Regulation Of Fluid Volume Research Articles

Pathophysiologic Findings in the Human Endolymphatic Sac in Endolymphatic Hydrops: Functional and Molecular Evidence.

The endolymphatic sac (ES) is a cystic structure situated on the posterior fossa dura and is connected to the luminal space of the vestibular organ through the endolymphatic duct, which branches into the utricular and saccular ducts. Unlike the cochlea and vestibule, the ES does not contain sensory epithelium in its luminal space, and a single layer of epithelial cells line the luminal surface area. The ES in the inner ear is thought to play a role in the regulation of inner ear homeostasis, fluid volume, and immune reaction. If these functions of the ES are disrupted, dysfunction of the inner ear may develop. The most well-known pathology arising from dysfunction of the ES is endolymphatic hydrops, characterized by an enlarged endolymphatic space due to the accumulation of excessive endolymphatic fluid. Although, molecular identities and functional evidence for the roles were identified in animal studies, basic studies of the human ES are relatively uncommon compared with those using animal tissues, because of limited opportunity to harvest the human ES. In this study, molecular and functional evidence for the role of the human ES in the development of endolymphatic hydrops are reviewed. Although evidence is insufficient, studies using the human ES have mostly produced findings similar to those of animal studies. This review may provide a basis for planning further studies to investigate the pathophysiology of disorders with the finding of endolymphatic hydrops.

Hormonal control of vas deferens fluid volume and aquaporin expression in rats.

Precise regulation of vas deferens fluid volume which is important for sperm survival might be influenced by testosterone. In order to investigate changes in vas deferens fluid volume and aquoporins (AQP) isoforms expression under testosterone influence, orchidectomized Sprague-Dawley rats were given 125 and 250µg/kg/day testosterone with or without flutamide, an androgen receptor blocker or finasteride, a 5alpha-reductase inhibitor for seven consecutive days. Following treatment completion, vas deferens was perfused and changes in the fluid secretion rate and osmolality were determined in the presence of acetazolamide. Rats were then sacrificed and vas deferens was harvested for histology, tissue expression and distribution analyses of AQP-1, AQP-2, AQP-5, AQP-7 and AQP-9 proteins by Western blotting and immunohistochemistry, respectively. Our findings indicate that testosterone causes vas deferens fluid secretion rate to increase, which was antagonized by acetazolamide. Fluid osmolality increased following testosterone treatment and further increased when acetazolamide was given. Co-administration of flutamide or finasteride with testosterone causing both fluid secretion rate and osmolality to decrease. Histology revealed increased size of vas deferens lumen with increased thickness of vas deferens stroma. Expression of AQP-1, AQP-2 and AQP-9 were detected in vas deferens but not AQP-5 and AQP-7, and the levels of these proteins were increased by testosterone treatment mainly at the apical membrane of vas deferens epithelium. In conclusion, increased in vas deferens fluid secretion rate under testosterone influence mediated via the up-regulation of AQP-1, 2 and 9 might be important for vas deferens fluid homeostasis in order to ensure normal male fertility.

High-Salt Diet Causes Expansion of the Lymphatic Network and Increased Lymph Flow in Skin and Muscle of Rats.

Objective- A commonly accepted pivotal mechanism in fluid volume and blood pressure regulation is the parallel relationship between body Na+ and extracellular fluid content. Several recent studies have, however, shown that a considerable amount of Na+ can be retained in skin without commensurate water retention. Here, we asked whether a salt accumulation shown to result in VEGF (vascular endothelial growth factor)-C secretion and lymphangiogenesis had any influence on lymphatic function. Approach and Results- By optical imaging of macromolecular tracer washout in skin, we found that salt accumulation resulted in an increase in lymph flow of 26% that was noticeable only after including an overnight recording period. Surprisingly, lymph flow in skeletal muscle recorded with a new positron emission tomography/computed tomography method was also increased after salt exposure. The transcapillary filtration was unaffected by the high-salt diet and deoxycorticosterone-salt treatment, suggesting that the capillary barrier was not influenced by the salt accumulation. A significant reduction in lymph flow after depletion of macrophages/monocytes by clodronate suggests these cells are involved in the observed lymph flow response, together with collecting vessels shown here to enhance their contraction frequency as a response to extracellular Na+. Conclusions- The observed changes in lymph flow suggest that the lymphatics may influence long-term regulation of tissue fluid balance during salt accumulation by contributing to fluid homeostasis in skin and muscle. Our studies identify lymph clearance as a potential disease-modifying factor that might be targeted in conditions characterized by salt accumulation like chronic kidney disease and salt-sensitive hypertension.

