V1a Receptor Blockade Research Articles

Effect of Neurohypophyseal Hormones on Excretion of Proteins by the Kidneys

Vasopressin (VP) is one of the main factors affecting intraglomerular hemodynamics, filtration pressure and the state of mesangial cells and contributing to the progression of proteinuria. The aim of this work was to study the effect of neurohypophyseal hormones (VP and oxytocin) on urinary protein excretion. Experiments were performed on Wistar rats, healthy and with microalbuminuria caused by minimal damage to the glomerular filter. Microalbuminuria was modeled by administration of D-nitroarginine methyl ester (D-NAME, 50 mg/kg, intraperitoneally). VP (0.05 and 1.5 nmol/kg) and oxytocin (0.15 nmol/kg) were administered to rats intramuscularly, V2-antagonist (15 nmol/kg) and V1a-antagonist (20 nmol/kg) intraperitoneally. To reduce the level of endogenous VP, animals were given water to drink (10 ml/kg), urine was collected for 2 h, and the levels of total protein, albumin, β2-microglobulin, and immunoglobulin G (IgG) were analyzed. In healthy rats, VP at a dose of 0.05 nmol/kg and oxytocin did not affect albumin excretion, but VP at a dose of 1.5 nmol/kg provoked microalbuminuria. In a model of impaired properties of the glomerular filter caused by the D-NAME administration, VP at a dose of 0.05 nmol/kg and oxytocin led to the normalization of albumin excretion, and VP at a dose of 1.5 nmol/kg caused pronounced proteinuria, albumin excretion increased by 100 times, IgG – by 10 times. Blockade of V2 receptors aggravated protein loss caused by D-NAME and VP (1.5 nmol/kg), while blockade of V1a receptors prevented it. Thus, at high concentrations in the blood, VP enhances protein filtration in the kidney. This effect is mediated by V1a receptors and, depending on the barrier properties of the glomerular filter, leads to the development of microalbuminuria or severe proteinuria. Oxytocin and VP at a dose at which it predominantly activates V2 receptors have an antiproteinuric effect. The revealed effects of neurohypophyseal hormones on albumin excretion open up new promising therapeutic targets for the correction of glomerular dysfunctions.

Effect of Vasopressin V1a Receptor Blockade on Renal Osmoregulatory Function in L-Thyroxine-Induced Hyperthyroid Rats with Different Blood Vasopressin Levels

Effect of Vasopressin V1a Receptor Blockade on Renal Osmoregulatory Function in L-Thyroxine-Induced Hyperthyroid Rats with Different Blood Vasopressin Levels

Another controller system for arterial pressure. AngII-vasopressin neural network of the parvocellular paraventricular nucleus may regulate arterial pressure during hypotension

Angiotensin II (AngII) immunoreactive cells, fibers and receptors, were found in the parvocelluar region of paraventricular nucleus (PVNp) and AngII receptors are present on vasopressinergic neurons. However, the mechanism by which vasopressin (AVP) and AngII may interact to regulate arterial pressure is not known. Thus, we tested the cardiovascular effects of blockade of the AngII receptors on AVP neurons and blockade of vasopressin V1a receptors on AngII neurons. We also explored whether the PVNp vasopressin plays a regulatory role during hypotension in anesthetized rat or not. Hypovolemic-hypotension was induced by gradual bleeding from femoral venous catheter. Either AngII or AVP injected into the PVNp produced pressor and tachycardia responses. The responses to AngII were blocked by V1a receptor antagonist. The responses to AVP were partially attenuated by AT1 antagonist and greatly attenuated by AT2 antagonist. Hemorrhage augmented the pressor response to AVP, indicating that during hemorrhage, sensitivity of PVNp to vasopressin was increased. By hemorrhagic-hypotension and bilateral blockade of V1a receptors of the PVNp, we found that vasopressinergic neurons of the PVNp regulate arterial pressure towards normal during hypotension. Taken together these findings and our previous findings about angII (Khanmoradi and Nasimi, 2017a) for the first time, we found that a mutual cooperative system of angiotensinergic and vasopressinergic neurons in the PVNp is a major regulatory controller of the cardiovascular system during hypotension.

