Assessment of hydration biomarkers including salivary osmolality during passive and active dehydration.

BACKGROUND/OBJECTIVES: Hydration state can be assessed via body mass change (BMΔ), serum and urine osmolality (Sosm, Uosm), urine-specific gravity (Usg) and urine volume (Uvol). As no hydration index has been shown to be valid in all circumstances, value exists in exploring novel biomarkers such as salivary osmolality (Vosm). Utilizing acute BMΔ as the reference standard, this research examined the efficacy of Sosm, Vosm, Uosm, Uvol and Usg, during passive (PAS) and active (ACT) heat exposure. SUBJECTS/METHODS: Twenty-three healthy men (age, 22±3 years; mass, 77.3±12.8 kg; height, 179.9±8.8cm; body fat, 10.6±4.5%) completed two randomized 5-h dehydration trials (36±1 °C). During PAS, subjects sat quietly, and during ACT, participants cycled at 68±6% maximal heart rate. Investigators measured all biomarkers at each 1% BMΔ. RESULTS: Average mass loss during PAS was 1.4±0.3%, and 4.1±0.7% during ACT. Significant between-treatment differences at -1% BMΔ were observed for Sosm (PAS, 296±4; ACT, 301±4 mOsm/kg) and Uosm (PAS, 895±207; ACT, 661±192 mOsm/kg). During PAS, only Uosm, Uvol and Usg increased significantly (-1 and -2% BMΔ versus baseline). During ACT, Vosm most effectively diagnosed dehydration 2% (sensitivity=86%; specificity=91%), followed by Sosm (sensitivity=83%; specificity=83%). Reference change values were validated for Sosm, Usg and BMΔ. CONCLUSIONS: The efficacy of indices to detect dehydration 2% differed across treatments. At rest (PAS), only urinary indices increased in concert with body water loss. During exercise (ACT), Sosm and Vosm exhibited the highest sensitivity and specificity. Sosm, Usg and BMΔ exhibited validity in serial measurements. These findings indicate hydration biomarkers should be selected by considering daily activities.

Extracellular volume estimation from ratios of bromide to chloride in urine or saliva.

Use of either urine or saliva samples to estimate extracellular water volume was investigated in 10 men using nonradioactive bromide (Br) and in seven newborn piglets using radioactive Br (82Br) and chloride (36Cl). The relation to Br to Cl concentrations in urine enabled an estimation of Br dilution volume from human urine (267 +/- 42 ml/kg, mean +/- SD) that was not significantly different (P = 1.0) from the Br dilution volume calculated from plasma Br concentration (268 +/- 20 ml/kg). Although the Br dilution volume estimated from saliva was not different from that of plasma, the error in the estimates of Br dilution volume from saliva was too large (mean difference, -36 +/- 64 ml/kg) to make its use practical. The data from piglets showed good agreement between 82Br and 36Cl dilution volumes calculated from 4-hr plasma samples (356 +/- 14 ml/kg and 347 +2- 12 ml/kg; P greater than 0.1) and between 82Br dilution volumes calculated from urine 82Br:36Cl and plasma 82Br (360 +/- 31 ml/kg and 356 +/- 14 ml/kg; P greater than 0.1). Extracellular water volume can be estimated in both adult and young animals using the Br dilution volume calculated from urine samples. It requires (i) two urine collections: one before and one 4 to 8 hr after administration of Br; (ii) a measurement or estimate of plasma Cl concentration; and (iii) a correction factor that describes the relationship of the ratio of Br to Cl in urine to that ratio in plasma.

A comparison of chloride, bromide, and sucrose dilution volumes in neonatal pigs.

Use of 36Cl, 82Br, and [3H]sucrose to estimate extracellular water volume was evaluated in 14 piglets (7-14 days old). 36Cl and 82Br were distributed in approximately the same volume, but a period of 5-6 hr after injection was required to reach equilibrium in the neonatal pig. Dilution volumes calculated before equilibration (2-5 hr) for 36Cl (326 +/- 11 ml/kg) and 82Br (328 +/- 13 ml/kg) were different from equilibration (6-8 hr) phase volumes (356 +/- 13 ml/kg and 355 +/- 13 ml/kg, respectively; P less than 0.001). A 3-hr sample estimated the same volume distribution calculated by extrapolation of the 6- to 8-hr period because of the relationship between the two slopes of the plasma clearance curves. After the 82Br and 36Cl had achieved equilibration, each was distributed in a volume equivalent to total body chloride space (362 +/- 29 ml/kg) measured by neutron activation; no statistical differences were found (P = 0.6). The early equilibration phase measured a 10% smaller, faster exchangeable fraction of total body Cl. Sucrose dilution volume (332 +/- 19 ml/kg) required multiple plasma samples for extrapolation and measured a dilution volume 7% smaller (P less than 0.05) than total body chloride space.

