Molecular pharmacology and modeling of vasopressin receptors.

AVP receptors represent a logical target for drug development. As a new class of therapeutic agents, orally active AVP analogs could be used to treat several human pathophysiological conditions including neurogenic diabetes insipidus, the syndrome of inappropriate secretion of AVP (SIADH), congestive heart failure, arterial hypertension, liver cirrhosis, nephrotic syndrome, dysmenorrhea, and ocular hypertension. By immunoprecipitation and immunoblotting, we elucidated the phosphorylation pattern of green fluorescent protein-tagged AVP receptors and showed interactions with the specific kinases PKC and GRK5 that are agonist-, time- and receptor subtype-dependent. The tyrosine residue of the NPWIY motif present in the 7th helix of AVP receptors is rapidly and transiently phosphorylated after agonist stimulation. This phosphorylation is instrumental in the genesis of the mitogenic cascade linked to the activation of this receptor, presumably by establishing key intramolecular contacts and by participating in the creation of a scaffold of proteins that produce the activation of downstream kinases. The random screening of chemical entities and optimization of lead compounds recently resulted in the development of orally active non-peptide AVP receptor agonists and antagonists. Furthermore, the identification of the molecular determinants of receptor-ligand interactions should facilitate the development of more potent and very selective orally active compounds via the approach of structure-based drug design. We developed three-dimensional molecular docking models of peptide and non-peptide ligands to the human V1 vascular, V2 renal and V3 pituitary AVP receptors. Docking of the peptide hormone AVP to the receptor ligand binding pockets reflects its dual polar and non-polar structure, but is receptor subtype-specific. The characteristics of non-peptide AVP analogs docking to the receptors are clearly distinct from those of peptide analogs docking. Molecular modeling of the results of site-directed mutagenesis experiments performed in CHO cells stably transfected with the human AVP receptor subtypes revealed that non-peptide antagonists establish key contacts with a few amino acid residues of the receptor subtypes that are different from those involved in agonist binding. Moreover, these interactions are species-specific. These findings provide further understanding of the signal transduction pathways of AVP receptors and new leads for elucidation of drug-receptor interactions and optimization of drug design. NOTE TO THE READER: The recent cloning and molecular characterization of AVP/OT receptor subtypes call for the revision of their nomenclature. For the sake of clarity and reference to their main site of expression, we call the V1a receptor the V1 vascular receptor, the V2 receptor the V2 renal receptor and the V1b or V3 receptor the V3 pituitary receptor in the present review.

Role of the human V1 vasopressin receptor COOH terminus in internalization and mitogenic signal transduction.

We studied the role played by the intracellular COOH-terminal region of the human arginine vasopressin (AVP) V1-vascular receptor (V1R) in ligand binding, trafficking, and mitogenic signal transduction in Chinese hamster ovary cells stably transfected with the human AVP receptor cDNA clones that we had isolated previously. Truncations, mutations, or chimeric alterations of the V1R COOH terminus did not alter ligand binding, but agonist-induced V1R internalization and recycling were reduced in the absence of the proximal region of the V(1)R COOH terminus. Coupling to phospholipase C was altered as a function of the COOH-terminal length. Deletion of the proximal portion of the V1R COOH terminus or its replacement by the V2-renal receptor COOH terminus prevented AVP stimulation of DNA synthesis and progression through the cell cycle. Mutation of a kinase consensus motif in the proximal region of the V1R COOH terminus also abolished the mitogenic response. Thus the V1R cytoplasmic COOH terminus is not involved in ligand specificity but is instrumental in receptor trafficking and facilitates the interaction between the intracellular loops of the receptor, G protein, and phospholipase C. It is absolutely required for transmission of the mitogenic action of AVP, probably via a specific kinase phosphorylation site.

Development and therapeutic indications of orally-active non-peptide vasopressin receptor antagonists.

