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Hyponatremia, especially if acute and severe, can be a life-threatening condition. Several conditions can trigger hyponatremia. In this review, we will discuss two conditions that can determine euvolemic hyponatremia: the cerebral/renal salt wasting (CRSW) syndrome and the syndrome of inappropriate secretion of antidiuretic hormone (SIADH), including the two subtypes: reset osmostat (RO) and nephrogenic syndrome of inappropriate antidiuresis (NSIAD) and their differential diagnoses. Despite the passage of over 70 years since its first description, to date, the true etiopathogenesis of CRSW syndrome, a rare cause of hypovolemic/euvolemic hyponatremia, is almost unknown. SIADH, including RO and NSIAD, is sometimes difficult to differentiate from CRSW syndrome; in its differential diagnosis, the clinical approach based on the evaluation of the extracellular volume (ECV) was proven insufficient. We therefore suggest a simple diagnostic algorithm based on the assessment of the degree of hyponatremia, urinary osmolality, and the assessment of the fraction of urate excretion (FEUa) in conditions of hyponatremia and after serum sodium correction, to be applied in children over 1 year of life., Author(s): Flaminia Bardanzellu [sup.1] , Maria Antonietta Marcialis [sup.1] , Roberta Frassetto [sup.1] , Alice Melis [sup.1] , Vassilios Fanos [sup.1] Author Affiliations: (1) grid.7763.5, 0000 0004 1755 3242, Neonatal [...]

Quantitative mass spectrometry was used to identify hormone-dependent signaling pathways in renal medullary thick ascending limb (mTAL) cells via phosphoproteomic analysis. Active transport of NaCI across the mTAL epithelium is accelerated by hormones that increase cAMP levels (vasopressin, glucagon, parathyroid hormone, and calcitonin), mTAL suspensions from rat kidneys were exposed (15 min) to a mixture of these four hormones. Tryptic phosphopeptides (immobilized metal affinity chromatography-enriched) were identified and quantified by mass spectrometry (LTQ-Orbitrap) using label-free methodology. We quantified a total of 654 phosphopeptides, of which 414 were quantified in three experimental pairs (hormone vs. vehicle). Of these phosphopeptides, 82% were statistically unchanged in abundance in response to the hormone mixture. In contrast, 48 phosphopeptides were significantly increased, whereas 28 were significantly decreased. The population of up-regulated phosphopeptides was highly enriched in basophilic kinase substrate motifs (AGC or calmodulin-sensitive kinase families), whereas the down-regulated sites were dominated by 'proline-directed' motifs (cyclin-dependent or MAP kinase families). Bioinformatic classification uncovered overrepresentation of transmembrane transporters, protein phosphatase regulators, and cytoskeletal binding proteins among the regulated proteins: Immunoblotting with phospho-specific antibodies confirmed cAMP/vasopressin-dependent phosphorylation at Thr96, Ser126, and Ser874 of the [Na.sup.+]:[K.sup.+]:2[CI.sup.-] cotransporter NKCC2, at Ser552 of the [Na.sup.+]:[H.sup.+] exchanger NHE3, and at Ser552 of [beta]-catenin. Vasopressin also increased phosphorylation of NKCC2 at both Ser126 (more than fivefold) and Ser874 (more than threefold) in rats in vivo. Both sites were phosphorylated by purified protein kinase A during in vitro assays. These results support the view that, although protein kinase A plays a central role in mTAL signaling, additional kinases, including those that target proline-directed motifs, may be involved. protein phosphatase | glucose transporters | mass spectrometry | ion transporters | protein kinase doi/ 10.1073/pnas.1007424107

Strait KA, Stricklett PK, Chapman M, Kohan DE. Characterization of vasopressin-responsive collecting duct adenylyl cyclases in the mouse. Am J Physiol Renal Physiol 298: F859-F867, 2010. First published December 2, 2009; doi: 10.1152/ajprenal.00109.2009.--Little is known about collecting duct adenylyl cyclase (AC) isoforms or regulation in the mouse. We performed RT-PCR for AC isoforms 1-9 in microdissected cortical (CCD) and outer medullary (OMCD) and acutely isolated inner medullary (IMCD) collecting duct. Ali collecting duct regions contained AC3, AC4, and AC6 mRNA, while CCD and OMCD, but not IMCD, also contained AC5 mRNA. Acutely isolated IMCD expressed AC3, AC4, and AC6 proteins by Western blot analysis. The mIMCD3 cell line expressed AC2, AC3, AC4, AC5, and AC6 mRNA; M-I CCD cells expressed AC2, 3, 4, and 6, while mpkCCD cell lines contained AC3, AC4, and AC6 mRNA. AVP stimulated cAMP accumulation in acutely isolated mouse IMCD; this was reduced by chelation of extracellular calcium (EGTA) and almost completely abolished by blockade of calmodulin (W-7). Blockade of calmodulin kinase with KN-93 or endoplasmic reticulum calcium ATPase (thapsigargin) also reduced the AVP response. A similar inhibitory effect of W-7, KN-93, and thapsigargin was seen on forskolin-stimulated cAMP content in acutely isolated mouse IMCD. These three agents had the same pattern of blockade of AVP- or forskolin-stimulated AC activity in acutely isolated rat IMCD. AVP responsiveness in primary cultures of mouse IMCD was also reduced by W-7, KN-93, and thapsigargin. Small interfering RNA (siRNA) designed to knock down AC3 or AC6 in primary cultured mouse IMCD significantly reduced AVP-stimulated cAMP accumulation. Together, these data are consistent with a role of AC3 and AC6 in the activation of mouse collecting duct by AVP. calcium; cAMP doj: 10.1152/ajprenal.00109.2009.

