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Biomedical subjects

T Wong

Publications and source records attributed to T Wong.

At least 181 records · Page 10Linked to original sources
PubMed1981

Hormonal induction of pulmonary maturation in the rabbit fetus: effects of maternal treatment with estradiol-17 beta on th endogenous levels of cholinephosphate, CDP-choline and phosphatidylcholine.

1. Administration of estradiol-17 beta to pregnant rabbits at 25 days gestation (term, 31 days) resulted n a significant increase in the incorporation of [14C]-choline, but not [14C]ethanolamine, into the lipids of fetal lung slices. The incorporation of [35S]methionine was not affected. 2. Enzymatic assays conducted in vitro revealed no significant effect on either the activities of several enzyme markers for subcellular organelles, the activities of the enzymes responsible for the production of phosphatidylglycerol and phosphatidylinositol, membrane-bound or aqueously dispersed phosphatidate-dependent phosphatidic acid phosphohydrolase activities or the activities of the auxiliary enzymes responsible for the synthesis of dipalmitoylphosphatidylcholine. 3. The activity of the enzymes involved in the choline pathway for the de novo biosynthesis of phosphatidylcholine were not significantly altered except for a 66% increase in the CTP:cholinephosphate cytidylyltransferase activity assayed in the cytosol. The addition of phosphatidylglycerol stimulated cholinephosphate cytidylyltransferase activity approx. 3-fold. However, in the presence of this lipid, the activities in cytosol from control and treated fetuses were similar, indicating that the increased activity noted in the absence of phosphatidylglycerol was due to an activation of existing cytidylyltransferase activity rather than an increase in total enzyme units. 4. Estrogen treatment of the does was also associated with a marked decrease in the levels of cholinephosphate in fetal lung and significant increases in the levels of CDPcholine and phosphatidylcholine. These alterations in pool size are consistent with an increase in the activity of cholinephosphate cytidyltransferase in vivo. The results suggest that cholinephosphate cytidylyltransferase may catalyse an important rate-determining reaction in the synthesis of phosphatidylcholine in fetal lung. The data also support the view that the reaction catalysed by CDPcholine:diacylglycerol cholinephosphotransferase also has a regulatory role during development.

Animals↗
PubMed1979

Glucocorticoid induction of pulmonary maturation in the rabbit fetus. The effect of maternal injection of betamethasone on the activity of enzymes in fetal lung.

1. Maternal administration of betamethasone (0.2 mg/kg) on day 25 or 26 of gestation produced a significant decrease in the lung/body weight ratio of the rabbit fetuses within 24 h. 2. The incorporation of [14C]choline but not [14C]ethanolamine into the lipids of fetal lung slices was significantly increased, indicating that there was a specific effect on phosphatidylcholine synthesis. 3. The activities of a number of marker enzymes for subcellular organelles were elevated, especially in the lungs of fetuses delivered on day 26. The increases in monoamine oxidase (mitochondrial outer membrane), beta-glycerophosphatase and aqueously dispersed phosphatidic acid-dependent phosphatidic acid phosphohydrolase (lysosomal) activities were significant. 4. Although the activity of cholinephosphotransferase was not affected by glucocorticoid treatment, the activities of glycerol-3-phosphate phosphatidyltransferase and the activities of two enzymes in the auxiliary pathways for the production of disaturated phosphatidylcholine (lysophosphatidylcholine:lysophosphatidylcholine transacylase and lysophosphatidylcholine:acyl-CoA acyl-transferase) were significantly increased. 5. Membrane-bound phosphatidic acid-dependent phosphatidic acid phosphohydrolase activity was elevated to a lesser extent than the aqueously dispersed phosphatidate-dependent activity and this increase was not significant. 6. The incorporation of E135S]methionine into protein by slices of fetal lung was significantly reduced after maternal treatment with betamethosone. 7. These results are consistent with the general view that glucocorticoids can induce pulmonary maturation and surfactant production in the rabbit fetus but indicate that some of the former hypotheses regarding the mechanism by which lipid synthesis is accelerated must be reevaluated.

Animals↗
PubMed1978

Further studies on the effect of red and far red light on rat retinal development.