Sex differences in vasopressin 1a receptor regulation of social communication within the lateral habenula and dorsal raphe of mice

The neuropeptide arginine-vasopressin (AVP) has long been implicated in the regulation of social behavior and communication in diverse taxa, often through its actions on the V1a receptor (V1aR) and in a sex-different and steroid-dependent way. One source of sex-different brain AVP is the steroid-sensitive and sexually-dimorphic AVP neurons in the bed nucleus of the stria terminalis (BNST), a cell population that regulates social behavior in a sex-dependent manner. Potential targets of these BNST-AVP cells include the lateral habenula (LHb) and dorsal raphe (DR), areas known to be important for social behavior, yet few studies have investigated AVP action within these regions. Consequently, to test if V1aR action in the LHb or DR controls social behavior in a sexually dimorphic manner, we administered a highly-specific V1aR antagonist (or saline vehicle) in the LHb or DR of C57BL/6 male and female mice and tested its effects on social investigation, social communication (urine marking, ultrasonic vocalizations), and territorial aggression. V1aR antagonism of the LHb or DR decreased male urine marking toward unfamiliar males, but not toward unfamiliar females. Additionally, V1aR blockade of the LHb decreased ultrasonic vocalizations generated in the presence of females. Social investigation, locomotion and aggressive behavior were not altered by V1aR antagonism in either area. Blocking V1aR in the LHb or DR of females had no effect, indicating V1aR action in the DR and LHb drives sex differences in social communication.

Exogenous vasopressin dose-dependently modulates gastric microcirculatory oxygenation in dogs via V1A receptor

BackgroundHypercapnia improves gastric microcirculatory oxygenation (μHbO2) and increases vasopressin plasma levels, whereas V1A receptor blockade abolishes the increase of μHbO2. The aim of this study was to evaluate the effect of exogenous vasopressin (AVP) in increasing doses on microcirculatory perfusion and oxygenation and systemic hemodynamic variables. Furthermore, we evaluated the role of the vasopressin V1A receptor in mediating the effects.MethodsIn repetitive experiments, six anesthetized dogs received a selective vasopressin V1A receptor inhibitor ([Pmp1, Tyr (Me)2]-Arg8-Vasopressin) or sodium chloride (control groups). Thereafter, a continuous infusion of AVP was started with dose escalation every 30 min (0.001 ng/kg/min–1 ng/kg/min). Microcirculatory variables of the oral and gastric mucosa were measured with reflectance spectrometry, laser Doppler flowmetry, and incident dark field imaging. Transpulmonary thermodilution was used to measure systemic hemodynamic variables. AVP plasma concentrations were measured during baseline conditions and 30 min after each dose escalation.ResultsDuring control conditions, gastric μHbO2 did not change during the course of experiments. Infusion of 0.001 ng/kg/min and 0.01 ng/kg/min AVP increased gastric μHbO2 to 87 ± 4% and 87 ± 6%, respectively, compared to baseline values (80 ± 7%), whereas application of 1 ng/kg/min AVP strongly reduced gastric μHbO2 (59 ± 16%). V1A receptor blockade prior to AVP treatment abolished these effects on μHbO2. AVP dose-dependently enhanced systemic vascular resistance (SVR) and decreased cardiac output (CO). After prior V1A receptor blockade, SVR was reduced and CO increased (0.1 ng/kg/min + 1 ng/kg/min AVP).ConclusionsExogenous AVP dose-dependently modulates gastric μHbO2, with an increased μHbO2 with ultra-low dose AVP. The effects of AVP on μHbO2 are abolished by V1A receptor inhibition. These effects are independent of a modulation of systemic hemodynamic variables.

