Vasopressin regulation of blood pressure and volume: findings from V1a receptor–deficient mice

The Regulatory Effect of the Paraventricular Nucleus on Hypertension

Hypertension is among the most harmful factors of cardiovascular and cerebrovascular diseases and poses an urgent problem for the development of human society. In addition to previous studies on its pathogenesis focusing on the peripheral sympathetic nervous system, investigating the central causes of high blood pressure involving the neuroendocrine and neuroinflammatory mechanisms of the hypothalamic paraventricular nucleus (PVN) is paramount. This nucleus is considered to regulate the output of neurohormones and sympathetic nerve activity. In this article, we focussed on the neuroendocrine mechanism, primarily exploring the specific contributions and interactions of various neurons and neuroendocrine hormones, including GABAergic and glutamatergic neurons, nitric oxide, arginine vasopressin, oxytocin, and the renin-angiotensin system. Additionally, the neuroinflammatory mechanism in the PVN was discussed, encompassing microglia, reactive oxygen species, inflammatory factors, and pathways, as well as immune connections between the brain and extracerebral organs. Notably, the two central mechanisms involved in the PVN not only exist independently but also communicate with each other, jointly maintaining the hypertensive state of the body. Furthermore, we introduce well-known molecules and signal transduction pathways within the PVN that can play a regulatory role in the two mechanisms to provide a basis and inspire ideas for further research.

Vasopressin V1a receptor and oxytocin receptor regulate murine sperm motility differently

Specific receptors for the neurohypophyseal hormones, arginine vasopressin (AVP) and oxytocin, are present in the male reproductive organs. However, their exact roles remain unknown. To elucidate the physiological functions of pituitary hormones in male reproduction, this study first focused on the distribution and function of one of the AVP receptors, V1a. In situ hybridization analysis revealed high expression of the Avpr1a in Leydig cells of the testes and narrow/clear cells in the epididymis, with the expression pattern differing from that of the oxytocin receptor (OTR). Notably, persistent motility and highly proportional hyperactivation were observed in spermatozoa from V1a receptor-deficient mice. In contrast, OTR blocking by antagonist atosiban decreased hyperactivation rate. Furthermore, AVP stimulation could alter the extracellular pH mediated by the V1a receptor. The results highlight the crucial role of neurohypophyseal hormones in male reproductive physiology, with potential contradicting roles of V1a and OTR in sperm maturation. Our findings suggest that V1a receptor antagonists are potential therapeutic drugs for male infertility.

The Role of Arginine-Vasopressin in Stroke and the Potential Use of Arginine-Vasopressin Type 1 Receptor Antagonists in Stroke Therapy: A Narrative Review

Stroke is a life-threatening condition in which accurate diagnoses and timely treatment are critical for successful neurological recovery. The current acute treatment strategies, particularly non-invasive interventions, are limited, thus urging the need for novel therapeutical targets. Arginine vasopressin (AVP) receptor antagonists are emerging as potential targets to treat edema formation and subsequent elevation in intracranial pressure, both significant causes of mortality in acute stroke. Here, we summarize the current knowledge on the mechanisms leading to AVP hyperexcretion in acute stroke and the subsequent secondary neuropathological responses. Furthermore, we discuss the work supporting the predictive value of measuring copeptin, a surrogate marker of AVP in stroke patients, followed by a review of the experimental evidence suggesting AVP receptor antagonists in stroke therapy. As we highlight throughout the narrative, critical gaps in the literature exist and indicate the need for further research to understand better AVP mechanisms in stroke. Likewise, there are advantages and limitations in using copeptin as a prognostic tool, and the translation of findings from experimental animal models to clinical settings has its challenges. Still, monitoring AVP levels and using AVP receptor antagonists as an add-on therapeutic intervention are potential promises in clinical applications to alleviate stroke neurological consequences.

Management of Hyponatremia in Heart Failure: Practical Considerations

Hyponatremia is commonly encountered in the setting of heart failure, especially in decompensated, fluid-overloaded patients. The pathophysiology of hyponatremia in patients with heart failure is complex, including numerous mechanisms: increased activity of the sympathetic nervous system and the renin-angiotensin-aldosterone system, high levels of arginine vasopressin and diuretic use. Symptoms are usually mild but hyponatremic encephalopathy can occur if there is an acute decrease in serum sodium levels. It is crucial to differentiate between dilutional hyponatremia, where free water excretion should be promoted, and depletional hyponatremia, where administration of saline is needed. An inappropriate correction of hyponatremia may lead to osmotic demyelination syndrome which can cause severe neurological symptoms. Treatment options for hyponatremia in heart failure, such as water restriction or the use of hypertonic saline with loop diuretics, have limited efficacy. The aim of this review is to summarize the principal mechanisms involved in the occurrence of hyponatremia, to present the main guidelines for the treatment of hyponatremia, and to collect and analyze data from studies which target new treatment options, such as vaptans.

Terlipressin combined with conservative fluid management attenuates hemorrhagic shock-induced acute kidney injury in rats

Hemorrhagic shock (HS), a major cause of trauma-related mortality, is mainly treated by crystalloid fluid administration, typically with lactated Ringer's (LR). Despite beneficial hemodynamic effects, such as the restoration of mean arterial pressure (MAP), LR administration has major side effects, including organ damage due to edema. One strategy to avoid such effects is pre-hospitalization intravenous administration of the potent vasoconstrictor terlipressin, which can restore hemodynamic stability/homeostasis and has anti-inflammatory effects. Wistar rats were subjected to HS for 60 min, at a target MAP of 30-40 mmHg, thereafter being allocated to receive LR infusion at 3 times the volume of the blood withdrawn (liberal fluid management); at 2 times the volume (conservative fluid management), plus terlipressin (10 µg/100 g body weight); and at an equal volume (conservative fluid management), plus terlipressin (10 µg/100 g body weight). A control group comprised rats not subjected to HS and receiving no fluid resuscitation or treatment. At 15 min after fluid resuscitation/treatment, the blood previously withdrawn was reinfused. At 24 h after HS, MAP was higher among the terlipressin-treated animals. Terlipressin also improved post-HS survival and provided significant improvements in glomerular/tubular function (creatinine clearance), neutrophil gelatinase-associated lipocalin expression, fractional excretion of sodium, aquaporin 2 expression, tubular injury, macrophage infiltration, interleukin 6 levels, interleukin 18 levels, and nuclear factor kappa B expression. In terlipressin-treated animals, there was also significantly higher angiotensin II type 1 receptor expression and normalization of arginine vasopressin 1a receptor expression. Terlipressin associated with conservative fluid management could be a viable therapy for HS-induced acute kidney injury, likely attenuating such injury by modulating the inflammatory response via the arginine vasopressin 1a receptor.

