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Biomedical subjects

J Mallard

Publications and source records attributed to J Mallard.

At least 19 recordsLinked to original sources
PubMed1996

Cloning and characterization of the 5' end and promoter region of the chicken acetyl-CoA carboxylase gene.

Acetyl-CoA carboxylase is a rate-limiting enzyme in the biogenesis of long-chain fatty acids. In the present study, the 5' end and flanking region of the acetyl-CoA carboxylase (ACC) gene was analysed in the chicken. A genomic clone was isolated containing the first three exons, the third one containing the ATG codon. Using nuclease-mapping experiments and primer-extension analyses, the transcription-initiation site was located 153 nucleotides upstream of the ATG codon. In contrast with rat ACC gene expression, reverse transcriptase PCR analysis performed on chicken liver mRNA did not reveal alternative splicing in the 5'-untranslated region of these messengers. The promoter region is very G+C rich, and contains no TATA or CAAT boxes. Analysis by transient transfection in a human hepatoma cell line (HepG2) demonstrates that the promoter activity requires the presence of symmetrical sequences located upstream of the GC boxes. Transcription of this gene is found to be controlled by tri-iodothyronine in HepG2 cells, but the sequence responsible for the tri-iodothyronine response is not the consensus tri-iodothyronine-responsive element localized in the promoter. These results bring new insights to the regulation of the chicken ACC gene which differs from that of the rat.

Acetyl-CoA Carboxylase↗
PubMed1993

Lipogenic enzyme and apoprotein messenger RNAs in long-term primary culture of chicken hepatocytes.

Hepatocytes isolated from 9-week-old chickens were cultured in a serum-free, hormonally defined medium. Relative amounts of mRNAs coding for lipogenic enzymes (acetyl-CoA carboxylase, fatty acid synthase, delta 9 desaturase, malic enzyme) and apoproteins (apoprotein A1 and apoprotein B) were determined until the 12th day. beta-actin and albumin mRNA, as well as albumin secretion, were also assessed. Cellular metabolic activity appeared to be very low for the first days of culture, but increased after the 7th day. All the mRNAs studied, except for that of malic enzyme, were present from this time throughout the culture lifespan. The biological significance of the observed results and the relevance of this chicken hepatocyte culture system for long-term metabolic and genetic studies are discussed.

Acetyl-CoA Carboxylase↗
PubMed1992

Identifying genes involved in the variability of genetic fatness in the growing chicken.

A precise knowledge of the genome involved in the expression of a quantitative trait could provide a useful tool in breeding programs; molecular genetic methods are capable of yielding this kind of information. An experimental procedure is presented here for identifying genes whose expression is related to weight variability of abdominal adipose tissue in the growing chicken. Quantitative traits are the result of metabolic pathways exhibiting some major regulation stages that are controlled genetically. These steps involve genes that may act as "major genes". With regard to chicken fat metabolism, most fatty acids are synthesized in the liver and incorporated into very low density lipoprotein (VLDL) particles before their secretion into the plasma. Accordingly, the present study focused on the expression of liver genes. The mRNA of lipogenic enzymes (acetyl-coenzyme-A carboxylase, fatty acid synthase, malic enzyme, and delta 9-desaturase) were analyzed. Also studied were apoprotein (apo)A1, apoVLDL-II, and apoB mRNA from 9-wk-old male chickens from two lines selected for high and low abdominal fat pads. Significant differences for apoA1 mRNA levels occurred between fat and lean birds. Moreover, the total quantity of mRNA provided an accurate estimation of the abdominal fat pad (r = .74 with P < .05).

Adipose Tissue↗
PubMed1990

ApoVLDLII gene transcription in immature cockerels without estradiol stimulation.

1. Previous studies have led to the conclusion that the gene encoding the apo very low density lipoprotein II (ApoVLDLII) is under full estrogen control. However, by using a sensitive hybridization technique we found a weak expression of this gene in some males in the absence of hormone. 2. As the vitellogenin II gene, which is also estrogen dependent, remains inactive in these animals it is likely that they carry a deregulated allele of the ApoVLDLII gene. 3. The highest level of ApoVLDLII mRNA is found in genetically fat males suggesting a possible involvement of the ApoVLDLII gene in fatness determinism.

Animals↗
PubMed1990

Quantitative imaging in vivo. Why? What is being done now? What are some of the problems? What may the future be?

The visual system is highly sophisticated, yet at the task of quantifying the information in images it is very easily misled. It is probably for this reason that medical imaging has often concentrated on the visual analysis of images and played down the value of extracting quantitative information. Yet nearly all modern medical imaging techniques use digital technology to some degree and numerical information can be readily extracted. Unless more use is made of this quantitative data, medical imaging will never make the transition from an art into a science.

Animals↗
PubMed1987

Lipid biosynthesis and deposition in genetically lean and fat chickens. Comparative in vivo studies with 14C acetate.

Following intravenous administration of 14C-acetate to genetically lean or fat chickens, the radioactivity in their liver, plasma, striated muscle and abdominal adipose tissue lipids and that in the breathed out CO2 were studied in function of time. As compared to the lean ones, the fat chickens showed a higher labelling of their triglyceride fatty acids in the plasma and adipose tissue, but not in the liver. Thus a higher rate of triglyceride secretion from the liver would be responsible for the higher abdominal fat weight in the fat line chickens.

