Search PubMed⌕ Search

Biomedical subjects

L Tang

Publications and source records attributed to L Tang.

At least 253 records · Page 14Linked to original sources
PubMed1994

Lovastatin increases arachidonic acid levels and stimulates thromboxane synthesis in human liver and monocytic cell lines.

The effect of lovastatin (LOV), the inhibitor of 3-hydroxy-3-methyl-glutaryl coenzyme A reductase, on linoleic acid (LA, 18:2n-6) metabolism was examined in human monocytic Mono Mac 6 (MM6) and hepatoma Hep G2 cells. The desaturation of LA was examined after LOV (72 h, 10 microM) or dimethylsulfoxide (LOV carrier, < 0.1%) and [14C]LA (last 18 h, 0.3 microCi, 5 microM). In both cell lines, LOV reduced the percentage of 14C label associated with LA and increased the percentage of label in the 20:4n-6 and the 22:5n-6 fractions. In Hep G2 but not MM6 cells, this effect was fully reversible by means of coincubation with mevalonic acid (500 microM), but not with cholesterol or lipoproteins. In both cell lines, the LOV-mediated increase in LA desaturation resulted in dose-dependent reductions of LA and elevations of AA in cellular phospholipids. The lipids secreted by LOV-treated Hep G2 cells were also enriched in arachidonic acid (AA). In the MM6 cells, LOV increased release of thromboxane upon stimulation with the calcium ionophore A23187. In summary, our findings of higher LA desaturation and AA enrichment of lipids secreted by the Hep G2 cells suggest that LOV treatment may increase the delivery of AA from the liver to extrahepatic tissues. The changes in membrane fatty acid composition can influence a variety of cellular functions, such as eicosanoid synthesis in monocytic cells. The mechanism appears to be related to the reduced availability of intermediates of cholesterogenesis.

Analysis of Variance↗
PubMed1994

[Preliminary estimation of malaria transmission potential in areas where Anopheles sinensis is the only vector].

The data, vectorial capacity of Anopheles sinensis in the suburb of Jining city, Shandong Province in 1975, in 1980-1984, and the average gland infection rate of Anopheles sinensis infected with Plasmodium vivax artificially, were calculated by using Macdonald formula (1957). The basic reproduction rates were 4.44, 6.47 and 4.25 in the years 1975, 1980 and 1981, respectively. In 1982-1984, the rate was reduced to 0.69, 0.41 and 0.1, respectively. Since 1982, the incidence rate of malaria in the areas was reduced by 80% annually, indicating that the malaria transmission had been decreased obviously.

Animals↗
PubMed1994

Dopamine D2 and D3 receptors inhibit dopamine release.

D2-like dopamine receptors are thought to control presynaptic dopamine synthesis and release. Because these receptors comprise a family which includes D2, D3 and D4 dopamine receptors, the question arises as to which subtype performs what role(s). To investigate the potential autoreceptor roles of these proteins, D2, D3 and D4 receptors were transfected into a mesencephalic clonal cell line which synthesizes and releases dopamine. Here we report that stimulation of transfected D2 and D3 receptors, but not D4 receptors, inhibits dopamine release from this dopaminergic cell line. This is the first report of a functional role for D3 receptors and establishes these cell lines as a convenient in vitro model system to study signal transduction mechanisms associated with autoreceptor function.

4-Aminopyridine↗
PubMed1994

Pharmacological and functional characterization of D2, D3 and D4 dopamine receptors in fibroblast and dopaminergic cell lines.

