Vasopressin V2 receptor antagonists

Association between serum osmolality and 28-day all-cause mortality in patients with heart failure and reduced ejection fraction: a retrospective cohort study from the MIMIC-IV database

Background

Previous studies have not thoroughly explored the impact of serum osmolality levels on early mortality in heart failure and reduced ejection fraction (HFrEF) patients. The purpose of this study was to investigate the relationship between serum osmolality levels and early all-cause mortality in patients with HFrEF.

Methods

The open access MIMIC-IV database was the source of data for our study. We collected demographic data, vital signs, laboratory parameters, and comorbidities of the included patients and divided them into 3 groups based on their initial serum osmolality on admission, with the primary outcome being all-cause mortality within 28 days of admission. Smoothing Spline Fitting Curve, the Kaplan-Meier survival curve, and Threshold effect analysis were used to assess the relationship between serum osmolality and early mortality in HFrEF patients.

Results

A total of 6228 patients (55.31% male) were included. All-cause mortality within 28 days on admission was 18.88% in all patients. After adjusting for confounders, higher serum osmolality levels were independently associated with an increased risk of 28-days all-cause mortality compared with the reference group (Reference group Q2: 290-309 mmol/L, Q4: HR, 1.82 [95% CI 1.19-2.78] P<0.05, Q5: HR, 1.99 [95% CI 1.02-3.91] P<0.05). Smooth spline fitting revealed a U-shaped association between serum osmolality and 28-days all-cause mortality. Further threshold effect analysis results suggested that each unit increase in serum osmolality level was associated with a 2% increase in 28-days all-cause mortality when serum osmolality levels were ≥ 298.8 mmol/L (HR, 1.019 [95% CI 1.012-1.025] P<0.05).

Conclusion

A U-shaped correlation between initial serum osmolality and 28-days all-cause mortality in HFrEF patients was identified, revealing higher osmolality levels significantly increase mortality risk. These results underscore serum osmolality's critical role in early mortality among HFrEF patients, highlighting the need for further, larger-scale studies for validation.

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

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

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.

Loss of body weight is accompanying cellular brain edema induced by water intoxication in the rat

Induction of cellular cerebral edema (CE) was achieved by a standard method of water intoxication which consisted of fractionated intraperitoneal administration of distilled water (DW) together with the injection of desmopressin (DP). Using metabolic cage, fluid and food balance was studied in two groups of eight animals: group C - control; group CE - cellular edema induced by water intoxication. For each rat the intake (food pellets and water) and excretion (solid excrements and urine) were recorded for 48 h together with the initial and final body weight. CE animals consumed significantly less food, drank less water and eliminated the smallest amount of excrements. The induction of cellular cerebral edema was accompanied with a significant loss of body weight (representing on average 13 % of the initial values) mainly due to a reduction of food intake. This phenomenon has not yet been reported.

High serum osmolarity at admission determines a worse outcome in patients with heart failure: Is a new target emerging?

AIMS

The osmolarity of human serum is restricted to a tightly regulated range, and any deviation has clinical implications. Our aim in this study was to establish whether differences in serum osmolarity in heart failure (HF) patients are related with a worse outcome.

METHODS

We evaluated the prognostic value of serum osmolarity in patients with HF from the Spanish National Registry on Heart Failure (RICA), a multicenter, prospective registry that enrolls patients admitted for decompensated HF and follows them for 1year. Patients were divided into quartiles according to osmolarity levels. Primary endpoint was the combination of all-cause mortality and hospital readmissions for HF.

RESULTS

A total of 2568 patients (47.46% men) were included. Patients with higher osmolarity were older, presented more comorbidities (especially diabetes mellitus and chronic kidney disease), and consequently had higher levels of glucose, urea, creatinine and potassium. During the 1-year follow-up, mortality among the quartiles was 18% (Q1), 18% (Q2), 23% (Q3) and 28% (Q4), p<0.001. After adjusting for baseline characteristics, high serum osmolarity was significantly associated with all-cause mortality (RR 1.02, 95% CI 1.01-1.03, p<0.001). We also found a significant increase in the combined endpoint of mortality and readmission among quartiles with higher osmolarity (p<0.001). Diabetes, eGFR, Barthel index, systolic blood pressure, body mass index, hemoglobin, NYHA class and beta-blocking agents were also independently associated with the primary endpoint.

CONCLUSIONS

In patients admitted for decompensated HF, high serum osmolarity predicts a worse outcome, and is associated with a higher comorbidity burden, supporting its use as a candidate prognostic target in HF.

Sequential aza-Piancatelli rearrangement/Friedel–Crafts alkylation for the synthesis of pyrrolo[1,2-d]benzodiazepine derivatives

2-Furylcarbinols undergo a smooth aza-Piancatelli rearrangement followed by Friedel–Crafts alkylation with (1H-pyrrol-1-yl)aniline, in the presence of In(OTf)₃ at room temperature to afford the corresponding hexahydrobenzo[b]cyclopenta[f]pyrrolo[1,2-d][1,4]diazepin-11(4aH)-one scaffolds.

Effect of increased water intake on plasma copeptin in patients with chronic kidney disease: results from a pilot randomised controlled trial

OBJECTIVES

Increased water intake may have a beneficial effect on the kidney through suppression of plasma vasopressin. We examined the effect of increased water intake on plasma copeptin (a marker of vasopressin) over 6 weeks in patients with chronic kidney disease.

DESIGN

Secondary analysis of a randomised controlled parallel-group pilot trial.

SETTING

Canada, 2012-2013.

PARTICIPANTS

28 patients with stage 3 chronic kidney disease randomised (2:1) to a hydration (n=17) or control group (n=11).

INTERVENTION

The hydration group was coached to increase water intake by up to 1.5 L/day for 6 weeks. The control group was asked to maintain regular water intake.

MEASURES AND OUTCOMES

Participants provided blood and 24 h urine samples at baseline and 6 weeks. Change in plasma copeptin was compared within and between study groups.

RESULTS

Participants were 64% male with a mean age of 62 years and an estimated glomerular filtration rate of 40 mL/min/1.73 m(2). Between baseline and 6 weeks, 24 h urine volume increased by 0.7 L/day in the hydration group, rising from 2.3 to 3.0 L/day (p=0.01), while decreasing by 0.3 L/day among controls, from 2.0 to 1.7 L/day (p=0.07); between-group difference: 0.9 L/day (95% CI 0.37 to 1.46; p=0.002). In the hydration group, median copeptin decreased by 3.6 pmol/L, from 15.0 to 10.8 pmol/L (p=0.005), while remaining stable among controls at 19 pmol/L (p=0.76; p=0.19 for the between-group difference in median change); the between-group difference in mean change was 5.4 pmol/L (95% CI -1.2 to 12.0; p=0.11).

