Physiology of the vasopressin receptors

Neurohypophysial and paracrine vasopressinergic signaling regulates aquaporin trafficking to hydrate marine teleost oocytes

The dual aquaporin (Aqp1ab1/Aqp1ab2)-mediated hydration of marine teleost eggs, which occurs during oocyte meiosis resumption (maturation), is considered a key adaptation underpinning their evolutionary success in the oceans. However, the endocrine signals controlling this mechanism are almost unknown. Here, we investigated whether the nonapeptides arginine vasopressin (Avp, formerly vasotocin) and oxytocin (Oxt, formerly isotocin) are involved in marine teleost oocyte hydration using the gilthead seabream (Sparus aurata) as a model. We show that concomitant with an increased systemic production of Avp and Oxt, the nonapeptides are also produced and accumulated locally in the ovarian follicles during oocyte maturation and hydration. Functional characterization of representative Avp and Oxt receptor subtypes indicates that Avpr1aa and Oxtrb, expressed in the postvitellogenic oocyte, activate phospholipase C and protein kinase C pathways, while Avpr2aa, which is highly expressed in the oocyte and in the follicular theca and granulosa cells, activates the cAMP-protein kinase A (PKA) cascade. Using ex vivo, in vitro and mutagenesis approaches, we determined that Avpr2aa plays a major role in the PKA-mediated phosphorylation of the aquaporin subdomains driving membrane insertion of Aqp1ab2 in the theca and granulosa cells, and of Aqp1ab1 and Aqp1ab2 in the distal and proximal regions of the oocyte microvilli, respectively. The data further indicate that luteinizing hormone, which surges during oocyte maturation, induces the synthesis of Avp in the granulosa cells via progestin production and the nuclear progestin receptor. Collectively, our data suggest that both the neurohypophysial and paracrine vasopressinergic systems integrate to differentially regulate the trafficking of the Aqp1ab-type paralogs via a common Avp-Avpr2aa-PKA pathway to avoid competitive occupancy of the same plasma membrane space and maximize water influx during oocyte hydration.

Rethinking Vasopressin: New Insights into Vasopressin Signaling and Its Implications

Vasopressin is a highly conserved peptide hormone that has been traditionally associated with water homeostasis. There is accumulating evidence in both humans and animal models that vasopressin is implicated in the regulation of metabolism. This review focuses on the effects that vasopressin exerts on the regulation of glucose and fatty acids with a particular emphasis on the potential repercussions of metabolic dysregulation in kidney disease.

Sodium Homeostasis, a Balance Necessary for Life

Body sodium (Na) levels must be maintained within a narrow range for the correct functioning of the organism (Na homeostasis). Na disorders include not only elevated levels of this solute (hypernatremia), as in diabetes insipidus, but also reduced levels (hyponatremia), as in cerebral salt wasting syndrome. The balance in body Na levels therefore requires a delicate equilibrium to be maintained between the ingestion and excretion of Na. Salt (NaCl) intake is processed by receptors in the tongue and digestive system, which transmit the information to the nucleus of the solitary tract via a neural pathway (chorda tympani/vagus nerves) and to circumventricular organs, including the subfornical organ and area postrema, via a humoral pathway (blood/cerebrospinal fluid). Circuits are formed that stimulate or inhibit homeostatic Na intake involving participation of the parabrachial nucleus, pre-locus coeruleus, medial tuberomammillary nuclei, median eminence, paraventricular and supraoptic nuclei, and other structures with reward properties such as the bed nucleus of the stria terminalis, central amygdala, and ventral tegmental area. Finally, the kidney uses neural signals (e.g., renal sympathetic nerves) and vascular (e.g., renal perfusion pressure) and humoral (e.g., renin-angiotensin-aldosterone system, cardiac natriuretic peptides, antidiuretic hormone, and oxytocin) factors to promote Na excretion or retention and thereby maintain extracellular fluid volume. All these intake and excretion processes are modulated by chemical messengers, many of which (e.g., aldosterone, angiotensin II, and oxytocin) have effects that are coordinated at peripheral and central level to ensure Na homeostasis.

Vasopressin-induced hyponatremia in an adult normotensive trauma patient: A case report

BACKGROUND

Arginine vasopressin is a neuropeptide produced in the hypothalamus and released by the posterior pituitary gland. In addition to maintaining plasma osmolarity, under hypovolemic or hypotensive conditions, it helps maintain plasma volume through renal water reabsorption and increases systemic vascular tone. Its synthetic analogues are widely used in the intensive care unit as a continuous infusion, in addition to hospital floors as an intravenous or intranasal dose. A limited number of cases of hyponatremia in patients with septic or hemorrhagic shock have been reported previously with vasopressin. We report for the first time a normotensive patient who developed vasopressin-induced hyponatremia.

CASE SUMMARY

A 39-year-old man fell off a forklift and sustained an axial load injury to his cranium. He had no history of previous trauma. Examination was normal except for motor and sensory deficits. The Imagine test showed endplate fracture at C7 and acute traumatic disc at C7 with cortical degeneration. He underwent cervical discectomy and fusion, laminectomy, and posterior instrumented fusion. After intensive care unit admission post-surgery, he developed hyponatremia of 121-124 mEq/L post phenylephrine and vasopressin infusion to maintain blood pressure maintenance. He was evaluated for syndrome of inappropriate secretion of antidiuretic hormone, hypothyroid, adrenal-induced, or diuretic-induced hyponatremia. At the end of extensive evaluation for the underlying cause of hyponatremia, vasopressin was discontinued. He was also put on fluid restriction, given exogenous desmopressin, and a dextrose 5% in water infusion to prevent osmotic demyelination syndrome caused by sodium overcorrection which improved his sodium level to 135 mmol/L.

CONCLUSION

The presentation of vasopressin-induced hyponatremia is uncommon in normotensive patients, and the most difficult aspect of this condition is determining the underlying cause of hyponatremia. Our case illustrates that, considering the vast differential diagnosis of hyponatremia in hospitalized patients, both hospitalists and intensivists should be aware of this serious complication of vasopressin therapy.

Use of vasopressin in neonatal hypertrophic obstructive cardiomyopathy: case series

OBJECTIVE

To determine the effect of vasopressin on arterial blood pressure in infants with neonatal hypertrophic obstructive cardiomyopathy (HOCM).

STUDY DESIGN

Retrospective case study in Neonatal ICU involving six infants; five born to mothers with diabetes mellitus (mean gestational age 37.5 ± 0.9 weeks). Vasopressin infusion was started at a mean dose of 0.3 ± 0.2 mU/kg/min.

RESULT

Initiation of vasopressin was followed by improved mean (p = 0.004), systolic (p = 0.028), and diastolic (p = 0.009) arterial pressure within 2 h. Heart rate (p = 0.025) and oxygen requirement (p = 0.021) also declined after initiation. Serum sodium declined initially and recovered by 72 h (p = 0.017).

