The effect of vasopressin and related compounds at V1a and V2 receptors in animal models relevant to human disease

Practice guidance for the use of terlipressin for liver cirrhosis-related complications

BACKGROUND

Liver cirrhosis is a major global health burden worldwide due to its high risk of morbidity and mortality. Role of terlipressin for the management of liver cirrhosis-related complications has been recognized during recent years. This article aims to develop evidence-based clinical practice guidance on the use of terlipressin for liver cirrhosis-related complications.

METHODS

Hepatobiliary Study Group of the Chinese Society of Gastroenterology of the Chinese Medical Association and Hepatology Committee of the Chinese Research Hospital Association have invited gastroenterologists, hepatologists, infectious disease specialists, surgeons, and clinical pharmacists to formulate the clinical practice guidance based on comprehensive literature review and experts' clinical experiences.

RESULTS

Overall, 10 major guidance statements regarding efficacy and safety of terlipressin in liver cirrhosis were proposed. Terlipressin can be beneficial for the management of cirrhotic patients with acute variceal bleeding and hepatorenal syndrome (HRS). However, the evidence regarding the use of terlipressin in cirrhotic patients with ascites, post-paracentesis circulatory dysfunction, and bacterial infections and in those undergoing hepatic resection and liver transplantation remains insufficient. Terlipressin-related adverse events, mainly including gastrointestinal symptoms, electrolyte disturbance, and cardiovascular and respiratory adverse events, should be closely monitored.

CONCLUSION

The current clinical practice guidance supports the use of terlipressin for gastroesophageal variceal bleeding and HRS in liver cirrhosis. High-quality studies are needed to further clarify its potential effects in other liver cirrhosis-related complications.

Desmopressin Stimulates Nitric Oxide Production in Human Lung Microvascular Endothelial Cells

Desmopressin (dDAVP) is the best characterized analogue of vasopressin, the endocrine regulator of water balance endowed with potent vasoconstrictive effects. Despite the use of dDAVP in clinical practice, ranging from the treatment of nephrogenic diabetes insipidus to bleeding disorders, much remains to be understood about the impact of the drug on endothelial phenotype. The aim of this study was, thus, to evaluate the effects of desmopressin on the viability and function of human pulmonary microvascular endothelial cells (HLMVECs). The results obtained demonstrate that the vasopressor had no cytotoxic effect on the endothelium; similarly, no sign of endothelial activation was induced by dDAVP, indicated by the lack of effect on the expression of inflammatory cytokines and adhesion molecules. Conversely, the drug significantly stimulated the production of nitric oxide (NO) and the expression of the inducible isoform of nitric oxide synthase, NOS2/iNOS. Since the intracellular level of cAMP also increased, we can hypothesize that NO release is consequent to the activation of the vasopressin receptor 2 (V2R)/guanylate cyclase (Gs)/cAMP axis. Given the multifaceted role of NOS2-deriving NO for many physio-pathological conditions, the meanings of these findings in HLMVECs appears intriguing and deserves to be further addressed.

Portopulmonary hypertension caused by portal hypertension that is complicated by central diabetes insipidus

We discuss the pathophysiology, diagnosis, differential diagnosis, and therapy of a case with central diabetes insipidus, idiopathic portal hypertension, and portopulmonary hypertension. This report reviews how vasopressin affects those diseases.

In vitro binding and receptor-mediated activity of terlipressin at vasopressin receptors V1 and V2

Terlipressin, a synthetic, systemic vasoconstrictor with selective activity at vasopressin-1 (V₁) receptors, is a pro-drug for the endogenous/natural porcine hormone [Lys₈]-vasopressin (LVP). We investigated binding and receptor-mediated cellular activities of terlipressin, LVP, and endogenous human hormone [Arg₈]-vasopressin (AVP) at V₁ and vasopressin-2 (V₂) receptors. Cell membrane homogenates of Chinese hamster ovary cells expressing human V₁ and V₂ receptors were used in competitive binding assays to measure receptor-binding activity. These cells were used in functional assays to measure receptor-mediated cellular activity of terlipressin, LVP, and AVP. Binding was measured by [³H]AVP counts, and the activity was measured by fluorometric detection of intracellular calcium mobilization (V₁) and cyclic adenosine monophosphate (V₂). Binding potency at V₁ and V₂ was AVP>LVP>>terlipressin. LVP and terlipressin had approximately sixfold higher affinity for V₁ than for V₂. Cellular activity potency was also AVP>LVP>>terlipressin. Terlipressin was a partial agonist at V₁ and a full agonist at V₂; LVP was a full agonist at both V₁ and V₂. The in vivo response to terlipressin is likely due to the partial V₁ agonist activity of terlipressin and full V₁ agonist activity of its metabolite, LVP. These results provide supportive evidence for previous findings and further establish terlipressin pharmacology for vasopressin receptors.

