Vasopressin Receptors

Exocrine scent marking: Coordinative role of arginine vasopressin in the systemic regulation of social signaling behaviors

Arginine vasopressin (AVP) is a neurohypophysial hormone that coordinatively regulates central socio-emotional behavior and peripheral control of antidiuretic fluid homeostasis. Most mammals, including rodents, utilize exocrine or urine-contained scent marking as a social signaling tool that facilitates social adaptation. The exocrine scent marking behavior is postulated to fine-tune sensory and cognitive abilities to recognize key social features via exocrine/urinary olfactory cues and subsequently control exocrine deposition or urinary marking through the mediation of osmotic fluid balance. AVP is implicated as a major player in controlling both recognition and signaling responses. This review provides constructive hypotheses on the coordinative processes of the AVP neurohypophysial circuits in the systemic regulations of fluid control and social-communicative behavior, via the expression of exocrine scent marking, and further emphasizes a potential role of AVP in a common mechanism underlying social communication in rodents.

Positron Emission Tomography in the Neuroimaging of Autism Spectrum Disorder: A Review

Autism spectrum disorder (ASD) is a basket term for neurodevelopmental disorders characterized by marked impairments in social interactions, repetitive and stereotypical behaviors, and restricted interests and activities. Subtypes include (A) disorders with known genetic abnormalities including fragile X syndrome, Rett syndrome, and tuberous sclerosis and (B) idiopathic ASD, conditions with unknown etiologies. Positron emission tomography (PET) is a molecular imaging technology that can be utilized in vivo for dynamic and quantitative research, and is a valuable tool for exploring pathophysiological mechanisms, evaluating therapeutic efficacy, and accelerating drug development in ASD. Recently, several imaging studies on ASD have been published and physiological changes during ASD progression was disclosed by PET. This paper reviews the specific radioligands for PET imaging of critical biomarkers in ASD, and summarizes and discusses the similar and different discoveries in outcomes of previous studies. It is of great importance to identify general physiological changes in cerebral glucose metabolism, cerebral blood flow perfusion, abnormalities in neurotransmitter systems, and inflammation in the central nervous system in ASD, which may provide excellent points for further ASD research.

Recovery from Liver Failure and Fibrosis in a Rat Portacaval Anastomosis Model after Neurointermediate Pituitary Lobectomy

Liver diseases, including cirrhosis, viral hepatitis, and hepatocellular carcinoma, account for approximately two million annual deaths worldwide. They place a huge burden on the global healthcare systems, compelling researchers to find effective treatment for liver fibrosis-cirrhosis. Portacaval anastomosis (PCA) is a model of liver damage and fibrosis. Arginine vasopressin (AVP) has been implicated as a proinflammatory-profibrotic hormone. In rats, neurointermediate pituitary lobectomy (NIL) induces a permanent drop (80%) in AVP serum levels. We hypothesized that AVP deficiency (NIL-induced) may decrease liver damage and fibrosis in a rat PCA model. Male Wistar rats were divided into intact control (IC), NIL, PCA, and PCA+NIL groups. Liver function tests, liver gene relative expressions (IL-1, IL-10, TGF-β, COLL-I, MMP-9, and MMP-13), and histopathological assessments were performed. In comparison with those in the IC and PCA groups, bilirubin, protein serum, and liver glycogen levels were restored in the PCA+NIL group. NIL in the PCA animals also decreased the gene expression levels of IL-1 and COLL-I, while increasing those of IL-10, TGF-β, and MMP-13. Histopathology of this group also showed significantly decreased signs of liver damage with lower extent of collagen deposition and fibrosis. Low AVP serum levels were not enough to fully activate the AVP receptors resulting in the decreased activation of cell signaling pathways associated with proinflammatory-profibrotic responses, while activating cell molecular signaling pathways associated with an anti-inflammatory-fibrotic state. Thus, partial reversion of liver damage and fibrosis was observed. The study supports the crucial role of AVP in the inflammatory-fibrotic processes and maintenance of immune competence. The success of the AVP deficiency strategy suggests that blocking AVP receptors may be therapeutically useful to treat inflammatory-fibrotic liver diseases.

Characterization of a functional V1B vasopressin receptor in the male rat kidney: evidence for cross talk between V1B and V2 receptor signaling pathways

