Kinetic and pharmacological characterization of vasopressin membrane receptors from human kidney medulla: relation to adenylate cyclase activation

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.

The multifunctional protein GC1q-R interacts specifically with the i3 loop arginine cluster of the vasopressin V2 receptor

In this study, we identified the multifunctional protein GC1q-R as a novel vasopressin V(2) receptor (V(2)R) interacting protein. For this purpose, we have developed a proteomic approach combining pull-down assays using a cyclic peptide mimicking the third intracellular loop of V(2)R as a bait and mass spectrometry analyses of proteins isolated from either rat or human kidney tissues or the HEK 293 cell line. Co-immunoprecipitation of GC1q-R with the c-Myc-tagged h-V(2)R expressed in a HEK cell line confirmed the existence of a specific interaction between GC1q-R and the V(2) receptor. Then, construction of a mutant receptor in i3 loop allowed us to identify the i3 loop arginine cluster of the vasopressin V(2) receptor as the interacting determinant for GC1q-R interaction. Using purified receptor as a bait and recombinant (74-282) GC1q-R, we demonstrated a direct and specific interaction between these two proteins via the arginine cluster.

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

Vasopressin, a neurohypophyseal peptide hormone, is the endogenous agonist at V1a, V1b and V2 receptors. The most important physiological function of vasopressin is the maintenance of water homeostasis through interaction with V2 receptors in the kidney. Vasopressin and related compounds are used in various clinical settings such as acute variceal bleeding associated with portal hypertension, septic shock, diabetes insipidus and coagulation disorders. The effect in the former two indications relates to the V1a receptor, and in the two latter indications the effect relates to the V2 receptor. Vasopressin and related compounds have demonstrated activity in animal models of portal hypertension, sepsis and septic shock, diabetes insipidus and coagulation disorders. The use of the compounds in animal models is reviewed. Generally, the effect of vasopressin and related compounds in animal models reflect the activity in the clinical setting, but in some cases important species differences exist.

Synthesis and pharmacological profile of non-peptide vasopressin antagonists

Recently we presented a series of 6-ethyl and 6-benzylthieno[2,3-b][1,4]thiazine derivatives with relaxing effects on vascular smooth muscle and terminal ileum. In this report the synthesis of further thieno[2,3-b][1,4]thiazine derivatives and related compounds with a thieno[2,3-b][1,4]thiazepine or thieno[3,2-b][1,4]thiazine ring system is described. The pharmacological effect of the agents was tested in isolated smooth (terminal ileum, pulmonary artery, aortic rings, myometrial strips) and heart (papillary muscle, spontaneously beating right atrium) muscle preparations of the guinea pig. Contractions were measured isometrically, and smooth muscle preparations were either precontracted with high K+ (60 or 90 mM KCl containing nutrient solution) or with agonists, while papillary muscles were electrically stimulated (1 Hz). The vasopressin antagonistic activity of the test compounds was tested in isolated papillary muscles in which the V1A-receptor subtype is located. The biphasic response to vasopressin was antagonized, dependent on the chemical structure of the test compound. Thieno[3,2-b][1,4]thiazines were more potent than thieno[2,3-b][1,4]thiazine and thieno[2,3-b][1,4]thiazepine compounds. In addition, substitution of a methyl substituted terminal benzyl ring instead of a phenyl- or dichlorobenzoyl moiety attenuated the vasopressin antagonistic effect.

Effects of YM218, a nonpeptide vasopressin V1A receptor-selective antagonist, on human vasopressin and oxytocin receptors

The binding and signal transduction characteristics of YM218 ((Z)-4'-{4,4-difluoro-5-[2-oxo-2-(4-piperidinopiperidino)ethylidene]-2,3,4,5-tetrahydro-1H-1-benzoazepine-1-carbonyl}-2-methyl-3-furanilide hemifumarate), a newly synthesized, potent arginine vasopressin (AVP) V(1A) receptor-selective antagonist, were examined using cloned human AVP receptors (V(1A), V(1B) and V(2)) stably expressed in Chinese hamster ovary (CHO) cells and human uterine smooth muscle cells (USMCs) expressing oxytocin receptors. YM218 potently inhibited specific binding of [(3)H] AVP to V(1A) receptors, exhibiting a K(i) value of 0.30 nM. In contrast, YM218 exhibited much lower affinity for V(1B), V(2) and oxytocin receptors, exhibiting K(i) values of 25,500 nM, 381 nM and 71.0 nM, respectively. In CHO cells expressing V(1A) receptors, YM218 potently inhibited the AVP-induced increase in intracellular Ca(2+) concentration ([Ca(2+)](i)), exhibiting an IC(50) value of 0.25 nM. However, in human USMCs expressing oxytocin receptors, YM218 exhibited a much lower potency in inhibiting the oxytocin-induced [Ca(2+)](i) increase, showing an IC(50) value of 607 nM, and had no effect on the AVP-induced [Ca(2+)](i) increase in CHO cells expressing V(1B) receptors. Furthermore, in CHO cells expressing V(2) receptors, YM218 did not potently inhibit the production of cAMP stimulated by AVP, showing an IC(50) value of 62.2 nM. In all assays used, YM218 did not exhibit any agonistic activity. These results demonstrate that YM218 is a potent, nonpeptide human V(1A) receptor-selective antagonist, and that YM218 will be a valuable new tool to gain further insight into the physiologic and pharmacologic actions of AVP.