Over-expression of V1A receptors in PVN modulates autonomic cardiovascular control

The hypothalamic paraventricular nucleus (PVN) is a key integrative site for the neuroendocrine control of the circulation and of the stress response. It is also a major source of the neuropeptide hormone vasopressin (VP), and co-expresses V1a receptors (V1aR). We thus sought to investigate the role of V1aR in PVN in cardiovascular control in response to stress. Experiments were performed in male Wistar rats equipped with radiotelemetric device. The right PVN was transfected with adenoviral vectors (Ads) engineered to over-express V1aR along with an enhanced green fluorescent protein (eGFP) tag. Control groups were PVN transfected with Ads expressing eGFP alone, or wild-type rats (Wt). Rats were recorded with and without selective blockade of V1aR (V1aRX) in PVN under both baseline and stressed conditions. Blood pressure (BP), heart rate (HR), their short-term variabilities, and baroreflex sensitivity (BRS) were evaluated using spectral analysis and the sequence method, respectively. Under baseline physiological conditions,V1aR rats exhibited reduced BRS and a marked increase of BP and HR variability during exposure to stress. These effects were all prevented by V1aRX pretreatment. In Wt rats, V1aRX did not modify cardiovascular parameters under baseline conditions, and prevented BP variability increase by stress. However, V1aRX pretreatment did not modify baroreflex desensitization by stress in either rat strain. It follows that increased expression of V1aR in PVN influences autonomic cardiovascular regulation and demarcates vulnerability to stress. We thus suggest a possible role of hypothalamic V1aR in cardiovascular pathology.

Vasopressin V1A receptors mediate the stabilization of intestinal mucosal oxygenation during hypercapnia in septic rats

BackgroundMicrovascular oxygen saturation (μHBO2) plays an essential role in the development and outcome of sepsis. Hypercapnia (HC) improves the microvascular oxygenation of the mucosa in both healthy and septic animals. Vasopressin V1A receptor blockade prevents this positive effect under otherwise physiological conditions. The aim of this study was to investigate the effects and mechanisms of the vasopressin system during hypercapnia under septic conditions. Methods80 rats were randomized into 8 groups (N=10). Colon ascendens stent peritonitis (CASP) or sham surgery was performed on 40 animals each to establish a moderate polymicrobial sepsis or sham control, respectively. 24h after sepsis induction the animals were subjected to 120min of volume-controlled and pressure-limited ventilation with either normocapnic (pCO2 35–45mmHg) or moderate hypercapnic (pCO2 of 65–75mmHg) ventilation targets. Animals received either vasopressin V1A receptor blockade (SR 49059, 1mgkg−1 i.v.) or vehicle solution (dimethyl sulfoxide, 1%). Blood pressure, heart rate, pO2 and pCO2 were measured and microcirculatory oxygenation (μHBO2) and microcirculatory flow (μflow) were recorded using tissue reflectance spectrophotometry. Oxygen supply (μDO2) and consumption (μVO2) were calculated from intermittent blood gas analysis. ResultsIn septic animals, μHBO2 declined during normocapnia (−11±10.3) but remained unchanged during hypercapnia. μHBO2 declined with vasopressin V1A receptor blockade both during normocapnia (−7.4±10.6) and hypercapnia (−9.2±9.8). Microcirculatory oxygen consumption was significantly reduced by hypercapnia in septic animals (−2.4·105 [AU]±2.4·105 [AU]). In sham animals, μHBO2 and μVO2 did not change. ConclusionVasopressin V1A receptors mediate the beneficial effects of hypercapnia on microcirculatory oxygenation during sepsis. The effects of vasopressin on μHBO2 might be related to decreased oxygen consumption during hypercapnia.

Abstract 035: Differential Sodium-evoked Activation of Pvn Magnocellular vs. Parvocellular Neurons in Rats Lacking Central GαI<SUB.2 Proteins Contributes to Sustained Elevations in Blood Pressure