CONCLUSION

Although there is limited experience with vasopressin use in neonatal HOCM, our case series suggests it may be beneficial for improving systemic hypotension and stabilization of hemodynamics. The potential for hyponatremia is high, necessitating careful fluid/electrolyte management. A prospective randomized trial is necessary to confirm safety and efficacy of vasopressin treatment in neonatal HOCM.

International Survey on the Use of Arginine Vasopressin in the Postoperative Management of Single Ventricle Patients

Management of patients with single ventricle physiology after surgical palliation is challenging. Arginine vasopressin has gained popularity in recent years as a non-catecholamine vasoactive medication due to its unique properties. However, data regarding its use in the pediatric population is limited. Therefore, we designed a survey to explore whether and how clinicians use this medication in intensive care units for the postoperative management of single ventricle patients. This international survey aimed to assess usage, practices, and concepts related to arginine vasopressin in pediatric intensive care units worldwide. Directors of pediatric intensive care units who are members of the following international professional societies: European Society of Pediatric Neonatal Intensive Care, Association for European Pediatric and Congenital Cardiology, and Pediatric Cardiac Intensive Care Society were invited to participate in this survey. Of the 62 intensive care unit directors who responded, nearly half use arginine vasopressin in the postoperative management of neonatal single ventricle patients, and 90% also use the drug in subsequent surgical palliation. The primary indications are vasoplegia, hemodynamic instability, and refractory shock, although it is still considered a second-line medication. Conceptual benefits include improved hemodynamics and end-organ perfusion and decreased incidence of low cardiac output syndrome. Those practitioners who do not use arginine vasopressin cite lack of availability, fear of potential adverse effects, unclear indication for use, and lack of evidence suggesting improved outcomes. Both users and non-users described increased myocardial afterload and extreme vasoconstriction as potential disadvantages of the medication. Despite the lack of conclusive data demonstrating enhanced clinical outcomes, our study found arginine vasopressin is used widely in the care of infants and children with single ventricle physiology after the first stage and subsequent palliative surgeries. While many intensive care units use this medication, few had protocols, offering an area for further growth and development.

Extrapontine myelinolysis caused by rapid correction of pituitrin-induced severe hyponatremia: A case report

BACKGROUND

Severe hyponatremia is considered a rare complication of pituitrin, which is widely used for the treatment of pulmonary hemorrhage. However, the management of pituitrin-associated hyponatremia can be challenging because a rapid correction of hyponatremia may cause the development of osmotic demyelination syndrome, resulting in life-threatening neurological injuries.

CASE SUMMARY

A 20-year-old Chinese man with massive hemoptysis developed symptomatic hyponatremia (116 mmol/L) after therapy by a continuous intravenous drip of pituitrin. To normalize his serum sodium, a hypertonic saline infusion was applied for 3 d, and the pituitrin administration was stopped concurrently. Then, an overly rapid increase in serum sodium level (18 mmol/L in 24 h) was detected after treatment. One day later, the patient experienced a sudden onset of generalized tonic-clonic seizures, as well as subsequent dysarthria and dystonia. Magnetic resonance imaging revealed increased signal intensity in the bilateral symmetric basal ganglia on the T2-weighted images, compatible with a diagnosis of extrapontine myelinolysis. The patient received an intravenous administration of high-dose corticosteroids, rehabilitation, and neurotrophic therapy. Finally, his clinical abnormalities were vastly improved, and he was discharged with few residual symptoms.

CONCLUSION

Physicians should be fully aware that pituitrin can cause profound hyponatremia and its correction must be performed at a controlled rate to prevent the development of osmotic demyelination syndrome.

Terlipressin infusion for prevention of vasoplegic syndrome in patients treated with angiotensin II receptor antagonist undergoing coronary artery bypass graft surgery: a randomized controlled study

Background and objectives

Preoperative use of renin angiotensin system antagonists has been considered an independent risk factor for development of vasoplegic syndrome. The aim of this study was to demonstrate efficacy of prophylactic terlipressin infusion for prevention of vasoplegic syndrome in patients treated with angiotensin receptor blocker undergoing coronary artery bypass graft surgery.

Patients and methods

One hundred patients on angiotensin II receptor antagonist [losartan] scheduled for coronary artery bypass surgery were enrolled into this prospective randomized controlled study. Anesthetic technique, surgical technique, and cardiopulmonary bypass management were standardized for all patients. With the start of rewarming, patients were randomized to receive either terlipressin infusion 1.3 μg.kg−1.hour−1, or normal saline infusion. Incidence of vasoplegic syndrome score was used as primary outcome. Hemodynamic parameters, inotropic score, and vasopressor dependency index were used as secondary outcome.

Results

Incidence of vasoplegic syndrome was significantly lower in terlipressin group compared to placebo group. Norepinephrine was required in 2 patients of terlipressin versus 15 patients of placebo group. Mean arterial blood pressure was significantly higher in terlipressin group compared to placebo group (81.7 ± 18.5 versus 69.3 ± 20.2 at 60 min after weaning from CBP). Cardiac index was significantly lower in terlipressin group compared to placebo group (2.52 ± 1.48 versus 3.2 ± 1.55). Systemic vascular resistance was significantly higher in terlipressin group compared to placebo group (2438.09 ± 735.13 versus 1575.05 ± 753.54). Inotropic score and vasopressor dependency index were significantly lower in terlipressin group compared to placebo group.

Conclusion

Prophylactic terlipressin infusion could prevent development of vasoplegic syndrome in patients treated with angiotensin II receptor antagonist undergoing coronary artery bypass graft surgery.

Trial registration

PACTR, PACTR201804003249274, Registered 25/03/2018—retrospectively registered, https://pactr.samrc.ac.za/TrialDisplay.aspx?TrialID=3249.

Effect of adding vasopressin on the distribution of lidocaine in tissues, anesthetic action, and circulatory dynamics

We examined whether vasopressin affects the distribution, anesthesia duration, and circulatory dynamics of lidocaine. Blood flow was measured after injecting 0.003, 0.03, or 0.3 U/mL vasopressin and 2% lidocaine (L) to the upper lip of rats. Radioactivity and distribution of ¹⁴C-labeled L (CL) in the palate, palatal mucosa, maxilla bone, and blood was measured by autoradiography after injecting CL and CL + 0.03 U/mL vasopressin. To evaluate anesthesia duration, somatosensory-evoked potentials, blood pressure, and pulse rate were measured after L, 0.03 U/mL vasopressin, and L + 0.03 U/mL vasopressin injection to the palatal mucosa. Blood flow from 10 to 60 min was significantly lower with 0.03 U/mL vasopressin and L + 0.03 U/mL vasopressin than with L. Radioactivity in the palatal mucosa and maxilla bone was significantly higher at 5-60 min and 2-60 min with CL + 0.03 U/mL vasopressin than with CL. Blood radioactivity reached the maximum at 0.5 and 50 min with CL and CL + 0.03 U/mL vasopressin, respectively. Autoradiogram showed higher distribution with CL + 0.03 U/mL vasopressin than CL. Peak-to-peak amplitude 30-60 min was significantly lower with L + 0.03 U/mL vasopressin than with L. Lidocaine did not affect blood pressure and pulse rate with 0.03 U/mL vasopressin-only or combined with 2%-lidocaine. Topical 0.03 U/mL vasopressin injection reduced the tissue blood flow, promoted the localization and retention, and extended the anesthesia duration of lidocaine, leaving circulatory dynamics unaffected.

