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Inhibition of vasopressin-stimulated prostaglandin E biosynthesis by chlorpropamide in the toad urinary bladder. Mechanism of enhancement of vasopressin-stimulated water flow.

Chlorpropamide is known to enhance the water permeability response of the toad urinary bladder to vasopressin and to theophylline. In other studies, we have shown that prostaglandin E synthesis by the toad bladder inhibits the water permeability response to arginine vasopressin and to theophylline. In this study, the effect of chlorpropamide on vasopressin-, theophylline-, and cyclic AMP-stimulated water flow and on prostaglandin E biosynthesis was investigated in the toad urinary bladder in vitro. Chlorpropamide inhibited prostaglandin E biosynthesis during vasopressin-, theophylline- and cyclic AMP-stimulated water flow. Tolbutamide and glyburide, two other sulfonylurea compounds, also enhanced vasopressin-stimulated water flow and inhibited vasopressin-stimulated prostaglandin E biosynthesis. We conclude that the mechanism of enhancement on vasopressin-stimulated water flow by the sulfonylureas is the inhibition of prostaglandin E biosynthesis.

Animals↗

A vasopressin analog that binds but does not activate V1 or V2 vasopressin receptors is not internalized into cells that express V1 or V2 receptors.

To assess whether receptor binding is sufficient to initiate vasopressin receptor endocytosis in cells expressing the vasopressin V1 or V2 receptors, we synthesized a novel fluorescent-labeled vasopressin analog, [1-(beta-mercapto-beta, beta-cyclopentamethylene propionic acid), 2-(O-ethyl)-D-tyrosine, 4-valine, 8-lysine-N6-carboxytetramethylrhodamine] vasopressin (R-CLVP), that binds to vasopressin receptors but does not activate intracellular events such as the mobilization of intracellular calcium or the activation of adenylate cyclase. We compared the manner in which this analog was endocytosed in cells expressing V1 (A-10, rat smooth muscle cells) or V2 (LLC-PK1, porcine kidney cells) receptors with that of a full agonist, [1-(beta-mercaptopropionic acid), 8-lysine-N6-carboxytetramethylrhodamine] vasopressin (R-MLVP) [Lutz et al. (1990) J. Biol. Chem. 265, 4657-4663; Lutz et al. (1990) Proc. Natl. Acad. Sci. U.S.A. 87,6507-6511]. We showed that R-CLVP bound to both types of receptors with good affinity. It failed to increase cyclic AMP concentrations in LLC-PK1 cells and did not increase the mobilization of intracellular calcium in A-10 cells. It bound to the surface of both these cell types in a diffuse manner and it did not undergo receptor endocytosis in either cell type. In contrast, R-MLVP, an agonist that bound to both receptor subtypes and elicited changes in intracellular cyclic AMP and calcium, bound to the surface of these cells in a diffuse manner at early times after exposure, and rapidly underwent endocytosis. We conclude that binding of vasopressin to its receptors alone is insufficient to cause receptor endocytosis, and other events distal to the receptor are required to initiate endocytosis. R-CLVP should be a useful analog in determining the factors responsible for initiating receptor endocytosis.

Amino Acid Sequence↗

A randomized trial of vasopressin and vasopressin plus nitroglycerin in the control of acute variceal hemorrhage.

A randomized trial was undertaken to determine efficacy of nitroglycerin when added to a vasopressin infusion in both reducing the complication rate and giving improved control of acute variceal hemorrhage. Seventy-two bleeding episodes in 57 patients were included, with vasopressin being used on 34 occasions and vasopressin plus nitroglycerin on 38 occasions, for an infusion period of 12 hr. At the end of the 12-hr period, hemorrhage had been controlled significantly more frequently in those receiving combined therapy (26 of 38; 68%) than in those given vasopressin alone (15 of 34; 44%, p less than 0.05), although this difference was not statistically significant if those patients in whom therapy was discontinued due to drug complications were excluded from the analysis [hemorrhage controlled in the combined group (68%) and vasopressin alone (48%); chi 2 = 2.4, p greater than 0.05]. Major complications requiring cessation of therapy were significantly less common in those given nitroglycerin--one occasion compared to seven in those given vasopressin alone (p less than 0.02). Thus, the addition of nitroglycerin to a vasopressin infusion results in a lower rate of complications and is more effective in controlling variceal hemorrhage.

