1-desamino-8-D-arginine vasopressin (DDAVP) as an agonist on V1b vasopressin receptor

Dysregulation of the fluid homeostasis system by aging

Chronic dehydration is a leading cause of morbidity for the elderly, but how aging alters the fluid homeostasis system is not well understood. Here, we used a combination of physiologic, behavioral and circuit analyses to characterize how fluid balance is affected by aging in mice. We found that old mice have a primary defect in sensing and producing the anti-diuretic hormone vasopressin, which results in chronic dehydration. Recordings and manipulations of the thirst circuitry revealed that old mice retain the ability to sense systemic cues of dehydration but are impaired in detecting presystemic, likely oropharyngeal, cues generated during eating and drinking, resulting in disorganized drinking behavior on short timescales. Surprisingly, old mice had increased drinking and motivation after 24-hour water deprivation, indicating that aging does not result in a general impairment in the thirst circuit. These findings reveal how a homeostatic system undergoes coordinated changes during aging.

Identification and Detection of a Peptide Biomarker and Its Enantiomer by Nanopore

Until now, no fast, low-cost, and direct technique exists to identify and detect protein/peptide enantiomers, because their mass and charge are identical. They are essential since l- and d-protein enantiomers have different biological activities due to their unique conformations. Enantiomers have potential for diagnostic purposes for several diseases or normal bodily functions but have yet to be utilized. This work uses an aerolysin nanopore and electrical detection to identify vasopressin enantiomers, l-AVP and d-AVP, associated with different biological processes and pathologies. We show their identification according to their conformations, in either native or reducing conditions, using their specific electrical signature. To improve their identification, we used a principal component analysis approach to define the most relevant electrical parameters for their identification. Finally, we used the Monte Carlo prediction to assign each event type to a specific l- or d-AVP enantiomer.

An Octopus-Derived Peptide with Antidiuretic Activity in Rats

Discovering new drug candidates with high efficacy and few side effects is a major challenge in new drug development. The two evolutionarily related peptides oxytocin (OXT) and arginine vasopressin (AVP) are known to be associated with a variety of physiological and psychological processes via the association of OXT with three types of AVP receptors. Over decades, many synthetic analogs of these peptides have been designed and tested for therapeutic applications; however, only a few studies of their natural analogs have been performed. In this study, we investigated the bioactivity and usefulness of two natural OXT/AVP analogs that originate from the marine invertebrate Octopus vulgaris, named octopressin (OTP) and cephalotocin (CPT). By measuring the intracellular Ca2+ or cyclic AMP increase in each OXT/AVP receptor subtype-overexpressing cell, we found that CPT, but not OTP, acts as a selective agonist of human AVP type 1b and 2 receptors. This behavior is reminiscent of desmopressin, the most widely prescribed antidiuretic drug in the world. Similar to the case for desmopressin, a single intravenous tail injection of CPT into Sprague-Dawley rats reduced urine output and increased urinary osmolality. In conclusion, we suggest that CPT has a significant antidiuretic effect and that CPT might be beneficial for treating urological conditions such as nocturia, enuresis, and diabetes insipidus.

Treatment with ddAVP improves platelet-based coagulation in a rat model of traumatic hemorrhagic shock

Objectives

Trauma-induced hemorrhagic shock is characterized by increased endothelial permeability and coagulopathy. Vasopressin analog ddAVP (desmopressin) acts by reorganizing and redistributing adhesive and tight junction molecules, enhancing endothelial barrier function. Furthermore, ddAVP increases von Willebrand factor (vWF) plasma levels and thereby potentially enhances platelet-based coagulation. The objective of this study was to assess whether the use of ddAVP results in improvement of both endothelial barrier function and platelet-based coagulation, thereby improving shock reversal and reduce organ failure in a rat model of trauma and transfusion.

Methods

Blood products were prepared from syngeneic rat blood according to blood bank standards. Polytrauma was induced in Sprague Dawley rats by a fractured femur and crush injury to the intestines and liver. The rats were hemorrhaged until a mean arterial pressure of 40 mm Hg and transfused with RBCs, fresh frozen plasmas and platelets in a 1:1:1 ratio, and randomized to receive a single dose of ddAVP (n=7 per group). Blood samples were taken up to 6 hours after trauma to assess biochemistry, markers of endothelial injury and coagulation status by rotational thromboelastometry (ROTEM). Organ damage was assessed by histopathology.

Results

Rats receiving ddAVP showed significantly better shock reversal compared with controls. Also, coagulation parameters remained stable in the ddAVP treated group, whereas rats in the control group showed deterioration of coagulation parameters, including decreased clot strength and decreased platelet functioning (89% (IQR 82% to 92%) of baseline values). Platelet count and vWF antigen levels at exsanguination did not differ between groups. ddAVP did not reduce markers of endothelial dysfunction nor markers of organ injury.

Conclusions

The use of ddAVP in a rat trauma-transfusion model improved shock parameters and ROTEM parameters of clot formation. However, this did not abrogate the amount of organ failure.

Level of evidence

Level III.

The usefulness of the combined high-dose dexamethasone suppression test and desmopressin stimulation test in establishing the source of ACTH secretion in ACTH-dependent Cushing's syndrome

Bilateral inferior petrosal sinus sampling (BIPSS) is the current gold standard test for differentially diagnosing ACTH-dependent Cushing's syndrome (CS). However, BIPSS is an invasive procedure, and its availability is limited. We retrospectively analysed the 24-hour urinary free cortisol (UFC) level during the high-dose dexamethasone suppression test (HDDST) and plasma ACTH/cortisol levels after the desmopressin stimulation test (DDAVP test) in subjects with confirmed Cushing's disease (CD) (n = 92) and ectopic ACTH-dependent CS (EAS) (n = 16), and evaluated the positive predictive value (PPV) of the two combined-tests in the aetiological diagnosis of ACTH-dependent CS. The percent changes in UFC levels after the HDDST and in ACTH/cortisol levels after DDAVP administration relative to the corresponding basal levels and the area under the receiver operating characteristic (ROC) curve (AUC) were analysed. UFC suppression below 62.7% suggested a pituitary origin with a sensitivity (SE) of 80% (95% CI: 70-88) and a specificity (SP) of 80% (95% CI: 52-96). A threshold increase in the ACTH level after DDAVP stimulation of 44.6% identified CD with an SE of 91% (95% CI: 83-97) and an SP of 75% (95% CI: 48-93). The combination of both tests yielded an SE of 95.5% and PPV of 98.4% for CD, and significantly improved the efficiency of the differential diagnosis between CD and EAS. These dual non-invasive endocrine tests may substantially reduce the need for BIPSS in the etiological investigation of ACTH-dependent CS.

Aldosterone is Aberrantly Regulated by Various Stimuli in a High Proportion of Patients with Primary Aldosteronism

CONTEXT

In primary aldosteronism (PA), aldosterone secretion is relatively independent of the renin-angiotensin system, but can be regulated by several other stimuli.

OBJECTIVE

To evaluate aldosterone response to several stimuli in a series of patients with PA secondary either to bilateral adrenal hyperplasia (BAH) or unilateral aldosterone-producing adenoma (APA).

DESIGN AND SETTING

Prospective cohort study conducted in a university teaching hospital research center.