CRISPR-Cas9 editing of the arginine-vasopressin V1a receptor produces paradoxical changes in social behavior in Syrian hamsters

Studies from a variety of species indicate that arginine–vasopressin (AVP) and its V1a receptor (Avpr1a) play a critical role in the regulation of a range of social behaviors by their actions in the social behavior neural network. To further investigate the role of AVPRs in social behavior, we performed CRISPR-Cas9–mediated editing at the Avpr1a gene via pronuclear microinjections in Syrian hamsters (Mesocricetus auratus), a species used extensively in behavioral neuroendocrinology because they produce a rich suite of social behaviors. Using this germ-line gene-editing approach, we generated a stable line of hamsters with a frame-shift mutation in the Avpr1a gene resulting in the null expression of functional Avpr1as. Avpr1a knockout (KO) hamsters exhibited a complete lack of Avpr1a-specific autoradiographic binding throughout the brain, behavioral insensitivity to centrally administered AVP, and no pressor response to a peripherally injected Avpr1a-specific agonist, thus confirming the absence of functional Avpr1as in the brain and periphery. Contradictory to expectations, Avpr1a KO hamsters exhibited substantially higher levels of conspecific social communication (i.e., odor-stimulated flank marking) than their wild-type (WT) littermates. Furthermore, sex differences in aggression were absent, as both male and female KOs exhibited more aggression toward same-sex conspecifics than did their WT littermates. Taken together, these data emphasize the importance of comparative studies employing gene-editing approaches and suggest the startling possibility that Avpr1a-specific modulation of the social behavior neural network may be more inhibitory than permissive.

Complementary Role of Oxytocin and Vasopressin in Cardiovascular Regulation

The neurons secreting oxytocin (OXY) and vasopressin (AVP) are located mainly in the supraoptic, paraventricular, and suprachiasmatic nucleus of the brain. Oxytocinergic and vasopressinergic projections reach several regions of the brain and the spinal cord. Both peptides are released from axons, soma, and dendrites and modulate the excitability of other neuroregulatory pathways. The synthesis and action of OXY and AVP in the peripheral organs (eye, heart, gastrointestinal system) is being investigated. The secretion of OXY and AVP is influenced by changes in body fluid osmolality, blood volume, blood pressure, hypoxia, and stress. Vasopressin interacts with three subtypes of receptors: V1aR, V1bR, and V2R whereas oxytocin activates its own OXTR and V1aR receptors. AVP and OXY receptors are present in several regions of the brain (cortex, hypothalamus, pons, medulla, and cerebellum) and in the peripheral organs (heart, lungs, carotid bodies, kidneys, adrenal glands, pancreas, gastrointestinal tract, ovaries, uterus, thymus). Hypertension, myocardial infarction, and coexisting factors, such as pain and stress, have a significant impact on the secretion of oxytocin and vasopressin and on the expression of their receptors. The inappropriate regulation of oxytocin and vasopressin secretion during ischemia, hypoxia/hypercapnia, inflammation, pain, and stress may play a significant role in the pathogenesis of cardiovascular diseases.

[Hypo- and hypernatremia in the intensive care unit : Pitfalls in volume management]

Hypo- and hypernatremias are very frequent in intensive care unit (ICU) patients and are closely related to volume disturbances and volume management in the ICU. They are associated with longer ICU stays and significant increases in mortality. Treating them is more complex than it may initially appear. Hyponatremias are differentiated based on tonicity and volume status. With hypertonic and isotonic hyponatremias, the primary focus of treatment is the underlying hyperglycemia. In case of hypotonic hypovolemic hyponatremia, the condition is treated with balanced crystalloid solutions. In eu-/hypervolemic hypotonic hyponatremias acute treatment with hypertonic saline is necessary. Hypervolemic hypernatremia occurs almost exclusively in ICU patients, often due to infusion of hypertonic solutions. There is little evidence to guide treatment, although hypotonic infusions in conjunction with diuretics may represent a legitimate approach. Great emphasis should be placed on prevention and the infusion of hypertonic solutions should be avoided. Disturbances in plasma sodium concentrations are common, requiring close attention. Exact diagnostic classification needs to be made and volume managed accordingly.

Cardiovascular Neuroendocrinology: Emerging Role for Neurohypophyseal Hormones in Pathophysiology

Arginine vasopressin (AVP) and oxytocin (OXY) are released by magnocellular neurosecretory cells that project to the posterior pituitary. While AVP and OXY currently receive more attention for their contributions to affiliative behavior, this mini-review discusses their roles in cardiovascular function broadly defined to include indirect effects that influence cardiovascular function. The traditional view is that neither AVP nor OXY contributes to basal cardiovascular function, although some recent studies suggest that this position might be re-evaluated. More evidence indicates that adaptations and neuroplasticity of AVP and OXY neurons contribute to cardiovascular pathophysiology.

Neuroprotective Effect of Aurantio-Obtusin, a Putative Vasopressin V1A Receptor Antagonist, on Transient Forebrain Ischemia Mice Model

Traditional Chinese medicines (TCMs) have been a rich source of novel drug discovery, and Cassia seed is one of the common TCMs with numerous biological effects. Based on the existing reports on neuroprotection by Cassia seed extract, the present study aims to search possible pharmacological targets behind the neuroprotective effects of the Cassia seeds by evaluating the functional effect of specific Cassia compounds on various G-protein-coupled receptors. Among the four test compounds (cassiaside, rubrofusarin gentiobioside, aurantio-obtusin, and 2-hydroxyemodin 1-methylether), only aurantio-obtusin demonstrated a specific V_1AR antagonist effect (71.80 ± 6.0% inhibition at 100 µM) and yielded an IC₅₀ value of 67.70 ± 2.41 μM. A molecular docking study predicted an additional interaction of the hydroxyl group at C6 and a methoxy group at C7 of aurantio-obtusin with the Ser341 residue as functional for the observed antagonist effect. In the transient brain ischemia/reperfusion injury C57BL/6 mice model, aurantio-obtusin attenuated the latency time that was reduced in the bilateral common carotid artery occlusion (BCCAO) groups. Likewise, compared to neuronal damage in the BCCAO groups, treatment with aurantio-obtusin (10 mg/kg, p.o.) significantly reduced the severity of damage in medial cornu ammonis 1 (mCA1), dorsal CA1, and cortex regions. Overall, the findings of this study highlight V_1AR as a possible target of aurantio-obtusin for neuroprotection.

Baroreceptor Modulation of the Cardiovascular System, Pain, Consciousness, and Cognition

Baroreceptors are mechanosensitive elements of the peripheral nervous system that maintain cardiovascular homeostasis by coordinating the responses to external and internal environmental stressors. While it is well known that carotid and cardiopulmonary baroreceptors modulate sympathetic vasomotor and parasympathetic cardiac neural autonomic drive, to avoid excessive fluctuations in vascular tone and maintain intravascular volume, there is increasing recognition that baroreceptors also modulate a wide range of non-cardiovascular physiological responses via projections from the nucleus of the solitary tract to regions of the central nervous system, including the spinal cord. These projections regulate pain perception, sleep, consciousness, and cognition. In this article, we summarize the physiology of baroreceptor pathways and responses to baroreceptor activation with an emphasis on the mechanisms influencing cardiovascular function, pain perception, consciousness, and cognition. Understanding baroreceptor-mediated effects on cardiac and extra-cardiac autonomic activities will further our understanding of the pathophysiology of multiple common clinical conditions, such as chronic pain, disorders of consciousness (e.g., abnormalities in sleep-wake), and cognitive impairment, which may result in the identification and implementation of novel treatment modalities. © 2021 American Physiological Society. Compr Physiol 11:1373-1423, 2021.

