mEq/l. Among the study population, 58 patients (28.3%) had hyponatremia at discharge. The data was analyzed using chi-square test. There were 19 patients who were readmitted within 30 days and 52.9% of them had hyponatremia at discharge. The effect of hyponatremic status at discharge to 30-day readmission rate was statistically significant (p = 0.03, OR = 3.19 95%CI 1.22-8.33). Conclusion Hyponatremia in heart failure patients at discharge is associated with increased risk of 30-day readmission.

Chemogenetic activation of endogenous arginine vasopressin exerts anorexigenic effects via central nesfatin-1/NucB2 pathway

We examined whether the chemogenetic activation of endogenous arginine vasopressin (AVP) affects central nesfatin-1/NucB2 neurons, using a transgenic rat line that was previously generated. Saline (1 mL/kg) or clozapine-N-oxide (CNO, 1 mg/mL/kg), an agonist for hM3Dq, was subcutaneously administered in adult male AVP-hM3Dq-mCherry transgenic rats (300–370 g). Food and water intake were significantly suppressed after subcutaneous (s.c.) injection of CNO, with aberrant circadian rhythmicity. The percentages of Fos expression in nesfatin-1/NucB2-immunoreactive neurons were significantly increased in the hypothalamus and brainstem at 120 min after s.c. injection of CNO. Suppressed food intake that was induced by chemogenetic activation of endogenous AVP was ablated after intracerebroventricularly administered nesfatin-1/NucB2-neutralizing antibody in comparison with vehicle, without any alteration of water intake nor circadian rhythmicity. These results suggest that chemogenetic activation of endogenous AVP affects, at least in part, central nesfatin-1/NucB2 neurons and may exert anorexigenic effects in the transgenic rats.

The relationship between cardiac resynchronization therapy and serum levels of copeptin in patients with chronic heart failure

Abstract Funding Acknowledgements Type of funding sources: Public Institution(s). Main funding source(s): The present study was supported by a grant from Slovak Hearth Rhythm Association (Prognostic value of MR-proANP and MR-proADM in patients undergoing cardiac resynchronization therapy). Background Chronic heart failure (CHF) is a complex syndrome characterized by an abnormal neurohormonal activation, including arginine vasopressin (AVP). Copeptin is an indicator of AVP activation, which levels are elevated in CHF and have prognostic importance. Cardiac resynchronization therapy (CRT) is an important device therapy for patients with advanced CHF, left ventricular (LV) systolic dysfunction and evidence of electromechanical dyssynchrony. The aim of the present study was to determine the possible relationship between CRT and serum copeptin levels. Methods We have included CRT patients with ischemic as well as nonischemic etiology of CHF. The levels of copeptin were measured at baseline and 12 months respectively after CRT implantation. Echocardiography was also performed pre and 12 months post CRT implantation. A CRT response was defined as a ≥ 15 % reduction in LV end-systolic volume (LVESV). Results The study population consisted of 41 patients. The mean copeptin level was 20.50 ± 15.77 pmol/l. Copeptin levels positively correlated with New York Heart Association class, left atrial diameter, creatinine levels and NT-proBNP levels. CRT responders have significant reduction in copeptin levels from baseline to 12 months (from 16.96 ± 12.80 pmol/l to 6.20 ± 6.44 pmol/l, p < 0.001). No significant changes in copeptin levels were observed in CRT nonresponders. Reduction > 45 % in copeptin levels was predictor of CRT-response (OR 6.72, 95 % CI 1.01 - 18.11, p = 0.045). Conclusion The copeptin serum levels can be a useful biomarker in the evaluation of the CRT response.