Familial neurohypophysial diabetes insipidus (FNDI) is a rare disease that is inherited in an autosomal dominant manner. In a previous study, we made a mouse model for FNDI, which showed progressive polyuria accompanied by inclusion bodies in the arginine vasopressin (AVP) neurons formed by aggregates in the endoplasmic reticulum. The present study was conducted to determine whether the activities of AVP neurons are related to the phenotype progression in the FNDI model. In the first experiment, female heterozygous mice were administered either desmopressin (dDAVP) or a vehicle (control) subcutaneously with osmotic minipumps for 30 days. The dDAVP treatment significantly decreased the urine volume, AVP mRNA expression, and inclusion bodies in the AVP neurons. Urine volume in the dDAVP group remained significantly less than the control for 14 days even after the minipumps were removed. In the second experiment, the males were fed either a 0.2% Na or 2.0% Na diet for 6 too. Urine AVP excretion was significantly increased in the 2.0% Na group compared with the 0.2% Na group for the first 2 mo but gradually decreased thereafter. Throughout the experiments, urine volume increased progressively in the 2.0% Na group but not in the 0.2% Na group. Immunohistochemical analyses revealed that inclusion bodies in the AVP cells had significantly increased in the 2.0% Na compared with the 0.2% Na group. These data demonstrated that activation of AVP neurons could accelerate the aggregate formation as well as the progression of the polyuria in the FNDI model mice. hereditary disease; aggregates doi: 10.1152/ajpregu.00529.2009

Our previous study showed that stimulation of adenosine [A.sub.1] receptors located in the nucleus of the solitary tract (NTS) exerts counteracting effects on the iliac vascular bed: activation of the adrenal medulla and [beta]-adrenergic vasodilation versus vasoconstriction mediated by neural and unknown humoral factors. In the present study we investigated the relative contribution of three major potential humoral vasoconstrictors: vasopressin, angiotensin II, and norepinephrine in this response. In urethane-chloralose anesthetized rats we compared the integral changes in iliac vascular conductance evoked by microinjections into the NTS of the selective [A.sub.1] receptor agonist [N.sup.6]-cyclopentyladenosine (CPA; 330 pmol in 50 nl) in intact (Int) animals and following: [V.sub.1] vasopressin receptor blockade (VX), angiotensin II [AT.sub.1] receptor blockade (ATX), bilateral adrenalectomy + ganglionic blockade (ADX + GX; which eliminated the potential increases in circulating norepinephrine and epinephrine), ADX + GX + VX and ADX + GX + VX + ATX. In Int animals, stimulation of NTS [A.sub.1] adenosine receptors evoked typical variable responses with prevailing pressor and vasoconstrictor effects. VX reversed the responses to depressor ones. ATX did not significantly alter the responses. ADX + GX accentuated pressor and vasoconstrictor responses, whereas ADX + GX + VX and ADX + GX + VX + ATX virtually abolished the responses. Stimulation of NTS [A.sub.1] adenosine receptors increased circulating vasopressin over fourfold (26.4 [+ or -] 10.4 vs. 117.0 [+ or -] 19 pg/ml). These data strongly suggest that vasopressin is a major vasoconstrictor factor opposing [beta]-adrenergic vasodilation in iliac vascular responses triggered by stimulation of NTS [A.sub.1] adenosine receptors, whereas angiotensin II and norepinephrine do not contribute significantly to the vasoconstrictor responses. purinergic receptors; [V.sub.1] receptor blockade; angiotensin II type 1 receptor blockade; ganglionic blockade; adrenalectomy; lumbar sympathectomy; iliac vascular conductance doi: 10.1152/ajpheart.00432.2009.

Byline: Caroline Guignant (1), Nicolas Voirin (2), Fabienne Venet (1), Francoise Poitevin (1), Christophe Malcus (1), Julien Bohe (3), Alain Lepape (3), Guillaume Monneret (1) Keywords: Septic shock; Mortality; Prognosis; Adrenomedullin; Vasopressin Abstract: Purpose Improvements in survival after septic shock will most likely rely on our capacity to manage individualized therapies based on the measurement of rapidly accessible biomarkers. As the early phase of septic shock is dominated by severe alterations of the cardiovascular system, the predictive value for mortality of pro-vasopressin (pro-AVP) and pro-adrenomedullin (pro-ADM), two vasoactive pro-hormones, was assessed. Methods In 99 consecutive patients, pro-hormone concentrations were measured (immunoluminometric assay) three times within the first week after the onset of septic shock. Results Pro-AVP and pro-ADM concentrations were significantly increased in non-survivors in comparison with survivors and were significantly associated with mortality after both univariate and multivariate analysis. Importantly, when assessed as a pair, pro-ADM and pro-AVP were even more informative. Conclusions Both Pro-ADM and pro-AVP appear to be good biomarkers for the prediction of 28-day mortality after septic shock. However, their association in a single variable tends to improve their predictive capacity. Author Affiliation: (1) Flow Cytometry Unit, Immunology Laboratory, Hopital E. Herriot, Hospices Civils de Lyon, 5, Place d'Arsonval, 69437, Lyon cedex 03, France (2) INSERM U271, Hospices Civils de Lyon, Hopital E. Herriot, Service d'Hygiene, Epidemiologie et Prevention, Universite de Lyon, Lyon, France (3) Intensive Care Units, Hospices Civils de Lyon, CH Lyon-Sud, Lyon, France Article History: Registration Date: 21/07/2009 Received Date: 06/01/2009 Accepted Date: 12/05/2009 Online Date: 07/08/2009 Article note: This article is discussed in the editorial available at: doi: 10.1007/s00134-009-1613-2. Electronic supplementary material The online version of this article (doi: 10.1007/s00134-009-1610-5) contains supplementary material, which is available to authorized users.

