Arg8]vasopressin Research Articles

Characterization of rat gastric myogenic contractions and modulation by oxytocin and arginine-vasopressin

BackgroundInterstitial cells of Cajal generate slow wave gastric electrical activity, initiating spontaneous muscle contractions. This becomes dysrhythmic during nausea when [Arg8]-vasopressin (AVP) is also released. In human stomach AVP increased spontaneous contraction activity and muscle tone, not neuronally-mediated contractions. Rodents cannot vomit, releasing the related hormone, oxytocin (OT) instead. We hypothesised that rat stomach would behave differently. Experimental approachSpontaneous and electrically-evoked (EFS) contractions were measured in rat forestomach and antrum circular muscle. Custom software defined spontaneous contractions by analysing eight motility parameters. ResultsThe forestomach was quiescent. Irregular antrum contractions became regular adjacent to the pylorus (1.7 ± 0.4 mN; 1.2 ± 0.1 contractions/min, n = 12). These were unaffected by tetrodotoxin (10−6 M), atropine (10−6 M) and L-NAME (3 × 10−4 M). In both regions, AVP (pEC50∼9.0) and OT (∼0.5 log10-unit less potent) caused contraction (greater in antrum), competitively antagonized by, respectively, SR49059 (pKB∼9.5) and L371257 (pKB∼9.0), reduced by tetrodotoxin but unaffected by atropine. In the antrum, AVP and OT (∼2 log10-units less potent/efficacious) regularized and increased spontaneous contraction amplitude, frequency, rates of contraction/decay. In both regions, EFS-evoked contractions, abolished by atropine/tetrodotoxin, were reduced by AVP and OT, with AVP more potent and efficacious, particularly in forestomach. ConclusionIrregular spontaneous contractions of gastric antrum suggest variable ICC-muscle coupling. AVP and less potently, OT, enhanced frequency and force of contractions via V1A and OT receptors. Compared with human, differences in contraction regularity, potency and ability of AVP/OT to affect neuronal function suggests caution when using rat stomach to model ICC functions and nauseagenic stimuli.

Arg-Vasotocin Directly Activates Isotocin Receptors and Induces COX2 Expression in Ovoviviparous Guppies.

Oxytocin (OT) is a crucial regulator of reproductive behaviors, including parturition in mammals. Arg-vasopressin (AVP) is a nonapeptide homologous to Arg-vasotocin (AVT) in teleosts that has comparable affinity for the OT receptor. In the present study, ovoviviparous guppies (Poecilia reticulata) were used to study the effect of AVT on delivery mediated by the activation of prostaglandin (PG) biosynthesis via isotocin (IT) receptors (ITRs). One copy each of it and avt and two copies of itrs were identified in guppies. The results of the affinity assay showed that various concentrations of AVT and IT (10−6, 10−7, and 10−8 mol/L) significantly activated itr1 (P < 0.05). In vitro experiments revealed significant upregulation (P < 0.05) of cyclooxygenase 2 (cox2), which is the rate-limiting enzyme involved in PG biosynthesis, and itr1 by AVT and IT. Furthermore, dual in situ hybridization detected positive signals for itr1 and cox2 at the same site, implying that ITR1 may regulate cox2 gene expression. Measurement of prostaglandin F2a (PGF2a) concentrations showed that AVT induced PGF2a synthesis (P < 0.05) and that the effect of IT was not significant. Finally, intraperitoneal administration of PGF2a significantly induced premature parturition of guppies. This study is the first to identify and characterize AVT and ITRs in guppies. The findings suggest that AVT promotes PG biosynthesis via ITR and that PGF2a induces delivery behavior in ovoviviparous guppies.