Although vasopressin V_1B receptor (V_1BR) mRNA has been detected in the kidney, the precise renal localization as well as pharmacological and physiological properties of this receptor remain unknown. Using the selective V_1B agonist d[Leu⁴, Lys⁸]VP, either fluorescent or radioactive, we showed that V_1BR is mainly present in principal cells of the inner medullary collecting duct (IMCD) in the male rat kidney. Protein and mRNA expression of V_1BR were very low compared with the V₂ receptor (V₂R). On the microdissected IMCD, d[Leu⁴, Lys⁸]VP had no effect on cAMP production but induced a dose-dependent and saturable intracellular Ca²⁺ concentration increase mobilization with an EC₅₀ value in the nanomolar range. This effect involved both intracellular Ca²⁺ mobilization and extracellular Ca²⁺ influx. The selective V_1B antagonist SSR149415 strongly reduced the ability of vasopressin to increase intracellular Ca²⁺ concentration but also cAMP, suggesting a cooperation between V_1BR and V₂R in IMCD cells expressing both receptors. This cooperation arises from a cross talk between second messenger cascade involving PKC rather than receptor heterodimerization, as supported by potentiation of arginine vasopressin-stimulated cAMP production in human embryonic kidney-293 cells coexpressing the two receptor isoforms and negative results obtained by bioluminescence resonance energy transfer experiments. In vivo, only acute administration of high doses of V_1B agonist triggered significant diuretic effects, in contrast with injection of selective V₂ agonist. This study brings new data on the localization and signaling pathways of V_1BR in the kidney, highlights a cross talk between V_1BR and V₂R in the IMCD, and suggests that V_1BR may counterbalance in some pathophysiological conditions the antidiuretic effect triggered by V₂R activation.NEW & NOTEWORTHY Although V_1BR mRNA has been detected in the kidney, the precise renal localization as well as pharmacological and physiological properties of this receptor remain unknown. Using original pharmaceutical tools, this study brings new data on the localization and signaling pathways of V_1BR, highlights a cross talk between V_1BR and V₂ receptor (V₂R) in the inner medullary collecting duct, and suggests that V_1BR may counterbalance in some pathophysiological conditions the antidiuretic effect triggered by V₂R activation.

Altered expression of Aquaporin-2 in one-kidney, one-clip hypertension

AIMS

The aim of the present study was to evaluate the regulation of Aquaporin-2 (AQP2) water channel in the kidney of one-kidney, one-clip rats (Goldblatt-1 model). In addition, some mechanisms that underlie the role of AQP2 in the Goldblatt-1 model were evaluated.

MAIN METHODS

Sprague-Dawley rats were divided in three groups: control two-kidney, no clip (C, 2 K-NC); nephrectomized one-kidney, no clip (N, 1 K-NC) and Goldblatt one-kidney, one-clip (G, 1 K-1C). AQP2 expression (by westernblot, real time PCR, immunohistochemistry and immunofluorescence), vasopressin V2 receptor expression (by real time PCR), cAMP concentration, NFkB and TonEBP (cytosol to nucleus ratio) were evaluated in the renal medulla.

KEY FINDINGS

AQP2 expression, V2 receptor expression and cAMP concentration were decreased in the renal medulla of 1 K-1C rats, NFkB translocation was favoured towards the nucleus suggesting its activation while TonEBP translocation was not altered in this model of hypertension.

SIGNIFICANCE

In this model of hypertension the decrease of AQP2 expression could be a mechanism that counteracts the high blood pressure promoting water excretion and this may be consequence of decreased vasopressin sensitivity and/or the increased activity of NFkB at renomedullary collecting duct level. Given that renovascular hypertension is among the most common causes of secondary hypertension, it is important to elucidate all the relevant mechanisms involved in the generation or in the compensation of the hypertensive state in order to improve the diagnoses and treatment of the patients.

Vasopressin stimulates the proliferation and differentiation of red blood cell precursors and improves recovery from anemia

Arginine vasopressin (AVP) made by hypothalamic neurons is released into the circulation to stimulate water resorption by the kidneys and restore water balance after blood loss. Patients who lack this antidiuretic hormone suffer from central diabetes insipidus. We observed that many of these patients were anemic and asked whether AVP might play a role in red blood cell (RBC) production. We found that all three AVP receptors are expressed in human and mouse hematopoietic stem and progenitor cells. The AVPR1B appears to play the most important role in regulating erythropoiesis in both human and mouse cells. AVP increases phosphorylation of signal transducer and activator of transcription 5, as erythropoietin (EPO) does. After sublethal irradiation, AVP-deficient Brattleboro rats showed delayed recovery of RBC numbers compared to control rats. In mouse models of anemia (induced by bleeding, irradiation, or increased destruction of circulating RBCs), AVP increased the number of circulating RBCs independently of EPO. In these models, AVP appears to jump-start peripheral blood cell replenishment until EPO can take over. We suggest that specific AVPR1B agonists might be used to induce fast RBC production after bleeding, drug toxicity, or chemotherapy.

Exploiting cancer's phenotypic guise against itself: targeting ectopically expressed peptide G-protein coupled receptors for lung cancer therapy

Lung cancer, claiming millions of lives annually, has the highest mortality rate worldwide. This advocates the development of novel cancer therapies that are highly toxic for cancer cells but negligibly toxic for healthy cells. One of the effective treatments is targeting overexpressed surface receptors of cancer cells with receptor-specific drugs. The receptors-in-focus in the current review are the G-protein coupled receptors (GPCRs), which are often overexpressed in various types of tumors. The peptide subfamily of GPCRs is the pivot of the current article owing to the high affinity and specificity to and of their cognate peptide ligands, and the proven efficacy of peptide-based therapeutics. The article summarizes various ectopically expressed peptide GPCRs in lung cancer, namely, Cholecystokinin-B/Gastrin receptor, the Bombesin receptor family, Bradykinin B1 and B2 receptors, Arginine vasopressin receptors 1a, 1b and 2, and the Somatostatin receptor type 2. The autocrine growth and pro-proliferative pathways they mediate, and the distinct tumor-inhibitory effects of somatostatin receptors are then discussed. The next section covers how these pathways may be influenced or 'corrected' through therapeutics (involving agonists and antagonists) targeting the overexpressed peptide GPCRs. The review proceeds on to Nano-scaled delivery platforms, which enclose chemotherapeutic agents and are decorated with peptide ligands on their external surface, as an effective means of targeting cancer cells. We conclude that targeting these overexpressed peptide GPCRs is potentially evolving as a highly promising form of lung cancer therapy.