Extracellular nucleotides are local, short-lived signaling molecules that inhibit renal tubular transport via both luminal and basolateral P2 receptors. Apparently, the renal epithelium itself is able to release nucleotides. The mechanism and circumstances under which nucleotide release is stimulated remain elusive. Here, we investigate the phenomenon of nucleotide secretion in intact, peffused mouse medullary thick ascending limb (mTAL) and cortical collecting duct (CCD). The nucleotide secretion was monitored by a biosensor adapted to register nucleotides in the tubular outflow. Intracellular [Ca.sup.2+] concentration ([[Ca.sup.2+]].sub.i]) was measured simultaneously in the biosensor cells and the renal tubule with fluo 4. We were able to identify spontaneous tubular nucleotide secretion in resting peffused toTAL. In this preparation, 10 nM AVP and 1-desamino-8-D-arginine vasopressin (dDAVP) induced robust [[Ca2+].sub.i] oscillations, whereas AVP in the CCD induced large, slow, and transient [[Ca.sup.2+]].sub.i] elevations. Importantly, we identify that AVP/ dDAVP triggers tubular secretion of nucleotides in the mTAL. After addition of AVP/dDAVP, the biosensor registered bursts of nucleotides in the tubular perfusate, corresponding to a tubular nucleotide concentration of ~0.2-0.3 [micro]M. A very similar response was observed after AVP stimulation of CCDs. Thus AVP stimulated tubular secretion of nucleotides in a burst-like pattern with peak tubular nucleotide concentrations in the low-micromolar range. We speculate that local nucleotide signaling is an intrinsic feedback element of hormonal control of renal tubular transport. ATP release; renal tubule; vasopressin; purinergic

Pharmacological studies demonstrated that ATP elevates intracellular calcium ([Ca.sup.2+]].sub.i]) in supraoptic nucleus (SON) neurons primarily by activation of P2X2 and P2Y1 purinergic receptors [P2Y1R; (18)]. The current studies provide evidence for the presence of P2Y 1R protein in SON neurons, evidence that activation of these P2Y 1Rs induces an increase in [[Ca.sup.2+].sub.i] from both intracellular stores and [Ca.sup.2+] influx, and functional evidence that activation of P2Y1Rs induces vasopressin (VP) and oxytocin (OT) hormone release. Pretreatment of Fura-2 AM-loaded explants of the hypothalamo-neurohypophyseal system (HNS) with thapsigargin (TG) significantly (~80%) reduced the increase in [[Ca.sup.2+]].sub.i] induced by the P2Y1R-specific agonist, 2-methylthio-ADP (2-MeSADP). In contrast, the increase in [[Ca.sup.2+]].sub.i] was slightly (~20%) decreased in calcium-free medium. The calcium response to 2-MeSADP was completely blocked by the P2Y1R-specific antagonist, MRS2179 or by a combination of TG pretreatment and calcium-free medium. It was absent in P2YIR knockout mice ([P2Y1R.sup.-/-]). 2-MeSADP significantly increased VP and OT release from perifused rat and wild-type mouse HNS explants compared with control. MRS2179 prevented this response in wild-type mouse, but it did not prevent ATP-induced hormone release from rat explants. 2-MeSADP did not induce hormone release from [P2YIR.sup.-/-] explants. These findings support a potential role for P2YIRs in regulation of VP and OT release. The finding that P2Y1R activation induces a small [Ca.sup.2+] influx suggests that P2Y1Rs may regulate VP release by modifying ion channels such as stretch-inactivated cation channels. ATP; hypothalamus; neurohypophyseal; supraoptic nucleus

Blood-brain barrier (BBB) Na transporters are essential for brain water and electrolyte homeostasis. However, they also contribute to edema formation during the early hours of ischemic stroke by increased transport of Na from blood into brain across an intact BBB. We previously showed that a luminal BBB Na-K-Cl cotransporter is stimulated by hypoxia, aglycemia, and AVP and that inhibition of the cotransporter by intravenous bumetanide significantly reduces edema and infarct in the rat middle cerebral artery occlusion (MCAO) model of stroke. More recently, we found evidence that intravenous cariporide (HOE-642), a highly potent Na/H exchange inhibitor, also reduces brain edema after MCAO. The present study was conducted to investigate which Na/H exchange protein isoforms are present in BBB endothelial cells and to evaluate the effects of ischemic factors on BBB Na/H exchange activity. Western blot analysis of bovine cerebral microvascular endothelial cells (CMEC) and immunoelectron microscopy of perfusion-fixed rat brain revealed that Na/H exchanger isoforms 1 and 2 (NHE1 and NHE2) are present in BBB endothelial cells. Using microspectrofluorometry and the pH-sensitive dye BCECF, we found that hypoxia (2% 02, 30 min), aglycemia (30 min), and AVP (1-200 nM, 5 min) significantly increased CMEC Na/H exchange activity, assessed as Na-dependent, HOE-642-sensitive [H.sup.+] flux. We found that AVP stimulation of CMEC Na/H exchange activity is dependent on intracellular Ca concentration and is blocked by [V.sub.1], but not [V.sub.2], vasopressin receptor antagonists. Our findings support the hypothesis that a BBB Na/H exchanger, possibly NHE1 and/or NHE2, is stimulated during ischemia to participate in cerebral edema formation. blood-brain barrier; stroke; cerebral ischemia; brain edema; cariporide