Intermittent hypobaric hypoxia and neuroendocrine reaction of the parvocellular neurons of the paraventricular hypothalamic nucleus

The neuroendocrine system occupies an important place in the systemic mechanisms of the body response to stress. The paraventricular nuclei of the hypothalamus (PVH) are one of the most important links of the brain`s neuroendocrine system which determine the reactivity of the hypothalamic-pituitary-adrenal axis (HPA) in response to the various stressors and thereby ensure the development of adaptive reactions by the formation of body resistance to the stress. The aim of the research was to study the functional state of the peptidergic neurons of the medial parvocellular nuclei of the paraventricular hypothalamic nucleus (PVHmp) during the multi-day action of intermittent hypobaric hypoxia and in the posthypoxic period. Materials and methods. The research was conducted on 24 male Wistar rats. Intermittent hypoxia was modeled by a daily 6-hour stay of rats at an altitude of 6000 m (pO 2 = 9.8 %) for 15 days, the posthypoxic period lasted for 10 days. The distribution of corticotropin-releasing hormone (CRH), [Arg 8 ]-vasopressin (AVP), β-endorphin, cFos and HIF-1α proteins was studied by quantitative immunofluorescence methods in serial frontal sections of the hypothalamus. Results. The intermittent hypobaric hypoxia stimulated the developing of mild hypertrophy of PVHmp neurons and increased the concentration of RNA in the cytoplasm by 37 %. An indicator of PVHmp neurons response to hypoxia was 2.5-fold increase in the concentration of the HIF-1α protein in them. IHH elevated the concentration of cFos protein in PVHmp by 37 %, increased the area of immunoreactivity to AVP by 2.5 times, to CRH and β-endorphin by 3 times. There was an increase in the synthesis of neuropeptides in response to hypoxia, which led to the elevation in the concentration of AVP in PVHmp by 6.6 times, β-endorphin by 7 times, and CRH by 8.5 times. The immunoreactivity indicators for the HIF-1α protein and its concentration in PVHmp remained at a high level in the posthypoxic period. At the same time, high immunoreactivity to CRH and β-endorphin in PVHmp was noted, as well as a high concentration of these neuropeptides in neurons against the background of AVP synthesis inhibition in neurons. It is possible that high rates of neurosecretory activity of PVHmp in the posthypoxic period may indicate the formation of neuroendocrine mechanisms of adaptation of the HPA axis to the long-term effect of hypoxia. Conclusions. Intermittent hypobaric hypoxia stimulates the neurosecretory activity of the PVHmp neurons, increases the synthesis and secretion of CRH and AVP hormones that activate the HPA axis. Synthesis of the secretory response indicator cFos protein and a central regulator of hypoxic responses HIF‑1α protein is also increasing in the peptidergic neurons of the PVHmp. High levels of the PVHmp neurosecretory activity at the posthypoxic period are preserved and indicate the formation of neuroendocrine mechanisms of the HPA axis adaptation to the long term intermittent hypoxia exposures.

Comparative characteristics of vasopressinergic neurons of the supraoptic and paraventricular nuclei of hypothalamus response in the intermittent hypoxic hypoxia

The vasopressinergic system of the hypothalamus occupies an important place in the neuroendocrine mechanisms of maintaining homeostasis, controlling autonomic reactions and the processes of adaptation of the organism to the acute and chronic stressors. The main portion of the magnocellular vasopressin-synthesizing neurons is localized in the supraoptic nucleus (SON) and in the lateral part of the posterior magnocellular subnuclei of the paraventricular nucleus (PVNpml). The aim of study was to establish the features of the vasopressinergic neurons of the hypothalamus magnocellular nuclei functional state under the inflence of prolonged intermittent hypoxic hypoxia and in the post-hypoxic period. Materials and methods. The research was carried out on 30 male Wistar rats. Intermittent hypoxia was modeled by daily 6 hour stay of rats at the simulated altitude of 6000 m (pO 2 = 9.8 %) for 15 days, the post-hypoxic period lasted 10 days. The distribution of [Arg 8 ]-vasopressin (AVP), cFos, HIF-1α, and HIF-3α proteins was investigated by quantitative immunoflorescence methods in serial frontal sections of hypothalamus. Results. The hypoxic hypoxia action led to SON neurons degeneration, inhibition of AVP synthesis in SON by 40 %, decrease of cFos protein content by 56 %, and the failure of reaction to hypoxia from the HIF-proteins family. In PVNpml neurons, intermittent hypoxia stimulated 6-fold increase in the AVP content along with cFos-protein increase by 80%. The response of PVNpml neurons to hypoxia was accompanied by 3-times increase of the HIF family proteins content. In the post-hypoxic ially restored in SON neurons, but decrease of cFos-protein synthesis indicated inhibition of secretory activity in SON. In the post-hypoxic period the content of the AVP and the HIF-proteins decreased signifiantly in PVNpml neurons, but the level of all proteins remained higher than in the control group. At the same time, the level of cFos secretory activity did not change signifiantly as compared with the hypoxic period. These data indicate the stability of the high level of functional activity of the PVNpml asopressinergic neurons during the 10-day post-hypoxic period. Conclusions. Intermittent hypoxia stimulates the functional activity of the PVNpml that manifests as an increase of vasopressin, cFos, HIF-1α, and HIF-3α proteins synthesis in magnocellular neurons. In the post-hypoxic period, a slight decrease in the synthesis of vasopressin, HIF-1α and HIF-3α proteins is observed without a decrease in the cFos protein content in PVNpml. Intermittent hypoxia inhibits the functional activity of SON neurons, which is partially restored in the post-hypoxic period.