Aim: To determine the role of brain Gαi 2 proteins in mediating sodium-evoked PVN neuronal activation and blood pressure regulation in conscious rats. Methods: 24-h intracerebroventricular scrambled (SCR) or Gαi 2 oligodeoxynucleotide (ODN; 25μg/5μl)-pretreated conscious Sprague-Dawley rats were monitored for changes in MAP in response to HS (IV 3M NaCl; 0.14 ml/100g). Rats were sacrificed at control (C), 10, 40, or 100-min post-HS for PVN cFos IHC and analysis of plasma AVP and NE. Separate groups received a V 1a receptor antagonist (IV; 10 μg/ml/kg) 5-min prior to HS. Results: No difference was observed in sodium-evoked peak change in MAP and MAP remained elevated at 100-min in Gαi 2 but not SCR ODN rats (MAP 100-min post-HS [mmHg] SCR 134±2 vs Gαi 2 146±3, P<0.05). Significant increases in the number of Fos + PVN magnocellular neurons were observed post-HS in SCR and Gαi 2 ODN groups ([Fos + cells] SCR C 3±1 vs 100-min 31±5; Gαi 2 C 2±0 vs 100-min 26±4, P <0.05). A rapid increase in circulating AVP was observed at 10-min in both SCR (plasma AVP [pg/mL] C 12.2±1.6 vs 10-min 62.8±6.9, P <0.05) and Gαi 2 ODN (plasma AVP [pg/mL] C 12.1±1.5 vs 10-min 67.7±7.7 P <0.05) groups and returned to control levels at 40- and 100-min. SCR ODN rats exhibited significant increases in the number of Fos + PVN parvocellular neurons ([Fos+ cells] C 15±1 vs 100-min 67±4, P <0.05) and a significant suppression in circulating NE post-HS (plasma NE [nmol/L] C 44.1±4.9 vs 10-min 17.4±3.9, P <0.05). Gαi 2 ODN rats exhibited significantly less Fos + parvocellular neurons compared to SCR ODN rats (100-min [Fos+ cells] SCR 67±4 vs Gαi 2 30±2, P <0.05) and failed to suppress circulating NE ( P >0.05). V 1a receptor blockade prevented a HS-evoked increase in MAP in SCR ODN rats while Gαi 2 ODN rats exhibited elevated MAP (MAP 100-min [mmHg] SCR 125±2 vs Gαi 2 135±0, P <0.05). Conclusion: Brain Gαi 2 proteins are required to mediate sodium-evoked parvocellular sympathetic, but not magnocellular vasopressinergic, responses to maintain physiological blood pressure regulation. A significant component of blood pressure control in this setting is regulated by the sympathetic nervous system, as supported by the attenuated activation of PVN parvocellular neurons and a failure to suppress circulating levels of NE in Gαi 2 ODN rats.

Sex-specific modulation of juvenile social play behavior by vasopressin and oxytocin depends on social context.

We recently demonstrated that vasopressin (AVP) in the lateral septum modulates social play behavior differently in male and female juvenile rats. However, the extent to which different social contexts (i.e., exposure to an unfamiliar play partner in different environments) affect the regulation of social play remains largely unknown. Given that AVP and the closely related neuropeptide oxytocin (OXT) modulate social behavior as well as anxiety-like behavior, we hypothesized that these neuropeptides may regulate social play behavior differently in novel (novel cage) as opposed to familiar (home cage) social environments. Administration of the specific AVP V1a receptor (V1aR) antagonist (CH2)5Tyr(Me2)AVP into the lateral septum enhanced home cage social play behavior in males but reduced it in females, confirming our previous findings. These effects were context-specific because V1aR blockade did not alter novel cage social play behavior in either sex. Furthermore, social play in females was reduced by AVP in the novel cage and by OXT in the home cage. Additionally, females administered the specific OXT receptor antagonist desGly-NH2,d(CH2)5−[Tyr(Me)2,Thr4]OVT showed less social play in the novel as compared to the home cage. AVP enhanced anxiety-related behavior in males (tested on the elevated plus-maze), but failed to do so in females, suggesting that exogenous AVP alters social play and anxiety-related behavior via distinct and sex-specific mechanisms. Moreover, none of the other drug treatments that altered social play had an effect on anxiety, suggesting that these drug-induced behavioral alterations are relatively specific to social behavior. Overall, we showed that AVP and OXT systems in the lateral septum modulate social play in juvenile rats in neuropeptide-, sex- and social context-specific ways. These findings underscore the importance of considering not only sex, but also social context, in how AVP and OXT modulate social behavior.