Corticotrophs in the fetal sheep become increasingly responsive to arginine vasopressin (AVP) in late gestation. We previously reported that this may be due in part to corresponding increases in signal transduction (inositol 1,4,5-trisphosphate, [IP.sub.3]). These ontogenic changes are prevented by hypothalamopituitary disconnection (HPD), which also prevents fetal plasma cortisol concentrations from increasing in late gestation. This led us to hypothesize that cortisol is involved in mediating the changes in pituitary responsiveness. HPD was performed on fetal sheep at 120 days gestational age (dGA). Half of the HPD fetuses were infused with cortisol for 3 days beginning at 135-137 dGA (HPD+C). The remaining HPD fetuses and a group of sham-operated control fetuses were infused with saline. Pituitary cells were isolated and cultured. After 48 h, a subset of cells was stimulated with 100 nM AVP for 2 h, and the medium was collected for ACTH analysis. Another subset of cells was stimulated with 100 nM AVP for 30 min, and the formation of [IP.sub.3] was determined. Plasma cortisol concentrations increased rapidly within the first 6 h after infusion (5.2 [+ or -] 1.9 to 29.7 [+ or -] 4.9 ng/ml) but did not increase thereafter. Cells from HPD+C and sham-operated fetuses secreted significantly more ACTH than those from HPD fetuses (% increase from control: 33.0 [+ or -] 8.8%, 47.9 [+ or -] I0.6%, and 11.9 [+ or -] 2.4%, respectively). [IP.sub.3] formation was significantly increased in ceils from HPD+C and sham-operated compared with HPD fetuses (% increase from control: 17.7 [+ or -] 4.4%, 18.9 [+ or -] 4.3%, and 4.6 [+ or -] 1.5%, respectively). These findings support the idea that cortisol plays a role in mediating the increase in pituitary responsiveness to AVP in the late-gestation fetal sheep. inositol 1,4,5-trisphosphate; ovine fetus; cortisol replacement; adrenocorticotropic hormone

Byline: Elisa Baldasso (1,2), Pedro Celiny Ramos Garcia (1,2), Jefferson Pedro Piva (1,2), Ricardo Garcia Branco (3), Robert Charles Tasker (3) Keywords: Vasopressin; Hypotension; Shock; Sedation; Paediatric intensive care; Mechanical ventilation Abstract: Objective To assess the safety of low-dose vasopressin infusion in critically ill children requiring prolonged mechanical ventilation (MV) at risk of developing sedation/analgesia-related hypotension. Method Randomized pilot safety study in children expected to require MV for at least 3 days. Children received either vasopressin (0.0005 U/kg/min) or sodium chloride (0.9%) infusion for a period of 48 h. Haemodynamic variables, urine output and serum electrolytes were closely monitored and analyzed. Results Twelve children in each group had similar baseline characteristics. Vasopressin infusion was associated with an 8 mmol/L fall in serum sodium concentration (p < 0.01) and with higher incidence of hyponatraemia (8 vs. 66%, p < 0.01). In normotensive children, low-dose vasopressin also induced a reversible decrease in urine output, and acutely increased blood pressure (p < 0.01). After stopping the vasopressin there was rebound hypotension (p < 0.01). Conclusion Low-dose vasopressin infusion in haemodynamically stable, but critically ill, children is associated with reduction in urine output and decreased serum sodium level, yielding a high incidence of hyponatraemia. We conclude that these effects limit further study of prophylactic vasopressin for sedation-related hypotension in a randomized controlled trial. Author Affiliation: (1) Pediatric Intensive Care Unit, Department of Pediatrics, Hospital Sao Lucas da PUCRS, Porto Alegre, Brazil (2) Department of Paediatrics, Medical School, Pontificia Universidade Catolica do Rio Grande do Sul (PUCRS), Porto Alegre, Brazil (3) Department of Paediatrics, Box 116, School of Clinical Medicine, University of Cambridge, Addenbrookes Hospital, Hills Road, Cambridge, CB2 2QQ, UK Article History: Registration Date: 23/12/2008 Received Date: 15/06/2008 Accepted Date: 17/11/2008 Online Date: 09/01/2009