The influence on the development of the outer segments of the rat retina of far red and red light in different sequences was investigated. The far red treatment appeared to be dominating, and for animals treated with far red light first, further treatment of red light could not bring the outer segment growth back to normal. The treatments also initiated different dopamine uptakes in the retinas.

Animals↗
PubMed1978

Regulation of cholesterol ester synthesis in cultured glial and neuronal cells. Relation to control of cholesterol synthesis.

Regulation of cholesterol ester synthesis was studied in cultured C-6 glial and neuroblastoma cells. Particular emphasis was placed on the relation of this regulation to control of cholesterol synthesis. The effectors studied were low density lipoprotein (LDL) and desmosterol. Distinct differences in regulation were observed between the glial and neuronal cells. In the neuronal cells cholesterol ester synthesis (from [14C]oleate) was not affected by even high concentrations of LDL or desmosterol. In contrast, cholesterol ester synthesis was stimulated as much as 12-fold in the glial cells after just 5 h exposure to LDL or desmosterol. Cholesterol synthesis (from [14C]acetate) was inhibited in a simultaneous and quantitatively similar manner. Suitable experiments indicated that alterations in pool sizes of intermediates did not contribute to the genesis of the observed responses and suggested that LDL and desmosterol produced their effects by stimulating esterification of primarily endogenous cholesterol. The data may have major implications concerning the controlling metabolic events prior to and at the onset of myelination.

Acetates↗
PubMedDate not supplied

Detection of immunoglobulin gene rearrangement in B-cell lymphomas by polymerase chain reaction gene amplification.

This is a report on our attempt to use polymerase chain reaction (PCR) to detect rearrangement of the immunoglobulin gene in the tissue specimens obtained from 30 patients with non-Hodgkin's lymphomas. There were 20 B-cell lymphomas and 10 T-cell. All 20 B-cell lymphomas but none of the 10 T-cell lymphomas had JH rearrangement by Southern analysis. Two pairs of primers (V670/OL-4 and VH26/OL-4) were designed to amplify the CDR3 region of the immunoglobulin gene heavy chain. The PCR analysis was positive using either one or both pairs of primers in 11 of the the 20 cases (55 per cent) of B-cell lymphomas which all had positive rearrangement by Southern analysis. The two pairs of primers seemed to produce complementary results as the specimens may be positive to one pair but negative to the other. The false negative rate of 45 per cent is however much higher than the respective figures of 18 per cent and 0 per cent observed in our patients with acute lymphoblastic leukemia and chronic lymphocytic leukemia in a previous study. Peripheral blood and bone marrow biopsy specimens obtained at the time of initial diagnosis were available from 10 patients with B-cell lymphomas whose lymph node biopsy specimens at the time of diagnosis were positive by both Southern analysis and PCR. All these peripheral blood and marrow specimens had no microscopic evidence of involvement by lymphoma cells and JH rearrangement was not detected by Southern analysis. However, rearranged bands identical to that of the lymph node biopsy specimen were detected by PCR in the peripheral and marrow blood of one of them. This PCR technique has been shown to have a sensitivity of 0.1 per cent in our previous report and may be more useful than morphology alone or Southern analysis in detecting minimal lymphomatous involvement in the peripheral blood and bone marrow at the time of initial diagnosis. Further clinical correlation is required to confirm the finding.

Base Sequence↗
PubMedDate not supplied

Computer-based imaging and interventional MRI: applications for neurosurgery.

Advances in computer technology and the development of open MRI systems definitely enhanced intraoperative image-guidance in neurosurgery. Based upon the integration of previously acquired and processed 3D information and the corresponding anatomy of the patient, this requires computerized image-processing methods (segmentation, registration, and display) and fast image integration techniques. Open MR systems equipped with instrument tracking systems, provide an interactive environment in which biopsies and minimally invasive interventions or open surgeries can be performed. Enhanced by the integration of multimodal imaging these techniques significantly improve the available treatment options and can change the prognosis for patients with surgically treatable diseases.

Biopsy↗
PubMedDate not supplied

X-ray surface dose measurements using TLD extrapolation.

