Normal Hydration Research Articles

Hydration status and cardiovascular function: effects of hydration enhancement on cardiovascular function at rest and during psychological stress

This study examined the effects of a 3-day enhanced hydration regimen on resting cardiac function and reactivity to acute stress. Healthy volunteers (14 male, 14 female) were assigned to one of two groups: Enhanced Hydration and Normal Hydration Group. Participants in the Enhanced Group were given six 1-l bottles of water and instructed to drink two bottles a day in addition to normal fluid intake for 3 days preceding their laboratory session; no extra water was given to the Normal Group. Heart rate (HR), systolic blood pressure (SBP), diastolic blood pressure (DBP), cardiac output (CO), stroke volume (SV), and total peripheral resistance (TPR) were recorded during a 10-min baseline, 6-min Paced Auditory Serial Addition Test (PASAT), 5-min recovery, 5-min intermediate baseline, and 3-min Cold Pressor Test. Repeated-measures ANOVA revealed a significant Hydration Group×Task interaction for DBP during the cold pressor ( p<0.01) with the Enhanced Group exhibiting greater DBP reactivity to cold stress relative to the Normal Group. Analysis revealed significant Hydration Group×Gender interactions for SV and TPR ( p<0.05) at rest and during both the PASAT and Cold Pressor Test. Females in the Enhanced Group displayed higher SV and lower TPR relative to Enhanced Group males, whereas females in the Normal Group displayed lower SV and greater TPR relative to Normal Group males. These results suggest that 3-day hydration enhancement influences blood pressure reactivity in both men and women, and that long-term hydration enhancement is related to resting gender differences in cardiac function.

Thoracic Impedance Measurements During Orthostatic Change Test and During Hemodialysis in Hemodialyzed Patients

Measurements were performed before and after hemodialysis (HD) in the supine and upright positions (orthostatic change test) and during HD session every 30 minutes in recumbent position on 11 HD patients. Two hydration states were compared: hyperhydration and normal hydration. Each patient served as his own control. Blood pressure and total body bioimpedance were obtained simultaneously. Thoracic impedance values (Zo) obtained during HD were significantly greater in the normal hydration state. There was strong correlation between Zo gain and total ultrafiltration; however, Zo gain divided through total ultrafiltration (calculated for every 100 ml) was also higher in this state. The ratio Zo/R (where R is resistance of total body bioimpedance) was stable during HD but was significantly higher in the normal hydration state. Zo gain during the orthostatic change test was significantly higher after HD than before HD in both hydration states. The anticipated difference in Zo gains between both hydration states was not significant. After echocardiographic analysis of patients, we determined that cardiac dysfunction or valvular defects in four patients were likely responsible for opposite reaction on orthostatic change test. During our measurements, we observed the influence of Zo changes on episodes such as intradialytic hypotension or acute atrial fibrillation. Thoracic impedance is an intriguing method for controlling pathophysiology of fluid distribution, but it requires the accurate definition of a patient's hemodynamics and strong conditions during measurement. During our measurements, we observed the influence of such episodes as intradialytic hypotension or acute atrial fibrillation on Zo changes.

Solubility-based gas separation with oligomer-modified inorganic membranes: Part III. Effects of synthesis conditions

As in previous papers in this series, we created membranes for solubility-based gas separations by reacting the surfaces of microporous alumina substrates with alkylchlorosilanes. In this paper, we explored our ability to rationally modify the permselectivity properties of these membranes through the control of several synthesis variables. In particular, we studied three different hydration states of the alumina surface (dehydrated, normal, and superhydrated), two different degrees of chlorosilane functionality (mono and tri), and two different sizes of alkyl group (methyl and octadecyl). We measured the permeability of the hybrid membranes to propane and nitrogen gases to characterize their separation properties; we also carried out X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) experiments to characterize the amount and nature of organic surface coverage. Our results showed significant correlations of permeation properties with all of the synthesis variables. Dehydration of the alumina surface before trichlorosilane treatment resulted in a lower organic surface coverage and a lower propane/nitrogen selectivity; superhydration resulted in the formation of a dense organic surface layer with a large number of macroscopic defects that virtually eliminated selectivity. Under normal hydration conditions, the octadecyltrichlorosilane yielded a far more selective membrane than the methyltrichlorosilane. Finally, the monochlorosilane reagents produced no significant organic surface coverage, based on both XPS and gas permeation analyses. We discuss our results in the context of previous work on (1) self-assembled monolayers on nonporous substrates and (2) the design of solubility-selective membranes.