The primary cilium of renal epithelial cells is a nonmotile sensory organelle, implicated in mechanosensory transduction signals. Recent studies from our laboratory indicate that renal epithelial primary cilia display abundant channel activity; however, the presence and functional role of specific membrane receptors in this organelle are heretofore unknown. Here, we determined a functional signaling pathway associated with the type 2 vasopressin receptor (V2R) in primary cilia of renal epithelial cells. Besides their normal localization on basolateral membrane, V2R was expressed in primary cilia of LLC-[PK.sub.1] renal epithelial cells. The presence of V2R in primary cilia was determined by spontaneous fluorescence of a V2R-gfp chimera and confirmed by immunocyto-chemical analysis of wild-type LLC-[PK.sub.1] cells stained with anti-V2R antibodies and in LLC-[PK.sub.1] cells overexpressing the V2R-Flag, with anti-Flag antibody. Ciliary V2R colocalized with adenylyl cyclase (AC) type V/VI in all cell types tested. Functional coupling of the receptors with AC was confirmed by measurement of cAMP production in isolated cilia and by testing AVP-induced cation-selective channel activity either in reconstituted lipid bilayers or subjected to membrane-attached patch clamping. Addition of either 10 [micro]M AVP (trans) or forskolin (cis) in the presence but not the absence of ATP (1 mM, cis) stimulated cation-selective channel activity in ciliary membranes. This channel activity was reduced by addition of the PKA inhibitor PKI. The data provide the first demonstration for the presence of V2R in primary cilia of renal epithelial cells, and a functional cAMP-signaling pathway, which targets ciliary channel function and may help control the sensory function of the primary cilium. apical vasopressin; cystic kidney disease; cAMP production; polycystin-2; ciliary function

BACKGROUND: Increasing evidence from animal and human studies indicates that chlorpyrifos (CPF), similar to other organophosphorus insecticides still widely used, is a developmental neurotoxicant. Developmental exposure to CPF in rodents [...]

Adjustment of [Na.sup.+] balance in extracellular fluids is achieved by regulated [Na.sup.+] transport involving the amiloride-sensitive epithelial [Na.sup.+] channel (ENaC) in the distal nephron. In this context, ENaC is controlled by a number of hormones, including vasopressin, which promotes rapid translocation of water and [Na.sup.+] channels to the plasma membrane and long-term effects on transcription of vasopressin-induced and -reduced transcripts. We have identified a mRNA encoding the deubiquitylating enzyme ubiquitin-specific protease 10 (Uspl0), whose expression is increased by vasopressin at both the mRNA and the protein level. Coexpression of Uspl0 in ENaC-transfected HEK293 cells causes a more than fivefold increase in amiloride-sensitive [Na.sup.+] currents, as measured by whole cell patch clamping. This is accompanied by a three- to fourfold increase in surface expression of [alpha]- and [gamma]-ENaC, as shown by cell surface biotinylation experiments. Although ENaC is well known to be regulated by its direct ubiquitylation, Uspl0 does not affect the ubiquitylation level of ENaC, suggesting an indirect effect. A two-hybrid screen identified sorting nexin 3 (SNX3) as a novel substrate of Usp10. We show that it is a ubiquitylated protein that is degraded by the proteasome; interaction with Uspl0 leads to its deubiquitylation and stabilization. When coexpressed with ENaC, SNX3 increases the channel's cell surface expression, similarly to Uspl0. In [mCCD.sub.c11] cells, vasopressin increases SNX3 protein but not mRNA, supporting the idea that the vasopressin-induced Usp10 deubiquitylates and stabilizes endogenous SNX3 and consequently promotes cell surface expression of ENaC. sorting nexin 3; epithelial sodium channel

Maliszewska-Scislo M, Chen H, Augustyniak RA, Seth D, Rossi NF. Subfornical organ differentially modulates baroreflex function in normotensive and two-kidney, one-clip hypertensive rats. Am J Physiol Regal Integr Comp Physiol 295: R74l-R750, 2008. First published July 2, 2008; doi:10.1152/ajpregu.00157.2008.--During activation of the renin-angiotensin system, hindbrain circumventricular organs such as the area postrema have been implicated in modulating the arterial baroreflex. This study was undertaken to test the hypothesis that the subfornical organ (SFO), a forebrain circumventricular structure, may also modulate the baroreflex. Studies were performed in rats with two-kidney, one-clip (2K, 1C) hypertension as a model of endogenously activated renin-angiotensin system. Baroreflex function was ascertained during ramp infusions of phenylephrine and nitroprusside in conscious sham-clipped and 5-wk 2K, 1C rats with either a sham or electrolytically lesioned SFO. Lesioning significantly decreased mean arterial pressure in 2K, 1C rats from 158 [+ or -] 7 to 131 [+ or -] 4 mmHg but not in sham-clipped rats. SFO-lesioned, sham-clipped rats had a significantly higher upper plateau and range of the renal sympathetic nerve activity-mean arterial pressure relationship compared with sham-clipped rats with SFO ablation. In contrast, lesioning the SFO in 2K, 1C rats significantly decreased both the upper plateau and range of the baroreflex control of renal sympathetic nerve activity, but only the range of the baroreflex response of heart rate decreased. Thus, during unloading of the baroreceptors, the SFO differentially modulates the baroreflex responses in shamclipped vs. 2K, 1C rats. Since lesioning the SFO did not influence plasma angiotensin II (ANG II), the effects of the SFO lesion are not caused by changes in circulating levels of ANG II. These findings support a pivotal role for the SFO in the sympathoexcitation observed in renovascular hypertension and in baroreflex regulation of sympathetic activity in both normal and hypertensive states. Goldblatt kidney; renal sympathetic nerve activity; angiotensin II: vasopressin