Liver cirrhosis reversion is improved in hamsters with a neurointermediate pituitary lobectomy

Regulating mechanisms of fibrosis is an important goal in the treatment of fibrosis and liver cirrhosis. The role of arginine vasopressin (AVP) in promoting fibrosis in several organs has been well documented. However, the result of an AVP deficiency during liver fibrosis has not been reported. We herein study the effects of an AVP deficiency, which was induced by neurointermediate pituitary lobectomy (NIL), on liver cirrhosis and liver cirrhosis reversion. Hamsters were intact (control) or underwent CCl₄-induced cirrhosis, the latter animals divided into four groups: Cirrhotic, NIL-cirrhotic, Cirrhotic-reversion (R) and NIL-cirrhotic-R. Liver function, liver histopathology (including the fibrosis area and collagen types) and liver expression of MMP-13 and TIMP-2 were assessed. Results show that the AVP deficiency decreased the levels of alkaline phosphatase in serum and the expression of type I collagen and TIMP-2, and increased type III collagen deposition, MMP-13 expression and the size of regeneration nodules in NIL-cirrhotic and NIL-cirrhotic-R animals. A significantly greater recovery was found in the NIL-cirrhotic-R than the Cirrhotic-R group. We conclude that an AVP deficiency participates importantly in hamster liver regeneration by: 1) prompting the fibroblasts to produce type III collagen deposit, 2) influencing the activity of AP from bile duct cells, and 3) inhibiting TIMP-2 expression while favoring the fibrolytic activity of MMP-13.

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.

Pharmacological characterization of FE 201874, the first selective high affinity rat V1A vasopressin receptor agonist

BACKGROUND AND PURPOSE

Distinct vasopressin receptors are involved in different physiological and behavioural functions. Presently, no selective agonist is available to specifically elucidate the functional roles of the V1A receptor in the rat, one of the most widely used animal models. FE 201874 is a new derivative of the human selective V1A receptor agonist F180. In this study, we performed a multi-approach pharmacological and functional characterization of FE 201874 to determine whether it is selective for V1A receptors.

EXPERIMENTAL APPROACH

We modified an available human selective V1A receptor agonist (F180) and determined its pharmacological properties in cell lines expressing vasopressin/oxytocin receptors (affinity and coupling to second messenger cascades), in an ex vivo model (aorta ring contraction) and in vivo in rats (proliferation of adrenal cortex glomerulosa cells and lactation).

KEY RESULTS

FE 201874 exhibited nanomolar affinity for the rat V1A receptor; it was highly selective towards the rat V1B and V2 vasopressin receptors and behaved as a full V1A agonist in all the pharmacological tests performed. FE 201874 bound to the oxytocin receptor, but with moderate affinity, and behaved as an oxytocin antagonist in vitro, but not in vivo.

CONCLUSIONS AND IMPLICATIONS

On functional grounds, all the data demonstrate that FE 201874 is the first selective agonist of the rat V1A receptor isoform available. Hence, FE 201874 may have potential as a treatment for the vasodilator-induced hypotension occurring in conditions such as septic shock and could be the most suitable compound for discriminating between the behavioural effects of arginine vasopressin and oxytocin.

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.

The physiological and pathophysiological functions of renal and extrarenal vasopressin V2 receptors

The arginine vasopressin (AVP) type 2 receptor (V2R) is unique among AVP receptor subtypes in signaling through cAMP. Its key function is in the kidneys, facilitating the urine concentrating mechanism through the AVP/V2 type receptor/aquaporin 2 system in the medullary and cortical collecting ducts. Recent clinical and research observations strongly support the existence of an extrarenal V2R. The clinical importance of the extrarenal V2R spans widely from stimulation of coagulation factor in the endothelium to as yet untested potential therapeutic targets. These include V2R-regulated membranous fluid turnover in the inner ear, V2R-regulated mitogensis and apoptosis in certain tumor tissues, and numerous other cell types where the physiological role of V2Rs still requires further research. Here, we review current evidence on the physiological and pathophysiological functions of renal and extrarenal V2Rs. These functions of V2R are important, not only in rare diseases with loss or gain of function of V2R but also in relation to the recent use of nonpeptide V2R antagonists to treat hyponatremia and possibly retard the growth of cysts and development of renal failure in autosomal dominant polycystic kidney disease. The main functions of V2R in principal cells of the collecting duct are water, salt, and urea transport by modifying the trafficking of aquaporin 2, epithelial Na(+) channels, and urea transporters and vasodilation and stimulation of coagulation factor properties, mainly seen with pharmacological doses of 1-desamino-8-D-AVP. The AVPR2 gene is located on the X chromosome, in a region with high probability of escape from inactivation; this may lead to phenotypic sex differences, with females expressing higher levels of transcript than males.