Blood Transfusion↗

Early postnatal appearance of enhanced noradrenaline content in the brain of vasopressin-deficient Brattleboro rat; normal adrenoceptor densities and aberrant influences of vasopressin treatment.

The course of postnatal development of noradrenaline (NA) and its unconjugated free metabolite 3-methoxy-4-hydroxyphenylglycol (MHPG), as well as the influence on early chronic vasopressin treatment, were investigated in various brain regions of the hereditary vasopressin-deficient (homozygous di/di) Brattleboro rat. In addition, the densities of the adrenergic receptor subtypes were measured in adult brain. Brain NA levels of di/di pups appeared enhanced already at 7 days of age when compared with data of heterozygous (+/di) controls. This was also seen in areas not known to receive a vasopressinergic input, e.g. the frontal cortex. Levels of MHPG also differed between genotypes, but changes were slight and either a decrease or increase, depending on age and region tested. Saturation analyses of alpha 1-, alpha 2-, and beta-adrenoceptor binding on crude membrane preparations of some brain regions revealed no differences in adulthood. Chronic treatment with vasopressin between 6 and 13 days of age reduced the enhanced NA brain levels throughout the brain of the di/di Brattleboro pups. The known vasopressin-mediated enhancement of NA turnover in adult brain was also measurable in +/di pups of this neonatal period (MHPG/NA ratios), indicating the early maturation of the interaction of vasopressinergic and NAergic systems. However, the dose-response in the di/di Brattleboro rat was biphasic with a decrease at a low dose of vasopressin. Since changes were found throughout the brain, it was concluded that vasopressin deficiency had altered the maturation of NA neurons of the locus coeruleus which may be due to the absence of a presumed inhibitory control of vasopressin on synthesis and storage mechanisms at the perikaryal level.

Animals↗

Intracerebroventricular choline increases plasma vasopressin and augments plasma vasopressin response to osmotic stimulation and hemorrhage.

Intracerebroventricular (i.c.v.) injection of choline (50-150 microg), a precursor of the neurotransmitter acetylcholine, produced a time-and dose-dependent increase in plasma vasopressin levels in conscious, freely moving rats. The increase in plasma vasopressin in response to i.c.v. choline (150 microg) was inhibited by pretreatment with the nicotinic receptor antagonist, mecamylamine (50 microg; i.c.v.), but not by the muscarinic receptor antagonist, atropine (10 microg; i.c.v). The choline-induced rise in plasma vasopressin levels was greatly attenuated by hemicholinium-3 (HC-3; 20 microg; i.c.v.), a neuronal choline uptake inhibitor. Choline (50 or 150 microg; i.c.v.) produced a much greater increase in plasma vasopressin levels in osmotically stimulated or hemorrhaged rats than in normal rats. Choline (150 microg; i.c.v.) also enhanced plasma vasopressin response to graded hemorrhage; the enhancing effect of choline was also attenuated by HC-3 (20 microg; i.c.v.). Choline and acetylcholine concentrations in hypothalamic dialysates increased significantly following i.c.v. injection of choline (150 microg). It is concluded that choline increases plasma vasopressin levels by stimulating central nicotinic receptors indirectly, through the enhancement of acetylcholine synthesis and release, and augments the ability of osmotic stimulations or hemorrhage to stimulate vasopressin release.

Acetylcholine↗

Ala-Gly- and Val-Asp-[Arg8]-vasopressin: bovine storage forms of arginine vasopressin with natriuretic activity.

Extracts of fresh-frozen bovine neurohypophysis were purified by chromatographic techniques to isolate and characterize the components that produce natriuresis in nondiuretic dogs. Two compounds with natiuretic properties similar to those of synthetic arginine vasopressin accounted for most of the natriuretic activity and appeared to be the prevalent vasopressin-like molecules in the extract. These peptides were Ala-Gly-[Arg8]-vasopressin and Val-Asp-[Arg8]-vasopressin; the natriuretic potency of each appeared to be similar to synthetic arginine vasopressin and could be observed with doses in the range of 50 picomoles. In the dog the most conspicuous difference between synthetic arginine vasopressin and the new vasopressin peptides was the smaller pressor responses to natriuretic doses of the new compounds.

