Chloride, bromide, sodium, and sucrose spaces in man

Volume Assessment in Patients Undergoing Long-Term Dialysis

Accurate assessment of fluid status is a priority for patients with kidney failure undergoing long-term dialysis. There is wide variation in current volume-related practices between dialysis units and an urgent need to develop better evidence to guide practice. Clinical decisions relating to volume management are implicitly based on assessment of volume status, and there are numerous different but imperfect methods of assessment. Isotope-based dilutions are impractical for clinical use and may not be a gold standard for patients with kidney failure. Individual trends in body weight and BP have been used as a pragmatic surrogate marker for volume status. Probing the target weight based on BP is still widely practiced but may pose risks related to volume depletion and accelerated loss of residual kidney function. Clinical signs, such as elevated jugular venous pressure and leg edema, are readily accessible but have poor diagnostic accuracy and wide interobserver variability that limit their reproducibility for volume assessment in clinical trials. Lung ultrasound and bioelectrical impedance analysis have a sound scientific rationale for the assessment of extracellular volume and are appropriately associated with clinical outcomes, but neither approach has demonstrated convincingly favorable clinical outcomes in clinical trials. Other technologies for volume assessment exist but require further assessment in clinical trials. Advancements in clinical care can be made with existing technologies through comparative effectiveness trials of different fluid management strategies, routine and standardized measurement of volumetric parameters and individual patient preferences, and innovative integration of existing volume assessment methods. A systematic and globally coordinated approach to improving volume assessment and management is required to improve outcomes in patients receiving long-term dialysis.

Combined spectroscopic, biochemical and chemometric approach toward finding of biochemical markers of obesity

BACKGROUND

Early-stage detection of subclinical obesity-driven systemic changes is a challenging area of medical diagnostics, where the most popular existing measures - such as body mass index - BMI - often fall short of providing a realistic estimate of adiposity and, therefore, of ongoing pathologies at the systemic, tissue and cellular level. In the quest for identifying new more robust diagnostic markers, whole-organ analysis of chemical elements is a promising approach for identifying candidate proxies of obesity status in the system.

METHODS

Total Reflection X-ray fluorescence (TXRF) coupled with biochemical assays, chemometrics and statistical validation was used as a new integrated pipeline for marker identification in external ear samples of obese animals. The specimens were taken from obese animals fed a high calorie diet as well as from lean intact animals fed a standard diet.

RESULTS

The most significant differences in the content of K, Fe, Br, and Rb between the studied groups of the animals were identified. However, with the methodology applied Rb was found the most robust biochemical discriminator of early-stage obesity effects, as validated by the logistic regression model. We observed no relationship between the levels of the elements consumed by the animals and their apparent content in the earlobe tissue samples.

CONCLUSIONS

Our preliminary study confirms that obesity alters tissue trace metal metabolism and shows the proposed new approach as an accurate and reliable methodology for detecting tissue elemental obesity-related alterations.

GENERAL SIGNIFICANCE

This result can be of practical significance for designing new point-of-care systems for obesity screening tests, taking advantage of direct/indirect Rb measurements.

Electrolyte-based calculation of fluid shifts after infusing 0.9% saline in severe hyperglycemia

Background

Early treatment of severe hyperglycemia involves large shifts of body fluids that entail a risk of hemodynamic instability. We studied the feasibility of applying a new electrolyte equation that estimates the degree of volume depletion and the distribution of infused 0.9% saline in this setting.

Methods

The new equation was applied to plasma and urinary concentrations of sodium and chloride measured before and 30 min after a 30-min infusion of 1 L of 0.9% saline on two consecutive days in 14 patients with severe hyperglycemia (mean age 50 years). The extracellular fluid (ECF) volume was also estimated based on the volume dilution kinetics of chloride.