CONCLUSIONS

Adults with stage 3 chronic kidney disease can be successfully randomised to drink approximately 1 L more per day than controls. This increased water intake caused a significant decrease in plasma copeptin concentration. Our larger 12-month trial will examine whether increased water intake can slow renal decline in patients with chronic kidney disease.

TRIAL REGISTRATION NUMBER

NCT01753466.

Synthesis and biological evaluation of substituted desloratadines as potent arginine vasopressin V2 receptor antagonists

Twenty-one non-peptide substituted desloratadine class compounds were synthesized as novel arginine vasopressin receptor antagonists from desloratadine via successive acylation, reduction and acylation reactions. Their structures were characterized by ¹H-NMR and HRMS, their biological activity was evaluated by in vitro and in vivo studies. The in vitro binding assay and cAMP accumulation assay indicated that these compounds are potent selective V2 receptor antagonists. Among them compounds 1n, 1t and 1v exhibited both high affinity and promising selectivity for V2 receptors. The in vivo diuretic assay demonstrated that 1t presented remarkable diuretic activity. In conclusion, 1t is a potent novel AVP V2 receptor antagonist candidate.

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.

Region-specific changes in transient receptor potential vanilloid channel expression in the vasopressin magnocellular system in hepatic cirrhosis-induced hyponatraemia

The present study aimed to measure the expression of transient receptor potential (TRP) channels in the magnocellular neurones of the paraventricular (PVN) and supraoptic nucleus (SON) in an animal model of hepatic cirrhosis associated with inappropriate vasopressin (AVP) release. In these studies, we used chronic bile duct ligation (BDL) in the rat, which is a commonly used model of hepatic cirrhosis, associated with elevated plasma AVP. The present study tested the hypothesis that changes in TRP vanilloid (TRPV) channel expression may be related to inappropriate AVP release in BDL rats. To test our hypothesis, we utilised laser capture microdissection of AVP neurones in the PVN and SON and western blot analysis from brain punches. Laser capture microdissection and quantitative reverse transcriptase-polymerase chain reaction demonstrated elevated TRPV2 mRNA in the PVN and SON of BDL compared to sham-ligated controls. AVP transcription was also increased as determined using intron specific primers to measure heteronuclear RNA. Immunohistochemistry demonstrated increased AVP and TRPV2 positive cells in both the PVN and SON after BDL. Also, there was an increased co-expression of TRPV2 and AVP cells after BDL. However, there was no change in the colocalisation counts of TRPV2 and oxytocin in both the magnocellular regions evaluated. In the SON but not the PVN, the transcription levels of TRPV4 were also significantly increased in BDL rats. Western blot analysis of punches containing the PVN and SON revealed that TRPV2 protein content was significantly increased in these brain regions in BDL rats compared to sham rats. Our data suggest that regionally specific changes in TRPV expression in the magnocellular neurosecretory cell AVP neurones could alter their osmosensing ability.

Effect of loading dose and formulation on safety and efficacy of conivaptan in treatment of euvolemic and hypervolemic hyponatremia

PURPOSE

The effect of loading dose and formulation on the safety and efficacy of conivaptan in the treatment of euvolemic and hypervolemic hyponatremia was studied.

METHODS

This parallel-group study randomized 121 hospitalized patients with euvolemic or hypervolemic hyponatremia to one of four treatment regimens: placebo loading dose followed by conivaptan continuous i.v. infusion using the ampul formulation (regimen 1), conivaptan loading dose followed by continuous i.v. infusion using the ampul formulation (regimen 2), placebo loading dose followed by conivaptan continuous i.v. infusion using the premixed formulation (regimen 3), or conivaptan loading dose followed by continuous i.v. infusion using the premixed formulation (regimen 4). The primary variable was the incidence and severity of injection-site reactions (ISRs), as evaluated using the ISR modified 5-point scale (ISRMS). Secondary outcomes included effects on serum sodium concentration (SSC), duration of effect, and safety and tolerability.

RESULTS

All four dosing regimens were efficacious, safe, and well tolerated. No significant differences in ISRMS scores or differences in changes from baseline SSC or in the duration of effects on SSC were observed between the regimens. Overly rapid SSC increases occurred in 7%, 7%, 3%, and 21% of patients treated with regimens 1, 2, 3, and 4, respectively. Overall, adverse events related to general disorders and ISRs occurred in 39%, 43%, 53%, and 55% of patients receiving regimens 1, 2, 3, and 4, respectively.

CONCLUSION

Intravenous conivaptan regimens with or without a loading dose, whether using the ampul or a premixed formulation, had similar safety, tolerability, and efficacy in patients with euvolemic or hypervolemic hyponatremia. The pre-mixed formulation used with a loading dose may be associated with an increased frequency of overly rapid increase in SSC compared with the other regimens studied.

Arginine vasopressin receptor antagonists (vaptans): pharmacological tools and potential therapeutic agents

Arginine vasopressin (AVP) attracted attention as a potentially important neurohormonal mediator of the heart failure (HF) syndrome and hyponatremic states in humans because AVP influences renal handling of free water, vasoconstriction and myocyte biology through activation of V₂ and V₁(a) receptors. Current research is exploring V₂- and dual V₁(a)/V₂ receptor antagonism for the treatment of hyponatremia, as well as for the congestion and edema associated with chronic HF, because vasopressin receptor antagonists might offer benefits in comparison with conventional loop diuretics. The purpose of this review is to update the current status of experimental and clinical studies with available vasopressin receptor antagonists (conivaptan and tolvaptan) and their potential role in the treatment of HF and hyponatremia of multiple causes.

Tolvaptan: a new tool for the effective treatment of hyponatremia in psychotic disorders

IMPORTANCE OF THE FIELD

Hyponatremia (serum sodium concentration < 136 mEq/liter) is a common and potentially life-threatening medical comorbidity seen in patients with psychotic disorders. Tolvaptan, a selective antagonist of the V(2)-receptor, is FDA-approved for the treatment of clinically significant hypervolemic and euvolemic hyponatremia. This represents a major development in the care of psychotic individuals with hyponatremia.

AREAS COVERED IN THE REVIEW

This review provides an overview of the existing literature on prevalence rates and risk factors associated with hyponatremia in psychotic patients (1923 - present). Tolvaptan is discussed as a potential advance in the treatment of hyponatremia in patients with psychotic disorders, and preliminary data are reviewed.

WHAT THE READER WILL GAIN

The reader will gain an appreciation of the prevalence of hyponatremia among psychotic individuals, an understanding of the distinctions between acute and chronic hyponatremia in this population, and awareness that effective treatments are becoming available.