Vasopressin (AVP) is a cyclic nonapeptide hormone that exhibits many physiological effects including free water reabsorption, vasoconstriction, cellular proliferation and adrenocorticotrophic hormone (ACTH) secretion. In a healthy organism, AVP plays an important role in the homeostasis of fluid osmolality and volume status. However, in several diseases or conditions such as the syndrome of inappropriate secretion of AVP (SIADH), congestive heart failure, arterial hypertension, liver cirrhosis, nephrotic syndrome, dysmenorrhoea and ocular hypertension, AVP may play an important role in their pathophysiology. Recently, orally-active non-peptide AVP receptor antagonists were developed by random screening of chemical entities and optimisation of lead compounds. These include agents specific for the V(1)-vascular and V(2)-renal AVP receptor subtypes. Dual V(1)/V(2) AVP receptor antagonists are also being studied. Some of these non-peptide receptor antagonists have been studied extensively, while others are currently under investigation. Potential therapeutic indications for AVP receptor antagonists comprise: 1) The blockade of V(1)-vascular AVP receptors in arterial hypertension, congestive heart failure, Raynaud's syndrome, peripheral vascular disease and dysmenorrhea. 2) The blockade of V(2)-renal AVP receptors in the syndrome of inappropriate secretion of vasopressin, congestive hart failure, liver cirrhosis, nephrotic syndrome and any state of excessive retention of free water and subsequent dilutional hyponatraemia. 3) The blockade of V(3)-pituitary AVP receptors in ACTH-secreting tumours. This review examines the pharmacology of orally-active non-peptide AVP receptor antagonists and their clinical applications.

The basic and clinical pharmacology of nonpeptide vasopressin receptor antagonists.

The neurohypophysial hormone arginine vasopressin (AVP) is a cyclic nonpeptide whose actions are mediated by the stimulation of specific G protein--coupled membrane receptors pharmacologically classified into V1-vascular (V1R), V2-renal (V2R) and V3-pituitary (V3R) AVP receptor subtypes. The random screening of chemical compounds and optimization of lead compounds recently resulted in the development of orally active nonpeptide AVP receptor antagonists. Potential therapeutic uses of AVP receptor antagonists include (a) the blockade of V1-vascular AVP receptors in arterial hypertension, congestive heart failure, and peripheral vascular disease; (b) the blockade of V2-renal AVP receptors in the syndrome of inappropriate vasopressin secretion, congestive heart failure, liver cirrhosis, nephrotic syndrome and any state of excessive retention of free water and subsequent dilutional hyponatremia; (c) the blockade of V3-pituitary AVP receptors in adrenocorticotropin-secreting tumors. The pharmacological and clinical profile of orally active nonpeptide vasopressin receptor antagonists is reviewed here.

Mediators of the mitogenic action of human V(1) vascular vasopressin receptors.

Arginine vasopressin (AVP) activation of V(1) vascular receptors (V(1)Rs) stimulates cell growth and proliferation in different tissues via cellular signaling pathways that remain to be identified. To explore the intracellular mediators of the mitogenic action of V(1)R, Chinese hamster ovary (CHO) cells were stably transfected with the human V(1)R cDNA clone we isolated previously. We assessed AVP effects on kinase activation (immunoblotting with phosphospecific antibodies), DNA synthesis (tritiated thymidine uptake), cell cycle progression (flow cytometry analysis after nuclear labeling with propidium iodide), and cell proliferation (conversion of the colorimetric reagent MTS) in the presence or absence of various pathway inhibitors. AVP stimulation of V(1)Rs leads to the phosphorylation of several kinases, an increase in DNA synthesis, a progression through the S and G(2)-M phases of the cell cycle, and an increase in cell proliferation. The mediators of the mitogenic action of V(1)R activation included calcium mobilization, coupling to a G(q) protein, and the simultaneous and parallel activation of several kinases, mainly calcium/calmodulin-dependent kinase II, phosphatidylinositol 3 kinase, protein kinase C, and p42/p44 mitogen-activated protein kinase.