Results

On day 1, the baseline ECF volume amounted to 11.5 L. The saline infusion expanded the ECF space by 160 mL and the intracellular fluid space by 375 mL. On day 2, the ECF volume was 15.5 L, and twice as much of the infused fluid remained in the ECF space. The chloride dilution kinetics yielded baseline ECF volumes of 11.6 and 15.2 L on day 1 and day 2, respectively. No net uptake of glucose to the cells occurred during the two 1-h measurement periods despite insulin administration in the intervening time period.

Conclusions

The electrolyte equation was feasible to apply in a group of hyperglycemic patients. The ECF space was 3 L smaller than expected on admission but normal on the second day. Almost half of the infused fluid was distributed intracellularly.

Fluid balance concepts in medicine: Principles and practice

The regulation of body fluid balance is a key concern in health and disease and comprises three concepts. The first concept pertains to the relationship between total body water (TBW) and total effective solute and is expressed in terms of the tonicity of the body fluids. Disturbances in tonicity are the main factor responsible for changes in cell volume, which can critically affect brain cell function and survival. Solutes distributed almost exclusively in the extracellular compartment (mainly sodium salts) and in the intracellular compartment (mainly potassium salts) contribute to tonicity, while solutes distributed in TBW have no effect on tonicity. The second body fluid balance concept relates to the regulation and measurement of abnormalities of sodium salt balance and extracellular volume. Estimation of extracellular volume is more complex and error prone than measurement of TBW. A key function of extracellular volume, which is defined as the effective arterial blood volume (EABV), is to ensure adequate perfusion of cells and organs. Other factors, including cardiac output, total and regional capacity of both arteries and veins, Starling forces in the capillaries, and gravity also affect the EABV. Collectively, these factors interact closely with extracellular volume and some of them undergo substantial changes in certain acute and chronic severe illnesses. Their changes result not only in extracellular volume expansion, but in the need for a larger extracellular volume compared with that of healthy individuals. Assessing extracellular volume in severe illness is challenging because the estimates of this volume by commonly used methods are prone to large errors in many illnesses. In addition, the optimal extracellular volume may vary from illness to illness, is only partially based on volume measurements by traditional methods, and has not been determined for each illness. Further research is needed to determine optimal extracellular volume levels in several illnesses. For these reasons, extracellular volume in severe illness merits a separate third concept of body fluid balance.

Diuretics and bioimpedance-measured fluid spaces in hypertensive patients

The authors examined the relationship between thiazide-type diuretics and fluid spaces in a cohort of hypertensive patients in a retrospective study of 60 stable hypertensive patients without renal abnormalities who underwent whole-body bioimpedance analysis. Overhydration was greater in the diuretic group, but only to a nonsignificant degree (5.9 vs. 2.9%; P=.21). The total body water did not differ in the two groups (41.8 L vs. 40.5 L; P=.64). Extracellular fluid volume (ECV) (19.7 L vs. 18.5 L; P=.35) and intracellular fluid volume (ICV) spaces (20.8 L vs. 21.3 L; P=.75) were also not significantly different in the two groups. The ratio of ICV:ECV, however, appeared different: 1.05 vs 1.15 (P=.017) and the effect was maintained in the linear regression-adjusted model (β coefficient: -0.143; P=.001). The diuretic-related distortion of ICV:ECV ratio indicates potential fluid redistribution in hypertensive patients, with ICV participating in the process.

Whole body acid-base and fluid-electrolyte balance: a mathematical model

A cellular compartment was added to our previous mathematical model of steady-state acid-base and fluid-electrolyte chemistry to gain further understanding and aid diagnosis of complex disorders involving cellular involvement in critically ill patients. An important hypothesis to be validated was that the thermodynamic, standard free-energy of cellular H(+) and Na(+) pumps remained constant under all conditions. In addition, a hydrostatic-osmotic pressure balance was assumed to describe fluid exchange between plasma and interstitial fluid, including incorporation of compliance curves of vascular and interstitial spaces. The description of the cellular compartment was validated by close comparison of measured and model-predicted cellular pH and electrolyte changes in vitro and in vivo. The new description of plasma-interstitial fluid exchange was validated using measured changes in fluid volumes after isoosmotic and hyperosmotic fluid infusions of NaCl and NaHCO3. The validated model was used to explain the role of cells in the mechanism of saline or dilutional acidosis and acid-base effects of acidic or basic fluid infusions and the acid-base disorder due to potassium depletion. A module was created that would allow users, who do not possess the software, to determine, for free, the results of fluid infusions and urinary losses of water and solutes to the whole body.

