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Biomedical subjects

H Tan

Publications and source records attributed to H Tan.

141 records · Page 8Linked to original sources
PubMed1988

Transforming genes in duck hepatic carcinoma--mht(raf) and Ha-ras.

The transfection of NIH 3T3 cells was performed with DNAs from 2 duck primary hepatic carcinomas (DHC 40K, 9K) and 1 tumor-adjacent liver tissue (TAL, 9N). Transfectants were found from 40K, 9K and 9N DNAs. The secondary transfectants were obtained after transfection of RAT-1 cells with DNAs from primary transfectants. After hybridization with Ha-ras, Ki-ras, N-ras and mht oncogenes, it was found that duck mht (5.2 and 3.2 kb EcoRI fragments) and duck Ha-ras (3.4 kb EcoRI fragments) were present in all these transformants. This is the first report on transforming genes in duck primary hepatic cancer as well as tumor-adjacent liver tissue.

Animals↗
PubMed1987

Peroxisomal acyl-coenzyme A oxidase multigene family of the yeast Candida tropicalis; nucleotide sequence of a third gene and its protein product.

We have determined the complete nucleotide sequence of gene POX2, which encodes one of the major peroxisomal polypeptides (PXPs) of Candida tropicalis. POX2 is linked to gene POX4, which codes for a subunit (PXP-4) of long-chain acyl-CoA oxidase. Southern blot analysis revealed that POX2 had a significant homology to POX4, and also to gene POX5 which encodes a subunit (PXP-5) of the isozyme of acyl-CoA oxidase. PXP-2, the protein product of POX2, was co-purified with PXP-4 from the isolated peroxisomes. PXP-2 itself was a flavoprotein and likely to form an equimolar complex with PXP-4, although its enzymatic activity was uncertain. POX2 corresponds to a single open reading frame of 724 amino acids and has no introns. The N-terminal sequence and the calculated Mr of the deduced polypeptide were consistent with those of isolated PXP-2. The primary structure was highly homologous to those of PXP-4 and PXP-5 in respect of the amino acid sequence and the hydropathy profile. We conclude that POX2 is a third gene of the peroxisomal acyl-COA oxidase multigene family.

Acyl-CoA Oxidase↗
PubMed1986

Effect of ammonium metavanadate on the murine immune response.

Female B6C3F1 mice were exposed to ammonium metavanadate (NH4VO3) by intraperitoneal injection every 3 d at 2.5, 5.0, or 10 mg V/kg for 3, 6, or 9 w and were then assayed for alterations in immunoresponsiveness. Resistance to Escherichia coli endotoxin lethality increased in a dose-dependent manner up to 6 w of exposure, while resistance to viable gram-positive Listeria lethality was depressed in a dose-dependent manner. Comparison of LD20 values indicated a 250-fold decrease in resistance to Listeria at the lowest vanadium exposure and a 40% increase in resistance to endotoxin after the highest vanadium exposure. Peritoneal macrophage phagocytic capacities were decreased in a dose-dependent manner, but viabilities remained unaffected. Rosetting capacity of splenic lymphocytes was increased following vanadium exposure. Liver and splenic enlargement was observed, and examination of splenic tissue indicated enhanced formation of megakaryocytes and red blood cell precursors. Subchronic exposure to vanadium may thus disrupt the normal function of the immune system.

Animals↗
PubMed1986

Reactions of aqueous chlorine and chlorine dioxide with model food compounds.

