Osmotic diuresis due to urea as the cause of hypernatraemia in critically ill patients

Hypernatraemia is common in critically ill patients and has been shown to be an independent predictor of mortality. Osmotic urea diuresis can cause hypernatraemia due to significant water losses but is often not diagnosed. Free water clearance (FWC) and electrolyte free water clearance (EFWC) were proposed to quantify renal water handling. We aimed to (i) identify patients with hypernatraemia due to osmotic urea diuresis and (ii) investigate whether FWC and EFWC are helpful in identifying renal loss of free water.

An unusual patient with hypercalciuria, recurrent nephrolithiasis, hypomagnesemia and G227R mutation of Paracellin-1. An unusual patient with hypercalciuria and hypomagnesemia unresponsive to thiazide diuretics

A 19-year-old female patient with hypercalciuria and recurrent nephrolithiasis/urinary tract infection unresponsive to thiazide type diuretics is presented. The patient first experienced nephrolithiasis at the age of 4 years. Afterwards, recurrent passages of stones and urinary tract infection occurred. On diagnostic evaluation at the age of 19 years, she also had hypocitraturia and hypomagnesemia. Her serum calcium concentrations were near the lower limit of normal (8.5-8.8 mg/dl; normal range: 8.5-10.5), her serum magnesium concentrations were 1.15-1.24 mg/dl (normal range: 1.4-2.5) and urinary calcium excretion was 900 mg/24 h. PTH concentrations were increased (110-156 pg/ml; normal range: 10-65). We tried to treat the patient with hydrochlorothiazide at a dose of 50 mg/day. During treatment with thiazide diuretics, PTH concentration remained high and the patient had recurrent urinary tract infections and passages of stones. Serum magnesium concentration did not normalize even under the parenteral magnesium infusion. Her mother had a history of nephrolithiasis 20 years ago. Severe hypomagnesemia in association with hypercalciuria/urinary stones is reported as a rare autosomal recessive disorder caused by impaired reabsorption of magnesium and calcium in the thick assending limp of Henle's loop. Recent studies showed that mutations in the CLDN16 gene encoding paracellin-1 cause the disorder. In exon 4, a homozygous nucleotide exchange (G679C) was identified for the patient. This results in a point mutation at position Glycine227, which is replaced by an Arginine residue (G227R). The mother was heterozygous for this mutation. G227 is located in the fourth transmembrane domain and is highly conserved in the claudin gene family. This case indicates the pathogenetic role of paracellin-1 mutation in familial hypomagnesemia with hypercalciuria and nephrocalcinosis and further underlines the risk of stone formation in heterozygous mutation carriers.

When do combinations of diuretics make sense?

Diuretics are commonly prescribed by physicians to contract the ECF volume. In two clinical situations combining different classes of diuretics make sense: First, if a loop diuretic at maximal dose alone does not lead to sufficient diuresis or second, if the side effect of a diuretic needs to be corrected by adding a diuretic of another class. The latter is clinically often used to counteract loop or thiazide diuretic-induced hypokalemia by the addition of a potassium sparing diuretic. Key to a reasonable combination of diuretics is understanding of the pharmaco-kinetics and knowledge of the molecular targets of the diuretics involved.

A versatile proline/alanine transporter in the unicellular pathogen Leishmania donovani regulates amino acid homoeostasis and osmotic stress responses

Unlike all other organisms, parasitic protozoa of the family Trypanosomatidae maintain a large cellular pool of proline that, together with the alanine pool, serve as alternative carbon sources as well as reservoirs of organic osmolytes. These reflect adaptation to their insect vectors whose haemolymphs are exceptionally rich in the two amino acids. In the present study we identify and characterize a new neutral amino acid transporter, LdAAP24, that translocates proline and alanine across the Leishmania donovani plasma membrane. This transporter fulfils multiple functions: it is the sole supplier for the intracellular pool of proline and contributes to the alanine pool; it is essential for cell volume regulation after osmotic stress; and it regulates the transport and homoeostasis of glutamate and arginine, none of which are its substrates. Notably, we provide evidence that proline and alanine exhibit different roles in the parasitic response to hypotonic shock; alanine affects swelling, whereas proline influences the rate of volume recovery. On the basis of our data we suggest that LdAAP24 plays a key role in parasite adaptation to its varying environments in host and vector, a phenomenon essential for successful parasitism.