TAKE HOME MESSAGE

A modest literature exists regarding prevalence rates and risk factors associated with hyponatremia in psychotic populations. Hyponatremia is common and serious enough to merit clinical concern. Perhaps, now that tolvaptan has been FDA-approved, progress will accelerate and new insights will develop that begin to bring relief from this medical comorbidity among psychotic patients.

Hyponatremia in heart failure

Hyponatremia is one of the newer and emerging risk factors for an adverse prognosis in chronic heart failure. Why decreased serum sodium is associated with worse prognosis remains unclear. It may reflect worsening heart failure and the deleterious effects of activation of neurohormones. The mechanism of hyponatremia in heart failure also remains unclear. A relatively greater degree of free-water retention compared to sodium retention is probably the major mechanism. The treatment of significant hyponatremia in heart failure is difficult. The conventional treatments such as fluid restriction, infusion of hypertonic saline, and aggressive diuretic therapies are not usually effective. Vasopressin receptor antagonists have been shown to enhance aquaresis and correct hyponatremia. However, long-term beneficial effects of such treatments in chronic heart failure have not been documented.

New topics in vasopressin receptors and approach to novel drugs: research and development of conivaptan hydrochloride (YM087), a drug for the treatment of hyponatremia

Hyponatremia is the most common electrolyte disorder in hospitalized patients and is associated with the risk of intractable seizures and death. The effectiveness of conventional therapies for hyponatremia is inconsistent, and the rapid correction of plasma sodium levels is thought to result in the occurrence of neurological complications. Arginine vasopressin (AVP) is the primary regulator of renal electrolyte-free water reabsorption via AVP-receptor type 2 (V2-R), and inappropriate or excessive AVP secretion independent of serum osmolality frequently causes excessive water retention, which is the etiological basis of hyponatremia. Therefore, the use of V2-R antagonists as anti-hyponatremic drugs in the clinical setting is anticipated to be reliable and safe. Conivaptan hydrochloride (YM087) is a novel dual AVP-R antagonist for AVP-R types 1a (V1a) and V2-R. In vitro studies have shown that it possesses high affinity for V1a-R and V2-R without any species differences. It also potently inhibited AVP-induced intracellular signaling through human V2 and V1a receptors with no agonistic activity. Conivaptan hydrochloride improved the plasma sodium concentration and plasma osmolality in hyponatremic rats, and its effectiveness was demonstrated in hyponatremic patients. This drug has been approved for use in the United States, which will bring relief to patients with hyponatremia.

Double-blind, placebo-controlled, multicenter trial of a vasopressin V2-receptor antagonist in patients with schizophrenia and hyponatremia

OBJECTIVES

Hyponatremia (serum sodium [Na+] concentration <136 mmol/L) is a prevalent and potentially life-threatening medical comorbidity for schizophrenic patients. No definitive pharmacological treatments have been established. Tolvaptan (OPC-41061), an oral non-peptide V2-receptor antagonist, was recently shown to correct hyponatremia in a diverse population of 448 hyponatremic patients. Efficacy in a sub-set of 19 schizophrenic patients with idiopathic hyponatremia included in that sample is specifically examined.

METHODS

Nineteen subjects were randomly assigned to receive placebo (n = 12) or tolvaptan (n = 7) once daily for 30 days. Dosage adjustment was based on serum Na+ changes, initially 15 mg, titratable to 30 or 60 mg. The average daily area under the curve (AUC) changes in serum Na+ from baseline to Day 4 and Day 30 were co-primary end points.

RESULTS

Increases in serum Na+ concentrations were significantly greater with tolvaptan than placebo at Day 4 (p = .0055) and at Day 30 (p < .0001). Two subjects receiving tolvaptan (28.6%) became dehydrated and experienced hypotension, and five subjects receiving placebo (41.7%) experienced symptoms associated with dilutional hyponatremia.

CONCLUSIONS

These results suggest that tolvaptan effectively normalizes idiopathic hyponatremia in schizophrenic patients. Clinicians are advised to carefully monitor fluid status especially at the beginning of treatment to prevent dehydration.

Effects of novel vasopressin receptor antagonists on renal function and cardiac hypertrophy in rats with experimental congestive heart failure

Arginine vasopressin (AVP) plays an important role in renal hemodynamic alterations, water retention, and cardiac remodeling in congestive heart failure (CHF). The present study evaluated the acute and chronic effects of vasopressin V(1a) receptor subtype (V(1a)) and vasopressin V(2) receptor subtype (V(2)) antagonists on renal function and cardiac hypertrophy in rats with CHF. The effects of acute administration of SR 49059 [(2S)1-[(2R,3S)-5-chloro-3-(2-chlorophenyl)-1-(3,4-dimethoxybenzene-sulfonyl)-3-hydroxy-2,3-dihydro-1H-indole-2-carbonyl]-pyrrolidine-2-carboxamide)] (0.1 mg/kg) and SR 121463B (1-[4-(N-tert-butylcarbamoyl)-2-methoxybenzenesulfonyl]-5-ethoxy-3-spiro-[4-(2-morpholinoethoxy)cyclohexane]indol-2-one, fumarate; equatorial isomer) (0.3 mg/kg), V(1a) and V(2) antagonists, respectively, on renal function, and of chronic treatment (3.0 mg/kg/day for 7 or 28 days, via osmotic minipumps or p.o.), on water excretion and cardiac hypertrophy were studied in rats with aortocaval fistula and control rats. CHF induction increased plasma AVP (12.8 +/- 2.5 versus 32.2 +/- 8.3 pg/ml, p < 0.05). Intravenous bolus injection of SR 121463B to controls produced dramatic diuretic response (from 5.5 +/- 0.8 to 86.3 +/- 21.9 microl/min; p < 0.01). In contrast, administration of SR 49059 did not affect urine flow. Likewise, administration of SR 121463B, but not SR 49059, to rats with CHF significantly increased urinary flow rate from 20.8 +/- 6.4 to 91.6 +/- 26.5 microl/min (p < 0.01). The diuretic effects of SR 121463B were associated with a significant decline in urinary osmolality and insignificant change of Na+ excretion. In line with its acute effects, chronic administration of SR 121463B to CHF rats increased daily urinary volume 2 to 5-fold throughout the treatment period. Both SR 121463B and SR 49059 significantly reduced heart weight in CHF rats when administered for 4 weeks, but not 1 week. These results suggest that V(2) and V(1a) antagonists improve water balance and cardiac hypertrophy in CHF and might be beneficial for the treatment of water retention and cardiac remodeling in CHF.