Tritiated water as a measure of body water in immature rats growing at different rates.

Rats were reared from birth in litters of 4, 10, and 16 to achieve different growth rates. Pups in the litters of 16 had no access to rat chow until days 21-28, when chow was made available to one of the litters to induce catch-up growth. Total body water was estimated by tritiated water (TBWHTO) on days 7, 14, 21, and 28 and then calculated from desiccation (TBWdes). TBWHTO was consistently larger than TBWdes for all groups. Differences were 10.9-16.9% on day 7 and 3.7-6.4% on day 28. On day 28, percent difference was higher in the slower-growing than the faster-growing groups. Nonaqueous hydrogen exchange was determined from tritium activity in the dried carcass. Less than 1% of the injected tritium exchanged with nonaqueous hydrogen during the equilibration period. Thus differences between TBWHTO and TBWdes in the younger animals could not be accounted for by nonaqueous hydrogen exchange but may have resulted from a larger loss of injected tritium, possibly in insensible water.

Total body water measurement by tritiated water in growing animals.

Data on 177 beagles were used to examine the hypothesis that the volume distribution of tritiated water (HTO) is significantly larger in some species of young growing animals than the volume of total body water (TBW) measured by desiccation in more mature animals. The beagles were divided into three groups. Group 1 consisted of 169 animals which ranged in age from 0 to 365 days and in weight from 0.25 to 13.5 kg. Group 2 consisted of 42 animals randomly selected from Group 1 over the entire age and weight range. Group 3 consisted of eight beagles which ranged in age from 2 to 5 years and in weight from 10.1 to 16.3 kg. Total body water was measured in Group 1 by HTO, in Group 2 by HTO and desiccation, and in Group 3 by HTO. The mean percentage difference between the measurements of TBW in Groups 1 and 2 increased between body weights of 0.2 to 3.4 kg (2 months old): in Group 1 from 14 to 28% and in Group 2 from 18 to 32%. From body weights of 4 to 13 kg, there was a progressive decrease in the mean difference between the two measures of TBW: in Group 1 from 28 to 4% and in Group 2 from 32 to 5%. Group 3 animals were a separate population statistically from other groups of beagles. At body weights of 12 and 13 kg, which overlapped with those of Group 2 dogs, there was no significant difference between the two measures of TBW. The present data support the proposed hypothesis.

Patterns of K/N ratios with growth of guinea pig, beagle, and pig.

The influence of age on patterns of K/N ratios (mEq/g) for fat-free whole body organs and tissues was analyzed for the guinea pig, ages 1 to 80 days (82 to 849 g); for the pig, 0 to 89 days (151 to 33,650); and for the beagle, 0 to 383 days (252 to 13,065 g). Strong correlations existed between total K, total N, and fat-free wet weight (FFWW). Mean whole body K/N ratios were 2.57 +/- 0.241 for guinea pigs, 2.53 +/- 0.50 for pigs, and 1.79 +/- 0.27 for beagles. Increase in body weight of the beagle and of the components, skeletal muscle and nonmuscle (whole animal minus skeletal muscle), were divisible into two statistically significant periods: the first from 0 to 62 days, the second from 63 to 383 days. For the first period, the K/N ratio for the whole animal was 1.70 +/- 0.33, for nonmuscle was 1.61 +/- 0.34, and for skeletal muscle was 2.08 +/- 0.50; for the second period, the values were 1.93 +/- 0.22, 1.25 +/- 0.18, and 2.82 +/- 0.83, respectively. Mean K/N ratios of organs and tissues of the pig and beagle differed significantly from mean whole body K/N ratios, with the exception of liver for the beagle and miscellaneous for the pig. Patterns of K/N ratios during increases in FFWW were species-specific for total body as well as for various tissues and organs. As FFWW increased, the whole body K/N ratio did not change significantly in the guinea pig, but decreased significantly in the pig because of the decreased ratio for skeletal muscle. As FFWW of the beagle increased in the first growth period, the slope for the whole body K/N ratio did not differ statistically from zero, although the mean measured ratio increased significantly for liver and skeletal muscle. This increase was counter-balanced by a statistically significant decrease in ratios for skin and skeleton. FFWW continued to increase in the second growth period and the whole body K/N ratio increased, primarily the result of significantly increased ratios for liver and skeletal muscle.(ABSTRACT TRUNCATED AT 400 WORDS)

Methane synthesis on nickel by a solid-state ionic method.