Vasopressin augments TNBS-induced colitis through enteric neuronal V1a receptor-mediated COX-2-dependent prostaglandin release from mast cells in mice.

Inflammatory bowel disease (IBD) is a functional disorder with chronic and relapsing clinical features. Vasopressin (VP) is a hormone responsible for water and stress homeostasis and also regulates gastrointestinal inflammation and motility. We explored whether VP was related to IBD pathogenesis and its possible pathway. Colitis was induced by 2,4,6-trinitrobenzenesulfonic acid (TNBS) in mice. The disease activity and colonic damage were evaluated through a scoring system. Locations of the V1a receptor were revealed by immunochemistry method in colon. Ussing chamber technique was performed for the electrophysiological characterization by using rat ileum. The (Arg8 )-Vasopressin (AVP)-evoked short-circuit current (Isc) was recorded in the presence of conivaptan (V1a and V2 receptor antagonist), tolvaptan (V1b receptor antagonist), tetrodotoxin (TTX), atropine, cyclooxygenase (COX) inhibitors (indomethacin, nonspecific COX antagonist; SC560, COX-1 antagonist; NS560, COX-2 antagonist), and a stabilizer of mast cell (cromolyn sodium), respectively. TNBS resulted in the obvious loss of body weight and tissue damages in mice. AVP significantly aggravated the TNBS-induced colitis, which was attenuated by conivaptan but not tolvaptan. V1a receptors were found immunopositive in neurons among the enteric nervous system. AVP evoked a pulsatile response in Isc. Its amplitude, frequency, and cycle duration were around 8-15µA/cm2 , 10-11mHz, and 1.5minutes, respectively. Notably, the AVP-evoked change in Isc was abolished by TTX, atropine, conivaptan, indomethacin, NS560, and cromolyn sodium, respectively. VP-V1a receptor played the proinflammatory role in TNBS-induced colitis by promoting COX-2-dependent prostaglandin release from mucosal mast cells, which was mediated by the cholinergic pathway.

In vitro binding and receptor-mediated activity of terlipressin at vasopressin receptors V1 and V2.

Terlipressin, a synthetic, systemic vasoconstrictor with selective activity at vasopressin-1 (V1) receptors, is a pro-drug for the endogenous/natural porcine hormone [Lys8]-vasopressin (LVP). We investigated binding and receptor-mediated cellular activities of terlipressin, LVP, and endogenous human hormone [Arg8]-vasopressin (AVP) at V1 and vasopressin-2 (V2) receptors. Cell membrane homogenates of Chinese hamster ovary cells expressing human V1 and V2 receptors were used in competitive binding assays to measure receptor-binding activity. These cells were used in functional assays to measure receptor-mediated cellular activity of terlipressin, LVP, and AVP. Binding was measured by [3H]AVP counts, and the activity was measured by fluorometric detection of intracellular calcium mobilization (V1) and cyclic adenosine monophosphate (V2). Binding potency at V1 and V2 was AVP>LVP>>terlipressin. LVP and terlipressin had approximately sixfold higher affinity for V1 than for V2. Cellular activity potency was also AVP>LVP>>terlipressin. Terlipressin was a partial agonist at V1 and a full agonist at V2; LVP was a full agonist at both V1 and V2. The in vivo response to terlipressin is likely due to the partial V1 agonist activity of terlipressin and full V1 agonist activity of its metabolite, LVP. These results provide supportive evidence for previous findings and further establish terlipressin pharmacology for vasopressin receptors.