Vasopressin-stimulated ORAI1 expression and store-operated Ca2+ entry in aortic smooth muscle cells

Vascular calcification may result from stimulation of osteogenic signalling with upregulation of the transcription factors CBFA1, MSX2 and SOX9, as well as alkaline phosphatase (ALPL), which degrades and thus inactivates the calcification inhibitor pyrophosphate. Osteogenic signalling further involves upregulation of the Ca²⁺-channel ORAI1. The channel is activated by STIM1 and then accomplishes store-operated Ca²⁺ entry. ORAI1 and STIM1 are upregulated by the serum & glucocorticoid inducible kinase 1 (SGK1) which is critically important for osteogenic signalling. Stimulators of vascular calcification include vasopressin. The present study explored whether exposure of human aortic smooth muscle cells (HAoSMCs) to vasopressin upregulates ORAI1 and/or STIM1 expression, store-operated Ca²⁺ entry and osteogenic signalling. To this end, HAoSMCs were exposed to vasopressin (100 nM, 24 h) without or with additional exposure to ORAI1 blocker MRS1845 (10 μM) or SGK1 inhibitor GSK-650394 (1 μM). Transcript levels were measured using q-RT-PCR, cytosolic Ca²⁺-concentration ([Ca²⁺]_i) by Fura-2-fluorescence, and store-operated Ca²⁺ entry from increase of [Ca²⁺]_i following re-addition of extracellular Ca²⁺ after store depletion with thapsigargin (1 μM). As a result, vasopressin enhanced the transcript levels of ORAI1 and STIM1, store-operated Ca²⁺ entry, as well as the transcript levels of CBFA1, MSX2, SOX9 and ALPL. The effect of vasopressin on store-operated Ca²⁺ entry as well as on transcript levels of CBFA1, MSX2, SOX9 and ALPL was virtually abrogated by MRS1845 and GSK-650394. In conclusion, vasopressin stimulates expression of ORAI1/STIM1, thus augmenting store-operated Ca²⁺ entry and osteogenic signalling. In HAoSMCs, vasopressin (VP) upregulates Ca²⁺ channel ORAI1 and its activator STIM1. VP upregulates store-operated Ca²⁺ entry (SOCE) and osteogenic signalling (OS). VP-induced SOCE, OS and Ca²⁺-deposition are disrupted by ORAI1 inhibitor MRS1845. VP-induced SOCE, OS and Ca²⁺-deposition are disrupted by SGK1 blocker GSK-650394. KEY MESSAGES: • In HAoSMCs, vasopressin (VP) upregulates Ca²⁺ channel ORAI1 and its activator STIM1. • VP upregulates store-operated Ca²⁺ entry (SOCE) and osteogenic signalling (OS). • VP-induced SOCE, OS and Ca²⁺-deposition are disrupted by ORAI1 inhibitor MRS1845. • VP-induced SOCE, OS and Ca²⁺-deposition are disrupted by SGK1 blocker GSK-650394.

The oxytocin receptor signalling system and breast cancer: a critical review

Breast cancer is making up one-quarter of all new female cancer cases diagnosed worldwide. Breast cancer surgeries, radiation therapies, cytotoxic chemotherapies and targeted therapies have made significant progress and play a dominant role in breast cancer patient management. However, many challenges remain, including resistance to systemic therapies, tumour recurrence and metastasis. The cyclic neuropeptide oxytocin (OT) elicits a plethora of biological responses via the oxytocin receptor (OTR) in both the central and peripheral nervous system, including social bonding, stress, maternal behaviour, sexual activity, uterus contraction, milk ejection and cancer. As a typical member of the G protein-coupled receptor family, OTR represents also an intriguing target for cancer therapy. There is emerging evidence that OTR plays a role in breast cancer development and progression, and several breast cancer cell lines express OTR. However, despite supporting evidence that OT lowers breast cancer risks, its mechanistic role in breast cancer development and the related signalling pathways are not fully understood. Here, we review the current knowledge of the OT/OTR signalling system in healthy breast tissue as well as in breast cancer, and discuss OTR as a potential therapeutic target for breast cancer management.

Vasopressin & Oxytocin in Control of the Cardiovascular System: An Updated Review

Since the discovery of vasopressin (VP) and oxytocin (OT) in 1953, considerable knowledge has been gathered about their roles in cardiovascular homeostasis. Unraveling VP vasoconstrictor properties and V1a receptors in blood vessels generated powerful hemostatic drugs and drugs effective in the treatment of certain forms of circulatory collapse (shock). Recognition of the key role of VP in water balance via renal V2 receptors gave birth to aquaretic drugs found to be useful in advanced stages of congestive heart failure. There are still unexplored actions of VP and OT on the cardiovascular system, both at the periphery and in the brain that may open new venues in treatment of cardiovascular diseases. After a brief overview on VP, OT and their peripheral action on the cardiovascular system, this review focuses on newly discovered hypothalamic mechanisms involved in neurogenic control of the circulation in stress and disease.

Camel Hemorphins Exhibit a More Potent Angiotensin-I Converting Enzyme Inhibitory Activity than Other Mammalian Hemorphins: An In Silico and In Vitro Study

Angiotensin-I converting enzyme (ACE) is a zinc metallopeptidase that has an important role in regulating the renin-angiotensin-aldosterone system (RAAS). It is also an important drug target for the management of cardiovascular diseases. Hemorphins are endogenous peptides that are produced by proteolytic cleavage of beta hemoglobin. A number of studies have reported various therapeutic activities of hemorphins. Previous reports have shown antihypertensive action of hemorphins via the inhibition of ACE. The sequence of hemorphins is highly conserved among mammals, except in camels, which harbors a unique Q>R variation in the peptide. Here, we studied the ACE inhibitory activity of camel hemorphins (LVVYPWTRRF and YPWTRRF) and non-camel hemorphins (LVVYPWTQRF and YPWTQRF). Computational methods were used to determine the most likely binding pose and binding affinity of both camel and non-camel hemorphins within the active site of ACE. Molecular dynamics simulations showed that the peptides interacted with critical residues in the active site of ACE. Notably, camel hemorphins showed higher binding affinity and sustained interactions with all three subsites of the ACE active site. An in vitro ACE inhibition assay showed that the IC50 of camel hemorphins were significantly lower than the IC50 of non-camel hemorphins.

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.

Dysregulation of the Renin-Angiotensin System and the Vasopressinergic System Interactions in Cardiovascular Disorders

Purpose of Review

In many instances, the renin-angiotensin system (RAS) and the vasopressinergic system (VPS) are jointly activated by the same stimuli and engaged in the regulation of the same processes.