PATIENTS

Forty-three patients with confirmed PA and subtyped by adrenal vein sampling (n = 39) were studied, including 11 with BAH, 28 with APA, and 4 with undefined etiology. We also studied 4 other patients with aldosterone and cortisol cosecretion.

INTERVENTIONS

We systematically explored aberrant regulation of aldosterone using an in vivo protocol that included the following stimulation tests performed over 3 days under dexamethasone suppression: upright posture, mixed meal, adrenocorticotropin (ACTH) 1-24, gonadotropin-releasing hormone (GnRH), vasopressin, and serotonin R4 agonist.

MAIN OUTCOME MEASURES

Positive response was defined as >50% renin or ACTH-independent increase in plasma aldosterone/cortisol concentration following the various stimulation tests.

RESULTS

Renin-independent aldosterone secretion increased in response to several aberrant stimuli (upright posture, GnRH) in up to 83% of patients with APA or BAH in whom ACTH 1-24 and HT4R agonists also produced aldosterone oversecretion in all patients. The mean significant aberrant responses per patient was similar in BAH (4.6) and in APA (4.0).

CONCLUSIONS

Aldosterone secretion in PA is relatively autonomous from the renin-angiotensin system, but is highly regulated by several other stimuli, which contributes to the large variability of aldosterone levels in PA patients.

A Self-Assembling Lipidic Peptide and Selective Partial V2 Receptor Agonist Inhibits Urine Production

Lipidised analgesic peptide prodrugs self-assemble into peptide nanofibers; with the nanofiber morphology protecting the peptide from plasma degradation and improving therapeutic efficacy. Extending this learning, we hypothesised that a self-assembling lipidized peptide arginine vasopressin (AVP) receptor agonist, that had not been designed as a prodrug, could prove pharmacologically active and control urine production. The only approved AVP receptor agonist, desmopressin is indicated for the treatment of central diabetes insipidus (DI), bedwetting, haemophilia A and von Willebrand disease. Desmopressin is well tolerated by most patients, however adverse effects, such as hyponatraemia and water intoxication necessitate a strict fluid intake, thus motivating the search for alternative DI treatments. Selective V2 receptor agonism is required for anti-DI activity and we hypothesised that our new lipidized peptide (METx) would lead to selective AVP receptor agonism. METx was synthesised and characterised and then tested for activity against the V2, V1a and OT uterine receptors and not tested against the V1b receptor as METx was not expected to cross the blood brain barrier. METx was also tested in vivo in a healthy rat model. METx forms nanofibers and is a partial V2 receptor agonist (determined by measuring MDCK cell line cAMP accumulation), producing 57% of AVP's maximal activity (EC50 = 2.7 nM) and is not a V1a agonist up to a concentration of 1 μM (determined by measuring A7r5 cell line D-myo-inositol-1-phosphate accumulation). METx is a weak OT receptor antagonist, reducing the frequency of OT induced contractions (EC50 = 350 nM) and increasing the OT EC50 from 0.081 nM to 21 nM at a concentration of 600 nM. METx (41 nM) had no effect on spontaneous uterine contractions and METx (100 nM) had no effect on OT induced uterine contractions. Simulated binding studies show that binding avidity to the receptors follows the trend: V2 > OT > V1a. On intravenous injection, a nanoparticle formulation of METx reduced urine production in a healthy rat model in a dose responsive manner, with 40 mg kg^-1 METx resulting in no urine production over 4 hours. The lipidized self-assembling peptide - METx - is a selective competitive V2 receptor agonist and an anti-diuretic.

A new experimental mouse model of water intoxication with sustained increased intracranial pressure and mild hyponatremia without side effects of antidiuretics

The most used experimental mouse model of hyponatremia and elevated intracranial pressure (ICP) is intraperitoneal injection of water in combination with antidiuretics. This model of water intoxication (WI) results in extreme pathological changes and death within 1 h. To improve preclinical studies of the pathophysiology of elevated ICP, we characterized diuresis, cardiovascular parameters, blood ionogram and effects of antidiuretics in this model. We subsequently developed a new mouse model with mild hyponatremia and sustained increased ICP. To investigate the classical protocol (severe WI), C57BL/6mice were anesthetized and received an intraperitoneal injection of 20% body weight of MilliQ water with or without 0.4 µg·kg^-1 desmopressin acetate (dDAVP). Corresponding Sham groups were also studied. In the new WI protocol (mild WI), 10% body weight of a solution containing 6.5 mM NaHCO₃, 1.125 mM KCl and 29.75 mM NaCl was intraperitoneally injected. By severe WI, ICP and mean arterial pressure increased until brain stem herniation occurred (23 ± 3 min after injection). The cardiovascular effects were accelerated by dDAVP. Severe WI induced a halt to urine production irrespective of the use of dDAVP. Following the new mild WI protocol, ICP also increased but was sustained at a pathologically high level without inducing herniation. Mean arterial pressure and urine production were not affected during mild WI. In conclusion, the new mild WI protocol is a superior experimental model to study the pathophysiological effects of elevated ICP induced by water intoxication.

Viral rescue of magnocellular vasopressin cells in adolescent Brattleboro rats ameliorates diabetes insipidus, but not the hypoaroused phenotype

Dysregulated arousal often accompanies neurodevelopmental disorders such as attention deficit hyperactivity disorder and autism spectrum disorder. Recently, we have found that adolescent homozygous Brattleboro (Hom) rats, which contain a mutation in the arginine vasopressin (AVP) gene, exhibit lower behavioral arousal than their heterozygous (Het) littermates in the open field test. This hypoaroused phenotype could be due to loss of AVP in magnocellular cells that supply AVP to the peripheral circulation and project to limbic structures or parvocellular cells that regulate the stress axis and other central targets. Alternatively, hypoarousal could be a side effect of diabetes insipidus - polydipsia and polyuria seen in Hom rats due to loss of AVP facilitation of water reabsorption in the kidney. We developed a viral-rescue approach to "cure" magnocellular AVP cells of their Brattleboro mutation. Infusion of a recombinant adeno-associated virus (rAAV) containing a functional Avp gene and promoter (rAAV-AVP) rescued AVP within magnocellular cells and fiber projections of the paraventricular nucleus of the hypothalamus (PVN) of male and female adolescent Hom rats. Furthermore, water intake was markedly reduced, ameliorating the symptoms of diabetes insipidus. In contrast, open field activity was unaffected. These findings indicate that the hyporaoused phenotype of adolescent Hom rats is not due to the loss of AVP function in magnocellular cells or a side effect of diabetes insipidus, but favors the hypothesis that central, parvocellular AVP mechanisms underlie the regulation of arousal during adolescence.

