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G Livesey

Publications and source records attributed to G Livesey.

At least 55 records · Page 3Linked to original sources
PubMed1988

Theory and validity of indirect calorimetry during net lipid synthesis.

A critical examination is made of the validity of indirect calorimetry when the nonprotein respiratory quotient is greater than 1. The different published stoichiometries for lipogenesis from glucose are excluded as a source of uncertainty in the interpretation of gaseous exchange measurements. The validity of indirect calorimetry is proved independently by an algebraic approach which, in contrast to previous attempts, makes minimal assumptions about stoichiometries. Although equations relating the respiratory quotient to the heat equivalent of oxygen are found valid, there is uncertainty in using these equations to predict accurately carbohydrate utilization and fat oxidized or synthesized. Reference tables interrelating respiratory data, the heat equivalent of oxygen, and net fuel utilization or synthesis for specified fuels are provided. A suggested framework for calculating energy expenditure in terms of ATP gain is given as an appendix.

Adipose Tissue↗
PubMed1988

Estimation of energy expenditure, net carbohydrate utilization, and net fat oxidation and synthesis by indirect calorimetry: evaluation of errors with special reference to the detailed composition of fuels.

Sources of error in the interpretation of respiratory data are evaluated and reviewed with special reference to the detailed composition of foods. Estimates of fuel utilization or synthesis are 12-fold more sensitive to errors in the nonprotein respiratory quotient than is the heat equivalent of oxygen. Estimates of protein oxidation from nitrogen excretion can be in error from +14 to -39% of the true value. Heat equivalents of oxygen, respiratory quotients, and urinary nitrogen-to-oxygen conversion ratios are considered for 60 artificial and 101 conventional food proteins, 36 artificial and 125 conventional food fats, and the different carbohydrates contained in these foods. It is concluded that there is considerable uncertainty when the mix of fuels utilized is assessed accurately. Accuracy is best within 5% of the true values. This analysis is completed with descriptions of some physiological sources of error in an appendix.

Algorithms↗
PubMed1987

The energy cost of triglyceride-fatty acid recycling in nonobese subjects after an overnight fast and four days of starvation.

The basal blood glycerol concentration was determined and the rate of glycerol turnover was assessed by a nonradioactive infusion technique in six healthy nonobese adults after an overnight fast and again after four days of total starvation. Simultaneously, estimates of total energy expenditure and net fat oxidation were made from measurements of oxygen consumption, carbon dioxide production, and urinary nitrogen excretion. The data were combined to provide quantitative estimates of the activity of the triglyceride/fatty acid cycle. The basal concentration of glycerol in venous blood rose from a mean value of 54 +/- 8 mumol/L (SEM) before starvation to 154 +/- 5 mumol/L on day 4 of starvation. Glycerol turnover rates correlated well with the basal blood glycerol concentration (r = .95) and increased from a mean value of 115 +/- 17 mumol/min before starvation (equivalent to mobilization of about 3.95 kJ triglyceride/min) to 304 +/- 20 mumol/min (equivalent to mobilization of about 18.41 kJ/min). The estimated rate of net fat oxidation was 3.00 +/- 0.47 kJ/min before starvation and 4.00 +/- 0.14 kJ/min on day +4 of starvation. The rate of triglyceride energy recycling or rate of deposition of triglyceride energy into fat stores was calculated from the difference in the rate of fat energy mobilization and the rate of energy released during net fat oxidation. The values were found to be 0.94 +/- 0.26 kJ/min before starvation and 6.29 +/- 0.54 kJ/min on day +4 of starvation.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1987

The metabolizable energy value of Polydextrose in a mixed diet fed to rats.