The feasibility of electrochemically synthesizing methane by a Fischer-Tropsch type reaction by use of a solid oxide electrolyte has been demonstrated. This solid-state ionic approach provides in situ control of the oxygen activity at the gascatalyst interface by imposing a suitable voltage drop across an oxygen-conducting solid electrolyte from an external source. Methanation rates for hydrogen-carbon monoxide and hydrogen-carbon dioxide synthesis gas mixtures upon nickel electrodes showed substantial enhancement with the use of this technique, reaching values nearly two orders of magnitude higher than their intrinsic rates.

Chemical maturation in growing guinea pigs.

Twenty-seven guinea pigs were analyzed chemically for total body water (TBW), fat, nitrogen (N), calcium (Ca), and sodium (Na); 26 were analyzed for potassium (K). Body weights ranged between 82 and 877 g. The data were analyzed by regression analysis. If the slope of a regression line did not differ significantly from zero (P less than 0.05), the mean and standard deviation were calculated. The slopes of the regression lines were significant for Na [meq/100 g fat-free wet weight (FFWW)] on body weight in grams, K in milliequivalents on FFWW in grams, and total body fat (TBF) (g) on body weight in grams. The means and standard deviations for the remaining constituents were in g/100 g FFWW; 76.0 +/- 2.5 for TBW and 2.52 +/- 0.28 for N, and in meq/100 g FFWW Ca 58.26 +/- 7.35 and K 6.35 +/- 0.74, and % TBF 8.57 +/- 3.44. The values for the following ratios were: K/N 2.609 +/- 0.247; K/TBW 0.087 +/- 0.011; and N/TBW 0.033 +/- 0.004 (K is in meq, N and H2O in g). The suggestion that the lower figure for TBW reported by earlier investigators compared to the present data could be the result of a systematic methodological error is discussed.

Comparison of measured and estimated fat-free weight, fat, potassium and nitrogen of growing guinea pigs.

Total body water (TBW), potassium (TBK), nitrogen (N), and fat were measured chemically on 27 guinea pigs ranging in weight from 82-849 g. Measured fat-free wet weight (FFWW) is the difference between body weight and fat extracted with ether. Estimated FFWW is either TBW or TBK divided by a measured or assumed concentration of either water or K in the FFWW. The coefficients of correlation between measured and estimated values of FFWW were identical, r = 0.99 with the 3 different concentration values used for K. By paired t analysis there were significant differences statistically between measured and estimated FFWW with the K "constants" 68.1 and 62.5, but no difference with the "constant" 65.5. The correlation coefficients between measured and estimated FFWW from water were r = 0.96 with the "constant" 73.2 g/100 g FFWW, and r = 0.99 with the "constant" 76.0 g/100 g FFWW. By the paired t test, measured and estimated FFWW differed significantly only with the "constant" 73.2. In the calculation of fat from K concentrations, only the value 65.5 could be used. The coefficients of correlation for measured and estimated fat were significant, although low. There was no difference correlations between N and body cell mass, body weight and measured and estimated FFWW, and between body cell mass and body weight and measured and estimated FFWW. There was statistically no difference between measured and estimated N by the paired t test.

Total body sodium, calcium, and chloride measured chemically and by neutron activation in guinea pigs.

Body sodium (Na), calcium (Ca), and chloride (Cl) of guinea pigs weighing between 227 and 600 g were measured by total body neutron activation analysis (TBNAA) followed by chemical analysis (CA) on 12-17 animals. Paired t test was used to compare any differences in the results obtained by the two methods. There was no significant difference in the results for the three elements. The means and standard deviation for Ca (g/100 g body wt) 1.070 +/- 0.132 (TBNAA) and 1.107 +/- 0.125 (CA); for Na 0.149 +/- 0.019 (TBNAA) and 0.143 +/- 0.021 (CA); and for Cl 0.126 +/- 0.009 (TBNAA) and 0.132 +/- 0.024 (CA). Neutron activation analysis alone, in a series of 27 animals, gave means (g/100 g body wt) and standard deviation of 1.110 +/- 0.084 for Ca, 0.120 +/- 0.009 for Cl, and 0.153 +/- 0.011 for Na. TBNAA has potential usefulness, particularly in longitudinal studies in the same animal, because of its accuracy and the rapidity and ease with which the measurements can be made.