Discovery of Potent, Selective, and Short-Acting Peptidic V2 Receptor Agonists

The vasopressin analogue desmopressin (desamino-d-arginine⁸ vasopressin, dDAVP, 1) is a potent vasopressin 2 (V₂) receptor (V₂R) agonist approved in many countries for the treatment of diabetes insipidus, primary nocturnal enuresis, nocturia, and coagulation disorders. Since 1 is primarily excreted via the kidneys, an age-related decline in kidney function leads to slower elimination, prolonged antidiuresis, and hyponatremia. In search of novel, potent, selective, and short-acting peptidic V₂R agonists, we synthesized a series of C-terminally truncated analogues of [Val⁴]dDAVP, 2, modified in positions 2, 3, and 7 and/or at the disulfide bridge. The peptides were evaluated for in vitro potency at the human V₂ receptor, selectivity versus the related receptors (human vasopressin 1a receptor, human vasopressin 1b receptor, and human oxytocin receptor), and pharmacokinetic profiles in rodents and other higher species. The truncated analogues show excellent potency at the V₂R, increased systemic clearance, and shorter half-life in rats. Two compounds 19 (c(Bua-Cpa-Thi-Val-Asn-Cys)-Pro-Agm) and 38 (c(Bua-Cpa-Thi-Val-Asn-Cys)-Pro-d-Arg-NEt₂) have been selected for clinical development for nocturia.

A case of ectopic ACTH syndrome due to DDAVP-sensitive but V1b receptor-negative bronchial typical carcinoid with lymphatic metastasis and plasma ProGRP elevation

Ectopic ACTH syndrome (EAS) is a potentially fatal endocrine disease that results from a variety of neuroendocrine tumors (NETs), such as small cell lung cancer (SCLC) and bronchial typical carcinoid. Typical carcinoid is usually slow growing, not associated with plasma progastrin releasing peptide (ProGRP) elevation. Here, we report a 47-year-old female smoker with progressive typical carcinoid and plasma ProGRP elevation. Several types of Cushingoid features were found on physical examination. In addition, laboratory examination showed elevated plasma ACTH and serum cortisol levels. These findings indicated ACTH-dependent Cushing's syndrome. Moreover, the serum cortisol level was not suppressed by overnight high-dose dexamethasone treatment, suggesting the presence of an extra-pituitary tumor. Contrast-enhanced brain MRI revealed no pituitary adenoma, which also supported the idea that EAS occurred in the present case. Strikingly, chest computed tomographic (CT) scan showed a single 18-mm peripheral nodule in the right middle lobe of the lung. Tumor marker analysis revealed an elevation in plasma ProGRP. These data suggested a possibility that SCLC secreted ACTH and caused EAS in this patient. Of note, the plasma ACTH level was increased (1.7 fold) in l-desamino-8-D-arginine vasopressin (DDAVP) test, also suggesting the specific clinical feature in this case. After additional imaging examinations, we performed surgical resection with the suspicion of limited SCLC. As a result, pathological examination revealed a vasopressin receptor Ib (V1b) receptor-negative bronchial typical carcinoid with ACTH production and mediastinal lymphatic metastasis. In summary, we present a case of EAS caused by progressive bronchial typical carcinoid with plasma ProGRP elevation. We propose a novel subtype of lung typical carcinoid.

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

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

Usefulness of desmopressin testing to predict relapse during long-term follow-up in patients in remission from Cushing's disease

Recurrence of Cushing's disease after successful transsphenoidal surgery occurs in some 30% of the patients and the response to desmopressin shortly after surgery has been proposed as a marker for disease recurrence. The aim of the present study was to evaluate the response to desmopressin over time after surgery. We tested 56 patients with Cushing's disease in remission after transsphenoidal surgery with desmopressin for up to 20 years after surgery. The ACTH and cortisol response to desmopressin over time was evaluated in patients on long-term remission or undergoing relapse; an increase by at least 27 pg/mL in ACTH levels identified responders. The vast majority of patients who underwent successful adenomectomy failed to respond to desmopressin after surgery and this response pattern was maintained over time in patients on long-term remission. Conversely, a response to desmopressin reappeared in patients who subsequently developed a recurrence of Cushing's disease, even years prior to frank hypercortisolism. It appears therefore that a change in the response pattern to desmopressin proves predictive of recurrence of Cushing's disease and may indicate which patients require close monitoring.

The Concise Guide to PHARMACOLOGY 2013/14: G protein-coupled receptors

The Concise Guide to PHARMACOLOGY 2013/14 provides concise overviews of the key properties of over 2000 human drug targets with their pharmacology, plus links to an open access knowledgebase of drug targets and their ligands (www.guidetopharmacology.org), which provides more detailed views of target and ligand properties. The full contents can be found at http://onlinelibrary.wiley.com/doi/10.1111/bph.12444/full. G protein-coupled receptors are one of the seven major pharmacological targets into which the Guide is divided, with the others being G protein-coupled receptors, ligand-gated ion channels, ion channels, catalytic receptors, nuclear hormone receptors, transporters and enzymes. These are presented with nomenclature guidance and summary information on the best available pharmacological tools, alongside key references and suggestions for further reading. A new landscape format has easy to use tables comparing related targets. It is a condensed version of material contemporary to late 2013, which is presented in greater detail and constantly updated on the website www.guidetopharmacology.org, superseding data presented in previous Guides to Receptors and Channels. It is produced in conjunction with NC-IUPHAR and provides the official IUPHAR classification and nomenclature for human drug targets, where appropriate. It consolidates information previously curated and displayed separately in IUPHAR-DB and the Guide to Receptors and Channels, providing a permanent, citable, point-in-time record that will survive database updates.

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.

Desmopressin accelerates the rate of urinary morphine excretion and attenuates withdrawal symptoms in rats

AIM

The aim of this study was to examine the effects of desmopressin on morphine withdrawal symptoms and vasopressin level in morphine-dependent subjects.

METHODS

Wistar male rats were injected s.c. with morphine once per day for 5 consecutive days to induce morphine dependence. After morphine use ceased on day 5, an equal number of rats were assigned to one of four groups for either saline or desmopressin by either intraperitoneal (i.p.) or intracerebroventricular (i.c.v.) injection. From days 5 to 10, urine was collected daily and tested for the presence of morphine, and withdrawal symptoms were monitored to assess the effects of desmopressin.

RESULTS

Significant weight loss occurred among all morphine-addicted rats during the withdrawal period. With both methods (i.p. and i.c.v.), the period of urinary morphine excretion was shorter for the two groups that were given desmopressin (experimental groups) than the two groups that were not given desmopressin (control groups), and no significant difference in urinary morphine excretion was found between the two experimental groups. During the early stage of withdrawal, the severity of the withdrawal symptoms in the experimental groups was significantly lower than that in the control groups.

CONCLUSION

Desmopressin decreases the extent of morphine withdrawal symptoms, indicating that this agent might be appropriate for treating morphine addiction. Desmopressin appears to reduce withdrawal symptoms not by exerting an anti-diuretic effect but rather by exerting an effect on the central nervous system.

Discovery of defense- and neuropeptides in social ants by genome-mining

Natural peptides of great number and diversity occur in all organisms, but analyzing their peptidome is often difficult. With natural product drug discovery in mind, we devised a genome-mining approach to identify defense- and neuropeptides in the genomes of social ants from Atta cephalotes (leaf-cutter ant), Camponotus floridanus (carpenter ant) and Harpegnathos saltator (basal genus). Numerous peptide-encoding genes of defense peptides, in particular defensins, and neuropeptides or regulatory peptide hormones, such as allatostatins and tachykinins, were identified and analyzed. Most interestingly we annotated genes that encode oxytocin/vasopressin-related peptides (inotocins) and their putative receptors. This is the first piece of evidence for the existence of this nonapeptide hormone system in ants (Formicidae) and supports recent findings in Tribolium castaneum (red flour beetle) and Nasonia vitripennis (parasitoid wasp), and therefore its confinement to some basal holometabolous insects. By contrast, the absence of the inotocin hormone system in Apis mellifera (honeybee), another closely-related member of the eusocial Hymenoptera clade, establishes the basis for future studies on the molecular evolution and physiological function of oxytocin/vasopressin-related peptides (vasotocin nonapeptide family) and their receptors in social insects. Particularly the identification of ant inotocin and defensin peptide sequences will provide a basis for future pharmacological characterization in the quest for potent and selective lead compounds of therapeutic value.