Vasopressin dysregulation and hyponatremia in hospitalized patients

Hyponatremia, which is often due to dysregulation of arginine vasopressin, occurs frequently in hospitalized patients and is associated with increased morbidity and mortality. Nonosmotic secretion of arginine vasopressin is central to the pathophysiology of hyponatremia in patients with euvolemic hyponatremia (due to, for example, the syndrome of inappropriate secretion of antidiuretic hormone) and those with hypervolemic hyponatremia secondary to congestive heart failure or cirrhosis with ascites. Arginine vasopressin-receptor antagonists, a novel class of agents that block the action of arginine vasopressin on V2 receptors in the renal collecting ducts, may provide specific correction of sodium and water imbalance in hyponatremia by promoting free water clearance while sparing electrolytes (aquaresis). Arginine vasopressin antagonism would treat hyponatremia directly, as opposed to other therapies that do not address the effects of arginine vasopressin dysregulation directly.

Recognition and treatment of hyponatremia in acutely ill hospitalized patients

OBJECTIVE

The objective of this paper was to discuss the diagnosis, pathophysiology, and management of hyponatremia among critically ill, hospitalized patients (eg, after surgery or in the intensive care unit).

METHODS

English-language literature published between 1967 and 2006 was searched using several key words (AVP receptor antagonists, hyponatremia, SIADH, conivaptan, tolvaptan, and lixivaptan) and by accessing MEDLINE and ScienceDirect. Meeting abstracts from scientific sessions (American Society of Nephrology Renal Week 2004 and the Endocrine Society's 87th Annual Meeting [2005]) were reviewed. The package insert for conivaptan hydrochloride injection was referenced from . Clinical trials included in this review were randomized and placebo controlled.

RESULTS

Based on the literature we researched, hyponatremia is the most common electrolyte disorder encountered in critical care and is associated with a variety of conditions, including congestive heart failure and the syndrome of inappropriate antidiuretic hormone secretion. Because hyponatremia can arise in hypervolemic, euvolemic, and hypovolemic states, clinicians may not recognize its presence and cause. Incorrect management can lead to significant morbidity and mortality. Physicians need to recognize risk factors and symptoms and use appropriate treatment guidelines for hyponatremia. Traditionally, therapy for hyponatremia has been limited by efficacy and safety concerns. Arginine vasopressin (AVP) receptor antagonists, therapeutic agents that promote aquaresis in patients with hyponatremia by targeting V(1a) receptors in the vascular smooth muscle, V(2) receptors in the kidney, or both, are under development. A dual-receptor antagonist targeting both V(1a) and V(2) receptors is now approved for the treatment of euvolemic hyponatremia in hospitalized patients.

CONCLUSIONS

Hyponatremia, an electrolyte abnormality found in critically ill patients, can be associated with significant morbidity and mortality. AVP receptor antagonists show promise as effective and tolerable treatments for patients with hyponatremia.

Vasopressin dysregulation: Hyponatremia, fluid retention and congestive heart failure

Arginine vasopressin (AVP) plays a central role in the regulation of water and electrolyte balance. Dysregulation of AVP secretion, along with stimulation of AVP V2 receptors, is responsible for hyponatremia (serum sodium concentration <135 mEq/L) in congestive heart failure (CHF). The stimulation of atrial and arterial baroreceptors in response to hypotension and volume depletion results in the nonosmotic release of AVP. The predominance of nonosmotic AVP secretion over osmotic AVP release plays a key role in the development of water imbalance and hyponatremia in CHF and other edematous disorders. The AVP-receptor antagonists are a new class of agents that block the effects of AVP directly at V2 receptors in the renal collecting ducts. AVP-receptor antagonism produces aquaresis, the electrolyte-sparing excretion of water, thereby allowing specific correction of water and sodium imbalance. This review summarizes recent data from clinical trials evaluating the efficacy and safety of these promising agents for the treatment of hyponatremia.

Vasopressin-receptor antagonist therapy in patients with hyponatraemia

Hyponatraemia often complicates the treatment of underlying conditions in patients who are seriously ill. Arginine vasopressin receptor antagonists block the action of arginine vasopressin and correct sodium and water imbalance in patients with euvolaemic or hypervolaemic hyponatraemia.

Sertraline, a selective serotonin reuptake inhibitor, affects thirst, salt appetite and plasma levels of oxytocin and vasopressin in rats

We investigated the effects of chronic administration of sertraline (SERT; approximately 20 mg kg(-1) day(-1) in drinking water), a selective serotonin reuptake inhibitor, on water and sodium intake and on plasma levels of oxytocin (OT) and vasopressin (AVP) in basal and stimulated conditions. Basal water intake was reduced in SERT-treated rats. After 24 h of water deprivation, rats treated with SERT for 21 days ingested less water than the control rats (9.7 +/- 0.5 versus 20.0 +/- 0.9 ml, respectively, at 300 min after water presentation, P < 0.0001). Subcutaneous injection of 2 m NaCl or isoproterenol evoked a lower dipsogenic response in rats treated with SERT for 21 days. Fluid and food deprivation also induced a weaker dipsogenic response in SERT-treated rats (1.6 +/- 0.5 versus 10.2 +/- 1.2 ml, at 300 min, P < 0.0001) but had no effect on saline intake. Sodium depletion induced a higher natriorexigenic response in the SERT group (5.6 +/- 1.3 versus 1.2 +/- 0.3 ml, at 300 min, P < 0.0002). Higher urinary density and lower plasma sodium levels were observed after SERT treatment. Sertraline also increased plasma levels of vasopressin and oxytocin (AVP, 2.65 +/- 0.36 versus 1.31 +/- 0.16 pg ml(-1), P < 0.005; OT, 17.16 +/- 1.06 versus 11.3 +/- 1.03 pg ml(-1), P < 0.0009, at the third week post-treatment). These data constitute the first evidence that chronic SERT treatment affects water and sodium intake in rats. These effects seem to be related to the hyponatraemia caused by the higher plasma levels of AVP and OT.

New agents for managing hyponatremia in hospitalized patients

PURPOSE

An overview of hyponatremia is provided, including its pathophysiology, clinical manifestations, signs and symptoms, and treatment, particularly with arginine vasopressin (AVP)-receptor antagonists.

SUMMARY

Hyponatremia (generally defined as a serum sodium concentration of <135 meq/L) is one of the most common electrolyte disorders in hospitalized and clinic patients. It may be caused by a number of conditions, including infections, heart disease, surgery, malignancy, and medication use. Clinical signs and symptoms such as hallucinations, lethargy, weakness, bradycardia, respiratory depression, seizures, coma, and death have been reported. Conventional treatment consists of fluid restriction and administration of hypertonic saline and pharmacologic agents, such as demeclocycline, lithium carbonate, and urea. These treatment options are often of limited effectiveness or difficult for patients to tolerate. AVP promotes the reabsorption of water in the renal collecting ducts by activation of V(2) receptors, resulting in water retention and dilution of serum solutes. The AVP-receptor antagonists, conivaptan, lixivaptan, and tolvaptan, are being studied for the treatment of hyponatremia. Conivaptan has been shown in clinical trials to increase free-water excretion and safely normalize serum sodium concentrations in patients with hyponatremia and is well tolerated. Also in clinical trials, lixivaptan and tolvaptan have safely improved serum sodium concentrations in patients with hyponatremia.