Chlorine and chlorine dioxide (ClO2), common disinfecting and bleaching chemicals used in the food industry, are potent oxidizing and chlorinating agents. Unfortunately, little is known about the nature of the reactions of chlorine with organic food constituents. This presentation reviews published information concerning the reactions of chlorine gas (Cl2[g]), aqueous chlorine, and ClO2 with model food compounds, the fate of chlorine during the chlorination of specific food products, and the potential toxicity of the reaction products. Fatty acids and their methyl esters react with chlorine with the degree of incorporation corresponding to their degree of unsaturation. Aqueous chlorine oxidizes and chlorinates lipids and amino acids much more readily than ClO2. Several amino acids are highly susceptible to oxidation and chlorination by chlorine compounds. Reactions of chlorine and ClO2 with several food products, including flour and shrimp, have also been characterized. In one model system, 99% of Cl2(g) either reacted with components of flour or was consumed by oxidation/chlorination reactions. The lipids extracted from the chlorinated flour contained significant amounts of chlorine. Exposure of shrimp to hypochlorous acid (HOCl) solution resulted in significant incorporation of chlorine into the edible portion. Although significant quantities of chlorine can be incorporated into specific model compounds and food products, the health risks associated with exposure to chlorinated organic products are unknown. Preliminary studies using the Ames Salmonella/microsome mutagenicity assay indicate that the reaction products from mixtures of aqueous chlorine and various lipids or tryptophan are nonmutagenic. Nevertheless, additional studies are warranted, so that the toxicological significance of these reaction products can be understood more fully.

Amino Acids↗
PubMed1977

Heterogeneity of human whole blood platelet subpopulations. I. Relationship between buoyant density, cell volume, and ultrastructure.

A quantitative high yield method utilizing isosmotic arabino-galactan (Stractan) solutions and isopycnic centrifugation was developed to isolate and to fractionate total human platelet populations into density-dependent subpopulations. Isolated platelets were free of factor VIII/von Willebrand factor and other plasma proteins. They responded to ADP, epinephrine, and collagen with a sensitivity equal to platelet-rich plasma platelets. The correlation of platelet density with volume and ultrastructure was examined for normal subjects. Recovery of total platelet populations averaged 92.76%+/-3.64% (SD). Normal individuals exhibited a narrow range of platelet buoyant density distribution. Computerized probability plot analysis of platelet volume distribution for 15 normal subjects' total platelet populations showed a mean volume of 5.17+/-0.46 cu mum (SD). Platelets with buoyant density less than or equal to 1.062 g/ml had a mean volume of 4.50+/-0.48 cu mum, while platelets with buoyant density greater than 1.071 g/ml, but less than or equal to 1.084 g/ml, had a mean volume of 5.32+/-0.63 cu mum (SD). The volume difference by paired t test was significant, p less than 0.001. Thin-section electron microscopy demonstrated a significant reduction of granule content in light platelets, as compared to heavy platelets, but an equal number of mitochondria for both groups. These differences of platelet volume and structure between light and heavy platelets suggested that aging may be a determinant of platelet heterogeneity.

Adult↗
PubMedDate not supplied

Effects of norepinephrine upon superficial layer neurons in the superior colliculus of the hamster: in vitro studies.

Intracellular recording techniques were used to evaluate the effects of norepinephrine (NE) on the membrane properties of superficial layer (stratum griseum superficiale and stratum opticum) superior colliculus (SC) cells. Of the 207 cells tested, 44.4% (N = 92) were hyperpolarized by > or = 3 mV and 8.7% (N = 18) were depolarized by > or = 3 mV by application of NE. Hyperpolarization induced by NE was dose dependent (EC50 = 8.1 microM) and was associated with decreased input resistance and outward current which had a reversal potential of -94.0 mV. Depolarization was associated with a very slight rise in input resistance and had a reversal potential of -93.1 mV for the single cell tested. Pharmacologic experiments demonstrated that isoproterenol, dobutamine, and p-aminoclonidine all hyperpolarized SC cells. These results are consistent with the conclusion that NE-induced hyperpolarization of SC cells is mediated by both alpha2 and beta1 adrenoceptors. The alpha1 adrenoceptor agonists, methoxamine and phenylephrine, depolarized 35% (6 of 17) of the SC cells tested by > or = 3 mV. Most of the SC cells tested exhibited responses indicative of expression of more than one adrenoceptor. Application of p-aminoclonidine or dobutamine inhibited transsynaptic responses in SC cells evoked by electrical stimulation of optic tract axons. Inhibition of evoked responses by these agents was usually, but not invariably, associated with a hyperpolarization of the cell membrane and a reduction in depolarizing potentials evoked by application of glutamate. The present in vitro results are consistent with those of the companion in vivo study which suggested that NE-induced response suppression in superficial layer SC neurons was primarily postsynaptic and chiefly mediated by both beta2 and beta1 adrenoceptors.