Recent Findings

Angiotensin II (Ang II) and arginine vasopressin (AVP), which are the main active compounds of the RAS and the VPS, interact at several levels. Firstly, Ang II, acting on AT1 receptors (AT1R), plays a significant role in the release of AVP from vasopressinergic neurons and AVP, stimulating V1a receptors (V1aR), regulates the release of renin in the kidney. Secondly, Ang II and AVP, acting on AT1R and V1aR, respectively, exert vasoconstriction, increase cardiac contractility, stimulate the sympathoadrenal system, and elevate blood pressure. At the same time, they act antagonistically in the regulation of blood pressure by baroreflex. Thirdly, the cooperative action of Ang II acting on AT1R and AVP stimulating both V1aR and V2 receptors in the kidney is necessary for the appropriate regulation of renal blood flow and the efficient resorption of sodium and water. Furthermore, both peptides enhance the release of aldosterone and potentiate its action in the renal tubules.

Summary

In this review, we (1) point attention to the role of the cooperative action of Ang II and AVP for the regulation of blood pressure and the water-electrolyte balance under physiological conditions, (2) present the subcellular mechanisms underlying interactions of these two peptides, and (3) provide evidence that dysregulation of the cooperative action of Ang II and AVP significantly contributes to the development of disturbances in the regulation of blood pressure and the water-electrolyte balance in cardiovascular diseases.

Elevated vasopressin in pregnant mice induces T-helper subset alterations consistent with human preeclampsia

The pathogenesis of preeclampsia (PreE), a hypertensive disorder of pregnancy, involves imbalanced T helper (TH) cell populations and resultant changes in pro- and anti-inflammatory cytokine release. Elevated copeptin (an inert biomarker of arginine vasopressin (AVP)), secretion precedes the development of symptoms in PreE in humans, and infusion of AVP proximal to and throughout gestation is sufficient to initiate cardiovascular and renal phenotypes of PreE in wild-type C57BL/6J mice. We hypothesize that AVP infusion in wild-type mice is sufficient to induce the immune changes observed in human PreE. AVP infusion throughout gestation in mice resulted in increased pro-inflammatory interferon γ (IFNg) (TH1) in the maternal plasma. The TH17-associated cytokine interleukin (IL)-17 was elevated in the maternal plasma, amniotic fluid, and placenta following AVP infusion. Conversely, the TH2-associated anti-inflammatory cytokine IL-4 was decreased in the maternal and fetal kidneys from AVP-infused dams, while IL-10 was decreased in the maternal kidney and all fetal tissues. Collectively, these results demonstrate the sufficiency of AVP to induce the immune changes typical of PreE. We investigated if T cells can respond directly to AVP by evaluating the expression of AVP receptors (AVPRs) on mouse and human CD4+ T cells. Mouse and human T cells expressed AVPR1a, AVPR1b, and AVPR2. The expression of AVPR1a was decreased in CD4+ T cells obtained from PreE-affected women. In total, our data are consistent with a potential initiating role for AVP in the immune dysfunction typical of PreE and identifies putative signaling mechanism(s) for future investigation.

A case report with shock induced by tolvaptan in an elderly patient with congestive heart failure

RATIONALE

Tolvaptan (TLV) is a new vasopressin type 2 receptor antagonist effective in patients with heart failure (HF). Accumulating evidences have revealed that treatment with TLV does not alter the blood pressure significantly.

PATIENT CONCERNS

An 84-year-old man was diagnosed with acute exacerbation of chronic HF due to ischemic cardiomyopathy, arrhythmia, mitral and aortic regurgitation. Treatment with TLV increased the urine volume and improved the dyspnea. After 4 days use of TLV (3.75 mg QD, 7.5 mg QD, 7.5 mg QD, and 15 mg QD, respectively), decrease in blood pressure to less than 90/60 mmHg was observed continuously and the lowest blood pressure was 80/37 mmHg. He was apyretic and felt only thirsty. Central venous pressure was 12 cmH2O.

DIAGNOSES

Because no other medications were changed and no signs of hypovolemic, septic, allergic, or cardiac shock were detected, we suspected an adverse reaction to TLV.

INTERVENTION

Intravenous hydration was performed with 250 mL of normal saline.

OUTCOMES

His blood pressure increased gradually and the statue of hypotention lasted for 14 hours. The dose of TLV was decreased to 7.5 mg/d from the next day to discharge. During this period, his blood pressure was stable at about 125/60 mmHg.

LESSONS

TLV has side effect of severe hypotension that is consistent with its physiological activity. The dose should be increased gradually to achieve the desired effect, while attention should be paid to potential drug interactions.

Selection of desmopressin preparations for the treatment of central diabetes insipidus

Central diabetes insipidus (CDI) is a severe pathology of the hypothalamic-pituitary system, based on a deficit of antidiuretic hormone (ADH). The disease is a life threating condition for patients without adequate replacement therapy by various preparations of arginine vasopressin. This review presents the current concepts on etiology, pathogenesis, diagnostic proсedures, and treatment of CDI. The article gives comparative pharmacological characteristics of various desmopressin forms for the treatment of the central form of disease. When choosing a therapy for the treatment of CDI, the article highlights the long-term high efficiency and safety of the original sublingual form of desmopressin (Mininin Melt), which is confirmed by real clinical practice and clinical trials, including the comparison with other forms of desmopressin.

Adrenomedullin and galanin responses to orthostasis in older persons

BACKGROUND

Neuroendocrine responses to orthostasis may be critical in the maintenance of mean arterial pressure in healthy individuals. A greater reduction in orthostatic tolerance with age may relate to modulation of hormonal responses such as adrenomedullin and galanin. Thus, we investigated (i) whether adrenomedullin and galanin concentrations increase during orthostatic challenge in older subjects, (ii) whether adrenomedullin and galanin concentrations are higher in older females compared with older males when seated and during orthostatic challenge, and (iii) whether postural changes in plasma concentrations of galanin are correlated with levels of adrenomedullin in either older females or males.

MATERIALS AND METHODS

Subjects (n = 18; 12 ♀; 55-80 years old) performed a sit-to-stand test in a 25°C sensory-minimised environment, with blood samples collected after 4 min of being seated and then when standing. Plasma adrenomedullin and galanin concentrations were determined.

RESULTS

Baseline plasma concentration of adrenomedullin (5·35 ± 0·74 (n = 12, females) vs. 7·40 ± 1·06 pg/mL (n = 5, males)) and galanin (64·07 ± 9·05 vs. 98·99 ± 16·90 pg/mL, respectively) did not significantly differ between genders. Furthermore, plasma adrenomedullin and galanin concentrations were not significantly affected by adoption of the upright posture in either gender and were not correlated in females or males.

CONCLUSIONS

Adrenomedullin and galanin concentrations were similar between genders and did not change following adoption of the standing posture. To further clarify the roles, these hormones play in orthostatic intolerance, adrenomedullin and galanin concentrations should be assessed in participants who show presyncopal symptoms during an orthostatic challenge.

Copeptin, a surrogate marker for arginine vasopressin, is associated with disease severity and progression in IgA nephropathy patients

Background

Besides its essential role for water homeostasis, arginine vasopressin (AVP) may have deleterious effects on the kidney. Copeptin, a surrogate marker for AVP, has been shown to be related to renal outcome in patients with diabetic nephropathy and polycystic kidney disease. We investigated the association of copeptin with disease severity and progression in immunoglobulin A nephropathy (IgAN).