Validity of extracellular water assessment with saliva samples using plasma as the reference biological fluid

Extracellular water (ECW) assessment is based on dilution techniques, commonly using blood sampling. However, plasma collection is an invasive procedure. We aimed to validate the use of saliva for ECW estimation by the bromide dilution technique using plasma as the reference method, in a sample of elite athletes. A total of 89 elite athletes with a mean age of 20.4 ± 4.4 years were evaluated. Baseline samples were collected before sodium bromide oral dose administration, and enriched samples were collected 3 h post-dose administration. The bromide concentration was assessed by high-performance liquid chromatography. Comparison of means, concordance coefficient correlation (CCC), multiple regression and Bland-Altman analysis were performed. The ECW from saliva explained 91% of the variance in ECW by plasma with a standard error of estimation of 0.91 kg. The CCC between alternative and reference methods was 0.952. No significant trend was observed between the mean and difference of the methods, with limits of agreement ranging between -1.5 and 2.1 kg. These findings reveal that bromide dilution volume calculated from saliva samples is a valid noninvasive method for ECW assessment in elite athletes.

Body fluid dynamics: back to the future

Pioneering investigations conducted over a half century ago on tonicity, transcapillary fluid exchange, and the distribution of water and solute serve as a foundation for understanding the physiology of body fluid spaces. With passage of time, however, some of these concepts have lost their connectivity to more contemporary information. Here we examine the physical forces determining the compartmentalization of body fluid and its movement across capillary and cell membrane barriers, drawing particular attention to the interstitium operating as a dynamic interface for water and solute distribution rather than as a static reservoir. Newer work now supports an evolving model of body fluid dynamics that integrates exchangeable Na(+) stores and transcapillary dynamics with advances in interstitial matrix biology.

Hemorrhage and operation cause a contraction of the extracellular space needing replacement—evidence and implications? A systematic review

BACKGROUND

Hemorrhagic hypotension or operative trauma is believed to cause a contraction of the extracellular fluid volume (ECV) beyond the measured fluid losses. The aim of this review was to explore the evidence and implications of ECV loss.

METHODS

We performed a systematic review of original trials measuring ECV changes during hemorrhage or operation. PubMed, relevant periodicals, and reference lists were searched until no further original articles appeared. The quality of both the scientific and the technical methods of the trials were evaluated.

RESULTS

A total of 61 original articles were found. The pattern appeared that all investigators reporting shock or operation to cause a disparate reduction of the ECV had measured the ECV with the same method. The ECV was calculated from very few blood samples that were withdrawn after 20 to 30 minutes of equilibration of a tracer (the (35)SO(4)-tracer). Trials calculating ECV from multiple blood samples, after longer equilibration times, or using other tracers did not find a contraction of the ECV. On the contrary, trials using a bromide tracer found the ECV to be expanded after operation.

CONCLUSIONS

The evidence supporting the idea that hemorrhage or operation cause a contraction of the ECV is weak, and probably a result of flawed methodology.

Sodium bromide by instrumental neutron activation analysis quantifies change in extracellular water space with wound closure in severely burned children

BACKGROUND

The ability to measure extracellular water (ECW) in critically ill patients can significantly enhance current methods of assessing fluid homeostasis, body composition, and response to nutritional therapy. We measured corrected bromide space to determine change in ECW with wound closure among acutely burned children.

METHODS

Fifteen children with burns over 30% of their total body surface area had their ECW determined following hemodynamic stabilization and when wound closure was complete. Plasma samples were obtained at baseline and 4 hours after receiving 25 mg/kg of sodium bromide. Plasma bromide was quantified by instrumental neutron activation analysis.