Vasopressin: a novel target for the prevention and retardation of kidney disease?

After several decades during which little attention was paid to vasopressin and/or urine concentration in clinical practice, interest in vasopressin has renewed with the availability of new, potent, orally active vasopressin-receptor antagonists--the vaptans--and with the results of epidemiological studies evaluating copeptin (a surrogate marker of vasopressin) in large population-based cohorts. Several experimental studies in rats and mice had previously shown that vasopressin, acting via vasopressin V2 antidiuretic receptors, contributes to the progression of chronic kidney disease; in particular, to autosomal dominant polycystic kidney disease. New epidemiological studies now suggest a role for vasopressin in the pathogenesis of diabetes mellitus and metabolic disorders via activation of hepatic V1a and/or pancreatic islet V1b receptors. The first part of this Review describes the adverse effects of vasopressin, as revealed by clinical and experimental studies in kidney diseases, hypertension, diabetes and the metabolic syndrome. The second part provides insights into vasopressin physiology and pathophysiology that may be relevant to the understanding of these adverse effects and that are linked to the excretion of concentrated nitrogen wastes and associated hyperfiltration. Collectively, the studies reviewed here suggest that more attention should be given to the vasopressin-thirst-urine concentration axis in clinical investigations and in patient care. Whether selective blockade of the different vasopressin receptors may provide therapeutic benefits beyond their present indication in hyponatraemia requires new clinical trials.

Effects of neurointermediate pituitary lobectomy and desmopressin on acute experimental autoimmune encephalomyelitis in Lewis rats

OBJECTIVE

The role of arginine vasopressin (AVP) as a direct immune regulator has not yet been clarified, and more work is needed to assess its involvement in the immunoneuroendocrine network. In the present study, the effects of neurointermediate pituitary lobectomy (NIL) and desmopressin (DP), an agonist of AVP, on acute experimental autoimmune encephalomyelitis (EAE) in female Lewis rats were evaluated. The activity of the hypothalamic-pituitary-adrenocortical (HPA) axis was also assessed.

METHODS

Five groups of rats were used, as follows: (1) sham-operated (SHAM) rats, (2) SHAM + DP rats, (3) NIL rats, (4) NIL + DP rats and (5) untreated normal control rats. DP treatment started 2 weeks after surgery, and immunization to induce EAE was carried out 1 week later.

RESULTS

SHAM rats developed full-blown clinical and histological signs of EAE and activation of the HPA axis. SHAM + DP animals had mild clinical signs of EAE, inflammatory infiltrations in the spinal cord and an activated HPA axis. NIL animals developed minimal EAE, scanty spinal cord inflammation and no changes in HPA axis activity. NIL + DP rats developed severe clinical signs of EAE, extensive spinal cord inflammatory infiltrations and marked activation of the HPA axis.

CONCLUSIONS

NIL decreased the cell-mediated immune response, while DP in NIL animals restored the immune response. AVP is directly involved in the maintenance of immune competence.

New, potent, selective, and short-acting peptidic V1a receptor agonists

[Arg(8)]vasopressin (AVP) produces vasoconstriction via V(1a) receptor (V(1a)R)-mediated vascular smooth muscle cell contraction and is being used to increase blood pressure in septic shock, a form of vasodilatory hypotension. However, AVP also induces V(2) receptor (V(2)R)-mediated antidiuresis, vasodilation, and coagulation factor release, all deleterious in septic shock. The V(1a)R agonist terlipressin (H-Gly(3)[Lys(8)]VP) also lacks selectivity vs the V(2)R and has sizably longer duration of action than AVP, preventing rapid titration of its vasopressor effect in the clinic. We designed and synthesized new short acting V(1a)R selective analogues of general structure [Xaa(2),Ile(3),Yaa(4),Zaa(8)]VP. The most potent and selective compounds in in vitro functional assays (e.g., [Phe(2),Ile(3),Asn(Me(2))(4),Orn(8)]VP (31), [Phe(2),Ile(3),Asn((CH(2))(3)OH)(4),Orn(8)]VP (34), [Phe(2),Ile(3),Hgn(4),Orn(iPr)(8)]VP (45), [Phe(2),Ile(3),Asn(Et)(4),Dab(8)]VP (49), [Thi(2),Ile(3),Orn(iPr)(8)]VP (59), [Cha(2),Ile(3),Asn(4),Orn(iPr)(8)]VP (68)) were tested by intravenous bolus in rats for duration of vasopressive action. Analogues 31, 34, 45, and 49 were as short-acting as AVP. Compound 45, FE 202158, is currently undergoing clinical trials in septic shock.