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

OBJECTIVES

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

DESIGNS

A prospective study of 29 patients with CD.

METHODS

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

RESULTS

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

CONCLUSIONS

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

Design, synthesis and biological activity of new neurohypophyseal hormones analogues conformationally restricted in the N-terminal part of the molecule. Highly potent OT receptor antagonists

In this study we present the synthesis and some pharmacological properties of fourteen new analogues of neurohypophyseal hormones conformationally restricted in the N-terminal part of the molecule. All new peptides were substituted at position 2 with cis-1-amino-4-phenylcyclohexane-1-carboxylic acid (cis-Apc). Moreover, one of the new analogues: [cis-Apc(2), Val(4)]AVP was also prepared in N-acylated forms with various bulky acyl groups. All the peptides were tested for pressor, antidiuretic, and in vitro uterotonic activities. We also determined the binding affinity of the selected compounds to human OT receptor. Our results showed that introduction of cis -Apc(2) in position 2 of either AVP or OT resulted in analogues with high antioxytocin potency. Two of the new compounds, [Mpa(1),cis-Apc(2)]AVP and [Mpa(1),cis-Apc(2),Val(4)]AVP, were exceptionally potent antiuterotonic agents (pA(2) = 8.46 and 8.40, respectively) and exhibited higher affinities for the human OT receptor than Atosiban (K (i) values 5.4 and 9.1 nM). Moreover, we have demonstrated for the first time that N -terminal acylation of AVP analogue can improve its selectivity. Using this approach, we obtained compound Aba[cis-Apc(2),Val(4)]AVP (XI) which turned out to be a moderately potent and exceptionally selective OT antagonist (pA(2) = 7.26).

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.

Ligand-based peptide design and combinatorial peptide libraries to target G protein-coupled receptors

G protein-coupled receptors (GPCRs) are considered to represent the most promising drug targets; it has been repeatedly said that a large fraction of the currently marketed drugs elicit their actions by binding to GPCRs (with cited numbers varying from 30-50%). Closer scrutiny, however, shows that only a modest fraction of (≈60) GPCRs are, in fact, exploited as drug targets, only ≈20 of which are peptide-binding receptors. The vast majority of receptors in the humane genome have not yet been explored as sites of action for drugs. Given the drugability of this receptor class, it appears that opportunities for drug discovery abound. In addition, GPCRs provide for binding sites other than the ligand binding sites (referred to as the "orthosteric site"). These additional sites include (i) binding sites for ligands (referred to as "allosteric ligands") that modulate the affinity and efficacy of orthosteric ligands, (ii) the interaction surface that recruits G proteins and arrestins, (iii) the interaction sites of additional proteins (GIPs, GPCR interacting proteins that regulate G protein signaling or give rise to G protein-independent signals). These sites can also be targeted by peptides. Combinatorial and natural peptide libraries are therefore likely to play a major role in identifying new GPCR ligands at each of these sites. In particular the diverse natural peptide libraries such as the venom peptides from marine cone-snails and plant cyclotides have been established as a rich source of drug leads. High-throughput screening and combinatorial chemistry approaches allow for progressing from these starting points to potential drug candidates. This will be illustrated by focusing on the ligand-based drug design of oxytocin (OT) and vasopressin (AVP) receptor ligands using natural peptide leads as starting points.

Benzamil prevents brain water accumulation in hyponatraemic rats

BACKGROUND

It has been recently shown that A6 cells exposed to hyponatraemic stress respond with increased sodium uptake via activation of benzamil-sensitive sodium channels. This study was performed, therefore, to explore the possible involvement of benzamil-sensitive sodium channels and cellular sodium influx in brain oedema formation in hyponatraemic rats.

METHODS

Four groups of male Wistar rats were studied (n = 13 in each group). Animals in group I with normonatraemia received intracerebroventricular (icv) 0.9% NaCl; animals in group II-IV were made hyponatraemic by intraperitoneal administration of isotonic glucose solution in a dose of 20% per body weight. Rats were pretreated with icv 0.9% NaCl (group II), 120 microg arginine vasopressin (AVP) (group III) or 4 microg benzamil-hydrochloride (group IV). Plasma sodium (ion-selective electrode) plasma osmolality (vapour pressure osmometer) and brain sodium and potassium content (flame photometer) as well as brain water content (desiccation method) were measured after a 2-h hydration period.

RESULTS

Plasma sodium, osmolality and tissue sodium and potassium contents were markedly depressed in hyponatraemic rats (group II-IV, p < 0.0005 for each group) irrespective of drug pretreatment. Brain water content, however, responded to hyponatraemia with an increase from 77.55 +/- 1.00% to 78.45 +/- 0.94% (p < 0.01), and it was further augmented to 79.35 +/- 0.80% (p < 0.0005) by icv AVP pretreatment. By contrast, benzamil administration prevented the rise of brain water caused by hyponatraemia (77.61 +/- 1.04%).

CONCLUSION

Early in the course of hyponatraemia, brain sodium channels may be activated, and the subsequent cellular sodium uptake may generate osmotic gradient to allow passive water flow into the cells. The simultaneous reduction of osmotic water conductivity of brain-specific aquaporin-4 by hyponatraemia, however, may limit water accumulation.

AVP-stimulated nucleotide secretion in perfused mouse medullary thick ascending limb and cortical collecting duct

Extracellular nucleotides are local, short-lived signaling molecules that inhibit renal tubular transport via both luminal and basolateral P2 receptors. Apparently, the renal epithelium itself is able to release nucleotides. The mechanism and circumstances under which nucleotide release is stimulated remain elusive. Here, we investigate the phenomenon of nucleotide secretion in intact, perfused mouse medullary thick ascending limb (mTAL) and cortical collecting duct (CCD). The nucleotide secretion was monitored by a biosensor adapted to register nucleotides in the tubular outflow. Intracellular Ca(2+) concentration ([Ca(2+)](i)) was measured simultaneously in the biosensor cells and the renal tubule with fluo 4. We were able to identify spontaneous tubular nucleotide secretion in resting perfused mTAL. In this preparation, 10 nM AVP and 1-desamino-8-D-arginine vasopressin (dDAVP) induced robust [Ca(2+)](i) oscillations, whereas AVP in the CCD induced large, slow, and transient [Ca(2+)](i) elevations. Importantly, we identify that AVP/dDAVP triggers tubular secretion of nucleotides in the mTAL. After addition of AVP/dDAVP, the biosensor registered bursts of nucleotides in the tubular perfusate, corresponding to a tubular nucleotide concentration of approximately 0.2-0.3 microM. A very similar response was observed after AVP stimulation of CCDs. Thus AVP stimulated tubular secretion of nucleotides in a burst-like pattern with peak tubular nucleotide concentrations in the low-micromolar range. We speculate that local nucleotide signaling is an intrinsic feedback element of hormonal control of renal tubular transport.