Diagnosis of diabetes insipidus observed in Swiss Duroc boars

BACKGROUND

Diabetes insipidus (DI) is a rare disease in humans and animals, which is caused by the lack of production, malfunction or dysfunction of the distal nephron to the antidiuretic effect of the antidiuretic hormone (ADH). Diagnosis requires a thorough medical history, clinical examination and further laboratory confirmation. This case report describes the appearance of DI in five Duroc boars in Switzerland.

CASE PRESENTATION

Two purebred intact Duroc boars at the age of 8 months and 1.5 years, respectively, with a history of polyuric and polydipsic symptoms had been referred to the Swine Clinic in Berne. Based on the case history, the results of clinical examination and the analysis of blood and urine, a tentative diagnosis of DI was concluded. Finally, the diagnosis was confirmed by findings from a modified water deprivation test, macroscopic examinations and histopathology. Following the diagnosis, three genes known to be involved in inherited DI in humans were analyzed in order to explore a possible genetic background of the affected boars.

CONCLUSION

The etiology of DI in pigs is supposed to be the same as in humans, although this disease has never been described in pigs before. Thus, although occurring only on rare occasions, DI should be considered as a differential diagnosis in pigs with polyuria and polydipsia. It seems that a modified water deprivation test may be a helpful tool for confirming a diagnosis in pigs. Since hereditary forms of DI have been described in humans, the occurrence of DI in pigs should be considered in breeding programs although we were not able to identify a disease associated mutation.

Vasopressin 1a receptor partial agonism increases sodium excretion and reduces portal hypertension and ascites in cirrhotic rats

Patients and rats with cirrhosis and ascites have portal hypertension and circulatory dysfunction. Synthetic arginine vasopressin (AVP) receptor agonists able to induce systemic and mesenteric vasoconstriction have shown their usefulness in reducing portal pressure (PP) in this condition. We assessed the potential therapeutic value of a new V1 a -AVP receptor partial agonist with a preferential splanchnic vasoconstrictor effect (FE 204038) in rats with cirrhosis and ascites. The hemodynamic effects of cumulative intravenous doses of FE 204038, terlipressin, or vehicle were investigated. Mean arterial pressure and PP were continuously recorded and cardiac output and systemic vascular resistance (SVR) assessed at 30-minute intervals for 90 minutes. Urine volume, urine osmolality, and urinary excretion of sodium and creatinine were measured in basal conditions and following twice-daily subcutaneous doses of FE 204038 or vehicle. PP, mean arterial pressure, cardiac output, SVR, and ascites volume were also measured after 6 days. The expression of an array of vasoactive genes was assessed in the thoracic aorta and the mesenteric circulation of control rats and rats with cirrhosis and ascites. FE 204038 dose-dependently decreased PP, did not modify mean arterial pressure, and increased SVR. The effect of the V1a -AVP receptor partial agonist on PP was associated with an improvement in urine volume and urinary excretion of sodium during the first day of treatment. SVR was higher and cardiac output and ascites volume were lower in rats with cirrhosis and ascites treated with FE 204038. V1a -AVP receptor expression in rats with cirrhosis and ascites was markedly enhanced in the mesenteric circulation compared to the thoracic aorta.

CONCLUSION

FE 204038 increases sodium excretion and reduces portal hypertension and ascites in experimental cirrhosis. V1a -AVP receptor partial agonism could be a useful pharmacological treatment in decompensated patients with cirrhosis.