The differential activation of cardiovascular hormones across distinct stages of portal hypertension predicts clinical outcomes

Background and aimsThe cardiovascular hormones renin/angiotensin/aldosterone (RAA), brain-type natriuretic peptide (BNP)and arginine-vasopressin (AVP) are key regulators of systemic circulatory homeostasis in portal hypertension (PH). We assessed (i) the activation of renin, BNP and AVP across distinct stages of PH and (ii) whether activation of these hormones correlates with clinical outcomes.MethodsPlasma levels of renin, proBNP and copeptin (AVP biomarker) were determined in 663 patients with advanced chronic liver disease (ACLD) undergoing hepatic venous pressure gradient (HVPG) measurement at the Vienna General Hospital between 11/2011 and 02/2019. We stratified for Child stage (A–C), HVPG (6–9 mmHg, 10–15 mmHg, ≥ 16 mmHg) and compensated vs. decompensated ACLD.ResultsWith increasing PH, hyperdynamic state was indicated by higher heart rates (6–9 mmHg: median 71.0 [IQR 18.0] bpm, 10–15 mmHg: 76.0 [19.0] bpm, ≥ 16 mmHg: 80.0 [22.0] bpm; p < 0.001), lower mean arterial pressure (6–9 mmHg: 103.0 [13.5] mmHg, 10–15 mmHg: 101.0 [19.5] mmHg, ≥ 16 mmHg: 99.0 [21.0] mmHg; p = 0.032) and lower serum sodium (6–9 mmHg: 139.0 [3.0] mmol/L, 10–15 mmHg: 138.0 [4.0] mmol/L, ≥ 16 mmHg: 138.0 [5.0] mmol/L; p < 0.001). Across HVPG strata (6–9 mmHg vs. 10–15 mmHg vs ≥ 16 mmHg), median plasma levels of renin (21.0 [50.5] vs. 25.1 [70.9] vs. 65.4 [219.6] µIU/mL; p < 0.001), proBNP (86.1 [134.0] vs. 63.6 [118.0], vs. 132.2 [208.9] pg/mL; p = 0.002) and copeptin (7.8 [7.7] vs. 5.6 [8.0] vs. 10.7 [18.6] pmol/L; p = 0.024) increased with severity of PH. Elevated renin levels independently predicted first hepatic decompensation (adjusted hazard ratio [aHR]: 1.69; 95% confidence interval [95% CI] 1.07–2.68; p = 0.025) and mortality in compensated patients (aHR: 3.15; 95% CI 1.70–5.84; p < 0.001) and the overall cohort aHR: 1.42; 95% CI 1.01–2.01; p = 0.046). Elevated copeptin levels predicted mortality in decompensated patients (aHR: 5.77; 95% CI 1.27–26.33; p = 0.024) and in the overall cohort (aHR: 3.29; 95% CI 1.36–7.95; p = 0.008). ProBNP levels did not predict clinical outcomes.ConclusionsThe cardiovascular hormones renin, proBNP and AVP are activated with progression of ACLD and PH. Renin activation is a risk factor for hepatic decompensation and mortality, especially in compensated patients. Increased plasma copeptin is a risk factor for mortality, in particular in decompensated patients.

Hypomagnesemia and Hypokalemia: The Possible Role of Vasopressinase in This Rare Presentation of Gestational Diabetes Insipidus

