HuR-Dependent Editing of a New Mineralocorticoid Receptor Splice Variant Reveals an Osmoregulatory Loop for Sodium Homeostasis.

Aldosterone and the Mineralocorticoid Receptor (MR) control hydroelectrolytic homeostasis and alterations of mineralocorticoid signaling pathway are involved in the pathogenesis of numerous human diseases, justifying the need to decipher molecular events controlling MR expression level. Here, we show in renal cells that the RNA-Binding Protein, Human antigen R (HuR), plays a central role in the editing of MR transcript as revealed by a RNA interference strategy. We identify a novel Δ6 MR splice variant, which lacks the entire exon 6, following a HuR-dependent exon skipping event. Using isoform-specific TaqMan probes, we show that Δ6 MR variant is expressed in all MR-expressing tissues and cells and demonstrate that extracelullar tonicity regulates its renal expression. More importantly, this splice variant exerts dominant-negative effects on transcriptional activity of the full-length MR protein. Collectively, our data highlight a crucial role of HuR as a master posttranscriptional regulator of MR expression in response to osmotic stress. We demonstrate that hypotonicity, not only enhances MR mRNA stability, but also decreases expression of the Δ6 MR variant, thus potentiating renal MR signaling. These findings provide compelling evidence for an autoregulatory feedback loop for the control of sodium homeostasis through posttranscriptional events, likely relevant in renal pathophysiological situations.

Aquaporin-4 and brain edema.

Aquaporin-4 (AQP4) is a water-channel protein expressed strongly in the brain, predominantly in astrocyte foot processes at the borders between the brain parenchyma and major fluid compartments, including cerebrospinal fluid (CSF) and blood. This distribution suggests that AQP4 controls water fluxes into and out of the brain parenchyma. Experiments using AQP4-null mice provide strong evidence for AQP4 involvement in cerebral water balance. AQP4-null mice are protected from cellular (cytotoxic) brain edema produced by water intoxication, brain ischemia, or meningitis. However, AQP4 deletion aggravates vasogenic (fluid leak) brain edema produced by tumor, cortical freeze, intraparenchymal fluid infusion, or brain abscess. In cytotoxic edema, AQP4 deletion slows the rate of water entry into brain, whereas in vasogenic edema, AQP4 deletion reduces the rate of water outflow from brain parenchyma. AQP4 deletion also worsens obstructive hydrocephalus. Recently, AQP4 was also found to play a major role in processes unrelated to brain edema, including astrocyte migration and neuronal excitability. These findings suggest that modulation of AQP4 expression or function may be beneficial in several cerebral disorders, including hyponatremic brain edema, hydrocephalus, stroke, tumor, infection, epilepsy, and traumatic brain injury.

Three distinct roles of aquaporin-4 in brain function revealed by knockout mice.

Aquaporin-4 (AQP4) is expressed in astrocytes throughout the central nervous system, particularly at the blood-brain and brain-cerebrospinal fluid barriers. Phenotype analysis of transgenic mice lacking AQP4 has provided compelling evidence for involvement of AQP4 in cerebral water balance, astrocyte migration, and neural signal transduction. AQP4-null mice have reduced brain swelling and improved neurological outcome in models of (cellular) cytotoxic cerebral edema including water intoxication, focal cerebral ischemia, and bacterial meningitis. However, brain swelling and clinical outcome are worse in AQP4-null mice in models of vasogenic (fluid leak) edema including cortical freeze-injury, brain tumor, brain abscess and hydrocephalus, probably due to impaired AQP4-dependent brain water clearance. AQP4 deficiency or knock-down slows astrocyte migration in response to a chemotactic stimulus in vitro, and AQP4 deletion impairs glial scar progression following injury in vivo. AQP4-null mice also manifest reduced sound- and light-evoked potentials, and increased threshold and prolonged duration of induced seizures. Impaired K+ reuptake by astrocytes in AQP4 deficiency may account for the neural signal transduction phenotype. Based on these findings, we propose modulation of AQP4 expression or function as a novel therapeutic strategy for a variety of cerebral disorders including stroke, tumor, infection, hydrocephalus, epilepsy, and traumatic brain injury.