Effects of exogenous oxytocin and atosiban antagonist on GABA in different region of brain

Gamma amino butyric acid (GABA) is the primary inhibitory neurotransmitter in the vertebral central nervous system. It functions by altering the membrane conductance of Cl- ions, maintaining the membrane potential close to the resting potential. The hormone oxytocin (OT) has a central action where it acts as a neuromodulatory peptide and exerts its action depending upon the distribution of OT receptors (OTR) in the target site. OTRs are G-protein-coupled receptors (GPCRs) comprising different subunits (Gq, Gi, and Gs). The G- protein isoforms have the ability to activate different pathways, but specific agonists and antagonists may show different affinities to OTRs, depending on the specific G-protein isoform to which they are coupled. It is well documented that OTR distribution varies with age and species and in regions of the brain. In this study, we attempted to observe the impact of OT and atosiban (OTA), an OT antagonist, on GABA levels in different regions of the brain. Study animals were exposed intraperitoneally (i.p.) to normal saline (0.89%), OT 0.0116 mg/kg, and OTA 1 mg/kg in different combinations, for 30days. It was observed that OT and OTA administration modulated GABA levels in different regions of brain, while normal saline had no effect. It may be due to OTR receptor expression in different regions of the brain. This is significant because region-specific expression of different receptors could be important in the development of new drugs targeting specific neuropsychiatric disorders.

Arginine vasopressin attenuates the effects of TNF-α in aortic endothelial cells by inducing ectodomain shedding of TNF receptor 1

In septic shock, arginine vasopressin (AVP) is commonly used as a vasopressor to restore blood pressure. Exogenous AVP may have anti-inflammatory effects as well. We investigated whether AVP modulates the effects of tumor necrosis factor-α (TNF-α) in human aortic endothelial cells (HAECs). TNF-α stimulated intercellular adhesion molecule-1 expression, while AVP pretreatment attenuated this effect of TNF-α. Upon treatment with AVP, extracellular Ca²⁺ entered the cells rapidly through L-type calcium channels, which in turn induced cell surface translocation of a disintegrin and metalloprotease 10 (ADAM10) and ectodomain shedding of tumor necrosis factor receptor 1 (TNFR1). On the other hand, siRNA depletion of ADAM10 suppressed AVP-induced ectodomain shedding of TNFR1 and eliminated the inhibitory effect of AVP against TNF-α. Depletion of oxytocin receptor also abolished AVP-induced extracellular Ca²⁺ influx, AVP-induced ectodomain shedding of TNFR1 and the inhibitory effect of AVP against TNF-α. These findings suggest that AVP decreases the responsiveness of HAECs to TNF-α by inducing ADAM10-dependent ectodomain shedding of TNFR1. Extracellular Ca²⁺ influx through L-type calcium channels was essential for ADAM10 activation. This effect of AVP was mediated through the oxytocin receptor.

Involvement of Vasopressin in the Pathogenesis of Pulmonary Tuberculosis: A New Therapeutic Target?

Tuberculosis (TB) is a highly complex infectious disease caused by the intracellular pathogen Mycobacterium tuberculosis (Mtb). It is characterized by chronic granulomatous inflammation of the lung and systemic immune-neuroendocrine responses that have been associated with pathophysiology and disease outcome. Vasopressin (VP), a neurohypophysial hormone with immunomodulatory effects, is abnormally high in plasma of some patients with pulmonary TB, and is apparently produced ectopically. In this study, a BALB/c mouse model of progressive pulmonary TB was used to determine whether VP may play a role in TB pathophysiology. Our results show that VP gene is expressed in the lung since early infection, increasing as the infection progressed, and localized mainly in macrophages, which are key cells in mycobacterial elimination. Pharmacologic manipulation using agonist and antagonist compounds showed that high and sustained stimulation of VPR resulted in increased bacillary burdens and fibrosis at lungs, while blockade of VP receptors reduced bacterial loads. Accordingly, treatment of infected alveolar macrophages with VP in cell cultures resulted in high numbers of intracellular Mtb and impaired cytokine production. Thus, we show that VP is ectopically produced in the tuberculous lungs, with macrophages being its most possible target cell. Further, it seems that chronic vasopressinergic stimulation during active late disease causes anti-inflammatory and tissue reparative effects, which could be deleterious while its pharmacologic suppression reactivates protective immunity and contributes to shorten conventional chemotherapy, which could be a new possible form of immune-endocrine therapy.

Identification of a transcriptome profile associated with improvement of organ function in septic shock patients after early supportive therapy

Background

Septic shock is the most severe complication of sepsis and this syndrome is associated with high mortality. Treatment of septic shock remains largely supportive of hemodynamics and tissue perfusion. Early changes in organ function assessed by the Sequential Organ Function Assessment (SOFA) score are highly predictive of the outcome. However, the individual patient’s response to supportive therapy is very heterogeneous, and the mechanisms underlying this variable response remain elusive. The aim of the study was to investigate the transcriptome of whole blood in septic shock patients with different responses to early supportive hemodynamic therapy assessed by changes in SOFA scores within the first 48 h from intensive care unit (ICU) admission.

Methods

We performed whole blood RNA sequencing in 31 patients: 17 classified as responders (R) and 14 as non-responders (NR). Gene expression was investigated at ICU admission (time point 1, or T1), comparing R with NR [padj < 0.01; Benjamini–Hochberg (BH)] and over time from T1 to T2 (48 h later) in R and NR independently (paired analysis, padj < 0.01; BH). Then the differences in gene expression trends over time were evaluated (Mann–Whitney, P <0.01). To identify enriched biological processes, we performed an over-representation analysis based on a right-sided hypergeometric test with Bonferroni step-down as multiple testing correction (padj < 0.05).

Results

At ICU admission, we did not identify differentially expressed genes (DEGs) between the two groups. In the transition from T1 to T2, the activation of genes involved in T cell–mediated immunity, granulocyte and natural killer (NK) cell functions, and pathogen lipid clearance was noted in the R group. Genes involved in acute inflammation were downregulated in both groups.

Conclusions

Within the limits of a small sample size, our results could suggest that early activation of genes of the adaptive immune response is associated with an improvement in organ function.

Electronic supplementary material

The online version of this article (10.1186/s13054-018-2242-3) contains supplementary material, which is available to authorized users.