CONCLUSION

Hyponatremia is a serious health condition for which treatment should be carefully performed. As new agents for treating hyponatremia, AVP-receptor antagonists have demonstrated efficacy and safety in clinical trials and may serve as significant improvements in the current treatment options for managing this disorder.

Evaluation and management of hyponatremia: an emerging role for vasopressin receptor antagonists

Vasopressin-2 receptor antagonists, collectively known as the 'vaptans', provide a new approach to the treatment of hyponatremia; therefore, an updated Review of the pathophysiology of hyponatremia is particularly timely. After briefly defining hyponatremia and introducing its clinical aspects and complications, we present an approach to the diagnosis and evaluation of hyponatremia that is based primarily on the often-underused concept of free water clearance and, more specifically, the electrolyte-free water clearance. Then we review the use of vasopressin receptor antagonists in the management of hyponatremia from the standpoint of their pharmacology, their mechanism of action, and available efficacy data from clinical trials.

Hyponatremia, arginine vasopressin dysregulation, and vasopressin receptor antagonism

Hyponatremia is often associated with arginine vasopressin (AVP) dysregulation that is regulated by the hypothalamo-neurohypophyseal tract in response to changes in plasma osmolality, commonly in patients with the syndrome of inappropriate antidiuretic hormone secretion (SIADH). Potentially lethal complications of hyponatremia most frequently involve the central nervous system and include anorexia, fatigue, lethargy, delirium, seizures, hypothermia and coma, and require prompt treatment. Chronic hyponatremia also complicates patient care and is associated with increased morbidity and mortality, particularly among patients with congestive heart failure. Conventional treatments for hyponatremia (e.g. fluid restriction, diuretic treatment, and sodium replacement) may not be effective in all patients and can lead to significant adverse events. Preclinical and clinical trial results have shown that AVP receptor antagonism is a promising approach to the treatment of hyponatremia that directly addresses the effects of increased AVP and consequent decreased aquaresis, the electrolyte-sparing excretion of free water. Agents that antagonize V(2) receptors promote aquaresis and can lead to increased serum sodium. Dual-receptor antagonism, in which both V(2) and V(1A) receptors are blocked, may provide additional benefits in patients with hyponatremia.

Hyponatremia, fluid-electrolyte disorders, and the syndrome of inappropriate antidiuretic hormone secretion: diagnosis and treatment options

OBJECTIVE

To review the types and causes of hyponatremia and examine the various strategies for treatment of this disorder.

METHODS

A systematic review of the current literature is provided, targeting endocrinology clinicians who consult with hospital medical and surgical staff when managing patients with hyponatremia. Treatment for euvolemic and hypervolemic hyponatremia with arginine vasopressin receptor antagonists is presented, which provides a new treatment option for patients with disorders of water metabolism.

RESULTS

Hyponatremia is recognized as the most common electrolyte disorder encountered in the clinical setting and is associated with a variety of conditions including dilutional disorders, such as congestive heart failure and the syndrome of inappropriate antidiuretic hormone secretion, and depletional disorders, such as diarrhea and vomiting or blood loss. Most cases of mild hyponatremia can be treated effectively. Acute, severe hyponatremia that is untreated or treated ineffectively, however, can lead to serious neurologic outcomes or death. With the poor prognosis for morbidity and mortality in patients with severe hyponatremia, hospital-based clinicians must identify those at risk for hyponatremia and suggest appropriate treatment intervention. A new class of drugs, the arginine vasopressin receptor antagonists, targets receptors on collecting duct cells of the nephron and causes aquaresis, the excretion of free water. This therapy leads to the restoration of sodium-water homeostasis in patients with euvolemic and hypervolemic hyponatremia.

CONCLUSION

With many hospitalized patients at risk for hyponatremia, especially elderly patients in critical care and postsurgical units, identification of involved patients, recommendation of appropriate treatment, and awareness of new therapeutic options are critical.

Hyponatremia in neurologic patients: consequences and approaches to treatment

BACKGROUND

Hyponatremia is a common fluid-electrolyte disturbance, particularly in patients with neurologic disorders, in part because of the major role the central nervous system (CNS) plays in the regulation of sodium and water homeostasis.

REVIEW SUMMARY

The classification of hyponatremia is based on an assessment of serum sodium concentration ([Na+]), serum and urine osmolality, and body volume status. In most cases, hyponatremia is associated with hypotonicity, which causes water to move into the brain. Adaptive responses limit the impact of cerebral edema in chronic hyponatremia, but CNS symptoms and death may occur in response to rapid or large decreases in serum [Na+]. The prompt correction of serum [Na+] is mandatory in symptomatic patients, but overly rapid correction must be avoided to limit the risk of myelinolysis. In neurologic disorders, euvolemic hyponatremia (usually caused by the syndrome of inappropriate secretion of antidiuretic hormone) must be distinguished from hypovolemic states such as cerebral salt wasting because the treatment of the 2 conditions differs. Vasopressin antagonists represent a new approach to the treatment of euvolemic and hypervolemic hyponatremia secondary to arginine vasopressin dysregulation.

CONCLUSION

The optimal treatment of hyponatremia is controversial, but appropriate treatment must be determined according to the osmolality and volume status of the patient. If left untreated, serious CNS complications and adverse outcomes, including an increased risk of death, can occur.

Vasopressin receptor antagonists. Therapeutic potential in the management of acute and chronic heart failure

Despite the use of ACE inhibitors and beta-blockers, the morbidity and mortality of patients with chronic heart failure remains quite high. This has stimulated the development of new therapies, many based on the neurohormonal hypothesis. There are now multiple agents being developed for the treatment of heart failure designed to block many of the neurohormones that are increased in these patients. One of the hormones that is increased in chronic heart failure is vasopressin. Vasopressin reduces free water secretion and at high concentrations, causes vasoconstriction in the peripheral vasculature. Antagonists to vasopressin will promote free water excretion (aquaresis) and vasodilatation with a subsequent reduction in afterload. In theory, these agents would be beneficial for both acute exacerbations of heart failure (free water excretion) and chronic heart failure (neurohormonal blockade). We review the potential uses of these antagonists for these two conditions and the promising results of small, hemodynamic trials with the new vasopressin antagonists that have already been performed.