The digestible energy (DE) and metabolizable energy (ME) values of a commercial Polydextrose product and the polymer that it contained were determined by metabolic energy balance in male Wistar rats and compared with values obtained by radiochemical balance using a radiochemical analogue. The energy values of the whole preparations and of the polymer fractions were estimated. In the energy-balance study of 6 d duration, 100 g maize starch/kg control diet were replaced by Polydextrose to provide a test diet. Polydextrose had no significant effects on food intake, body-weight gain, digestibility of nitrogen and N retention but significantly increased the water consumption to 143% of the control value (P less than 0.05) and the water content of fresh faecal pellets from 548 (SE 10) to 646 (SE 15) g/kg wet weight (P less than 0.01). By energy balance the DE in the Polydextrose product and in the polymer that it contained were 13.5 and 12.8 (SE 1.9) kJ/g respectively. The corresponding ME values were 12.7 and 12.1 (SE 1.8) kJ/g respectively. These values were higher (P less than 0.05) than the corresponding values obtained by the radiochemical balance procedure: DE 8.8 and 8.6 (SE 0.4) kJ/g polymer respectively and ME 8.0 and 7.8 (SE 0.5) kJ/g polymer respectively. These findings indicate relatively high energy values for Polydextrose by comparison with previously published values and illustrate a potential difficulty when using energy values obtained by certain radiochemical methods to estimate the energy values of a mixed diet given to rats. Several alternative explanations of the discrepancies are advanced.

Animals↗
PubMed1987

Food energy values of dietary fibre components and decreased deposition of body fat.

The effects of guar gum (GG) and solka floc cellulose (SF) on food intake, stomach emptying and body fat deposition in rats were assessed together with their food energy values. Voluntary food intake in meal-fed rats (ca 100 g, male Wistar kept at 21C) was depressed initially by 40 per cent on adding 10 g GG to 100 g fibre free (FF) semisynthetic diet. This effect was not sustained, intake doubling within 15 d. Similar effects were not observed with SF. In pair-fed animals neither GG nor SF affected the rate of stomach emptying after 28 days. Digestible energy (DE) intake per rat over the 28 days was GG diet = 4616, SF diet = 4410, FF diet = 4373 kJ but body fat was lower in GG (25%) and SF (16%) fed rats than in FF fed rats. The calculated DE values of the fibre components were 10.1 kJ/g GG and 1.5 kJ/g SF (sem 1 kJ/g). After including body fat into the equations for metabolizable energy, the energy values were -7.1 kJ/g GG and -4.8 kJ/g SF (sem 2 kJ/g). This is equivalent to an increased energy expenditure of 17.2 kJ/g GG and 6.3 kJ/g SF. For GG an increased intestinal mucosal mass and cell turnover explains part of the apparent increase in energy demand. Our overall conclusion is that under certain circumstances and with regard to fat deposition some fibre components can be attributed negative energy values.

Adipose Tissue↗
PubMed1985

Food energy values of artificial feeds for man.

The gross and metabolizable energy values of artificial enteral and parenteral feeds have been calculated from detailed composition data for amino acid, fatty acid, saccharide and other oxidizable substrates and compared with similar values calculated for conventional foods. The background to the derivation and application of calorie conversion factors is briefly reviewed. There is evidence of widespread inappropriate application of calorie conversion factors for carbohydrates and amino acid mixtures. Appropriate digestibility or availability factors for the oxidizable fractions of artificial feeds is discussed for normal adult man and the intrinsic difficulty of obtaining availability values for subjects with varying types of malabsorption or urinary and tissue losses is emphasized. The nitrogen:protein conversion ratio and the availability of energy at a biochemical level (i.e. net ATP yield per calorie) is also considered. Finally, a more uniform and appropriate approach to calculating energy values for artificial feeds for the purposes of labelling, product description and estimating energy intake of patients is called for.

Journal Article↗
PubMed1985

Alanine and glutamine release from the human forearm: effects of glucose administration.