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.

Sodium excretion in response to vasopressin and selective vasopressin receptor antagonists

The mechanisms by which arginine vasopressin (AVP) exerts its antidiuretic and pressor effects, via activation of V2 and V1a receptors, respectively, are relatively well understood, but the possible associated effects on sodium handling are a matter of controversy. In this study, normal conscious Wistar rats were acutely administered various doses of AVP, dDAVP (V2 agonist), furosemide, or the following selective non-peptide receptor antagonists SR121463A (V2 antagonist) or SR49059 (V1a antagonist). Urine flow and sodium excretion rates in the next 6 h were compared with basal values obtained on the previous day, after vehicle treatment, using each rat as its own control. The rate of sodium excretion decreased with V2 agonism and increased with V2 antagonism in a dose-dependent manner. However,for comparable increases in urine flow rate, the V2 antagonist induced a natriuresis 7-fold smaller than did furosemide. Vasopressin reduced sodium excretion at 1 mug/kg but increased it at doses >5 umg/kg,an effect that was abolished by the V1a antagonist. Combined V2 and V1a effects of endogenous vasopressin can be predicted to vary largely according to the respective levels of vasopressin in plasma,renal medulla (acting on interstitial cells), and urine (acting on V1a luminal receptors). In the usual range of regulation, antidiuretic effects of vasopressin may be associated with variable sodium retention. Although V2 antagonists are predominantly aquaretic, their possible effects on sodium excretion should not be neglected. In view of their proposed use in several human disorders, the respective influence of selective (V2) or mixed (V1a/V2) receptor antagonists on sodium handling in humans needs reevaluation.

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.

Vasopressin: behavioral roles of an "original" neuropeptide

Vasopressin (Avp) is mainly synthesized in the magnocellular cells of the hypothalamic supraoptic (SON) and paraventricular nuclei (PVN) whose axons project to the posterior pituitary. Avp is then released into the blood stream upon appropriate stimulation (e.g., hemorrhage or dehydration) to act at the kidneys and blood vessels. The brain also contains several populations of smaller, parvocellular neurons whose projections remain within the brain. These populations are located within the PVN, bed nucleus of the stria terminalis (BNST), medial amygdala (MeA) and suprachiasmatic nucleus (SCN). Since the 1950s, research examining the roles of Avp in the brain and periphery has intensified. The development of specific agonists and antagonists for Avp receptors has allowed for a better elucidation of its contributions to physiology and behavior. Anatomical, pharmacological and transgenic, including "knockout," animal studies have implicated Avp in the regulation of various social behaviors across species. Avp plays a prominent role in the regulation of aggression, generally of facilitating or promoting it. Affiliation and certain aspects of pair-bonding are also influenced by Avp. Memory, one of the first brain functions of Avp that was investigated, has been implicated especially strongly in social recognition. The roles of Avp in stress, anxiety, and depressive states are areas of active exploration. In this review, we concentrate on the scientific progress that has been made in understanding the role of Avp in regulating these and other behaviors across species. We also discuss the implications for human behavior.

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.

Agonist selectivity in the oxytocin/vasopressin receptor family: new insights and challenges

The design and development of selective agonists acting at the OT (oxytocin)/AVP (vasopressin) receptors has been and continues to be a difficult task because of the great similarity among the different receptor subtypes as well as the high degree of chemical similarity between the active ligands. In recent decades, at least a thousand synthetic peptides have been synthesized and examined for their ability to bind to and activate the different OT/AVP receptors; an effort that has led to the identification of several receptor subtype-selective agonists in the rat. However, owing to species differences between rat and human AVP/OT receptors, these peptides do not exhibit the same selectivities in human receptor assays. Furthermore, the discovery of receptor promiscuity, which is the ability of a single receptor subtype to couple to several different G-proteins, has led to the definition of a completely new class of compounds, referred to here as coupling-selective ligands, which may activate, within a single receptor subtype, only a specific signalling pathway. Finally, the accumulating evidence that GPCRs (G-protein-coupled receptors) do not function as monomers, but as dimers/oligomers, opens up the design of another class of specific ligands, bivalent ligands, in which two agonist and/or antagonist moieties are joined by a spacer of the appropriate length to allow the simultaneous binding at the two subunits within the dimer. The pharmacological properties and selectivity profiles of these bivalent ligands, which remain to be investigated, could lead to highly novel research tools and potential therapeutic agents.

Small-molecule vasopressin-2 receptor antagonist identified by a g-protein coupled receptor "pathway" screen

G-protein-coupled receptors (GPCRs) such as the vasopressin-2 receptor (V(2)R) are an important class of drug targets. We developed an efficient screen for GPCR-induced cAMP elevation using as read-out cAMP activation of cystic fibrosis transmembrane conductance regulator (CFTR) Cl(-) channels. Fischer rat thyroid cells expressing CFTR and a halide-sensing yellow fluorescent protein (H148Q/I152L) were transfected with V(2)R. Increased cell Cl(-) conductance after agonist-induced cAMP elevation was assayed using a plate reader from cell fluorescence after solution I(-) addition. The Z' factor for the assay was approximately 0.7 with the V(2)R agonist [deamino-Cys1, Val4, d-Arg8]-vasopressin (1 nM) as positive control. Primary screening of 50,000 small molecules yielded a novel, 5-aryl-4-benzoyl-3-hydroxy-1-(2-arylethyl)-2H-pyrrol-2-one class of V(2)R antagonists that are unrelated structurally to known V(2)R antagonists. The most potent compound, V(2)R(inh)-02, which was identified by screening 35 structural analogs, competitively inhibited V(2)R-induced cAMP elevation with K(i) value of approximately 70 nM and fully displaced radiolabeled vasopressin in binding experiments. V(2)R(inh)-02 did not inhibit forskolin or beta(2)-adrenergic receptor-induced cAMP production and was more than 50 times more potent for V(2)R than for V(1a)R. The favorable in vitro properties of the pyrrol-2-one antagonists suggests their potential usefulness in aquaretic applications. The CFTR-linked cAMP assay developed here is applicable for efficient, high-throughput identification of modulators of cAMP-coupled GPCRs.

Relief of Nocturnal Enuresis by Desmopressin Is Kidney and Vasopressin Type 2 Receptor Independent

Primary nocturnal enuresis (PNE) is a common problem in childhood and adolescence. Although various treatments are highly effective, a common underlying hypothesis on the pathogenesis is lacking. The success of desmopressin, a synthetic analogue of the antidiuretic hormone vasopressin, has been attributed to increased renal water reabsorption that is mediated by activation of the renal vasopressin V2 receptor (V2R). However, this effect does not explain other symptoms of PNE, such as the failure to arouse upon bladder distension. This study identified a family in which one child displayed PNE and coexisting nephrogenic diabetes insipidus, as a result of a novel nonsense mutation in the V2R gene (C358X). Cell-biologic investigations revealed that V2R-C358X is retained in the endoplasmic reticulum and is unstable, which explains his nephrogenic diabetes insipidus. Consistently, extrarenal V2R-mediated responses were absent in the patient who was treated with desmopressin. Administration of desmopressin, however, changed his PNE into nocturia, because he now still voided unchanged high urinary volumes at night but woke up and went to the bathroom. Withdrawal of desmopressin was accompanied by bedwetting, whereas reintroduction again relieved the symptoms. Therefore, these data indicate that neither a functioning renal concentration system nor a functional V2R is needed for the therapeutic benefit of desmopressin in PNE. Rather, it suggests that another vasopressin receptor and other organ(s) is the target for desmopressin to relieve PNE.