A review of body composition studies with emphasis on total body water and fat.

Tritiated water meausres a volume 4 to 15% body weight larger than that by desiccation, and, at present, only 0.5 to 2.0% of the overestimation can be explained by the exchange of hydrogen of tritiated water with those of the proteins and carbohydrates of the body. The remainder of the error is unexplained. Water in the lumen of the gut is an appreciable percentage of total body water (TBW) in many mammalian species, with the pig and the human as possible exceptions, and it should be considered an integral part of TBW. Consequently, the exclusion or inclusion of this transcellular water as part of TBW significantly affects the final TBW volume. As tritiated water exchanges with water in the gut, a comparison of the data from the indirect method with the data from the direct method can only be made when water in the gut is included in the desiccation method. Conceptually, the amount of water in lean body mass is a reflection of the actively metabolizing cell mass of the body. However, water in the gut is outside this cell mass, and if included, it significantly overestimates the water associated with the lean body mass compartment. The percentage of water in fat-free wet weight for most mature animals is estimated at 73.2%, although the mean values in the literature range from 63% for the beagle to 80% for the mouse, with the mean for the majority of species between 70 and 76%. If the percentage of water in fat-free wet weight lies between 70 and 76% for most species, then the error in calculating fat using the figure 73.2% in the equation (% fat = 100 - % TBW/0.732) is significant. In the application of this equation, the largest potential error lies in the estimation of TBW with tritiated water.

Growth of the pig: changes in red cell and plasma volumes.

In the pig, plasma volume increased from 58.0 +/- 2.53 ml/kg on day 1 to 66.7 +/- 3.35 (P less than 0.05) on day 2, and decreased between days 7 and 9 to 56.4 +/- 1.16 (P less than 0.02). The next significant change in volume occurred at weaning: from 53.1 +/- 1.24 ml/kg at week 4 to 44.16 +/- 2.2 at week 5. It then increased to 56.1 +/- 1.41 ml/kg by week 7 and decreased to 48.5 +/- 1.44 by week 9; then between weeks 10 and 11 it increased to 59.33 +/- 3.01 (P less than 0.005). Red cell volume on day 1 was 32.3 +/- 1.25 ml/kg and decreased to 20.2 +/- 1.37 (P less than 0.01) on day 2. The only other change of significance in red cell volume over the 12-week growth period was a small increasan 0.05) at week 6. The mean for BVRcells was 0.88 +/- 0.01 for the growth period. The pattern of changes in plasma and red cell volumes differed from those for the beagle.

Relationship between red cell mass, body weight, lean body mass, and body cell mass in growing pigs and beagles.

During growth in 55 pigs (from birth through week 12) and 42 beagles studied (from birth through year 1), there was an equally close association between red cell mass (RCM) and body weight, lean body mass (LBM) and body cell mass (BCM); the coefficients of correlation were between 0.94-0.99. The association of RCM with body weight was the result of BCM, extracellular tissue (ECT), and fat, each increasing at a constant rate relative to body weight. The primary relationship appears to be between RCM, the oxygen-delivery system, and BCM, the principla oxygen-using system; and the close association of RCM with body weight and LBM the results of the growth patterns of their components.

Growth of the pig: patterns of changes in electrolytes, water, and protein.

In 246 pigs studied from day of birth through week 12, mean plasma concentration of Na was 144.2; K, 3.89; and Cl, 103 mEq/1. Fifty-five pigs were analyzed for total body water (TBW), Na, K, Cl, protein, and fat. TBW was 83% fat-free wet weight (FFWW) at birth and declined, but not significantly, over the 12 weeks. Water content of tissues differed from each other as well as in the rates at which their water content changed. Concentration of electrolytes Na, K, Cl (mEg/100 g FFWW) decreased significantly in whole pig, viscera, brain, and skin; while Na increased and K and Cl decreased significantly in skeletal muscle. Of the tissues, skeletal muscle contributed 32% (fat-free tissue weight as per cent of total FFWW) at birth and 44% at week 12; and viscera, 15% at birth and 21% at week 12. The contribution of skeleton decreased over the same period from 22 to 15%, skin from 14 to 6%, and brain from 2 to 0.5%. The contribution of total water by the various organs changes in the same direction as the contribution to total FFWW. Na, K, Cl, and protein as a per cent of total in skin also show the same directional change. In skeletal muscle there was a decrease in conribution to total Na and Cl, but an increase to total K and protein. In the skeleton, except for protein, there is an increase in contribution of total Na, K, and Cl. There was a correlation of 0.99 and 0.94 between the sum of total Na and K in milliequivalents and TBW in millimeters for the whole pig and skeletal muscle respectively.

