Renal sodium handling in acute and chronic salt loading/depletion protocols: the confounding influence of acute water loading.

OBJECTIVES: Renal tubular sodium handling was measured in healthy subjects submitted to acute and chronic salt-repletion/salt-depletion protocols. The goal was to compare the changes in proximal and distal sodium handling induced by the two procedures using the lithium clearance technique. METHODS: In nine subjects, acute salt loading was obtained with a 2 h infusion of isotonic saline, and salt depletion was induced with a low-salt diet and furosemide. In the chronic protocol, 15 subjects randomly received a low-, a regular- and a high-sodium diet for 1 week. In both protocols, renal and systemic haemodynamics and urinary electrolyte excretion were measured after an acute water load. In the chronic study, sodium handling was also determined, based on 12 h day- and night-time urine collections. RESULTS: The acute and chronic protocols induced comparable changes in sodium excretion, renal haemodynamics and hormonal responses. Yet, the relative contribution of the proximal and distal nephrons to sodium excretion in response to salt loading and depletion differed in the two protocols. Acutely, subjects appeared to regulate sodium balance mainly by the distal nephron, with little contribution of the proximal tubule. In contrast, in the chronic protocol, changes in sodium reabsorption could be measured both in the proximal and distal nephrons. Acute water loading was an important confounding factor which increased sodium excretion by reducing proximal sodium reabsorption. This interference of water was particularly marked in salt-depleted subjects. CONCLUSION: Acute and chronic salt loading/salt depletion protocols investigate different renal mechanisms of control of sodium balance. The endogenous lithium clearance technique is a reliable method to assess proximal sodium reabsorption in humans. However, to investigate sodium handling in diseases such as hypertension, lithium should be measured preferably on 24 h or overnight urine collections to avoid the confounding influence of water.

Bit loading for MIMO with statistical channel information at the transmitter and ZF receivers

For single-user MIMO communication with uncoded and coded QAM signals, we propose bit and power loading schemes that rely only on channel distribution information at the transmitter. To that end, we develop the relationship between the average bit error probability at the output of a ZF linear receiver and the bit rates and powers allocated at the transmitter. This relationship, and the fact that a ZF receiver decouples the MIMO parallel channels, allow leveraging bit loading algorithms already existing in the literature. We solve dual bit rate maximization and power minimization problems and present performance resultsthat illustrate the gains of the proposed scheme with respect toa non-optimized transmission.

Musik bei der Arbeit: Top oder Flop?

Ob sich Musikhören am Arbeitsplatz positiv oder negativ auf die Mitarbeitenden und auf die Arbeit auswirkt, hängt von einer komplexen Kombination von Faktoren ab. Nämlich von der Musik, von der Art der Arbeitstätigkeit, vom Individuum und seiner Persönlichkeit und vom generellen Arbeitskontext.

Identification and characterization of the Arabidopsis PHO1 gene involved in phosphate loading to the xylem.

The Arabidopsis mutant pho1 is deficient in the transfer of Pi from root epidermal and cortical cells to the xylem. The PHO1 gene was identified by a map-based cloning strategy. The N-terminal half of PHO1 is mainly hydrophilic, whereas the C-terminal half has six potential membrane-spanning domains. PHO1 shows no homology with any characterized solute transporter, including the family of H(+)-Pi cotransporters identified in plants and fungi. PHO1 shows highest homology with the Rcm1 mammalian receptor for xenotropic murine leukemia retroviruses and with the Saccharomyces cerevisiae Syg1 protein involved in the mating pheromone signal transduction pathway. PHO1 is expressed predominantly in the roots and is upregulated weakly under Pi stress. Studies with PHO1 promoter-beta-glucuronidase constructs reveal predominant expression of the PHO1 promoter in the stelar cells of the root and the lower part of the hypocotyl. There also is beta-glucuronidase staining of endodermal cells that are adjacent to the protoxylem vessels. The Arabidopsis genome contains 10 additional genes showing homology with PHO1. Thus, PHO1 defines a novel class of proteins involved in ion transport in plants.

In vivo loading increases mechanical properties of scaffold by affecting bone formation and bone resorption rates.