The effect of glucose infusion alone (175 mg/kg bolus dose followed by 4 mg min-1 kg-1 for 70 min) and in combination with forearm exercise on the exchange of glucose, alanine, glutamine and other metabolites and amino acids across forearm muscle was studied in six healthy individuals after an overnight fast. Arterial and deep venous blood was sampled and a mercury strain gauge plethysmograph was used to measure forearm blood flow. Total body energy expenditure and net glucose and fat oxidation were assessed by indirect calorimetry. The infusion of glucose increased the mean arterial blood glucose concentration from 4.95 +/- 0.19 (SEM) to a plateau of 9.6-9.9 mmol/l (P less than 0.01). The arterial blood concentrations of alanine and glutamine were not significantly altered but that of lactate increased from 0.50 +/- 0.02 to 0.65 +/- 0.05 mmol/l (P less than 0.02) and that of pyruvate increased from 46 +/- 5 to 72 +/- 6 mumol/l (P less than 0.01). In the resting state glucose administration did not significantly affect the lactate/pyruvate ratio in arterial or venous blood. Arterial plasma insulin concentration increased four-fold and total ketone body concentration decreased two- to three-fold. After glucose administration, alanine release was suppressed (in all subjects) from a mean value of 153 +/- 22 to 57 +/- 16 nmol min-1 100 ml-1 of forearm (P less than 0.02) whereas that of glutamine was not significantly affected (160 +/- 30 to 143 +/- 29 nmol min-1 100 ml-1 of forearm). Lactate release, like that of alanine, decreased, whereas pyruvate was slowly released in the basal state and was taken up during glucose administration (P less than 0.01). These changes were associated with a decrease in the uptake of total ketone bodies to one-fifth to one-tenth of that in the basal state. The net amino acid balance across the forearm muscle bed was negative throughout the study but decreased from a mean value of -567 in the basal state to -300 nmol min-1 100 ml-1 of forearm after glucose administration for 60 min. This was predominantly due to decreased release of effluxing amino acids, particularly alanine.(ABSTRACT TRUNCATED AT 400 WORDS)

Adult↗
PubMed1985

Differences in intestinal protein synthesis and cellular proliferation in well-nourished rats consuming conventional laboratory diets.

Male Wistar rats (100 g) were given a commercial pellet feed or a semi-synthetic diet ad lib. Although the pellet-fed group grew slightly faster than the other group during the early part of the feeding period, there was no significantly difference between the final weights of the groups. The fractional rates of protein synthesis in jejunum, proximal ileum and liver were measured by a technique based on the determination of L-[4-3H]phenylalanine incorporation over a short time period. Protein synthesis was higher in both jejunum and ileum of the pellet-fed rats compared with those eating the semi-synthetic diet, but there was no difference between the rates of protein synthesis measured in the livers of the groups. The rate of mucosal cell division was significantly faster in the ileal mucosa of the pellet-fed group compared with the other group, and there were significant differences in some aspects of mucosal morphology. The maintenance of higher rates of cell turnover and protein synthesis in animals given a commercial pellet feed is unexplained, but it may be related to the presence of non-absorbable polysaccharides or other complex plant materials in the pellet feed.

Animal Feed↗
PubMed1985

Mitochondrial uncoupling and the isodynamic equivalents of protein, fat and carbohydrate at the level of biochemical energy provision.

The effects of uncoupling of mitochondrial oxidative phosphorylation on the efficiency of energy conservation during oxidation of amino acids, fatty acids, glycerol, glucose and 101 food proteins have been examined in order to compare how uncoupling at coupling site 1 affects energy yields compared with uncoupling at sites 2 + 3 and uncoupling by proton leakage. The effects of uncoupling by each mechanism on the isodynamic equivalents of carbohydrate, fat and protein at the level of cytoplasmic ATP yield have been estimated. Energy conservation during amino acid oxidation decreased relative to that for glucose as uncoupling by all three mechanisms increases. This effect is least when uncoupling is at site 1 and is associated with a fall in the isodynamic equivalent for protein:glucose of 4% maximally, and a fall in the cytoplasmic ATP yield for glucose of 25% (15-30%) when accounting for uncertainty in the choice of proton stoichiometries). Variation in the efficiency of energy conservation for the different amino acids is large for both highly coupled and uncoupled mitochondria but the range of efficiencies for the oxidation of 101 food proteins is relatively small (less than 6% of the mean) for a tightly coupled system. This range increases absolutely (minimally fourfold) and relatively (minimally 44% of the mean value) with severely uncoupled mitochondria but is nearly constant (changes by less than 1% relative to the mean) within the probable physiologically relevant range of uncoupling in the whole body and in the full range of uncoupling at site 1.(ABSTRACT TRUNCATED AT 250 WORDS)

Adenosine Triphosphate↗
PubMed1985

Intestinal cellular proliferation and protein synthesis in zinc-deficient rats.