Arg-vasopressin facilitates calcium channel currents in osteoblasts.

The hypothalamic nonapeptide and neurohypophyseal hormone arg-vasopressin (AVP), also known as antidiuretic hormone, is best known for its effects on water reabsorption in kidney. Osteoblasts play a major role in bone formation, employing intracellular Ca(2+) as a second messenger to modulate hormonal responses and as a cofactor for mineralization. Voltage-dependent Ca(2+) channels (VDCCs) mediate the influx of Ca(2+) in response to membrane depolarization. The purpose of this study was to investigate the effects of AVP on VDCC currents in osteoblasts using a patch-clamp recording method. An application of 1μM AVP facilitated VDCC currents in osteoblasts. To our knowledge, the data presented here demonstrate for the first time that AVP facilitates VDCCs in osteoblasts.

Mothers of autistic children: lower plasma levels of oxytocin and Arg-vasopressin and a higher level of testosterone.

BackgroundAutism is a pervasive neurodevelopmental disorder,thought to be caused by a combination of genetic heritability and environmental risk factors. Some autistic-like traits have been reported in mothers of autistic children. We hypothesized that dysregulation of oxytocin (OXT), Arg-vasopressin (AVP) and sex hormones, found in autistic children, may also exist in their mothers.MethodsWe determined plasma levels of OXT (40 in autism vs. 26 in control group), AVP (40 vs. 17) and sex hormones (61 vs. 47) in mothers of autistic and normal children by enzyme immunoassay and radioimmunoassay, respectively and investigated their relationships with the children’s autistic behavior scores (Childhood Autism Rating Scale (CARS) and Autism Behavior Checklist (ABC)).ResultsSignificantly lower plasma concentrations of OXT (p<0.001) and AVP (p<0.001), as well as a higher level of plasma testosterone (p<0.05), were found in mothers of autistic children vs. those of control. The children’s autistic behavior scores were negatively associated with maternal plasma levels of OXT and AVP.ConclusionsThese results suggest that dysregulation of OXT, AVP and/or testosterone systems exist in mothers of autistic children, which may impact children’s susceptibility to autism.

Molecular mechanisms regulating skeletal muscle homeostasis: effects of V1a AVP receptor over- expression

The maintenance of a working skeletal musculature is conferred by its capacity to regenerate after mechanical or pathological injury. Most muscle pathologies are characterized by the progressive loss of muscle tissue due to chronic degeneration combined with the inability of the regeneration machinery to replace damaged myofibers. Cachexia or muscle wasting is characterized by a loss of adipose and muscle mass associated with a compromised muscle regenerative ability. Arg-vasopressin (AVP) is a potent myogenesis promoting factor and activates both the calcineurin and CaMK pathways, whose combined activation leads to the formation of transcription factor complexes in vitro. The local over-expression of V1a AVP receptor (V1aR) in injured muscle results in enhanced regeneration. V1aR over-expressing muscle exhibits early activation of satellite cells and regeneration markers and accelerated differentiation. Here we investigated the role of V1aR over-expression in animals undergoing cachexia as a result of muscle over-expression of a specific cytokine (TNF). In these conditions, the local V1aR over-expression counteracts the negative effects of cachexia on muscle, as demonstrated by morphological and biochemical analysis. In particular, the presence of V1aR results in increased Pax-7, myogenin and myosin expression levels both in wild type and in cachectic muscles. The positive effects of V1aR on muscle homeostasis are due to the promotion of the calcineurin-IL-4 pathway and to the inhibition of atrophic genes expression mediated by FOXO phosphorylation. This study highlights a novel in vivo role for the AVP-dependent pathways which may suggest a potential gene therapy approach for many diseases affecting muscle homeostasis.