Involvement of vasopressin V1b receptor in anti-anxiety action of SSRI and SNRI in mice

Arginine vasopressin (AVP) is critical in the regulation of hypothalamic-pituitary-adrenal axis activity, a major component of the stress response. The vasopressin V1b receptor (V1bR) mediates the stimulatory effect of AVP on adrenocorticotropin release. Previous studies showed that AVP facilitates aggression while serotonin inhibits aggression by blocking the activity of the vasopressin system. To examine whether the interaction of the V1bR and serotonin in the central nervous system controls anxiety-related behavior, we investigated the effects of acute and chronic treatment with a selective serotonin reuptake inhibitor (SSRI) and with a serotonin noradrenalin reuptake inhibitor (SNRI) on V1bR knockout (KO) mice and on V1bR antagonist (SSR149415)-treated mice. The effects were evaluated in experiments using an elevated plus-maze (EPM) test and a hole-board (HB) test, well established tests for evaluating anxiety-like behavior. For both the V1bR KO mice and V1bR antagonist-treated mice, acute treatment with either SSRI or SNRI did not change the time spent on the EPM open arms or the number of head dips in the HB. Chronic treatment of V1bR KO mice with SSRI did not change the amount of time spent on the open arms, the number of head dips, or the number of rearings, while chronic treatment with SNRI significantly increased the time spent on the open arms and the number of head dips. These results suggest that the anti-anxiety action of 5-HT reuptake inhibitors might partly involve V1bR regulating the anxiety behaviors.

Anti-apoptotic actions of vasopressin in H32 neurons involve MAP kinase transactivation and Bad phosphorylation

Vasopressin (VP) secreted within the brain modulates neuronal function acting as a neurotransmitter. Based on the observation that VP prevented serum deprivation-induced cell death in the neuronal cell line, H32, which expresses endogenous V1 receptors, we tested the hypothesis that VP has anti-apoptotic properties. Flow cytometry experiments showed that 10 nM VP prevented serum deprivation-induced cell death and annexin V binding. Serum deprivation increased caspase-3 activity in a time and serum concentration dependent manner, and VP prevented these effects through interaction with receptors of V1 subtype. The signaling pathways mediating the anti-apoptotic effect of VP involve mitogen activated protein (MAP) kinase and extracellular signal-regulated kinases (ERK), Ca(2+)/calmodulin dependent kinase (CaMK) and protein kinase C (PKC). Western blot analyses revealed time-dependent decreases of Bad phosphorylation and increases in cytosolic levels of cytochrome c following serum deprivation, effects which were prevented by 10 nM VP. These data demonstrate that activation of endogenous V1 VP receptors prevents serum deprivation-induced apoptosis, through phosphorylation-inactivation of the pro-apoptotic protein, Bad, and consequent decreases in cytosolic cytochrome c and caspase-3 activation. The data suggest that VP has anti-apoptotic activity in neurons and that VP may act as a neuroprotective agent in the brain.

Desmopressin increases IGF-binding protein-1 in humans

CONTEXT

IGF binding protein-1 (IGFBP-1) is essential for IGF-I bioavailability. High levels of IGFBP-1 are encountered in critically ill patients and are a good predictor marker in acute myocardial infarction. The mechanisms responsible for the elevated IGFBP-1 levels in these conditions are still unclear. Interestingly, high levels of vasopressin have been reported in the above-mentioned conditions.

OBJECTIVE

To study the effect of vasopressin on IGFBP-1 in humans.

DESIGN

Placebo-controlled cross-over study in patients with central diabetes insipidus (CDI) in whom potential interference from endogenous vasopressin secretion is minimized. After a 3-day desmopressin washout period, each patient received i.v. saline on day 1 and desmopressin (3 mug) on day 2. Blood samples were taken after administration, every 2 h during the whole night, starting at 2000 h.

PATIENTS AND SETTING

Fourteen inpatients with CDI in an endocrinology department of a university hospital.

RESULTS

Serum IGFBP-1 increased within 4 h after 1-desamino-8-d-arginine vasopressin (DDAVP) by 375+/-73%, compared with a spontaneous fasting increase by 252+/-46% following placebo administration (P<0.05). No changes were registered in the levels of either classically regulators of IGFBP-1 (insulin, glucagon, and cortisol) or of IGF-I and glucose. The decrease in plasma osmolarity induced by DDAVP did not precede the increase in IGFBP-1.

CONCLUSIONS

DDAVP increases serum levels of IGFBP-1. Further investigation is essential to unravel the clinical potential of this interaction in conditions associated with high IGFBP-1 levels.

Identification and synthesis of major metabolites of Vasopressin V2-receptor agonist WAY-151932, and antagonist, Lixivaptan®

Small molecule agonists and antagonists of the V(2)-vasopressin receptor have been discovered and have undergone clinical trials. In conjunction with these discovery programs, the synthesis and biological testing of various metabolites associated with these clinical targets were actively pursued. We now report the results of our synthetic efforts and the corresponding biological data generated for several of the metabolites of WAY-151932 and CL-347985 (Lixivaptan).