Background: Gestational diabetes insipidus (GDI) is a rare but recognized complication of pregnancy. We are reporting the case of a 33-year-old patient who presented in her 3rd trimester with GDI, severe asymptomatic hypokalemia & hypomagnesemia. This presentation of GDI has not been reported yet to our knowledge. Clinical Case: A 33-year-old G2P1 patient who presented to the hospital due to the discovery of new onset severe asymptomatic hypokalemia on routine labs. Further evaluation revealed K of 2.8 mEq/L, Mg of 1.4 mg/dL & Na of 142mEq/L. She endorsed polyuria & polydipsia and a 24-hour urine collection of 9.35L confirmed diabetes insipidus. Labs also revealed a serum osmolality of 286mOsm/kg & urine K of 15mEq/L. Her urine osmolality was inappropriately low at 138mOsm/kg. She received K & Mg supplementation. In pregnant patients suspected of having GDI who have normal serum Na, water restriction test can be done for further evaluation. It must performed with close monitoring because dehydration can lead to uteroplacental insufficiency. Given her history of previous fetal demise & report of headaches with attempts of water restriction, we opted not to do the test. She was given subcutaneous 1 mcg of desmopressin overnight with her thirst & polyuria improving only briefly. Due to her suboptimal response, we began her on 10 mcg of intranasal spray of desmopressin once in the evening. Her symptoms resolved on this regimen after a few days of observation. Her Mg & eventually K levels reached and remained at normal levels after repletion. The rest of her pregnancy went on without complications and she delivered a healthy male infant via scheduled cesarean section at 36 weeks gestation. She discontinued intranasal desmopressin after 2 weeks and has remained asymptomatic. Labs at follow up 4 weeks later remained normal. It is known that vasopressinase which is made by placental trophoblasts during pregnancy degrade endogenous ADH1. We are hypothesizing that since ADH has been shown to be effective in conserving magnesium in rats by stimulating its uptake in the distal convoluted tubule cells2, a similar mechanism could be present in humans. We believe that the loss of endogenous ADH, leads to the depletion of Mg and consequently hypokalemia in susceptible patients. Conclusion: To our knowledge this is the first case presenting the possible role of vasopressinase in the development of hypomagnesemia & hypokalemia in a patient with GDI. Reference: 1. Gordge MP, Williams DJ, Huggett NJ, Payne NN, and Neild GH. Loss of biological activity of arginine vasopressin during its degradation by vasopressinase from pregnancy serum. Clinical Endocrinology, vol. 42, no. 1, pp. 51- 58, 1995. 2. Dai LJ, Bapty B, Ritchie G, Quamme GA. Glucagon and arginine vasopressin stimulate Mg2+ uptake in mouse distal convoluted tubule cells. Am J Physiol. 1998 Feb;274(2):F328-35. doi: 10.1152/ajprenal.1998.274.2.F328. PMID: 9486227.

Diagnosis and management of diabetes insipidus for the internist: an update.

Diabetes insipidus is a disorder characterized by excretion of large amounts of hypotonic urine. Four entities have to be differentiated: central diabetes insipidus resulting from a deficiency of the hormone arginine vasopressin (AVP) in the pituitary gland or the hypothalamus, nephrogenic diabetes insipidus resulting from resistance to AVP in the kidneys, gestational diabetes insipidus resulting from an increase in placental vasopressinase and finally primary polydipsia, which involves excessive intake of large amounts of water despite normal AVP secretion and action. Distinguishing between the different types of diabetes insipidus can be challenging. A detailed medical history, physical examination and imaging studies are needed to detect the aetiology of diabetes insipidus. Differentiation between the various forms of hypotonic polyuria is then done by the classical water deprivation test or the more recently developed hypertonic saline or arginine stimulation together with copeptin (or AVP) measurement. In patients with idiopathic central DI, a close follow-up is needed since central DI can be the first sign of an underlying pathology. Treatment of diabetes insipidus or primary polydipsia depends on the underlying aetiology and differs in central diabetes insipidus, nephrogenic diabetes insipidus and primary polydipsia. This review will discuss issues and newest developments in diagnosis, differential diagnosis and treatment, with a focus on central diabetes insipidus.

Activation of Orexin 1 Receptors in the Paraventricular Nucleus Contributes to the Development of Deoxycorticosterone Acetate-Salt Hypertension Through Regulation of Vasopressin.

Salt-sensitivity is a major factor in the development of hypertension. The brain orexin system has been observed to play a role in numerous hypertensive animal models. However, orexin’s role in the pathology of salt-sensitive hypertension (SSH) remains to be adequately explored. We assessed the impact of orexin hyperactivity in the pathogenesis of the deoxycorticosterone acetate (DOCA) – salt rat model, specifically through modulation of Arginine Vasopressin (AVP). Adult male rats were separated into three groups: vehicle control, DOCA-salt, and DOCA-salt+OX1R-shRNA. DOCA-salt rats received subcutaneous implantation of a 21-day release, 75 mg DOCA pellet in addition to saline drinking water (1% NaCl and 0.2% KCl). DOCA-salt+OX1R-shRNA rats received bilateral microinjection of AAV2-OX1R-shRNA into the paraventricular nucleus (PVN) to knockdown function of the Orexin 1-Receptor (OX1R) within that area. Following 2-week to allow full transgene expression, a DOCA pellet was administered in addition to saline drinking solution. Vehicle controls received sham DOCA implantation but were given normal water. During the 3-week DOCA-salt or sham treatment period, mean arterial pressure (MAP) and heart rate (HR) were monitored utilizing tail-cuff plethysmography. Following the 3-week period, rat brains were collected for either PCR mRNA analysis, as well as immunostaining. Plasma samples were collected and subjected to ELISA analysis. In line with our hypothesis, OX1R expression was elevated in the PVN of DOCA-salt treated rats when compared to controls. Furthermore, following chronic knockdown of OX1R, the hypertension development normally induced by DOCA-salt treatment was significantly diminished in the DOCA-salt+OX1R-shRNA group. A concurrent reduction in PVN OX1R and AVP mRNA was observed in concert with the reduced blood pressure following AAV2-OX1R-shRNA treatment. Similarly, plasma AVP concentrations appeared to be reduced in the DOCA-salt+OX1R-shRNA group when compared to DOCA-salt rats. These results indicate that orexin signaling, specifically through the OX1R in the PVN are critical for the onset and maintenance of hypertension in the DOCA-salt model. This relationship is mediated, at least in part, through orexin activation of AVP producing neurons, and the subsequent release of AVP into the periphery. Our results outline a promising mechanism underlying the development of SSH through interactions with the brain orexin system.

