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PubMed2001

Detergent-phospholipid mixed micelles with a crystalline phospholipid core.

An unusual micelle was discovered in mixtures of the nonionic detergent octaethyleneglycol-mono-n-dodecylether with disaturated phospholipids such as 1,2-dimyristoyl-sn-glycero-3-phosphocholine or 1,2-dipalmitoyl-sn-glycero-3-phosphocholine in water. These mixtures undergo a structural transition upon cooling through the chain-melting temperatures of the respective phospholipids, resulting in the formation of mixed micelles. Structural features of the micellar particles were studied here by synchrotron x-ray scattering. The translucent micellar solutions showed characteristic wide-angle reflections that were attributed to ordered hydrocarbon chains, whereas the absence of small-angle x-ray reflections indicated that there is no long-range order in these mixtures. The presence of ordered phospholipid acyl chains was confirmed by differential scanning calorimetry and isothermal titration calorimetry. The endothermic differential scanning calorimetry signals observed in the up-scan mode were tentatively ascribed to chain melting and mixing of the components. Isothermal titration of the mixed-micellar solutions into an excess of the detergent octaethyleneglycol-mono-n-dodecylether resulted in sudden uptake of the latent heat by the gel-state phospholipids. The heat uptake per mol of phospholipid decreased with increasing detergent/phospholipid molar ratio. A simple geometric model is presented assuming that the dominating particle species in the mixtures is a discoidal phospholipid aggregate with ordered acyl chains, surrounded by a toroidal detergent hoop. The model implies that the fraction of ordered phospholipid chains decreases with increasing detergent/phospholipid molar ratio, in agreement with the calorimetric results and high-resolution NMR spectroscopy.

Calorimetry, Differential Scanning↗
PubMed1996

Thermodynamics of monosaccharide and disaccharide binding to Erythrina corallodendron lectin.

Isothermal titration calorimetry measurements of the binding of 2'-fucosyllactose, lactose, N-acetyllactosamine, galactopyranose, 2-acetamido-2-deoxygalactopyranoside, methyl alpha-N-dansylgalactosaminide (Me-alpha-DNS-GalN), methyl alpha-D-galactopyranoside, methyl beta-D-galactopyranoside, and fucose to Erythrina corallodendron lectin (ECorL), a dimer with one binding site per subunit, were performed at 283-286 and 297-299 K. The site binding enthalpies, DeltaHb, with the exception of Me-alpha-DNS-GalN, are the same at both temperatures and range from -47.1 +/- 1.0 kJ mol-1 for N-acetyllactosamine to -4.4 +/- 0.3 kJ mol-1 for fucose, and the site binding constants range from 3.82 +/- 0.9 x 10(5)M-1 for Me-alpha-DNS-GalN at 283.2 K to 0.46 +/- 0.05 x 10(3) M-1 for fucose at 297.2 K. The binding reactions are mainly enthalpically driven except for fucose and exhibit enthalpy-entropy compensation. The binding enthalpies of the disaccharides are about twice the binding enthalpies of the monosaccharides in contrast to concanavalin A where the binding enthalpies do not double for the disaccharides. Differential scanning calorimetry measurements show that denaturation of the ECorL dimer results in dissociation into its monomer subunits. The binding constants from the increase in denaturation temperature of ECorL in the presence of saccharides are in agreement with values from isothermal titration calorimetry results. The thermal denaturation of ECorL occurs around 333 K, well below the 344-360 K denaturation temperature of other legume lectins of similar size and tertiary structure, undoubtedly due to the difference in its quaternary structure relative to other legume lectins. This is also apparent from the independent unfolding of its two domains.

Binding Sites↗
PubMed2003

The negative transcriptional regulator NmrA discriminates between oxidized and reduced dinucleotides.