CHARACTERIZATION OF RWJ-351647, A NOVEL NONPEPTIDE VASOPRESSIN V2 RECEPTOR ANTAGONIST

1. Antagonists of the V(2) vasopressin (AVP) receptor are aquaretic agents, inhibiting water resorption without stimulating electrolyte excretion. In this set of experiments, a novel V(2) receptor antagonist, RWJ-351647, was characterized in vitro and in vivo. 2. RWJ-351647 displaced (3)H-AVP binding from cloned human V(2) and V(1A) receptors with Ki values of 1 nmol/L and 24 nmol/L. In assays using transfected HEK293 cells expressing either human or rat V(2) receptors, RWJ-351647 inhibited AVP-induced cAMP accumulation with Ki values of 3 nmol/L and 6 nmol/L, respectively. 3. RWJ-351647 was very selective in binding assays and showed only weak functional antagonist activity at either the cloned human V(1B) and oxytocin receptors or the human platelet V(1A) receptor. No agonist activity was seen with the compound at any receptor. 4. Pharmacokinetic studies in rats showed RWJ-351647 to be 41.9% bioavailable after a single oral administration. After repeated daily dosing over 5 days, the oral bioavailability remained at 43.9% with no change in the compound peak plasma levels or clearance rate. 5. In efficacy studies, RWJ-351647 increased urine output and decreased urine osmolality with oral doses as low as 0.1 mg/kg and 1.0 mg/kg in rats and cynomolgus monkeys, respectively. In a multiple dose study in primates, RWJ-351647 maintained a consistent aquaretic effect over 10 days without increasing sodium or potassium excretion. 6. In summary, RWJ-351647 was shown to be a selective and potent V(2) receptor antagonist with sustainable aquaretic activity in both rats and primates. The preclinical data suggest that RWJ-351647 is a potent and effective aquaretic agent with potential for use in diseases characterized by water retention.

Vasopressin receptor antagonists: pharmacological tools and potential therapeutic agents

The present survey deals with the development and applications of non-peptidergic vasopressin receptor antagonists. The existence of at least three vasopressin receptors (V(1), V(2) and V(3) respectively) is firmly established. V(1)-receptors play a relevant role in the regulation of vascular tone, whereas V(2)-receptors are known to mediate the antidiuretic activity of vasopressin at the level of the renal collecting ducts. The V(3)-receptor appears to be involved in the release of the adreno-corticotropic hormone. Vasopressin receptor antagonists which are peptides have been known for several decades, more recently, both V(1)- and V(2)-receptor blockers which are non-peptidergic have been introduced, as well as agents with affinity for both V(1)- and V(2)-receptor subtypes. A survey of these non-peptidergic antagonists is presented here. Such compounds are useful as pharmacological tools, and they can also be thought of as therapeutic agents as therapeutic agents in cardiovascular and renal diseases. Selective V(1)- and V(2)-receptor antagonists were used to study the interaction between vasopressin receptors and sympathetic neurones. Depending on the experimental model used this interaction can occur at either the pre- or postsynaptic sites. In both cases predominantly V(1)-receptors are involved. A brief survey is given of the potential use of V-receptor antagonists in the drug therapy of syndrome of inappropriate antidiuretic hormone secretion and other water retaining disorders, congestive heart failure and certain forms of hypertension (in particular in the Negroid hypertensive patients).

Sustained aquaretic effect of the V2-AVP receptor antagonist, RWJ-351647, in cirrhotic rats with ascites and water retention

1 A disturbance in body water homeostasis is a common feature in advanced cirrhosis. This disturbance is always associated with the existence of ascites and is characterized by an inability to adjust the amount of water excreted in the urine to the amount of water ingested. Vasopressin (AVP) is of major importance in the pathogenesis of water retention and hyponatremia in cirrhosis. 2 The current study assessed the renal, hormonal and hemodynamic effects induced by 10-day chronic oral administration of RWJ-351647 (0.5 mg kg(-1) daily), a new nonpeptide V(2)-AVP antagonist, in rats with CCl(4)-induced cirrhosis, ascites and severe water retention. Urine volume (UV), urine osmolality and sodium and potassium excretion were measured daily. At the end of the study, systemic hemodynamic parameters were also assessed. 3 Long-term administration of RWJ-351647 has an aquaretic effect in rats with cirrhosis, ascites, water retention and hypo-osmolality. It increases UV (ANOVA: F=7.32, P<0.0001) and reduces urine osmolality (ANOVA: F=12.69, P<0.0001) throughout the entire period of treatment, thereby leading to a greater renal ability to excrete a water load at the end of the 10-day treatment period (the percentage of water load excreted improved from 30+/-8 to 92+/-21%, P<0.025). 4 The nonpeptide AVP V(2)-receptor antagonist RWJ-351647 also increased sodium excretion without affecting creatinine clearance and blood pressure. 5 These data suggest that RWJ-351647 could be therapeutically useful in the treatment of water retention in human cirrhosis.

Hyponatremia and Arginine Vasopressin Dysregulation: Mechanisms, Clinical Consequences, and Management

Hyponatremia, the most common electrolyte disorder, occurs frequently in older people and in hospitalized patients. Physiological changes of aging that interact with diseases and drugs commonly present in older people put this population at greater risk for hyponatremia. It can accompany central nervous system disorders, pulmonary and renal disease, cancer, congestive heart failure, and liver cirrhosis, as well as many commonly used drugs. Delayed recognition can lead to symptomatic hyponatremia with consequent cerebral edema and possibly irreversible neurological damage. Symptoms and signs of hyponatremia may be subtle or not attributed to hyponatremia. Most cases are of the euvolemic type, in which extracellular fluid volume is normal and is often due to the syndrome of inappropriate secretion of antidiuretic hormone. Hyponatremia can also occur in association with hypervolemia or hypovolemia. Common to all of these circumstances is increased secretion of arginine vasopressin (AVP). Understanding of the pathophysiological basis of hyponatremia and of brain compensatory mechanisms is critical to safe treatment. Fluid restriction or infusion of hypertonic saline can improve symptoms and normalize serum sodium levels but does not address excess AVP, which in most cases is the underlying cause of the disorder. A major new approach to treatment of hyponatremia is the development of aquaretics: AVP-receptor antagonists that provide a targeted therapeutic approach to correcting the many kinds of hyponatremia caused by excess AVP levels.