Pharmacological characterization of YM471, a novel potent vasopressin V(1A) and V(2) receptor antagonist

The pharmacologic profile of YM471 ((Z)-4'-[4,4-difluoro-5-[2-(4-dimethylaminopiperidino)-2-oxoethylidene]-2,3,4,5-tetrahydro-1H-1-benzoazepine-1-carbonyl]-2-phenylbenzanilide monohydrochloride), a novel potent vasopressin V(1A) and V(2) receptor antagonist, was investigated using several in vitro and in vivo techniques. YM471 showed high affinity for rat vasopressin V(1A) and V(2) receptors, exhibiting K(i) values of 0.16 and 0.77 nM, respectively. In contrast, YM471 exhibited much lower affinity for rat vasopressin V(1B) and oxytocin receptors, with K(i) values of 10.5 microM and 31.0 nM, respectively. In conscious rats, oral administration of YM471 (0.1-3.0 mg/kg) produced dose-dependent inhibition of the pressor response caused by exogenous vasopressin and increased urine excretion and decreased urine osmolality; this effect lasted more than 8 h. In all biological assays used, YM471 exhibited no agonistic activity. These results demonstrate that YM471 exerts potent and long-lasting antagonistic activity on both vasopressin V(1A) and V(2) receptors, and that this compound may be a useful tool for clarifying the physiologic and pathophysiologic roles of vasopressin and the therapeutic usefulness of the vasopressin receptor antagonist.

Variant amino acids in the extracellular loops of murine and human vasopressin V2 receptors account for differences in cell surface expression and ligand affinity

Cloning and sequencing of the murine chromosomal region XB harboring the murine vasopressin V(2) receptor (mV(2)R) gene and comparison with the orthologous human Xq28 region harboring the human vasopressin V(2) receptor (hV(2)R) revealed conservation of the genomic organization and a high degree of sequence identity in the V(2)R coding regions. Despite an identity of 87% of the amino acid sequences, both receptors show marked functional differences upon stable expression in Chinese hamster ovary cells: the mV(2)R displayed a 5-fold higher affinity for [(3)H]AVP than the human ortholog; similar differences were found for the AVP-mediated activation of adenylyl cyclase. Saturation binding experiments with transiently transfected intact COS.M6 cells showed that the mV(2)R was 3- to 5-fold less abundantly expressed at the cell surface than the hV(2)R. Laser scanning microscopy of fusion proteins consisting of the V(2)Rs and green fluorescent protein (GFP) (mV(2)R/GFP, hV(2)R/GFP) demonstrated that the hV(2)R/GFP was efficiently transported to the plasma membrane, whereas the mV(2)R/GFP was localized mainly within the endoplasmic reticulum. Chimeric hV(2)Rs, in which the first and/or second extracellular loop(s) were replaced by the corresponding loop(s) of the mV(2)R, revealed that the second extracellular loop accounts for the differences in ligand binding, but the first extracellular loop accounts for the reduced cell surface expression. The exchange of lysine 100 by aspartate in the first extracellular loop of hV(2)R was sufficient to reduce cell surface expression, which was accompanied by intracellular retention as observed in laser scanning microscopy analysis. Conversely, the exchange of aspartate 100 by lysine in the mV(2)R increased the cell surface expression and resulted in predominant plasma membrane localization. Thus, a single amino acid difference in the first extracellular loop between mV(2)R and hV(2)R determines the efficiency of cell surface expression.

Effects of YM471, a nonpeptide AVP V(1A) and V(2) receptor antagonist, on human AVP receptor subtypes expressed in CHO cells and oxytocin receptors in human uterine smooth muscle cells

YM471, (Z)-4'-[4,4-difluoro-5-[2-(4-dimethylaminopiperidino)-2-oxoethylidene]-2,3,4,5-tetrahydro-1H-1-benzoazepine-1-carbonyl]-2-phenylbenzanilide monohydrochloride, is a newly synthesized potent vasopressin (AVP) receptor antagonist. Its effects on binding to and signal transduction by cloned human AVP receptors (V(1A), V(1B) and V(2)) stably expressed in Chinese hamster ovary (CHO) cells, and oxytocin receptors in human uterine smooth muscle cells (USMC) were studied. YM471 potently inhibited specific [(3)H]-AVP binding to V(1A) and V(2) receptors with K(i) values of 0.62 nM and 1.19 nM, respectively. In contrast, YM471 exhibited much lower affinity for V(1B) and oxytocin receptors with K(i) values of 16.4 microM and 31.6 nM, respectively. In CHO cells expressing V(1A) receptors, YM471 potently inhibited AVP-induced intracellular Ca(2+) concentration ([Ca(2+)](i)) increase, exhibiting an IC(50) value of 0.56 nM. However, in human USMC expressing oxytocin receptors, YM471 exhibited much lower potency in inhibiting oxytocin-induced [Ca(2+)](i) increase (IC(50)=193 nM), and did not affect AVP-induced [Ca(2+)](i) increase in CHO cells expressing V(1B) receptors. Furthermore, in CHO cells expressing V(2) receptors, YM471 potently inhibited the production of cyclic AMP stimulated by AVP with an IC(50) value of 1.88 nM. In all assays, YM471 showed no agonistic activity. These results demonstrate that YM471 is a potent, nonpeptide human V(1A) and V(2) receptor antagonist which will be a valuable tool in defining the physiologic and pharmacologic actions of AVP.