NmrA, a transcription repressor involved in the regulation of nitrogen metabolism in Aspergillus nidulans,is a member of the short-chain dehydrogenase reductase superfamily. Isothermal titration calorimetry and differential scanning calorimetry have been used to show NmrA binds NAD+ and NADP+ with similar affinity (average KD 65 microM) but has a greatly reduced affinity for NADH and NADPH (average KD 6.0 mM). The structure of NmrA in a complex with NADP+ reveals how repositioning a His-37 side chain allows the different conformations of NAD+ and NADP+ to be accommodated. Modeling NAD(P)H into NmrA indicated that steric clashes, attenuation of electrostatic interactions, and loss of aromatic ring stacking can explain the differing affinities of NAD(P)+/NAD(P)H. The ability of NmrA to discriminate between the oxidized and reduced forms of the dinucleotides may be linked to a possible role in redox sensing. Isothermal titration calorimetry demonstrated that NmrA and a C-terminal fragment of the GATA transcription factor AreA interacted with a 1:1 stoichiometry and an apparent KD of 0.26 microM. NmrA was unable to bind the nitrogen metabolite repression signaling molecules ammonium or glutamine.

Aspergillus nidulans↗
PubMed2005

Solid state and dissolution rate characterization of co-ground mixtures of nifedipine and hydrophilic carriers.

Co-ground powders of the poorly water-soluble drug nifedipine and a hydrophilic carrier, [partially hydrolyzed gelatin (PHG), polyvinylpyrrolidone (PVP), sodium dodecyl sulfate (SDS), hydroxypropyl methylcellulose (HPMC), polyethylene glycol (PEG), urea or Pluronic F108] were prepared in order to improve the dissolution rate of nifedipine. The effects of type of grinding equipment, grinding time, and type of hydrophilic carrier on the crystallinity of nifedipine (x-ray diffraction and differential scanning calorimetry) on the interaction between drug and carriers (differential scanning calorimetry), on the particle size and appearance (scanning electron microscopy), on the wettability (contact angle measurements), and on the drug release were investigated. Grinding nifedipine together with these carriers improved the dissolution rate. PHG-ground mixtures resulted in the fastest dissolution rate followed by PVP, SDS, HPMC, Pluronic, urea, and PEG. This effect was not only due to particle size reduction, which increased in the order PHG<PEG=SDS<Pluronic<drug<urea<HPMC<PVP, but also resulted from the ability of some carriers (PVP and HPMC) to prevent reaggregation of the finely divided drug particles. PVP, HPMC, and PHG formed a powder with amorphous drug. The carriers improved the wettability of the ground products in the order HPMC<drug<urea<PVP<SDS<PHG<PEG<Pluronic. Differential scanning calorimetry (DSC) measurements gave valuable information about the nature of drug crystallinity and the interactions with the carriers within the ground mixtures.

Calcium Channel Blockers↗
PubMed2004

A small-body portable graphite calorimeter for dosimetry in low-energy clinical proton beams.

Calorimetry has been recommended and performed in proton beams for some time, but never has graphite calorimetry been used as a reference dosimeter in clinical proton beams. Furthermore, only a few calorimetry measurements have been reported in ocular proton beams. In this paper we describe the construction and performance of a small-body portable graphite calorimeter for clinical low-energy proton beams. Perturbation correction factors for the gap effect, volume averaging effect, heat transfer phenomena and impurity effect are calculated and applied in a comparison with ionization chamber dosimetry following IAEA TRS-398. The ratio of absorbed dose to water obtained from the calorimeter measurements and from the ionization measurements varied between 0.983 and 1.019, depending on the beam type and the ionization chamber calibration modality. Standard uncertainties on these values varied between 1.9% and 2.5% including a substantial contribution from the kQ values in IAEA TRS-398. The (Wair/e)p values inferred from these measurements varied between 33.6 J C(-1) and 34.9 J C(-1) with similar standard uncertainties. A number of improvements for the small-body portable graphite calorimeter and the experimental set-up are suggested for potential reduction of the uncertainties.

Calibration↗
PubMed1986

24-hour energy expenditure and the menstrual cycle.