Combined experimental and computer simulation study of the kinetics of solute release from a relaxing swellable polymer matrix. II. Release of an osmotically active solute

AbstractThe performance of a model monolithic controlled release device, consisting of a swellable polymeric matrix subject to structural relaxation (cellulose acetate), loaded with a simple osmotically active solute (NaCl) and activated by the ingress of solvent (water), was studied experimentally and by computer simulation. The former study involved detailed monitoring of the kinetics of both solute release and solvent absorption (followed in due course by desorption of osmotically imbibed excess solvent). The computer simulation study was based on extensive previous modeling work. Values of the relevant input model parameters were derived from independent experimental measurements of the sorption and diffusion properties of solvent (cf. Part I) and solute (reported in the present article). The resulting simulation was highly successful, considering that it proved possible to simulate closely and consistently the kinetics of both solute release (over practically the whole experimental range) and concurrent solvent absorption (including correct prediction of the magnitude of the osmotically induced excess swelling of the polymeric matrix). Simulation of the final desorption of osmotically imbibed water was facilitated by the realization that this process actually reflects the kinetics of a long‐term deswelling relaxation of the polymer structure back to the state of normal hydration, the rate of which could be measured to a good approximation on the pure deswelling polymer. The results presented here are of obvious practical significance in relation to progress toward computer‐assisted design of monolithic controlled release devices exhibiting relatively complex kinetic behavior. They should also prove useful by calling attention to an important caveat when desorption into water is used as a method for the straightforward determination of solute diffusivity in hydrated polymers, in cases of osmotically active solutes diffusing in nonhydrophilic polymers. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 2468–2479, 2004

Preparation and hydration control of corneal tissue strips for experimental use.

The purpose of this study was to develop an experimental protocol to maintain corneal tissue strips at normal hydration and avoid swelling or dehydration during experimental studies on corneal biomechanics and thermal stability. The corneal thickness of 9 whole Eye-Bank eyes was brought back to normal values by immersion in a 25% dextran solution for 24 hours. Corneal buttons were then removed and cut into 2 x 6 mm strips. The 9 strips were immersed successively in Dextran solutions at 25%, 22.5%, and 20% concentration at 35 degrees C. The thickness of the immersed strip in solution was measured every 5 minutes for 1 hour using a modified optical comparator. The mean final thickness for the nine corneal strips after one hour in 25%, 22.5%, and 20% dextran solution was 508 +/- 38, 563 +/- 56, and 592 +/- 33 microm, respectively. Average swelling in 25%, 22.5%, and 20% dextran solutions was 1.06 +/- 0.03, 1.20 +/- 0.07, and 1.24 +/- 0.07 times the initial thickness, respectively. The hydration of corneal tissue strips is maintained at normal values when the strips are immersed in 25% Dextran solution. Corneal strips swell to thicknesses above normal values in solutions with lower molecular weights.

Hydration status of community-dwelling seniors.

Dehydration is the most common fluid or electrolyte disorder among older persons. This study was designed to examine the hydration status of community-dwelling seniors. Blood and urine samples were collected from 67 independently living volunteers (65-93 yrs) who had functional limitations but no condition that contraindicated 10 min of moderate exercise. Forty-six subjects who were not diabetic, had fasted for 12 hours, and had blood glucose levels < or = 115 mg/dL were thus included. Urine and serum samples were analyzed for osmolality (mosm/kg), Na+ (mmol/L) and K+ (mmol/L). Whole blood was analyzed for hemoglobin (Hb, g/dL) and hematocrit (Hct, %) and urine for specific gravity (USG). Means and standard deviations for the current data were compared with normal values. All values were within normal ranges except urine osmolality. While changes associated with aging may predispose an individual to dehydration, functionally limited, independently living older individuals demonstrate normal hydration status following a 12-hr fast. This suggests that dehydration is not solely a function of the aging process, but may be more related to concomitant medical conditions or dependent living.