Dynamic interaction of human vasopressin/oxytocin receptor subtypes with G protein-coupled receptor kinases and protein kinase C after agonist stimulation.

Examination of the structure of [Arg(8)]-vasopressin receptors (AVPRs) and oxytocin receptors (OTRs) suggests that G protein-coupled receptor kinases (GRKs) and protein kinase C (PKC) are involved in their signal transduction. To explore the physical association of AVPRs and OTRs with GRKs and PKC, wild types and mutated forms of these receptor subtypes were stably expressed as green fluorescent protein fusion proteins and analyzed by fluorescence, immunoprecipitation, and immunoblotting. Addition of a C-terminal GFP tag did not interfere with ligand binding, internalization, and signal transduction. After agonist stimulation, PKC dissociated from the V(1)R, did not associate with the V(2)R, but associated with the V(3)R and the OTR. After AVP stimulation, only GRK5 briefly associated with AVPRs following a time course that varied with the receptor subtype. No GRK associated with the OTR. Exchanging the V(1)R and V(2)R C termini altered the time course of PKC and GRK5 association. Deletion of the V(1)R C terminus resulted in no PKC association and a ligand-independent sustained association of GRK5 with the receptor. Deletion of the GRK motif prevented association and reduced receptor phosphorylation. Thus, agonist stimulation of AVP/OT receptors leads to receptor subtype-specific interactions with GRK and PKC through specific motifs present in the C termini of the receptors.

A molecular model of agonist and nonpeptide antagonist binding to the human V(1) vascular vasopressin receptor.

The affinity of the nonpeptide antagonist OPC-21268 is greater for the rat V(1) arginine vasopressin (AVP) receptor (V(1)R) than for the human V(1)R. Site-specific mutagenesis was carried out to identify the residues that determine interspecies selectivity for nonpeptide antagonist binding. The introduction of rat amino acids in position 224, 310, 324, or 337 of the human V(1)R sequence dramatically altered OPC-21268 affinity for the receptor, whereas binding of AVP, the peptide V(1)R antagonist d(CH(2))(5)Tyr(Me)AVP, and the nonpeptide V(1)R antagonist SR49059 was not altered by these mutations. Computer modeling explained the mutagenesis results. Docking of OPC-21268 onto a homology-built model of the V(1)R receptor yielded a model for the bound ligand in which the hydrophobic part is deeply embedded in the transmembrane region, whereas the polar part is located on the surface of the extracellular side. The increased affinity of the G337A mutant is due to two additional van der Waals contacts of the alanine methyl group with carbon atoms on the antagonist. The I310V mutant reduces the hydrophobicity in the vicinity of the polar oxygen atom of the antagonist. The I224V mutant relieves overcrowding in a hydrophobic binding pocket involving the aromatic residues Trp(175), Phe(179), Phe(307), and Trp(304). Finally, the E324D mutant enables the formation of a hydrogen bond of the carboxylate side chain with the amide side chain of Gln(311), which in turn forms a hydrogen bond with the N57 nitrogen atom of OPC-21268. Thus, a few residues, distinct from those involved in agonist binding, control interspecies selectivity toward OPC-21268 nonpeptide antagonist binding.

Study of V(1)-vascular vasopressin receptor gene microsatellite polymorphisms in human essential hypertension.