To determine whether 24-h energy expenditure changes during the menstrual cycle, 10 normally menstruating women in their 20s and 40s were measured repeatedly for periods of 36 and 46 h by simultaneous direct and indirect calorimetry. A standardized sedentary daily schedule included three meals to provide food intake equal to expenditure. Eight of the 10 women showed increases of 8-16% during the 14-day luteal phase following ovulation, a significant increase (p less than 0.00002 by direct calorimetry, p less than 0.001 by indirect calorimetry). One subjects, whose increase was 14% following ovulation, showed no significant change during a month when she took an oral contraceptive. Progesterone from the corpus luteum is the likely cause of a 9% increase in 24-h energy expenditure in normally menstruating women.

Adult↗
PubMed1995

Energy expenditure measurements in relation to energy requirements.

Long-term good health for weight-stable adults requires balance between energy intake (EI) and energy expenditure (EE). Both EI and EE measurements can be used to estimate energy requirement. Results from studies conducted at Beltsville Human Nutrition Research Center in which two or more methods were used to measure EE are compared to determine relative differences in measurement techniques. Comparison of EI estimated from dietary intake records (7 d minimum) with EI measured in 12 controlled feeding studies (45 d minimum) in 266 subjects indicated that diet records underestimate energy requirement by 18%. Comparison of EE measured in a room calorimeter and by doubly labeled water (2H(2)18O) in nine subjects showed no significant difference between methods within the calorimeter environment (1.6 +/- 2.6%) but free-living EE measured by 2H(2)18O was greater (13.2 +/- 7.1%) due to physical activity. Comparison of metabolizable energy (ME) intake, 2H(2)18O, and direct or indirect calorimetry in four subjects indicated no difference between ME and EE measured by 2H(2)18O (-1.0 +/- 1.3%) or between direct and indirect calorimetry (0.6 +/- 0.9%); however, free-living EE measured by 2H(2)18O was greater than the value calculated by calorimetry (15.3 +/- 5.0%). Each method has associated limitations that include availability, accuracy, precision, and cost. Appropriate application and interpretation of results for all methods are essential.

Adult↗
PubMed1981

Effect of energy restriction on total heat production, basal metabolic rate, and specific dynamic action of food in rats.

Man and experimental animals are able to adapt to restricted levels of energy intake mainly by a reduction in basal metabolic rate (BMR) while the effects of energy restriction on the specific dynamic action (SDA) of food and the spontaneous activity are less well established. In this study, growing rats were fed ad libitum or restricted amounts of diet during 28-31 days. Then total heat production (THP) and BMR during 22 hours, as well as SDA of a test meal, were measured on individual rats by indirect calorimetry. After the calorimeter study rats were kept in metabolic cages for 6 days after which they were killed and analyzed for total body composition. The energy balance of the rats over the last 7 days of the study was calculated from changes in body composition and measurements of food intake during this period. During the calorimeter experiment an indirect estimation of the spontaneous activity of the rat was made. Results showed that THP, BMR and SDA of restricted rats were significantly lower than for ad libitum-fed rats. From body composition measurements, rats restricted in food intake before the calorimetry study were found to mobilize more protein and less fat compared to rats fed ad libitum until the calorimetry and body composition studies were carried out. No difference in spontaneous activity was observed between the two dietary treatments.

Adipose Tissue↗
PubMed1985

Measured and predicted caloric expenditure in the acutely ill.

Predicted energy requirements calculated from the Harris-Benedict basal energy expenditure (BEE) formulas, and caloric allowances recommended by the Food and Nutrition Board National Research Council, were compared to metabolic expenditures measured by indirect calorimetry, using a feedback-controlled gas replenishment technique with a prototype device for the continuous determination of oxygen consumption (VO2) and carbon dioxide production (VCO2). In a group of 50 acutely ill surgical patients, predicted metabolic requirements based on ideal body weight (1.75 BEE) averaged 59% greater than metabolic expenditures measured by indirect calorimetry. Metabolic requirements based on actual body weight averaged 52% greater; recommended caloric allowances averaged 39% greater. Thus, accepted methods of predicting metabolic requirements significantly overestimated the caloric needs of these acutely ill patients. These results should encourage the development of new bedside equipment for measuring VO2 and VCO2, so that indirect calorimetry can be used to guide nutritional support in the clinical setting.