Physical inactivity is an independent risk factor for cardiovascular disease. Sedentary animals compared to physically active controls exhibit enhanced sympathoexcitatory responses, including arterial baroreflexmediated sympathoexcitation. Hypotension-induced sympathoexcitation is also associated with the release of vasoactive hormones. We hypothesized that sedentary conditions may enhance release of the vasoactive hormones AVP and ANG II. To test this hypothesis, the humoral response to hypotension was examined in conscious rats after 9-12 wk of sedentary conditions or 'normally active' conditions. Normally active conditions were produced by allowing rats access to running wheels in their home cages. Running distance peaked after 4 wk (4.5 [+ or -] 0.7 km/day), and the total distance run after 9 wk was 174 [+ or -] 23 km (n = 25). Similar levels of hypotension were induced in conscious sedentary or physically active animals with the arterial vasodilator, diazoxide (25 mg/kg iv). Control experiments used a saline injection of equivalent volume. Plasma samples were collected and assayed for plasma AVP concentration and plasma renin activity (PRA). Sedentary conditions significantly enhanced resting and hypotension-induced PRA relative to normal physical activity. In contrast, resting and hypotension-induced AVP levels were not statistically different between groups. These data suggest that baroreflex-mediated activation of the renin-angiotensin system, but not AVP secretion, is enhanced by sedentary conditions. We speculate that augmented activation of the renin-angiotensin system may be related to enhanced sympathetic outflow observed in sedentary animals and may contribute to increased risk of cardiovascular disease in the sedentary population. physical activity; physical inactivity; neurohumoral control; angiotensin II

The role(s) of central G[alpha]-proteins in the regulation of cardiovascular and renal function is unknown. We examined how inhibition/downregulation of central G[alpha]i/G[alpha]o, G[alpha]z or G[alpha]q proteins altered the characteristic cardiovascular (depressor), renal excretory (diuretic), and plasma AVP (inhibitory) responses to intracerebroventricular injection of nociceptin/ orphanin FQ (N/OFQ) in rats. Before investigation, rats were pretreated intracerebroventricularly with saline vehicle (5 [micro]l, 48 h, n = 6), pertussis toxin (PTX; 48-h, 1 [micro]g, n = 6), or G[alpha]z, G[alpha]q, or scrambled oligodeoxynucleotide (ODN) (25 [micro]g, 24 h, n = 6 per group). On the study day, intracerebroventricular N/OFQ (5.5 nmol) or vehicle (5 [micro]l) was injected into pretreated conscious rats. Mean arterial pressure (MAP) and heart rate (HR) were recorded, and urine was collected for 90 min. In vehicle or scrambled ODN groups, intracerebroventricular N/OFQ decreased MAP and HR and produced water diuresis (sensitive to UFP-101, N/OFQ receptor antagonist). The hypotension and bradycardia, but not diuresis, to N/OFQ were abolished in PTX-pretreated rats. In contrast, intracerebroventricular ODN pretreatment markedly blunted (G[alpha]z) or augmented (G[alpha]q) the diuresis to intracerebroventricular N/OFQ. In separate studies, the action of central N/OFQ to decrease plasma AVP levels in naive water-restricted rats was differentially altered by intracerebroventricular G[alpha]z ODN (blunted) and G[alpha]q ODN (augmented) pretreatment. These studies demonstrate central G[alpha]i/G[alpha]o activity mediates intracerebroventricular N/OFQ's cardiovascular depressor function. Alternatively, central G[alpha]z (inhibitory) and G[alpha]q (stimulatory) activity differentially modulates AVP release to control the pattern of diuresis to intracerebroventricular N/OFQ. These findings highlight the novel selective central G[alpha]-subunit protein-mediated control of cardiovascular vs. renal excretory function. central G[alpha]-subunit proteins; central nervous system; cardiovascular and renal excretory function; vasopressin/antidiuretic hormone; nociceptin/orphanin FQ

By phosphoproteome analysis, we identified a phosphorylation site, serine 264 (pS264), in the COOH terminus of the vasopressin-regulated water channel, aquaporin-2 (AQP2). In this study, we examined the regulation of AQP2 phosphorylated at serine 264 (pS264-AQP2) by vasopressin, using a phospho-specific antibody (anti-pS264). Immunohistochemical analysis showed pS264-AQP2 labeling of inner medullary collecting duct (IMCD) from control mice, whereas AQP2 knockout mice showed a complete absence of labeling. In rat and mouse, pS264-AQP2 was present throughout the collecting duct system, from the connecting tubule to the terminal IMCD. Immunogold electron microscopy, combined with double-labeling confocal immunofluorescence microscopy with organelle-specific markers, determined that the majority of pS264 resides in compartments associated with the plasma membrane and early endocytic pathways. In Brattleboro rats treated with [deamino-Cys-1, D-Arg-8]vasopressin (dDAVP), the abundance of pS264-AQP2 increased 4-fold over controls. Additionally, dDAVP treatment resulted in a time-dependent change in the distribution of pS264 from predominantly intracellular vesicles, to both the basolateral and apical plasma membranes. Sixty minutes after dDAVP exposure, a proportion of pS264-AQP2 was observed in clathrin-coated vesicles, early endosomal compartments, and recycling compartments, but not lysosomes. Overall, our results are consistent with a dynamic effect of AVP on the phosphorylation and subcellular distribution of AQP2. concentrating mechanism | immunohistochemistry | kidney | trafficking