Fever and sepsis during neutropenia are associated with expansion of extracellular and loss of intracellular water.

BACKGROUND AND AIMS: Shifts from intracellular to extracellular water are features of a catabolic reaction to sepsis. Bedside assessment of fluid shifts was carried out in neutropenic patients at high risk of systemic infection. METHODS: Multifrequency bioelectrical impedance analysis was performed in 41 patients with leukemia or high-malignant lymphoma and chemotherapy-induced neutropenia. RESULTS: Hydration was stable during afebrile periods except for transient intra- and extracellular dehydration after chemotherapy. The risk of over-hydration and dehydration increased 3-fold during fever. Over-hydration was more severe when occurring during fever. Extracellular water was highly variable and tended to increase, and intracellular water was slowly depleted. During sepsis, these alterations were enhanced. Changes in hydration status did not predict subsequent progression to sepsis because it developed more slowly than other symptoms of infection. CONCLUSIONS: Extracellular over-hydration and intracellular dehydration are observed in febrile infection in neutropenia, similar to severe sepsis. If the technical limits of bioelectrical impedance are taken into account, this method may be useful for non-invasive monitoring of these features of metabolic stress.

[Optimization of hydrodynamic conditions in transurethral resection of benign prostatic hyperplasia]. / Oprimizatsiia gidrodinamicheskikh uslovii pri transuretral'noi rezektsii dobrokachestvennoi giperplazii prostaty.

Water intoxication remains a serious complication of transurethral resection (TUR) occurring more frequently in patients with large-size benign prostatic hyperplasia (BPH) and in those who was operated for more than 1 hour. An advanced irrigation system employing mechanical valve "Floval" and active aspiration provides controlled irrigation of the bladder preventing spontaneous rise of intravesical pressure in conducting TUR in BPH patients.

[Addition of ethanol to the distension medium in surgical hysteroscopy as screening to prevent "fluid overload". A prospective randomized comparative study of ablative versus non-ablative surgical hysteroscopy and different ethanol concentration]. / Ethanol-Beimengung im Distensionsmedium bei der operativen Hysteroskopie als Screening zur Vermeidung eines "Fluid overloads". Eine prospektiv-randomisierte Vergleichsstudie von ablativer versus nicht-ablativer operativer Hysteroskopie und unterschiedlichen Ethanol-Konzentrationen.

For answering the question at which hysteroscopical procedures an intraoperative screening method is necessary to avoid a fluid overload and whether a beginning fluid absorption can be diagnosed early by adding ethanol to the distension medium, a prospectively randomised comparative study of ablative versus non-ablative operative hysteroscopy with differing ethanol concentrations was performed (n = 120). Purisole (a mannit/sorbit solution) was used a distension medium. The measuring parameters (breath alcohol, amount of absorbed fluid, haematocrit and haemoglobin values, central venous pressure, heart frequency) were intraoperatively determined at 5-minute intervals. The results of the study show that with those hysteroscopical procedures during which the endometrium is not or only minimally injured (e.g. syneciolysis, hysteroscopic proximal tubal catheterisation). Intraoperative screening is not necessary due to the low absorbing amounts. With hysteroscopical procedures such as resection of myoma, endometrium ablation and septum resection, however, an addition of ethanol of 2% to the distension medium has proved useful, because with this method absorption amounts of 400 ml and more can be detected by positive values of breath alcohol. As the result of a further absorption of fluid, delayed in time compared to the first positive value of breath alcohol, there is an increase in central venous pressure and hyponatraemia. Intraoperative ethanol monitoring is a non-invasive procedure which can be performed during ablative-operative hysteroscopies and has no negative influence on the course of the intervention and the general condition of the patients.