Acute Disease↗
PubMed1995

Effect of hemorrhagic shock and reperfusion on the respiratory quotient in swine.

OBJECTIVES: Respiratory quotient, the ratio of CO2 production to oxygen consumption (VO2), is principally affected by the fuel source used for aerobic metabolism. Since the respiratory quotient, VO2, and CO2 production cannot be directly measured easily, indirect calorimetry is commonly used to determine the value of these variables at the airway level (i.e., airway respiratory quotient, airway VO2, and airway CO2 production). However, under nonsteady-state conditions, a variety of phenomena can alter the relationship between true metabolic activity and measurements determined by indirect calorimetry. During exercise, for example, airway respiratory quotient increases as anaerobic threshold is reached because of the disproportionate increase in airway CO2 production that results from the CO2 liberated through the buffering of excess hydrogen ions by bicarbonate. We hypothesized that hemorrhage and reinfusion might change airway respiratory quotient in a consistent manner as shock is produced and reversed. DESIGN: Prospective laboratory study. SETTING: University animal laboratory. SUBJECTS: Eight pigs (25 +/- 2 [SD] kg), anesthetized with fentanyl and relaxed with pancuronium bromide, and mechanically ventilated on room air. INTERVENTIONS: The animals were sequentially hemorrhaged and then autotransfused while metabolic and hemodynamic measurements were obtained, using continuous indirect calorimetry and continuous applications of the Fick principle. Hemoglobin, arterial lactate concentration, and blood gases for calibration were measured serially. Analysis of variance was used to compare various periods in time. MEASUREMENTS AND MAIN RESULTS: Between baseline and peak hemorrhage, and between peak hemorrhage and postreinfusion, all of the following variables changed significantly (p < .05): airway VO2 (baseline 6.4 +/- 0.9 mL/min/kg, peak hemorrhage 3.9 +/- 0.6 mL/min/kg, postreinfusion 7.0 +/- 1.4 mL/min/kg); airway CO2 production (baseline 5.5 +/- 0.9 mL/min/kg, peak hemorrhage 4.5 +/- 0.9 mL/min/kg, postreinfusion 6.0 +/- 1.4 mL/min/kg); airway respiratory quotient (baseline 0.87 +/- 0.07, peak hemorrhage 1.16 +/- 0.07, postreinfusion 0.87 +/- 0.05); lactate concentration (baseline 2.4 +/- 1.2 mmol/L, peak hemorrhage 6.7 +/- 1.9 mmol/L, postreinfusion 5.1 +/- 2.0 mmol/L); and delta PCO2 (venous PCO2-PaCO2) (baseline 4.5 +/- 3.6 torr [0.6 +/- 0.5 kPa], peak hemorrhage 12.1 +/- 5.3 torr [1.6 +/- 0.7 kPa], postreinfusion 2.7 +/- 2.7 torr [0.4 +/- 0.4 kPa]). CONCLUSIONS: Airway respiratory quotient increases in hemorrhagic shock and decreases again as shock is reversed during reinfusion. This phenomenon appears related to the buffering of excess of hydrogen ion during hemorrhagic shock.

Animals↗
PubMed1990

Assessing nutritional needs for the burned patient.

Assessment of nutritional needs following thermal injury remains an important adjunct to providing dietary therapy designed to minimize the detrimental effects of hypermetabolism and subsequent catabolism. Most anthropometric measurements, frequently utilized in nonburned patients, have relatively little usefulness in assessing burned individuals. Energy expenditure can be adequately estimated for most patients by direct calorimetry, indirect calorimetry, or formulae. Direct calorimetry is the most expensive and complicated method, while use of a formula is the most inexpensive and least complicated. All yield good results in the clinical setting. Differences in estimated energy expenditure by the multiple formulae may be statistically significant, but rarely are clinically significant. Therefore selection of a formula should be based on simplicity. Estimations by formula require readjustment at intervals of 1 to 2 weeks. In general, enteral feedings remain superior to parenteral delivery of nutrients. Finally, current animal research suggests significant differences in metabolic and immunologic effects of the diet depending on qualitative make-up of dietary fat sources.

