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T Preston

Publications and source records attributed to T Preston.

At least 91 records · Page 5Linked to original sources
PubMed1990

Early experiences with the stable isotope method in children.

A new technique to estimate water uptake by the gastrointestinal tract was tested in infants undergoing elective surgery. Patients were randomly allocated to receive either sterile water or a glucose-electrolyte solution labeled with the stable isotope H2O18. After absorption, the isotopic O18 comes to rapid equilibrium with plasma bicarbonate and subsequently appears in the breath as C18O2. Breath and blood samples were collected at five-minute intervals after administration of the test solution. Mass spectrometric analysis enabled detection of isotopic O18 enrichment at parts per million levels in blood and in breath CO2. Enrichment of blood and breath C18O2 above baseline levels is detectable within five minutes of administration of the labeled test solution and rises to a plateau between 30 and 90 minutes. It is hypothesized that the rate of increase of enrichment is proportional to the unidirectional flux of water from lumen to gut.

Anesthesia↗
PubMed1990

Body composition and exercise in racing pigeons.

Exercise-related changes in body protein 'turnover' and in the absolute amounts of body protein were studied in racing pigeons. Whole body radioactivity was followed in racing and control (limited exercise) birds after protein labelling by the injection of 75Seselenomethionine. Because of re-utilisation of the label this does not give a true picture of body protein turnover but the comparative data suggested an increased turnover in racing compared to control birds. Carcase analysis on a group of pigeons demonstrated a water content for lean body mass of 72.7 per cent +/- 3.54. Lean body mass and exchangeable body potassium were used as indices of total body protein in a group of pigeons participating in an endurance race (15 + hours of flying). The results indicated that no body protein had been used as an energy source. These findings are compatible with the presence in pigeons of a small labile pool or pools of protein. The presence and characteristics of such pools remains to be determined.

Animal Nutritional Physiological Phenomena↗
PubMed1990

A study of protein turnover in preterm neonates using 15N enrichment of urinary ammonia.

Hydrolysed yeast protein labelled with 15N was used to measure protein turnover, protein synthesis and protein breakdown in preterm infants. The yeast tracer was given as a bolus intragastric dose and protein turnover was determined from the 15N enrichment of urinary ammonia over known periods of about 12 h. Six boys (birthweight less than 1500 g) with gestation of 27-35 weeks were studied either two or three times at post-natal ages ranging from 13 to 54 d. There was no significant correlation between protein turnover with increasing post-conceptional or post-natal age. There was considerable interindividual variation and reproducibility varied between different infants. We suggest that this is a convenient non-invasive technique for monitoring serially nitrogen and protein metabolism in infants and that as such it merits further assessment.

Ammonia↗
PubMed1989

Analysis of 18O enrichment in biological fluids by continuous flow-isotope ratio mass spectrometry.

A novel method is described for the analysis of 18O in urine by continuous flow-isotope ratio mass spectrometry (CF-IRMS), after sample equilibration with CO2. The method is shown to be fast, precise and accurate and therefore facilitates studies of total body water and water turnover in the clinical field. The method uses existing CF-IRMS instrumentation with minor hardware modification which does not compromise routine analysis of 13C and 15N. This method emphasizes the versatility of CF-IRMS and thus its economy for the biomedical research group using stable isotope tracers.

Humans↗
PubMed1989

15N tracer studies of protein metabolism in low birth weight preterm infants: a comparison of 15N glycine and 15N yeast protein hydrolysate and of human milk- and formula-fed babies.

Nitrogen flux and protein synthesis and degradation were estimated using a single oral bolus of 15N glycine or 15N yeast protein hydrolysate and measuring the 15N enrichment of urinary ammonia in five low birth wt infants fed a low birth wt formula and in six who were receiving their own mother's breast milk. Results derived from using 15N-glycine and 15N-yeast hydrolysate tracers in a randomized crossover study in 10 studies on seven infants showed, with one exception, higher turnover rates and more interindividual variation with the 15N yeast. Both tracers showed good reproducibility in two infants who had repeated studies. Although wt gain was similar in both groups, nitrogen intake and retention were greater (p less than 0.01) in the formula-fed group. Mean nitrogen turnover was similar in both groups, but there was a greater variance in the human milk-fed group which also had a greater nitrogen turnover/U absorbed nitrogen (p less than 0.025) and a lower excretion of nitrogen/U flux.