A successful bone tissue engineering strategy entails producing bone-scaffold constructs with adequate mechanical properties. Apart from the mechanical properties of the scaffold itself, the forming bone inside the scaffold also adds to the strength of the construct. In this study, we investigated the role of in vivo cyclic loading on mechanical properties of a bone scaffold. We implanted PLA/β-TCP scaffolds in the distal femur of six rats, applied external cyclic loading on the right leg, and kept the left leg as a control. We monitored bone formation at 7 time points over 35 weeks using time-lapsed micro-computed tomography (CT) imaging. The images were then used to construct micro-finite element models of bone-scaffold constructs, with which we estimated the stiffness for each sample at all time points. We found that loading increased the stiffness by 60% at 35 weeks. The increase of stiffness was correlated to an increase in bone volume fraction of 18% in the loaded scaffold compared to control scaffold. These changes in volume fraction and related stiffness in the bone scaffold are regulated by two independent processes, bone formation and bone resorption. Using time-lapsed micro-CT imaging and a newly-developed longitudinal image registration technique, we observed that mechanical stimulation increases the bone formation rate during 4-10 weeks, and decreases the bone resorption rate during 9-18 weeks post-operatively. For the first time, we report that in vivo cyclic loading increases mechanical properties of the scaffold by increasing the bone formation rate and decreasing the bone resorption rate.

Laboratory Study of Structural Behavior of Alternative Dowel Bars, April 2006

Load transfer across transverse joints has always been a factor contributing to the useful life of concrete pavements. For many years, round steel dowels have been the conventional load transfer mechanism. Many problems have been associated with the round steel dowels. The most detrimental effect of the steel dowel is corrosion. Repeated loading over time also damages joints. When a dowel is repeatedly loaded over a long period of time, the high bearing stresses found at the top and bottom edge of a bar erode the surrounding concrete. This oblonging creates multiple problems in the joint. Over the past decade, Iowa State University has performed extensive research on new dowel shapes and materials to mitigate the effects of oblonging and corrosion. This report evaluates the bearing stress performance of six different dowel bar types subjected to two different shear load laboratory test methods. The first load test is the AASHTO T253 method. The second procedure is an experimental cantilevered dowel test. The major objective was to investigate and improve the current AASHTO T253 test method for determining the modulus of dowel support, k0. The modified AASHTO test procedure was examined alongside an experimental cantilever dowel test. The modified AASHTO specimens were also subjected to a small-scale fatigue test in order to simulate long-term dowel behavior with respect to concrete joint damage. Loss on ignition tests were also performed on the GFRP dowel specimens to determine the resin content percentage. The study concluded that all of the tested dowel bar shapes and materials were adequate with respect to performance under shear loading. The modified AASHTO method yielded more desirable results than the ones obtained from the cantilever test. The investigators determined that the experimental cantilever test was not a satisfactory test method to replace or verify the AASHTO T253 method.

Effect of sodium loading/depletion on renal oxygenation in young normotensive and hypertensive men.

The goal of this study was to investigate the effect of sodium intake on renal tissue oxygenation in humans. To this purpose, we measured renal hemodynamics, renal sodium handling, and renal oxygenation in normotensive (NT) and hypertensive (HT) subjects after 1 week of a high-sodium and 1 week of a low-sodium diet. Renal oxygenation was measured using blood oxygen level-dependent magnetic resonance. Tissue oxygenation was determined by the measurement of R2* maps on 4 coronal slices covering both kidneys. The mean R2* values in the medulla and cortex were calculated, with a low R2* indicating a high tissue oxygenation. Ten male NT (mean age: 26.5+/-7.4 years) and 8 matched HT subjects (mean age: 28.8+/-5.7 years) were studied. Cortical R2* was not different under the 2 conditions of salt intake. Medullary R2* was significantly lower under low sodium than high sodium in both NT and HT subjects (28.1+/-0.8 versus 31.3+/-0.6 s(-1); P<0.05 in NT; and 27.9+/-1.5 versus 30.3+/-0.8 s(-1); P<0.05, in HT), indicating higher medullary oxygenation under low-sodium conditions. In NT subjects, medullary oxygenation was positively correlated with proximal reabsorption of sodium and negatively with absolute distal sodium reabsorption, but not with renal plasma flow. In HT subjects, medullary oxygenation correlated with the 24-hour sodium excretion but not with proximal or with the distal handling of sodium. These data demonstrate that dietary sodium intake influences renal tissue oxygenation, low sodium intake leading to an increased renal medullary oxygenation both in normotensive and young hypertensive subjects.

Endotoxin impairs cardiac hemodynamics by affecting loading conditions but not by reducing cardiac inotropism.