RESULTS

Mean CBS decreased with wound closure (9.1 +/- 4.1 vs 7.9 +/- 3.9 liters; P =.04), indicating a significant decrease in ECW over the course of recovery. A decline in weight also occurred over the same period (32.4 +/- 15.2 vs 29.1 +/- 13.5 kg; P =.007); however, change in corrected bromide space as a proportion of weight was not statistically significant.

CONCLUSION

A significant decrease in ECW accompanies the weight loss observed in patients following wound closure. Measurement of bromide dilution space is a convenient method for monitoring ECW that can be done at the bedside.

Pharmacokinetics and clinical utility of sodium bromide (NaBr) as an estimator of extracellular fluid volume in horses

The purpose of this study was to describe the pharmacokinetics of bromide in horses and to evaluate the corrected bromide space as an indicator of extracellular fluid volume (ECFV) in horses after the administration of a single dose of bromide by intravenous infusion. Sodium bromide (30 mg/kg of body weight, IV) was administered to 6 clinically healthy mares over a period of 3 minutes. Blood samples were collected before infusion and at intervals between 0.5 hours and 53 days after infusion. Mean elimination half-life (harmonic mean) was 126 hours (5.2 days), clearance was 1.4 +/- 0.09 mL/(kg x h), area under the curve was 17,520 +/- 1,100 microg x h/mL. and volume of distribution (steady state) was 0.255 +/- 0.015 L/kg. The mean corrected bromide space was determined from the volume of distribution (steady state) and the serum concentrations of bromide at equilibration. Corrected bromide space, an estimate of ECFV, was 0.218 +/- 0.01 L/kg. The conclusion was made that ECFV of horses can be estimated by measuring bromide concentrations in a preinfusion serum sample and a sample obtained 5 hours after the administration of bromide.

Body water content of extremely preterm infants at birth

BACKGROUND

Preterm birth is often associated with impaired growth. Small for gestational age status confers additional risk.

AIM

To determine the body water content of appropriately grown (AGA) and small for gestational age (SGA) preterm infants in order to provide a baseline for longitudinal studies of growth after preterm birth.

METHODS

All infants born at the Hammersmith and Queen Charlotte's Hospitals between 25 and 30 weeks gestational age were eligible for entry into the study. Informed parental consent was obtained as soon after delivery as possible, after which the extracellular fluid content was determined by bromide dilution and total body water by H(2)(18)O dilution.

RESULTS

Forty two preterm infants were studied. SGA infants had a significantly higher body water content than AGA infants (906 (833-954) and 844 (637-958) ml/kg respectively; median (range); p = 0.019). There were no differences in extracellular and intracellular fluid volumes, nor in the ratio of extracellular to intracellular fluid. Estimates of relative adiposity suggest a body fat content of about 7% in AGA infants, assuming negligible fat content in SGA infants and lean body tissue hydration to be equivalent in the two groups.

CONCLUSIONS

Novel values for the body water composition of the SGA preterm infant at 25-30 weeks gestation are presented. The data do not support the view that SGA infants have extracellular dehydration, nor is their regulation of body water impaired.

Human body composition: in vivo methods

In vivo methods used to study human body composition continue to be developed, along with more advanced reference models that utilize the information obtained with these technologies. Some methods are well established, with a strong physiological basis for their measurement, whereas others are much more indirect. This review has been structured from the methodological point of view to help the reader understand what can be examined with each technique. The associations between the various in vivo methods (densitometry, dilution, bioelectrical impedance and conductance, whole body counting, neutron activation, X-ray absorptiometry, computer tomography, and magnetic resonance imaging) and the five-level multicompartment model of body composition are described, along with the limitations and advantages of each method. This review also provides an overview of the present status of this field of research in human biology, including examples of reference body composition data for infants, children, adolescents, and adults.