Byline: Serge Brimioulle (1), Carlos Orellana-Jimenez (1), Adel Aminian (1), Jean-Louis Vincent (1) Keywords: Antidiuretic hormone; Natriuretic factor; Natriuretic peptide; Subarachnoid hemorrhage; Brain trauma; Intracranial disease Abstract: Objective To assess whether hyponatremia in acute neurological patients is associated with the syndrome of inappropriate antidiuretic hormone secretion (SIADH) or with the cerebral salt-wasting syndrome (CSWS). Design Clinical, controlled, prospective study. Setting Department of intensive care of a tertiary care academic hospital. Patients Forty acute neurological patients with hyponatremia suggesting SIADH or CSWS (20) or with normonatremia (20). Interventions None. Measurements and main results Measurement of clinical and biological variables. Measurement of blood, plasma, and red blood cell volumes to discriminate SIADH and CSWS. Renal, adrenal and thyroid functions were normal in all patients. Average blood, plasma, and red blood cell volumes were 54, 37 and 17a-ml/kg in control patients and 54, 37 and 18a-ml/kg in hyponatremic patients, respectively. Conclusions The adequate blood volumes in hyponatremic patients confirm the diagnosis of SIADH and do not support the concept of CSWS. Author Affiliation: (1) Department of Intensive Care, Erasme University Hospital, Free University of Brussels, Lennik Road 808, 1070, Brussels, Belgium Article History: Registration Date: 25/09/2007 Received Date: 16/02/2007 Accepted Date: 23/09/2007 Online Date: 19/10/2007 Article note: Electronic supplementary material The online version of this article (doi: 10.1007/s00134-007-0905-7) contains supplementary material, which is available to authorized users.

A case study of a 62-year-old woman suffering from the syndrome of inappropriate secretion of antidiuretic hormone (SIADH), frequent cause of hyponatremia is presented. A computed tomographic (CT) scan of the thorax showed a mass in the lower lobe of the left lung that proved to be a small-cell carcinoma which when treated could correct the hyponatremia.

We recently identified a novel phosphorylation site, serine-261 (pS261), in the COOH-terminus of the vasopressin-regulated water channel, aquaporin-2 (AQP2). To address whether phosphorylation at this site is regulated by vasopressin, a rabbit polyclonal phospho-specific antibody was generated. Dot blot and immunoblot analysis demonstrated that this antibody specifically recognizes AQP2 phosphorylated at pS261, and that phosphorylation of S256 (pS256), a site already known to be regulated by vasopressin, does not interfere with antibody recognition. Immunohistochemical analysis revealed intense pS261 labeling of inner medullary collecting duct (IMCD) from wild-type mice, while sections from AQP2 knockout animals showed a general absence of labeling. AQP2 pS261 was present in principal cells of all mouse and rat distal tubule segments from the connecting tubule to the terminal IMCD. Co-immunolabeling of collecting duct with phospho-specific and total AQP2 antibodies revealed that pS261 and pS256 have distinct subcellular distributions. Levels of pS256 increased, while the amount of pS261 significantly decreased in freshly isolated rat IMCD samples incubated with 1 nM [deamino-[Cys.sup.1], D-[Arg.sup.8]]vasopressin for 30 min. Similarly, based on immunohistochemical labeling, the amount of pS261 was reduced in all collecting duct segments of Brattleboro rats treated with [deamino-[Cys.sup.1],D-[Arg.sup.8]]vasopressin for 2 h. This study reveals a reciprocal change in S256 and S261 phosphorylation in response to short-term vasopressin exposure, suggesting that these residues may serve distinct roles in regulation of AQP2 subcellular distribution and collecting duct water permeability. IMCD; water transport; serine-256; channel; inner medullary

Diabetes mellitus (DM), as chronic stress activates the hypothalamopituitary-adrenocortical axis. We examined whether arginine vasopressin (AVP) and the hypothalamic paraventricular nucleus (PVN) participate in DM-induced chronic stress symptoms. AVP-deficient Brattleboro or PVN-lesioned Wistar rats were used with heterozygous or sham-operated controls. The rats were studied 2 wk after a single injection of streptozotocin. The appearance of DM (enhanced water consumption and blood glucose elevation) and the chronic stress-like somatic changes (body weight decrease, thymus involution, adrenal gland hypertrophy) were not influenced by the lack of AVP. By contrast, PVN lesion significantly attenuated DM-induced thymus involution and adrenal gland hypertrophy as well as the increase in water consumption. The corticotropin-releasing hormone mRNA in PVN was diminished by DM and elevated by the lack of AVP without interaction. DM elevated the proopiomelanocortin (POMC) mRNA in the anterior lobe of the pituitary. The lack of AVP had no effect, whereas lesioning the PVN significantly diminished the elevation. The elevated basal corticosterone plasma levels detectable in DM were influenced neither by the lack of AVP nor by lesioning the PVN. Thus the lack of AVP had no influence on DM-induced chronic stress symptoms, but lesioning the PVN attenuated part of them. However, the lack of elevation in POMC mRNA after PVN lesion, together with the maintained corticosterone elevation, suggests that direct adrenal gland activation occurs in untreated DM. chronic stress; Brattleboro rats; corticosterone; proopiomelanocortin; corticotropin-releasing hormone; diabetes mellitus; hypothalamopituitary-adrenocortical axis