Amino Acid Sequence↗

The effects of several vasopressin receptor antagonists on normal intraocular pressure and the intraocular distribution of vasopressin receptor subtypes.

The aim of the present paper is to study the relation between vasopressin antagonism and the regulation of intraocular pressure (IOP). From the studies on the effect of several vasopressin receptor antagonists, VP-343, OPC-21268, YM087, OPC-31260 and SR121463, on normal IOP and the effect of VP-343 on pupil diameter in rabbit, it was shown that some vasopressin antagonists decreased normal IOP and VP-343 had no influence on pupil diameter. A vasopressin receptor mapping study in normal cynomolgus monkey eye revealed a high density binding site for a [H3]vasopressin V1 antagonist in the region of iris. These findings suggest that a vasopressin antagonist should decrease normal IOP without miosis and that vasopressin V1 receptors are present in iris.

Animals↗

Biosynthesis of the common precursor to vasopressin and neurophysin in vitro in transplantable human oat cell carcinoma of the lung with ectopic vasopressin production.

Transplantable human oat cell carcinoma cells of the lung with ectopic vasopressin production were incubated with labeled amino acids and immunoreactive neurophysins in cell extracts were analyzed by isoelectric focusing. When the cells were incubated with L-(35S)-cysteine for 20 h, one major peak (isoelectric point; pI=5.3) and several minor peaks (pI=6.1, 5.7, 5.1, 4.9 and 4.7) of labeled proteins were observed. On sodium dodecyl sulfate-polyacrylamide gel electrophoresis, the relative molecular mass (Mr) of the pI 5.7 protein was estimated to be 20,000 and that of the pI 6.1 species to be 19,000, while the remainder had a Mr of approximately 10,000. The result of the pulse-labeling experiment has clearly shown that the pI 5.7 and 6.1 proteins, which have affinity for concanavalin A, are biosynthetic precursors for the smaller form of neurophysin with a pI 5.3. When subjected to limited proteolysis with trypsin, the pI 5.7 protein generated a Mr 10,000 protein and a smaller peptide. The Mr 10,000 protein thus produced was identified as neurophysin on the basis of its pH-dependent affinity for vasopressin and the migration pattern on isoelectric focusing. The smaller peptide coeluted with synthetic arginine vasopressin and bound to neurophysin suggesting that it possesses a cysteine-tyrosyl sequence at its N-terminus. Similarly, the pI 6.1 protein liberated neurophysin and vasopressin-like peptide after incubation with trypsin. These results suggests that the glycosylated protein with a pI of 5.7 and a Mr of 20,000 is the common precursor to vasopressin and neurophysin in human oat cell carcinoma of the lung with ectopic vasopressin production. The pI 6.1 protein may be an intermediate in the conversion of the precursor to vasopressin and neurophysin.

Carcinoma, Small Cell↗

Arginine vasopressin antagonism of oxytocin-stimulated PGE2 release from rabbit amnion cells and the activities of thioanalogs of oxytocin and arginine vasopressin.

Using rabbit amnion membranes devoid of arginine vasopressin receptors, we have shown that arginine vasopressin acts as a partial agonist and oxytocin antagonist. We examined peptides with modifications in position 8 to determine the basis for partial agonism/antagonism. The 8-thioanalog of oxytocin had about 40% of oxytocin activity in eliciting PGE2 release by amnion cells and a corresponding 40% affinity for oxytocin binding sites on amnion membranes. Arginine vasotocin, which has arginine at the position 8 and about 90% homology with arginine vasopressin also acted as a full agonist. These results suggest that determination of the oxytocin antagonist activity of arginine vasopressin is largely dependent on the amino acid at position 3. We also synthesized the 8-thioanalog of arginine vasopressin, which had a very low affinity for arginine vasopressin binding sites in rat liver (V1 receptors) and rat kidney medulla (V2 receptors) membranes. These findings suggest that arginine vasopressin receptors are much more sensitive to modifications of the peptide bond between positions 8 and 9 than are oxytocin receptors.