Extracellular water: sodium bromide dilution estimates compared with other markers in patients with acquired immunodeficiency syndrome

Extracellular fluid and closely related extracellular water (ECW) provide information on nutritional status in health and disease. Although various methods exist for ECW determination, little is known about their comparability in patients with wasting diseases such as acquired immunodeficiency syndrome (AIDS). One practical method, the dilution of sodium bromide (NaBr), is used widely in clinical research, although its relationship to other ECW markers has not been well characterized. The present study sought to compare ECW estimates as determined by NaBr and three other methods in 11 male patients with AIDS (mean +/- SD; age, 44+/-12 years; body weight, 64.5+/-8.8 kg; and height, 172+/-4 cm). ECW volumes were determined from NaBr dilution, total body chlorine (TBCl) by delayed gamma-neutron activation analysis, total body water (TBW) by tritium dilution combined with total body potassium (TBK) by whole body 40K counting, and radioactive sulfate dilution (35SO4). All correlations between the NaBr method and other methods were statistically significant (NaBr vs TBCl [r = .91; p < .001]; vs TBW/TBK [r = .76; p < .01]; and vs 35SO4 [r = .89; p < .001]). As expected from previous studies, ECW (L) derived by NaBr provided a group mean (15.1+/-2.2 L) similar to the TBCl method (15.4+/-1.7 L; p = .32), a significantly smaller ECW than by the TBW/TBK method (18.6+/-3.4 L; p = .0004), and a significantly larger ECW than by 35SO4 method (13.3+/-3.0 L; p = .002). Estimating ECW by NaBr dilution was comparable with other research-based ECW methods and, thus, offers a practical alternative for evaluating ECW in patients with AIDS.

Bioimpedance spectroscopy technique: intra-, extracellular, and total body water

The purpose of this study was to test the validity of a multiple frequency bioimpedance spectroscopy (BIS) technique that estimates extracellular fluid volume (ECV), intracellular fluid volume (ICV), and total body water (TBW). Thirteen healthy males (mean +/- SD: age, 23 +/- 3 yr; body mass, 80.6 +/- 14.7 kg) had their TBW and ECV measured by ingesting dilution tracers (7.27 g deuterium oxide, 1.70 g sodium bromide; blood samples at 0 and 4 h). ICV was calculated as TBW minus ECV. Impedance was measured (50-500 kHz) at rest, on a nonconducting surface, with a BIS analyzer. Electrode placement, posture, exercise, food/fluid intake, and ambient temperature were controlled. Dilution measures (TBW, 51.00 +/- 9.30; ECV, 19.88 +/- 3.14; ICV, 31.12 +/- 6.80 L) and BIS volumes (TBW, 50.03 +/- 7.67; ECV, 20.95 +/- 3.33; ICV, 29.04 +/- 4.51 L) were significantly different for ECV (P < 0.01) and ICV (P < 0.05); some individual differences were large. The correlation coefficients of dilution versus BIS volumes (r = 0.93 to 0.96) were significant at P < 0.0001; SEEs were: TBW, 2.23 L; ECV, 1.26 L; and ICV, 1.71 L. We concluded that BIS is valid for between-subject comparisons of body fluid compartments, is appropriate in clinical settings where change in ECV/ICV ratio is important, and should be used by comparing the required level of accuracy to the inherent technique error/variance.

Simultaneous transcranial Doppler and arterial blood pressure response to lower body negative pressure

Microgravity induces fluid shifts which can alter the cardiovascular responses of astronauts both during space flight and on return to Earth. The decrease in orthostatic tolerance in astronauts returning from a weightless environment can be modelled in ground-based studies using lower body negative pressure (LBNP). This study examined the physiological changes induced by LBNP and determined a reliable method of predicting the onset of presyncope to enable evaluation of countermeasures for loss of orthostatic tolerance, such as glycerol-induced hyperhydration. Six healthy male subjects, aged 18 to 45 years, were each subjected to two LBNP tests, with or without glycerol ingestion. Continuous, non-invasive measurements of middle cerebral artery blood flow velocities (CBF) by transcranial Doppler, arterial blood pressure (Finapres ABP), ECG and LBNP box pressures were recorded during each test. Negative pressure was increased in three minute intervals until symptoms of presyncope were observed. An increase in heart rate (HR), a relatively constant mean ABP and a steady decline in mean CBF were consistently observed as the box pressure was decreased. The continuous on-line measurements clearly showed consistent dynamic changes in both CBF and ABP waveforms in response to changes in LBNP. At the onset of presyncope, sudden drops in mean ABP, HR and mean CBF were typically noted, the latter providing the earliest indication of presyncope. The time required to re-establish original baseline values of CBF and ABP after release of box pressure varied widely from six to over ten minutes.(ABSTRACT TRUNCATED AT 250 WORDS)