Methods

We included a prospective cohort of 59 patients with biopsy proven IgAN. Urinary excretion of α1 microglobulin (α1m), β 2 microglobulin (β2m), kidney injury molecule-1, neutrophil gelatinase-associated lipocalin and total protein were measured at baseline. Plasma copeptin was determined from stored baseline serum samples. Cox regression was performed for the composite renal outcome defined as doubling of serum creatinine, end-stage renal disease (ESRD) or start of immunosuppressive therapy, and for the individual components during 5-year follow-up.

Results

In IgAN patients [male: 72%, age: 42 ± 13 years, mean arterial pressure (MAP): 101 ± 12 mmHg, proteinuria: 1.4 (0.7-2.3) g/day, estimated glomerular filtration rate (eGFR): 48 ± 21 mL/min/1.73 m 2 ] median copeptin was 9.4 (5.3-18.4) pmol/L. At baseline, copeptin was associated with α1m [standardized beta (St. β) = 0.34, P = 0.009], β2m (St. β = 0.33, P = 0.01) and proteinuria (St. β = 0.36, P = 0.053), adjusted for sex and eGFR. During follow-up, the highest tertile of baseline copeptin was positively associated with the incidence of the composite renal outcome as well as with the individual components of doubling of creatinine, ESRD and start of immunosuppressive therapy. In Cox regression models, copeptin showed prognostic value over MAP, proteinuria and eGFR for the composite renal outcome.

Conclusions

Copeptin is associated with disease severity and prognosis in IgAN patients and may have additional prognostic value besides established risk markers.

Copeptin in obese children and adolescents: relationships to body mass index, cortisol and gender

OBJECTIVE

Copeptin has been reported to be associated with stress, obesity and the metabolic syndrome (MetS) in adults. However, data in childhood are scarce. Therefore, we studied the relationships between copeptin, cortisol, puberty and parameters of the MetS in children.

DESIGN

Cross-sectional study.

PATIENTS

A total of 51 obese children (10·8 ± 3·2 years, 39% male, 45% prepubertal, body mass index standard deviation score (BMI-SDS) 2·77 ± 0·56) and 24 lean children of similar age, gender and pubertal stage.

MEASUREMENTS

Copeptin, serum cortisol, 24-h urinary free cortisol, BMI-SDS and, as parameters of the MetS, insulin resistance index (HOMA), HbA1c, uric acids, blood pressure and lipids.

RESULTS

Copeptin levels were significantly (P = 0·047) higher in obese children (5·8 ± 2·8pmol/l) compared to lean children (4·6 ± 2·2pmol/l). BMI-SDS (β-coefficient 0·38 ± 0·35, P =0·033), but not any parameter of the MetS, was significantly related to copeptin in multiple linear regression analyses adjusted for age, gender and pubertal stage. A 24-h urinary free cortisol (β-coefficient 0·13 ± 0·06, P < 0·001), but not serum cortisol, was significantly related to copeptin in multiple linear regression analyses adjusted for age, gender, pubertal stage and BMI-SDS. Pubertal boys (6·6 ± 2·8pmol/l) demonstrated significantly (P = 0·042) higher copeptin levels compared to pubertal girls (4·8 ± 2·6pmol/l), while copeptin concentrations did not differ between prepubertal girls and boys.

CONCLUSIONS

Copeptin levels are related to 24-h urinary free cortisol in obese children. Pubertal boys, but not prepubertal boys, demonstrated higher copeptin levels than girls, suggesting that sex hormones are involved in the regulation of copeptin levels. Further studies are necessary to understand the relationship between obesity, cortisol, gender, pubertal stage and copeptin levels.

Copeptin, resistant hypertension and renal sympathetic denervation

BACKGROUND

Renal denervation is used as a treatment option for patients with resistant hypertension. But only a subgroup of patients benefits from renal sympathetic denervation (RDN). Biomarkers might be helpful to identify patients who respond to RDN. Copeptin as a surrogate for vasopressin levels is increased in hypertension and other cardiovascular diseases. This study aims to evaluate the effect of RDN on Copeptin and its prognostic value for response to RDN.

METHOD AND RESULTS

A total of 40 patients have been included in the study. The responder rate was 47.5% on 24 h ambulatory blood pressure measurements. The mean systolic 24 h blood pressure dropped from 152 ± 10 mmHg to 147 ± 17 mmHg (p = .044) in the six month follow up. The mean baseline level of Copeptin was 7.4 pmol/l (interquartile range 3.7-11.6) for responders and 8.4 pmol/l (interquartile range 5.7-11-8) for non-responders (p = .53). The Copeptin levels did not change over time after renal denervation.

CONCLUSION

Baseline measurements of Copeptin in patients undergoing RDN for resistant hypertension have no predictive value for response to RDN. Despite lowering the blood pressure RDN has no influence on Copeptin levels in this short time follow up period.

Tissue inflammation and nitric oxide-mediated alterations in cardiovascular function are major determinants of endotoxin-induced insulin resistance

BACKGROUND

Endotoxin (i.e. LPS) administration induces a robust inflammatory response with accompanying cardiovascular dysfunction and insulin resistance. Overabundance of nitric oxide (NO) contributes to the vascular dysfunction. However, inflammation itself also induces insulin resistance in skeletal muscle. We sought to investigate whether the cardiovascular dysfunction induced by increased NO availability without inflammatory stress can promote insulin resistance. Additionally, we examined the role of inducible nitric oxide synthase (iNOS or NOS2), the source of the increase in NO availability, in modulating LPS-induced decrease in insulin-stimulated muscle glucose uptake (MGU).

METHODS

The impact of NO donor infusion on insulin-stimulated whole-body and muscle glucose uptake (hyperinsulinemic-euglycemic clamps), and the cardiovascular system was assessed in chronically catheterized, conscious mice wild-type (WT) mice. The impact of LPS on insulin action and the cardiovascular system were assessed in WT and global iNOS knockout (KO) mice. Tissue blood flow and cardiac function were assessed using microspheres and echocardiography, respectively. Insulin signaling activity, and gene expression of pro-inflammatory markers were also measured.

RESULTS

NO donor infusion decreased mean arterial blood pressure, whole-body glucose requirements, and MGU in the absence of changes in skeletal muscle blood flow. LPS lowered mean arterial blood pressure and glucose requirements in WT mice, but not in iNOS KO mice. Lastly, despite an intact inflammatory response, iNOS KO mice were protected from LPS-mediated deficits in cardiac output. LPS impaired MGU in vivo, regardless of the presence of iNOS. However, ex vivo, insulin action in muscle obtained from LPS treated iNOS KO animals was protected.

CONCLUSION

Nitric oxide excess and LPS impairs glycemic control by diminishing MGU. LPS impairs MGU by both the direct effect of inflammation on the myocyte, as well as by the indirect NO-driven cardiovascular dysfunction.