Function and molecular basis of action of vasopressin 4-8 and its analogues in rat brain

VP 4-8 as a highly potent behavioral-active metabolite of arginine-vasopressin (VP) has been studied in detail at four levels, i.e. ligand level, membrane binding level, intracellular level and nuclear level. The purpose of this chapter is to review and discuss the main results obtained from our recent pharmacological and biochemical investigations which are described as follows: 1, structure-function relationship of VP 4-8 and its analogs; 2, some characters of VP 4-8-specific binding, the distribution of the binding sites in the rat brain and the consequent effect on long-term potentiation of synaptic transmission; 3, a putative receptor-mediated signaling pathway involving second messenger IP3, immediately-early gene c-fos transcription and protein kinase PKC, CaMKII and MAPK; 4, peptide-induced enhancement of some crucial functional proteins such as calmodulin, nerve growth factor (NGF) and brain-derived nerve growth factor (BDNF). The physiological significance of the events following VP 4-8 administration and particularly, its possible role in learning and memory processes are discussed.

Properties of a new radioiodinated antagonist for human vasopressin V2 and V1a receptors

A vasopressin receptor antagonist, [1-(beta-mercapto-beta,beta-pentamethylenepropionic acid), 2-o-ethyl-D-tyrosine, 4-valine, 9-tyrosylamide] arginine vasopressin (d(CH2)5[o-ethyl-D-Tyr2,Val4,Tyr-NH9(2)]AVP), has been prepared. This antagonist is a potent antiantidiuretic, antivasopressor and antioxytocic peptide with pA2 values of 7.69-7.94 and affinities of 1.12-11.0 nM. When radioiodinated at the phenyl moiety of the tyrosylamide residue at position 9, this peptide was demonstrated to bind to vasopressin V2 and V1a receptors with a dissociation constant of 0.22-0.75 nM. This ligand is a good tool for further studies on human vasopressin V2 receptor localization and characterization, when used in combination with a selective vasopressin V1a ligand.

Characterization of SR 121463A, a highly potent and selective, orally active vasopressin V2 receptor antagonist

SR 121463A, a potent and selective, orally active, nonpeptide vasopressin V2 receptor antagonist, has been characterized in several in vitro and in vivo models. This compound displayed highly competitive and selective affinity for V2 receptors in rat, bovine and human kidney (0.6 < or = Ki [nM] < or = 4.1). In this latter preparation, SR 121463A potently antagonized arginine vasopressin (AVP)-stimulated adenylyl cyclase activity (Ki = 0.26+/-0.04 nM) without any intrinsic agonistic effect. In autoradiographic experiments performed in rat kidney sections, SR 121463A displaced [3H]AVP labeling especially in the medullo-papillary region and confirmed that it is a suitable tool for mapping V2 receptors. In comparison, the nonpeptide V2 antagonist, OPC-31260, showed much lower affinity for animal and human renal V2 receptors and lower efficacy to inhibit vasopressin-stimulated adenylyl cyclase (Ki in the 10 nanomolar range). Moreover, OPC-31260 exhibited a poor V2 selectivity profile and can be considered as a V2/V1a ligand. In normally hydrated conscious rats, SR 121463A induced powerful aquaresis after intravenous (0.003-0.3 mg/kg) or oral (0.03-10 mg/kg) administration. The effect was dose-dependent and lasted about 6 hours at the dose of 3 mg/kg p.o. OPC-31260 had a similar aquaretic profile but with markedly lower oral efficacy. The action of SR 121463A was purely aquaretic with no changes in urine Na+ and K+ excretions unlike that of known diuretic agents such as furosemide or hydrochlorothiazide. In addition, no antidiuretic properties have been detected with SR 121463A in vasopressin-deficient Brattleboro rats. Thus, SR 121463A is the most potent and selective, orally active V2 antagonist yet described and could be a powerful tool for exploring V2 receptors and the therapeutical usefulness of V2 blocker aquaretic agents in water-retaining diseases.

Molecular neurobiology and pharmacology of the vasopressin/oxytocin receptor family

1. VP and OT mediate their wealth of effects via 4 receptor subtypes V1a, V1b, V2, and OT receptors. 2. We here review recent insights in the pharmacological properties, structure activity relationships, species differences in ligand specificity, expression patterns, and signal transduction of VP/OT receptor. 3. Furthermore, the existence of additional VP/OT receptor subtypes is discussed.

An extracellular residue determines the agonist specificity of V2 vasopressin receptors

The specific V2 agonist 1-deamino [8-D-arginine]-vasopressin (dDAVP), used for treatment of central diabetes insipidus, binds to vasopressin V2 receptors from human, bovine and rat kidney with an affinity that is similar to that of the natural hormone vasopressin. In contrast, the V1 receptors and the porcine V2 receptor do not tolerate a D-arginine in position 8 of vasopressin. By site directed mutagenesis of the cloned bovine and porcine V2 receptors we identified a residue (Asp-103) in the first extracellular loop of vasopressin receptors which is responsible for high affinity binding of dDAVP.