Immature male Wistar rats were given a low-zinc semi-synthetic diet (2 mg Zn/kg) for 28 d. Control groups received a similar diet supplemented with 58 mg Zn/kg either ad lib. or in amounts matched to the consumption of the Zn-deficient group. Rates of growth, food consumption and small intestinal length were significantly reduced in the Zn-depleted rats. Zn deficiency in the rat was associated with a reduction in the ratio, crypt: villus and a lower rate of crypt cell division in the jejunum. This resulted in a substantial decrease in the net influx of new cells into the villi of the Zn-deficient animals compared with controls. The fractional rates of protein synthesis in jejunal mucosa were measured by a technique based on the determination of L-[4-3H]phenylalanine incorporation. There was no evidence of a decline in the protein synthetic rate in total mucosa from Zn-deficient rats. It is suggested that a reduction in cell influx into the villi may be responsible for the morphological and functional changes observed in the small intestine of rats fed on a low-Zn diet.

Animals↗
PubMed1984

The energy equivalents of ATP and the energy values of food proteins and fats.

Heats of combustion and energy equivalents of cytoplasmic ATP have been estimated for glucose, 101 food proteins and 116 food fats based on amino acid and fatty acid composition data from food composition tables and the heats of combustion and energy equivalents of cytoplasmic ATP of each individual amino acid, fatty acid, glycerol and glucose. The isodynamic equivalents of carbohydrate, fat and protein at the biochemical level have been investigated. Heats of combustion of food proteins and fats derived from compositional data were within 1% of published values obtained by calorimetry. Cytoplasmic ATP equivalents for glucose, fat and protein range from 9.0 to 14.7, 8.6 to 14.6 and 6.4 to 13.2 mol cytoplasmic ATP/MJ of metabolizable energy respectively, depending on the choice of mitochondrial proton stoichiometries for these estimations. The range is extended further when considering the level and type of mitochondrial 'uncoupling'. Isobioenergetic relationships between the efficiencies of glucose (G) and fat (F) (F = 1.05 G - 0.9) and glucose and protein (P) (P = G(1.02 - 0.19 f) - (1.8 + 0.5 f] energy conversions (where f is the fraction of protein oxidized via gluconeogenesis) were obtained and were essentially independent of the choice of mitochondrial proton stoichiometry and the level and type of uncoupling of oxidative phosphorylation. Potential errors in previous estimates of ATP yield from protein are shown to be as much as -17.6 to greater than 118%; accounting for the efficiency of mitochondrial oxidative phosphorylation narrows this to between -7.9 and 17.4% and accounting for the fraction of protein oxidized via gluconeogenesis limits this further to between -7.9 and 11.1%. Remaining uncertainty is attributed mostly to lack of knowledge about the energy cost of substrate absorption from the gut and transport across cell membranes. Coefficients of variation (cv) in the cytoplasmic ATP yield/g protein and /g protein nitrogen for the 101 food proteins were large (0.033 and 0.058 respectively). This is attributed mostly to variation in the metabolizable heats of combustion (cv 0.033 and 0.053 respectively) and to a much smaller extent in the efficiency with which cytoplasmic ATP equivalents are generated/MJ of metabolizable energy (cv 0.01). It is concluded that the current understanding of biochemical energy transduction is sufficient to permit only a crude estimate of the energy equivalents of cytoplasmic ATP but that these equivalents vary by less than 5% between both different food proteins and different food fats.(ABSTRACT TRUNCATED AT 400 WORDS)

Adenosine Triphosphate↗
PubMed1983

The fate of homologous 125I-labelled immunoglobulin G within rat visceral yolk sacs incubated in vitro.

