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Biomedical subjects

D Halliday

Publications and source records attributed to D Halliday.

At least 163 records · Page 9Linked to original sources
PubMed1983

The effect of enteral nutritional support on skeletal muscle protein synthesis and whole-body protein turnover in fasted surgical patients.

Whole-body and muscle protein turnover have been studied in surgical patients, before abdominal surgery after an 18-h fast, using infusion of 1-[13C]leucine. Four patients received an unmodified hospital diet and four received extra nutritional support (1800 kcal, 70 g protein) by naso-jejunal tube for 7-10 d previously. In patients who received nutritional support there were significantly greater values of whole-body protein synthesis (+42 per cent, P less than 0.05) and breakdown (+45 per cent, P less than 0.01) and muscle protein synthesis (+36 per cent, P less than 0.05) than in those who received the unmodified hospital diet.

Aged↗
PubMed1982

Muscle protein synthesis measured by stable isotope techniques in man: the effects of feeding and fasting.

1. Measurements have been made of whole-body and skeletal muscle protein synthesis in fed and fasted adults with L-[1-13C]leucine. 2. The marked increase in whole-body synthesis on feeding largely reflects the changes in protein synthesis in muscle, which doubles on feeding, compared with a 40% increase in that of the rest of the body. 3. Skeletal muscle in fed man contributes more than half to total protein synthesis occurring in the whole body.

Adult↗
PubMed1982

Effect of exercise on protein metabolism in humans as explored with stable isotopes.

Exercising for 3.75 h on a treadmill at 50% VO2 max in the fed state induced an increased excretion of 71 mg nitrogen/kg over the 18 h after exercise. However, measurements of the time course of changes in 13CO2 excretion from ingested [1-13C]leucine indicated that all of this increased nitrogen production occurs during the exercise period. Because of the reduced renal clearance and slow turnover of the urea pool, urea excretion lags behind urea production. Measurements of nitrogen flux from the plateau labeling of urinary ammonia achieved by repeated oral doses of 15N-labeled glycine indicated that the nitrogen loss resulted from an increase in protein degradation and a decrease in protein synthesis. Further studies with [1-13C]leucine indicated that a 2-h treadmill exercise induced an increase in the nitrogen loss from 5.4 to 16 mg . kg-1 . h-1 measured with a primed constant infusion of [1-13C]leucine. This resulted from a fall in whole-body protein synthesis. Glucose given at the rate of 0.88 g . kg-1 . h-1 depressed the rate of whole-body protein degradation and appeared to suppress the exercise-induced increase in nitrogen excretion. When leucine oxidation rates were measured at increasing work rates, a linear relationship between percentage of VO2 max and leucine oxidation was observed up to 89% VO2 max when 54% of the flux of leucine was oxidized. These changes may involve nonmuscle as well as muscle tissue. Thus the source of the increased nitrogen losses is probably liver. In muscle, protein degradation is actually decreased judged by methylhistidine excretion, whereas in liver, protein degradation may be increased. Also the fall in whole-body protein synthesis may reflect changes in nonmuscle tissues because in running rats protein synthesis in muscle is maintained. As far as leucine metabolism is concerned, because the increase in leucine oxidation occurs when leucine and its keto acid concentration falls, exercise must specifically activate the 2-oxoacid dehydrogenase.

Amino Acids↗
PubMed1981

Regulation of leucine metabolism in man: a stable isotope study.

Leucine catabolism is regulated by either of the first two degradative steps: (reversible) transamination to the keto acid or subsequent decarboxylation. A method is described to measure rates of leucine transamination, reamination, and keto acid oxidation. The method is applied directly to humans by infusing the nonradioactive tracer, L-[15N,1-13C]leucine. Leucine transamination was found to be operating several times faster than the keto acid decarboxylation and to be of equal magnitude in adult human males under two different dietary conditions, postabsorptive and fed. These results indicate that decarboxylation, not transamination, is the rate-limiting step in normal human leucine metabolism.

Adult↗
PubMed1981

Effect of exercise on protein turnover in man.

1. We have investigated the effects of moderate long-term exercise on protein turnover in fed man by measuring the extent of whole-body nitrogen production, the labelling of urinary ammonia from ingested [15N]glycine and plasma, muscle and urine free amino acid concentrations. 2. Judged both from nitrogen production, and from the extent of 13CO2 production from ingested L-[1-13C]leucine, exercise causes a substantial rise in amino acid catabolism. 3. Amino acids catabolized during exercise appear to become available through a fall in whole-body protein synthesis and a rise in whole-body protein breakdown. After exercise, protein balance becomes positive through a rise in the rate of whole-body synthesis in excess of breakdown. 4. Studies of free 3-methylhistidine in muscle, plasma and urine samples suggest that exercise decreases the fractional rate of myofibrillar protein breakdown, in contrast with the apparent rise in whole-body breakdown.

Adult↗
PubMed1981

The degree of conversion of alpha-keto acids to valine and phenylalanine in health and uraemia.

13C-labelled alpha-keto acid analogues of valine and phenylalanine were given by mouth and by intravenous route to three healthy and four uraemic individuals who were used as their own controls. The excretion of 13CO2 in expired air and of 13C-labelled keto acid in urine was measured together with plasma and, in some cases, intramuscular concentrations of total and 13C-labelled free valine and phenylalanine. A minimum and maximum limit of degree of conversion of these two alpha-keto acids to essential amino acids were calculated and was of the order of 25-50 per cent for both keto acids given by either route in health and uraemia.