メニエール病とVasopressin系

Wistar rats were intraperitoneally injected with 0.02 units/g of AVP (Pitressin; Arg-vasopressin. Daiichi-Sankyo, Japan) in all the experiments in this study. ABR thresholds gradually increased significantly up to 60 min after the injection. When dehydration load pretreatment for 24h was added, ABR thresholds rapidly increased significantly up to 10 min after the injection. However, the morphological endolymphatic hydrops in the cochlea was not detected under light microscopy. On the other hand, the enlargement of an area lacking intracellular organelles in the intermediate cells in the stria vascularis or a so called “vacuole” was detected under transmission electron microscopy after the AVP injection. When the dehydration load pretreatment for 24h was added, the vacuole area increased with AVP injection. However, when a V2R antagonist (OPC-31260, donated by Otsuka Pharmaceutical) was administered before AVP, vacuole formation was suppressed significantly. Conversely, vacuole formation was not suppressed when a V1aR antagonist (OPC-21268, donated by Otsuka Pharmaceutical) was administered before AVP injection. As a clinical application based on above mentioned basic studies, we conducted hydration therapy for Meniere's disease. In the hydration therapy, basically the patients drank 35 ml/kg/day of water daily in addition to the normal daily beverages and foods for 2 years. Medication of 21 g was given whenever a vertiginous spell or hearing loss or aural fullness reoccurred. The outcomes were determined according to the criteria of the AAO-HNS 1995 guidelines. In the hydration therapy group, the definitive spells were controlled in 93% of the patients. The hearing in the hydration therapy group was improved significantly in comparison with the conventional therapy group.

Vasopressin facilitates GABAergic transmission in rat hippocampus via activation of V1A receptors

Whereas vasopressin has been shown to enhance memory possibly by increasing long-term potentiation and direct excitation of the pyramidal neurons in the hippocampus, the effects of vasopressin on GABAergic transmission in the hippocampus remain to be determined. Here we examined the effects of vasopressin on GABAergic transmission onto CA1 pyramidal neurons and our results demonstrate that bath application of [Arg8]-vasopressin (AVP) dose-dependently increased the frequency of spontaneous IPSCs (sIPSCs) recorded from CA1 pyramidal neurons via activation of V1A receptors. Immunohistological staining and western blot further confirmed that both CA1 pyramidal neurons and interneurons expressed V1A receptors. Bath application of AVP altered neither the frequency nor the amplitude of miniature IPSCs in the presence of tetradotoxin and failed to change significantly the amplitude of evoked IPSCs recorded from CA1 pyramidal neurons. AVP increased the firing frequency of action potentials by depolarizing the GABAergic interneurons in the stratum radiatum of CA1 region. AVP-mediated depolarization of interneurons was mediated by inhibition of a background K+ conductance which was insensitive to extracellular tetraethylammonium, Cs+, 4-aminopyridine, tertiapin-Q and Ba2+. AVP-induced depolarization of interneurons was dependent on Gαq/11 but independent of phospholipase C, intracellular Ca2+ release and protein kinase C. The inhibitory effects of AVP-mediated modulation of GABA release onto CA1 pyramidal neurons were overwhelmed by its strong excitation of CA1 pyramidal neurons in physiological condition but revealed when its direct excitation of the pyramidal neurons was blocked suggesting that AVP-mediated modulation of GABAergic transmission fine-tunes the excitability of CA1 pyramidal neurons.

Simultaneous oxytocin and arg-vasopressin measurements in microdialysates using capillary liquid chromatography–mass spectrometry

Oxytocin (OXT) and arg-vasopressin (AVP) are nonapeptides with many important functions both peripherally and centrally. Intracerebral microdialysis has helped characterize their importance in regulating complex social and emotional processes. Radioiummunoassay is the most commonly used analytical method used for OXT and AVP measurements in microdialysates. These measurements have several well-known issues including single peptide per assay limit, possible cross-reactivity between structurally related peptides, and laborious sample preparation with radioactive materials. Here we demonstrate the use of capillary LC–MS3 for measuring OXT and AVP simultaneously in dialysates at a 10min sampling frequency. Microdialysate samples required no preparation and instrumentation was commercially available. Microdialysis probes made with polyacrylonitrile membranes were suitable for high level recovery of the peptides in vitro and in vivo. Responses were linear from 1 to 100pM. Matrix effect was assessed by standard addition experiments and by comparing signal intensities of OXT and AVP standards made in aCSF or dialysate. It was determined that the online washing step used on this setup was adequate for removing contaminants which interfere with electrospray ionization efficiency. In vivo, both peptides were stimulated by high K+ (75mM) aCSF perfusion in the paraventricular nucleus (PVN). Also, a systemic injection of high Na+ (2M) caused a rapid and transient increase in PVN OXT while AVP increased only after 1.5h. Our findings suggest that capillary LC–MS3 is a straightforward method for monitoring OXT and AVP simultaneously from complex samples such as dialysates.