Design and Synthesis of the First Selective Agonists for the Rat Vasopressin V1bReceptor: Based on Modifications of Deamino-[Cys]arginine Vasopressin at Positions 4 and 8

The neurohypophyseal peptides arginine vasopressin (AVP) and oxytocin (OT) mediate a wide variety of peripheral and central physiological and behavioral effects by acting on four different G-protein coupled receptors, termed V1a (vascular), V1b (pituitary), V2 (renal), and OT (uterine). We recently reported that d[Cha4]AVP (A), d[Leu4]AVP (B), d[Orn4]AVP (C), and d[Arg4]AVP (D) have high affinity and are selective agonists for the human V1b receptor. However, peptides A-D were subsequently shown to be potent antidiuretic agonists in the rat and are, thus, not selective V1b agonists in the rat. Peptides A-D served as leads for the studies reported here. They were modified at position 8 by Lys, ornithine (Orn), diaminobutyric acid (Dab), and diaminopropionic acid (Dap) to give d[Cha4,Lys8]VP (1), d[Cha4,Orn8]VP (2), d[Cha4,Dab8]VP (3), d[Cha4,Dap8]VP (4), d[Leu4,Lys8]VP (5), d[Leu4,Orn8]VP (6), d[Leu4,Dab8]VP (7), d[Leu4,Dap8]VP (8), d[Orn4,Lys8]VP (9), d[Orn4,Orn8]VP (10), d[Arg4,Lys8]VP (11), d[Arg4,Orn8]VP (12), and d[Arg4,Dab8]VP (13). All peptides were synthesized by the Merrifield solid-phase method. Their binding and functional properties were evaluated in rat AVP V1a, V1b, and V2 receptors and on the rat OT receptor expressed either in native tissues or in stably transfected cells. They were also examined in rat vasopressor, antidiuretic, and in in vitro (no Mg++) oxytocic assays. Functional studies performed on chinese hamster ovary cells expressing the different AVP/OT receptors confirm that d[Cha4,Lys8]VP (1), d[Cha4,Dab8]VP (3), d[Leu4,Lys8]VP (5), and d[Leu4,Dap8]VP (8) are the first selective agonists for the rat V1b receptor. These selective V1b agonists are promising new tools for studies of the role of the V1b receptor in the rat.

A Novel Vasopressin Dual V1A/V2 Receptor Antagonist, Conivaptan Hydrochloride, Improves Hyponatremia in Rats with Syndrome of Inappropriate Secretion of Antidiuretic Hormone (SIADH)

We investigated the effects of intravenous administration of conivaptan hydrochloride, a dual vasopressin V1A and V2 receptor antagonist, on blood electrolytes and plasma osmolality in rats with an experimental syndrome of inappropriate secretion of antidiuretic hormone (SIADH). The experimental SIADH rat model was developed by means of continuous administration of arginine vasopressin (AVP) via a subcutaneously implanted osmotic mini pump, and hyponatremia was induced by additional water loading. This model possesses similar characteristics to those observed in patients with SIADH, specifically decreases in blood sodium concentration and plasma osmolality. In this experimental model, intravenous administration of conivaptan (0.1, 1 mg/kg) significantly increased blood sodium concentration and plasma osmolality. On the other hand, intravenous administration of furosemide (10 mg/kg) did not increase either blood sodium concentration or plasma osmolality in the SIADH rats. Moreover, furosemide significantly lowered blood potassium concentration. These results show that conivaptan improves hyponatremia in rats with SIADH, supporting the therapeutic potential of conivaptan in treatment of patients with hyponatremia associated with SIADH.

Development of lithium-induced nephrogenic diabetes insipidus is dissociated from adenylyl cyclase activity

In antidiuresis, vasopressin (AVP) occupation of V2 receptors in renal collecting ducts activates adenylyl cyclase, resulting in increased intracellular cAMP levels, which activates protein kinase A (PKA). PKA phosphorylates both the cAMP responsive element binding protein, which induces aquaporin-2 (AQP2) transcription, and AQP2, which then is translocated to the apical membrane, allowing urine concentration. Lithium treatment often causes nephrogenic diabetes insipidus (NDI), which coincides with decreased AQP2 expression and which generally is ascribed to reduced adenylyl cyclase activity. However, the underlying mechanism by which lithium causes NDI is poorly understood. This study demonstrated that the mouse cortical collecting duct mpkCCD(c14) cells are a good model; the deamino-8 D-arginine vasopressin (dDAVP)-induced endogenous AQP2 expression and plasma membrane localization was time-dependently reduced by treatment with clinically relevant lithium concentrations. Lithium did not affect AQP2 stability but decreased its mRNA levels. Surprising, the effect of lithium was cAMP independent; it did not alter AVP-stimulated cAMP production or PKA-dependent phosphorylation of AQP2 or cAMP responsive element binding protein. In vivo, kidney tissue of rats with lithium-induced NDI indeed generated less dDAVP-induced cAMP than that of controls, but this could be due to elevated blood AVP levels in rats with lithium-induced NDI. Indeed, Brattleboro rats, which lack endogenous AVP, with clamped blood dDAVP levels, showed no difference in dDAVP-generated cAMP generation between kidneys of rats with lithium-induced NDI and control rats. In conclusion, the first proper cell model to study lithium-induced NDI was developed, and it was demonstrated that the lithium-induced downregulation of AQP2 and development of NDI occur independent of adenylyl cyclase activity in vitro and in vivo.

Position 4 analogues of [deamino-Cys1] arginine vasopressin exhibit striking species differences for human and rat V2/V1b receptor selectivity