Action Potentials↗
PubMedDate not supplied

Bulk acoustic wave bacterial growth sensor applied to analysis of antimicrobial properties of tea.

A bulk acoustic wave (BAW) bacterial growth sensor has been proposed for study of inhibitory effects of tea by continuous monitoring of disturbances in Proteus growth in the aqueous extracts of various teas, e.g. green tea, Fuzhuan brick tea, Oolong tea, Kudin tea, and black tea. The kinetic parameters, e.g. asymptote (A), maximum specific growth rate (microm), lag time (lambda), and generation time (g), accurately estimated by using the growth response model, have been first used to characterize antimicrobial properties of tea. All of the parameters were changed via the inhibitory effects by tea. Green tea gives the weakest inhibitory action while others show stronger inhibitory actions. These inhibitory effects have also been examined by using the pour plate count technique. Both of the results show that, in addition to the antimicrobial properties of tea polyphenols and catechins, etc., the inhibitory effects may be attributed to the metabolites produced during the fermentation processing of these teas except green tea. The conventional disk diffusion test has been used to determine the minimum inhibitory concentration (MIC) against P. rettgeri. The MICs of green tea, Fuzhuan brick tea, Oolong tea, and black tea were found to be 1113, 818.0, 681.2, and 510.4 microg/mL, respectively. The BAW bacterial growth sensor has shown to have advantages over other techniques, including the disk diffusion test, photometry, and the impedance method.

Acoustics↗
PubMedDate not supplied

Pelvic ultrasound measurements in normal girls: relation to puberty and sex hormone concentration.

Pelvic ultrasonography was performed on 75 normal girls. Values were obtained for uterine length, fundal/cervical ratio (FCR), ovarian volume and sex hormones. The resultant data were grouped according to age and pubertal stage (Tanner). For uterine length, FCR and ovarian volume, the data were positively skewed, and the variance increased with age and pubertal stage (p < 0.001). The uterus underwent a regular increase in size and the corpus gradually became larger than the cervix. Uterine length, right ovary volume, FCR and hormones (serum estradiol, follicle-stimulating hormone and luteinizing hormone) showed a correlation with the Tanner score (p < 0.001). Although the correlations were significant, the best correlation was between pubertal stage and serum estradiol level.

Adolescent↗
PubMedDate not supplied

Serum thyroid hormone and thyroid gland weight measurements in protein-energy malnutrition.

Protein-energy malnutrition (PEM) is a problem which concerns about half the world's children. We investigated the effects of malnutrition on thyroid gland weight and thyroid hormone levels. 22 children suffering from malnutrition (14 children suffering from marasmus and 8 children suffering from kwashiorkor) and 7 healthy controls were studied. Malnutrition was confirmed clinically and according to the Wellcome classification definition of malnutrition. Serum thyroid hormone concentrations were measured by radioimmunoassay and the weights of the thyroid gland were evaluated scintigraphically. In the groups with marasmus and kwashiorkor the mean TT4, TT3 and FT3 levels were significantly lower, and TSH levels were significantly higher, compared to controls. FT4 was not influenced by PEM. The mean thyroid gland weights of the groups with marasmus and kwashiorkor were higher than that of the control group. We found no significant differences in all these parameters between groups with marasmus and kwashiorkor. In each of the three groups, the most marked positive correlation was between thyroid gland weight and ratio of thyroid gland weight to body surface area.

Body Surface Area↗