Acetates↗
PubMed1987

Hepatic lipogenesis in genetically lean and fat chickens. In vitro studies.

1. Acetyl-coenzyme A carboxylase, malic enzyme, glucose 6-phosphate dehydrogenase and delta 9-desaturase activity was measured in liver extracts from 5- to 11-week-old genetically lean or fat chickens. 2. A significant difference between the two lines of chickens was shown as concerns desaturating activity only, which was 45% higher in the fat animals than in the lean ones. 3. This result is consistent with the hypothesis of a higher rate of lipoprotein processing and secretion in the liver of the fat line chickens.

Acetyl-CoA Carboxylase↗
PubMed1983

Nuclear magnetic resonance of iron and copper disease states.

The tissue levels of paramagnetic ions are an important factor in the determination of T1 values as observed by nuclear magnetic resonance (NMR) imaging. The increased levels of iron present in human disease states such as hemochromatosis lead to decreased T1 values. The mean liver T1 of three patients with iron storage disease was determined to be 130 msec, significantly different from the value of 154 msec, the mean for 14 normal controls. Whether NMR will be able to detect the increased copper levels in liver and brain in Wilson disease remains for further clinical trials to evaluate. NMR imaging, however, does serve as a noninvasive method for the diagnosis of states of iron overload and as a technique to follow progression of disease or response to medical therapy.

Abdomen↗
PubMed1980

In vivo n.m.r. imaging in medicine: the Aberdeen approach, both physical and biological.

A novel magnetic field and radio frequency (1.7 MHz) pulse sequence is described for a whole body n.m.r. imaging machine under construction. Selective excitation is used to obtain signals from successive lines of proton spins(water) across the body to build up an image of a transverse section. The images display spin concentration and spin-lattice relaxation time, T1, separately. For a 50% change in T1 to be discerned in the human trunk, a spatial resolution of 2 cm3 is expected for a 2 min scan and 0.5 cm3 for a 30 min scan. Very preliminary images at the present incomplete stage of development show the geometrical accuracy and T1 discrimination: an in vivo image demonstrates some of the difficulties to be overcome. In vitro measurements of normal rabbit tissue samples have been made at 24 MHz to map the T1 distributions that can be expected from normal subjects. The transposition of this information from rabbit to man, and from 24 MHz to 2.5 MHz have been checked and the comparison shown to be meaningful. Of pathological samples, human breast tumour and human liver metastases offer a good contrast to their surrounding tissue, and an experimental investigation has shown that tissue immediately surrounding a tumour also has an elevated T1 value. A wide range of abnormalities that are associated with abnormal fluid formation in the body may be amenable to imaging by the n.m.r. technique. Potential hazards are believed to be small in the present generation of equipment.

Animals↗
PubMed1980

Nuclear imaging.

Explore the source record for details and available documents.

Bone Neoplasms↗
PubMed1979

Imaging by nuclear magnetic resonance and its bio-medical implications.

The distribution of proton spin concentration (water concentration) and the proton spin-lattice relaxation time (T1) can be imaged in a sample by placing it in a magnetic field gradient, applying appropriate radio-frequency (rf) pulses, and measuring the rf radiated from the sample. The Aberdeen machine is designed to image the human body in vivo at 400 gauss and 1.7 MHz. The spatial resolution predicted is about 1 cm for a 20% difference of T1. Measurements of T1 for small samples of tissue in vitro show a five-fold range of values for some soft tissues. Breast tumours and liver metastases have shown T1 values very different from the surrounding tissue. The method has the potential of perhaps imaging any pathology which changes water concentration, forms fluid pools or affects the binding of water to macromolecules. The potential hazards, which need more investigation, seem slight.

Animals↗
PubMed1978

The influence of size and radiopharmaceutical concentration ratio on the detection of abnormalities in clinical radionuclide imaging.

The effect of the size of an abnormality on its detectability was measured. The cylindrical abnormalities studied, with diameters ranging from 3 mm to 4 cm, were superimposed on a uniform background. To avoid artefacts produced by the imaging devices, the images were simulated by computer. The method of constant stimulus was used to determine the detectability of the abnormalities. By using a Perspex phantom filled with 99Tcm, measurements were made of the concentration ratio between abnormality and background which permitted detection of the abnormality. This allowed evaluation of the effectiveness of 99Tcm pertechnetate in the detection of small abnormalities. Assuming a concentration ratio between abnormal and normal tissue of 22.5:1, then at a depth of 50 mm in the brain a cylindrical abnormality of about 8 mm diameter was the smallest detectable under the chosen scanning conditions.

Brain Diseases↗
PubMed1976

The measurement of the performance of the display system of radioisotope imaging device: the multi-element band display.

An assessment has been made of the performance of the type of display system in which each display signal intensity, i.e. grey shade or colour, represents a range of count densities or counting rates. In the particular commercially available system used in this investigation eight different grey shades are used to display the image, a range of count densities beingallocated to each grey shade. It is shown experimentally that changes in the distribution of radioisotope can fail to be detected solely due to the manner in which the display is used, viz. The way in which the count density is allocated to the available grey shades. Also, it is shown experimentally that the best display performance can be achieved by using one in which the range of count densities represented by each grey shade is less than three standard deviations of the mean background [corrected] count density.

Background Radiation↗