Pharmacological and physiological characterization of d[Leu4, Lys8]vasopressin, the first V1b-selective agonist for rat vasopressin/oxytocin receptors

Recently, we synthesized and characterized the first selective V(1b) vasopressin (VP)/oxytocin receptor agonist, d[Cha(4)]arginine vasopressin. However, this agonist was only selective for the human receptors. We thus decided to design a selective V(1b) agonist for the rodent species. We started from previous observations showing that modifying [deamino(1),Arg(8)]VP in positions 4 and 8 altered the rat VP/oxytocin receptor selectivity. We synthesized a series of 13 [deamino(1),Arg(8)]VP analogs modified in positions 4 and 8. Among them, one seemed very promising, d[Leu(4), Lys(8)]VP. In this paper, we describe its pharmacological and physiological properties. This analog exhibited a nanomolar affinity for the rat, human, and mouse V(1b) VP receptors and a strong V(1b) selectivity for the rat species. On AtT20 cells stably transfected with the rat V(1b) receptor, d[Leu(4), Lys(8)]VP behaved as a full agonist on both phospholipase C and MAPK assays. Additional experiments revealed its ability to induce the internalization of enhanced green fluorescent protein-tagged human and mouse V(1b) receptors as expected for a full agonist. Additional physiological experiments were performed to further confirm the selectivity of this peptide. Its antidiuretic, vasopressor, and in vitro oxytocic activities were weak compared with those of VP. In contrast, used at low doses, its efficiency to stimulate adrenocorticotropin or insulin release from mouse pituitary or perfused rat pancreas, respectively, was similar to that obtained with VP. In conclusion, d[Leu(4), Lys(8)]VP is the first selective agonist available for the rat V(1b) VP receptor. It will allow a better understanding of V(1b) receptor-mediated effects in rodents.

Biological characterization of rodent and human vasopressin V1b receptors using SSR-149415, a nonpeptide V1b receptor ligand

[3H]SSR-149415 is the first tritiated nonpeptide vasopressin V1b receptor (V1bR) antagonist ligand. It was used for studying rodent (mouse, rat, hamster) and human V1bR from native or recombinant origin. Moreover, a close comparison between the human and the mouse V1bR was performed using SSR-149415/[3H]SSR-149415 in binding and functional studies in vitro. [3H]SSR-149415 binding was time-dependent, reversible, and saturable. Scatchard plot analysis gave a single class of high-affinity binding sites with apparent equilibrium dissociation constant ( Kd) ∼1 nM and maximum binding density (Bmax) values from 7,000 to 300,000 sites/cell according to the cell line. In competition experiments, [3H]SSR-149415 binding was stereospecific and dose-dependently displaced by reference peptide and nonpeptide arginine vasopressin (AVP)/OT ligands following a V1b rank order of affinity: SSR-149415 = AVP > dCha > dPen > dPal > dDavp > SSR-126768A > SR-49059 > SSR-149424 > OT > SR-121463B. Species differences between human, rat, mouse, and hamster V1bR were observed. Autoradiography studies with [3H]SSR-149415 on rat and human pituitary showed intense specific labeling confined to corticotroph cells and absence of labeling in the other tissues examined. SSR-149415 potently and stereospecifically antagonized the AVP-induced inositol phosphate production and intracellular Ca2+ increase (EC50 from 1.83 to 3.05 nM) in recombinant cell lines expressing either the mouse or the human V1bR. AVP (10−7 M) exposure of AtT20 cells expressing mouse or human EGFP-tagged V1bR induced their rapid internalization. Preincubation with 10−6 M SSR-149415 counteracted the internalization process. Moreover, recycling of internalized receptors was observed upon 10−6 M SSR-149415 treatment. Thus SSR-149415/[3H]SSR-149415 are unique tools for studying animal and human V1bR.

Selectivity of d[Cha4]AVP and SSR149415 at human vasopressin and oxytocin receptors: evidence that SSR149415 is a mixed vasopressin V1b/oxytocin receptor antagonist

1 A possible role of arginine vasopressin (AVP) V(1b) receptor subtype in stress-related disorders has been recently highlighted by the discovery of the agonist [1-deamino-4-cyclohexylalanine] AVP (d[Cha(4)]AVP) and the antagonist SSR149415. Both compounds have been proposed to target specifically V(1b) receptors, since the reported affinities for the related V(1a), V(2) and oxytocin receptors are in the micromolar or submicromolar range. In the present study, we further investigated the binding affinities of d[Cha(4)]AVP and SSR149415 at recombinant human vasopressin V(1b) (hV(1b)) and oxytocin (hOT) receptors expressed in Chinese hamster ovary (CHO) cells and functional properties of both compounds at hV(1b), hV(1a), hV(2) and hOT receptors. 2 d[Cha(4)]AVP bound to hV(1b) receptors and hOT receptors with pK(i) values of 9.68+/-0.06 and 7.68+/-0.09, respectively. SSR149415 showed pK(i) values of 9.34+/-0.06 at hV(1b) and 8.82+/-0.16 at hOT receptors. 3 d[Cha(4)]AVP stimulated [Ca(2+)](i) increase in hV(1b)-CHO cells with a pEC(50) value of 10.05+/-0.15. It showed pEC(50) values of 6.53+/-0.17 and 5.92+/-0.02 at hV(1a) and hV(2) receptors, respectively, and behaved as a weak antagonist at hOT receptors (pK(B)=6.31+/-0.12). SSR149415 inhibited the agonist-induced [Ca(2+)](i) increase with pK(B) values of 9.19+/-0.07 in hV(1b)-CHO and 8.72+/-0.15 in hOT-CHO cells. A functional pK(i) value of 7.23+/-0.10 was found for SSR1494151 at hV(1a) receptors, whereas it did not inhibit 20 nM AVP response at hV(2) receptors up to 3 microM. 4 Data obtained confirmed the high potency and selectivity of d[Cha(4)]AVP at hV(1b) receptors, but revealed that SSR149415, in addition to the high potency at hV(1b) receptors, displays a significant antagonism at hOT receptors.