Surface dose measurements in therapeutic x-ray beams are of importance in determining the dose to the skin of patients undergoing radiotherapy. Measurements were performed in the 6-MV beam of a medical linear accelerator with LiF thermoluminescence dosimeters (TLD) using a solid water phantom. TLD chips (surface area 3.17 x 3.17 cm2) of three different thicknesses (0.230, 0.099, and 0.038 g/cm2) were used to extrapolate dose readings to an infinitesimally thin layer of LiF. This surface dose was measured for field sizes ranging from 1 x 1 cm2 to 40 x 40 cm2. The surface dose relative to maximum dose was found to be 10.0% for a field size of 5 x 5 cm2, 16.3% for 10 x 10 cm2, and 26.9% for 20 x 20 cm2. Using a 6-mm Perspex block tray in the beam increased the surface dose in these fields to 10.7%, 17.7%, and 34.2% respectively. Due to the small size of the TLD chips, TLD extrapolation is applicable also for intracavity and exit dose determinations. The technique used for in vivo dosimetry could provide clinicians information about the build up of dose up to 1-mm depth in addition to an extrapolated surface dose measurement.

Electrons↗
PubMedDate not supplied

Dosimetry of 6-MV x-ray beam penumbra.

The measurement of x-ray beam dose profiles in the penumbral region, using silicon diode, ionization chamber, TLD, and film dosimetry, has been investigated for a 6-MV beam defined by independent collimators. Penumbral width (80%-20%) at dmax, as measured by diode, film, and TLD was found to be 3.6, 3.6, and 3.4 mm, respectively. These results reflect the relative sensitive widths of each of the measurement systems (2.5, 2.0, and 1.0 mm, respectively). An empirical forming function was used to relate the penumbral shape measured with a finite-sized detector to that which would be measured with a point detector, the width of the point detector penumbra calculated from the diode penumbra is 3.4 mm, indicating that the TLD rods are a good approximation to a point detector. An alternative method of determining the width of a point detector penumbra is to extrapolate the penumbral widths obtained using two or more detectors of sensitive width. With this method, using Farmer and RK ionization chambers, a point detector penumbra width of 3.1 mm is obtained. An EGS4 Monte Carlo simulation, where a point source was assumed, gave a penumbral width of 2.8 mm. Negligible differences between the penumbra of beams defined by symmetric and asymmetric collimators was observed.

Biophysical Phenomena↗
PubMedDate not supplied

Cellular distribution of enzymes involved in phosphatidylcholine synthesis in developing rat lung.

The incorporation of radioactive choline into phosphatidylcholine and disaturated phosphatidylcholine in rat lung slices increased markedly before term and peaked after birth. The specific activity of cholinephosphate cytidylyltransferase in the microsomal fraction increased before birth but fell after delivery. The specific activity of this enzyme in the cytosol showed a marked increased at birth. The developmental profile for the total cytosolic activity per gram lung was similar to the pattern observed with choline incorporation. Although the specific activity of cholinephosphotransferase in the whole homogenate remained relatively constant throughout pulmonary maturation, there was a marked increase in the specific activity of this enzyme in the microsomal fraction at term. Similar findings were obtained with the microsomal marker NADPH-cytochrome c reductase. The basis of this disparity in specific activity profiles is being investigated further. The specific activity of lysophosphatidylcholine:lysophosphatidylcholine transacylase in rat lung homogenates increased during gestation but rose a further 10-fold between day 3 after birth and the adult. The specific activity of lysophosphatidylcholine:palmitoyl-CoA acyltransferase remained relatively constant throughout development. At term, the specific activity of the acylation enzyme was 10- to 15-fold greater than the specific activity of the transacylation enzyme. These observations are consistent with previous studies indicating that the accumulation of phosphatidylcholine and dipalmitoyl phosphatidylcholine during the perinatal period may be due to alterations in the activity of cholinephosphate cytidylyltransferase. Cholinephosphotransferase could also play a regulatory role. The formation of dipalmitoyl phosphatidylcholine appears to occur via the acylation, rather than the transacylation pathway.

1-Acylglycerophosphocholine O-Acyltransferase↗