Central vasopressin V1A receptor blockade alters patterns of cellular activation and prevents glucocorticoid habituation to repeated restraint stress exposure

Our previous experiments implicated a role for the arginine vasopressin (AVP) V1A receptor subtype in mediating the normal decline (habituation) of hypothalamic-pituitary-adrenal (HPA) axis responses to repeated restraint exposure. To explore pathways mediating the endogenous effects of central AVP on stress HPA axis habituation, here we compared cellular (Fos) and hormone responses in male rats receiving chronic icv infusion of vehicle or a V1A receptor antagonist that began 7 d before stress testing, continued through the duration of acute and repeat restraint exposure. As a group, rats with V1A antagonism displayed a modest reduction in ACTH habituation, whereas the decline in corticosterone was completely prevented. V1A antagonized rats also showed reduced evidence of habituated Fos responses in the paraventricular nucleus of the hypothalamus, medial amygdala, and within the anterior division of the bed nucleus of the stria terminalis. Based on these cellular and neuroendocrine responses, we then examined whether repeated restraint is reflected by changes in V1A receptor binding. Relative to stress naïve animals, repeatedly exposed rats showed lower levels of V1A binding in the dentate gyrus of the hippocampus, thalamus and central amygdala, but higher levels in the septum and anterior BST. Taken together, these findings suggest that AVP may act within multiple targets to regulate the normal decline in stress-induced drive to the HPA axis, and that this may involve the net of V1A receptor stimulatory and inhibitory influences on neuroendocrine habituation.

Chronic blockade of vasopressin type1a receptor and/or type2 receptor improves both cardiac and renal damage and dysfunction in hypertensive rats

Background: Vasopressin (AVP) type 1a receptor (V1aR) antagonist could theoretically benefit heart failure (HF) patients by decreasing afterload and ameliorating remodeling. However, the conflicting results have been reported. Also, there is a concern that increased AVP may have detrimental effects through V1aR in HF patients treated with oral type 2 receptor (V2R) antagonist, tolvaptan. Therefore, we examined whether the chronic administration of V1a antagonist may exert beneficial effects and also its additive effects to tolvaptan treatment in rat hypertensive HF model. Methods and results: In Dahl salt-sensitive hypertensive rats, not only circulating AVP level, but also myocardial AVP and V1a receptor (V1aR), and renal V1aR and V2R expressions were significantly activated during the transition to HF (18-21 weeks). First, they were chronically treated with vehicle, V1aR antagonist (OPC21268), tolvaptan, or OPC21268 plus tolvaptan (combination) from pre-hypertrophic stage (6 weeks). All three treatments did not affect blood pressure. In OPC21268 and tolvaptan groups, the median survival time was significantly improved from 112 day (vehicle) to 141 day and 160 day, respectively. It was improved to a greater extent with the combined treatment (175 day). Echocardiography showed the improvement of fractional shortening (FS) was observed in all three treatment groups and the suppression of LV hypertrophy (LVH) only in OPC 21268 and combination groups. Furthermore, renal histopathologic damage (glomerulosclerosis and tubulointerstitial fibrosis) was ameliorated, and renal function (creatinine clearance) was also improved in all three treatment groups at HF stage. When these treatments were started at the established LVH phase (11 weeks), the improvement of survival was observed only in tolvaptan group and no additive improvement in the combined treatment. Conclusions: These findings suggest that V1aR blockade may ameliorate the development of LVH and HF in the treatment of hypertensive HF with renal injuries, and have limited effects starting after the establishment of LVH. Also, the chronic administration of both V1a and V2 antagonists exerts further beneficial effects. The underlying mechanism may be related to protection of myocardial and renal damages independent of blood pressure.

