Effects of arginine vasopressin on cell volume regulation in brain astrocyte in culture.
Astrocytes initially swell when exposed to hypotonic medium but rapidly return to normal volume by the process of regulatory volume decrease (RVD). The role that arginine vasopressin (AVP) plays in hypotonically mediated RVD in astrocytes is unknown. This study was therefore designed to determine whether AVP might play a role in astrocyte RVD. With the use of 3-O-[3H]methyl-D-glucose to determine water space, AVP treatment resulted in significantly increased 3-O-methyl-D-glucose water space within 30 s of hypotonic exposure (P = 0.0001) and remained significantly elevated above baseline (1. 75 microliter/mg protein) at 5 min (P < 0.021). In contrast, in untreated cells, complete RVD was achieved by 5 min. At 30 s, cell volume with AVP treatment was 37% greater than in cells that received no treatment (2.9 vs. 2.26 microliter/mg protein, respectively; P < 0.006). The rate of cell volume increase (dV/dt) over 30 s was highly significant (0.038 vs. 0.019 microliter. mg protein-1. s-1 in the AVP-treated vs. untreated group; P = 0.0004 by regression analysis). Additionally, the rate of cell volume decrease over the next 4.5 min was also significantly greater with vasopressin treatment (-dV/dt = 0.0027 vs. 0.0013 microliter. mg protein-1. s-1; P = 0.0306). The effect of AVP was concentration dependent with EC50 = 3.5 nM. To determine whether AVP action was receptor mediated, we performed RVD studies in the presence of the V1-receptor antagonists benzamil and ethylisopropryl amiloride and the V2-receptor agonist 1-desamino-8-D-arginine vasopressin (DDAVP). Both V1-receptor antagonists significantly inhibited AVP-mediated volume increase by 40-47% (P < 0.005), whereas DDAVP had no stimulatory effects above control. Taken together, these data suggest that AVP treatment of brain astrocytes in culture appears to increase 3-O-methyl-D-glucose water space during RVD through V1 receptor-mediated mechanisms. The significance of these findings is presently unclear. (+info)
An acutely painful elbow as a first presentation of von Willebrand's disease.
A 26 year old woman presented to the accident and emergency department with a painful right elbow. There had been no history of trauma. Clinical examination suggested an effusion, which was confirmed on radiological examination. Her elbow was aspirated and revealed a haemarthrosis. Subsequent investigations revealed a diagnosis of von Willebrand's disease (vWD). A spontaneously occurring effusion of the elbow may be due to a haemarthrosis. Aspiration of blood in the absence of trauma may lead to a diagnosis of an occult coagulopathy in addition to relieving pain. The diagnosis and treatment of vWD is discussed. (+info)
Vasopressin regulates apical targeting of aquaporin-2 but not of UT1 urea transporter in renal collecting duct.
In the renal inner medullary collecting duct (IMCD), vasopressin regulates two key transporters, namely aquaporin-2 (AQP2) and the vasopressin-regulated urea transporter (VRUT). Both are present in intracellular vesicles as well as the apical plasma membrane. Short-term regulation of AQP2 has been demonstrated to occur by vasopressin-induced trafficking of AQP2-containing vesicles to the apical plasma membrane. Here, we have carried out studies to determine whether short-term regulation of VRUT occurs by a similar process. Cell surface labeling with NHS-LC-biotin in rat IMCD suspensions revealed that vasopressin causes a dose-dependent increase in the amount of AQP2 labeled at the cell surface, whereas VRUT labeled at the cell surface did not increase in response to vasopressin. Immunoperoxidase labeling of inner medullary thin sections from Brattleboro rats treated with 1-desamino-8-D-arginine vasopressin (DDAVP) for 20 min revealed dramatic translocation of AQP2 to the apical region of the cell, with no change in the cellular distribution of VRUT. In addition, differential centrifugation of inner medullary homogenates from Brattleboro rats treated with DDAVP for 60 min revealed a marked depletion of AQP2 from the low-density membrane fraction (enriched in intracellular vesicles) but did not alter the quantity of VRUT in this fraction. Finally, AQP2-containing vesicles immunoisolated from a low-density membrane fraction from renal inner medulla did not contain immunoreactive VRUT. Thus vasopressin-mediated regulation of AQP2, but not of VRUT, depends on regulated vesicular trafficking to the plasma membrane. (+info)
Plasma vasopressin and response to treatment in primary nocturnal enuresis.
AIMS: To examine the relation between nocturnal vasopressin release and response to treatment with the vasopressin analogue 1-desamino-8-D-arginine vasopressin (DDAVP) in children with primary monosymptomatic nocturnal enuresis. DESIGN: Children were recruited from a specific enuresis clinic and entered into a defined treatment programme. Nocturnal vasopressin concentrations were measured every 15 minutes over a four hour period during overnight admission. RESULTS: Sixty seven children were eligible for entry into the study, 35 of whom agreed to overnight sampling. There was a quadratic relation between mean plasma AVP and response to treatment with DDAVP, with very high or very low concentrations being unresponsive. Plasma AVP profiles ranged from low concentrations with little variability to high concentrations with wide variability. CONCLUSION: The ability to respond to DDAVP is related to endogenous AVP production and is influenced by neuronal patterning in early infancy. The best predictors of success with treatment were a past history of breast feeding, mean nocturnal AVP concentration, and the height of the child. The response was adversely affected by poor weight at birth and poor linear growth. The study suggests differing causes of nocturnal enuresis related to different patterns of AVP release. (+info)
Hyponatraemic convulsion secondary to desmopressin treatment for primary enuresis.