Animals↗
PubMed1999

Comparison of accelerometers with oxygen consumption in older adults during exercise.

PURPOSE: The purpose of this study was to compare two commercially available accelerometers with indirect calorimetry in a group of older adults (x +/- SD; 70.6+/-3.7 yr; N = 86, 44 males and 42 females). METHODS: The accelerometers (Caltrac and Tritrac, Hemokinetics, Madison, WI) were worn while performing three submaximal, discontinuous (5 min exercise, 2 min recovery), progressive levels of treadmill walking and bench stepping. The treadmill exercise averaged 3.4 mph, at 0.4% grade, 3.0% grade, and 5.1% grade, while the stepping work rates (24 steps x min(-1)) were performed on 15.2-, 20.3-, and 25.4-cm steps. Estimated energy expenditure (EE) from the two accelerometers was compared with EE as measured by indirect calorimetry. RESULTS: The Caltrac significantly (P < 0.05) overestimated EE at the three treadmill work rates (10-52% difference) and underestimated EE at the three stepping work rates (-19% to -28% difference). When comparing the changes in EE between work rates one, two and three, the Caltrac was not sensitive to the changes (increase in EE) that occurred during graded treadmill walking but did detect some changes in the stepping exercise. The Tritrac significantly (P < 0.05) underestimated EE for the three work rates of both the treadmill and stepping exercise when compared with indirect calorimetry but did detect differences in EE among work rates during stepping exercise (P < 0.05). CONCLUSIONS: These data indicate that the magnitude of the differences between measured and estimated EE is affected by exercise mode and intensity and that caution is warranted when using the accelerometers in an attempt to quantify EE in older adults.

Aged↗
PubMed2002

Field evaluation of energy expenditure in women using Tritrac accelerometers.

PURPOSE: To investigate the use of Tritrac accelerometers to measure energy expenditure (EE) of various activities for women in the field setting, as compared with portable indirect calorimetry. METHODS: Twenty women (age 20-29) performed a choreographed routine of six activities (walking, jogging, stair climbing, walking on an incline, stationary cycling, and arm ergometry) while wearing a Tritrac-R3D accelerometer (Hemokinetics Inc., Madison WI) and the Cosmed K4b(2) portable metabolic cart (Cosmed, Rome, Italy). RESULTS: Comparing the mean error scores (K4b(2) - Tritrac), the Tritrac overestimated the EE (kcal x min(-1)) of walking (-1.45) and jogging (-1.75), whereas underestimating the EE of stair climbing (2.76), stationary cycling (2.75), and arm ergometry (1.20). Walking on an incline showed the lowest mean error score (-0.11). Intraclass correlations were moderate for walking (r = 0.568, < 0.05), jogging (r = 0.666, < 0.05), and stairs (r = 0.503, < 0.05) but for the other activities ranged from r = 0.290 ( > 0.05) to r = 0.480 ( < 0.05). The raw data from the Tritrac was applied to a previously developed nonlinear model to adjust the Tritrac scores to the standard of whole-room indirect calorimetry. This resulted in statistically significant improvements in the agreement between the adjusted Tritrac value and the K4b for walking, jogging, and walking on an incline ( < 0.05). CONCLUSION: When compared with portable indirect calorimetry, the Tritrac overestimates the EE of walking and jogging, whereas underestimating that of stair climbing, stationary cycling, and arm ergometry. This limits the use of such a technique to measure EE in the field. The main issues appear to be the type and intensity of the activity and the need for movement in order for the Tritrac to register EE. Activity specific linear regression equations are proposed as a tool to improve the measurement of EE using the Tritrac in the field.

Acceleration↗
PubMed2006

Energy expenditure and balance following pediatric intensive care unit admission: a longitudinal study of critically ill children.