Vasopressin V1A receptors mediate the increase in gastric mucosal oxygenation during hypercapnia

Hypercapnia (HC) improves systemic oxygen delivery (DO₂) and microvascular hemoglobin oxygenation of the mucosa (μHbO₂). Simultaneously, HC increases plasma levels of vasopressin. Although vasopressin is generally regarded a potent vasoconstrictor particularly in the splanchnic region, its effects on splanchnic microcirculation during HC is unclear. The aim of this study was to evaluate the role of endogenous vasopressin on gastric mucosal oxygenation and hemodynamic variables during physiological (normocapnia) and hypercapnic conditions. Five dogs were repeatedly anesthetized to study the effect of vasopressin V(1A) receptor blockade ([Pmp¹,Tyr(Me)²]-Arg⁸-Vasopressin, 35 μg/kg) on hemodynamic variables and μHbO₂ during normocapnia or HC (end-tidal CO₂ 70 mmHg). In a control group, animals were subjected to HC alone. μHbO₂ was measured by reflectance spectrophotometry, systemic DO₂ was calculated from intermittent blood gas analysis, and cardiac output was measured by transpulmonary thermodilution. Data are presented as mean±s.e.m. for n=5 animals. During HC alone, DO₂ increased from 12±1 to 16±1 ml/kg per min and μHbO₂ from 70±4 to 80±2%. By contrast, additional vasopressin V(1A) receptor blockade abolished the increase in μHbO₂ (80±2 vs. 69±2%) without altering the increase in DO₂ (16±1 vs. 19±2 ml/kg per min). Vasopressin V1A receptor blockade (VB) during normocapnia neither affected DO₂ (13±1 vs. 14±1 ml/kg per min) nor μHbO₂ (75±3 vs. 71±5%). Vasopressin V(1A) receptor blockade abolished the increase in μHbO₂ during HC independent of DO₂. Thus, in contrast to its generally vasoconstrictive properties, the vasopressin V1A receptors seem to mediate the increase in gastric microcirculatory mucosal oxygenation induced by acute HC.

Central Vasopressin V1A Receptor Blockade Impedes Hypothalamic–Pituitary–Adrenal Habituation to Repeated Restraint Stress Exposure in Adult Male Rats

Previous studies suggest that central arginine vasopressin (AVP) signaling can inhibit the hypothalamic-pituitary-adrenal (HPA) axis. To test a role for the AVP V1A receptor in stress HPA axis habituation, adult male rats were exposed to 5 consecutive days of 3 h restraint with or without continuous intracerebroventricular infusion of the V1A receptor antagonist d(CH2)5Tyr(Me)AVP (10 μg/day). Assessment of neuropeptide expression and HPA output under basal conditions revealed no effects of V1A receptor antagonism in stress naive animals. Between the first and last day of restraint exposure, controls showed marked declines in ACTH and corticosterone responses, and maintained plasma concentrations of testosterone. In contrast, V1A receptor antagonized animals displayed significantly smaller declines in ACTH and corticosterone responses, and a decrease in plasma testosterone. Despite their reduced expression of HPA axis habituation, antagonized animals continued to show stress-induced increases in AVP mRNA in the hypothalamic paraventricular nucleus and bed nucleus of the stria terminalis, and even higher levels of AVP expression in the medial amygdala relative to controls. The data leave open the nature and extent to which these and other AVP-containing pathways are recruited during repeated restraint, but nevertheless reveal a critical role for central V1A receptors in stress adaptation. As the effects of V1A receptor antagonism were restricted to the repeated restraint condition, we conclude that normal adaptation to stress involves a shift toward enhanced AVP utilization and/or V1A receptor signaling.