Growth of the pig: changes in body weight and body fluid compartments.

Body weight and the rate of change in TBW, ECW, and ICW were measured in 252 anesthetized pigs during the first 12 weeks after birth. After TBW was measured with 3H2O, 55 of the pigs were killed and TBW measured by desiccation. 3H2O overestimated TBW by 6.5% of body weight and 4.9% of fat-free wet weight, compared to desiccation (P less than 0.001); mean figures for 3H2O were 78.6 +/- 1.02% of body weight, and for desiccation, 72.1 +/- 0.45%; on a FFWW basis, 88.6 +/- 0.94% for 3H2O, and 83.7 +/- 0.13% for desiccation. TBW decreased significantly from 85.0% of body weight at birth (1.5 dg) to 75% at 5 kg (day 28) at a rate of ---3.2% body wt/kg body wt (P less than 0.001 from a zero rate). After that the rate of decrease was not different from zero: --0.117% body wt/kg body wt. ECW decreased significantly from 48% at birth to 35% at day 28 at a rate of --3.802% body wt/kg body wt (P less than 0.001 from a zero rate), and after day 28 the rate of decrease was not different from zero (--0.149% body wt/kg body wt) through week 12. ICW decreased, but not significantly, at a rate of --0.099% body wt/kg body wt. The changes in the rate of decrease in TBW and ECW coincided with weaning, and it was speculated that there was a direct relationship between the two events.

Changes in water, protein, sodium, potassium, and chloride in tissues with growth of the beagle.

Changes in total body and tissue composition of 43 beagles were analyzed from 0 day (birth) to 1 year. The tissues studied were skeletal muscle, viscera (heart, lungs, gut, liver, kidneys), skeleton, skin, and brain, and the data were expressed as follows: fat-free tissue weight (FFTW) as a per cent of total fat-free wet weight (FFWW); water and protein in grams per kilogram FFTW; and Na, Cl, K in milliequivalents FFTW. The mass of skeletal muscle increased from 21% of FFWW at birth to 36% at 1 year while the contribution of the remainder of the tissues decreased: skeleton from 30 to 25%, viscera 23 to 15%, skin 18 to 13%, and brain 4 to 0.9%. Over the same period, total body water decreased from 780 g/kg to 665, water of skeletal muscle from 771 to 665, of viscera from 782 to 621, of skeleton from 644 to 424, of skin from 765 to 669, of brain from 853 to 692; Total protein increased from 113 g/kg to 196, in skeletal muscle from 122 to 253, in viscera from 114 to 195, in skeleton from 71 to 112, in skin from 170 to 227, and in brain from 63 to 164. Total Na was 84 mEq/kg throughout the first year of growth, 101 for skeleton, and 89 for skin, while Na increased in viscera from 66 to 75 and in brain from 63 to 77, but decreased in skeletal muscle from 75 to 59. Total K increased from 31 mEq/kg at birth to 62 at 1 year, and from 38 to 107 in skeletal muscle, from 49 to 78 in viscera, and decreased from 27 to 11 in skin, and 42 to 122 in brain. Total Cl decreased from 58 to 49, in skeletal muscle from 52 to 34, in skeleton from 43 to 33, while that in viscera increased from 56 to 78. The contribution of skeletal muscle and viscera (the major metabolic cell mass) to total FFWW increased from 44 to 52%, and it contributed over 50% of total water, protein, Cl, and 89% of K. Skeletal muscle accounted for the increases. Skin and skeleton contributed 38% of FFWW, 17% of water, 29% of Na, 19% of Cl, 16% of protein, and 10% of K. The rates of change in these parameters fell into three patterns: (1) the content of the chemical component did not change significanly in the first year of growth; (2) it increased or decreased at a constant rate; or (3) there were two rates at which the concentration changed; the break between them occurred between the third and fourth months and coincided with evidence of increasing sexual maturation. A specific pattern of change was characteristic of a particular tissue and appeared independent of that of the total dog and other tissues. These data support the conclusion that there are mechanisms intrinsic to each tissue which exert a degree of control during growth over its chemical composition; therefore, growth itself can be considered an intrinsic regulatory mechanism.