Vasopressin (AVP) actions on vascular tone and blood pressure are mainly mediated by the V(1)-vascular receptor (V(1)R). We recently reported the structure and functional expression of the human V(1)R cDNA and described the genomic characteristics, tissue expression, chromosomal localization, and regional mapping of the human V(1)R gene, AVPR1A. To test whether the V(1)R is a marker for human essential hypertension, we sequenced the human AVPR1A gene and its 5; upstream region and found several DNA microsatellite motifs. One (GT)(14)-(GA)(13)-(A)(8)microsatellite is located 2983 bp downstream of the transcription start site, within a 2.2 kbp intron interrupting the coding sequence of the receptor. Three other microsatellites are present in the 5; flanking DNA of the AVPR1A gene: a (GT)(25)dinucleotide repeat, a complex (CT)(4)-TT-(CT)(8)-(GT)(24)motif and a (GATA)(14)tetranucleotide repeat located respectively 3956 bp, 3625 bp and 553 bp upstream of the transcription start site. Analysis of these polymorphisms in 79 hypertensive and 86 normotensive subjects for the (GT)(14)-(GA)(13)-(A)(8)and the (GT)(25)motifs revealed a high percentage of heterozygosity but no difference in alleles frequencies between the two groups. A linkage study using the affected sib pair method and the (GT)(25)repeat in 446 hypertensive sib pairs from 282 French Caucasian pedigrees showed no excess of alleles sharing at the AVPR1A locus. No linkage was found in the subgroups of patients with early onset hypertension (diagnosis before age 40) or severe hypertension (diastolic blood pressure >/=100 mmHg or requirement for >/=two medications). These findings suggest that molecular variants of the V(1)R gene are not involved in unselected forms of essential hypertension.

Effects of the nonpeptide V(1) vasopressin receptor antagonist SR49059 in hypertensive patients.

We assessed the clinical and pharmacological profile of the orally active V(1) vascular vasopressin (AVP) receptor nonpeptide antagonist SR49059 (SR) during the osmotic stimulation of AVP release in hypertensive patients. In a double-blind crossover-versus-placebo study, 24 untreated stage I or II essential hypertensive patients (12 whites and 12 blacks) received a single 300 mg oral dose of SR 2 hours before the stimulation of AVP secretion with a 5% hypertonic saline infusion. Hemodynamic, humoral, and hormonal parameters were monitored for up to 28 hours after drug administration. SR did not alter blood pressure or heart rate before the saline infusion and did not reduce the blood pressure increment induced by the hypertonic saline infusion. However, the blood pressure peak at the end of the hypertonic saline infusion was slightly lower in the presence of SR (P=0.04). Heart rate was significantly faster between 4 and 6 hours after SR administration (P=0.02). The rise in plasma sodium and osmolality triggered by the saline infusion was not modified by SR, but AVP release was slightly greater in the presence of SR (P<0.0003). AVP-induced aggregation of blood platelets in vitro was significantly reduced by SR, with a peak effect 2 hours after drug administration that coincided with the SR peak plasma concentration. Plasma renin activity and aldosterone before and after the saline infusion were not modified by SR. Urine volume and osmolality were not altered by SR administration. SR effects were similar in the 2 ethnic groups as well as in salt-sensitive versus salt-resistant patients. In a situation of AVP osmotic release and volume expansion in hypertensive patients, a single oral dose of the V(1) vascular AVP receptor nonpeptide antagonist SR49059, which is able to block AVP-induced platelet aggregation, exerts a transient vasodilation effect that is not associated with a sustained blood pressure reduction. SR49059 is a pure V(1) vascular receptor antagonist that is devoid of V(2) renal receptor actions.

Human vascular endothelial cells express oxytocin receptors.