Dendritic release of VP mediates crosstalk between neuroendocrine and presympathetic PVN neurons: Role in osmotically‐driven homeostatic responses

Dendritic release of vasopressin (VP) in the SON and PVN nuclei plays an important role in the autoregulation of VP neuronal activity. Here, we tested the hypothesis that dendritically‐released VP acts in a diffusible manner to influence the activity of neighboring presympathetic neurons. Patch‐clamp recordings in brain slices showed that focally applied VP depolarized and increased presympathetic PVN‐RVLM neurons (~450%, P< 0.01), an effect that persisted in the presence of GABA/glutamate receptor blockers. Activation of a single, identified eGFP‐VP neuron using photolysis of caged NMDA induced a Ca2+‐dependent, V1a‐mediated increased firing discharge in neighboring PVN‐RVLM neurons. Blockade of V1a receptors per se reduced PVN‐RVLM firing discharge (~75%, P< 0.02). Increasing (high K+, aminopeptidase blockade) and decreasing (κ opiod agonist) endogenous VP ambient levels, respectively, further increased/decreased PVN‐RVLM firing activity. Finally, a central osmotic stimulation (NaCl 0.3–2.1 omosl/l ICA) induced a prompt increase in RSNA, and effect that was blunted (~50%) when V1a receptors were locally blocked within the PVN (P<0.001). Collectively, our results demonstrate that dendritic release of VP mediates a functional crosstalk between neurosecretory and presympathetic PVN neurons, playing an important role in the generation of osmotically‐driven homeostatic responses. Supported by NIH HL‐090948 to JES and NIH HL‐62222 to KKP.

Central vasopressin V1a receptors modulate neural processing in mothers facing intruder threat to pups

Vasopressin V1a receptors in the rat brain have been studied for their role in modulating aggression and anxiety. In the current study blood-oxygen-level-dependent (BOLD) functional MRI was used to test whether V1a receptors modulate neural processing in the maternal brain when dams are exposed to a male intruder. Primiparous females were given an intracerebroventricular (ICV) injection of vehicle or V1a receptor antagonist ([deamino-Pen 1, O–Me–Tyr, Arg 8]-Vasopressin, 125 ng/10 μL) 90–120 min before imaging. During fMRI, awake dams were presented with a male intruder threat to pups using a specialized chamber that contained separate compartments for pups and a male intruder. Our results indicate that the number of activated voxels was reduced in the cortical amygdala with V1a receptor blockade, while an increase was observed in the anterior olfactory nucleus and other areas. Dams treated with V1a antagonist showed significantly greater BOLD responses in the anterior olfactory nucleus, infralimbic prefrontal cortex, gustatory cortex, somatosensory cortex, and substantia innominata when presented with a novel male intruder. BOLD responses were reduced in the cortical amygdala and ventromedial hypothalamus. The V1a receptor sensitive areas play roles in the processing of smell, taste and touch and emotional reactivity. Thus one interpretation of the present fMRI data is that vasopressin, acting through V1a receptors, may modulate sensory processing and perhaps coordinate this effect with changes in visceromotor activity during the initial stages of maternal aggressive motivation and/or anxiogenic responses.

Locally released vasopressin increases presympathetic PVN neuronal activity in a calcium‐dependent manner

Accumulating evidence indicates that the vasopressin (VP) is locally released within the supraoptic and paraventricular (PVN) nuclei, autoregulating VP neuronal activity. Here, we tested if intranuclear VP release also influences presympathetic PVN neuronal activity. Patch‐clamp recordings from presympathetic PVN‐RVLM neurons showed that focal application of VP (1µM) evoked an inward current (~8pA, P< 0.002), depolarized Vm (4mV, P< 0.0001), and increased PVN‐RVLM firing activity (~780%, P< 0.0001), effects blocked by a V1a receptor antagonist. The expression of V1a receptors in PVN‐RVLM neurons was confirmed immunohistochemically. V1a receptor blockade hyperpolarized Vm (~4mV, P< 0.001) and reduced ongoing firing activity of PVN‐RVLM neurons (~70%, P< 0.002). VP excitatory effect on PVN‐RVLM neurons was blocked by rapid chelation of intracellular Ca2+ (P< 0.02), but was not dependent on an influx of extracellular Ca2+. Finally, the effect of endogenously released VP was dependent on the activity of endogenous aminopeptidases. In summary, our results indicate that endogenously released VP, likely from a magnocellular neurosecretory source, tonically excites presympathetic PVN neurons, constituting a functionally relevant intercellular signaling pathway in the generation of homeostatic patterns of neuroendocrine and autonomic activities by the PVN. Supported by NIH HL68725