Asymmetric vasopressin signaling spatially organizes the master circadian clock

The suprachiasmatic nucleus (SCN) is the neural network that drives daily rhythms in behavior and physiology. The SCN encodes environmental changes through the phasing of cellular rhythms across its anteroposterior axis, but it remains unknown what signaling mechanisms regulate clock function along this axis. Here we demonstrate that arginine vasopressin (AVP) signaling organizes the SCN into distinct anteroposterior domains. Spatial mapping of SCN gene expression using in situ hybridization delineated anterior and posterior domains for AVP signaling components, including complementary patterns of V1a and V1b expression that suggest different roles for these two AVP receptors. Similarly, anteroposterior patterning of transcripts involved in Vasoactive Intestinal Polypeptide- and Prokineticin2 signaling was evident across the SCN. Using bioluminescence imaging, we then revealed that inhibiting V1A and V1B signaling alters period and phase differentially along the anteroposterior SCN. V1 antagonism lengthened period the most in the anterior SCN, whereas changes in phase were largest in the posterior SCN. Further, separately antagonizing V1A and V1B signaling modulated SCN function in a manner that mapped onto anteroposterior expression patterns. Lastly, V1 antagonism influenced SCN period and phase along the dorsoventral axis, complementing effects on the anteroposterior axis. Together, these results indicate that AVP signaling modulates SCN period and phase in a spatially specific manner, which is expected to influence how the master clock interacts with downstream tissues and responds to environmental changes. More generally, we reveal anteroposterior asymmetry in neuropeptide signaling as a recurrent organizational motif that likely influences neural computations in the SCN clock network.

Subtle modifications to oxytocin produce ligands that retain potency and improved selectivity across species

Oxytocin and vasopressin mediate various physiological functions that are important for osmoregulation, reproduction, cardiovascular function, social behavior, memory, and learning through four G protein-coupled receptors that are also implicated in high-profile disorders. Targeting these receptors is challenging because of the difficulty in obtaining ligands that retain selectivity across rodents and humans for translational studies. We identified a selective and more stable oxytocin receptor (OTR) agonist by subtly modifying the pharmacophore framework of human oxytocin and vasopressin. [Se-Se]-oxytocin-OH displayed similar potency to oxytocin but improved selectivity for OTR, an effect that was retained in mice. Centrally infused [Se-Se]-oxytocin-OH potently reversed social fear in mice, confirming that this action was mediated by OTR and not by V1a or V1b vasopressin receptors. In addition, [Se-Se]-oxytocin-OH produced a more regular contraction pattern than did oxytocin in a preclinical labor induction and augmentation model using myometrial strips from cesarean sections. [Se-Se]-oxytocin-OH had no activity in human cardiomyocytes, indicating a potentially improved safety profile and therapeutic window compared to those of clinically used oxytocin. In conclusion, [Se-Se]-oxytocin-OH is a novel probe for validating OTR as a therapeutic target in various biological systems and is a promising new lead for therapeutic development. Our medicinal chemistry approach may also be applicable to other peptidergic signaling systems with similar selectivity issues.

Effect of Endogenous Arginine-Vasopressin Arising from the Paraventricular Nucleus on Learning and Memory Functions in Vascular Dementia Model Rats

The hippocampus is a key structure for encoding and processing memory and for spatial orientation, which are among the cognitive functions most sensitive to cerebral ischemia, hypoxia, and vascular dementia (VD). Since hippocampal formation is one of the principle forebrain targets for arginine-vasopressin (AVP) innervations arising in the hypothalamic paraventricular nucleus (PVN), we explored the contributions of AVP to VD pathogenesis. To this end, we randomly assigned pathogen-free, male Wistar rats to one of seven groups in a VD model and tested AVP treatment effects on spatial learning and memory using the Morris water maze. We also measured the superoxide dismutase (SOD) activity and malondialdehyde (MDA) concentration in brain samples and monitored the expression of AVP-positive neurons in the hippocampus by immunohistochemistry. The VD model with repeated cerebral ischemia-reperfusion injury evoked impairment of cognitive function and reduced cerebral concentrations of the antioxidation markers. Lesioning the rat PVN showed a similar effect on learning and memory and reduced antioxidation markers in the brain tissue. However, AVP injection into the PVN improved cognitive performance in VD rats, while enhancing/rectifying the changes in antioxidation markers. We conclude that our VD model may decrease AVP secretion in the PVN and subsequently reduce antioxidant capacity in the hippocampus, leading to impaired cognitive function.

Oxytocin and Vasopressin: Powerful Regulators of Social Behavior

For many, the terms oxytocin and vasopressin immediately evoke images of animals interacting with one another, as both of these neuropeptides have been implicated as being part of the neurochemical "glue" that socially binds animals. However, social environments and social interactions are complex and include behaviors that bring animals together as well as behaviors that keep animals apart. It is at the intersection of social context, social experience, and an individual's sex that oxytocin and vasopressin act to modulate social behavior and social cognition. In this review, this complexity will be explored across mammalian species, with a focus on social memory, cooperative behaviors, and competitive behaviors. Implications for humans as well as future directions will also be considered.

The role of vasopressin and the vasopressin type V1a receptor agonist selepressin in septic shock

Septic shock remains one of the major causes of morbidity and mortality in the critically ill. Despite early goal therapy and administration of cathecholaminergic agents, up to 30% of patients succumb to the disease. In this manuscript, we first summarize the standard of care of patients with septic shock and current guidelines. We review the physiologic role of vasopressin and its role in septic shock management. We then review the most up-to-date evidence on the potential role of V1a receptor agonists such as Selepressin, in septic shock. Exciting new trials are being completed in order to elucidate the role of V1a receptor agonists as potential first-line vasopressor alternatives in the therapy of circulatory shock in septic patients.

Vasopressin in Pediatric Critical Care

Vasopressin is a unique hormone with complex receptor physiology and numerous physiologic functions beyond its well-known vascular actions and osmoregulation. While vasopressin has in the past been primarily used in the management of diabetes insipidus and acute gastrointestinal bleeding, an increased understanding of the physiology of refractory shock, and the role of vasopressin in maintaining cardiovascular homeostasis prompted a renewed interest in the therapeutic roles for this hormone in the critical care setting. Identifying vasopressin-deficient individuals for the purposes of assessing responsiveness to exogenous hormone and prognosticating outcome has expanded research into the evaluation of vasopressin and its precursor, copeptin as useful biomarkers. This review summarizes the current evidence for vasopressin in critically ill children, with a specific focus on its use in the management of shock. We outline important considerations and current guidelines, when considering the use of vasopressin or its analogues in the pediatric critical care setting.

The modulatory effect of nitric oxide in pro- and anti-convulsive effects of vasopressin in PTZ-induced seizures threshold in mice

Vasopressin neuropeptides play an important role in the several cognitive, social, and neuroendocrine functions. Also, several studies report the involvement of nitrergic system in the vasopressin functions in central nervous system. This study investigates the effect of Arginine-Vasopressin (AVP) in pentylenetetrazol (PTZ)-induced seizures threshold and the probable role of nitric oxide (NO). AVP is administered intraperitoneally (0.01-20μg/kg, i.p.) 30min before induction of seizures. Administration of AVP (0.1μg/kg) significantly lowered the PTZ-induced seizures threshold. But, administration of AVP (10 and 20μg/kg) increased the seizures threshold, significantly. Pretreatment of SR 49059 (V1a receptor antagonist, 2mg/kg, i.p.) just reversed the pro-convulsant effect of AVP. Meanwhile, SSR 149415 (V1b receptor antagonist, 10mg/kg, i.p.) pretreatment reversed both pro-and anti-convulsant effects of AVP. The nitric oxide precursor, L-arginine (60mg/kg, i.p.) increased pro-convulsant effect of AVP, but did not change anticonvulsant activity. The nitric oxide synthase (NOS) inhibitor L-NAME (10mg/kg, i.p.) reversed both pro- and anti-convulsant effect of AVP. Selective inducible NOS inhibitor, aminoguanidine (100mg/kg, i.p.) just reversed the anti-convulsant effects of AVP. The results of the present study showed nitric oxide system may contribute to the biphasic effects of AVP on PTZ-induced seizures. V1a receptor may modulate only the proconvulsive effect. While, V1b receptors can mediate both the pro- and anti-convulsive effect of AVP.