Distribution of messenger RNA for the vasopressin V1a receptor in the CNS of male and female rats

The distribution of cells expressing mRNA encoding a vasopressin V1a receptor (V1aR) was examined in Long-Evans male and female rats by in situ hybridization using a [35S]cRNA probe. Specific hybridization to the vasopressin V1aR mRNA was evident in cells of the frontal cortex, piriform cortex, internal granular layer and the medial, dorsal, ventral and lateral portion of the anterior olfactory nucleus, zona limitans of the islands of Calleja, suprachiasmatic nucleus, CA1, CA2, CA3 and dentate gyrus of the hippocampus, paraventricular hypothalamic nucleus, ventromedial hypothalamic nucleus, arcuate nucleus, lateral habenular nucleus, and the molecular and granular cell layers of the cerebellum. The cerebellum, olfactory nucleus and the dentate gyrus appeared to be the most intensely labeled areas, while all other areas exhibited a lower level of expression. The anatomical distribution and the amount (as measured by optical density) of V1aR mRNA labeling was identical between male and female rats. This indicates that unlike the vasopressin gene itself, the expression of the vasopressin V1aR mRNA does not exhibit sexual dimorphism. These data demonstrate a wide spread distribution in the expression of the vasopressin V1aR mRNA in the CNS of male and female rats. This information on the anatomical distribution of the V1aR mRNA when combined with data concerning the anatomical distribution of the V1a binding sites, provides new information on the possible pre- and post-synaptic location of these neuropeptide receptors.

Circulating vasopressin influences area postrema neurons

Extracellular single-unit recordings were obtained from 107 area postrema and 74 nucleus tractus solitarius neurons in sodium pentobarbital anaesthetized rats. Systemic administration of vasopressin (1-10 ng) decreased the firing frequency of 45.8% of area postrema neurons and 58.1% of nucleus tractus solitarius neurons tested while the firing frequency of 38.3% of area postrema neurons and 21.6% of nucleus tractus solitarius neurons was increased by this peptide. To determine whether these neurons were specifically influenced by vasopressin or the accompanying pressor response, the effects of alpha-adrenergic agonists on neuronal activity were also determined. Cells that responded similarly to vasopressin and the change in blood pressure elicited by alpha-adrenergic agonists were classified as "blood pressure-sensitive", whereas those neurons that responded differently to both agents were classified as "vasopressin-sensitive" neurons. The majority (85.2%) of area postrema cells that decreased firing frequency in response to vasopressin were determined to be "vasopressin-sensitive", while 68.8% of area postrema neurons responding to vasopressin with increases in firing frequency were classified as "blood pressure-sensitive". In contrast, 78.6% of nucleus tractus solitarius neurons that decreased firing frequency in response to vasopressin and 55.5% of those that increased firing frequency were classified as "blood pressure-sensitive" neurons. To determine whether the actions of vasopressin in the area postrema were mediated by V1 receptors the effect of vasopressin after V1 receptor blockade was examined in seven "vasopressin-sensitive" area postrema neurons. All seven neurons tested showed no response to vasopressin after such V1 receptor blockade. These data suggest that there exists a population of area postrema neurons specifically responsive to circulating vasopressin as a result of actions of this peptide at V1 receptors. They also implicate these neurons in the physiological mechanisms through which circulating vasopressin acts in the area postrema to influence baroreceptor reflex sensitivity.

Molecular cloning and functional characterization of V2 [8-lysine] vasopressin and oxytocin receptors from a pig kidney cell line

[Arg8]vasopressin and oxytocin are the two main members of the neurohypophysial hormone family found to be present in nearly all mammals. [Lys8]vasopressin ([Lys8]VP) has been identified as the antidiuretic hormone in pig and some marsupial families. The porcine-derived kidney epithelial cell line, LLC-PK1, expresses both [Lys8]VP receptors coupled to the activation of adenylate cyclase (V2 receptors) and oxytocin receptors. Here we report the molecular cloning of the V2 [Lys8]VP receptor and the oxytocin receptor from LLC-PK1 cells. The cloned V2 [Lys8]VP receptor differs from human and rat V2 [Arg8] receptors mainly in its N-terminal region, in residues located in the extracellular loops and in intracellular phosphorylation sites. When expressed in COS7 cells, the V2 [Lys8]VP receptor exhibits the relative order of ligand affinity [Lys8]VP = [Arg8]VP >> 1-deamino[D-Arg8]VP > or = oxytocin and adenylate-cyclase stimulation, expected for the porcine V2 [Lys8]VP receptor but different from V2 [Arg8]VP receptors. Adenylate-cyclase activation by [Lys8]VP was inhibited in COS7 cells by a V2 antagonist. The cloned oxytocin receptor exhibits in COS7 cells a ligand specificity typical of mammalian oxytocin receptors. mRNA-distribution analysis revealed a single 5.5-kb transcript in the uterus from pregnant guinea pig.

Biochemical and pharmacological properties of SR 49059, a new, potent, nonpeptide antagonist of rat and human vasopressin V1a receptors

SR 49059, a new potent and selective orally active, nonpeptide vasopressin (AVP) antagonist has been characterized in several in vitro and in vivo models. SR 49059 showed high affinity for V1a receptors from rat liver (Ki = 1.6 +/- 0.2) and human platelets, adrenals, and myometrium (Ki ranging from 1.1 to 6.3 nM). The previously described nonpeptide V1 antagonist, OPC-21268, was almost inactive in human tissues at concentrations up to 100 microM. SR 49059 exhibited much lower affinity (two orders of magnitude or more) for AVP V2 (bovine and human), V1b (human), and oxytocin (rat and human) receptors and had no measurable affinity for a great number of other receptors. In vitro, AVP-induced contraction of rat caudal artery was competitively antagonized by SR 49059 (pA2 = 9.42). Furthermore, SR 49059 inhibited AVP-induced human platelet aggregation with an IC50 value of 3.7 +/- 0.4 nM, while OPC-21268 was inactive up to 20 microM. In vivo, SR 49059 inhibited the pressor response to exogenous AVP in pithed rats (intravenous) and in conscious normotensive rats (intravenous and per os) with a long duration of action (> 8 h at 10 mg/kg p.o). In all the biological assays used, SR 49059 was devoid of any intrinsic agonistic activity. Thus, SR 49059 is the most potent and selective nonpeptide AVP V1a antagonist described so far, with marked affinity, selectivity, and efficacy toward both animal and human receptors. With this original profile, SR 49059 constitutes a powerful tool for exploring the therapeutical usefulness of a selective V1a antagonist.