Amino Acid Sequence↗

Vasopressin regulates adrenal functions by acting through different vasopressin receptor subtypes.

In mammals, vasopressin is known to be synthesized in the hypothalamus and released in the blood stream at the pituitary level. This neuropeptide is also synthesized and secreted by the adrenal medulla in many species including human. Moreover, agents like acetylcholine and corticotropin releasing factor stimulates its basal secretion. V1a vasopressin receptors are present in the adrenal cortex and are involved in steroids secretion (aldosterone in the zona glomerulosa and glucocorticoids in the zona fasciculata of some species). These receptors are coupled to phospholipase C beta and to dihydropyridine-sensitive calcium channels via heterotrimeric G proteins differing by their sensitivities to pertussis toxin. The adrenal medulla, from many species, exhibits V1a vasopressin receptors. In rat adrenal medulla, functional V1b vasopressin receptors could also be characterized. These receptors stimulate catecholamines secretion via activation of phospholipase C beta and subsequent mobilization of intracellular calcium. The adrenal medulla secretes AVP and exhibits functional vasopressin receptors. The adrenal cortex also possesses functional vasopressin receptors and is in contact with adrenal medulla via "medullary rays". We may thus reasonably conclude that AVP physiologically regulates adrenal gland functions via autocrine/paracrine mechanisms.

Adrenal Cortex↗

Desensitization of vasopressin sensitive adenylate cyclase by vasopressin and phorbol esters.

Desensitization of vasopressin V2 receptor-mediated adenylate cyclase was studied in canine kidney cell line, MDCK cells. Overnight treatment of MDCK cells with arginine vasopressin (AVP) resulted in a loss of vasopressin receptors and an inhibition of cAMP accumulation in response to AVP. Both the loss of receptor and reduction in cAMP accumulation were time- and AVP concentration-dependent. Desensitization was selective for AVP because cAMP formation in response to isoproterenol, prostaglandin E1 (PGE1) and forskolin was not affected by AVP pre-treatment. Pre-treatment of MDCK cells with phorbol dibutyrate (PDBu) also caused a dose-dependent inhibition of AVP mediated cAMP accumulation, but not of isoproterenol-, PGE1- and forskolin-induced cAMP accumulation. PDBu pre-treatment did not cause loss of vasopressin receptors. Instead, the affinity for vasopressin was changed by PDBu treatment. Pre-treatment of the cells with pertussis toxin (PT) had no effect on the desensitization and downregulation of vasopressin (V2) receptors, suggesting that the desensitization may not be mediated by pertussis toxin sensitive G-protein. Our data suggest that pre-treatment of MDCK cells with AVP or PDBu caused desensitization of AVP-mediated cAMP accumulation and that downregulation of V2 receptors required agonist occupancy of the receptors, whereas the affinity of the receptors was changed by phorbol ester treatment.

Adenylyl Cyclases↗

Effect of a vasopressin antagonist d(CH2)5Tyr(Met)AVP on the development of renal vasospasm induced by estrin plus vasopressin administration in rats.

The authors studied rats pretreated with estrin acetate to determine the renal circulation changes caused by vasopressin and how these changes are influenced by the pressor effect of an antagonist of vasopressin d(CH2)5Tyr(MET)AVP. Abdominal angiography was performed with contrast material administered via a catheter introduced through the common carotid artery up to the aortic arch. After vasopressin administration, a marked spasm occurred in the larger renal arteries, the arteriovenous time increased, and the parenchymal filling became defective. Renal circulation remained undisturbed if the vasopressin antagonist was administered simultaneously. The results suggest that the vasopressin antagonist prevents renal vasospasm after vasopressin administration in rats pretreated with estrin.

Animals↗

Iodinated photoreactive vasopressin antagonists: labelling of hepatic vasopressin receptor subunits.