Selective V(1a) agonism attenuates vascular dysfunction and fluid accumulation in ovine severe sepsis

Vasopressin analogs are used as a supplement to norepinephrine in septic shock. The isolated effects of vasopressin agonists on sepsis-induced vascular dysfunction, however, remain controversial. Because V(2)-receptor stimulation induces vasodilation and procoagulant effects, a higher V(1a)- versus V(2)-receptor selectivity might be advantageous. We therefore hypothesized that a sole, titrated infusion of the selective V(1a)-agonist Phe(2)-Orn(8)-Vasotocin (POV) is more effective than the mixed V(1a)-/V(2)-agonist AVP for the treatment of vascular and cardiopulmonary dysfunction in methicillin resistant staphylococcus aureus pneumonia-induced, ovine sepsis. After the onset of hemodynamic instability, awake, chronically instrumented, mechanically ventilated, and fluid resuscitated sheep were randomly assigned to receive continuous infusions of either POV, AVP, or saline solution (control; each n = 6). AVP and POV were titrated to maintain mean arterial pressure above baseline - 10 mmHg. When compared with that of control animals, AVP and POV reduced neutrophil migration (myeloperoxidase activity, alveolar neutrophils) and plasma levels of nitric oxide, resulting in higher mean arterial pressures and a reduced vascular leakage (net fluid balance, chest and abdominal fluid, pulmonary bloodless wet-to-dry-weight ratio, alveolar and septal edema). Notably, POV stabilized hemodynamics at lower doses than AVP. In addition, POV, but not AVP, reduced myocardial and pulmonary tissue concentrations of 3-nitrotyrosine, VEGF, and angiopoietin-2, thereby leading to an abolishment of cumulative fluid accumulation (POV, 9 ± 15 ml/kg vs. AVP, 110 ± 13 ml/kg vs. control, 213 ± 16 ml/kg; P < 0.001 each) and an attenuated cardiopulmonary dysfunction (left ventricular stroke work index, PaO(2)-to-FiO(2) ratio) versus control animals. Highly selective V(1a)-agonism appears to be superior to unselective vasopressin analogs for the treatment of sepsis-induced vascular dysfunction.

Effects of vasopressinergic receptor agonists on sublingual microcirculation in norepinephrine-dependent septic shock

INTRODUCTION

The present study was designed to determine the effects of continuously infused norepinephrine (NE) plus (1) terlipressin (TP) or (2) arginine vasopressin (AVP) or (3) placebo on sublingual microcirculation in septic shock patients. The primary study end point was a difference of ≥ 20% in the microvascular flow index of small vessels among groups.

METHODS

The design of the study was a prospective, randomized, double-blind clinical trial. NE was titrated to maintain mean arterial pressure (MAP) between 65 and 75 mmHg after establishment of normovolemia in 60 septic shock patients. Thereafter patients (n = 20 per group) were randomized to receive continuous infusions of either TP (1 μg/kg/hour), AVP (0.04 U/minute) or placebo (isotonic saline). In all groups, open-label NE was adjusted to maintain MAP within threshold values if needed. The sublingual microcirculatory blood flow of small vessels was assessed by sidestream dark-field imaging. All measurements, including data from right heart catheterization and norepinephrine requirements, were obtained at baseline and 6 hours after randomization.

RESULTS

TP and AVP decreased NE requirements at the end of the 6-hour study period. The data are medians (25th and 75th interquartile ranges (IQRs)): 0.57 μg/kg/minute (0.29 to 1.04) vs. 0.16 μg/kg/minute (0.03 to 0.37) for TP and 0.40 μg/kg/minute (0.20 to 1.05) vs. 0.23 μg/kg/minute (0.03 to 0.77) for AVP, with statistical significance of P < 0.05 vs. baseline and vs. placebo. There were no differences in sublingual microcirculatory variables, systemic hemodynamics, oxygen transport and acid-base homeostasis among the three study groups during the entire observation period. The proportions of perfused vessels increased in relation to baseline within all study groups, and there were no significant differences between groups. The specific data were as follows (median (IQR)): 9.7% (2.6 to 19.8) for TP, 8.9% (0.0 to 17.8) for AVP, and 6.9% (3.5 to 10.1) for placebo (P < 0.05 vs. baseline for each comparison), as well as perfused vessel density 18.6% (8.6 to 36.9) for TP, 20.2% (-3.0 to 37.2) for AVP, and 11.4% (-3.0 to 19.4) for placebo (P < 0.05 vs. baseline for each comparison).

CONCLUSIONS

The present study suggests that to achieve a MAP of 65 to 75 mmHg in septic patients treated with NE, the addition of continuously infused low-dose TP or AVP does not affect sublingual microcirculatory blood flow. In addition, our results suggest that microcirculatory flow abnormalities are mainly related to other factors (for example, volume status, timing, hemodynamics and progression of the disease) rather than to the vasopressor per se.

TRIAL REGISTRATION

ClinicalTrial.gov NCT00995839.