Glycerol Regulates Stratum Corneum Hydration in Sebaceous Gland Deficient (Asebia) Mice

The only known function of human sebaceous glands is the provocation of acne. We assessed here whether sebum influences stratum corneum hydration or permeability barrier function in asebia J1 and 2 J mice, with profound sebaceous gland hypoplasia. Asebia J1 mice showed normal permeability barrier homeostasis and extracellular lamellar membrane structures, but they displayed epidermal hyperplasia, inflammation, and decreased (>50%) stratum corneum hydration, associated with a reduction in sebaceous gland lipids (wax diesters/monoesters, sterol esters). The triglyceride content of both asebia and control stratum corneum was low, consistent with high rates of triglyceride hydrolysis within the normal pilosebaceous apparatus, despite high rates of triglyceride synthesis. Although a mixture of synthetic, sebum-like lipids (sterol/wax esters, triglycerides) did not restore normal stratum corneum hydration to asebia skin, topical glycerol, the putative product of triglyceride hydrolysis in sebaceous glands, normalized stratum corneum hydration, and the glycerol content of asebia stratum corneum was 85% lower than in normal stratum corneum. In contrast, another potent endogenous humectant (urea) did not correct the abnormality. The importance of glycerol generation from triglyceride in sebaceous glands for stratum corneum hydration was demonstrated further by (i) the absence of sebaceous-gland-associated lipase activity in asebia mice, whereas abundant enzyme activity was present in the glands of control mice; and (ii) the inability of high concentrations of topical triglyceride to correct the hydration abnormality, despite the presence of abundant lipase activity in asebia stratum corneum. These results show that sebaceous-gland-derived glycerol is a major contributor to stratum corneum hydration.

Impedance vector distribution by body mass index and conventional bioelectrical impedance analysis in obese women

Background and Aim: To compare the body fluid status assessments provided by conventional bioelectrical impedance analysis (BIA) and vector BIA in moderate and severe obesity. Methods and Results: We studied 516 normotensive Caucasian women (mean age: 48±9.2 years), who were agematched and divided into four groups on the basis of their body mass index (BMI): 99 normal weight women with a BMI of 19–25 Kg/m 2; 228 preboese overweight women with a BMI of 25–30 Kg/m 2; 132 women with class I–II obesity (BMI: 30–35 Kg/m 2), and 57 women with class III obesity (BMI: 40–64 Kg/m 2). Single-frequency (50 kHz) tetrapolar (hand-foot) bioelectrical impedance measurements were made, and total body water (TBW) and extracellular water (ECW) were estimated using conventional BIA regression equations. The RXc graph method was used for vector BIA, with the set of 327 women with a BMI of 19–30 Kg/m 2 being adopted as the reference population. Mean vector displacement followed a definite pattern, with progressive vector shortening as the BMI increased, and along a fixed phase angle. This pattern indicates more TBW due to a greater soft tissue mass with average normal hydration. Short and downsloping vectors indicating fluid overload were more frequent in the group with class III obesity than in the group with class I obesity (19 vs 5%). The absolute values of TBW and ECW were significantly higher in the obese and overweight subjects than in those with normal weight subjects. TBW as a percentage of body weight was significantly lower in the obese subjects. Conclusions: BMI influenced the impedance vector distribution pattern, which proved to be consistent up to a BMI of 64 Kg/m 2. Obese women with an altered body composition can be identified and monitored using vector BIA.

Bayesian Modeling of Markers of Day-Specific Fertility

Cervical mucus hydration increases during the fertile interval before ovulation. Because sperm can only penetrate mucus having a high water content, cervical secretions provide a reliable marker of the fertile days of the menstrual cycle. This article develops a Bayesian approach for modeling of daily observations of cervical mucus and applies the approach to assess heterogeneity among women and cycles from a given woman with respect to the increase in mucus hydration during the fertile interval. The proposed model relates the mucus observations to an underlying normal mucus hydration score, which varies relative to a peak hydration day. Uncertainty in the timing of the peak is accounted for, and a novel weighted mixture model is used to characterize heterogeneity in distinct features of the underlying mean function. Prior information on the mucus hydration trajectory is incorporated, and a Markov chain Monte Carlo approach is developed. Based on data from a study of daily fecundability, there appears to be substantial heterogeneity among women in detected preovulatory increases in mucus hydration, but only minimal differences among cycles from a given woman.