The synthesis of arginine vasopressin (AVP) in the magnocellular neurons of the supraoptic (SON) and paraventricular nuclei (PVN) is physiologically regulated by plasma osmolality and volume. To clarify how the regulation of AVP gene transcription is affected by chronic dehydration, we examined changes in the transcriptional activities of AVP gene by plasma osmolality and volume in both euhydrated and dehydrated conditions. Euhydrated rats had free access to water, whereas dehydrated rats had been deprived of water for 3 days before experiments. Rats in both conditions were subjected to acute hypertonic stimuli or hypovolemia, and changes in AVP heteronuclear (hn)RNA levels, an indicator of gene transcription, in the SON and PVN were examined with in situ hybridization. The intraperitoneal (ip) injection (2% body wt) of hypertonic (1.5 M) saline increased plasma Na levels by ~40 meq/1 in both euhydrated and dehydrated conditions. However, expression levels of AVP hnRNA in the SON and PVN were increased only in euhydrated, not dehydrated, rats. On the other hand, ip injection of polyethylene glycol decreased the plasma volume by ~16-20%, and AVP hnRNA levels in the SON and PVN were significantly increased in both conditions. Thus it is demonstrated that signaling pathways regulating AVP gene transcription in the magnocellular neurons were completely refractory to acute osmotic stimuli under the chronic dehydration and that AVP gene transcription could probably respond to acute hypovolemia through different intracellular signal transduction pathways from those for osmoregulation. dehydration; hyperosmolality; hypovolemia

The health burden of stress-related diseases, including depression and anxiety disorders, is rapidly increasing, whereas the range of available pharmacotherapies to treat these disorders is limited and suboptimal with regard to efficacy and tolerability. Recent findings support a major role for neuropeptides in mediating the response to stress and thereby identify neuropeptide systems as potential novel therapeutic targets for the treatment of depression and anxiety disorders. In preclinical models, pharmacological and/or genetic manipulation of substance P, corticotropin-releasing factor (CRF), vasopressin, neuropeptide Y and galanin function alters anxiety- and depression-related responses. Recently, specific and highly potent small-molecule neuropeptide receptor agonists and antagonists have been developed that can readily cross the blood--brain barrier. Clinical assessment of several compounds is currently underway, with antidepressant efficacy confirmed in double-blind, placebo-controlled trials of tachykinin N[K.sub.1] (substance P) receptor antagonists, and preliminary evidence of antidepressant activity in an open-label trial of a CR[F.sub.1] receptor antagonist.

Byline: N. E. Chepurnova (1), A. A. Ponomarenko (1), S. A. Chepurnov (1) Keywords: PACAP; arginine-vasopressin; hyperthermia; convulsions; neurosecretion Abstract: This report addresses the verification of the hypothesis that arginine-vasopressin affects the formation of hyperthermia-evoked convulsions in early ontogenesis in rats on days 3, 5, 7, and 9 of postnatal life. The modification of experimental febrile convulsions by PACAP (pituitary adenylate cyclase-activating peptide) was investigated PACAP is a physiological regulator of the neurosecretion of arginine-vasopressin. Arginine-vasopressin (10 ug/rat) and PACAP (0.01 ug/rat) decreased the latency of generalized tonic-clonic convulsions and the time of truncal generalization of convulsive activity on days 3 and 5 of rat development. Animals given arginine-vasopressin (0.1--10 ug/rat) sowed significant increases in the duration of generalized convulsions to the level of status epilepticus on day 9 of life. Conversely, administration of higher doses of PACAP (0.1 ug/rat) increased the threshold of tonic-clonic convulsions on days 3 and 5 and decreased it on days 7 and 9 of postnatal development. The indirect involvement of PACAP in the mechanisms of experimental febrile convulsions is suggested to act via changes in arginine-vasopressin neurosecretion. Author Affiliation: (1) Department of Human and Animal Physiology, M. V. Lomonosov Moscow State University, Vorob'evy Heights, 119899, Moscow, Russia Article History: Registration Date: 09/10/2004

Renal resistance to vasopressin in poorly controlled type 1 diabetes mellitus. Am J Physiol Endocrinol Metab 279: E155-E160, 2000.--To investigate the hypothesis that diabetes induces nephrogenic diabetes insipidus, we studied the urine-concentrating ability in response to vasopressin (AVP) in 12 patients with insulin-dependent diabetes mellitus (IDDM) and 12 nondiabetic controls. Subjects were euglycemic-clamped, and after oral water loading, AVP was infused intravenously for 150 min. AVP induced a greater (P [is less than] 0.001) rise in urine osmolality in controls (67.6 [+ or -] 10.7 to 720 [+ or -] 31.1 mosmol/kg, P [is less than] 0.001) than in IDDM patients (64.3 [+ or -] 21.6 to 516.7 [+ or -] 89.3 mosmol/kg, P [is less than] 0.001). Urinary aquaporin-2 concentrations after AVP infusion were higher in controls (611.8 [+ or -] 105.6 fmol/mg creatinine) than in IDDM (462.0 [+ or -] 94.9 fmol/mg creatinine, P = 0.003). Maximum urine osmolality in IDDM was inversely related to chronic blood glucose control, as indicated by Hb [A.sub.Ic] (r = -0.87, P = 0.002). To test the hypothesis that improved glycemic control could reverse resistance to AVP, 10 IDDM subjects with poor glycemic control (Hb [A.sub.Ic] [is greater than] 9%) were studied before (B) and after (A) intensified glycemic control. Maximum urine osmolality in response to AVP increased with improved glycemic control (B, 443.8 [+ or -] 49.0; A, 640.0 [+ or -] 137.2 mosmol/kg, P [is less than] 0.001), and urinary aquaporin-2 concentrations after AVP increased from 112.7 [+ or -] 69 to 375 [+ or -] 280 fmol/mg creatinine (P = 0.006), with improved glycemic control. Poorly controlled IDDM is associated with reversible renal resistance to AVP. osmoregulation; antidiuresis; nephrogenic diabetes insipidus