OBJECTIVE: Longitudinal comparison of prescribed energy, actually administered energy, and energy expenditure (EE) predicted by Schofield's equations to actual EE, as determined by daily indirect calorimetry measurements in critically ill children during the first 7 days following admission. DESIGN: Observational study. SETTING: Pediatric intensive care unit, high and medium care wards, in a university hospital. PATIENTS: Forty-six mechanically ventilated and spontaneously breathing infants and children (0-18 yrs) who were admitted with sepsis or following major abdominal or thoracic surgery or trauma. INTERVENTIONS: Daily indirect calorimetry measurements and assessment of energy balance. MEASUREMENTS AND MAIN RESULTS: Energy balance studies were performed for a total of 298 admission days in 13 sepsis, 27 surgery, and 6 trauma patients. Indirect calorimetry measurements were performed on 89% of the days. Mean measured EE was 44.6 +/- 15 kcal/kg.d and equaled predicted EE (44.2 +/- 12 kcal/kg.d; p = .56). Measured EE did not change over time, neither overall nor in diagnostic subgroups. Overall, median (range) administered energy was 31.1 (0-119) kcal/kg.d, which was significantly lower than measured EE (p < .001) and predicted EE (p < .001). Patients were underfed on 60% of days and overfed on 28% of days. Administered energy rose significantly in the course of admission, independently of diagnostic category, and did not differ from prescribed energy (p = .42). Energy intake was significantly higher in sepsis patients than in surgery and trauma patients during the whole course of the study (p < .01). The cumulative energy balance was positive only in sepsis patients. The administration of parenteral feeding was the single significant factor determining energy intake in mixed-effect modeling. CONCLUSIONS: Measured EE was stable and not significantly different from predicted values over the course of hospitalization. Underfeeding was frequently present and mainly due to prescription and administration of energy amounts inferior to measured EE values in enterally fed patients.

Adolescent↗
PubMed2004

The conformational stability of the Streptomyces coelicolor histidine-phosphocarrier protein. Characterization of cold denaturation and urea-protein interactions.

Thermodynamic parameters describing the conformational stability of the histidine-containing phosphocarrier protein from Streptomyces coelicolor, scHPr, have been determined by steady-state fluorescence measurements of isothermal urea-denaturations, differential scanning calorimetry at different guanidinium hydrochloride concentrations and, independently, by far-UV circular dichroism measurements of isothermal urea-denaturations, and thermal denaturations at fixed urea concentrations. The equilibrium unfolding transitions are described adequately by the two-state model and they validate the linear free-energy extrapolation model, over the large temperature range explored, and the urea concentrations used. At moderate urea concentrations (from 2 to 3 m), scHPr undergoes both high- and low-temperature unfolding. The free-energy stability curves have been obtained for the whole temperature range and values of the thermodynamic parameters governing the heat- and cold-denaturation processes have been obtained. Cold-denaturation of the protein is the result of the combination of an unusually high heat capacity change (1.4 +/- 0.3 kcal.mol(-1).K(-1), at 0 m urea, being the average of the fluorescence, circular dichroism and differential scanning calorimetry measurements) and a fairly low enthalpy change upon unfolding at the midpoint temperature of heat-denaturation (59 +/- 4 kcal.mol(-1), the average of the fluorescence, circular dichroism and differential scanning calorimetry measurements). The changes in enthalpy (m(DeltaH(i) )), entropy (m(DeltaS(i) )) and heat capacity (m(DeltaC(pi) )), which occur upon preferential urea binding to the unfolded state vs. the folded state of the protein, have also been determined. The m(DeltaH(i) ) and the m(DeltaS(i) ) are negative at low temperatures, but as the temperature is increased, m(DeltaH(i) ) makes a less favourable contribution than m(DeltaS(i) ) to the change in free energy upon urea binding. The m(DeltaC(pi) ) is larger than those observed for other proteins; however, its contribution to the global heat capacity change upon unfolding is small.

Bacterial Proteins↗
PubMed2004

Measurement of resting energy expenditure in infants.