Diabetes Insipidus: A Pragmatic Approach to Management.

Diabetes insipidus (DI) is a disorder of water balance characterized by polyuria and polydipsia. It can occur due to genetic and acquired causes that affect the secretion or action of arginine vasopressin (AVP) or antidiuretic hormone (ADH).Markedly increased thirst and urination are not only quite distressing but also increases the risk of volume depletion and hypernatremia in severe situations. A careful diagnosis of the type of DI and its etiology is based on careful clinical evaluation, measurement of urine and serum osmolality, and water deprivation test. Management includes the correction of any water deficit and the use of specific pharmacological agents, including desmopressin, thiazides, and amiloride.

Sex differences in vasopressin 1a receptor regulation of social communication within the lateral habenula and dorsal raphe of mice

The neuropeptide arginine-vasopressin (AVP) has long been implicated in the regulation of social behavior and communication in diverse taxa, often through its actions on the V1a receptor (V1aR) and in a sex-different and steroid-dependent way. One source of sex-different brain AVP is the steroid-sensitive and sexually-dimorphic AVP neurons in the bed nucleus of the stria terminalis (BNST), a cell population that regulates social behavior in a sex-dependent manner. Potential targets of these BNST-AVP cells include the lateral habenula (LHb) and dorsal raphe (DR), areas known to be important for social behavior, yet few studies have investigated AVP action within these regions. Consequently, to test if V1aR action in the LHb or DR controls social behavior in a sexually dimorphic manner, we administered a highly-specific V1aR antagonist (or saline vehicle) in the LHb or DR of C57BL/6 male and female mice and tested its effects on social investigation, social communication (urine marking, ultrasonic vocalizations), and territorial aggression. V1aR antagonism of the LHb or DR decreased male urine marking toward unfamiliar males, but not toward unfamiliar females. Additionally, V1aR blockade of the LHb decreased ultrasonic vocalizations generated in the presence of females. Social investigation, locomotion and aggressive behavior were not altered by V1aR antagonism in either area. Blocking V1aR in the LHb or DR of females had no effect, indicating V1aR action in the DR and LHb drives sex differences in social communication.

Vasopressin actions in the kidney renin angiotensin system and its role in hypertension and renal disease.

Vasopressin, also named antidiuretic hormone (ADH), arginine vasopressin (AVP) is the main hormone responsible for water maintenance in the body through the antidiuretic actions in the kidney. The posterior pituitary into the blood releases vasopressin formed in the hypothalamus. Hypothalamic osmotic neurons are responsible to initiate the cascade for AVP actions. The effects of AVP peptide includes activation of V2 receptors which stimulate the formation of cyclic AMP (cAMP) and phosphorylation of water channels aquaporin 2 (AQP2) in the collecting duct. AVP also has vasoconstrictor effects through V1a receptors in the vasculature, while V1b is found in the nervous system. V1a and b receptors increases intracellular Ca2+ while activation of V2 receptors of signaling pathways are related to cAMP-dependent phosphorylation in kidney collecting ducts acting in coordination to stimulate water and electrolyte homeostasis. AVP potentiate formation of intratubular angiotensin II (Ang II) through V2 receptors-dependent distal tubular renin formation, contributing to Na+ reabsorption. On the same way, Ang II receptors are able to potentiate the effects of V2-dependent stimulation of AQP2 abundance in the plasma membrane. The role of AVP in hypertension and renal disease has been demonstrated in pathological states with the involvement of V2 receptors in the progression of kidney damage in diabetes and also on the stimulation of intracellular pathways linked to the development of polycystic kidney.