Collective timekeeping among cells of the master circadian clock

The suprachiasmatic nucleus (SCN) of the anterior hypothalamus is the master circadian clock that coordinates daily rhythms in behavior and physiology in mammals. Like other hypothalamic nuclei, the SCN displays an impressive array of distinct cell types characterized by differences in neurotransmitter and neuropeptide expression. Individual SCN neurons and glia are able to display self-sustained circadian rhythms in cellular function that are regulated at the molecular level by a 24h transcriptional-translational feedback loop. Remarkably, SCN cells are able to harmonize with one another to sustain coherent rhythms at the tissue level. Mechanisms of cellular communication in the SCN network are not completely understood, but recent progress has provided insight into the functional roles of several SCN signaling factors. This review discusses SCN organization, how intercellular communication is critical for maintaining network function, and the signaling mechanisms that play a role in this process. Despite recent progress, our understanding of SCN circuitry and coupling is far from complete. Further work is needed to map SCN circuitry fully and define the signaling mechanisms that allow for collective timekeeping in the SCN network.

Oxytocin (OT) and arginine-vasopressin (AVP) act on OT receptors and not AVP V1a receptors to enhance social recognition in adult Syrian hamsters (Mesocricetus auratus)

Social recognition is a fundamental requirement for all forms of social relationships. A majority of studies investigating the neural mechanisms underlying social recognition in rodents have investigated relatively neutral social stimuli such as juveniles or ovariectomized females over short time intervals (e.g., 2h). The present study developed a new testing model to study social recognition among adult males using a potent social stimulus. Flank gland odors are used extensively in social communication in Syrian hamsters and convey important information such as dominance status. We found that the recognition of flank gland odors after a 3min exposure lasted for at least 24h, substantially longer than the recognition of other social cues in rats and mice. Intracerebroventricular injections of OT and AVP prolonged the recognition of flank gland odor for up to 48h. Selective OTR but not V1aR agonists, mimicked these enhancing effects of OT and AVP. Similarly, selective OTR but not V1aR antagonists blocked recognition of the odors after 20min. In contrast, the recognition of non-social stimuli was not blocked by either the OTR or the V1aR antagonists. Our findings suggest both OT and AVP enhance social recognition via acting on OTRs and not V1aRs and that the recognition enhancing effects of OT and AVP are limited to social stimuli.

Oxytocin, Vasopressin, and the Motivational Forces that Drive Social Behaviors

The motivation to engage in social behaviors is influenced by past experience and internal state, but also depends on the behavior of other animals. Across species, the oxytocin (Oxt) and vasopressin (Avp) systems have consistently been linked to the modulation of motivated social behaviors. However, how they interact with other systems, such as the mesolimbic dopamine system, remains understudied. Further, while the neurobiological mechanisms that regulate prosocial/cooperative behaviors have been extensively examined, far less is understood about competitive behaviors, particularly in females. In this chapter, we highlight the specific contributions of Oxt and Avp to several cooperative and competitive behaviors and discuss their relevance to the concept of social motivation across species, including humans. Further, we discuss the implications for neuropsychiatric diseases and suggest future areas of investigation.

Novel mutations associated with nephrogenic diabetes insipidus. A clinical-genetic study

Molecular diagnosis is a useful diagnostic tool in primary nephrogenic diabetes insipidus (NDI), an inherited disease characterized by renal inability to concentrate urine. The AVPR2 and AQP2 genes were screened for mutations in a cohort of 25 patients with clinical diagnosis of NDI. Patients presented with dehydration, polyuria-polydipsia, failure to thrive (mean ± SD; Z-height -1.9 ± 2.1 and Z-weight -2.4 ± 1.7), severe hypernatremia (mean ± SD; Na 150 ± 10 mEq/L), increased plasma osmolality (mean ± SD; 311 ± 18 mOsm/Kg), but normal glomerular filtration rate. Genetic diagnosis revealed that 24 male patients were hemizygous for 17 different putative disease-causing mutations in the AVPR2 gene (each one in a different family). Of those, nine had not been previously reported, and eight were recurrent. Moreover, we found those same AVPR2 changes in 12 relatives who were heterozygous carriers. Further, in one female patient, AVPR2 gene study turned out to be negative and she was found to be homozygous for the novel AQP2 p.Ala86Val alteration.

CONCLUSION

Genetic analysis presumably confirmed the diagnosis of nephrogenic diabetes insipidus in every patient of the studied cohort. We emphasize that we detected a high presence (50 %) of heterozygous females with clinical NDI symptoms.

WHAT IS KNOWN

• In most cases (90 %), inherited nephrogenic diabetes insipidus (NDI) is an X-linked disease, caused by mutations in the AVPR2 gene. • In rare occasions (10 %), it is caused by mutations in the AQP2 gene. What is new: • In this study, we report 10 novel mutations associated with NDI. • We have detected a high presence (50 %) of heterozygous carriers with clinical NDI symptoms.

Regulation of blood pressure and renal function by NCC and ENaC: lessons from genetically engineered mice

The activity of the thiazide-sensitive Na(+)/Cl(-) cotransporter (NCC) and of the amiloride-sensitive epithelial Na(+) channel (ENaC) is pivotal for blood pressure regulation. NCC is responsible for Na(+) reabsorption in the distal convoluted tubule (DCT) of the nephron, while ENaC reabsorbs the filtered Na(+) in the late DCT and in the cortical collecting ducts (CCD) providing the final renal adjustment to Na(+) balance. Here, we aim to highlight the recent advances made using transgenic mouse models towards the understanding of the regulation of NCC and ENaC function relevant to the control of sodium balance and blood pressure. We thus like to pave the way for common mechanisms regulating these two sodium-transporting proteins and their potential implication in structural remodeling of the nephron segments and Na(+) and Cl(-) reabsorption.

Extrapontine myelinolysis associated with pituitrin: case report and literature review

Background

Hyponatremia is the most common electrolyte abnormality encountered in hospitalized patients, resulting from a varied spectrum of conditions. Both the primary disturbance and its correction can result in life-threatening neurological consequences. Extrapontine myelinolysis is one such complication that is associated with the rapid correction of hyponatremia. Here we describe a patient who developed extrapontine myelinolysis unexpectedly after the correction of hyponatremia, which involved the drug pituitrin.