[3H]desGly-NH2(9)-d(CH2)5[D-Ileu2,Ileu4]AVP: an AVP V2 receptor antagonist radioligand

Binding characteristics of the selective V2 antagonist radioligand [3H]desGly-NH2(9)-d(CH2)5[D-Ileu2,Ileu4]AVP to rat kidney were determined. Binding was specific, saturable and reversible. The peptide bound to a single class of high-affinity binding sites with Bmax 69.4 +/- 6.8 fmol/mg protein and KD 2.8 +/- 0.3 nM. AVP and other related peptides displaced [3H]desGly-NH2(9)-d(CH2)5[D-Ileu2,Ileu4]AVP binding. The order of potency of inhibition was desamino-D-AVP greater than AVP greater than d(CH2)5[D-Ileu2,Ileu4]AVP greater than oxytocin greater than d(CH2)5[Tyr(Me)2]AVP greater than d(CH2)5[sarcosine7]AVP, which is typical of a selective V2 radioligand. Autoradiographic localization of [3H]desGly-NH2(9)-d(CH2)5[D-Ileu2,Ileu4]AVP binding sites in kidney showed dense binding in the inner and outer medulla with less binding in the cortex, which is consistent with known renal V2 receptor distribution.

Feedback inhibition of cyclic adenosine monophosphate-stimulated Na+ transport in the rabbit cortical collecting duct via Na(+)-dependent basolateral Ca++ entry

Arginine vasopressin (AVP) transiently stimulates Na+ transport in the rabbit cortical collecting duct (CCD). However, the sustained effect of both AVP and its putative second messenger, cyclic adenosine monophosphate (cAMP), on Na+ transport in the rabbit CCD is inhibitory. Because maneuvers that increase [Ca++]i inhibit Na+ transport, the effects of AVP and cell-permeable cAMP analogues, on [Ca++]i were investigated in fura-2-loaded in vitro microperfused rabbit CCDs. Low-dose AVP (23-230 pM) selectively stimulated Ca++ influx, whereas 23 nM AVP additionally released calcium from intracellular stores. 8-chlorophenylthio-cAMP (8CPTcAMP) and 8-bromo-cAMP (8-Br-cAMP) also increased CCD [Ca++]i. The 8CPTcAMP-stimulated [Ca++]i increase was totally dependent on basolateral [Ca++]. In the absence of cAMP, peritubular Na+ removal produced a marked increase in [Ca++]i, which was also dependent on bath [Ca++], suggesting the existence of basolateral Na+/Ca++ exchange. Luminal Na+ removal in the absence of cAMP did not alter CCD [Ca++]i, but it completely blocked the cAMP-stimulated [Ca++]i increase. Thus the cAMP-dependent Ca++ increase is totally dependent on both luminal Na+ and basolateral Ca++, suggesting the [Ca++]i increase is secondary to cAMP effects on luminal Na+ entry and its coupling to basolateral Na+/Ca++ exchange. 8CPTcAMP inhibits lumen-to-bath 22Na flux [JNa(l-b)] in CCDs bathed in a normal Ca++ bath (2.4 mM). However, when bath Ca++ was lowered to 100 nM, a maneuver that also blocks the 8CPTcAMP [Ca++]i increase, 8CPTcAMP stimulated, rather than inhibited JNa(l-b). These results suggest that cAMP formation initially stimulates CCD Na+ transport, and that increased apical Na+ entry secondarily activates basolateral Ca++ entry. The cAMP-dependent [Ca++]i increase leads to inhibition Na+ transport in the rabbit CCD.

Binding Sites for Vasopressin in the Human Pituitary are Associated with Corticotrophs and may Differ from Other Known Vasopressin Receptors

Abstract In view of the fact that Vasopressin can induce pituitary adrenocorticotrophin release, we performed an autoradiographical study of [(3)H]arginine vasopressin binding in human pituitary tissue obtained post-mortem from adults and foetuses. Sites of specific, high affinity binding (IC(50) 3 to 5 nM) were detected as patches in the anterior lobe and at the junction between the anterior and neural lobes. The neural lobe was not labelled. Immunocytochemical studies performed on human pituitary tissue showed that [(3)H]arginine vasopressin only marked zones which correspond to areas rich in cells immunoreactive to adrenocorticotrophin. We conclude that in the human pituitary, corticotrophs bear vasopressin binding sites. Since non-radioactive synthetic structural analogues of vasopressin acting as V(1) and V(2) agonists or antagonists failed to compete for binding of radioligand in the human pituitary, while a V(1)-type agonist displaced [(3)H]arginine vasopressin binding in the rat pituitary, we postulate that binding sites in the human pituitary may differ from the previously known vasopressin receptors.