Pharmacological studies in humans and animals suggest the existence of vascular endothelial vasopressin (AVP)/oxytocin (OT) receptors that mediate a vasodilatory effect. However, the nature of the receptor subtype(s) involved in this vasodilatory response remains controversial, and its coupled intracellular pathways are unknown. Thus, we set out to determine the type and signaling pathways of the AVP/OT receptor(s) expressed in human vascular endothelial cells (ECs). Saturation binding experiments with purified membranes of primary cultures of ECs from human umbilical vein (HUVEC), aorta (HAEC), and pulmonary artery (HPAEC) and [3H]AVP or [3H]OT revealed the existence of specific binding sites with a greater affinity for OT than AVP (Kd = 1.75 vs. 16.58 nM). Competition binding experiments in intact HUVECs (ECV304 cell line) with the AVP antagonist [125I]4-hydroxyphenacetyl-D-Tyr(Me)-Phe-Gln-Asn-Arg-Pro-Arg-NH2 or the OT antagonist [125I]D(CH2)5[O-Me-Tyr-Thr-Orn-Tyr-NH2]vasotocin, and various AVP/OT analogs confirmed the existence of a single class of surface receptors of the classical OT subtype. RT-PCR experiments with total RNA extracted from HUVEC, HAEC, and HPAEC and specific primers for the human V1 vascular, V2 renal, V3 pituitary, and OT receptors amplified the OT receptor sequence only. No new receptor subtype could be amplified when using degenerate primers. DNA sequencing of the coding region of the human EC OT receptor revealed a nucleotide sequence 100% homologous to that of the uterine OT receptor reported previously. Stimulation of ECs by OT produced mobilization of intracellular calcium and the release of nitric oxide that was prevented by chelation of extra- and intracellular calcium. No stimulation of cAMP or PG production was noted. Finally, OT stimulation of ECs led to a calcium- and protein kinase C-dependent cellular proliferation response. Thus, human vascular ECs express OT receptors that are structurally identical to the uterine and mammary OT receptors. These endothelial OT receptors produce a calcium-dependent vasodilatory response via stimulation of the nitric oxide pathway and have a trophic action.

Signal transduction pathways of the human V1-vascular, V2-renal, V3-pituitary vasopressin and oxytocin receptors.

Vasopressin (VP) and oxytocin (OT) are cyclic nonapeptides whose actions are mediated by stimulation of specific G protein-coupled receptors (GPCRs) currently classified into V1-vascular (V1R), V2-renal (V2R) and V3-pituitary (V3R) VP receptors and OT receptors (OTR). The recent cloning of the different members of the VP/OT family of receptors now allows the extensive characterization of the molecular determinants involved in ligand binding and signal transduction pathways coupled to a given VP/OT receptor subtype in stably transfected mammalian cell lines. In this article, we review the present knowledge of the signal transduction pathways coupled to the different VP/OT receptor subtypes and we present new observations derived from the study of each human VP or OT receptor subtype stably expressed in CHO cells.

Molecular pharmacology of human vasopressin receptors.

Vasopressin (AVP) and oxytocin (OT) are cyclic nonapeptides whose actions are mediated by activation of specific G protein-coupled receptors (GPCRs) currently classified into V1-vascular (V1R), V2-renal (V2R) and V3-pituitary (V3R) AVP receptors and OT receptors (OTR). The cloning of the different members of the AVP/OT family of receptors now allows the extensive molecular pharmacological characterization of a single AVP/OT receptor subtype in stably transfected mammalian cell lines. The human V1-vascular (CHO-V1), V2-renal (CHO-V2), V3-pituitary (CHO-V3) and oxytocin (CHO-OT) receptors stably expressed in CHO cells display distinct binding profiles for 18 peptide and 5 nonpeptide AVP/OT analogs. Several peptide and nonpeptide compounds have a greater affinity for the V1R than AVP itself. V2R peptide agonists and antagonists tend to be non-selective ligands whereas nonpeptide V2R antagonists are potent and subtype-selective. None of the 22 AVP/OT analogs tested has a better affinity for the human V3R than AVP itself. Several peptide antagonists do not select well between V1R and OTR. These results underscore the need for developing specific and potent analogs interacting specifically with a given human AVP/OT receptor subtype.

Development and therapeutic indications of orally-active non-peptide vasopressin receptor antagonists.