Absolute measurements of total-body calcium using prompt gamma neutron analysis and internal chlorine standardization: results in renal patients

Measurement of total-body calcium (TBCa) is important in the study of several medical conditions. Neutron activation analysis (NAA) is sufficiently precise for serial measurements, but in order to provide single, absolute determinations of TBCa, it requires a correction for body habitus. A method is described for the absolute determination of TBCa by comparing the total-body chlorine, obtained by NAA, with that obtained by stable bromine dilution. The method is applied to a group of thirty patients who had been treated for chronic renal failure, and significant differences are found between measured values of TBCa and those predicted for 'normal' healthy subjects. The overall experimental error in the absolute determination of TBCa is estimated to be 8%, for a dose equivalent of 3.1 mSv (based on skin dose, and a quality factor of 10 for neutrons).

The toxicology of bromide ion

Inorganic bromide is widely distributed in nature. Its natural physiological role in animal life is unknown. More than a century ago bromide was introduced in medicine as an antiepileptic drug. Nowadays, man is primarily exposed to bromide via food as the result of use of bromide-containing fumigants in intensive horticulture and in the treatment of food stocks. In this review exposure of man to bromide is described, and the pharmacological and toxicological effects of bromide ion are discussed.

Non-radioisotopic estimate of extracellular volume during isotonic expansion in anuric dogs

In six anuric dogs infused in two steps with isonatremic (= having the same sodium concentration as each dog's initial extracellular space) sodium chloride solutions, stable chloride space was computed by mass conservation and was compared to radiosulphate space. There was close agreement between estimates of preinfusion extracellular volume by radiosulphate and stable chloride spaces. Computed increases in radiosulphate and stable chloride spaces agreed with the infused volumes in each step.

[On the toxicology of carbromal. II. Pharmacokinetics of carbromal and its hypnotically active metabolites in the rat (author's transl)]

Oral doses up to 20 mg/kg of carbromal and of bromoethylbutyramide were rapidly absorbed in the rat. Absorption from the stomach ligated at the pyloric end was 5-8 fold less than absorption of carbromal injected directly into the small intestine. Oral doses greater than 20 mg/kg of carbromal disappeared more slowly from the gastro-intestinal tract because gastric emptying was delayed. Both carbromal and bromoethylbutyramide were able to reduce the basal tone and the acetylcholine-induced contraction of isolated rat fundus strips. Carbromal and bromoethylbutyramide distributed evenly between serum, brain and skeletal muscle. Concentrations in adipose tissue were three times those in the other three tissues. Concentrations of both carbromal and of bromoethylbutyramide in all four tissues declined at the same rate. Thus, serum concentration of either compound may be used to estimate the total body content. Intraperitoneally injected carbromal, bromoethylbutyramide and ethylbutyrylurea disappeared from the brain and from the serum with half-life of 3-4 h and 5-7 h, respectively. Traces only of unchanged carbromal, bromoethylbutyramide, or ethylbutyrylurea were excreted with urine or feces indicating rapid and extensive biotransformation of the three compounds in this species. No evidence was obtained of secretion of either carbromal or its two metabolites into the lumen of the stomach. The findings are discussed as to their relevance for acute carbromal poisoning in humans.

