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C Leung

Publications and source records attributed to C Leung.

14 recordsLinked to original sources
PubMed1992

Effect of cigarette smoking on salivary epidermal growth factor (EGF) and EGF receptor in human buccal mucosa.

The mouth acts as a primary target for cigarette smoke which is associated with several oral diseases and cancer. The present study investigated the effect of cigarette smoking on salivary EGF and the buccal EGF receptor. Samples of whole saliva and buccal biopsy were obtained from 15 healthy volunteers (10 smokers and 5 non-smokers). The smokers smoked 20 or more cigarettes/day for more than 5 years. Salivary cotinine (a major metabolite of nicotine) was determined by radioimmunoassay (RIA). The salivary cotinine level was consistent with the self-reported smoking status (smokers, 106-530 ng/ml saliva; non-smokers, < 2 ng/ml saliva). As compared to the non-smokers, the salivary EGF concentration (determined by RIA) was 32% lower in those smokers whose salivary cotinine level was 250 ng/ml or higher (non-smokers, 2.21 +/- 0.16; smokers, 1.57 +/- 0.09 ng/ml saliva; mean +/- S.E.M., P < 0.01). There was no significant difference in 125I-labeled EGF binding to the buccal receptor between the two groups. However, EGF stimulated the autophosphorylation of a 170-kDa protein band in the sample of non-smokers, but not in the smokers. The immunoblot analysis using anti-EGF receptor antibody indicated that the smoking-related deficiency in EGF receptor autophosphorylation was due to the functional alteration of the receptor proteins. In conclusion, cigarette smoking reduces the salivary EGF level and impairs the function of buccal EGF receptor, which may be associated with the pathology of smoking-related oral disease.

Blotting, Western↗
PubMed1992

Heritability of dark pulse triggering of paradoxical sleep in rats.

A previous study showed that albino Lewis (L) rats could be triggered into paradoxical sleep (PS) by dark pulse stimulation, i.e., turning off cage lights, whereas brown Norway (BN) rats showed no evidence of PS triggering by dark pulses (2). The transmission of the PS triggering behavior was studied in L x [L x BN]F1 hybrid backcross (BC) animals. Albino BC rats increased PS% during 5-minute dark pulses to three times the average PS% for the preceding 5 minutes of lights-on. In contrast, no significant PS triggering was observed in pigmented BC rats. These data support the hypothesis that PS triggering by dark pulse stimulation is related to albinism in these rat strains. The absence of a connection between PS triggering and total daily amounts of PS suggests independent genetic transmission of these two parameters.

Albinism↗
PubMed1992

[Effect of light on total micro-bilirubin values in vitro].

In order to elucidate the effect of light on total bilirubin values in vitro, 616 capillary blood samples were collected from jaundiced newborn infants at the nursery of Veterans General Hospital-Taipei. Samples were divided into 3 groups: 1. Phototherapy light group-133 samples were irradiated with blue fluorescent light (spectral irradiance 425-475 nm = 4 mu watt/cm2/nm); 2. Room light group-202 samples were irradiated with white fluorescent light (spectral irradiance 425-475 nm = 0.2 mu watt/cm2/nm); 3. Dark group-the last 215 samples were placed in the dark. Total bilirubin values were checked with spectrophotometry, at 0, 2, 4, 6, 24 and 48 hours after being placed in different environments. Total bilirubin values varied significantly in different light source and time groups (p less than 0.0001), plus both had statistical interactions (p less than 0.0001). There were significant decreases in the bilirubin values of the phototherapy group beginning at 2 hours (p less than 0.05), and in the room light group beginning at 6 hours (p less than 0.05), but there was no change in the dark group. We conclude that blood samples for total bilirubin values should not be placed under the light of phototherapy even 2 hours. If blood samples are exposed to room light inevitably, it is safe to be checked within 4 hours. If immediate measurements are unavailable, the samples can be placed in a dark environment allowing the values to remain unchanged for 48 hours.

Bilirubin↗
PubMed1991

Rat strain differences in response to dark pulse triggering of paradoxical sleep.