Diuretics modify [Arg8]vasopressin-stimulated cAMP but not atrial natriuretic peptide-stimulated cGMP formation in renal cells

The present study was undertaken to examine whether sulfonamide-derived diuretics affect [Arg8]vasopressin (AVP)-stimulated or atrial natriuretic peptide (ANP)-stimulated cyclic nucleotide formation in cells cultured from rat or dog kidney. In rat renal cells, all four sulfonamide-derived diuretics examined significantly suppressed 10(-9) M AVP-stimulated cAMP formation at concentrations of 10(-4) and 10(-3) M, while basal cAMP formation was unchanged by the diuretics. When cells were stimulated with 10(-7) M AVP, low ceiling diuretics (indapamide and trichlormethiazide) did not suppress cAMP formation, while high ceiling diuretics (furosemide and azosemide) significantly suppressed cAMP formation at concentrations of 10(-4) and 10(-3) M. The suppressive effect of the diuretics on AVP-stimulated cAMP formation in vitro paralleled the reported diuretic potency of the agents in vivo. In dog renal cells, all four diuretics significantly suppressed 10(-9) M AVP-stimulated cAMP formation at concentrations from 10(-6) to 10(-5) M, while these diuretics did not change basal cAMP levels. High ceiling diuretics suppressed 10(-7) M AVP-stimulated cAMP formation, whereas low ceiling diuretics did not. The difference in effective doses between rats and dogs seems to be consistent with the species difference observed in vivo. None of the diuretics affected basal levels of intracellular cGMP or ANP-stimulated cGMP formation in cultured rat renal cells. In addition to the inhibition of the Na/K/Cl co-transporter, it is suggested that most sulfonamide-derived diuretics act, at least in part, by inhibiting the actions of AVP.

Vasopressin receptors in human seminal vesicles: identification, pharmacologic characterization, and comparison with the vasopressin receptors present in the human kidney

Because of the presence of a high density of vasopressin receptors in the epithelial cells of porcine seminal vesicles similar to the V2 vasopressin receptors of renal tubules, human seminal vesicles and kidney were investigated using quantitative binding and adenylate cyclase studies. Tissues were obtained at surgery from 17 patients with urologic diseases. A homogeneous class of vasopressin binding sites have been found in both seminal vesicles and renal medulla. However, the vasopressin receptors present in these tissues are different in terms of ligand specificity and adenylate cyclase activation. In seminal vesicles, the V1 vasopressin antagonist d(CH2)5 TyrMeAVP is 36-fold, more potent than the V2 agonist dVDAVP in displacing [3H]AVP binding, while in the medullopapillary portion of kidney dVDAVP is 24-fold, more selective than d(CH2)5 TyrMeAVP for the arginine vasopressin binding site. Furthermore, arginine vasopressin induces a dose-dependent increase in adenylate cyclase activity in renal membranes, while it was ineffective in seminal vesicle membranes. These results indicate that a very high affinity (0.2 nM), low capacity (14 fmoles/mg protein) class of vasopressin receptors is present in human seminal vesicles, having pharmacologic characteristics similar to the V1 subtype of vasopressin receptors. The presence of a high affinity (1.6 nM), high capacity (350 fmoles/mg protein) V2 subtype of vasopressin receptors in human renal membranes is also confirmed. The density of the vasopressin receptors present in human seminal vesicles is inversely correlated with patient age, consistent with a physiologic role for vasopressin in the regulation of accessory sex gland activity.

[3H]AVP binding to rat renal tubular receptors during long-term treatment with an antagonist of arginine vasopressin

The interaction of an antagonist of arginine vasopressin (AVP), d(CH2)5-D-Tyr(Et)VAVP, with renal tubular V2 receptors were studied in medullary membrane preparations from kidneys of Sprague-Dawley and Brattleboro rats. In both rat strains, V2 receptors had comparable KD and Bmax values for binding of [3H]AVP. In vitro studies revealed that the V2-antagonist was more potent than cold AVP in displacing [3H]AVP. In vivo treatment of Sprague-Dawley rats with the antagonist over one week resulted only in a transient state of diabetes insipidus (DI). No specific [3H]AVP binding was detectable throughout the period of administration. Chronic treatment of Brattleboro rats resulted in a complete normalization of water intake. This agonistic effect was also associated with undetectable [3H]AVP binding. After stopping the infusion of d(CH2)5-D-Tyr(Et)VAVP, Bmax values tended to rise but had still not reached base line values after 6 days. In contrast, the chronic infusion of AVP in Brattleboro rats resulted in a reduction in water intake which was accompanied by a decreased Bmax. [3H]AVP binding remained detectable during the entire treatment period. Thereafter Bmax was restored to base line values within 2 days of stopping the infusion. These results suggest that d(CH2)5-D-Tyr(Et)VAVP has a high affinity for V2 receptors in both Sprague-Dawley and Brattleboro rats. Its rate of dissociation from the receptor appears to be much slower than that of AVP. In Brattleboro rats, the binding of d(CH2)5-D-Tyr(Et)VAVP leads to an antidiuretic response. In Sprague-Dawley rats, a transient diuretic response is followed by a progressive normalization in water intake. This occurs despite persistent and complete blockade of renal medullary V2 receptors.

Degradation of radiolabelled arginine vasopressin (125I-AVP) by the human placenta perfused in vitro

The capacity of the human placenta to degrade 125I-labelled arginine vasopressin (125I-AVP) was studied in vitro using a dual circuit perfused lobule preparation. Seven placentas were perfused with the perfusate on the maternal side of the lobule containing 125I-AVP at the upper limit of the physiological range. On average, over a 30-min period, 48% of the 125I-AVP appeared to have been metabolized. With one exception, a patient whose labour was augmented with intravenous oxytocin, no 125I-AVP apparently crossed the placental lobule to the fetal circulation. These data indicate that the human placenta has a considerable capacity to degrade AVP.