A randomized, controlled trial of the effectiveness of nebulized therapy with epinephrine compared with albuterol and saline in infants hospitalized for acute viral bronchiolitis

Objective: In previously well infants hospitalized with acute viral bronchiolitis, the effectiveness of repeated nebulized therapy with epinephrine (EPI) was compared with treatment with albuterol (ALB) or saline placebo (PLAC). Study design: In this randomized, double-blind, parallel-group, controlled trial, infants received study nebulizations every 1 to 6 hours and were assessed twice daily by the research team. The primary outcome was length of hospital stay (LOS). Secondary outcomes included the time from admission until the infant had normal hydration, oxygenation, and minimal respiratory distress. Results: A total of 149 infants were randomized; 50 were allocated to receive racemic EPI, 51 were given ALB, and 48 received PLAC. Baseline characteristics and pre-enrollment symptoms, signs, and therapy were similar between groups. There were no group differences in the primary outcome measure, mean LOS (hours)(± SD): EPI = 59.8 (62), ALB = 61.4 (54), and PLAC = 63.3 (47); P =.95 by intent-to-treat analysis. Group differences were not statistically significant in any of the secondary outcomes. Conclusions: There were no group differences in the effectiveness of therapy for infants hospitalized with bronchiolitis. Based on these results, we do not recommend routine use of either nebulized EPI or ALB in this patient group. (J Pediatr 2002;141:818-24)

Choosing fluids in traumatic hypovolemic shock: the role of crystalloids, colloids, and hypertonic saline.

Choosing fluids in traumatic hypovolemic shock: the role of crystalloids, colloids, and hypertonic saline.

Hydration of high-calcium quicklime with methanol–water mixtures

In this study, hydration of quicklime was accomplished with different methanol–water mixtures. The greater the percentage of methanol, the more intense was the suppression of the hydration conditions. The reactivity was not greatly affected by the presence of methanol up to 20%, while for hydration mixtures with 30 to 60% methanol a great reduction of reactivity was observed. In all cases of hydration the complete conversion of CaO into Ca(OH) 2 was established by the XRD method. From the SEM study it was ascertained that in a percentage of up to 20% methanol, a normal hydration was observed, expressed by aggregates of hydrated lime grains, whereas the hydration in mixtures of 30–60% methanol, progressively leads to the formation of tabular crystals, the size of which increases with the methanol percentage. What is more important is that the maximum hydration temperature decreases up to 12.5 °C for hydration mixtures up to 20% methanol without the quality of the produced hydrated lime being affected.

Acute hypermagnesemia: a rare complication of antacid administration after bone marrow transplantation

Introduction: We reported a case of hypermagnesemia in whom hypotension, hypothermia, and coma developed after repetitive doses of a seemingly harmless antacid for epigastric pain following bone marrow transplantation. Methods: For this case, serial electrolytes, blood urea nitrogen, creatinine, calcium, and magnesium were obtained. Issues addressed were the restoration of normal hydration by normal saline, together with forced diuresis to hasten the renal excretion of magnesium, and eventual changes in its levels. Results: The highest measured magnesium concentration was 5.9 mmol/l. She recovered without dialysis. The patient's condition improved with intravenous doses of calcium gluconate, saline solution infusion, and cardiovascular support. Conclusion: Hypermagnesemia is rare in allogeneic stem cell recipients receiving cyclosporine therapy for prevention of acute graft-vs.-host disease (GVHD). A posttransplant status with possible GVHD, poor nutritional intake, impaired intestinal absorption, dehydration, and the use of aluminum magnesia oral suspension may have resulted in magnesium imbalance. This case report highlights several associated nonrenal risk factors for hypermagnesemia, which include gastrointestinal tract disease, dehydration, and concomitant medications, particularly, the antacids that contain magnesium.

Solubility behavior of Ca-, S-, Al-, and Si-bearing solid phases in Portland cement pore solutions as a function of hydration time

The concentrations of Ca, S, Al, Si, Na, and K in the pore solutions of ordinary Portland cement (OPC) and white Portland cement (WPC) pastes were measured during the first 28 days of hydration at room temperature. Saturation indices (SI) with respect to various solid phases known to occur in cement pastes were calculated from a thermodynamic analysis of the elemental concentrations, resulting in good agreement between the two pastes. In agreement with other published work, gypsum was saturated during the first several hours of hydration and then undersaturated thereafter, while portlandite was modestly supersaturated after the first few hours. High levels of supersaturation with respect to ettringite and calcium monosulfoaluminate were calculated, particularly prior to the consumption of gypsum at around 10 h. Results are consistent with published thermodynamic studies that show calcium monosulfoaluminate is metastable with respect to ettringite under normal hydration conditions. Three different ion activity product (IAP) equations for C-S-H were applied to the data. From 10 h onward, each of the IAP values declined gradually over time and the values for the OPC and WPC pastes were in close agreement. The same IAP equations were applied to experimental data from the pure CaO–SiO 2–H 2O system, resulting in good agreement between the cement paste pore solutions and the equilibrium between portlandite and the upper, or metastable, C-S-H solubility curve.