Hyponatremia in congestive heart failure

Hyponatremia has been identified as a risk factor for increased morbidity and mortality in patients with congestive heart failure (CHF) and other edematous disorders and can lead to severe neurologic derangements. Low cardiac output and blood pressure associated with CHF triggers a compensatory response by the body that activates several neurohormonal systems designed to preserve arterial blood volume and pressure. Hyponatremia in patients with CHF is primarily caused by increased activity of arginine vasopressin (AVP). AVP increases free-water reabsorption in the renal collecting ducts, increasing blood volume and diluting plasma sodium concentrations. Hyponatremia may also be triggered by diuretic therapy used in the management of symptoms of CHF. Hyponatremic disorders occur when the normal ratio of solutes to body water content is altered by parallel changes in serum sodium and osmolality. Hyponatremia is generally defined as a serum sodium ion concentration <135 to 136 mmol/L and can be broadly categorized into 2 types, dilutional or depletional. Dilutional hyponatremia is the most common form of hyponatremia and is caused by excess water retention. Depletional hyponatremia is usually hypovolemic, with an absolute deficiency of water but a relative excess of body water compared with sodium concentration.

Consequences of inadequate management of hyponatremia

Dilutional hyponatremia is a commonly observed disorder in hospitalized patients. It represents an excess of water in relation to prevailing sodium stores and is most often associated with a high plasma level of arginine vasopressin, including that found in patients with the syndrome of inappropriate antidiuretic hormone secretion. Hyponatremia may be classified as either acute or chronic depending on the rate of decline of serum sodium concentration, and can lead to a wide range of deleterious changes involving almost all body systems. Serious complications of dilutional hyponatremia most frequently involve the central nervous system. In fact, acute severe hyponatremia is potentially life-threatening and must be treated promptly and aggressively. Chronic hyponatremia often develops in patients with nonrenal diseases and is associated with increased morbidity and mortality. In patients hospitalized for congestive heart failure, hyponatremia is linked to a poor prognosis and increased length of hospital stay. Prompt recognition and optimal management of hyponatremia in hospitalized patients may reduce in-hospital mortality and symptom severity, allow for less intensive hospital care, decrease the duration of hospitalization and associated costs, and improve the treatment of underlying comorbid conditions and patients' quality of life. The proper treatment of dilutional hyponatremia, especially when chronic, must avoid increasing serum sodium too rapidly, which can lead to permanent or fatal neurologic sequelae. The treatment of hyponatremia may be facilitated by emerging therapies that block the actions of arginine vasopressin at V2 and V1a receptors to promote aquaresis, the electrolyte-sparing elimination of free water, and elevate serum sodium concentrations.

Neuroendocrine evaluation of cardiac disease

Current evidence favors the view that regardless of etiology, there is a predictable sequence of neuroendocrine activation that operates in most dogs and cats with progressive heart disease and that it is largely, but not entirely, independent of etiology. The natriuretic peptides and sympathetic nervous system seem to be early responders to developing cardiac and hemodynamic perturbations in both species. BNP plays a particularly prominent role in cats, possibly as a reflection of disease etiology. Shortly thereafter, plasma endothelin concentrations rise, reflecting the impact of the hemodynamic alterations on the vasculature. Endothelin and the natriuretic peptides directly suppress plasma renin release but have divergent effects on aldosterone. Activation of the tissue RAAS may operate early on to further the progression of heart failure, but evidence of plasma RAAS activation occurs comparatively late and near the time of development of overt CHF. Finally, in animals with severe CHF that are prone to hypotension,vasopressin levels may also rise, contributing to the retention of free water and congestion that is refractory to diuretics. Although oversimplified, this scenario seems to be consistent with data obtained in human, canine, and feline patients. These observations provide some impetus for evaluating ACE inhibitors in cats and beta-receptor-blocking drugs in dogs and cats. Perhaps we are also a little closer to identifying useful biochemical markers that can aid in the diagnosis of heart disease, guide therapy, and improve our understanding of the biologic processes occurring in our patients.

Opioid receptor-like 1 stimulation in the collecting duct induces aquaresis through vasopressin-independent aquaporin-2 downregulation

Nociceptin, the endogenous ligand of the inhibitory G protein-coupled opioid receptor-like 1 receptor, produces aquaresis (i.e., increases the excretion of solute-free urine) in rats. However, the mechanism underlying this effect has not yet been explained. Using immunohistochemistry, we found the opioid receptor-like 1 receptor in the rat kidney colocalized with the vasopressin-regulated water channel aquaporin-2 in inner medullary collecting ducts. We investigated the aquaretic effect of opioid receptor-like 1 receptor stimulation by infusing the selective nociceptin analog ZP120C; volume depletion was prevented by computer-driven, servo-controlled intravenous volume replacement with 50 mM glucose. ZP120C induced a marked and sustained aquaresis in normal and congestive heart failure rats in the absence of changes in vasopressin plasma concentrations. The ZP120C-induced aquaresis was associated with downregulation of the aquaporin-2 protein level in both rat groups, suggesting that opioid receptor-like 1 receptor stimulation produces aquaresis by inhibiting the vasopressin type-2 receptor-mediated stimulation on collecting duct water reabsorption. However, substantial amounts of PKA-mediated serine 256 phosphorylated aquaporin-2 were still present after 4 h of ZP120C treatment. Furthermore, neither preincubation with nociceptin nor ZP120C inhibited vasopressin-mediated cAMP accumulation in isolated collecting ducts. We conclude that renal opioid receptor-like 1 receptor stimulation in normal and congestive heart failure rats produces aquaresis by a direct renal effect, via aquaporin-2 downregulation, through a mechanism not involving inhibition of vasopressin type-2 receptor-mediated cAMP production.

Chronic experimental myocardial infarction produces antinatriuresis by a renal nerve-dependent mechanism

The present study focused on the role of sympathetic renal nerve activity, in mediating congestive heart failure-induced sodium retention following experimental chronic myocardial infarction. Groups of male Wistar rats (240-260 g) were studied: sham-operated coronary ligation (CON3W, N = 11), coronary ligation and sham-operated renal denervation (INF3W, N = 19), 3 weeks of coronary ligation and sympathetic renal nerve denervation (INF3WDX, N = 6), sham-operated coronary ligation (N = 7), and 16 weeks of coronary ligation (INF16W, N = 7). An acute experimental protocol was used in which the volume overload (VO; 5% of body weight) was applied for 30 min after the equilibration period of continuous iv infusion of saline. Compared to control levels, VO produced an increase (P < 0.01, ANOVA) in urine flow rate (UFR; 570%) and urinary sodium excretion (USE; 1117%) in CON3W. VO induced a smaller increase (P < 0.01) in USE (684%) in INF3W. A similar response was also observed in INF16W. In INF3WDX, VO produced an immediate and large increase (P < 0.01) in UFR (547%) and USE (1211%). Similarly, in INF3W VO increased (P < 0.01) UFR (394%) and USE (894%). Compared with INF3W, VO induced a higher (P < 0.01) USE in INF3WDX, whose values were similar to those for CON3W. These results suggest that renal sympathetic activity may be involved in sodium retention induced by congestive heart failure. This premise is supported by the observation that in bilaterally renal denervated INF3WDX rats myocardial infarction was unable to reduce volume expansion-induced natriuresis. However, the mechanism involved in urinary volume regulation seems to be insensitive to the factors that alter natriuresis.