Interactive computerized microscopy as a tool for quantifying vascular remodelling: Effects of diabetes and V1a receptor antagonist SR 49059 on rat mesenteric arterial bed

A methodology using interactive computerized microscopy (ICM) was developed to quantify in the mesenteric arterial bed the morphometric changes associated with diabetes and the influence of treatment with SR 49059, an antagonist of vasopressin V1a receptors. Four groups of rats were studied: untreated normal (N) or streptozotocin- (60 mg/kg i.v.) induced diabetic (D), and treated (0.4 mg/g SR 49059 included in food) normal (NT) or diabetic (DT) animals. Treatment was initiated 4 days after diabetes induction and continued for 3 weeks. Nested (hierarchical) analysis of variance of ICM data was performed on raw diameter or after logarithmic normalization of area and nuclei values. Diabetes was associated with an increase in arterial diameters, and in total vessel, wall, media, adventitia, and lumen areas. The same parameters, with the exception of the lumen, were also increased in DT as compared to D. The number of nuclei in the media or adventitia was increased in D as compared to N, and in DT as compared to D. In summary, ICM is allowed to further characterize the vascular mesenteric changes and describe for the first time the enlargement of adventitia associated with diabetes. Our study also suggested that the blockade of V1a receptors is unable to prevent diabetes-related vascular changes, although the slight increase in food intake associated with SR 49059 treatment may have had an indirect influence on angiopathy development.

Chronic Vasopressin Antagonism in Two-Kidney, One-Clip Renovascular Hypertension

The role of vasopressin (AVP) in the maintenance of hypertension in the rat model of two-kidney, one-clip (2K1C) Goldblatt hypertension was assessed using the nonpeptide orally effective V1a receptor antagonist, OPC-21268. Rats were studied eight weeks after surgery when mean arterial pressure (MAP) was significantly increased in 2K1C rats compared to SHAM operated controls (2K1C 139 ±6, SHAM 106±3, P<0.01). Neither acute (OPC-21268, 30mg/kg) nor chronic (OPC-21268, 30mg/kg twice daily) V1a receptor blockade reduced blood pressure in either 2K1C or SHAM rats. The results of binding kinetic studies confirmed that OPC-21268 was effective at its putative site of action, the V1a receptor in both 2K1C and SHAM rats. These results indicate AVP is not involved in the maintenance of blood pressure in the 2K1C model of renovascular hypertension.

Attenuation of genetic hypertension after short-term vasopressin V1A receptor antagonism.

Abnormalities of the vasopressin system are found in genetic hypertension. This study compares the delayed effects of a brief period of vasopressin V1A receptor blockade and angiotensin-converting enzyme inhibition in young female and male spontaneously hypertensive rats (SHR) on the development of hypertension in adult life. In a separate study, the role of vasopressin in the maintenance of blood pressure in adult SHR was assessed. Young SHR received either the nonpeptide vasopressin V1A receptor antagonist OPC-21268, the angiotensin-converting enzyme inhibitor ramipril, or vehicle from 6 to 10 weeks of age. During the treatment period, OPC-21268 and ramipril reduced systolic blood pressure compared with control SHR (P < .001). Blood pressure in male SHR 7 weeks after treatment withdrawal was 178 +/- 1 mm Hg in ramipril-treated, 184 +/- 1 mm Hg in OPC-21268-treated, and 200 +/- 2 mm Hg in control SHR (P < .001). Similar results were seen in female SHR, although both OPC-21268 and ramipril were less effective antihypertensive agents in female compared with male SHR. The sustained attenuation in blood pressure was not associated with significant cardiovascular structural changes (left ventricular-to-body weight ratio, renal weight-to-body weight ratio, mesenteric resistance artery media-to-lumen ratio). Results of vasopressin V1A receptor binding kinetics and plasma renin or aldosterone concentrations did not suggest a lasting effect of OPC-21268 on the vasopressin system or of ramipril on the renin-angiotensin system following treatment withdrawal.(ABSTRACT TRUNCATED AT 250 WORDS)