Effects of Schisandra chinensis extract on the contractility of corpus cavernosal smooth muscle (CSM) and Ca2+ homeostasis in CSM cells

What's known on the subject? And what does the study add? Schisandra chinensis extract (SCE) has been known to have relaxative effects on penile smooth muscle. A recent study showed that SCE could enhance slidenafil citrate-induced relaxation of penile corpus cavernosum. The current study investigated the mechanism of action of SCE and its constituents on corporal smooth muscle cells. And this study shows that SCE induced relaxation of CSM primarily through an endothelium independent pathway and the relaxation effects of SCE on corporal smooth muscle are, in part, due to the activation of K(+) channels and inhibition of TRPC6 channels, resulting in decreased [Ca(2+)]. • To evaluate the relaxant effects of Schisandra chinensis extract (SCE) on corporal tissue in the penis and to investigate the mechanism of action of SCE and its constituents on corporal smooth muscle (CSM) cells. • The fruit of SC was collected and extracted with ethanol. Six SC lignans (schisandrol A, schisandrol B, schisandrin A, schisandrin B, gomisin N, and schisandrin C) were isolated and purified, and the chemical structures were confirmed by (1)H-nuclear magnetic resonance (NMR) and (13)C-NMR data. • Isolated rabbit CSM strips were mounted in an organ-bath system, and the effects of SCE were evaluated. • To estimate the intracellular Ca(2+) level ([Ca(2+)](i)), we used a Fura-2 fluorescent technique, and a conventional whole-cell patch-clamp technique was used to measure the calcium-sensitive K(+) channels (K(Ca)), inward rectifier K(+) channels (K(IR)), and canonical transient receptor potential cation channel 6 (TRPC6) currents. • SCE induced concentration-dependent relaxation in contracted CSM tissue, and the removal of the endothelium did not significantly affect their relaxation potencies. • In CSM cells, extracellular application of SCE significantly increased whole-cell K(Ca) currents (117.4%) and K(IR) currents (110.0%). These effects were completely abolished by charybdotoxin or BaCl(2). • In contrast, carbachol-induced TRPC6 channel activity was significantly inhibited (87.3%) by SCE in green fluorescent protein-TRPC6 pcDNA transfected HEK 293 cells. [Ca(2+)](i) measurements showed that SCE effectively reduced basal [Ca(2+)](i) in both cell lines (CSM cells and A7r5 cells) and the [Arg8]-vasopressin (AVP)-induced [Ca(2+)](i) increase in A7r5 cells. • Among the six SC lignans, schisandrin A and schisandrin B most effectively attenuated the AVP-induced [Ca(2+)](i) increase. • SCE induced relaxation of CSM that occurred primarily via an endothelium-independent pathway. • The relaxation effects of SCE on CSM were, in part, due to the activation of K(+) channels and inhibition of TRPC6 channels, resulting in decreased [Ca(2+)](i).

Controlled and Cardiac-Restricted Overexpression of the Arginine Vasopressin V1A Receptor Causes Reversible Left Ventricular Dysfunction Through Gα q -Mediated Cell Signaling

[Arg8]-vasopressin (AVP) activates 3 G-protein-coupled receptors: V1A, V2, and V1B. The AVP-V1A receptor is the primary AVP receptor in the heart; however, its role in cardiac homeostasis is controversial. To better understand AVP-mediated signaling in the heart, we created a transgenic mouse with controlled overexpression of the V1A receptor. The V1A receptor transgene was placed under the control of the tetracycline-regulated, cardiac-specific α-myosin heavy chain promoter (V1A-TG). V1A-TG mice had a normal cardiac function phenotype at 10 weeks of age; however, by 24 weeks of age, tetracycline-transactivating factor/V1A-TG mouse hearts had reduced cardiac function, cardiac hypertrophy, and dilatation of the ventricular cavity. Contractile dysfunction was also observed in isolated adult cardiac myocytes. When V1A receptor transgene was induced to be expressed in adult mice (V1A-TG(Ind)), left ventricular dysfunction and dilatation were also seen, albeit at a later time point. Because the V1A receptor mediates cell signaling through Gα(q) protein, we blocked Gα(q) signaling by crossing tetracycline-transactivating factor/V1A mice with transgenic mice that expressed a small inhibitory peptide against Gα(q). Gα(q) blockade abrogated the development of the heart failure phenotype in tetracycline-transactivating factor/V1A-TG mice. The heart failure phenotype could be reversed by administration of doxycycline. Our results demonstrate a role for V1A-mediated signaling in the development of heart failure and support a role for V1A blockade in the treatment of patients with elevated levels of vasopressin.