Previous studies of inbred rats have shown that Brown Norway (BN) rats had more daily paradoxical sleep (PS) than Lewis (L) rats, while F1 progeny had intermediate amounts, suggesting codominant or polygenic transmission. Amount of PS and the induction of PS episodes may be under separate genetic control. Earlier work had shown that five-minute exposures to cage lights-off every half-hour can trigger PS in outbred albino strains. To explore the genetic controls for PS induction, PS triggering by dark pulse stimulation was examined in L and BN rats. L rats showed a five-fold increase in PS during dark pulse stimulation. Although, as in the earlier study, BN rats had more total daily PS than L rats, they exhibited no dark pulse triggering of PS. Thus L and BN rats show significant strain differences in two independent parameters of PS, and may be a useful model for studying genetic and neurologic factors which regulate PS.

Animals↗
PubMed1986

O6-methylguanine-DNA methyltransferase activity and sensitivity to N-methyl-N'-nitro-nitrosoguanidine during human T-lymphocyte differentiation.

The activity of O6-methylguanine-DNA methyltransferase (MT) was assayed in various human lymphoid cell populations. It was found that during T-cell differentiation the activity of MT increased from 7000 MT molecules in thymocytes to 31,000 MT molecules in mature T-lymphocytes. The number of MT molecules also increased 2- to 3-fold in the course of the cell division cycle but the specific activity of MT did not change significantly. T-cell tumors and T-cell lines contained a higher number of MT molecules (70,000-125,000 molecules/cell) compared to normal T-lymphocytes. The sensitivities of various lymphoid cells to the DNA methylating agent N-methyl-N'-nitro-N-nitrosoguanidine correlated well with MT activities observed in cell extracts.

Cell Differentiation↗
PubMed1985

Characterization of mouse lymphoma cells with altered nucleoside transport.

A mutant clone (NT-1) of a T-cell lymphoma was selected for its ability to grow in HAT medium (hypoxanthine, aminopterin and thymidine) in the presence of the nucleoside transport inhibitor P-nitrobenzyl-6-mercaptoinosine (NBMI). NT-1 cells contain half the number of NBMI binding sites present on the parental S49 cells and are partially able to transport nucleosides in the presence of the transport inhibitor (NBMI). These observations suggest that the mutant cells are heterozygous for nucleoside transport proteins and contain two types of transport proteins: the first protein can both bind and is inhibited by NBMI similar to the wild type phenotype, and the second is an altered protein. The altered transport protein apparently lost its NBMI binding sites without a parallel loss of nucleoside transport ability suggesting that the nucleoside transported sites are separate from the binding sites of the transport inhibitor.

Adenosine↗
PubMed1978

Recognition of lysozyme by lymphocyte subsets.

Extensive studies with antisera from a variety of animals have failed to detect any cross-reactivity between egg white lysozyme and its reduced, S-carboxymethylated (CM-) derivative. In contrast, a number of studies addressing the specificity of T lymphocytes have revealed that these two forms of lysozyme cross-react rather extensively at that level. Preliminary attempts to eliminate this latter cross-reactivity by further denaturation and/or chemical modification have so far proven unsuccessful. In a second line of experimentation the response to CM-lysozyme of mice which are genetically unresponsive to native lysozyme was assessed and found deficient. The implications of these findings are discussed.

Animals↗
PubMed1975

Immune plasma-dependent cytotoxicity of immune and non-immune peripheral lymphoid cells for target cells coated with bacterial outer unit membrane.

The development of a model system for use in the study of lymphoid cell cytotoxicity to bacterial membrane antigens was attempted. In this system 51 Cr-labelled chicken red blood target cells were coated with pieces of the outer unit membrane of leptospirae rather than with soluble antigens. Using the model system to study dog peripheral immune lymphoid cell cytotoxicity to coated target cells we found that both immune and non-immune lymphocytes are antibody dependent for the expression of their cytotoxicity. It was also found that the unit membrane preparation from leptospirae can serve as a good antigenic stimulant to immune dog lymphoid cells as measured by increased [3H]thymidine uptake.

Animals↗