Pyridobenzodiazepines: A novel class of orally active, vasopressin V2 receptor selective agonists

Our efforts in seeking low molecular weight agonists of the antidiuretic peptide hormone arginine vasopressin (AVP) have led to the identification of the clinical candidate WAY-151932 (VNA-932). Further exploration of the structural requirements for agonist activity has provided another class of potent, orally active, non-peptidic vasopressin V2 receptor selective agonists exemplified by the 5,11-dihydro-pyrido[2,3-b][1,5]benzodiazepine as a candidate for further development.

Mechanisms of Cell-surface Rerouting of an Endoplasmic Reticulum-retained Mutant of the Vasopressin V1b/V3 Receptor by a Pharmacological Chaperone

Cell-surface expression and biological functions of several intracellular-retained G protein-coupled receptors are restored by membrane-permeable ligands called pharmacological chaperones. We have previously demonstrated that a mutation of the hydrophobic motif 341FNX2LLX3L350 in the C terminus of the human pituitary vasopressin V3 receptor (MUT V3R) led to it being retained in the endoplasmic reticulum (ER). Here, we establish the precise role of this motif and investigate whether SSR149415, a non-peptide V3R antagonist, behaves as a pharmacological chaperone for the ER-retained MUT V3R. The absence of the mutated receptor in the plasma membrane is linked to its prolonged association with the molecular chaperone calnexin in the ER and to its intensive degradation by the ubiquitin-proteasomal machinery. However, this is not because of a lack of oligomerization, as demonstrated by the presence of MUT V3R homodimers in the ER. Treatment with SSR149415 restores expression of the mutated receptor on the cell surface and its correct maturation, resulting into the functional recovery of its signaling properties. SSR149415 acts by stabilizing a native-like conformation of the V3R, reducing its association with calnexin and, thus, favoring a secretory pathway rather than the proteasomal degradation pathway. In conclusion, the FN(X)2LL(X)3L sequence is an important motif for the V3R conformation, and the misfolding resulting from its mutation alters the receptor export but can be reverted by SSR149415.

Enhanced Ca2+ response to AVP in preglomerular vessels from rats with genetic hypertension during different hydration states

Exaggerated arginine vasopressin (AVP)-induced calcium signaling and renal vasoconstriction, characteristic in young spontaneously hypertensive rats (SHR) during euvolemia, are related to greater amounts of V1a receptor mRNA and V1a protein in preglomerular resistance arterioles. The present study determined whether V1a receptor density and calcium signal transduction in the renal vasculature of young SHR is regulated appropriately during physiological changes in hydration state. [3H]AVP ligand binding documented two- to threefold greater density of V1a receptors in euvolemic SHR vs. Wistar-Kyoto (WKY) rats. Parallel changes in V1a receptor density were observed in both strains during chronic water loading (plus approximately 50 fmol/mg) and during dehydration (minus approximately 50 fmol/mg). Affinity was unchanged. Real-time RT-PCR demonstrated that V1a mRNA in preglomerular arterioles was three times greater in euvolemic SHR. Dehydration decreased expression approximately 50% in renal vessels independent of rat strain; water loading increased V1a mRNA. Thus V1a receptor regulation correlated with changes in mRNA in a normal manner in response to chronic changes in AVP concentration, albeit set at a higher level in SHR. In dehydrated animals, AVP increased the cytosolic Ca2+ concentration ([Ca2+]i) by 60 +/- 5 and 112 +/- 13 nM cytosolic Ca2+ in WKY and SHR, respectively (P < 0.01), whereas in hydrated animals the [Ca2+]i increase was 168 +/- 10 and 220 +/- 18 nM, respectively (P < 0.05). In all hydration states, calcium signaling was greater in SHR compared with WKY (P < 0.05). Calcium signaling paralleled changes in the receptor density and mRNA. Mechanisms other than hydration state per se are likely to be responsible for the two- to threefold difference in the V1a receptor density between WKY and SHR in the renal vasculature at the critical age of 6 wk.