Case presentation

A 24-year-old Chinese woman was transferred to our neurology department with the symptoms of dysarthria and quadriparesis developing one day after the correction of hyponatremia (from 118 mmol/L to 140 mmol/L), which followed with a continuous intravenous drip of pituitrin used to control hemoptysis in the emergency room. During the course, she developed involuntary movement. Magnetic resonance imaging changes were consistent with extrapontine myelinolysis.

Conclusion

This present case describes the mechanism of profound hyponatremia involving pituitrin, and the subsequent development of extrapontine myelinolysis. Physicians may approach effective clinical management of patients through awareness of the adverse effect of pituitrin on serum sodium levels, and avoid rapid correction of hyponatremia in clinical practice.

The selective vasopressin type 1a receptor agonist selepressin (FE 202158) blocks vascular leak in ovine severe sepsis*

OBJECTIVE

To determine if the selective vasopressin type 1a receptor agonist selepressin (FE 202158) is as effective as the mixed vasopressin type 1a receptor/vasopressin V2 receptor agonist vasopressor hormone arginine vasopressin when used as a titrated first-line vasopressor therapy in an ovine model of Pseudomonas aeruginosa pneumonia-induced severe sepsis.

DESIGN

Prospective, randomized, controlled laboratory experiment.

SETTING

University animal research facility.

SUBJECTS

Forty-five chronically instrumented sheep.

INTERVENTIONS

Sheep were anesthetized, insufflated with cooled cotton smoke via tracheostomy, and P. aeruginosa were instilled into their airways. They were then placed on assisted ventilation, awakened, and resuscitated with lactated Ringer's solution titrated to maintain hematocrit ± 3% from baseline levels. If, despite fluid management, mean arterial pressure fell by more than 10 mm Hg from baseline level, an additional continuous IV infusion of arginine vasopressin or selepressin was titrated to raise and maintain mean arterial pressure within no less than 10 mm Hg from baseline level. Effects of combination treatment of selepressin with the selective vasopressin V2 receptor agonist desmopressin were similarly investigated.

MEASUREMENTS AND MAIN RESULTS

In septic sheep, MAP fell by ~30 mm Hg, systemic vascular resistance index decreased by ~50%, and ~7 L of fluid were retained over 24 hours; this fluid accumulation was partially reduced by arginine vasopressin and almost completely blocked by selepressin; and combined infusion of selepressin and desmopressin increased fluid accumulation to levels similar to arginine vasopressin treatment.

CONCLUSIONS

Resuscitation with the selective vasopressin type 1a receptor agonist selepressin blocked vascular leak more effectively than the mixed vasopressin type 1a receptor/vasopressin V2 receptor agonist arginine vasopressin because of its lack of agonist activity at the vasopressin V2 receptor.

Severe signs of hyponatremia secondary to desmopressin treatment for enuresis: a systematic review

OBJECTIVE

Dilutional hyponatremia is a serious adverse effect of desmopressin, a vasopressin analog that is widely prescribed to manage monosymptomatic enuresis. The presentation of hyponatremia, largely related to cerebral dysfunction, can include severe signs like altered mental status and seizures.

METHODS

We reviewed the literature dealing with altered mental status or seizures in enuretic subjects on desmopressin. The retained publications included patients who were described individually, revealing data on mode of administration, further identifiable factors predisposing to hyponatremia, presentation and clinical course.

RESULTS

We found 54 cases of hyponatremia secondary to desmopressin treatment presenting with altered mental status or seizures. In most cases the complication developed 14 days or less after starting desmopressin. An intranasal formulation had been used in 47 patients. Excess fluid intake was documented as a contributing factor in at least 22 cases. In 6 cases severe signs of hyponatremia developed in the context of intercurrent illnesses.

CONCLUSION

Altered mental status or seizures are very rare but recognized complications of desmopressin in enuresis. This complication mostly develops in subjects managed with the intranasal formulation 14 days or less after starting the medication, following excess fluid intake and during intercurrent illnesses.

Physiology of hemodynamic homeostasis

Homeostasis of hemodynamics refers to the regulation of the blood circulation to meet the demands of the different organ and tissue systems. This homeostasis involves an intimate interaction between peripheral metabolic needs, vascular adaptations to meet these needs and cardiac adaptation to provide the driving force to circulate the blood. The three variables that reflect the homeostasis of cardiovascular regulation are mean systemic arterial pressure, cardiac output and total systemic vascular resistance in the circulation. Regulation of the blood circulation depends on a static component, based on the physical properties of the different vessels and the characteristics of the fluid going through these vessels. Superimposed on this static regulation, is the dynamic regulation which is based on local control systems and the controls systems that adjust hemodynamic status to meet the needs of the body as a whole. This global circulation throughout the body is regulated by hormonal and neural control systems. All these systems closely interact to maintain blood pressure between the normal levels.

Exogenous Vasopressin-Induced Hyponatremia in Patients With Vasodilatory Shock: Two Case Reports and Literature Review

Vasopressin has gained wide support as an adjunct vasopressor in patients with septic shock. This agent exerts its vasoconstriction effects through smooth muscle V1 receptors and also has antidiuretic activity via renal V2 receptors. This interaction with the renal V2 receptors results in the integration of aquaporin 2 channels in the apical membrane of the renal collecting duct leading to free water reabsorption. Thus, water intoxication with subsequent hyponatremia, although rare, is a potentially serious side effect of exogenous vasopressin administration. We present 2 patients who developed hyponatremia within hours of initiation of vasopressin infusion. Extensive diuresis followed its discontinuation with subsequent normalization of serum sodium. One of the patients required the use of hypertonic saline for more rapid normalization of serum sodium due to concerns for potential seizure activity. A review of the literature relevant to the incidence of vasopressin-induced hyponatremia is provided as well as discussion on additional factors relevant to septic shock that should be considered when determining the relative risk of hyponatremia in patients receiving vasopressin.

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.

The effect of vasopressin 1b receptor (V1bR) blockade on HPA axis activity in rats exposed to acute heat stress

Thermal stressors such as low and high ambient temperature elicit an abundance of neuroendocrine responses including activation of the hypothalamo-pituitary-adrenal (HPA) axis and arginine vasopressin (AVP) release. The exposure to heat is a particularly interesting model for studying AVP action because this kind of stressor represents not only an unpleasant experience but also a threat to osmotic homeostasis. As AVP has long been recognized as a hormone involved in the modulation of HPA axis activity, the aim of this study was to elucidate the role of AVP in acutely heat-exposed rats using Nelivaptan, a selective vasopressin 1b receptor (V1bR) antagonist. Rats were exposed to high ambient temperature (38°C) for 60 min. The circulating hormones were determined by ELISA or chemiluminescence, and intrapituitary adrenocorticotropic hormone (ACTH) and V1bR level were determined by western blot. The results obtained show that V1bR blockade negatively affected the increase in blood ACTH caused by heat exposure. This treatment alone, or in combination with Nelivaptan, decreased intrapituitary V1bR levels while circulating AVP concentration was increased under the same conditions. Furthermore, a strong correlation was observed between blood ACTH and corticosterone concentration. In conclusion, our results directly confirm the positive role of AVP in the regulation of ACTH secretion from the pituitary in animals exposed to heat. Moreover, the results suggest that AVP from the general circulation influences pituitary V1bR.