Vasopressin (AVP) and oxytocin (OT) are cyclic nonapeptides whose actions are mediated by the stimulation of specific G-protein-coupled receptors (GPCRs) currently classified into V(1)-vascular (V(1)R), V(2)-renal (V(2)R) and V(3)-pituitary (V(3)R) AVP receptors and OT receptors (OTR). The signal transduction pathways coupled to the different subtypes of AVP/OT receptors are reviewed. The recent cloning of the different members of the AVP/OT family of receptors now allows the extensive characterisation of the molecular determinants involved in agonist and antagonist binding, as well as signal transduction coupling. Potential therapeutic uses of AVP receptor antagonists include: the blockade of V(1)-vascular AVP receptors in arterial hypertension, congestive heart failure (CHF) and peripheral vascular diseases; the blockade of V(2)-renal AVP receptors in the syndrome of inappropriate vasopressin secretion, CHF, liver cirrhosis, nephrotic syndrome and any state of excessive retention of free water and subsequent hyponatraemia; the blockade of V(3)-pituitary AVP receptors in adrenocorticotropin (ACTH)-secreting tumours. The pharmacological and clinical profile of orally-active non-peptide AVP receptor antagonists is reviewed.

The human V3 pituitary vasopressin receptor: ligand binding profile and density-dependent signaling pathways.

The vasopressin (AVP) V3 pituitary receptor (V3R) is a G protein-coupled corticotropic phenotypic marker that is overexpressed in ACTH-hypersecreting tumors. Studies of the agonist/antagonist binding profile and signal transduction pathways linked to the human V3R have been limited because of the scarcity of this protein. To define the signals activated by V3Rs and the eventual changes triggered by developmental or pathological receptor regulation, we developed Chinese hamster ovary (CHO)-V3 cells stably expressing low, medium, or high levels of human V3Rs (binding capacity, <10, 10-25, and 25-100 pmol/mg, respectively). The affinity of the V3R for 21 peptide and nonpeptide AVP analogs was clearly distinct from that exhibited by the human V1R and V2R. AVP triggered stimulation of phospholipase C in CHO-V3 cells (partially sensitive to treatment with pertussis toxin) with a potency directly proportional to receptor density. V3R-mediated arachidonic acid release also was also sensitive to pertussis toxin and more efficacious in cells exhibiting medium than in those with high receptor density. AVP also stimulated the pertussis toxin-insensitive uptake of [3H]thymidine in CHO-V3 cells. The concentration-response curves for this effect were monophasic in cells expressing low and medium levels of V3Rs; on the contrary, a biphasic curve was observed in cells with high V3R density. Coupling of V3R to increased production of cAMP was only observed in CHOV3 high cells, suggesting a negative relationship between increased cAMP production and DNA synthesis. Activation of mitogen-activated protein kinases by V3R was pertussis toxin insensitive, but was dependent on activation of phospholipase C and protein kinase C; both the level and duration of activation were a function of the receptor density. Thus, the human V3R has a pharmacological profile clearly distinct from that of the human V1R and V2R and activates several signaling pathways via different G proteins, depending on the level of receptor expression. The increased synthesis of DNA and cAMP levels observed in cells expressing medium and high levels of V3Rs, respectively, may represent important events in the tumorigenesis of corticotroph cells.

Structure, sequence, expression, and chromosomal localization of the human V1a vasopressin receptor gene.

We recently reported the structure and functional expression of a human V1a vasopressin receptor (V1aR) cDNA isolated from human liver cDNA libraries. To understand further the expression and regulation of the V1aR, we now describe the genomic characteristics, tissue expression, chromosomal localization, and regional mapping of the human V1aR gene, AVPR1A. Tissue distribution of the human V1aR mRNA explored by Northern blot analysis of various human tissues or organs revealed the presence of a 5.5-kb mRNA transcript expressed in the liver and to a lesser degree in the heart, the kidney, and skeletal muscle. Screening of human genomic libraries revealed that the human AVPR1A gene is included entirely within a 6.4-kb EcoRI fragment and comprises two coding exons separated by a 2.2-kb intron located before the corresponding seventh transmembrane domain of the receptor sequence. The first exon also contains 2 kb of 5'-untranslated region, and the second exon includes 1 kb of 3'-untranslated region. 5'-RACE analysis of human liver mRNA by PCR localized the V1aR mRNA transcription start site 1973 bp upstream of the translation initiation site. Specific oligonucleotides derived from the intron sequence were used as primers in polymerase chain reaction (PCR) analysis of human/rodent somatic cell hybrids. AVPR1A was localized by PCR analysis of a somatic cell hybrid panel to chromosome 12. Fluorescence in situ hybridization using a yeast artificial chromosome physically mapped AVPR1A to region 12q14-q15.