Key Amino Acids Located within the Transmembrane Domains 5 and 7 Account for the Pharmacological Specificity of the Human V1b Vasopressin Receptor

In mammals, the vasopressin V(1b) receptor (V(1b)-R) is known to regulate ACTH secretion and, more recently, stress and anxiety. The characterization of the molecular determinant responsible for its pharmacological selectivity was made possible by the recent discovery of the first V(1b) antagonist, SSR149415. Based upon the structure of the crystallized bovine rhodopsin, we established a three-dimensional molecular model of interaction between the human V(1b)-R (hV(1b)-R) and SSR149415. Four amino acids located in distinct transmembrane helices (fourth, fifth, and seventh) were found potentially responsible for the hV(1b)-R selectivity. To validate these assumptions, we selectively replaced the leucine 181, methionine 220, alanine 334, and serine 338 residues of hV(1a)-R by their corresponding amino acids present in the hV(1b)-R (phenylalanine 164, threonine 203, methionine 324, and asparagine 328, respectively). Four mutants, which all exhibited nanomolar affinities for vasopressin and good coupling to phospholipase C pathway, were generated. hV(1a) receptors mutated at position 220 and 334 exhibited striking increase in affinity for SSR149415 both in binding and phospholipase C assays at variance with the hV(1a)-R modified at position 181 or 338. In conclusion, this study provides the first structural features concerning the hV(1b)-R and highlights the role of few specific residues in its pharmacological selectivity.

Comparative pharmacology of bovine, human and rat vasopressin receptor isoforms

In this study, we characterized the bovine vasopressin V(1a), V(1b), V(2) receptor isoforms and compared their pharmacological properties to those of corresponding rat and human vasopressin receptor subtypes. Specific binding sites of high affinity for vasopressin were found in all bovine tissues tested (kidney, liver and pituitary). Using a large series of recent peptidic and non-peptidic selective vasopressin agonists or antagonists, we demonstrated the presence of vasopressin V(2), V(1a) or V(1b) receptors in the kidney, liver and pituitary bovine tissues, respectively. This extensive characterization of bovine vasopressin receptor isoforms validates the pharmacological vasopressin receptor classification earlier established for the rat and human species. As expected, the bovine vasopressin receptors look much more like human receptors than rat ones. Interestingly, among the three vasopressin receptor isoforms studied, the vasopressin V(1b) receptor subtype is the best conserved for the three species studied.

Effects of vasopressin on isolated rat adrenal chromaffin cells

It has been demonstrated that arginine vasopressin (AVP) is synthesized not only in specific hypothalamic nuclei, but also in the adrenal medulla where it is thought to regulate adrenal functions by autocrine and paracrine mechanisms. In order to further characterise the effects of AVP on rat adrenal chromaffin cells, we examined: (a) the mRNA expression for V(1a) and V(1b) AVP receptors in these cells; (b) the effects of AVP on the membrane potential and membrane currents measured with the whole-cell patch-clamp technique; and (c) effect of AVP on catecholamine release from single adrenal chromaffin cells measured with carbon fibre microelectrodes. Reverse transcription-polymerase chain reaction (RT-PCR) on tissue punch samples obtained from the adrenal medulla demonstrated message for both the V(1a) and V(1b) receptors, while material obtained from the adrenal cortex showed expression of the V(1a) receptor only. Single-cell RT-PCR conducted on acutely isolated chromaffin cells showed message for the V(1a) receptor in 84% of cells, while 38% of cells also contained message for the V(1b) receptor (n=45). Under current-clamp recording, responses to AVP application (4-40 microM) were variable; 22/34 (65%) tested cells were depolarised, 29% hyperpolarised, and the remaining cells showed a biphasic response. Changes in membrane potential of either direction were dose-dependent and accompanied by a decrease in cell membrane resistance. Under voltage-clamp (V(hold)=-60 mV), AVP evoked inward current in 27/52 (52%) and outward current in 16/52 (31%) chromaffin cells. Both types of AVP-evoked responses were blocked by co-application of a nonselective V(1a)/V(1b) antagonist. Application of AVP evoked prolonged bursts of amperometric currents (indicative of catecholamine release) in 4/9 tested cells, but reduced the currents evoked by ACh application in all tested cells (n=7). These findings demonstrate a complex action of AVP on adrenal chromaffin cells, with individual adrenal chromaffin cells responding with either excitation or inhibition. This response pattern may be related to the expression of V(1) receptor subtypes.

Integration of sodium and osmosensory signals in vasopressin neurons

Vasopressin (antidiuretic hormone) release has been thought to be controlled by interacting osmoreceptors and Na(+)-detectors for > 20 years. Only recently, however, have molecular and cellular advances revealed how changes in the external concentration of Na+ and osmolality are detected during acute and chronic osmotic perturbations. In rat vasopressin-containing neurons, local osmosensitivity is conferred by intrinsic stretch-inactivated cation channels and by taurine release from surrounding glia. Na+ detection is accomplished by acute regulation of the permeability of stretch-inactivated channels and by changes in Na+ channel gene expression. These features provide a first glimpse of the integrative processes at work in a central osmoregulatory reflex.

Veni, vidi, vici: the neurohypophysis in the twentieth century

We outline the key discoveries in the first 70 years of research on the neurohypophysis that provided the foundations for more recent studies in the last 30 years. We consider the extent to which these recent studies, which have exploited molecular technologies, cellular electrophysiological techniques and mechanistic behavioural investigations, have advanced or changed our understanding of the functions of oxytocin and vasopressin. The different evolutionary pressures on the oxytocin and vasopressin systems are discussed. Lastly, we focus on the mechanisms underlying the burst-firing activity of oxytocin neurones in lactation as a problem not yet solved, and probably requiring a presently improbable conceptual leap to understand.