Plasma corticotrophin response to desmopressin in patients with Cushing's disease correlates with the expression of vasopressin receptor 2, but not with that of vasopressin receptor 1 or 3, in their pituitary tumours

OBJECTIVES

Most patients with Cushing's disease (CD) respond to corticotrophin-releasing hormone (CRH) or desmopressin with increased corticotrophin (ACTH) and cortisol levels. Although the vasopressin receptor subtype located on normal corticotrophs is the V3 receptor (V3R), desmopressin is a selective V2 receptor (V2R) agonist and it is unclear whether corticotrophinomas exhibit aberrant V2R expression. Furthermore, no studies have determined the relationship between the in vivo response of CD patients to desmopressin and vasopressin receptor expression, or between the response to CRH and CRH receptor (CRHR) expression. Therefore, the aim of this study was to investigate the expression of vasopressin receptors (V1R, V2R, and V3R) and CRHR on corticotroph tumours and its possible relation to the in vivo response.

DESIGNS

A prospective study of 29 patients with CD.

METHODS

Patients underwent desmopressin and CRH stimulation tests before surgery. The expression of vasopressin receptors and CRHR on corticotrophinomas was determined by immunocytochemistry.

RESULTS

Most of the corticotrophinomas exhibited abundant expression of V1R, V3R, and CRHR, whereas the expression of V2R varied greatly and was lower in macroadenomas than in microadenomas. Both the percentage increment of ACTH and net area under the curve (AUC) of ACTH in the desmopressin stimulation test were found to be correlated with tumour volume. After adjustment for tumour volume, a positive correlation was found between the percentage increment of ACTH and the degree of V2R expression, but not between that of V1R or V3R. No relationship between the level of expression of CRHR on tumour tissues and the percentage increment or netAUC of ACTH to CRH was observed in CD patients.

CONCLUSIONS

We concluded that V2R was expressed on corticotrophinomas and that the level of its expression correlated well with the ACTH response to desmopressin in CD patients, although abundant expression of V1R and V3R was also found in almost all corticotroph tumours. Further studies are needed to elucidate the role of these receptors in the pathogenesis of CD.

The use of Arginine Vasopressin in neonates following the Norwood procedure

BACKGROUND

Following the Norwood palliation, neonates may require an escalation of inotropic and vasoactive support. Arginine Vasopressin may be uniquely useful in supporting this population.

MATERIALS AND METHODS

A retrospective evaluation of neonates at this institution between November, 2007 and October, 2010 who received Arginine Vasopressin following the Norwood procedure. Data were recorded from the patient records at one hour prior to, and then 1, 2, 3, 4, 6, and 24 hours following Arginine Vasopressin initiation.

RESULTS

We included 28 neonates. The mean dose of Arginine Vasopressin was 0.0005 plus or minus 0.0003 units per kilogram per minute. There was an early response (less than 6 hours) characterised by an 8% increase in systolic blood pressure (p = 0.0004), a 100% increase in urine output (p = 0.02), and a 29% decrease in total fluid administration (p = 0.04). The late response (at 24 hours) revealed further increases in systolic blood pressure and urine output as well as a 53% decrease in serum lactate (p = 0.007) and increase in arterial pH from 7.36 to 7.45 (p less than 0.0001). These changes were not accompanied by increases in heart rate or inotrope score.

CONCLUSIONS

The initiation of Arginine Vasopressin in post-operative Norwood patients was temporally associated with an improvement in markers of perfusion including systolic blood pressure, urine output, lactate, and pH. Further studies are required to ascertain the efficacy of Arginine Vasopressin in this population.

The effect of acute heat exposure on rat pituitary corticotroph activation: the role of vasopressin

The increased ambient temperature affects the function of hypothalamic-pituitary-adrenal (HPA) axis. Since the correlation among vasopressin (VP), adrenocorticotropic hormone (ACTH) and corticosterone (CORT) responses to various stressors have been long recognized, the aim of this study was to reveal the aforementioned hormones production and morphology of the pituitary gland after exposure to acute heat. Rats were exposed to high ambient temperature (38 °C) for 20 or 60 minutes. The circulating hormones were determined by an ELISA test or chemiluminescence's method. The results obtained show the elevation in ACTH and CORT secretion depending on the duration of heat exposure. The VP concentration increased only after prolonged exposure to heat (60 min). The pituitary morphology was examined by routine and fluorescent immunohistochemistry as well as electron microscopy. Observed changes in the anterior and posterior pituitary well corresponded to circulating hormones, regarding the volume density of ACTH-immunopositive cells, percentage of ACTH immunopositive area v. total area and number of VP-immunopositive containing varicose fibers per total area. Acute heat exposure also induced changes in shapes of ACTH-immunopositive cells. Cells appeared stellate with numerous slender cytoplasmic processes and degranulated, which is the most obvious after 20 min. In addition, immunopositivity of endothelial and anterior pituitary cells for VP suggests its influence on ACTH secretion.

Nitric oxide in enteric nervous system mediated the inhibitory effect of vasopressin on the contraction of circular muscle strips from colon in male rats

BACKGROUND

Arginine vasopressin (AVP) is widely used in the treatment of critical diseases with hypotension, but the reports about its effect on gastrointestinal motility are controversial. The purpose of this study was to characterize the role of AVP in the regulation of colonic motility and the underlying mechanism.

METHODS

The contraction of the circular muscle strips (CM) of colon in male rats was monitored by a polygraph. The expressions of cytoplasmic inducible nitric oxide synthase (iNOS), I-κB, and the nuclear P65 in proximal colon were measured by Western blot. The V(1) receptors (V(1) Rs) and iNOS were localized by immunohistochemistry. The content of nitric oxide (NO) in the colon was measured by Griess reagent at the absorbance of 560 nm.

KEY RESULTS

Arginine vasopressin (10(-10) -10(-6) mol L(-1)) caused a concentration-dependent inhibition on CM contraction. Pretreatment with one of the following chemicals, including V-1880 (10(-7) mol L(-1)), TTX (10(-5) mol L(-1)), L-NAME (10(-4) mol L(-1)), NPLA (10(-7) mol L(-1)), SMT (10(-3) mol L(-1)), and PDTC (10(-3) mol L(-1)), attenuated the inhibitory effect of AVP on CM contraction. Arginine vasopressin increased the expression of iNOS and the content of NO in proximal colon. These effects were attenuated by pretreatment with PDTC (10(-3) mol L(-1)). Following AVP administration, the amount of cytoplasmic I-κB decreased, but that of nuclear P65 increased. Double immunofluorescence labeling revealed that V(1) Rs and iNOS were co-localized on the cells of myenteric plexus in proximal colon.

CONCLUSIONS & INFERENCES

Arginine vasopressin inhibited the contraction of CM in proximal colon. This effect was mediated by NO produced from NF-κB-iNOS pathway and neuronal NOS activation in myenteric plexus.