Localization and pharmacological characterization of high affinity binding sites for vasopressin and oxytocin in the rat brain by light microscopic autoradiography

Sites which bind tritiated vasopressin (AVP) with high affinity were detected in the brain of male, adult rats, by light microscopic autoradiography. Their anatomical localization differed markedly from that of high affinity binding sites for tritiated oxytocin (OT) determined in the same animal. Co-labelling was minimized by using low concentrations of [3H]AVP and [3H]OT. Binding of the former occurred predominantly in several structures of the limbic system (septum, amygdala, bed nucleus of the stria terminalis, accumbens nucleus), in two hypothalamic nuclei (suprachiasmatic and dorsal tuber) and in the area of the nucleus of the solitary tract. Binding of OT was evidenced in the olfactory tubercle, the ventromedial hypothalamic nucleus, the central amygdaloid nucleus and the ventral hippocampus. The ligand specificity of the binding sites was assessed in competition experiments. Synthetic structural analogues were used, allowing to discriminate OT receptors (OH[Thr4,Gly7]OT) from V2 receptors (dDAVP and d[Tyr(Me)2]VDAVP), V1 receptors ([Phe2,Orn8]VT) and V1b receptors (desGly9d(CH2)5AVP). Our main conclusions are, firstly, that AVP and OT binding sites can be readily distinguished, and that there is virtually no overlap in their distribution in the rat brain. Second, we showed that the sites which bind AVP with high affinity in the brain are V1 receptors, different both from the renal V2 receptors and from the anterior pituitary V1b receptors. Our results support the conjecture that AVP and OT play a role in interneuronal communication in the brain.

Vasopressin binds to microvessels from rat hippocampus

Recent evidence suggests that vasopressin may influence the permeability of the endothelium of brain capillaries. We measured the binding of [125I]arginine-8-vasopressin ([125I]AVP) to microvessels isolated from different regions of the rat brain. The study revealed saturable and specific binding of [125I]AVP to microvessels isolated from hippocampus. Scatchard analysis confirmed a single class of high affinity sites with an equilibrium dissociation constant, Kd, of 3.2 nM and an apparent maximal binding capacity of 205 fmol/mg protein. No binding was observed to microvessels from neocortex and striatum.

Regulation of (3H) arginine8 vasopressin binding to the rat renal medulla by guanine nucleotides

In rat renal medullary membranes, we have examined modulatory effects of guanine nucleotides on binding of arginine8 vasopressin (AVP) to its receptor. Equilibrium binding studies analyzed by an iterative curve fitting program revealed an interaction of (3H) AVP with a single class of binding sites with a dissociation constant of 1.4 +/- 0.2 nM and a binding site concentration of 201 +/- 37 fmol/mg protein (n = 6). With the addition of 100 microM guanylyl-imidodiphosphate (Gpp(NH)p), the binding site concentration was significantly (p less than 0.01) reduced to 151 +/- 36 fmol/mg protein with no change in receptor affinity. The nonhydrolyzable analogues, guanosine-5'-0-(3-thiophosphate) and Gpp(NH)p were the most potent inhibitors of (3H) AVP binding. Guanosine 5'-triphosphate and guanosine-5'-diphosphate were both relatively poor inhibitors. Guanosine-5'-monophosphate and adenosine 5'-triphosphate did not inhibit (3H) AVP binding at concentrations up to 100 microM. Furthermore, 100 microM Gpp(NH)p accelerated the dissociation of (3H) AVP from the receptor. We conclude that guanine nucleotides are important modulators of AVP binding to the V2 receptor subtype in the renal medulla.

Effects of vasopressin antagonist on vasopressin binding, adenylate cyclase activation, and water flux

We studied the effect of an arginine vasopressin (AVP) analogue, (1-[beta-mercapto-beta, beta-cyclopentamethylenepropionic acid],2-O-ethyltyrosine, 4-valine)AVP(d[CH2]5Tyr[Et]VAVP), on the stimulation of adenylate cyclase by various hormones in the isolated nephron segments and 3H-AVP binding to renal papillary membranes from the rat. The net water flux across the renal cortical collecting tubules of the rabbit was also examined. We found that d(CH2)5Tyr(Et)VAVP significantly inhibited adenylate cyclase activation by AVP in cortical, medullary, and papillary collecting tubules and in the medullary thick ascending limb. In contrast, the AVP analogue did not alter the stimulation of adenylate cyclase by parathyroid hormone in the cortical thick ascending limb, by glucagon in the medullary thick ascending limb, and by calcitonin in cortical collecting tubules. In addition, d(CH2)5Tyr(Et)VAVP blocked [3H]AVP binding to renal papillary membranes. The enhanced net water transport induced by AVP in isolated, perfused rabbit cortical collecting tubules also was completely blocked by this AVP analogue. These results indicate that d(CH2)5Tyr(Et)VAVP specifically antagonizes the cellular action of AVP on the medullary thick ascending limb and on the cortical, medullary, and papillary collecting tubules. Evidence is also presented for competitive antagonism as the cellular mechanism of action.

Strategies in neuropeptide receptor binding research

Strategies and general approaches used in neuropeptide receptor binding assays are described. Special attention is given to the nature of the ligand, its physical and chemical stability and the demonstration of an appropriate ligand selectivity pattern. Examples are given to illustrate critical aspects of neuropeptide receptor binding assays. Strong correlation between binding and bioassay data is also stressed.