Role of diuretics, blockers, and statins in increasing the risk of diabetes in patients with impaired glucose tolerance: reanalysis of data from the NAVIGATOR study

OBJECTIVE To examine the degree to which use of β blockers, statins, and diuretics in patients with impaired glucose tolerance and other cardiovascular risk factors is associated with new onset diabetes. DESIGN Reanalysis of data from the Nateglinide and Valsartan in Impaired Glucose Tolerance Outcomes Research (NAVIGATOR) trial. SETTING NAVIGATOR trial. PARTICIPANTS Patients who at baseline (enrolment) were treatment naïve to β blockers (n=5640), diuretics (n=6346), statins (n=6146), and calcium channel blockers (n=6294). Use of calcium channel blocker was used as a metabolically neutral control. MAIN OUTCOME MEASURES Development of new onset diabetes diagnosed by standard plasma glucose level in all participants and confirmed with glucose tolerance testing within 12 weeks after the increased glucose value was recorded. The relation between each treatment and new onset diabetes was evaluated using marginal structural models for causal inference, to account for time dependent confounding in treatment assignment. RESULTS During the median five years of follow-up, β blockers were started in 915 (16.2%) patients, diuretics in 1316 (20.7%), statins in 1353 (22.0%), and calcium channel blockers in 1171 (18.6%). After adjusting for baseline characteristics and time varying confounders, diuretics and statins were both associated with an increased risk of new onset diabetes (hazard ratio 1.23, 95% confidence interval 1.06 to 1.44, and 1.32, 1.14 to 1.48, respectively), whereas β blockers and calcium channel blockers were not associated with new onset diabetes (1.10, 0.92 to 1.31, and 0.95, 0.79 to 1.13, respectively). CONCLUSIONS Among people with impaired glucose tolerance and other cardiovascular risk factors and with serial glucose measurements, diuretics and statins were associated with an increased risk of new onset diabetes, whereas the effect of β blockers was non-significant.

Disorders of serum sodium in emergency patients: salt in the soup of emergency medicine

Electrolyte disorders are common and potentially fatal laboratory findings in emergency patients. Approximately 20 % of patients in the emergency department present with either hyponatremia or hypernatremia. Recently it was shown that disorders of serum sodium are not only an expression of the severity of the underlying disease but independent predictors for the outcome of patients. They directly influence patient daily life by causing not only gait and concentration disturbances but also an increased tendency to fall together with a reduced bone mass. Given these new data it is even more important to detect and adequately correct dysnatremia in patients in the emergency department. Acute, symptomatic dysnatremia should be corrected promptly by use of 3 % NaCl for hyponatremia and 5 % glucose for hypernatremia. A close monitoring of serum sodium concentration is, however, essential in any case of correction of hyponatremia or hypernatremia in order to avoid rapid overcorrection and subsequent complications. A profound knowledge of the mechanisms underlying the development of hyponatremia, e.g. diuretics, syndrome of inappropriate antidiuretic hormone secretion (SIADH), heart failure and cirrhosis of the liver and hypernatremia, e.g. dehydration, infusions, diuretics and osmotic diuresis is essential. The present article describes the epidemiology, etiology and correction of hyponatremia and hypernatremia on the basis of current knowledge with special emphasis on emergency department patients.

Use of diuretics and risk of incident gout: a population-based case-control study

OBJECTIVE Use of diuretics has been associated with an increased risk of gout. Data on different types of diuretics are scarce. We undertook this study to investigate the association between use of loop diuretics, thiazide or thiazide-like diuretics, and potassium-sparing agents and the risk of developing incident gout. METHODS We conducted a retrospective population-based case-control analysis using the General Practice Research Database established in the UK. We identified case patients who were diagnosed as having incident gout between 1990 and 2010. One control patient was matched to each case patient for age, sex, general practice, calendar time, and years of active history in the database. We used conditional logistic regression to calculate odds ratios (ORs) and 95% confidence intervals (95% CIs), and we adjusted for potential confounders. RESULTS We identified 91,530 incident cases of gout and the same number of matched controls. Compared to past use of diuretics from each respective drug class, adjusted ORs for current use of loop diuretics, thiazide diuretics, thiazide-like diuretics, and potassium-sparing diuretics were 2.64 (95% CI 2.47-2.83), 1.70 (95% CI 1.62-1.79), 2.30 (95% CI 1.95-2.70), and 1.06 (95% CI 0.91-1.23), respectively. Combined use of loop diuretics and thiazide diuretics was associated with the highest relative risk estimates of gout (adjusted OR 4.65 [95% CI 3.51-6.16]). Current use of calcium channel blockers or losartan slightly attenuated the risk of gout in patients who took diuretics. CONCLUSION Use of loop diuretics, thiazide diuretics, and thiazide-like diuretics was associated with an increased risk of incident gout, although use of potassium-sparing agents was not.