Increased thirst and vasopressin secretion after myocardial infarction in rats

Impaired regulation of salt and water balance in left ventricular dysfunction and heart failure can lead to pulmonary and peripheral edema and hyponatremia. Previous studies of disordered water regulation in heart failure have used models of low cardiac output with normal cardiac function (e.g., inferior vena cava ligation). We investigated thirst and vasopressin (AVP) secretion in a rat myocardial infarction model of chronic left ventricular dysfunction/heart failure in response to a 24-h water deprivation period. Thirst (implied from water drunk), hematocrit, plasma renin activity, and plasma AVP concentrations increased with water deprivation vs. ad libitum water access. Thirst and plasma AVP concentrations were significantly positively correlated with infarct size after 24-h water deprivation but not under ad libitum water access conditions. The mechanism by which this occurs is unclear but could involve increased osmoreceptor sensitivity, altered stimulation of baroreceptors, the renin-angiotensin system, or altered central neural control.

Inhibition of renal cystic disease development and progression by a vasopressin V2 receptor antagonist

The polycystic kidney diseases (PKDs) are a group of genetic disorders causing significant renal failure and death in children and adults. There are no effective treatments. Two childhood forms, autosomal recessive PKD (ARPKD) and nephronophthisis (NPH), are characterized by collecting-duct cysts. We used animal models orthologous to the human disorders to test whether a vasopressin V2 receptor (VPV2R) antagonist, OPC31260, would be effective against early or established disease. Adenosine-3',5'-cyclic monophosphate (cAMP) has a major role in cystogenesis, and the VPV2R is the major cAMP agonist in the collecting duct. OPC31260 administration lowered renal cAMP, inhibited disease development and either halted progression or caused regression of established disease. These results indicate that OPC31260 may be an effective treatment for these disorders and that clinical trials should be considered.

Mechanisms of renal hyporesponsiveness to ANP in heart failure

The atrial natriuretic peptide (ANP) plays an important role in chronic heart failure (CHF), delaying the progression of the disease. However, despite high ANP levels, natriuresis falls when CHF progresses from a compensated to a decompensated state, suggesting emergence of renal resistance to ANP. Several mechanisms have been proposed to explain renal hyporesponsiveness, including decreased renal ANP availability, down-regulation of natriuretic peptide receptors and altered ANP intracellular transduction signal. It has been demonstrated that the activity of neutral endopeptidase (NEP) is increased in CHF, and that its inhibition enhances renal cGMP production and renal sodium excretion. In vitro as well as in vivo studies have provided strong evidence of an increased degradation of intracellular cGMP by phosphodiesterase in CHF. In experimental models, ANP-dependent natriuresis is improved by phosphodiesterase inhibitors, which may arise as new therapeutic agents in CHF. Sodium-retaining systems likely contribute to renal hyporesponsiveness to ANP through different mechanisms. Among these systems, the renin-angiotensin-aldosterone system has received particular attention, as angiotensin II and ANP have renal actions at the same sites and inhibition of angiotensin-converting enzyme and angiotensin-receptor blockade improve ANP hyporesponsiveness. Less is known about the interactions between the sympathetic nervous system, endothelin or vasopressin and ANP, which may also blunt ANP-induced natriuresis. To summarize, renal hyporesponsiveness to ANP is probably multifactorial. New treatments designed to restore renal ANP efficiency should limit sodium retention in CHF patients and thus delay the progression to overt heart failure.

Structure-activity study of novel tricyclic benzazepine arginine vasopressin antagonists

Novel tricyclic benzazepine derivatives were synthesized as arginine vasopressin (AVP) antagonists. Several tricyclic compounds showed potent antagonistic activity in rat AVP receptors V(1a) and V(2). Derivatives containing pyrrolo-tricyclic amines, 13i-k, 30, and 31 also showed selectivity for the V(2) receptor.

Evaluation and management of hypo-osmolality in hospitalized patients

Hyponatremia is the most common electrolyte disorder encountered in the clinical setting. Abnormalities of the mechanisms that maintain normal water and sodium metabolism are often present in hospitalized patients, including defects in renal water excretion. All of the current therapeutic approaches in patients with the syndrome of inappropriate antidiuretic hormone secretion and other forms of vasopressin-induced hyponatremia have significant limitations. Studies in animal models and humans have demonstrated that antagonists of the AVP V2 receptor in the kidney are effective in correcting hyponatremia. These new agents have been termed "aquaretics" because of their ability to induce a free water diuresis without the natriuresis or kaliuresis characteristic of diuretic drugs. When approved for clinical use, selective V2, and possibly also combined V1 + V2 receptor antagonists will be helpful in therapy.

Vasopressin-induced facilitation of adrenergic responses in the rat mesenteric artery is V1-receptor dependent

1. The present study was designed to analyse the possible involvement of V1- and V2-receptors in vasopressin (AVP)-induced facilitation of the sympathetic nervous system. Furthermore, we aimed to determine whether the site of facilitation by AVP is located pre- or postsynaptically. 2. Electrical field stimulation (EFS) was applied on the rat mesteric artery to activate the sympathetic nervous system. In addition, we evaluated the direct vascular effects of AVP. The postsynaptic effect of AVP on the sympathetic nervous system was investigated by exposing the vessels to exogenous noradrenaline. These experiments were performed in the absence or presence of selective V1 and V2 receptor antagonists SR 49059 and SR 121463, respectively. Desmopressin was applied as a selective V2 agonist. 3. The direct vasoconstrictor effect of AVP was antagonized by SR 49059 and not by SR 121463. Desmopressin neither showed any direct vasoconstrictor effect nor produced vasodilatation after a precontraction induced by noradrenaline (10 microM). The EFS-induced rise in vascular tone could be increased by a sub-pressor concentration of AVP. This fascilitation could be antagonized by SR 49059, but not by SR 121463. Desmopressin did not influence the increase in vascular tone during EFS. Vasoconstriction induced by exogenous noradrenaline could be facilitated by a sub-pressor concentration of AVP and this selective postsynaptic effect could be antagonized by V1-receptor blockade. 4. In conclusion, the AVP-induced facilitation of the sympathetic nervous system is completely V1-receptor dependent and at least partly postsynaptically mediated.