Diabetes insipidus.

Diabetes insipidus (DI) is a disorder characterized by excretion of large amounts of hypotonic urine. Central DI results from a deficiency of the hormone arginine vasopressin (AVP) inthe pituitary gland or the hypothalamus, whereas nephrogenic DI results from resistance to AVP in the kidneys. Central and nephrogenic DI are usually acquired, but genetic causes must be evaluated, especially if symptoms occur in early childhood. Central or nephrogenic DI must bedifferentiated from primary polydipsia, which involves excessive intake of large amounts of water despite normal AVP secretion and action. Primary polydipsia is most common in psychiatric patients and health enthusiasts but the polydipsia in a small subgroup of patients seems to be dueto an abnormally low thirst threshold, a condition termed dipsogenic DI. Distinguishing between the different types of DI can be challenging and is done either by a water deprivation test or by hypertonic saline stimulation together with copeptin (or AVP) measurement. Furthermore, a detailed medical history, physical examination and imaging studies are needed toensure an accurate DI diagnosis. Treatment of DI or primary polydipsia depends on the underlying aetiology and differs in central DI, nephrogenic DI and primary polydipsia.

New insights into the transcriptional regulation of aquaporin-2 and the treatment of X-linked hereditary nephrogenic diabetes insipidus.

The kidney collecting duct (CD) is a tubular segment of the kidney where the osmolality and final flow rate of urine are established, enabling urine concentration and body water homeostasis. Water reabsorption in the CD depends on the action of arginine vasopressin (AVP) and a transepithelial osmotic gradient between the luminal fluid and surrounding interstitium. AVP induces transcellular water reabsorption across CD principal cells through associated signaling pathways after binding to arginine vasopressin receptor 2 (AVPR2). This signaling cascade regulates the water channel protein aquaporin-2 (AQP2). AQP2 is exclusively localized in kidney connecting tubules and CDs. Specifically, AVP stimulates the intracellular translocation of AQP2-containing vesicles to the apical plasma membrane, increasing the osmotic water permeability of CD cells. Moreover, AVP induces transcription of the Aqp2 gene, increasing AQP2 protein abundance. This review provides new insights into the transcriptional regulation of the Aqp2 gene in the kidney CD with an overview of AVP and AQP2. It summarizes current therapeutic approaches for X-linked nephrogenic diabetes insipidus caused by AVPR2 gene mutations.

MON-442 Evaluation of Copeptin as a Surrogate for AVP in the Diagnosis of Water Metabolism Disorders

Arginine vasopressin (AVP) plays a key role in maintaining fluid balance and vascular tone and is useful in diagnosing diabetes insipidus (DI) and polyuria-polydipsia. Central DI is characterized by decreased AVP secretion leading to polyuria and polydipsia caused by diminished renal ability to concentrate urine. Alternatively, nephrogenic DI is characterized by a decrease in the ability to concentrate urine because of resistance of the distal nephron to AVP action. While AVP measurement can be diagnostic, reliable measurement of AVP can be hindered by several factors. AVP is tightly bound to platelets and is influenced by their number and incomplete removal, as well as pre-analytical processing. In addition, AVP is also highly unstable in isolated plasma - even at frozen temperatures. Copeptin comprises the C-terminal portion of the AVP precursor “pre-pro-vasopressin”. Equimolar amounts of AVP and copeptin released from this precursor during prohormone processing. Unlike the AVP molecule, copeptin is stable at room and refrigerated temperatures. In the current study, our objective was to confirm that copeptin can serve as a sensitive surrogate marker for AVP release in diagnosis. Our laboratory validated the B·R·A·H·M·S™ Copeptin proAVP assay on the automated KRYPTOR® platform. The measuring principle of the assay is based on Time-Resolved Amplified Cryptate Emission (TRACE®) technology, which measures the signal that is emitted with time delay from an immunocomplex. The molecules of copeptin present in the patient samples are sandwiched between the antibodies of the immunoassay. The intensity of the signal is proportional to the amount of copeptin. Extensive comparison studies, between AVP and copeptin, were conducted during the assay validation process. Approximately 245 patient samples previously tested for AVP were also tested in the copeptin assay. Using the respective reference intervals (RI) for AVP and copeptin, there was a 78.3% clinical concordance between the 2 assays; 53 samples (21.6%) were clinically discordant. Of the 245 patients, 4.5% (11 ) were above the AVP RI and 22.9% (56) were above the copeptin RI. Correlation plots showed a large degree of scatter between AVP and copeptin, which likely reflects the dissimilar stabilities of the two analytes. In conclusion, validation data suggest that there is clinical concordance for most patients tested using copeptin and AVP assays.