Regulation of amniotic fluid volume: insights derived from amniotic fluid volume function curves.

Recent advances in understanding the regulation of amniotic fluid volume (AFV) include that AFV is determined primarily by the rate of intramembranous absorption (IMA) of amniotic fluid across the amnion and into fetal blood. In turn, IMA rate is dependent on the concentrations of yet-to-be identified stimulator(s) and inhibitor(s) that are present in amniotic fluid. To put these concepts in perspective, this review 1) discusses the evolution of discoveries that form the current basis for understanding the regulation of AFV, 2) reviews the contribution of IMA to this regulation, and 3) interprets experimentally induced shifts in AFV function curves and amnioinfusion function curves in terms of the activity of the amniotic fluid stimulator and inhibitor of IMA. In the early 1980s, it was not known whether AFV was regulated. However, by the late 1980s, IMA was discovered to be a "missing link" in understanding the regulation of AFV. Over the next 25 years the concept of IMA evolved from being a passive process to being an active, unidirectional transport of amniotic fluid water and solutes by vesicles within the amnion. In the 2010s, it was demonstrated that a renally derived stimulator and a fetal membrane-derived inhibitor are present in amniotic fluid that regulate IMA rate and hence are the primary determinants of AFV. Furthermore, AFV function curves and amnioinfusion function curves provide new insights into the relative efficacy of the stimulator and inhibitor of IMA.

MAGED2: a novel form of antenatal Bartter's syndrome.

Antenatal Bartter's syndrome (aBS) is the most severe form of Bartter's syndrome, requiring close follow-up, in particular during the neonatal period, primarily because of prematurity. The recent identification of a novel and very severe form of aBS merits an update on this topic. Despite the identification of several genes involved in Bartter's syndrome, about 20% of patients clinically diagnosed with aBS remained without genetic explanation for decades. We recently identified mutations in MAGED2 as a cause of an X-linked form of aBS characterized by a very early onset of severe polyhydramnios and extreme prematurity leading to high mortality. Remarkably, all symptoms in surviving patients with MAGE-D2 mutations resolve spontaneously, within weeks after preterm birth. Interestingly, MAGE-D2 affects the expression of the sodium chloride cotransporters NKCC2 and NCC, explaining thereby the severity of the disease. Importantly, a more recent analysis of MAGED2 in a large French cohort of patients with aBS confirmed our data and showed that females can also be affected. MAGE-D2 is critical for renal salt reabsorption in the fetus, amniotic fluid volume regulation, and maintenance of pregnancy. Most importantly, MAGED2 must be included in the genetic screening of every form of aBS.

Aquaporin 1 gene deletion affects the amniotic fluid volume and composition as well as the expression of other aquaporin water channels in placenta and fetal membranes

ObjectiveTo explore the role of aquaporin 1 (AQP1) in regulation of amniotic fluid volume and composition. To investigate the effects of AQP1 gene knockout on expression of other aquaporin water channels (AQP3, AQP8 and AQP9) in placentas and fetal membranes. MethodsMice were sacrificed at 9.5, 13.5 and 16.5 gestational day (GD). Amniotic fluid volume, osmolality and composition, fetal membranes, placental and fetal weights as well as placenta areas were recorded in Aqp1 homozygote conceptus group, heterozygote conceptus group and wild-type group, respectively. The expression of AQP1, AQP3, AQP8 and AQP9 mRNA and protein in placenta and fetal membranes were examined by quantitative Reverse Transcription-Polymerase Chain Reaction (RT-PCR) and Western blotting. ResultsAqp1 homozygote conceptus had a greater volume of amniotic fluid, lower osmolality and calcium concentration than their wild-type counterparts at 16.5 GD. There was no significant difference in expression of AQP1, AQP3, AQP8 and AQP9 in placentas among three groups. While expression of AQP8 was increased at 13.5 and 16.5 GD in fetal membranes, the expression of AQP9 was significantly decreased in fetal membranes in Aqp1 homozygote group compared with Aqp1 heterozygote and wild-type groups. ConclusionAQP1 may play an important role in the homeostasis of maternal-fetal fluid at late gestation days. The mechanism of mutual compensation among AQPs gene needs further investigation.