HYDRATION STATUS OF COMMUNITY DWELLING SENIORS

Dehydration is the most common fluid or electrolyte disorder among older persons. However, it is primarily an acute condition diagnosed in hospitalized or institutionalized individuals. Age related attenuations of thirst and kidney function do occur, but it is unclear if these changes predispose community dwelling individuals to dehydration. Some have suggested that older individuals are in a state of ‘chronic dehydration' PURPOSE: To examine the hydration status of independent, community dwelling seniors. METHODS: Sixty-seven independently living volunteers (65–93 yr.) were participants in a larger study. They were functionally limited (≥ 12 sec to ascend 21 stairs and ≤ 24 on the MOS SF-36), but did not have any conditions that contraindicated 10 min of moderate exercise. Of these subjects, 46 were not diabetic, had fasted for the requisite 12 hours, and had blood glucose levels ≤ 115 mg/dl, thus were included in this study. Blood and urine samples were collected from each subject. Urine and blood (serum) samples were analyzed for osmolality (mosm/L), Na+ (meq/L) and K+ (meq/L). Whole blood was analyzed for hemoglobin (Hb, g/dl) and hematocrit (Hct, %) and urine for specific gravity (USG) when enough volume was available. Means and standard deviations were calculated for all variables. The current data was then compared to normal values from the literature. RESULTS: Except for urine osmolality, all of the values measured fall within a normal range. Higher urine osmolality is expected as the urine becomes more concentrated following a fast. CONCLUSION: While changes associated with aging may predispose an individual to dehydration, functionally limited, independently living older individuals demonstrate normal hydration status following a 12 hr fast. Supported by NIH NR 04929-01A1Table: No Caption Avilable

DETERMINATION OF DRY WEIGHT IN HEMODIALYSIS PATIENTS BY MONITORING CHANGES IN THE SLOPE OF EXTRACELLULAR VOLUME (ECV) DURING DIALYSIS

Correct estimation of dry weight in hemodialysis (HD) patients is imprecise. Since leg is more hydrated than other body segments, monitoring ECV changes in leg could determine if patients achieve dry weight. We hypothesize that if change in the slope of ΔECV (ΔECV = ECV/ECV0) approach zero at the end of HD, patients have achieved dry weight. Measurement of electrical resistivity ρ = R.A/L [ohm cm) in leg provides a quantitative measure for comparison to normal hydration in controls. Ten HD patients (3f/7m, age 56±8 years), were studied twice at different post dialysis body weight in one week. Relative change in ECV in leg was continuously measured during HD by Xitron 40006. The % change in ΔECV (ΔECV20) during the last 20 min of HD was used to indicate fluid status of legs. Resistivity was measured at the beginning and end of HD sessions. * P < 0.05 vs Dry Weight. Resistivity was significantly greater and mean arterial blood pressure (MAP) was significantly less before HD when dry weight was attained in these patients, with a decrease of about 1.8 kg body weight. In the period when dry weight was not achieved, resistivity was significantly less than controls (591±89) (P < 0.05). The slope of ΔECV20 during last 20 min. was significantly less when dry weight was achieved. Monitoring changes in slope and resistivity could become a reliable and accurate method to establish dry weight during HD.Table

Effect of Concentration and Hydration on Restriction of Albumin by Lung Interstitium