Vasopressin receptors in islets enhance glucose tolerance, pancreatic beta-cell secretory function, proliferation and survival

Arginine vasopressin (AVP), a peptide secreted from the posterior pituitary, is chiefly regarded as a hormone involved in the regulation of body fluid balance and osmolality. However, recent evidence has revealed that posterior pituitary hormones can exert important actions on endocrine pancreatic function. In the present study, the presence of AVP receptors, namely Avpr1a (V1a), Avpr1b (V1b) and Avpr2 (V2) was demonstrated in murine islets as well as rodent BRIN BD11 and human 1.1B4 beta-cells. Further to this, AVP was shown to induce significant concentration-dependent (10−12 – 10−6 M) increases of insulin release from both rodent and human beta-cells, as well as mouse islets. Insulinotropic actions of AVP were completely annulled by specific V1a or V1b receptor antagonists, and partially abolished by an oxytocin receptor antagonist. In addition, beta-cell insulin secretory actions of AVP were augmented by both IBMX (200 μM) and KCl (30 mM) and linked to significantly increased cAMP production and [Ca2+]i. AVP substantially increased proliferation of rodent and human beta-cells. Moreover, AVP fully protected against cytokine-induced beta-cell apoptosis. AVP had no effect on glucagon secretion. Immunohistochemical examination of beta- and alpha-cells revealed co-expression of AVP with glucagon, and particularly insulin. Finally, administration of AVP in combination with glucose to mice significantly reduced blood glucose, which was associated with increased plasma insulin. These data indicate that AVP possesses novel and potentially important effects on pancreatic endocrine function. Understanding disturbances in islet AVP receptor signalling could reveal insight into the beta-cell defects associated with diabetes.

Polyuria‐polydipsia syndrome: a diagnostic challenge

The main determinants for the maintenance of water homeostasis are the hormone arginine vasopressin (AVP) and thirst. Disturbances in these regulatory mechanisms can lead to polyuria-polydipsia syndrome, which comprises of three different conditions: central diabetes insipidus (DI) due to insufficient secretion of AVP, nephrogenic DI caused by renal insensitivity to AVP action and primary polydipsia due to excessive fluid intake and consequent physiological suppression of AVP. It is crucial to determine the exact diagnosis because treatment strategies vary substantially. To differentiate between the causes of the polyuria-polydipsia syndrome, a water deprivation test combined with desmopressin administration is the diagnostic 'gold standard'. Thereby, AVP activity is indirectly evaluated through the measurement of urine osmolality after prolonged dehydration. However, this test has several limitations and may fail to distinguish precisely between patients with primary polydipsia and mild forms of central and nephrogenic DI. The direct measurement of AVP during the water deprivation test, which was reported in the 1980s, has not been widely adopted due to availability, assay issues and diagnostic performance. Recently, copeptin, the c-terminal portion of the larger precursor peptide of AVP, has been evaluated in the setting of polyuria-polydipsia syndrome and appears to be a useful candidate biomarker for the differential diagnosis. A standardised method for the water deprivation test is presented as part of a joint initiative of the Endocrine Society of Australia, the Australasian Association of Clinical Biochemists and the Royal College of Pathologists of Australasia to harmonise dynamic endocrine tests across Australia.