Slippery When Wet: Airway Surface Liquid Homeostasis and Mucus Hydration.

The ability to regulate cell volume is crucial for normal physiology; equally the regulation of extracellular fluid homeostasis is of great importance. Alteration of normal extracellular fluid homeostasis contributes to the development of several diseases including cystic fibrosis. With regard to the airway surface liquid (ASL), which lies apically on top of airway epithelia, ion content, pH, mucin and protein abundance must be tightly regulated. Furthermore, airway epithelia must be able to switch from an absorptive to a secretory state as required. A heterogeneous population of airway epithelial cells regulate ASL solute and solvent composition, and directly secrete large mucin molecules, antimicrobials, proteases and soluble mediators into the airway lumen. This review focuses on how epithelial ion transport influences ASL hydration and ASL pH, with a specific focus on the roles of anion and cation channels and exchangers. The role of ions and pH in mucin expansion is also addressed. With regard to fluid volume regulation, we discuss the roles of nucleotides, adenosine and the short palate lung and nasal epithelial clone 1 (SPLUNC1) as soluble ASL mediators. Together, these mechanisms directly influence ciliary beating and in turn mucociliary clearance to maintain sterility and to detoxify the airways. Whilst all of these components are regulated in normal airways, defective ion transport and/or mucin secretion proves detrimental to lung homeostasis as such we address how defective ion and fluid transport, and a loss of homeostatic mechanisms, contributes to the development of pathophysiologies associated with cystic fibrosis.

Vesicular uptake of macromolecules by human placental amniotic epithelial cells

IntroductionStudies in animal models have shown that unidirectional vesicular transport of amniotic fluid across the amnion plays a primary role in regulating amniotic fluid volume. Our objective was to explore vesicle type, vesicular uptake and intracellular distribution of vesicles in human amnion cells using high- and super-resolution fluorescence microscopy. MethodsPlacental amnion was obtained at cesarean section and amnion cells were prepared and cultured. At 20%–50% confluence, the cells were incubated with fluorophore conjugated macromolecules for 1–30 min at 22 °C or 37 °C. Fluorophore labeled macromolecules were selected as markers of receptor-mediated caveolar and clathrin-coated vesicular uptake as well as non-specific endocytosis. After fluorophore treatment, the cells were fixed, imaged and vesicles counted using Imaris® software. ResultsVesicular uptake displayed first order saturation kinetics with half saturation times averaging 1.3 min at 37 °C compared to 4.9 min at 22 °C, with non-specific endocytotic uptake being more rapid at both temperatures. There was extensive cell-to-cell variability in uptake rate. Under super-resolution microscopy, the pattern of intracellular spatial distribution was distinct for each macromolecule. Co-localization of fluorescently labeled macromolecules was very low at vesicular dimensions. ConclusionsIn human placental amnion cells, 1) vesicular uptake of macromolecules is rapid, consistent with the concept that vesicular transcytosis across the amnion plays a role in the regulation of amniotic fluid volume; 2) uptake is temperature dependent and variable among individual cells; 3) the unique intracellular distributions suggest distinct functions for each vesicle type; 4) non-receptor mediated vesicular uptake may be a primary vesicular uptake mechanism.