Polydipsia and hyponatremia in psychiatric patients: challenge to creative nursing care.

Among patients with psychiatric disorders, especially schizophrenia, a pattern of extreme polydipsia and polyuria sometimes emerges, usually without readily identifiable medical causes. Hyponatremia may develop and progress to water intoxication, with symptoms including restlessness, confusion, seizures, or even death. We review the clinical features and pathophysiology of this syndrome and discuss nursing roles in identifying and managing patients with polydipsia and hyponatremia. While the causes of polydipsia and hyponatremia are unclear, relevant factors seem to include a possible dysfunction in central nervous system (CNS) thirst and osmoregulatory centers, the inappropriate secretion of or sensitivity to antidiuretic hormone (ADH), and psychoactive drugs. Management techniques for affected patients concentrate on careful observation, fluid restriction, and the minimization of possible exacerbating factors such as high neuroleptic dosage and cigarette consumption.

Effects of l- and d-timolol on cyclic AMP synthesis and intraocular pressure in water-loaded, albino and pigmented rabbits.

Topical 2% l- or d-timolol reduced the elevation of intraocular pressure induced by water-loading in conscious rabbits. This drug effect appeared on the peak elevation (in pigmented eyes) and on the down-phase (in albino and pigmented eyes) of elevated intraocular pressure. The contralateral eye and the treated eye responded similarly. In urethane anesthetized, water-loaded rabbits, a greater inhibitory effect of l-timolol was observed in pigmented eyes than in albino eyes. Two per cent l-timolol caused alterations of heart rate and arterial blood pressure in water-loaded anesthetized rabbits, but time courses of these alterations did not correlate with the inhibitory effect on the elevation of intraocular pressure. The beta-adrenergic antagonistic activity of l-timolol and d-timolol were compared by their ability to inhibit l-isoproterenol-stimulated cyclic AMP synthesis in the rabbit iris-ciliary body preparation in vitro. The I50S for l- and d-timolol differ by about 1.5 log units. In our studies, d-timolol has little of the intraocular pressure lowering and the beta-adrenergic antagonistic activity of l-timolol. Thus, the conscious, water-loaded, pigmented rabbit can be used as a model for studying the effects of beta-adrenergic antagonists on intraocular pressure.

Further characterization of the natriuretic factor derived from kidney tissue of volume-expanded rats. Effects on short-circuit current and sodium-potassium-adenosine triphosphatase activity.

Boiled homogenates of kidneys from volume-expanded and hydropenic rats were subjected to column chromatography. The fraction eluting within the range of partition coefficients (Kav) 0.76-0.89 (fraction III) was lyophilized and the effects of this semipurified preparation were assessed on short-circuit current (SCC) across isolated frog skin, on rat kidney cortex Na-K-ATPase activity, and on sodium excretion by the rat in vivo. At a dose of 500 mug/ml, fraction III from expanded rat kidney inhibited SCC by 21 +/- 5% (P less than 0.01), whereas the same fraction from hydropenic rat kidney produced an insignificant change in SCC of 2 +/- 8 %. In a dose-response study, 50, 150, 500, and 1,500 mug/ml of fraction III from expanded rat kidney inhibited SCC by 4, 8, 19, and 28%, respectively; 500, 1,000 and 1,500 mug/ml inhibited Na-K-ATPase activity by 11, 22, and 49%, respectively. An identical study with fraction III from hydropenic animals showed no significant effect in either assay. Also, fractions from expanded and hydropenic rats, eluted after fraction III (fractions IV and V), had no effect on SCC or Na-K-ATPase activity. Fraction III also produced significant natriuresis in vivo at a dose of 500 mug/ml, confirming our observations that a natriuretic principle may be recovered from the kidneys of volume-expanded rats. We suggest that this natriuretic principle may act by reducing active sodium transport via inhibition of Na-K-ATPase.