Arginine vasopressin (AVP) mediates a wide variety of biological actions by acting on three distinct G-protein coupled receptors, termed V(1a) (vascular), V(1b) (pituitary) and V(2) (renal). It also binds to the oxytocin (OT) receptor. As part of a program aimed at the design of selective agonists for the human V(1b) receptor, we recently reported the human V(1b), V(1a), V(2) and OT receptor affinities of the following position 4 substituted analogues of [deamino-Cys(1)] arginine vasopressin (dAVP)-(1) d[Leu(4)]AVP, (2) d[Orn(4)]AVP, (3) d[Lys(4)]AVP, (4) d[Har(4)]AVP, (5) d[Arg(4)]AVP, (6) d[Val(4)]AVP, (7) d[Ala(4)]AVP, (8) d[Abu(4)]AVP, (9) d[Nva(4)]AVP, (10) d[Nle(4)]AVP, (11) d[Ile(4)]AVP, (12) d[Phe(4)]AVP, (13) d[Asn(4)]AVP, (14) d[Thr(4)]AVP: (15) d[Dap(4)]AVP. With the exception of Nos. 7 and 12, all peptides exhibit very high affinities for the human V(1b) receptor. Furthermore, peptides 1-4 exhibit high selectivities for the human V(1b) receptor with respect to the V(1a), V(2) and OT receptors and, with d[Cha(4)]AVP, in functional tests, are the first high affinity selective agonists for the human V(1b) receptor (Cheng LL et al., J. Med. Chem. 47: 2375-2388, 2004). We report here the pharmacological properties of peptides 1-4, 5 (from a resynthesis), 7, 9-13, 15 in rat bioassays (antidiuretic, vasopressor and oxytocic) (in vitro: no Mg(++)) with those previously reported for peptides 5, 6, 8, 14. We also report the rat V(1b), V(1a), V(2) and OT receptor affinities of peptides 1-5 and the rat V(2) receptor affinities for peptides: 7-15.The antidiuretic activities in units/mg of peptides 1-15, are: 1=378; 2=260; 3=35; 4=505; 5=748; 6=1150; 7=841; 8=1020; 9=877; 10=1141; 11=819, 12=110; 13=996; 14=758; 15=1053. Peptides 1-4 exhibit respectively the following rat and human (in brackets) V(2) receptor affinities: 1=3.1 nm (245 nm); 2=3.4 nm (1125 nm); 3=24.6 nm (11,170 nm); 4=0.6 nm (1386 nm). Their rat V(1b) receptor affinities are 1=0.02 nm; 2=0.45 nm; 3=9.8 nm; 4=0.32 nm. Their rat V(1a) receptor affinities are 1=1252 nm; 2=900 nm; 3=1478 nm; 4=32 nm. Their rat oxytocin (OT) receptor affinities are 1=481 nm; 2=997 nm; 3=5042 nm; 4=2996 nm. All four peptides have high affinities and selectivities for the rat V(1b) receptor with respect to the rat V(1a) and OT receptors. However, in contrast to their high selectivity for the human V(1b) receptor with respect to the human V(2) receptor, they are not selective for the V(1b) receptor with respect to the V(2) receptor in the rat. These findings confirm previous observations of profound species differences between the rat and human V(2) receptors. Peptides 1-4 are promising leads to the design of the first high affinity selective agonists for the rat V(1b) receptor.

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.

Design of potent and selective agonists for the human vasopressin V1b receptor based on modifications of [deamino-cys1]arginine vasopressin at position 4

The glutamine(4) residue in [deamino-Cys(1)]arginine vasopressin (dAVP) was replaced by a broad series of aliphatic, aromatic, polar, and charged amino acids to give the following peptides: d[Gly(4)]AVP (1), d[Ala(4)]AVP (2), d[Abu(4)]AVP (3), d[Nva(4)]AVP (4), d[Nle(4)]AVP (5), d[Leu(4)]AVP (6), d[Ile(4)]AVP (7), d[Thi(4)]AVP (8), d[Phe(4)]AVP (9), d[Tyr(4)]AVP (10), d[Trp(4)]AVP (11), d[Asn(4)]AVP (12), d[Ser(4)]AVP (13), d[Thr(4)]AVP (14), d[Dap(4)]AVP (15), d[Dab(4)]AVP (16), d[Orn(4)]AVP (17), d[Lys(4)]AVP (18), d[Arg(4)]AVP (19), d[Har(4)]AVP (20), and d[Glu(4)]AVP (21). All peptides were synthesized by solid-phase methods using BOC chemistry for all but one peptide (8), which required the use of Fmoc chemistry. The binding and functional properties of these position 4 substituted analogues of dAVP (d[X(4)]AVP) and the previously reported d[Cha(4)]AVP (Derick et al. Endocrinology 2002, 143, 4655-4664) were evaluated on human arginine vasopressin (AVP) V(1a), V(1b), and V(2) receptors and on the human oxytocin (OT) receptor expressed in living Chinese hamster ovary (CHO) cells. Binding studies revealed that broad modifications of the fourth residue of dAVP do not significantly alter affinity for the human V(1b) receptor. Only aromatic (Phe, Tyr, Trp) or negatively charged (Glu) residues reduce V(1b) affinity. By contrast, the human V(1a) and more particularly the human V(2) and the OT receptors are more sensitive to many of these modifications. Thus, the replacement of the Gln(4) residue of dAVP by aliphatic (Leu, Cha) or positively charged (Orn, Lys, Arg, Har) amino acids led to analogues exhibiting drastic reductions of their affinity for the human V(1a), V(2), and OT receptors. Consequently, in addition to the previously reported d[Cha(4)]AVP, peptides 6 and 17-20 display excellent selectivities for the human V(1b) receptor. The key structural requirement responsible for optimal V(1b) selectivity appears to be the length and branching of the aliphatic side chain of the fourth residue of dAVP. Functional studies performed on CHO cells expressing the different human AVP/OT receptors confirm the V(1b) selectivity of peptides 6, 17, 18, 20, and d[Cha(4)]AVP. However, d[Arg(4)]AVP (19), which triggers an excellent coupling between the human V(2) receptor and adenylyl cyclase, was found to exhibit both V(1b) and V(2) agonism in functional tests. More interestingly, these functional experiments revealed that, depending on the AVP/OT receptor, a given d[X(4)]AVP analogue may behave as a full agonist or as a partial agonist. This strongly suggests that the fourth residue of dAVP plays an important role in the coupling between the hormone-receptor complex, the heterotrimeric G protein, and the effectors. In conclusion, the synthesis of these d[X(4)]AVP analogues led to the discovery of new V(1b) agonists with high affinity and greatly enhanced selectivities. Thus, in addition to d[Cha(4)]AVP, d[Leu(4)]AVP (6), d[Orn(4)]AVP (17), d[Lys(4)]AVP (18), and d[Har(4)]AVP (20) are useful new tools for studying the structure and the function of the human V(1b) receptor.

Evidence against a synergistic effect of desmopressin with conditioning in the treatment of nocturnal enuresis

OBJECTIVE

To test the hypothesis that desmopressin facilitates acquisition of continence, we aimed to establish whether, in children with nocturnal enuresis who are desmopressin nonresponders, adjunct desmopressin increases the rate of sustained continence after treatment with a conditioning alarm. Study design Patients with nocturnal enuresis (n=358; age range, 6-16 years) completed a 4-week "run-in" course of intranasal desmopressin (20-40 microg). Of these, 207 defined as nonresponders (<50% reduction in wet nights) were randomly assigned to receive either desmopressin (n=101) or placebo (n=106) nasal spray, together with conditioning alarm therapy for 8 weeks. Principal outcome measures were remission (28 continuous dry nights) and relapse (>2 wet nights in 2 weeks after having achieved remission).

RESULTS

Remission rates were similar in both groups (51.5% desmopressin, 48.1% placebo; 95% CI on difference, -10%, 17%; P=.63), and relapse rates were not significantly different (13.5% vs 5.9%; 95% CI on difference, -3.7%, 19%; P=.19). Although remission rates were similar, children treated with desmopressin had significantly more dry nights during treatment than those in the placebo group.

CONCLUSIONS

Desmopressin did not act synergistically with alarm treatment to achieve remission. Therefore, we infer that in partial or nonresponders, desmopressin does not enhance learning.