Hydration and beyond: neuropeptides as mediators of hydromineral balance, anxiety and stress-responsiveness

Challenges to body fluid homeostasis can have a profound impact on hypothalamic regulation of stress responsiveness. Deficiencies in blood volume or sodium concentration leads to the generation of neural and humoral signals relayed through the hindbrain and circumventricular organs that apprise the paraventricular nucleus of the hypothalamus (PVH) of hydromineral imbalance. Collectively, these neural and humoral signals converge onto PVH neurons, including those that express corticotrophin-releasing factor (CRF), oxytocin (OT), and vasopressin, to influence their activity and initiate compensatory responses that alleviate hydromineral imbalance. Interestingly, following exposure to perceived threats to homeostasis, select limbic brain regions mediate behavioral and physiological responses to psychogenic stressors, in part, by influencing activation of the same PVH neurons that are known to maintain body fluid homeostasis. Here, we review past and present research examining interactions between hypothalamic circuits regulating body fluid homeostasis and those mediating behavioral and physiological responses to psychogenic stress.

Neurohypophyseal Hormones: Novel Actors of Striated Muscle Development and Homeostasis

Since the 1980’s, novel functional roles of the neurohypophyseal hormones vasopressin and oxytocin have emerged. Several studies have investigated the effects of these two neurohormones on striated muscle tissues, both in vitro and in vivo. The effects of vasopressin on skeletal myogenic cells, developing muscle and muscle homeostasis have been documented. Oxytocin appears to have a greater influence on cardiomyocite differentiation and heart homeostasis. This review summarizes the studies on these novel roles of the two neurohypophyseal hormones, and open the possibility of new therapeutic approaches for diseases affecting striated muscle.

Renal vasoconstriction by vasopressin V1a receptors is modulated by nitric oxide, prostanoids, and superoxide but not the ADP ribosyl cyclase CD38

Renal blood flow (RBF) responses to arginine vasopressin (AVP) were tested in anesthetized wild-type (WT) and CD38(-/-) mice that lack the major calcium-mobilizing second messenger cyclic ADP ribose. AVP (3-25 ng) injected intravenously produced dose-dependent decreases in RBF, reaching a maximum of 25 ± 2% below basal RBF in WT and 27 ± 2% in CD38(-/-) mice with 25 ng of AVP. Renal vascular resistance (RVR) increased 75 ± 6% and 78 ± 6% in WT and CD38(-/-) mice. Inhibition of nitric oxide (NO) synthase with nitro-L-arginine methyl ester (L-NAME) increased the maximum RVR response to AVP to 308 ± 76% in WT and 388 ± 81% in CD38(-/-) (P < 0.001 for both). Cyclooxygenase inhibition with indomethacin increased the maximum RVR response to 125 ± 15% in WT and 120 ± 14% in CD38(-/-) mice (P < 0.001, <0.05). Superoxide suppression with tempol inhibited the maximum RVR response to AVP by 38% in both strains (P < 0.005) but was ineffective when administered after L-NAME. The rate of RBF recovery (relaxation) after AVP was slowed by L-NAME and indomethacin (P < 0.001, <0.005) but was unchanged by tempol. All vascular responses to AVP were abolished by an AVP V1a receptor antagonist. A V2 receptor agonist or antagonist had no effect on AVP-induced renal vasoconstriction. Taken together, the results indicate that renal vasoconstriction by AVP in the mouse is strongly buffered by vasodilatory actions of NO and prostanoids. The vasoconstriction depends on V1a receptor activation without involvement of CD38 or concomitant vasodilatation by V2 receptors. The role of superoxide is to enhance the contractile response to AVP, most likely by reducing the availability of NO rather than directly stimulating intracellular contraction signaling pathways.

Age dependency of vasopressin pulmonary vasodilatory effect in rats

BACKGROUND

Vasopressin is a systemic vasoconstrictor. Its pulmonary vasodilatory effect is controversial, and limited data are available on its use in neonates with pulmonary hypertension. Hypothesizing that the vasopressin-induced pulmonary vasodilation is developmentally regulated, we evaluated its pulmonary and systemic arterial response in newborn and adult rats.

METHODS

Vessels were mounted on a wire myograph, and the vasopressin-induced changes in vasomotor tone measured. The vessel- and age-dependent differences in vasopressin V1a and V2 receptors' expression were evaluated by western blotting.

RESULTS

Vasopressin induced a dose-dependent increase in mesenteric arterial tone at both ages, but of greater magnitude in adult vessels (P < 0.01). At lower concentrations, vasopressin induced pulmonary vasodilation in adult vessels and vasoconstriction in newborn arteries. The adult vasopressin-induced pulmonary vasodilation was inhibited by ibuprofen, suggesting that the response is prostaglandin mediated. Pulmonary tissue V1a receptor protein expression was higher in adult, when compared with newborn arteries (P < 0.01). The adult vessels V1a expression predominated in the pulmonary arteries, and V2 was only detected in mesenteric arteries.

CONCLUSION

The vasopressin-induced pulmonary vasodilation is absent in newborn rats likely due to the lower tissue V1a expression early in life. These animal data challenge the therapeutic use of vasopressin in neonatal pulmonary hypertension.

Serum copeptin levels in adolescents with primary hypertension

BACKGROUND

The prevalence of hypertension continues to rise in the pediatric population. In recent years, there has been an increasing amount of reports on serum arginine vasopressin and its derivative, copeptin, in blood pressure control, but its role is still unclear. The objective of this study was to assess serum copeptin in adolescents with essential hypertension.

METHODS

The study cohort consisted of 84 subjects (30 girls and 54 boys) aged 11-18 years, divided into two groups: hypertension (HT) - 53 subjects with confirmed primary hypertension and R - reference group - 31 subjects in whom hypertension was excluded on the basis of ambulatory blood pressure monitoring (ABPM) (white-coat hypertension). Serum copeptin concentration was measured using a commercially available enzyme-linked immunosorbent assay kit (USCN).

RESULTS

Hypertensive patients had higher serum copeptin levels (median, 267 [Q1-Q3: 151.1-499.7 pg/ml]) than controls (median, 107.3 [Q1-Q3: 36.7-203.4 pg/ml]), (p < 0.01). Statistically significant difference was found both in males and females. In both groups, positive correlations between serum copeptin and uric acid levels (r = 0.31, p < 0.01), albuminuria (r = 0.45, p < 0.01), serum triglycerides (r = 0.3, p < 0.05), body mass index (BMI) standard deviation score (SDS) (r = 0.24, p < 0.05) and 24-h systolic blood pressure (SBP) (r = 0.37, p < 0.01) and diastolic blood pressure (DBP) (r = 0.23, p < 0.05) were found.

CONCLUSIONS

In summary, higher serum copeptin levels, a surrogate for arginine vasopressin (AVP) release, are associated not only with systolic and diastolic blood pressure but also with several components of metabolic syndrome including obesity, elevated concentration of triglycerides, albuminuria, and serum uric acid level. However, for the time being, more research is needed in order to confirm the role of serum copeptin as a novel marker of elevated blood pressure and predictor of metabolic syndrome.