When 125I-labelled rat IgG (immunoglobulin G) is incubated in vitro with visceral yolk sacs from 17.5-day-pregnant rats, the protein is readily degraded. The major radioactive digestion product that accumulates in the medium is [125I]iodo-L-tyrosine. When rotenone (10 microM) is also present in the incubation medium, the rate of digestion of IgG is inhibited to the same extent as the rate of pinocytosis of 125I-labelled polyvinylpyrrolidone. Proteolysis is likewise inhibited when either NH4Cl (30 mM) or leupeptin (30 micrograms/ml) is present in the medium. The above findings strongly suggest that the observed proteolysis occurs within lysosomes. Normally, yolk sacs that have been exposed in vitro to radiolabelled substrates release radioactivity slowly when the tissue is re-incubated, unless the substrate can be degraded within lysosomes and released in the form of low-molecular-weight hydrolysis products. However, in such experiments 125I-labelled rat IgG shows quite exceptional behaviour in being rapidly released in an apparently intact form (as well as being degraded). If an agent that inhibits pinocytosis (e.g. rotenone or 2,4-dinitrophenol) is present in the incubation medium during exposure of the tissue to 125I-labelled rat IgG, it abolishes release of macromolecular radioactivity on re-incubation of the tissue. Enhanced tissue accumulation of 125I-labelled rat IgG, induced by the presence of leupeptin in the medium during the uptake phase, resulted in no concomitant increase in the amount of 125I-labelled IgG released in macromolecular form on re-incubation of the tissue. These findings indicate that the observed rapid release of 125I-labelled IgG is unlikely to represent release from lysosomes and is more compatible with release from a separate class of vesicle that does not fuse with lysosomes.

2,4-Dinitrophenol↗
PubMed1983

Bovine serum albumin decreases 4-methyl-2-oxovalerate utilization by isolated rat hepatocytes.

Binding of 4-methyl-2-oxo[1-14C]valerate to defatted bovine serum albumin inhibited the utilization of this 2-oxo acid by fed-rat hepatocytes in vitro. With 0-50g of albumin/l in the presence of 0.05mM 2-oxo acid or on increasing the 2-oxo acid concentration from 0 to 2mM in the presence of 26g of albumin/l, the extent of inhibition was essentially dependent on the change in the free 2-oxo acid concentration. Intrahepatocyte 4-methyl-2-oxo[1-14C]valerate concentrations were similar to extracellular free 2-oxo acid concentrations, suggesting equilibration so that the plasma membrane appears not to be rate-limiting for the utilization of this substrate by the isolated liver cells.

Animals↗
PubMed1982

Binding of branched-chain 2-oxo acids to bovine serum albumin.

1. Binding of branched-chain 2-oxo acids to defatted bovine serum albumin was shown by gel chromatography and equilibrium dialysis. 2. Equilibrium-dialysis data suggest a two-side model for binding in Krebs-Henseleit saline at 37 degrees C with n1 = 1 and n2 = 5. Site association constants were: 4-methyl-2-oxovalerate, k1 = 8.7 x 10(3) M-1, k2 = 0.09 x 10(3) M-1; 3-methyl-2-oxovalerate, k1 = 9.8 x 10(3) M-1, k2 = 0.08 x 10(3) M-1; 3-methyl-2-oxobutyrate, k1 = 1.27 x 10(3) M-1, k2 = less than 0.05 x 10(3) M-1. 3. Binding of 4-methyl-2-oxovalerate to defatted albumin in a phosphate-buffered saline, pH 7.4, gave the following thermodynamic parameters: primary site delta H0(1) = -28.6kJ . mol-1 and delta S0(1) = -15.2J . mol-1 . K-1 (delta G0(1) = -24.0kJ . mol-1 at 37 degrees C) and secondary sites delta H0(2) = -25.4kJ . mol-1 and delta S0(2) = -46.1J . mol-1 . K-1 (delta G0(1) = -11.2kJ . mol-1 at 37 degrees C). Thus binding at both sites is temperature-dependent and increases with decreasing temperature. 4. Inhibition studies suggest that 4-methyl-2-oxovalerate may associate with defatted albumin at a binding site for medium-chain fatty acids. 5. Binding of the 2-oxo acids in bovine, rat and human plasma follows a similar pattern to binding to defatted albumin. The proportion bound in bovine and human plasma is much higher than in rat plasma. 6. Binding to plasma protein, and not active transport, explains the high concentration of branched-chain 2-oxo acids leaving rat skeletal muscle relative to the concentration within the tissue, but does not explain the 2-oxo acid concentration gradient between plasma and liver.