The case of a 6 year old child who presented with convulsions and coma after unsupervised self administration of intranasal desmopressin (DDAVP) for nocturnal enuresis is presented. Children with enuresis can be embarassed by their condition and may believe that multiple doses of their nasal spray may bring about a rapid resolution. Water intoxication is an uncommon but serious adverse effect of treatment with intranasal DDAVP. These patients may present with seizure, mental state changes, or both. Basic management consists of stopping the drug, fluid restriction, and suppressive treatment for seizures. Recovery is usually rapid and complete. Administration of the nasal spray in children should be supervised by parents to prevent highly motivated children from accidental overdose. The risks of high fluid intake need to be carefully explained to both parents and children. (+info)
V1a- and V2-type vasopressin receptors mediate vasopressin-induced Ca2+ responses in isolated rat supraoptic neurones.
1. The pharmacological profile of receptors activated by vasopressin (AVP) in freshly dissociated supraoptic magnocellular neurones was investigated using specific V1a- and V2-type AVP receptor agonists and antagonists. 2. In 97 % of AVP-responding neurones (1-3000 nM) V1a or V2 receptor type agonists (F-180 and dDAVP, respectively) elicited dose-dependent [Ca2+]i transients that were suppressed by removal of external Ca2+. 3. The [Ca2+]i response induced by 1 microM F-180 or dDAVP was selectively blocked by 10 nM of V1a and V2 antagonists (SR 49059 and SR 121463A, respectively). The response to V1a agonist was maintained in the presence of the V2 antagonist, and the V2 agonist-induced response persisted in the presence of the V1a antagonist. 4. The [Ca2+]i response induced by 1 microM AVP was partially (61 %) blocked by 10 nM SR 121463A. This blockade was increased by a further 31 % with the addition of 10 nM SR 49059. Similarly, the AVP-induced response was partially (47 %) decreased by SR 49059, and a further inhibition of 33 % was achieved in the presence of SR 121463A. 5. We demonstrate that AVP acts on the magnocellular neurones via two distinct types of AVP receptors that exhibit the pharmacological profiles of V1a and V2 types. However, since V2 receptor mRNA is not expressed in the supraoptic nucleus (SON), and since V1b receptor transcripts are observed in the SON, we propose that the V2 receptor agonist and antagonist act on a 'V2-like' receptor or a new type of AVP receptor that remains to be elucidated. The possibility that V2 ligands act on the V1b receptor cannot be excluded. (+info)
Effect of DDAVP on nocturnal enuresis in a patient with nephrogenic diabetes insipidus.
The case of an 8 year old boy with both nocturnal enuresis and nephrogenic diabetes insipidus is presented. Diagnosis of nephrogenic diabetes insipidus was based on a typical medical history, the characteristic result of a fluid restriction test, the lack of an effect of 1-desamino-8-D-arginine (DDAVP) on both urine osmolality and plasma coagulation factors and, finally, the detection of a hemizygous missense mutation within the arginine vasopressin (AVP) receptor gene. Hydrochlorothiazide treatment and dietary measures reduced the patient's urine volume to one third of its original volume. However, this had no effect on enuresis. The daily intranasal application of DDAVP did not further reduce urine output but dramatically decreased the frequency of bed wetting. This observation contradicts the common notion that the therapeutic effect of DDAVP in nocturnal enuresis is the result of compensation for a nocturnal AVP deficit. Rather, it points to a different mode of action of DDAVP in patients with enuresis. It is hypothesised that central AVP receptors are a target of DDAVP and that they might play an important role in the pathogenesis of nocturnal enuresis. (+info)
An enhanced effect of arginine vasopressin in bradykinin B2 receptor null mutant mice.
Under water restriction, arginine vasopressin (AVP) is released and promotes water reabsorption in the distal nephron, mainly through AVP V2-receptors. It has been proposed that renal kinins counteract the hydro-osmotic effect of AVP. We hypothesized that kinins acting through B2 receptors antagonize the urinary concentrating effect of AVP. To test this, bradykinin B2 receptor knockout mice (B2-KO) and 129/SvEv mice (controls) were placed in metabolic cages and urine collected for 24 hours (water ad libitum). After that, urine was again collected from the same mice during 24 hours of water restriction. Urinary volume (UV), urinary osmolarity (UOsm), and urinary Na+ (UNaV) and K+ (UKV) excretion were determined. On water restriction, UV in controls decreased by approximately 25%, whereas in B2-KO mice there was almost a 60% drop in urinary output (P=0.001 versus controls). In the controls, water restriction increased UOsm by 347 mOsm/kg H2O, approximately 14% above baseline (NS), whereas in knockout mice the increase was 3 times that seen in the controls: >1000 mOsm/kg H2O (P=0.001 versus controls). Compared with normohydration, UNaV and UKV in the water-restricted state increased more in controls than in B2-KO mice. This difference in electrolyte excretion could be explained by greater dehydration in the controls (dehydration natriuresis). In a second protocol, we tried to mimic the effect of endogenous AVP by exogenous administration of an AVP V2-receptor agonist, desmopressin (DDAVP). To suppress endogenous AVP levels before DDAVP administration, mice were volume-overloaded with dextrose and alcohol. UOsm was 685+/-125 and 561+/-58 mOsm/kg H2O in water-loaded controls and B2-KO mice, respectively. After DDAVP was injected subcutaneously at a dose of 1 microgram/kg, UOsm increased to 1175+/-86 mOsm/kg H2O (Delta+490 mOsm) in the controls and 2347+/-518 mOsm/kg H2O (Delta+1786 mOsm) in B2-KO mice (P<0.05 versus controls). We concluded that water restriction or exogenous administration of an AVP V2-receptor agonist has a greater urinary concentrating effect in B2-KO mice than in controls, suggesting that endogenous kinins acting through B2 receptors oppose the antidiuretic effect of AVP in vivo. (+info)