Vasopressin and oxytocin in control of the cardiovascular system

Vasopressin (VP) and oxytocin (OT) are mainly synthesized in the magnocellular neurons of the paraventricular (PVN) and supraoptic nucleus (SON) of the hypothalamus. Axons from the magnocellular part of the PVN and SON project to neurohypophysis where VP and OT are released in blood to act like hormones. Axons from the parvocellular part of PVN project to extra-hypothalamic brain areas (median eminence, limbic system, brainstem and spinal cord) where VP and OT act like neurotransmitters/modulators. VP and OT act in complementary manner in cardiovascular control, both as hormones and neurotransmitters. While VP conserves water and increases circulating blood volume, OT eliminates sodium. Hyperactivity of VP neurons and quiescence of OT neurons in PVN underlie osmotic adjustment to pregnancy. In most vascular beds VP is a potent vasoconstrictor, more potent than OT, except in the umbilical artery at term. The vasoconstriction by VP and OT is mediated via V1aR. In some vascular beds, i.e. the lungs and the brain, VP and OT produce NO dependent vasodilatation. Peripherally, VP has been found to enhance the sensitivity of the baro-receptor while centrally, VP and OT increase sympathetic outflow, suppresse baro-receptor reflex and enhance respiration. Whilst VP is an important mediator of stress that triggers ACTH release, OT exhibits anti-stress properties. Moreover, VP has been found to contribute considerably to progression of hypertension and heart failure while OT has been found to decrease blood pressure and promote cardiac healing.

Vasotocin analogues with selective natriuretic, kaliuretic and antidiuretic effects in rats

The aim of the present study was an investigation of mechanisms mediating selective effect of vasotocin analogues on water, sodium, and potassium excretion. We tested vasotocin analogues: Mpa(1)-vasotocin (dAVT), Mpa(1)-Arg(4)-vasotocin (dAAVT) and Mpa(1)-DArg(8)-vasotocin (dDAVT). The effects on water, sodium, and potassium transport were evaluated in experiments using normal and water-loaded Wistar rats. It was shown that all tested peptides exerted antidiuretic activity. Vasotocin and dAVT induced natriuresis and kaliuresis in rats. V1a agonist (Phe(2)-Ile(3)-Orn(8)-vasopressin) reproduced the renal effects of dAVT on sodium and potassium excretion but not on water reabsorption. dAAVT, dDAVT and V2 agonist (desmopressin) induced kaliuresis without any effect on sodium excretion. Natriuresis was associated with increase in cGMP excretion, whereas kaliuresis was correlated with rise of cAMP excretion. V1a antagonist (Pmp(1)-Tyr(Me)(2)-vasopressin) significantly reduced the dAVT-stimulated natriuresis and did not influence on urinary potassium excretion. V2 antagonist (Pmp(1)-DIle(2)-Ile(4)-vasopressin) significantly reduced the dAVT- and dAAVT-induced kaliuresis. It is assumed that effects of the nonapeptides on sodium and potassium transport are independent of their antidiuretic activity and mediated by different subtypes of V receptors (the V1a or V1a-like receptor for natriuretic effect and V2 or V2-like one for kaliuretic). In accordance to the data obtained, there is a possibility of selective regulation of renal water reabsorption and urinary sodium and potassium excretion with involvement of neurohypophysial hormones.

Estradiol and testosterone regulate arginine-vasopressin expression in SH-SY5Y human female neuroblastoma cells through estrogen receptors-α and -β

The expression of arginine-vasopressin (AVP) is regulated by estradiol and testosterone (T) in different neuronal populations by mechanisms that are not yet fully understood. Estrogen receptors (ERs) have been shown to participate in the regulation of AVP neurons by estradiol. In addition, there is evidence of the participation of ERβ in the regulation of AVP expression exerted by T via its metabolite 5α-dihydrotestosterone (5α-DHT) and its further conversion in the androgen metabolite and ERβ ligand 3β-diol. In this study we have explored the role of ERs in the regulation exerted by estradiol and T on AVP expression, using the human neuroblastoma cell line SH-SY5Y. Estradiol treatment increased AVP mRNA levels in SH-SY5Y cells in comparison with cells treated with vehicle. The stimulatory effect of estradiol on AVP expression was imitated by the ERα agonist 4,4',4',-(4-propyl-[1H]-pyrazole-1,3,5-triyl)trisphenol and blocked by the ER antagonist, ICI 182,780, and the ERα antagonist 1,3-bis(4-hydroxyphenyl)-4-methyl-5-[4-(2-piperidinylethoxy)phenol]-1hpyrazoledihydrochloride. In contrast, the ERβ agonist 2,3-bis(4-hydroxyphenyl)-propionitrile reduced AVP expression, whereas the ERβ antagonist 4-[2-phenyl-5,7-bis(trifluoromethyl) pyrazolo[1,5-a]pyrimidin-3-yl]phenol enhanced the action of estradiol on AVP expression. T increased AVP expression in SH-SY5Y cells by a mechanism that was dependent on aromatase but not on 5α-reductase activity. The T effect was not affected by blocking the androgen receptor, was not imitated by the T metabolite 5α-DHT, and was blocked by the ERα antagonist 1,3-bis(4-hydroxyphenyl)-4-methyl-5-[4-(2-piperidinylethoxy)phenol]-1hpyrazoledihydrochloride. In contrast, 5α-DHT had a similar effect as the ERβ agonists 2,3-bis(4-hydroxyphenyl)-propionitrile and 3β-diol, reducing AVP expression. These findings suggest that estradiol and T regulate AVP expression in SH-SY5Y cells through ERs, exerting a stimulatory action via ERα and an inhibitory action via ERβ.

Hypertension in mice with transgenic activation of the brain renin-angiotensin system is vasopressin dependent

An indispensable role for the brain renin-angiotensin system (RAS) has been documented in most experimental animal models of hypertension. To identify the specific efferent pathway activated by the brain RAS that mediates hypertension, we examined the hypothesis that elevated arginine vasopressin (AVP) release is necessary for hypertension in a double-transgenic model of brain-specific RAS hyperactivity (the "sRA" mouse model). sRA mice experience elevated brain RAS activity due to human angiotensinogen expression plus neuron-specific human renin expression. Total daily loss of the 4-kDa AVP prosegment (copeptin) into urine was grossly elevated (≥8-fold). Immunohistochemical staining for AVP was increased in the supraoptic nucleus of sRA mice (~2-fold), but no quantitative difference in the paraventricular nucleus was observed. Chronic subcutaneous infusion of a nonselective AVP receptor antagonist conivaptan (YM-087, Vaprisol, 22 ng/h) or the V(2)-selective antagonist tolvaptan (OPC-41061, 22 ng/h) resulted in normalization of the baseline (~15 mmHg) hypertension in sRA mice. Abdominal aortas and second-order mesenteric arteries displayed AVP-specific desensitization, with minor or no changes in responses to phenylephrine and endothelin-1. Mesenteric arteries exhibited substantial reductions in V(1A) receptor mRNA, but no significant changes in V(2) receptor expression in kidney were observed. Chronic tolvaptan infusion also normalized the (5 mmol/l) hyponatremia of sRA mice. Together, these data support a major role for vasopressin in the hypertension of mice with brain-specific hyperactivity of the RAS and suggest a primary role of V(2) receptors.