OBJECTIVE: The method for measurement of basal metabolic rate (BMR) using indirect calorimetry in adults is well established but is impractical in infants. METHODS: In this prospective study energy expenditure was measured using indirect calorimetry in 14 infants when sleeping and when lying quietly awake. RESULTS: Sleeping metabolic rate (SMR) was lower than energy expenditure (EE) measured in the same infants in a quiet resting state (mean difference [SD]: 297 [162] kJ/d; P < 0.005; 55 [33.4] kJ/kg per day; P < 0.005). The correlation within individuals suggests that these differences are related to the level of arousal. Awake EE, but not SMR, was significantly greater than estimated BMR using the FAO/WHO/UNU predictive equation. CONCLUSIONS: In infants, the level of arousal during measurement of EE can significantly impact on the interpretation of EE results. A standardized method for the measurement of EE in infants using indirect calorimetry is proposed.

Basal Metabolism↗
PubMed2000

Kinetics of intramuscular triglyceride fatty acids in exercising humans.

UNLABELLED: A pulse ([(14)C]palmitate)-chase ([(3)H]palmitate) approach was used to study intramuscular triglyceride (imTG) fatty acid and plasma free fatty acid (FFA) kinetics during exercise at approximately 45% peak O(2) consumption in 12 adults. Vastus lateralis muscle was biopsied before and after 90 min of bicycle exercise; (3)H(2)O production, breath (14)CO(2) excretion and lipid oxidation (indirect calorimetry) rates were measured during exercise. RESULTS: during exercise, 8.2+/-1.2 and 8.4+/-0.7 micromol x kg(-1) x min(-1) of imTG fatty acids and plasma FFA, respectively, were oxidized according to isotopic measurements. The sum of these two values was not different (P = 0.6) from lipid oxidation by indirect calorimetry (15.4 +/-1.6 micromol x kg(-1) x min(-1)); the isotopic and indirect calorimetry values were correlated (r = 0.79, P<0.005). During exercise, imTG turnover rate was 0.32+/-0.07%/min (6.0+/-2.0 micromol of imTG x kg wet muscle(-1) x min(-1)) and plasma FFA were incorporated into imTG at a rate of 0.7+/-0.1 micromol x kg wet muscle(-1) x min(-1). The imTG pool size did not change during exercise. This pulse-chase, dual tracer appears to be a reasonable approach to measure oxidation and synthesis kinetics of imTG.

Adult↗
PubMed2001

A self-correcting indirect calorimeter system for the measurement of energy balance in small animals.

Indirect calorimetry involves measurement of CO(2) produced and O(2) consumed by an organism. These measurements are then used to calculate energy output, metabolic rate (MR), and respiratory quotient (RQ), a relative assessment of carbohydrate and lipid oxidation. By far the most difficult aspect of indirect calorimetry is measurement of O(2). Moreover, the abundance of O(2) (20.95%) relative to CO(2) (0.03%) in ambient conditions dictates that measurement errors of O(2) have greater implications on calculations of MR and RQ. Because compressed air is not feasible for use with animals in long-term experiments, changes in ambient conditions are nearly unavoidable. A self-correcting indirect calorimetry system was designed and constructed utilizing differential O(2) and CO(2) analyzers and a blank cage to monitor ambient conditions periodically. The system was validated by changing ambient O(2) and CO(2) concentrations by infusing N(2) into the system during a test butane burn. MR and RQ were largely unaffected by these changes in ambient conditions, and inclusion of a blank cage in the system accounted for slight calibration offsets. MR and RQ were measured in mice (n = 95) with and without correction for any small changes in ambient conditions measured in the blank cage. Coefficients of variation for MR and RQ were significantly decreased by taking into account ambient conditions measured in the blank cage (P < 0.001), which resulted in a 2.3% increase in precision for measurement of MR. This system will be used to more accurately assess long-term measurements of energy balance in the many murine models of leanness and obesity to gain better insights into pathophysiology and treatment of human obesity.

Animals↗