Humans↗
PubMed1988

Influence of whole body protein turnover rate on resting energy expenditure in patients with cancer.

Whole body protein turnover and resting energy expenditure are measured simultaneously in weight stable and weight losing patients with lung (n = 22) or colorectal cancer (n = 38). These results were compared with those from weight stable and weight losing non-cancer controls (n = 22). Rates of whole body protein turnover were calculated from the plateau isotopic enrichment of urinary ammonia and urea following a primed, continuous, 24-h infusion of [15N]glycine. Resting energy expenditure was measured by indirect calorimetry. All groups of cancer patients had significantly elevated rates of whole body protein turnover (P less than 0.05) and synthesized, on average, 1.9 g/kg/day more protein compared with weight stable non-cancer controls. In contrast, the resting energy expenditure of cancer patients and controls was similar. Moreover, there was no correlation between individual rates of whole body protein turnover. Thus, although cancer patients had rates of whole body protein turnover which were 50-70% greater than controls, this did not result in a measurable increase in resting energy expenditure. The assumption that elevation of whole body protein turnover or resting energy expenditure causes weight loss in cancer patients must be an oversimplification. An acute phase protein response was observed in the majority of cancer patients. Although the presence of such an inflammatory response did not correlate with the rate of whole body protein turnover, the role of inflammatory mediators in the pathogenesis of disturbed protein metabolism in cancer patients merits further investigation.

Aged↗
PubMed1988

Rapid sample throughput for biomedical stable isotope tracer studies.

Typical 13C or 15N tracer studies generate large numbers of samples. Instrumentation capable of rapid automated analysis is therefore of importance as a practical alternative to conventional isotope methodology. Although biomedical sample nature is diverse, experimenters often require analysis of substrates and products of particular biochemical pathways. Clearly, reaction products can contain considerably less isotope tracer than precursors. Analytical techniques thus need to accommodate samples of widely varying nature, size and isotope enrichment. In the clinical field, where stable isotopes are increasingly used to study protein, carbohydrate and fat metabolism, analysis of the isotope ratio of a substrate infused into the plasma and a product of its metabolism is often required. Conventional analytical approaches demand access to two mass spectrometers: isotope ratio mass spectrometry (IRMS) for isotope analysis of the relatively large concentrations of low-enrichment metabolic product, and gas chromatography/mass spectrometry (GC/MS) for analysis of the infused substrate often present at high enrichment but low concentration offers a practical alternative to the conventional approaches that is rapid and automatic. In addition to providing a considerably less complex and costly alternative to conventional instrumentation, a single CF-IRMS instrument can also analyse small quantities of low-enrichment metabolites with superior performance than either of the alternative approaches. CF-IRMS is illustrated using results from constant-infusion studies in human protein and fat metabolism which require measurement of the isotope enrichment in submicromolar quantities of plasma substrates together with analysis of larger quantities of their oxidation products, urinary nitrogen and breath CO2.

Ammonia↗
PubMed1988

Cancer cachexia: influence of systemic ketosis on substrate levels and nitrogen metabolism.

The aim of this study was to determine whether a ketogenic diet could decrease nitrogen losses in cachectic cancer patients and at the same time reduce the supply of glucose for tumor energy metabolism. Five patients with malignant disease and severe weight loss (mean 32%) were fed via a fine bore nasogastric tube. A normal diet was given for 6 d and this was followed by 7 d of an isonitrogenous, isocaloric, ketogenic diet. Both diets were well tolerated. At 7 d the mean ketone body concentration in the blood of patients fed the ketogenic diet was 1.21 +/- 0.33 mM. This ketosis was associated with a significant reduction of the concentration in blood of glucose, lactate, and pyruvate (p less than 0.05). There was, however, no significant alteration in host N balance or whole-body protein synthesis, degradation, or turnover rates. Whether the change from glucose- to fat-derived energy substrates might reduce tumor growth rates in the long term remains to be determined.

Acidosis↗
PubMed1988

Comparison of the Quantum II, API Yeast Ident, and AutoMicrobic systems for identification of clinical yeast isolates.