[On the toxicology of carbromal. I. Estimation of carbromal and its hypnotically active metabolites in rats and humans (author's transl)]

To analyze the toxic effects of carbromal it was necessary to have information on the concentrations of carbromal and of its metabolites in the organism. This information can be obtained by a simple method based on gaschromatography that allows rapid, specific, sensitive and quantitative estimation of carbromal and of its hypnotically active metabolites bromoethylbutyramide and ethylbutyrylurea. Employing different detectors (flame ionisation or electron capture detector) the limit of detection for carbromal and of its two metabolites was 2-3 nmoles/g of tissue. The method was used to study in rats the absorption and elimination of carbromal including biotransformation of carbromal to bromoethylbutyramide and ethylbutyrylurea. Both metabolites, significant amounts of which were found in serum and brain, distribute evenly between serum and brain as does carbromal. Both metabolites were detectable in the organism for a longer time than carbromal. Carbromal was given orally to 4 healthy volunteers at a dose of 1 g (4.2 nmoles). Highest serum concentrations (30 nmoles/ml) were found 30 min after ingestion. Serum concentrations declined rapidly. Twenty-four hours later 3-4% of the values were present in the serum. Beside carbromal considerable amounts (up to 20 nmoles/ml) of bromoethylbutyramide were detected but only small amounts (2-3 nmoles/ml) of ethylbutyrylurea. Peak concentrations of these metabolites were recorded 4-5 h after ingestion of carbromal. As was the case in rats both metabolites were present in the organism for a longer time than carbromal.

A comparison between the gastric and salivary concentration of iodide, pertechnetate, and bromide in man

The concentration of iodide (I(-)) and pertechnetate (TcO(4) (-)) and bromide (Br(-)) has been measured simultaneously in gastric juice and parotid saliva. The combined gastric and salivary clearance for iodide and pertechnetate is more than twice the clearance of these ions by the thyroid gland. The concentration of the ions was in the order I(-)>TcO(4) (-)>Br(-) in both gastric juice and saliva. Differences exist between the secretion of iodide, pertechnetate, and bromide. Bromide, in contrast to iodide and pertechnetate, was found to be more concentrated in gastric juice than in saliva. The ratio of the iodide to pertechnetate clearance was greater in gastric juice than in saliva.

Extracellular fluid in individual tissues and in whole animals: the distribution of radiosulfate and radiobromide

Radiosulfate, (35)SO(4), and radiobromide, (82)Br, were administered simultaneously to rats and dogs. In rats, the apparent volume of distribution of (82)Br averaged 30% of body weight and was constant between 0.5 and 35 hr after injection. The apparent volume of distribution of (35)SO(4), corrected for urinary loss, increased by 6% body weight/hr: the extrapolated volume at zero time was 88% of bromide space. Analysis of individual tissues and carcasses for (82)Br and inorganic (35)SO(4) showed that equilibration of both isotopes in several organs and in the whole carcass was rapidly achieved within 1 to 2 hr: no further increase in measured spaces occurred in 24 hr. The carcass inorganic sulfate space was 92%+/-2% of the bromide space in intact rats, and showed no increase with time. However, a progressively greater fraction of the injected (35)SO(4) was not recovered, owing to metabolic alteration. In eviscerated rats, the inorganic sulfate space was a smaller and much more constant fraction (79.8% +/-0.4%) of the bromide space, showing that at least 20% of body bromide (and hence chloride) is nonextracellular. The viscera chiefly responsible for the higher ratio of spaces in the intact animal were the liver, small bowel, and kidney. In the last two organs, excess inorganic (35)SO(4) (beyond the bromide space) was attributable to trapped transcellular fluid in which sulfate had been concentrated more than chloride (or bromide). Excess sulfate in liver and cartilage could not be explained in this manner: the results suggest passive binding of sulfate, but could reflect active cell uptake in these tissues. No excess sulfate was found in skin or tail. The implications of these observations with respect to the distribution of body chloride and the measurement of extracellular space are discussed. The extracellular volume of the rat is estimated to be 24% of body weight.