Role of vasopressin V1Areceptor in the urethral closure reflex in rats

An enhanced urethral closure reflex via the spinal cord is related to urethral resistance elevation during increased abdominal pressure. However, with the exception of monoamines, neurotransmitters modulating this reflex are not understood. We investigated whether the vasopressin V(₁A) receptor (V(₁A)R) is involved in the urethral closure reflex in urethane-anesthetized female rats. V(₁A)R mRNA was highly expressed among the vasopressin receptor family in the total RNA purified from lamina IX in the spinal cord L6-S1 segment. In situ hybridization analysis of the spinal L6-S1 segment confirmed that these positive signals from the V(₁A)Rs were only detected in lamina IX. Intrathecally injected Arg⁸-vasopressin (AVP), an endogenous ligand, significantly increased urethral resistance during an intravesical pressure rise, and its effect was blocked by the V(₁A)R antagonist. AVP did not increase urethral resistance in rats in which the pelvic nerves were transected bilaterally. Urethral closure reflex responses to the intravesical pressure rise increased by up to threefold compared with the baseline response after AVP administration in contrast to no increase by vehicle. In addition, intravenously and intrathecally injected V(₁A)R antagonists decreased urethral resistance. These results suggest that V(₁A)R stimulation in the spinal cord enhances the urethral closure reflex response, thereby increasing urethral resistance during an abdominal pressure rise and that V(₁A)R plays a physiological role in preventing urine leakage.

Enhanced glucose tolerance in the Brattleboro rat

[Arg 8]-vasopressin (AVP) plays a crucial role in regulating body fluid retention, which is mediated through the vasopressin V 2 receptor in the kidney. In addition, AVP is involved in the regulation of glucose homeostasis via vasopressin V 1A and vasopressin V 1B receptors. Our previous studies demonstrated that vasopressin V 1A receptor-deficient (V 1AR−/−) and V 1B receptor-deficient (V 1BR−/−) mice exhibited hyperglycemia and hypoglycemia with hypoinsulinemia, respectively. These findings indicate that vasopressin V 1A receptor deficiency results in decreased insulin sensitivity whereas vasopressin V 1B receptor deficiency results in increased insulin sensitivity. In addition, vasopressin V 1A and vasopressin V 1B receptor double-deficient (V 1ABR−/−) mice exhibited impaired glucose tolerance, suggesting that the effects of vasopressin V 1B receptor deficiency do not influence the development of hyperglycemia promoted by vasopressin V 1A receptor deficiency, and that the blockage of both receptors could lead to impaired glucose tolerance. However, the contributions of the entire AVP/vasopressin receptors system to the regulation of blood glucose have not yet been clarified. In this study, to further understand the role of AVP/vasopressin receptors signaling in blood glucose regulation, we assessed the glucose tolerance of AVP-deficient homozygous Brattleboro ( di/ di) rats using an oral glucose tolerance test (GTT). Plasma glucose and insulin levels were consistently lower in homozygous di/ di rats than in heterozygous di/+ rats during the GTT, suggesting that the blockage of all AVP/vasopressin receptors resulting from the AVP deficiency could lead to enhanced glucose tolerance.