Vasopressin inhibits cyclic AMP accumulation and adenylate cyclase activity in cerebral preparations

Arginine-vasopressin (AVP) and lysine vasopressin (LVP) elicited a dose-dependent inhibition of noradrenaline-sensitive cyclic AMP accumulation in rat cerebral cortical slices, and of forskolin-stimulated adenylate cyclase activity in a rat cerebral cortical membrane preparation. In both cases LVP was more potent than AVP, and exerted half-maximal effects at concentrations similar to those found effective in binding studies on rat hippocampal membranes. In hippocampal slices, AVP did not affect cyclic AMP accumulation at low concentrations but potentiated the effect of noradrenaline at higher concentrations. In caudate membranes, AVP inhibited dopamine-stimulated adenylate cyclase with a similar dose-dependency to that seen for forskolin activation in cortex membranes.

Effects of vasopressin on noradrenaline-induced cyclic AMP accumulation in rat brain slices

Addition of arginine vasopressin (AVP) or 1-desamino-8-D-arginine vasopressin (DDAVP) to rat cortical slices resulted in significant inhibition of the rise in cyclic AMP produced by incubation with 50 microM noradrenaline. A single injection of DDAVP (20 micrograms/rat) produced a reduced response to noradrenaline in derived cortex and caudate slices. In animals pretreated at day 5 of life with IP desipramine and intracisternal 6-hydroxydopamine (6-OHDA), both acute and chronic treatments with DDAVP resulted in a reduction in response in derived cortical, caudate and hippocampal slices. The 6-OHDA pretreated animals also showed reduced open-field behavioural activity after both acute and chronic DDAVP, while animals which were not pretreated responded to acute treatment only. The relationship between the effects of vasopressin on noradrenaline-induced cyclic AMP accumulation and its action on learning and memory is discussed.

[1,6-alpha-aminosuberic acid,3-(p-azidophenylalanine), 8-arginine] vasopressin as a photoaffinity label for renal vasopressin receptors: an evaluation

The photoreactive analog of vasopressin [1,6-alpha-aminosuberic acid,3-(p-azidophenylalanine), 8-arginine]vasopressin was labeled with tritium (specific radioactivity: 39 Ci/mmole). In the absence of UV-light, the tritium-labeled ligand retained a high binding affinity to the vasopressin receptor in plasma membranes from bovine kidney inner medulla (apparent dissociation constant KD: 1.4 X 10(-8) M). Renal plasma membranes were irradiated under conditions of a high ratio of specific versus non-specific binding of the reactive ligand. Sodium dodecyl sulfate gel electrophoresis after solubilization and reduction demonstrated the preferential labeling of a polypeptide with an apparent molecular weight of Mr = 32 000. A comparison with stained gels revealed that this protein is a minor constituent of the bovine kidney membrane. Our results suggest the 32 000-dalton polypeptide is either a component of the vasopressin receptor or that it is located in the immediate vicinity of the vasopressin binding protein.

Plasma antidiuretic hormone levels and liver vasopressin receptors in the jerboa, Jaculus orientalis, and rat

V1 vasopressin, angiotensin, alpha-adrenergic, and glucagon receptors in liver were studied on membrane fractions prepared from two groups of jerboas ( Jaculus orientalis) given dry or water-enriched diets for periods of 4 to 7 weeks, and from rats acutely treated with pharmacological amounts of arginine-vasopressin (AVP) or (1-deamino-8-D-arginine)-vasopressin (dDAVP). Tritiated (8-lysine)-vasopressin ([3H]vasopressin), tritiated (1-asparagine-5-valine)-angiotensin II ([3H]angiotensin II), tritiated dihydroergocryptine ([3H] DHEC ), and iodinated glucagon ([125I]-glucagon) were used as specific labeled ligands of these receptors. The V1 vasopressin, angiotensin, alpha-adrenergic, and glucagon receptors detected in both groups of jerboas were identical to receptors found in rat liver plasma membranes in regard to the apparent dissociation constants for their respective labeled ligands. Furthermore, vasopressin receptors in jerboa liver membranes discriminated as efficiently as rat liver receptors between the natural neurohypophyseal peptides arginine-vasopressin and lysine-vasopressin on the one hand and the structural analogs (1-deamino-8-D-arginine)-vasopressin and (4-valine-8-D-arginine)-vasopressin on the other. The reduction of antidiuretic hormone (ADH) secretion in jerboas fed a water-enriched diet compared to those on a dry diet (75 +/- 25 pM versus 372 +/- 86 pM) was accompanied by an increase in the number of liver vasopressin receptors (2.79 +/- 0.53 versus 1.25 +/- 0.14 pmol [3H]vasopressin bound/mg protein). The modifications observed were specific for vasopressin receptors, as judged by the maximal binding capacities of [3H]angiotensin II, [3H] DHEC , and [125I]-glucagon, which remained unchanged in jerboas whatever the levels of endogenous circulating ADH. Similarly, administration of pharmacological doses of AVP by iv infusion to rats induced, 2 hr later, a loss of about 50% of V1 liver vasopressin receptors, while the numbers and apparent dissociation constants of angiotensin, alpha-adrenergic, and glucagon liver receptors remained unchanged, and V2 kidney vasopressin receptors were almost desensitized. For V1 liver and V2 kidney vasopressin receptors, the desensitization process was strikingly dependent on the antidiuretic/glycogenolytic activity ratio of the peptide used. Thus, im injection to rats of dDAVP (an analog possessing a very high antidiuretic/glycogenolytic activity ratio) induced, 1 hr later, a total loss of V2 kidney receptors without modification of the number and apparent dissociation constant of V1 liver receptors.