The “chloride theory”, a unifying hypothesis for renal handling and body fluid distribution in heart failure pathophysiology

Body fluid volume regulation is a complex process involving the interaction of various afferent (sensory) and neurohumoral efferent (effector) mechanisms. Historically, most studies focused on the body fluid dynamics in heart failure (HF) status through control of the balance of sodium, potassium, and water in the body, and maintaining arterial circulatory integrity is central to a unifying hypothesis of body fluid regulation in HF pathophysiology. The pathophysiologic background of the biochemical determinants of vascular volume in HF status, however, has not been known. I recently demonstrated that changes in vascular and red blood cell volumes are independently associated with the serum chloride concentration, but not the serum sodium concentration, during worsening HF and its recovery. Based on these observations and the established central role of chloride in the renin-angiotensin-aldosterone system, I propose a unifying hypothesis of the “chloride theory” for HF pathophysiology, which states that changes in the serum chloride concentration are the primary determinant of changes in plasma volume and the renin-angiotensin-aldosterone system under worsening HF and therapeutic resolution of worsening HF.

Hypothalamic Signaling in Body Fluid Homeostasis and Hypertension.

The central nervous system plays a pivotal role in the regulation of extracellular fluid volume and consequently arterial blood pressure. Key hypothalamic regions sense and integrate neurohumoral signals to subsequently alter intake (thirst and salt appetite) and output (renal excretion via neuroendocrine and autonomic function). Here, we review recent findings that provide new insight into such mechanisms that may represent new therapeutic targets. Implementation of cutting edge neuroscience approaches such as opto- and chemogenetics highlight pivotal roles of circumventricular organs to impact body fluid homeostasis. Key signaling mechanisms within these areas include the N-terminal variant of transient receptor potential vannilloid type-1, NaX, epithelial sodium channel, brain electroneutral transporters, and non-classical actions of vasopressin. Despite the identification of several new mechanisms, future studies need to better define the neurochemical phenotype and molecular profiles of neurons within circumventricular organs for future therapeutic potential.

Interplay between renal endothelin and purinergic signaling systems.

Alterations in extracellular fluid volume regulation and sodium balance may result in the development and maintenance of salt-dependent hypertension, a major risk factor for cardiovascular disease. Numerous pathways contribute to the regulation of sodium excretion and blood pressure, including endothelin and purinergic signaling. Increasing evidence suggests a link between purinergic receptor activation and endothelin production within the renal collecting duct as a means of promoting natriuresis. A better understanding of the relationship between these two systems, especially in regard to sodium homeostasis, will fill a significant knowledge gap and may provide novel antihypertensive treatment options. Therefore, this review focuses on the cross talk between endothelin and purinergic signaling as it relates to the renal regulation of sodium and blood pressure homeostasis.

Generation of a Three-Dimensional Kidney Structure from Pluripotent Stem Cells.

The kidney is a vital organ that has an important role in the maintenance of homeostasis by fluid volume regulation and waste product excretion. This role cannot be performed without the three-dimensional (3D) structure of the kidney. Therefore, it is important to generate the 3D structure of the kidney when inducing functional kidney tissue or the whole organ from pluripotent stem cells. In this chapter, we describe the detailed methods to induce kidney progenitor cells from pluripotent stem cells, which are based on embryological development. We also provide a method to generate 3D kidney tissue with vascularized glomeruli upon transplantation.

Paracellular transport in the collecting duct.

The paracellular pathway through the tight junction provides an important route for chloride reabsorption in the collecting duct of the kidney. This review describes recent findings of how defects in paracellular chloride permeation pathway may cause kidney diseases and how such a pathway may be regulated to maintain normal chloride homeostasis. The tight junction in the collecting duct expresses two important claudin genes - claudin-4 and claudin-8. Transgenic knockout of either claudin gene causes hypotension, hypochloremia, and metabolic alkalosis in experimental animals. The claudin-4 mediated chloride permeability can be regulated by a protease endogenously expressed by the collecting duct cell - channel-activating protease 1. Channel-activating protease 1 regulates the intercellular interaction of claudin-4 and its membrane stability. Kelch-like 3, previously identified as a causal gene for Gordon's syndrome, also known as pseudohypoaldosteronism II, directly interacts with claudin-8 and regulates its ubiquitination and degradation. The dominant pseudohypoaldosteronism-II mutation (R528H) in Kelch-like 3 abolishes claudin-8 binding, ubiquitination, and degradation. The paracellular chloride permeation pathway in the kidney is an important but understudied area in nephrology. It plays vital roles in renal salt handling and regulation of extracellular fluid volume and blood pressure. Two claudin proteins, claudin-4 and claudin-8, contribute to the function of this paracellular pathway. Deletion of either claudin protein from the collecting duct causes renal chloride reabsorption defects and low blood pressure. Claudins can be regulated on posttranslational levels by several mechanisms involving protease and ubiquitin ligase. Deregulation of claudins may cause human hypertension as exemplified in the Gordon's syndrome.