Measuring the mechanical properties of plant cells by combining micro-indentation with osmotic treatments

Growth in plants results from the interaction between genetic and signalling networks and the mechanical properties of cells and tissues. There has been a recent resurgence in research directed at understanding the mechanical aspects of growth, and their feedback on genetic regulation. This has been driven in part by the development of new micro-indentation techniques to measure the mechanical properties of plant cells in vivo. However, the interpretation of indentation experiments remains a challenge, since the force measures results from a combination of turgor pressure, cell wall stiffness, and cell and indenter geometry. In order to interpret the measurements, an accurate mechanical model of the experiment is required. Here, we used a plant cell system with a simple geometry, Nicotiana tabacum Bright Yellow-2 (BY-2) cells, to examine the sensitivity of micro-indentation to a variety of mechanical and experimental parameters. Using a finite-element mechanical model, we found that, for indentations of a few microns on turgid cells, the measurements were mostly sensitive to turgor pressure and the radius of the cell, and not to the exact indenter shape or elastic properties of the cell wall. By complementing indentation experiments with osmotic experiments to measure the elastic strain in turgid cells, we could fit the model to both turgor pressure and cell wall elasticity. This allowed us to interpret apparent stiffness values in terms of meaningful physical parameters that are relevant for morphogenesis.

Efficacy and safety of calcium channel blocker/diuretics combination therapy in hypertensive patients: a meta-analysis.

Although recent guidelines recommend the combination of calcium channel blockers (CCBs) and thiazide (-like) diuretics, this combination is not widely used in clinical practice. The aim of this meta-analysis was to assess the efficacy and safety of this combination regarding the following endpoints: all-cause and cardiovascular mortality, myocardial infarction, and stroke. Four studies with a total of 30,791 of patients met the inclusion criteria. The combination CCB/thiazide (-like) diuretic was associated with a significant risk reduction for myocardial infarction (risk ratio [RR], 0.83; 95% confidence interval [CI], 0.73-0.95) and stroke (RR, 0.77; CI, 0.64-0.92) compared with other combinations, whereas it was similarly effective compared with other combinations in reducing the risk of all-cause (RR, 0.89; CI, 0.75-1.06) and cardiovascular (RR, 0.89; CI 0.71-1.10) mortality. Elderly patients with isolated systolic hypertension may particularly benefit from such a combination, since both drug classes have been shown to confer cerebrovascular protection.

Rapidly excised and cryofixed rat tissue

All preparation efforts of biological samples in electron microscopy are focused to preserve structures as close as possible to the native state. To achieve this goal with tissues, it is of advantage to have a very short time between excision and fixation. The most common approach is chemical fixation: cross-linking of the tissue samples with aldehydes followed by postfixation with osmium tetroxide. Here, the fastest approach for tissue samples is perfusion. However, the diffusion of the fixation solution from blood vessels into the depth of the tissue is still slow and does not allow an overall instant fixation of a single cell. As a result, osmotic effects become evident (swelling or shrinkage of cell organelles). Another possibility is to take a tissue sample from the experimental animal. Excision of tissue can last quite some time, which results in even more pronounced autolytic induced osmotic effects. Furthermore, the animal does not survive the procedure in most cases. Alternatively, microbiopsies are an elegant technique to rapidly excise small quantities of tissue. Some tissues, such as liver and muscle, may be obtained using a non-lethal approach. To avoid the artifacts introduced by chemical fixation, high-pressure freezing of microbiopsies (brain, liver, kidney, and muscle) is a powerful alternative to chemical fixation. Here, we describe the microbiopsy method, and high-pressure freezing/freeze-substitution (HPF/FS) as a follow-up procedure. Cryosectioning of high-pressure frozen samples is optimally preserving the ultrastructure; however, it is not considered to be a routine approach yet.

Nephrolithiasis-associated bone disease: pathogenesis and treatment options

Nephrolithiasis remains a formidable health problem in the United States and worldwide. A very important but underaddressed area in nephrolithiasis is the accompanying bone disease. Epidemiologic studies have shown that osteoporotic fractures occur more frequently in patients with nephrolithiasis than in the general population. Decreased bone mineral density and defects in bone remodeling are commonly encountered in patients with calcium nephrolithiasis. The pathophysiologic connection of bone defects to kidney stones is unknown. Hypercalciuria and hypocitraturia are two important risk factors for stone disease, and treatments with thiazide diuretics and alkali, respectively, have been shown to be useful in preventing stone recurrence in small prospective trials. However, no studies have examined the efficacy of these agents or other therapies in preventing continued bone loss in calcium stone formers. This manuscript reviews the epidemiology, pathophysiology, and potential treatments of bone disease in patients with nephrolithiasis.