The effect of vasopressin on choroidal blood flow, intraocular pressure, and orbital venous pressure in rabbits

PURPOSE

To investigate the effects of arginine-vasopressin (AVP) on intraocular pressure (IOP), orbital venous pressure (OVP), and choroidal blood flow (ChorBF) regulation in anesthetized rabbits.

METHODS

Mean arterial pressure (MAP), IOP, and OVP were measured by direct cannulation of the central ear artery, the vitreous, and the orbital venous sinus, respectively. Laser Doppler flowmetry was used to record ChorBF. To change the perfusion pressure (PP), MAP was manipulated mechanically with occluders around the aorta and vena cava. In the first group of animals (n = 11) the dose-response relationship was measured. In the second group of animals (n = 8) pressure-flow relationships were determined at baseline and in response to intravenous application of a low (0.08 ng/kg/min) and a high (1.33 ng/kg/min) infusion rate of AVP.

RESULTS

AVP caused a dose-dependent increase of MAP and choroidal vascular resistance (ChorR), whereas IOP, OVP, ChorBF, and heart rate (HR) were decreased. In contrast to the high infusion rate, the low infusion rate of AVP had no effect on baseline ChorBF. However, the pressure-flow relationship was shifted downward significantly by both infusion rates at PP below baseline.

CONCLUSIONS

AVP reduces IOP and OVP significantly and is a potent vasoconstrictor in the choroidal vascular bed. In the choroid, the effect of AVP is not only dose-dependent, but also PP-dependent, which is indicated by the reduced perfusion relative to control with low-dosed AVP at low PP.

Effects of two different dosing regimens of terlipressin on organ functions in ovine endotoxemia

OBJECTIVE AND DESIGN

To test the hypothesis that a continuous infusion of the vasopressin analog terlipressin is associated with less organ dysfunction as compared to intermittent bolus infusion in an ovine sepsis model.

SUBJECTS

Twenty-seven adult female sheep.

TREATMENT

All sheep were subjected to a Salmonella typhosa endotoxin infusion (10 ng/kg/min). After 16 h of endotoxemia, the surviving animals (n = 24) were randomized to (1) an untreated control group, (2) a continuous terlipressin group (2 mg/24 h), or (3) a terlipressin bolus group (1 mg/6 h).

METHODS

Hemodynamic variables were measured and blood was withdrawn at specific time points for the assessment of organ functions.

RESULTS

Continuous terlipressin infusion was associated with improved surrogate parameters of myocardial, renal, and hepatic function as compared with terlipressin bolus infusion. Reduced vascular hyperpermeability was evidenced by an attenuated decrease in plasma protein concentrations in sheep treated with continuous terlipressin infusion as compared to bolus injection or no treatment.

CONCLUSIONS

Continuous infusion of low-dose terlipressin preserved several surrogate parameters of organ function better than intermittent bolus injections in sheep with systemic inflammation.

Role of selective V2-receptor-antagonism in septic shock: a randomized, controlled, experimental study

Introduction

V₂-receptor (V₂R) stimulation potentially aggravates sepsis-induced vasodilation, fluid accumulation and microvascular thrombosis. Therefore, the present study was performed to determine the effects of a first-line therapy with the selective V₂R-antagonist (Propionyl₁-D-Tyr(Et)₂-Val₄-Abu₆-Arg_8,9)-Vasopressin on cardiopulmonary hemodynamics and organ function vs. the mixed V_1aR/V₂R-agonist arginine vasopressin (AVP) or placebo in an established ovine model of septic shock.

Methods

After the onset of septic shock, chronically instrumented sheep were randomly assigned to receive first-line treatment with the selective V₂R-antagonist (1 μg/kg per hour), AVP (0.05 μg/kg per hour), or normal saline (placebo, each n = 7). In all groups, open-label norepinephrine was additionally titrated up to 1 μg/kg per minute to maintain mean arterial pressure at 70 ± 5 mmHg, if necessary.