Modeling of Kidney Hemodynamics: Probability-Based Topology of an Arterial Network.

Through regulation of the extracellular fluid volume, the kidneys provide important long-term regulation of blood pressure. At the level of the individual functional unit (the nephron), pressure and flow control involves two different mechanisms that both produce oscillations. The nephrons are arranged in a complex branching structure that delivers blood to each nephron and, at the same time, provides a basis for an interaction between adjacent nephrons. The functional consequences of this interaction are not understood, and at present it is not possible to address this question experimentally. We provide experimental data and a new modeling approach to clarify this problem. To resolve details of microvascular structure, we collected 3D data from more than 150 afferent arterioles in an optically cleared rat kidney. Using these results together with published micro-computed tomography (μCT) data we develop an algorithm for generating the renal arterial network. We then introduce a mathematical model describing blood flow dynamics and nephron to nephron interaction in the network. The model includes an implementation of electrical signal propagation along a vascular wall. Simulation results show that the renal arterial architecture plays an important role in maintaining adequate pressure levels and the self-sustained dynamics of nephrons.

Identification of genetic markers for skill and athleticism in sub-elite Australian football players: a pilot study.

Natural genetic variation contributes towards athletic performance in various strength/power and endurance based sports. To date, no studies have explored the genetic predisposition towards skill and athletic performance in Australian Football (AF) players. The present pilot study recruited 30 sub-elite AF players who completed tests of endurance, power and technical skill. Specific polymorphisms in nine genes were screened, and assessed for a possible association with athletic and skill traits. Statistical analysis using generalized linear models identified a number of polymorphisms predictive of endurance and technical skill. The angiotensin-converting enzyme (ACE), normally responsible for regulation of body fluid volume, was a significant factor in predicting 'all round' athletic performance and skill. Specifically, the deletion allele (DD) of ACE was identified as a predictor for AF power (P≤0.008), endurance (P=0.001) and skill assessments (P≤0.003). In addition, polymorphisms in the brain-derived neurotrophic factor, D2 dopamine receptor, and catechol-O-methyltransferase genes were also shown to contribute to kicking skill outcomes (P≤0.044). This is the first study to implicate the ACE deletion allele for a multidimensional sport in such a way. Further, the results from this study have identified several new candidate genes in predicting athletic and technical skill outcomes.

Electrostatic, elastic and hydration-dependent interactions in dermis influencing volume exclusion and macromolecular transport

Interstitial exclusion refers to the limitation of space available for plasma proteins and other macromolecules based on collagen and negatively charged glycosaminoglycans (GAGs) in the interstitial space. It is of particular importance to interstitial fluid and plasma volume regulation. Here we present a novel mechanical and mathematical model of the dynamic interactions of structural elements within the interstitium of the dermis at the microscopic level that may explain volume exclusion of charged and neutral macroparticles. At this level, the interstitium is considered to consist of elements called extracellular matrix (ECM) cells, again containing two main interacting structural components on a fluid background including anions and cations setting up osmotic forces: one smaller GAG component, having an intrinsic expansive electric force, and one bigger collagen component, having an intrinsic elastic force. Because of size differences, the GAG component interacts with a fraction of the collagen component only at normal hydration. This fraction, however, increases with rising hydration as a consequence of the modeled form of the interaction force between the GAGs and collagen. Collagen is locally displaced at variable degrees as hydration changes. Two models of GAGs are considered, having largely different geometries which demands different, but related, forms of GAG–collagen interaction forces. The effects of variable fixed charges on GAGs and of GAG density in tissue are evaluated taking into account observed volume exclusion properties of charged macromolecules as a function of tissue hydration. The presented models may improve our biophysical understanding of acting forces influencing tissue fluid dynamics. Such knowledge is significant when evaluating the transport of electrically charged and neutral macromolecules into and through the interstitium, and therefore to drug uptake and the therapeutic effects of macromolecular agents.