In previous studies, the flow of albumin solution through hydrated lung interstitial segments was higher than a prior flow of Ringer solution (A. Tajaddinni et al., 1994, J. Appl. Physiol. 76, 578–583). We wondered whether this effect was caused by an increased pore size. We measured the flow of albumin solutions through interstitial segments subjected to a driving pressure of 5 cm H2O and various mean interstitial pressures (Pif). The ratio of albumin concentration (Calb) of the output solution to that of the input solution (Cout/Cin, sieving ratio) was measured using tracer 125I-albumin. At normal hydration (0 cm H2O Pif), Cout/Cin was minimal (0.6) with the flow of Ringer solution, increased to 0.8 with the flow of 5 g/dl albumin solution, and increased to 1 with increased hydration at 15 cm H2O Pif. We modeled the interstitium as a membrane subjected to flows of high Peclet numbers. Accordingly, the albumin reflection coefficient [ς = 1 − (Cout/Cin)] at 0 cm H2O Pif was 0.4 with the flow of Ringer solution and decreased to 0 at 5 g/dl Calb and 15 cm H2O Pif. This behavior suggests that the flow of albumin occurred through interstitial pores that increased in size as either Calb or hydration increased. We conceive of an interstitium that consists of pores with permeable moveable walls across which osmotic interaction occurs between the pore liquid and the surrounding tissue.

Effect of temperature, pH and ageing time on hydration of rho alumina by studying phase composition and surface properties of transition alumina obtained after thermal dehydration

Crystallization of alumina hydrates from rho alumina at different hydration conditions has been studied by using combined loss on ignition (LOI) and XRD technique. Extreme pH conditions during hydration of rho alumina favoured gibbsite growth while higher temperature favoured crystallization rate. Alumina hydrates obtained at different pH and temperature conditions were calcined at 450°C and evaluated for surface properties for comparison with those of pure transition alumina phases. Hydrated product obtained under normal hydration conditions exhibited closely spaced bimodal pore size distribution. The distribution resolved further with increase in temperature whereas pore widening was observed with increase in pH. The results of this study will help to manipulate the required surface properties and phase mixture of transition alumina by exercising control during hydration of rho alumina.

RENAL BLOOD FLOW INCREASE DURING VOLUME EXPANSION IN HYDRONEPHROTIC RATS

We assessed the renal blood flow pattern in experimental hydronephrosis during normal hydration and extracellular volume expansion. Partial obstruction of the left ureter was created in 3-week-old Sprague-Dawley rats by embedding the ureter in a psoas muscle groove. Moderate hydronephrosis without kidney weight reduction developed in all cases. The effects on renal hemodynamics were studied with real-time ultrasound flowmetry 3 weeks later during normal hydration and then during volume expansion. The degree of hydronephrosis was classified as mild, moderate or severe. Under baseline conditions renal blood flow was normal in mild and moderate hydronephrosis but low in severe hydronephrosis. During volume expansion renal blood flow increased significantly in all experimental animals (mean 14%) compared to that in controls, which remained unaffected or decreased (mean -3%). The flow increase was related to the degree of dilatation, which was 2% in mild, 13% in moderate and 44% in severe hydronephrosis when the groups were considered separately. A significant increase in renal blood flow proportional to the degree of hydronephrosis occurred as a result of volume expansion. This finding may be explained by a state of vasodilatation combined with a reduction in the filtration coefficient.

Gene expression of the taurine transporter and taurine biosynthetic enzymes in rat kidney after antidiuresis and salt loading.

Taurine is thought to be an osmolyte in the kidney medulla. We have investigated the gene expression of the taurine transporter (TauT) and the enzymes of taurine biosynthesis, cysteine dioxygenase (CDO) and cysteine sulfinate decarboxylase (CSD). We achieved this by measuring their mRNA levels using reverse transcriptase polymerase chain reaction (RT-PCR) in five kidney regions of rats in various hydration states; namely, normal hydration, after 2 days of antidiuresis following chronic diuresis and finally after acute salt loading. The mRNA levels of the well-established tonicity-sensitive genes coding for the aldose reductase (AR), the sodium myo-inositol transporter (SMIT) and the betaine transporter (BGT1) were also determined for the sake of comparison. In normally hydrated rats, TauT-, CDO-, and CSD-mRNA were enriched in the outer stripe of the outer medulla (OS). Following antidiuresis, the mRNA levels of TauT, CDO, CSD, SMIT, BGT1 and AR were all similarly increased in the papilla when compared with levels in rats submitted to a chronic diuresis. After acute salt loading, the mRNA level of TauT, like that of SMIT and BGT1, was overexpressed in OS whereas the mRNA levels of CDO and CSD remained unchanged. Like SMIT, BGT1 and AR genes, TauT, CDO and CSD genes appear to be tonicity-sensitive genes which can be activated in vivo by hypertonicity in the rat kidney. However, tonicity-induced activation of the TauT gene is more sensitive than that of CDO and CSD genes.