The Quantum II Yeast Identification System (Abbott Laboratories) is a microprocessor-based spectrophotometric system for identification of clinical yeast isolates within 24 h. We compared the Quantum II system with the API Yeast Ident (Analytab Products) and the AutoMicrobic System Yeast Biochemical Card (AMS-YBC; Vitek Systems, Inc.) for the identification of 221 clinical yeast isolates, including 120 common clinical isolates (Candida albicans, C. tropicalis, C. parapsilosis, Torulopsis glabrata, and Cryptococcus neoformans) and 101 relatively uncommon clinical isolates. The API 20C (Analytab) was used as the reference system. The Quantum II and AMS-YBC systems correctly identified 181 (82%) and 184 (83%) isolates, respectively, whereas the Yeast Ident system correctly identified 132 (60%) isolates. Of the 120 common clinical isolates, 113 (94%) were correctly identified by Quantum II, 103 (86%) were correctly identified by AMS-YBC, and 83 (69%) were correctly identified by Yeast Ident. Of the 101 uncommon clinical isolates tested, 68 (67%) were correctly identified by Quantum II, 81 (80%) were correctly identified by AMS-YBC, and 49 (49%) were correctly identified by Yeast Ident. The overall accuracy of the Quantum II, AMS-YBC, and API Yeast Ident was not sufficient to recommend any of these systems for routine use in the clinical microbiology laboratory without substantial expansion of the respective data bases.

Diagnostic Errors↗
PubMed1987

Effects of the amount and quality of dietary protein on nitrogen metabolism and protein turnover of pigs.

1. The interrelation between protein accretion and whole-body protein turnover were studied by varying the quantity and quality of protein given to growing pigs. 2. Diets with 150 or 290 g lysine-deficient protein/kg were given in hourly meals, with or without lysine supplementation, to female pigs (mean weight 47 kg). 3. After the animals were adapted to the diets, a constant infusion of [14C]urea was given intra-arterially for 30 h, during the last 6 h of which an infusion of [4,5-3H]leucine was also infused at a constant rate. At the same time, yeast-protein labelled with 15N was given in the diet for 50 h. 4. The rate of urea synthesis was estimated from the specific radioactivity (SR) of plasma urea. The rate of leucine flux was estimated from the SR of plasma leucine. The irrevocable breakdown of leucine was estimated from the 3H-labelling of body water. Total N flux was estimated from the 15N-labelling of urinary urea. 5. Addition of lysine to the low-protein diet significantly increased N retention, with a substantial reduction in leucine breakdown, but there was no significant change in the flux of leucine or of total N. 6. Increasing the quantity of the unsupplemented protein also increased N retention significantly, with concomitant increases in leucine breakdown and in the fluxes of leucine and of total N. 7. It is concluded that a doubling of protein accretion brought about by the improvement of dietary protein quality is not necessarily associated with an increased rate of whole-body protein turnover.

Amino Acids↗
PubMed1986

Body composition of Atlantic salmon (Salmo salar L.) studied by neutron activation analysis.

This paper describes the measurement of whole body Ca, Cl, K, N, Na, O and P in Atlantic salmon parr, adults and kelts by neutron activation analysis (NAA). This technique is based on counting the specific gamma activity in samples which is present naturally or is produced by neutron irradiation. Body composition (fat, mineral, protein and water) are estimated from these data. NAA has advantages over chemical methods with the potential for in vivo measurements. Anthropogenic 137Cs was found in sea-water (SW) salmon but not found in the freshwater (FW) stages (parr and kelts). Presence of this isotope in fish caught in FW indicates recent SW residence.

Aging↗
PubMed1986

In vitro inhibitory and bactericidal activity of cefpiramide and seven antipseudomonal agents against Pseudomonas aeruginosa.

Cefpiramide was tested against 493 clinical isolates of Pseudomonas aeruginosa and the results of minimal inhibitory concentration, minimal bactericidal concentration, bactericidal rate, and time-kill synergy studies were compared with those obtained with seven other antipseudomonal agents. The minimal inhibitory concentrations of cefpiramide for P. aeruginosa were comparable to all of the agents tested. Minimal bactericidal concentration results were generally within one twofold dilution of the minimal inhibitory concentration values for all agents tested. Bactericidal rate studies showed that at concentrations of four times the minimal inhibitory concentration, all of the agents produced rapid killing. Results of time-kill synergy studies showed a marked synergistic interaction between cefpiramide and each of three aminoglycosides, gentamicin, tobramycin, and amikacin. These results suggest that cefpiramide may be useful in the therapy of infections due to P. aeruginosa.