Academic-industrial collaboration in the development of the first angiotensin receptor blocker: neprilysin inhibitor in the treatment of heart failure.

The important roles of the renin–angiotensin–aldosterone system (RAAS) and the natriuretic peptide system (NPS) in the regulation of arterial pressure and fluid volume in both health and disease have been well established for decades. Activation of the former causes vasoconstriction and sodium retention, while activation of the latter has opposing actions—vasodilatation, natriuresis, and diuresis. It is highly desirable to suppress the activity of the RAAS and to enhance the activity of the NPS in patients with heart failure, as well as in patients with hypertension. Considerable efforts to accomplish this both effectively and safely have recently met with success with the development of an angiotensin receptor blocker-neprilysin inhibitor (ARNi), likely the first of a new class of drugs. Cardiologists, many in the wider medical community, and millions of patients with heart failure were excited in March 2014 …

Регуляция объема амниотической жидкости

Регуляция объема амниотической жидкости

A noninvasive method to study regulation of extracellular fluid volume in rats using nuclear magnetic resonance

Time-domain nuclear magnetic resonance (TD-NMR)-based measurement of body composition of rodents is an effective method to quickly and repeatedly measure proportions of fat, lean, and fluid without anesthesia. TD-NMR provides a measure of free water in a living animal, termed %fluid, and is a measure of unbound water in the vascular and extracellular spaces. We hypothesized that injecting a bolus of fluid into the peritoneal cavity would lead to an abrupt increase in %fluid and the rate of clearance monitored with TD-NMR would provide a noninvasive assessment of the free water homeostasis in an awake rat. Several strains of laboratory rats were injected intraperitoneally with 10 ml/kg isotonic or hypertonic saline and %fluid was monitored repeatedly with a Bruker "Minispec" TD-NMR body composition system. Following isotonic saline, %fluid increased immediately by 0.5% followed by a recovery over ∼6 h. Injecting hypertonic (3 times normal saline) resulted in a significantly greater rise in %fluid and longer recovery. Intraperitoneal and subcutaneous fluid injection led to similar rates of clearance. The Wistar-Kyoto rat strain displayed significantly slower recovery to fluid loads compared with Long-Evans and Sprague-Dawley strains. Rats exercised chronically showed significant increases in %fluid, but the rate of clearance of fluid was similar to that of sedentary animals. We conclude that this technique could be used to study vascular and extracellular volume homeostasis noninvasively in rats.

Electrogenic transport and K(+) ion channel expression by the human endolymphatic sac epithelium.

The endolymphatic sac (ES) is a cystic organ that is a part of the inner ear and is connected to the cochlea and vestibule. The ES is thought to be involved in inner ear ion homeostasis and fluid volume regulation for the maintenance of hearing and balance function. Many ion channels, transporters, and exchangers have been identified in the ES luminal epithelium, mainly in animal studies, but there has been no functional study investigating ion transport using human ES tissue. We designed the first functional experiments on electrogenic transport in human ES and investigated the contribution of K+ channels in the electrogenic transport, which has been rarely identified, even in animal studies, using electrophysiological/pharmacological and molecular biological methods. As a result, we identified functional and molecular evidence for the essential participation of K+ channels in the electrogenic transport of human ES epithelium. The identified K+ channels involved in the electrogenic transport were KCNN2, KCNJ14, KCNK2, and KCNK6, and the K+ transports via those channels are thought to play an important role in the maintenance of the unique ionic milieu of the inner ear fluid.