Nonapeptide Hormones Oxytocin and Vasopressin Distinctly Regulate Cav1.2 L-type Calcium Channel Expression in Cardiomyocytes

Background: The neurohypophyseal hormones oxytocin (OT) and [Arg8]‐vasopressin (AVP) have recently been implicated in cardiac function. This study was designed to investigate actions of OT and AVP on regulation of the voltage‐gated Ca2+ channel in cardiomyocytes.Methods and Results: Cultured neonatal rat cardiomyocytes were stimulated with OT or AVP (10‐8 M to 10‐6 M) for 24‐72 h, followed by real‐time PCR and patch clamp studies. Although OT did not exert any modulatory effect on L‐type Ca2+ channel current, as a shortterm effect, stimulation of cardiomyocytes with OT but not AVP decreased the expression of Cav1.2 mRNA with a reduced L‐type Ca2+ channel current. A transcription factor CREB mRNA expression was down‐regulated by OT treatment, although T‐type Ca2+ channels (Cav3.1, Cav3.2) were unaffected by OT or AVP.Conclusion: OT but not AVP down‐regulates L‐type Ca2+ channel expression through the inhibition of CREB transcriptional, suggesting a novel mechanism of OT action in the cardiac electrophysiology.

Arginine vasopressin prevents against Aβ 25–35-induced impairment of spatial learning and memory in rats

Amyloid β protein (Aβ) is thought to be responsible for loss of memory in Alzheimer's disease (AD). A significant decrease in [Arg 8]-vasopressin (AVP) has been found in the AD brain and in plasma; however, it is unclear whether this decrease in AVP is involved in Aβ-induced impairment of spatial cognition and whether AVP can protect against Aβ-induced deficits in cognitive function. The present study examined the effects of intracerebroventricular ( i.c.v.) injection of AVP on spatial learning and memory in the Morris water maze test and investigated the potential protective function of AVP against Aβ-induced impairment in spatial cognition. The results were as follows: (1) i.c.v. injection of 25 nmol Aβ 25 – 35 resulted in a significant decline in spatial learning and memory; (2) 1 nmol and 10 nmol, but not 0.1 nmol, AVP injections markedly improved learning and memory; (3) pretreatment with 1 nmol or 10 nmol, but not 0.1 nmol, AVP effectively reversed the impairment in spatial learning and memory induced by Aβ 25 – 35; and (4) none of the drugs, including Aβ 25 – 35 and different concentrations of AVP, affected the vision or swimming speed of the rats. These results indicate that Aβ 25 – 35 could significantly impair spatial learning and memory in rats, and pretreatment with AVP centrally can enhance spatial learning and effectively prevent the behavioral impairment induced by neurotoxic Aβ 25 – 35. Thus, the present study provides further insight into the mechanisms by which Aβ impairs spatial learning and memory, suggesting that up-regulation of central AVP might be beneficial in the prevention and treatment of AD.

Nonapeptide Hormones Oxytocin and Vasopressin Distinctly Regulate CaV1.2 L-type Calcium Channel Expression in Cardiomyocytes

Background: The neurohypophyseal hormones oxytocin (OT) and [Arg8]-vasopressin (AVP) have recently been implicated in cardiac function. This study was designed to investigate actions of OT and AVP on regulation of the voltage-gated Ca2+ channel in cardiomyocytes. Methods and Results: Cultured neonatal rat cardiomyocytes were stimulated with OT or AVP (10-8 M to 10-6 M) for 24-72 h, followed by real-time PCR and patch clamp studies. Although OT did not exert any modulatory effect on L-type Ca2+ channel current, as a shortterm effect, stimulation of cardiomyocytes with OT but not AVP decreased the expression of Cav1.2 mRNA with a reduced L-type Ca2+ channel current. A transcription factor CREB mRNA expression was down-regulated by OT treatment, although T-type Ca2+ channels (Cav3.1, Cav3.2) were unaffected by OT or AVP. Conclusion: OT but not AVP down-regulates L-type Ca2+ channel expression through the inhibition of CREB transcriptional, suggesting a novel mechanism of OT action in the cardiac electrophysiology.

Selective V1a agonism reduces vascular leakage and cardiopulmonary dysfunction in methicillin-resistant Staphylococcus aureus sepsis

This randomized, controlled experimental trial was performed to compare the effects of the selective V1a-receptor agonist (Phe2Orn8) vasotocin (POV) and the mixed V1a/V2-receptor agonist (Arg8) vasopressin (AVP) on vascular leakage and cardiopulmonary dysfunction associated with methicillin-resistant Staphylococcus aureus (MRSA) pneumonia-induced septic shock using an established ovine model.