Amikacin↗
PubMed1985

Failure of systemic ketosis to control cachexia and the growth rate of the Walker 256 carcinosarcoma in rats.

The Walker 256 carcinosarcoma was shown to lack the enzyme 3-ketoacid CoA transferase. This suggests that ketone bodies cannot be used as a major substrate for the energy metabolism of this tumour. Systemic ketosis (1-2 mM acetoacetate plus 3-hydroxybutyrate) was induced both in tumour-bearing and in non-tumour-bearing rats with a diet containing 70% medium chain triglyceride. However, in rats bearing the Walker 256 tumour, this dietary ketosis did not reduce the tumour growth rate nor did it prevent the subsequent decrease in host body weight. Host body nitrogen losses were similarly unaffected. The ketosis induced in tumour bearing rats was shown to be abnormal since the blood glucose concentration of ketotic, tumour-bearing rats was significantly higher compared with that of ketotic non-tumour bearing rats (5.2 +/- 0.4 mM cf 3.4 +/- 0.6 mM, P less than 0.01). These results may partly explain why systemic ketosis failed to alter the growth and cachexia induced by the Walker 256 carcinosarcoma.

Acetyl-CoA C-Acetyltransferase↗
PubMed1985

A comparison of body protein determination in rats by in vivo neutron activation and carcass analysis.

Total body nitrogen (TBN) was determined in 16 rat carcasses ranging in weight from 55 to 550 g, by non-destructive 14 MeV neutron activation analysis (NAA). The rat carcasses were subsequently analysed for TBN by Kjeldahl digestion, for total body water (TBW) by loss of weight after freeze-drying and for body fat by adiabatic bomb calorimetry after subtraction of protein energy. TBN results by the two methods were in good agreement, the precision by NAA (coefficient of variation = 1.5%) being superior to that by chemical analysis (coefficient of variation = 2.8%). Body fat calculated by difference from a combination of measured TBW and NAA data agreed closely with bomb calorimetry measurements. The use of indirect estimates of TBW to determine fat gave poor results. A group of four growing rats was analysed sequentially by NAA four times in 2 weeks. The maximum total radiation dose received by each animal was less than 50 rem (less than 500 mSv) and no significant differences in growth rate were observed compared with non-irradiated control groups. 14 MeV NAA in vivo can be conducted with sufficient precision to measure 0.14 g TBN changes in growing rats at 2 weeks post-weaning.

Animals↗
PubMed1984

Indications for pacing in the treatment of bradyarrhythmias. Report of an independent study group.

Indications for permanent pacing in the bradyarrhythmias are summarized. In the absence of symptoms, pacing is justified only when Mobitz type II block or complete atrioventricular (AV) block is localized in the bundle-branch system. All other abnormalities of impulse generation or conduction (incomplete AV block of any type, atrial fibrillation with slow ventricular response, or sinus node dysfunction) must be shown to be stable and intrinsic and to cause CNS symptoms or hemodynamic compromise to justify pacing. Isolated intra-Hisian abnormality without failure of AV conduction is benign. Measurement of HV interval does not contribute significant information. Correlation of carotid sinus sensitivity with carotid sinus syncope is poor (5%). Bradyarrhythmia produced by minimal effective doses of an essential drug is a rare indication for pacing and requires special documentation. Inadequate indications, sources of error, and misconceptions are discussed. Generally, it is important to exclude drug effect, transient clinical states, and correctable systemic disease as causes of the abnormality before making a conclusion about pacing.

Atrial Fibrillation↗
PubMed1979

An attempt to objectify the therapeutic process: a working model.

On the basis of their observations in daily psychoanalytic work the authors developed five objective criteria for "bad" analytic hours. These criteria involve affect, intellectualization, isolation, lack of feedback, and dissatisfaction. The authors developed a formulation to help them preconsciously recognize the presence of these factors during therapeutic work and found that it was helpful in turning a potentially bad hour into a productive one.

Cognition↗