Results

Compared to AVP- and placebo-treated animals, the selective V₂R-antagonist stabilized cardiopulmonary hemodynamics (mean arterial and pulmonary artery pressure, cardiac index) as effectively and increased intravascular volume as suggested by higher cardiac filling pressures. Furthermore, left ventricular stroke work index was higher in the V₂R-antagonist group than in the AVP group. Notably, metabolic (pH, base excess, lactate concentrations), liver (transaminases, bilirubin) and renal (creatinine and blood urea nitrogen plasma levels, urinary output, creatinine clearance) dysfunctions were attenuated by the V₂R-antagonist when compared with AVP and placebo. The onset of septic shock was associated with an increase in AVP plasma levels as compared to baseline in all groups. Whereas AVP plasma levels remained constant in the placebo group, infusion of AVP increased AVP plasma levels up to 149 ± 21 pg/mL. Notably, treatment with the selective V₂R-antagonist led to a significant decrease of AVP plasma levels as compared to shock time (P < 0.001) and to both other groups (P < 0.05 vs. placebo; P < 0.001 vs. AVP). Immunohistochemical analyses of lung tissue revealed higher hemeoxygenase-1 (vs. placebo) and lower 3-nitrotyrosine concentrations (vs. AVP) in the V₂R-antagonist group. In addition, the selective V₂R-antagonist slightly prolonged survival (14 ± 1 hour) when compared to AVP (11 ± 1 hour, P = 0.007) and placebo (11 ± 1 hour, P = 0.025).

Conclusions

Selective V₂R-antagonism may represent an innovative therapeutic approach to attenuate multiple organ dysfunction in early septic shock.

Identification of novel selective V2 receptor non-peptide agonists

Peptides with agonist activity at the vasopressin V(2) receptor are used clinically to treat fluid homeostasis disorders such as polyuria and central diabetes insipidus. Of these peptides, the most commonly used is desmopressin, which displays poor bioavailability as well as potent activity at the V(1b) receptor, with possible stress-related adverse effects. Thus, there is a strong need for the development of small molecule chemistries with selective V(2) receptor agonist activity. Using the functional cell-based assay Receptor Selection and Amplification Technology (R-SAT((R))), a screening effort identified three small molecule chemotypes (AC-94544, AC-88324, and AC-110484) with selective agonist activity at the V(2) receptor. One of these compounds, AC-94544, displayed over 180-fold selectivity at the V(2) receptor compared to related vasopressin and oxytocin receptors and no activity at 28 other G protein-coupled receptors (GPCRs). All three compounds also showed partial agonist activity at the V(2) receptor in a cAMP accumulation assay. In addition, in a rat model of central diabetes insipidus, AC-94544 was able to significantly reduce urine output in a dose-dependent manner. Thus, AC-94544, AC-88324, and AC-110484 represent novel opportunities for the treatment of disorders associated with V(2) receptor agonist deficiency.

Vasopressin and vasopressin receptor antagonists

Vasopressin, a neurohypophyseal peptide hormone, is the endogenous agonist at V1a, V1b, and V2 receptors. The most important physiological function of vasopressin is the maintenance of water homeostasis through interaction with V2 receptors in the kidney. Vasopressin binds to V2 receptor and increases the number of aquaporin-2 at the apical plasma membrane of collecting duct principal cells. That induces high water permeability across the membrane. Several non-peptide vasopressin receptor antagonists have been developed and are being studied primarily for treating conditions characterized by hyponatremia and fluid overload. Further studies are needed to determine how they are best used in these situations.

Vasopressin vs. terlipressin in the treatment of cardiovascular failure in sepsis

BACKGROUND

Arginine vasopressin (AVP) and terlipressin (TP) are increasingly used as adjunct vasopressors in the treatment of septic shock. Despite important pharmacological differences between the two drugs (e.g., receptor selectivity, effective half-life) the use of either substance is determined mainly by local availability and institutional inventory. We briefly describe the pathophysiology and pharmacology of septic shock relevant to the treatment with vasopressin analogues. In addition, differences in pharmacokinetics and pharmacodynamics between AVP and TP are discussed.

DISCUSSION

The current literature suggests that neither AVP nor TP should be administered in high doses in patients with septic shock. Furthermore, increasing evidence indicates that early administration of vasopressin analogues may improve outcome as compared to a last-resort treatment. Low-dose infusion of AVP (0.6-2.4 U/h) has been demonstrated to be a safe adjunct in the management of septic shock. The V2 agonistic effects of AVP may exert favorable effects on hepatosplanchnic, renal, pulmonary, and coronary perfusion. However, the higher V1 receptor selectivity of TP may prove more potent in restoring arterial blood pressure and avoiding rebound hypotension, while carrying the risk of sustained global and regional vasoconstriction after bolus injection.

CONCLUSIONS

Evidence from experimental studies and initial clinical reports suggests that continuous low-dose infusion of TP may stabilize hemodynamics in septic shock with reduced side effects. However, randomized, controlled trials are necessary to determine the role of bolus or continuous infusion of TP in the treatment of septic shock before this approach can be recommended for routine clinical use.