Essential hypertension: racial/ethnic differences in pathophysiology.

Essential hypertension is a complex polygenetic disorder with different "intermediate phenotypes" among diverse racial/ethnic groups. Differences have been identified in the renin-angiotensin system, prevalence of salt sensitivity, ion-transport mechanisms, and calcium homeostasis, yet no unifying hypothesis as to the genetic mechanisms responsible for the excess prevalence and severity of hypertension among African Americans has emerged. Environmental factors, such as access to health care, socioeconomic status, stress, diet, and obesity, account for some of the differences in the prevalence of hypertension worldwide.

The genetics of hypertension.

In the past few years, a number of key insights have been made concerning the genetic basis of hypertension and blood pressure regulation. The genes responsible for two Mendelian forms of hypertension, glucocorticoid-remediable aldosteronism and Liddle's syndrome, were identified. In addition, research into the role of the renin-angiotensin system in blood pressure regulation has further implicated the angiotensinogen and angiotensin-converting enzyme loci in hypertension and its complications, such as myocardial infarction. Finally, several new candidate genes for hypertension have been identified through the use of genome scanning and contemporary gene expression assays in model organisms.

Cloning and characterization of the human V3 pituitary vasopressin receptor.

Arginine-vasopressin (AVP) plays a determinant role in the normal ACTH response to stress in mammals. We cloned a human cDNA coding a 424 amino acid G-protein coupled receptor structurally related to the vasopressin/oxytocin receptor family. When expressed in COS cells, this receptor binds AVP with a high affinity (Kd = 0.55 +/- 0.13 nM) and is functionally coupled to phospholipase C. Competition studies with peptidic or non peptidic AVP analogues reveal that it is pharmacologically distinct from V1a and V2 AVP receptors and therefore it is designated V3. RT-PCR analysis shows that the human V3 receptor is expressed in normal pituitary and also in kidney, but is undetectable in liver, myometrium and adrenal gland. Northern blot analysis reveals a approximately 4.8 kb messenger in human corticotropic pituitary adenomas.

[G-proteins coupled receptors]. / Les récepteurs couplés aux protéines G.

The superfamily of G protein-coupled receptors plays a major role in the transmission and amplification of extracellular stimuli. These membrane receptors have a common structure made of a single polypeptide chain including seven transmembrane spanning domains. The comparison of amino acid sequences of the various G protein-coupled receptors reveals several conserved amino acids and regions playing a key role in ligand binding, G protein coupling, and activation of intracellular second messengers. Mutations of amino acid sequences of seven transmembrane domain receptors and their coupled G proteins are responsible for various human diseases including certain kinds of cancer.

[Congenital nephrogenic diabetes insipidus]. / Diabète insipide néphrogénique congénital.

Congenital nephrogenic diabetes insipidus is a rare hereditary disease characterized by a renal insensitivity to circulating vasopressin. Genetic linkage studies have demonstrated that the gene responsible for congenital nephrogenic diabetes insipidus is located in region 28 of the X chromosome long arm. That the gene coding for the vasopressin V2 receptor is also located in the q28-qter of chromosome X suggests that the signalisation defect in congenital nephrogenic diabetes insipidus is at the level of the receptor itself. Indeed, congenital nephrogenic diabetes insipidus is a genetically heterogeneous disease since several point mutations in the vasopressin V2 receptor gene nucleotide sequence have been observed in different families of afflicted patients. Moreover, the observation that one of these mutations leads to a lack of cyclic AMP production in response to vasopressin confirms that mutations of the vasopressin V2 receptor sequence are the molecular defects responsible for congenital nephrogenic diabetes insipidus.