Vasopressin V1a and V1b Receptors: From Molecules to Physiological Systems

The neurohypophysial hormone arginine vasopressin (AVP) is essential for a wide range of physiological functions, including water reabsorption, cardiovascular homeostasis, hormone secretion, and social behavior. These and other actions of AVP are mediated by at least three distinct receptor subtypes: V1a, V1b, and V2. Although the antidiuretic action of AVP and V2 receptor in renal distal tubules and collecting ducts is relatively well understood, recent years have seen an increasing understanding of the physiological roles of V1a and V1b receptors. The V1a receptor is originally found in the vascular smooth muscle and the V1b receptor in the anterior pituitary. Deletion of V1a or V1b receptor genes in mice revealed that the contributions of these receptors extend far beyond cardiovascular or hormone-secreting functions. Together with extensively developed pharmacological tools, genetically altered rodent models have advanced the understanding of a variety of AVP systems. Our report reviews the findings in this important field by covering a wide range of research, from the molecular physiology of V1a and V1b receptors to studies on whole animals, including gene knockout/knockdown studies.

The fifth neurohypophysial hormone receptor is structurally related to the V2-type receptor but functionally similar to V1-type receptors

The neurohypophysial peptides of the vasopressin (VP) and oxytocin (OT) families regulate salt and water homeostasis and reproduction through distinct G protein-coupled receptors. The current thinking is that there are four neurohypophysial hormone receptors (V1aR, V1bR, V2R, and OTR) in vertebrates, and their evolutionary history is still debated. We report the identification of a fifth neurohypophysial hormone receptor (V2bR) from the holocephalan elephant fish. This receptor is similar to conventional V2R (V2aR) in sequence, but induced Ca(2+) signaling in response to vasotocin (VT), the non-mammalian VP ortholog; such signaling is typical of V1-type receptors. In addition, V1aR, V1bR and OTR were also isolated from the elephant fish. Further screening revealed that orthologous V2bRs are widely distributed throughout the jawed vertebrates, and that the V2bR family is subdivided into two subfamilies: the fish specific type-1, and a type-2 that is characteristically found in tetrapods. Analysis suggested that the mammalian V2bR may have lost its function. Based on molecular phylogenetic, synteny and functional analyses, we propose a new evolutionary history for the neurohypophysial hormone receptors in vertebrates as follows: the first duplication generated V1aR/V1bR/OTR and V2aR/V2bR lineages; after divergence from the V2bR lineage, the V2aRs evolved to use cAMP as a second messenger, while the V2bRs retained the original Ca(2+) signaling system. Future studies on the role of V2bR in the brain, heart, kidney and reproductive organs, in which it is highly expressed, will open a new research field in VP/VT physiology and evolution.

Location, location, location: genetic regulation of neural sex differences

Sex differences in many behaviors such as cognition, mood, and motor skills are well-documented in animals and humans and are regulated by many neural circuits. Sexual dimorphisms within cell populations in these circuits play critical roles in the production of these behavioral dichotomies. Here we focus on three proteins that have well described sexual dimorphisms; calbindin-D28k, a calcium binding protein, tyrosine hydroxylase, the rate limiting enzyme involved in dopamine synthesis and vasopressin, a neuropeptide with central and peripheral sites of action. We describe the sex differences in subpopulations of these proteins, with particular emphasis on laboratory mice. Our thrust is to examine genetic bases of sex differences and how the use of genetically modified models has advanced our understanding of this topic. Regional sex differences in the expression of these three proteins are driven by sex chromosome complement, steroid receptors or in some instances both. While studies of sex differences attributable to sex chromosome genes are still few in number it is exciting to note that this variable factors into expression differences for all three of these proteins. Different genetic mechanisms, which elaborate sex differences, may be employed stochastically in different cell populations. Alternately, general patterns involving the timing of differentiation of the sex differences, relative to the "critical period" in hormonal differences between males and female neonates may emerge. In conclusion, future directions in this area should include examination of the importance of location, timing, steroidal receptor/sex chromosome gene synergy and epigenetics in molding neural sex differences.

Vasopressin V1a receptor is required for nucleocytoplasmic transport of mineralocorticoid receptor

We previously reported that a deficiency in the vasopressin V1a receptor (V1aR) results in type 4 renal tubular acidosis, which suggests that vasopressin exerts direct effects on the physiological actions of aldosterone. We investigated the role of vasopressin for nucleocytoplasmic transport of mineralocorticoid receptor (MR) in the intercalated cells. Vasopressin V1aR-deficient (V1aR(-/-)) mice showed largely decreased expression of MR and 11β-hydroxysteroid dehydrogenase type 2 (11βHSD2) in the medulla of the kidney, which was partially ameliorated by fludrocortisone treatment. The incubation of IN-IC cells, an intercalated cell line established from temperature-sensitive SV40 large T antigen-expressing rats, with aldosterone or vasopressin increased the nuclear-to-cytoplasmic ratio of the MR from 11.2 to 47.2% and from 18.7 to 61.2%, respectively, in 30 min without any changes in MR expression from the whole cell extract. The immunohistochemistry analysis of the IN-IC cells revealed the nuclear accumulation of MRs after a 30-min incubation with aldosterone or vasopressin. These effects were accompanied by an increase in regulator of chromosome condensation-1 (RCC-1) due to aldosterone and a decrease in Ran GTPase-activating protein 1 (Ran Gap1) due to vasopressin. RNA interference against V1aR abolished the nuclear accumulation of MR induced by aldosterone or vasopressin. Vasopressin increased PKCα and -β(1) expression, and aldosterone increased PKCδ and -ζ expression, but these effects were abolished with a V1aR knockdown. These results suggest that vasopressin directly regulates the nucleocytoplasmic transport of MRs via the V1aR in the intercalated cells of the collecting ducts.

A urine-concentrating defect in 11β-hydroxysteroid dehydrogenase type 2 null mice

In aldosterone target tissues, 11β-hydroxysteroid dehydrogenase type 2 (11βHSD2) is coexpressed with mineralocorticoid receptors (MR) and protects the receptor from activation by glucocorticoids. Null mutations in the encoding gene, HSD11B2, cause apparent mineralocorticoid excess, in which hypertension is thought to reflect volume expansion secondary to sodium retention. Hsd11b2(-/-) mice are indeed hypertensive, but impaired natriuretic capacity is associated with significant volume contraction, suggestive of a urine concentrating defect. Water turnover and the urine concentrating response to a 24-h water deprivation challenge were therefore assessed in Hsd11b2(-/-) mice and controls. Hsd11b2(-/-) mice have a severe and progressive polyuric/polydipsic phenotype. In younger mice (∼2 mo of age), polyuria was associated with decreased abundance of aqp2 and aqp3 mRNA. The expression of other genes involved in water transport (aqp4, slc14a2, and slc12a2) was not changed. The kidney was structurally normal, and the concentrating response to water deprivation was intact. In older Hsd11b2(-/-) mice (>6 mo), polyuria was associated with a severe atrophy of the renal medulla and downregulation of aqp2, aqp3, aqp4, slc14a2, and slc12a2. The concentrating response to water deprivation was impaired, and the natriuretic effect of the loop diuretic bumetanide was lost. In older Hsd11b2(-/-) mice, the V2 receptor agonist desmopressin did not restore full urine concentrating capacity. We find that Hsd11b2(-/-) mice develop nephrogenic diabetes insipidus. Gross changes to renal structure are observed, but these were probably secondary to sustained polyuria, rather than of developmental origin.