The influence of vasopressin deficiency and acute desmopressin administration on melatonin secretion in patients with central diabetes insipidus

Melatonin secretion is modulated by the light-dark schedule, mainly through a sympathetic input to the pineal gland. Besides this, arginine vasopressin (AVP) has been found in the pineal glands of several animal species and there is experimental evidence that AVP modulates melatonin secretion in animals. However, the interaction between vasopressin and melatonin secretion in humans has not been systematically investigated. We proposed to study the nocturnal melatonin pattern in patients with central diabetes insipidus (CDI) who lack endogenous secretion of AVP, and the effect on their melatonin secretion of the agonist for V2 type receptors: desmopressin (1-Desamino [8-D Arginine] vasopressin). Plasma melatonin levels were measured in 14 patients with CDI, every 2 h starting from 22:00 h until 06:00 h, following iv injection of saline (day 1) and 3 microg desmopressin (day 2) at 20:00 h. The lights were turned off at 22:30 h and the samples were taken in a dim light. The plasma melatonin secretion pattern was normal in patients with CDI. Desmopressin at a dose 3 times higher than the antidiuretic one did not modify the melatonin levels or the time of the peak secretion. In conclusion melatonin secretion is not modulated by AVP in humans.

Pancreatic vasopressin V1b receptors: characterization in In-R1-G9 cells and localization in human pancreas

Vasopressin (AVP) receptors present in In-R1-G9 cells, a hamster glucagon-secreting alpha-pancreatic cell line, were characterized using SSR-149415, a selective nonpeptide V1b receptor antagonist, and reference AVP compounds. Binding experiments, using [3H]AVP as a ligand, identified a single population of high-affinity binding sites. SSR-149415 competitively inhibited this binding and exhibited nanomolar and stereospecific affinity for these sites. The affinity of various AVP/oxytocin ligands confirmed a V1b binding profile. In functional studies, AVP was a potent stimulant in inducing intracellular Ca2+ increase, glucagon secretion, and cell proliferation. These effects were fully antagonized by SSR-149415 with a nanomolar potency, whereas its diasteroisomer as well as two selective V1a and V2 receptor antagonists were much less potent. Additionally, the order of potency of AVP agonists and antagonists was in agreement with V1b-mediated effects. By RT-PCR, we confirmed the presence of V1b receptor mRNA in both In-R1-G9 cells and in human pancreas. The distribution pattern of V1b receptors investigated in human pancreas by immunohistochemistry showed strong labeling in islets of Langerhans, and colocalization studies indicated that this receptor was expressed in alpha-glucagon, beta-insulin, and somatostatin pancreatic cells. Thus, in In-R1-G9 cells, AVP mediates intracellular Ca2+ increase, glucagon secretion, and cell proliferation by activating V1b receptors, and these effects are potently antagonized by SSR-149415. Moreover, the presence of V1b receptors also found in human Langerhans islets could suggest hormonal control of AVP in human pancreas.

cDNA array identification of genes regulated in rat renal medulla in response to vasopressin infusion

With the aim of identifying possible gene targets for direct or indirect regulation by vasopressin in the renal medulla, we have carried out cDNA array experiments in inner medullas of Brattleboro rats infused with the V(2) receptor-selective vasopressin analog desamino-Cys1,d-Arg8 vasopressin (dDAVP) for 72 h. Of the 1,176 genes on the array, 137 transcripts were increased by 2-fold or more, and 10 transcripts were decreased to 0.5-fold or less. Quantitative, real-time RT-PCR measurements confirmed increases seen for six selected transcripts (Wilms' tumor protein, beta-arrestin 2, neurofibromin, casein kinase IIbeta, aquaporin-3, and aquaporin-4). To correlate changes in mRNA expression with changes in protein expression, we carried out quantitative immunoblotting for 28 of the proteins whose cDNAs were on the array. For several targets including aquaporin-2, transcript abundance and protein abundance changes did not correlate. However, for most genes examined, changes in mRNA abundances were associated with concomitant protein abundance changes. Targets with demonstrated increases in both protein and mRNA abundances included neurofibromin, casein kinase IIbeta, the beta-subunit of the epithelial Na channel (beta-ENaC), 11beta-hydroxysteroid dehydrogenase type 2, and c-Fos. Additional cDNA arrays revealed that several transcripts that were increased in abundance after 72 h of dDAVP were also increased after 4 h, including casein kinase IIbeta, beta-ENaC, aquaporin-3, UT-A, and syntaxin 2. These studies have identified several transcripts whose abundances are regulated in the inner medulla in response to infusion of dDAVP and that could play roles in the regulation of salt and water excretion.

[1-deamino-4-cyclohexylalanine] arginine vasopressin: a potent and specific agonist for vasopressin V1b receptors

To date, there are no vasopressin (VP) agonists that exhibit a high affinity and selectivity for the VP V1b receptor with respect to the V1a, V2, and oxytocin receptors. In this study, we describe the synthesis and pharmacological properties of [1-deamino-4-cyclohexylalanine] arginine vasopressin (d[Cha4]AVP). Binding experiments performed on various membrane preparations revealed that d[Cha(4)]AVP exhibits a nanomolar affinity for V1b receptors from various mammalian species (rat, bovine, human). It exhibits high V1b/V1a and V1b/oxytocin selectivity for rat, human, and bovine receptors. Furthermore, it exhibits high V1b/V2 specificity for both bovine and human vasopressin receptors. Functional studies performed on biological models that naturally express V1b receptors indicate that d[Cha4]AVP is an agonist. Like VP, it stimulated basal and corticotropin-releasing factor-stimulated ACTH secretion and basal catecholamine release from rat anterior pituitary and bovine chromaffin cells, respectively. In vivo experiments performed in rat revealed that d[Cha4]AVP was able to stimulate both ACTH and corticosterone secretion and exhibits negligible vasopressor activity. It retains about 30% of the antidiuretic activity of VP. This long-sought selective VP V1b receptor ligand with nanomolar affinity will allow a better understanding of V1b-mediated VP physiological effects and is a promising new tool for V1b receptor structure-function studies.

Pharmacological characterization of F-180: a selective human V(1a) vasopressin receptor agonist of high affinity

1. The pharmacological properties of F-180, a vasopressin (VP) structural analogue, were determined on CHO cells expressing the different human vasopressin and oxytocin (OT) receptor subtypes. Binding experiments revealed that F-180 exhibited a high affinity for the human V(1a) receptor subtype (K(i)=11 nM) and was selective for this receptor subtype. 2. Functional studies performed on CHO cells expressing human V(1a) receptors indicate that similarly to AVP, F-180 can stimulate the accumulation of inositol phosphate. The activation constant (K(act)) for both F-180 and AVP was 1.7 nM. F-180 was also an agonist for the human V(2) and V(1b) receptor subtypes and an antagonist for the human OT receptor. 3. Since marked species pharmacological differences for vasopressin receptors have been described, we studied the properties of F-180 on various mammalian species. F-180 showed high affinity and good selectivity for human and bovine V(1a) receptors, but weak affinity and non selective properties for rat V(1a) receptors. 4. To assess the functional properties of F-180 on a native biological model, we performed studies on primary cultures of cells from bovine zona fasciculata (ZF). As AVP, F-180 stimulated inositol phosphate accumulation and cortisol secretion with similar efficiency. 5. In conclusion, we demonstrate that F-180 is the first selective V(1a) agonist described for human and bovine vasopressin receptors. Therefore F-180 can be used as a powerful pharmacological tool to characterize the actions of vasopressin that are mediated by V(1a) receptor subtypes.