To identify and characterize V1 vasopressin receptors, photoreactive antagonists of the glycogenolytic and vasoconstrictor activity of vasopressin have been synthesized. The following analogues with 3-mercapto-3,3-cyclopentamethylene-propionic acid (Mca) and N-methylalanine (MeAla) in position 1 and 7 of vasopressin (VP) were effective V1 antagonists: [Mca1, D-Tyr2, MeAla7, Lys8]VP (1), [Mca1, MeAla7, Arg8, Lys9]VP (2), [Mca1, MeAla7, Arg8, D-Lys9]VP (3). Introduction of the photoreactive 4-azidophenylamidino group into the side-chain of Lys8 in analogue 1 or into Lys9 in analogues 2 and 3 increased the potency (for analogue 1 a tenfold increase in the antiglycogenolytic effect and a fivefold increase in the antivasopressor effect) and binding affinity for the rat hepatic V1 receptor. Mono-iodination at Tyr2 with 125I resulted in photoreactive antagonists of high specific radioactivity, which had roughly the same binding affinity as vasopressin for the rat hepatic V1 receptor (Kd = 0.9-1.8 nM). In photoaffinity labelling experiments with purified rat liver membranes, containing 2--3 pmol V1 receptor/mg protein, the analogues labelled specifically two proteins with the relative molecular masses (Mr) of 30,000 and 38,000. These results and the results of a recent study using 3H-labelled photoreactive vasopressin agonists [Boer, R. and Fahrenholz, F. (1985) J. Biol. Chem. 260, 15051-15054] provide evidence that both vasopressin agonists and antagonists can interact with the same two subunits of the heterodimeric hepatic V1 receptor. Furthermore the radioiodinated photoreactive V1 antagonists should be helpful to identify V1 receptor proteins in membranes of other cell types.

Affinity Labels↗

The diurnal rhythm in vasopressin V1a receptor expression in the suprachiasmatic nucleus is not dependent on vasopressin.

The mammalian suprachiasmatic nucleus is the site of the circadian rhythm generator. The degrees of expression there of several neuropeptides, including vasopressin and vasoactive intestinal polypeptide, follow a diurnal rhythm. The vasopressin V1a receptor, whose activation results in phosphoinositol hydrolysis and mobilization of intracellular calcium, is expressed in this nucleus. This study used double simultaneous hybridization histochemistry to show that V1a receptor transcripts are present in both vasopressin and vasoactive intestinal polypeptide neurons and that their levels follow a diurnal rhythm. Furthermore, the expression of the V1a receptor is 12 h out of phase from that of vasopressin. However, the receptor's diurnal rhythm is still maintained in the vasopressin-deficient Brattleboro rat, indicating that the V1a receptor's rhythm is independent of any vasopressin feedback.

Animals↗

Effect of bacitracin on the degradation of a vasopressin receptor ligand with high affinity for the V1 and V2 vasopressin isoreceptors.

We previously described a new iodinated vasopressin analogue (N epsilon-[125I]L-Tyr-[Lys8]-vasopressin) with high affinity for the vasopressin V1 and V2 isoreceptors. The aim of the present study was: i) to analyse the degradation pathway of N epsilon-[125I]L-Tyr-[Lys8]-vasopressin and (ii) to look for an effective inhibitor of radioligand degradation. N epsilon-[125I]L-Tyr-[Lys8]-vasopressin was processed in a temperature-dependent manner by crude cell membranes from LLC-PK1 cells. Only one degradation product was seen using RP-HPLC. The degradation product co-eluted with monoiodotyrosine. The stereoisomer, N epsilon-[125I]D-Tyr-[Lys8]-vasopressin, underwent the same degradation process. Bacitracin prevented degradation at doses as low as 40 mg/l without alterating the binding affinity.

Animals↗

Dose-response relationships for arginine vasopressin and synthetic analogs on three types of rat blood vessels: possible evidence for regional differences in vasopressin receptor sites within a mammal.