Mechanism of 1-deamino-arginine vasotocin induced natriuresis in rats

1-Deamino-arginine vasotocin (1dAVT) induced diuresis and a considerable increase in urinary sodium excretion in female Wistar rats. Sodium fractional excretion rose up to 19.3 ± 1.1%. An increase in urine flow rate after 1dAVT (0.5 nmol/kg body-weight [bw]) injection was accompanied by a significant rise of the solute-free water reabsorption. The 1dAVT-induced natriuresis was as high as natriuresis produced by injection of a maximal dose of furosemide (10mg/kg bw). V(1)-receptor antagonists (ОРС-21268, [β-mercapto-β,β-cyclopentamethylenepropionyl(1),O-Me-Tyr(2),Arg(8)]-vasopressin) blocked the increase in urinary sodium excretion after the 1dAVT injection. The 1dAVT-induced natriuresis was strongly correlated with an increase in the urinary cGMP and prostaglandin E(2) excretion. The natriuretic effect of 1dAVT did not depend on the formation of nitric oxide (NO) or atrial natriuretic peptide of which concentration in the rat blood serum remained stable. The above results indicate that the 1dAVT has unique effects on rat kidney compared to all other known diuretics - it induces extremely high natriuresis and stimulates solute-free water reabsorption. Mechanism of the natriuretic effect of 1dAVT includes decrease in tubular sodium reabsorption due to activation of V(1)-like receptors and formation of cGMP and PGЕ(2).

Proinflammatory role of vasopressin through V1b receptors in hapten-induced experimental colitis in rodents: implication in IBD

Vasopressin and its receptors modulate several gut functions, but their role in intestinal inflammation is unknown. Our aims were to determine 1) the localization of V1b receptors in human and rodent colon, 2) the role of vasopressin and V1b receptors in experimental colitis using two approaches: V1b⁻(/)⁻ mice and a selective V1b receptor antagonist, SSR149415, and 3) the mechanisms involved. V1b receptors were localized in normal and inflamed colon from humans and rats. Experimental colitis was induced in rats and mice and some groups were treated before or after colitis induction with oral SSR149415 (3-30 mg/kg). Other groups of mice were submitted to dehydration to increase vasopressin plasma levels, prior to colitis induction. Body weight, damage scores, MPO, and TNF-α tissue levels were determined. Finally, colonic segments of wild-type (WT) and V1b⁻(/)⁻ mice were mounted in Ussing chambers and paracellular permeability in response to vasopressin was studied. V1b receptors were expressed in enterocytes and ganglia cells of the enteric nervous system of human and rat intestine. Expression levels were independent from inflammatory status. Colitis was less severe in rodents treated by either preventive or curative SSR149415 and in V1b⁻(/)⁻ mice. 2,4,6-Trinitrobenzene sulfonic acid induced a strong mortality in dehydrated animals that was reversed by preventive SSR149415 or mast cell stabilizer. Vasopressin significantly increased paracellular permeability in WT, but not in V1b⁻(/)⁻ mice. Preincubation of colon tissues with SSR149415 abolished the vasopressin effect. Similarly, vasopressin had no effect in colonic preparations from WT mice pretreated with mast cell stabilizers. Vasopressin, through V1b receptor interaction, has proinflammatory properties linked to mast cell activation and downstream alterations of the colonic epithelial barrier. These findings underline the potential interest of V1b receptor blockers in gut inflammatory diseases.

Hyponatremia and the syndrome of inappropriate secretion of antidiuretic hormone (SIADH)

The syndrome of inappropriate ADH secretion (SIADH), also recently referred to as the "syndrome of inappropriate antidiuresis", is an often underdiagnosed cause of hypotonic hyponatremia, resulting for instance from ectopic release of ADH in lung cancer or as a side-effect of various drugs. In SIADH, hyponatremia results from a pure disorder of water handling by the kidney, whereas external Na+ balance is usually well regulated. Despite increased total body water, only minor changes of urine output and modest edema are usually seen. Renal function and acid-base balance are often preserved, while neurological impairment may range from subclinical to life-threatening. Hypouricemia is a distinguishing feature. The major causes and clinical variants of SIADH are reviewed, with particular emphasis on iatrogenic complications and hospital-acquired hyponatremia. Effective treatment of SIADH with water restriction, aquaretics, or hypertonic saline + loop diuretics, as opposed to worsening of hyponatremia during parenteral isotonic fluid administration, underscores the importance of an early accurate diagnosis and careful follow-up of these patients.

Vasopressin regulation of renal sodium excretion

Vasopressin promotes renal water reabsorption decreasing excretion of free water to dilute plasma and lower serum osmolality. We have good understanding of the causes, mechanisms and consequences of this vasopressin-dependent renal water movement. In comparison, vasopressin actions on renal electrolytes including sodium excretion and its consequences have been less well understood. This is so for investigation and discussions of the renal actions of vasopressin are framed primarily around water metabolism rather than any direct effect on salt handling. The fact that water moves in biological systems, to include the mammalian kidney, only by osmosis passively down its concentration gradient is implicit in such discussion but often not overtly addressed. This can cause confusion. Moreover, although vasopressin action on renal sodium excretion via the V2 receptor is critical to water transport, it is masked easily being situational--for instance, dependent on hydration state. It is now clear that an increase in sodium reabsorption along the distal nephron (CNT + CD) mediated by activation of the epithelial Na(+) channel (ENaC) by vasopressin makes an important contribution to maintenance of the axial corticomedullary osmotic gradient necessary for maximal water reabsorption. Thus, we need to modify slightly our understanding of vasopressin and its renal actions to include the idea that while vasopressin decreases free water excretion to dilute plasma, it does this, in part, by promoting sodium reabsorption and consequently decreasing sodium excretion via ENaC activated along the distal nephron.

Best vasopressor for advanced vasodilatory shock: should vasopressin be part of the mix?

Since the publication of the Surviving Sepsis Campaign guidelines, a number of additional and highly relevant studies have been published addressing the issue of vasopressor use during septic shock. While these new results are provocative, none of the studies are definitive. In sum, they suggest that maybe we should not be thinking of one vasopressor versus another in a winner-takes-all sense. Rather, we should be looking for the best balance of vasopressor agents and, further, the choice likely depends on clinical context. Clinical context may drive the choice of adrenergic agonist; for example, norepinephrine may be superior to dopamine when the potential for arrhythmias is of concern. Norepinephrine may be superior to epinephrine if elevated lactate associated with epinephrine use confounds the clinical picture. The Vasopressin and Septic Shock Trial (VASST) identified an effective dose of arginine vasopressin (AVP) when adrenergic agonist doses are low, but higher doses of AVP may be appropriate in the context of very high adrenergic agonist doses. The effect may be a direct beneficial AVP effect or indirect sparing of adrenergic agonist use. The choice to add AVP may also be influenced by the clinical context, including renal function or the concomitant use of corticosteroids. These interim conclusions, in truth, are hypotheses warranting randomized controlled trials adequately powered to test for survival differences in these severely ill patients.