Animals↗
PubMed1982

Heterogeneity of binding site for adsorptive pinocytosis of simple proteins by rat yolk sacs.

1. When rat yolk sacs were incubated in serum-free medium 199, the 125I-labelled forms of both formaldehyde-treated bovine serum albumin and ribonuclease were captured far more rapidly than 125I-labelled polyvinylpyrrolidone. Extensive adsorption of these proteins to the plasma membrane is the main cause of this effect. 2. Quantitative analysis of the adsorptive-phase pinocytosis of these two proteins showed curved Hofstee plots, suggesting either the presence of multiple classes of binding site on the surface of pinocytically-active yolk-sac cells or a single class of binding site that exhibits negative cooperativity in the binding of these proteins. The values of Km were similar, ranging over 0.6-11.8 microM for 125I-labelled ribonuclease and over 0.31-4.7 microM for formaldehyde-treated 125I-labelled albumin. 3. Competitive uptake studies, in which tracer amounts of each of the 125I-labelled proteins were ingested from serum-free medium containing a higher concentration of one of a series of unlabelled proteins, revealed marked differences between the two radiolabelled proteins. These findings suggest that formaldehyde-denatured albumin is captured by binding to hydrophobic binding sites on the plasma membrane whereas ribonuclease is captured by binding to negatively charged sites.

Adsorption↗
PubMed1981

Rates of pinocytic capture of simple proteins by rat yolk sacs incubated in vitro.

The rates of pinocytic uptake of a number of small 125I-labelled simple proteins (insulin, ribonuclease A and lysozyme) by rat yolk sacs incubated in vitro were determined both before and after treating these proteins with reagents that are known to increase the rate of capture of 125I-labelled bovine serum albumin. Uptake of the untreated forms of all three proteins was extremely rapid, indicating that adsorptive pinocytosis is the principal mechanism by which yolk-sac cells capture these simple proteins, but these rates show no simple correlation with molecular charge. In contrast with albumin, the rates of uptake of treated proteins were either unchanged or lower than that of the corresponding untreated protein preparations; polymeric forms of 125I-labelled lysozyme larger than dimers were ingested at rates significantly lower than that of the monomer.

Animals↗
PubMed1981

Effects of microbial proteinase inhibitors on the degradation of endogenous and internalized proteins by rat yolk sacs.

1. The effects of leupeptin and other microbial proteinase inhibitors were measured in rat yolk sacs on the uptake and degradation of formaldehyde-denatured 125I-labelled bovine serum albumin as well as on the degradation of 3H-labelled endogenous protein. 2. Leupeptin, at concentrations between 1 and 100 micrograms/ml, inhibits the degradation of added albumin without affecting pinocytic uptake. Accordingly large amounts of undegraded albumin accumulate within the tissue. 3. Removal of leupeptin produces a rapid recovery of the capacity to degrade albumin. 4. Endogenous protein degradation is rapidly inhibited by leupeptin, but to a far lesser extent than the breakdown of albumin. However, the inhibition is only slightly reversed on removal of leupeptin. 5. Degradation of both albumin and endogenous protein in intact yolk sacs is inhibited by the microbial proteinase inhibitors in the order: leupeptin greater than antipain greater than chymostatin; elastatinal, pepstatin and bestatin are ineffective. 6. Similar results are found when albumin is incubated in yolk-sac homogenates at pH 4 with the inhibitors. 7. The marked inhibitory effects of leupeptin, antipain and chymostatin suggest that cathepsin B and possibly cathepsin L participate in the degradation of 125I-labelled albumin in yolk sacs. By comparison, the smaller inhibitory effects of the proteinase inhibitors on endogenous protein breakdown imply a minor role of lysosomal cathepsins in this process.

Animals↗