These experiments were undertaken to determine the comparative relationships between chemical structure and biologic (contractile) activity of a series of vasopressin hormone analogs on different rat blood vessels (e.g., aorta, mesenteric arteriole and mesenteric venule). The functional contributions to, and interactions with, phenolic hydroxyl and aromatic groups as well as basicity in positions 2, 3 and 8, respectively, to or with hormone-receptor affinity and intrinsic (contractile) activity, were determined by analyzing the dose-response curves of five vasopressin peptides lacking one or more of these functional groups. The findings demonstrate that: 1) the structure-action relationships for vasopressin peptide-induced contractions on rat blood vessels vary with the particular type of macro- or microvessel (i.e., aorta, arteriole and venule); 2) the phenolic and aromatic groups in positions 2 and 3, respectively, are not only important for hormone-receptor affinity but intrinsic activity as well; 3) the potency (EC50) values for arginine vasopressin as well as the potencies and intrinsic activities of synthetic vasopressin analogs varied between the three different types of rat blood vessels examined; and 4) circulating levels (i.e., 10- minus 11- minus 10- minus 12 M) of [8-arginine]-vasopressin are capable of inducing contractile effects on mesenteric arterioles and venules. The quantitative data obtained in this study support the notion that a heterogeneity of the receptor, which subserves contraction, probably exists in blood vessels within and between vascular beds of a single mammalian species.

Amino Acid Sequence↗

Biotinyl analogues of vasopressin as biologically active probes for vasopressin receptor expression in cultured cells.

Biotinyl analogues of [Arg8]vasopressin were synthesized with the biotinyl moiety at position 4. This involved the substitution of 2, 4-diaminobutyric acid (Dab) for Gln4 in [1-deamino-Arg8]vasopressin to give the parent peptide des-[Dab4,Arg8]vasopressin. Two biotinyl analogues with different spacers between the side chain of Dab4 and the biotinyl residue were then prepared and characterized in detail. The analogues retained high binding affinities for the V2-receptor in both bovine kidney membranes and LLC-PK1 renal epithelial cells and for the V1-receptor in rat liver membranes. Both analogues were as potent as [Arg8] vasopressin in stimulating the cAMP-dependent protein kinase and the production of urokinase-type plasminogen activator in LLC-PK1 cells, with concentration dependence consistent with receptor binding affinities. Avidin or streptavidin did not appear to reduce receptor binding or biological activity of the biotinyl analogues. The use of the biotinylated vasopressin analogue des-[Dab-(biotinylamido)hexanoyl4, Arg8]vasopressin together with fluorescein-labeled streptavidin as a fluorescent probe for the V2-receptor in LLC-PK1 cells demonstrated the following: 1) Specific binding of the biotinyl analogue shown by quantitative single-cell fluorescence measurements using the technique of fluorescence microphotolysis; 2) the V2-receptor visualized by fluorescence microscopy; and 3) the expression of the V2-receptor detected by flow cytometry.

Amino Acid Sequence↗

Controlled trial of vasopressin plus nitroglycerin vs. vasopressin alone in the treatment of bleeding esophageal varices.

Thirty-nine patients admitted during a 16-month period for acute bleeding from varices confirmed by emergency endoscopy were randomized to receive either continuous intravenous infusions of vasopressin alone (0.66 units per min) (Group I: 19 patients) or vasopressin plus sublingual nitroglycerin (0.6 mg every 30 min for 6 hr) (Group II: 20 patients). The two groups of patients were similar in the type and severity of their cirrhosis. Bleeding was controlled initially in 47% (9/19) of the patients in Group I and 55% (11/20) of the patients in Group II after 6 hr of infusion (not statistically significant). Complete control of bleeding during 24 hr of infusion was achieved in only 4 of 19 patients in Group I (21%) but in 9 of 20 in Group II (45%). This difference is not statistically significant. The total number of patients with complications during infusions were significantly different statistically in the vasopressin and vasopressin-nitroglycerin groups, respectively (17/19 vs. 7/20, p less than 0.001). Major complications requiring immediate cessation of infusions were observed in 6 of 19 of the patients in Group I (32%) and in 2 of 20 in Group II (10%) (p less than 0.05). Mortality (58% in Group I, 55% in Group II) and transfusion requirements were similar in the two groups. This study shows that the addition of sublingual nitroglycerin to intravenous vasopressin does not alter the efficacy of vasopressin alone in controlling hemorrhage from esophageal varices, but it does significantly reduce the complications.

Administration, Oral↗