Administration, Oral↗
PubMed1980

The use of 13-methyltetradecanoic acid as an indicator of adipose tissue turnover.

We show in this paper that 13-methyltetradecanoic acid (13-MTD) can be used as a structually labeled marker for investigating the mobility of fatty acyl chains in adipose tissue in the rat. The presence of an omega-1 methyl group allows easy quantitation by gas liquid chromatography (GLC) and permits an assessment to be made of any oxidation and chain elongation reactions with reincorporation of the label into the adipose tissue, since the iso-acyl chain is well resolved from odd or even-numbered homologous fatty acids with straight chains. The kinetics of uptake and loss of the structural label were different for adipose tissue taken from the various sites which were sampled, namely post abdominal, mesenteric, perirenal, pericardiac and subcutaneous adipose tissue as well as the epidydimal fat pads. We also report preliminary results in man which confirm that the method is applicable to human clinical studies and that 13-MTD kinetics differ for adipose tissue taken from the 3 different subcutaneous sites--waist, arm and thigh.

Adipose Tissue↗
PubMed1979

Site differences in the fatty acid composition of subcutaneous adipose tissue of obese women.

1. Adipose tissue samples were obtained by needle biopsy from three subcutaneous sites (thigh, abdomen and upper arm) in twenty-two obese women. The fatty acid composition was determined using gas-liquid chromatography and the results presented relate to eleven component fatty acids. 2. The fatty acid composition of adipose tissue obtained from the arm and abdomen was remarkably similar, with the exception of the levels of lauric acid. 3. The analyses showed that the majority of the saturated fatty acids were present in smaller proportions whilst the majority of unsaturated fatty acids were present in larger proportions in the thigh than in the two other sites. Highly significant inter-site differences were demonstrated for six of the major fatty acids and also for both the total amounts of saturated and unsaturated fatty acids and their ratios. 4. No marked differences in the fatty acid composition of adipose tissue from obese subjects were revealed during this study when compared with previously reported results obtained from 'normal-weight' subjects.

Abdomen↗
PubMed1979

A new method for measuring the body density of obese adults.

1. A new apparatus is described with which it is possible to measure the volume (and hence density) of obese patients without requiring them to immerse totally in water. Replicate measurements of subjects with 6, 23 and 38 kg body fat had a standard deviation not greater than 0.3 kg fat. 2. In nineteen obese women body fat was measured by density, total body water, and total body potassium at the beginning, and again at the end, of a period of 3--4 weeks on a reducing diet, during which they lost 5.43 (SD 1.83) kg in weight. The composition of weight loss was also estimated both by energy balance and nitrogen balance during the interval between the two measurements of body composition. 3. The estimates of fat content of the ninetten women at the start of the balance period were 45.63 (SD 14.50) kg by density, 48.07 (SD 13.88) kg by K and 47.09 (SD 13.85) kg by water. The correlation coefficient between the density and K estimate was 0.949, and for the density and water estimate it was 0.971. 4. It is concluded that measurement of density by the new method provides a convenient method for estimating body fatness, and change in fat content, which compares favourably with estimates based on total body water or total body K. However, these methods cannot be used to provide an accurate estimate of the composition of a small weight loss in an individual since deviations up to 4 kg fat occur between fat loss based on change in density and those based on the more reliable (but more tedious) energy balance method.

Adipose Tissue↗
PubMed1979

Changes in fat, fat-free mass and body water in human normal pregnancy.

Measurements of body weight, total body water and total body potassium (40K) were made serially on three occasions during pregnancy and once post partum in 27 normal pregnant women. Skinfold thickness and fat cell diameter were also measured. A model of body composition was formulated to permit the estimation of changes in fat, lean tissue and water content of the maternal body. Total maternal body fat increased during pregnancy, reaching a peak towards the end of the second trimester before diminishing. Serial measurements of fat cell diameter showed poor correlation, whilst total body fat calculated from skinfold thickness correlated well with our estimated values for total body fat in pregnancy.

Adipose Tissue↗
PubMed1979

3-Methylhistidine excretion as an index of myofibrillar protein catabolism in neuromuscular disease.

Myofibrillar protein catabolism has been calculated in a variety of neuromuscular diseases from the amount of 3-methylhistidine excreted in the urine. It was found to be significantly raised in Duchenne type muscular dystrophy, motor neurone disease, polymyositis, and thyrotoxic myopathy. In Becker type muscular dystrophy the level was slightly raised. It was normal in scapuloperoneal and limb girdle dystrophy, dystrophia myotonica, extrapyramidal disease, and multiple sclerosis. It was significantly decreased in hypothyroid myopathy.

Histidine↗
PubMed1979

Resting metabolic rate, weight, surface area and body composition in obese women.

Resting metabolic rate was measured in 22 women with varying degrees of obesity. Body composition was estimated from total body potassium and from total body water, and creatinine excretion in urine was measured over a period of three weeks while the patients were on a creatinine and creatine-free reducing diet. Resting metabolic rate was highly significantly correlated with body weight, surface area, creatinine excretion and lean body mass calculated either from potassium or water measurements (P less than 0.001). Correlation with adipose tissue was less strong, and when multiple regression of both fat and lean on metabolic rate was performed, the relationship was seen to depend mostly on the mass of lean rather than adipose tissue. In obese people the water content of fat-free tissue is greater than that in normal subjects, so it is not valid to assume that fat content can be calculated accurately from a measurement of total body water.

Adipose Tissue↗