Impact of diuretic therapy-associated electrolyte disorders present on admission to the emergency department: a cross-sectional analysis

Diuretics are among the most commonly prescribed medications and, due to their mechanisms of action, electrolyte disorders are common side effects of their use. In the present work we investigated the associations between diuretics being taken and the prevalence of electrolyte disorders on admission as well as the impact of electrolyte disorders on patient outcome.

Pitfalls when examining gap junction hemichannels: interference from volume-regulated anion channels

Human HeLa cells transfected with mouse connexin45 were used to explore the experimental conditions suitable to measure currents carried by gap junction hemichannels. Experiments were performed with a voltage-clamp technique and whole-cell recording. Lowering [Ca(2+)](o) from 2 mM to 20 nM evoked an extra current, I (m), putatively carried by Cx45 hemichannels. However, the variability of I (m) (size, voltage sensitivity, kinetics) suggested the involvement of other channels. The finding that growth medium in the incubator increased the osmolarity with time implied that volume-regulated anion channels (VRAC) may participate. This assumption was reinforced by the following observations. On the one hand, keeping [Ca(2+)](o) normal while the osmolarity of the extracellular solution was reduced from 310 to 290 mOsm yielded a current characteristic of VRAC; I (VRAC) activated/deactivated at negative/positive voltage, giving rise to the conductance functions g (VRAC,inst)=f(V (m)) (inst: instantaneous; V (m): membrane potential) and g (VRAC,ss)=f(V (m)) (ss: steady state). Moreover, it was reversibly inhibited by mibefradil, a Cl(-)channel blocker (binding constant K (d)=38 microM, Hill coefficient n=12), but not by the gap junction channel blocker 18alpha-glycyrrhetinic acid. On the other hand, minimizing the osmotic imbalance while [Ca(2+)](o) was reduced led to a current typical for Cx45 hemichannels; I (hc) activated/deactivated at positive/negative voltage. Furthermore, it was reversibly inhibited by 18alpha-glycyrrhetinic acid or palmitoleic acid, but not by mibefradil. Computations based on g (VRAC,ss)=f(V (m)) and g (hc,ss)=f(V (m)) indicated that the concomitant operation of both currents results in a bell-shaped conductance-voltage relationship. The functional implications of the data presented are discussed. Conceivably, VRAC and hemichannels are involved in a common signaling pathway.

Influence of diurnal hyperosmotic loading on the metabolism and matrix gene expression of a whole-organ intervertebral disc model

It is generally agreed that the mechanical environment of intervertebral disc cells plays an important role in maintaining a balanced matrix metabolism. The precise mechanism by which the signals are transduced into the cells is poorly understood. Osmotic changes in the extracellular matrix (ECM) are thought to be involved. Current in-vitro studies on this topic are mostly short-term and show conflicting data on the reaction of disc cells subjected to osmotic changes which is partially due to the heterogenous and often substantially-reduced culture systems. The aim of the study was therefore to investigate the effects of cyclic osmotic loading for 4 weeks on metabolism and matrix gene expression in a full-organ intervertebral disc culture system. Intervertebral disc/endplate units were isolated from New Zealand White Rabbits and cultured either in iso-osmotic media (335 mosmol/kg) or were diurnally exposed for 8 hours to hyper-osmotic conditions (485 mosmol/kg). Cell viability, metabolic activity, matrix composition and matrix gene expression profile (collagen types I/II and aggrecan) were monitored using Live/Dead cell viability assay, tetrazolium reduction test (WST 8), proteoglycan and DNA quantification assays and quantitative PCR. The results show that diurnal osmotic stimulation did not have significant effects on proteoglycan content, cellularity and disc cell viability after 28 days in culture. However, hyperosmolarity caused increased cell death in the early culture phase and counteracted up-regulation of type I collagen gene expression in nucleus and annulus cells. Moreover, the initially decreased cellular dehydrogenase activity recovered with osmotic stimulation after 4 weeks and aggrecan gene down-regulation was delayed, although the latter was not significant according to our statistical criteria. In contrast, collagen type II did not respond to the osmotic changes and was down-regulated in both groups. In conclusion, diurnal hyper-osmotic stimulation of a whole-organ disc/endplate culture partially inhibits a matrix gene expression profile as encountered in degenerative disc disease and counteracts cellular metabolic hypo-activity.