Acute myocardial dysfunction is a typical manifestation of septic shock. Experimentally, the administration of endotoxin [lipopolysacharride (LPS)] to laboratory animals is frequently used to study such dysfunction. However, a majority of studies used load-dependent indexes of cardiac function [including ejection fraction (EF) and maximal systolic pressure increment (dP/dt(max))], which do not directly explore cardiac inotropism. Therefore, we evaluated the direct effects of LPS on myocardial contractility, using left ventricular (LV) pressure-volume catheters in mice. Male BALB/c mice received an intraperitoneal injection of E. coli LPS (1, 5, 10, or 20 mg/kg). After 2, 6, or 20 h, cardiac function was analyzed in anesthetized, mechanically ventilated mice. All doses of LPS induced a significant drop in LV stroke volume and a trend toward reduced cardiac output after 6 h. Concomitantly, there was a significant decrease of LV preload (LV end-diastolic volume), with no apparent change in LV afterload (evaluated by effective arterial elastance and systemic vascular resistance). Load-dependent indexes of LV function were markedly reduced at 6 h, including EF, stroke work, and dP/dt(max). In contrast, there was no reduction of load-independent indexes of LV contractility, including end-systolic elastance (ejection phase measure of contractility) and the ratio dP/dt(max)/end-diastolic volume (isovolumic phase measure of contractility), the latter showing instead a significant increase after 6 h. All changes were transient, returning to baseline values after 20 h. Therefore, the alterations of cardiac function induced by LPS are entirely due to altered loading conditions, but not to reduced contractility, which may instead be slightly increased.

Studies of the renal effects of angiotensin II receptor blockade: the confounding factor of acute water loading on the action of vasoactive systems.

The acute renal tubular effects of two pharmacologically distinct angiotensin II receptor antagonists have been evaluated in normotensive volunteers on various salt diets. In the first study, the renal response to a single oral dose of losartan (100 mg) was assessed in subjects on a low (50 mmol Na/d) and on a high (200 mmol Na/d) salt intake. In a second protocol, the renal effects of 50 mg irbesartan were investigated in subjects receiving a 100 mmol Na/d diet. Both angiotensin II antagonists induced a significant increase in urinary sodium excretion. With losartan, a modest, transient increase in urinary potassium and a significant increase in uric acid excretion were found. In contrast, no change in potassium and uric acid excretions were observed with irbesartan, suggesting that the effects of losartan on potassium and uric acid are due to the intrinsic pharmacologic properties of losartan rather than to the specific blockade of renal angiotensin II receptors. Assessment of segmental sodium reabsorption using lithium as a marker of proximal tubular reabsorption demonstrated a decreased distal reabsorption of sodium with both antagonists. A direct proximal tubular natriuretic effect of the angiotensin II antagonist could be demonstrated only with irbesartan. This apparent discrepancy allowed us to reveal the importance of acute water loading as a possible confounding factor in renal studies. The results of the present analysis show that acute water loading per se may enhance renal sodium excretion and hence modify the level of activity of the renin-angiotensin system expected from a given sodium diet. Since acute water loading is a common practice in clinical renal studies, this confounding factor should be taken into account when investigating the renal effects of vasoactive systems.

Authors', Institutions' and Countries' rankings in regional and urban science : an analysis for nine top international journals from 1991 to 2000

This paper examines the most productive authors, institutions and countries in regional and urban science from 1991 to 2000 using information on published articles (and pages) from a sample of widely recognized journals in this field: ARS, JUE, JRS, IJURR, IRSR, PRS, RSUE, RS and US. We also consider the relation between the country of the institution named in articles and the country in which the journal is published, in order to know if there are a home publication bias in regional and urban science. Analysis was made for the whole decade and by subperiods, this allowed us to make a more dynamic interpretation of the results

Top income shares in Portugal over the twentieth century

[cat] L’objectiu d’aquest article és presentar nova evidència estadística sobre l’evolució de les desigualtats econòmiques a Portugal a llarg termini. L’explotació de les fonts fiscals portugueses ha permès l’estimació annual de les top income shares des de 1936. La construcció d’aquesta nova sèrie s’ha fet seguint la metodologia emprada per Piketty (2001). Aquesta nova sèrie revela una caiguda de les top income shares durant la Segona Guerra Mundial, seguida d’una recuperació fins a principis dels anys cinquanta. Des de mitjans dels cinquanta fins a principis dels anys vuitanta hi ha una caiguda dràstica de les top income shares. Per acabar, durant els anys noranta les top income shares tornen a augmentar. Aquesta pauta és molt similar a la viscuda en altres països: la reducció de les top income shares durant l’època daurada és compartida per tots els països estudiats i el seu increment als anys noranta sembla que alinea Portugal amb la pauta seguida pels països Anglosaxons.

Properties of top soil and the relationship between soil and trees in a boreal Scots pine stand

Summary