In order to study the properties of the D2-like dopamine receptors, D2, D3 and D4 clones were transfected into mouse Ltk- fibroblasts, CCL1.3, and a neuronal mesencephalic cell line, MN9D. Most of the derived antagonist and agonist inhibition constants were the same for a given receptor in either cell line as determined by saturation and competition binding experiments. The rank order potencies for antagonists are: eticlopride, D2 > D3 > D4; YM-09151-2, D2 = D4 > D3; spiperone, D2 = D3 > D4; (+)-butaclamol, D2 > D3 > D4; clozapine, D4 > D2 > D3; and for agonists, quinpirole, D3 = D4 > D2; 7-hydroxy-2-(di-n-propyl)-aminotetralin, D3 > D2 = D4. Functionally, D2 stimulation increases inositol phosphate levels in CCL1.3 cells but not in MN9D, whereas D2 activation inhibits forskolin-stimulated cyclic AMP levels in both cell lines. D4 stimulation has no effect on inositol phosphate metabolism in either cell type, but inhibits adenylate cyclase in MN9D cells. Both the D2 and D4 mediated decreases in cyclic AMP can be blocked by preincubation with pertussis toxin. D3 does not couple to these pathways in either cell line. Reverse transcription/polymerase chain reaction techniques were used to determine the availability of cellular signalling systems. Both CCL1.3 and MN9D cells have high levels of G alpha i2 expression, whereas neither cell expresses G alpha i1 or G alpha i3. These data imply that the D2 receptor couples to the G alpha i2 subtype in both cell lines, whereas D4 does not.(ABSTRACT TRUNCATED AT 250 WORDS)

Adenylyl Cyclase Inhibitors↗
PubMed1993

Fibrin(ogen) mediates acute inflammatory responses to biomaterials.

Although "biocompatible" polymeric elastomers are generally nontoxic, nonimmunogenic, and chemically inert, implants made of these materials may trigger acute and chronic inflammatory responses. Early interactions between implants and inflammatory cells are probably mediated by a layer of host proteins on the material surface. To evaluate the importance of this protein layer, we studied acute inflammatory responses of mice to samples of polyester terephthalate film (PET) that were implanted intraperitoneally for short periods. Material preincubated with albumin is "passivated," accumulating very few adherent neutrophils or macrophages, whereas uncoated or plasma-coated PET attracts large numbers of phagocytes. Neither IgG adsorption nor surface complement activation is necessary for this acute inflammation; phagocyte accumulation on uncoated implants is normal in hypogammaglobulinemic mice and in severely hypocomplementemic mice. Rather, spontaneous adsorption of fibrinogen appears to be critical: (a) PET coated with serum or hypofibrinogenemic plasma attracts as few phagocytes as does albumin-coated material; (b) in contrast, PET preincubated with serum or hypofibrinogenemic plasma containing physiologic amounts of fibrinogen elicits "normal" phagocyte recruitment; (c) most importantly, hypofibrinogenemic mice do not mount an inflammatory response to implanted PET unless the material is coated with fibrinogen or the animals are injected with fibrinogen before implantation. Thus, spontaneous adsorption of fibrinogen appears to initiate the acute inflammatory response to an implanted polymer, suggesting an interesting nexus between two major iatrogenic effects of biomaterials: clotting and inflammation.

Ancrod↗
PubMed1993

Molecular modelling and epitope prediction of gp29 from lymphatic filariae.

The sequence of the major soluble protein component of the cuticle of filarial nematodes is homologous to that of bovine glutathione peroxidase, for which an X-ray structure is available. Due to the high degree of sequence identity (42%), it has been possible to build an apparently reliable three-dimensional model of the gp29 cuticular protein from Brugia spp. that will aid studies of the molecule both as a target immunogen and secreted enzyme. The modelled core of the gp29 structure is conserved compared to the bovine enzyme, consisting of a beta-sheet surrounded by alpha-helices. Experimental data showed that Brugia spp. gp29 has four subunits, and a tetrameric form of gp29 has also been modelled. The two N-linked glycosylation sites per subunit were predicted to lie on the surface of the tetramer. Most of the variation in amino acid sequence compared to that of mammalian enzymes, occurs in the surface loops, several of which are larger and more exposed in gp29. Deglycosylated gp29 was demonstrated to be immunogenic in human infection, and six likely B-cell epitopes have been predicted on the basis of a high protrusion index and sequence variability.

Amino Acid Sequence↗
PubMed1993

Production of polyclonal antisera to parathyroid hypertensive factor from spontaneously hypertensive rats.

OBJECTIVE: Parathyroid hypertensive factor (PHF) is a newly described hypertensive factor which may cause elevation of blood pressure in approximately 40% of North American essential hypertensive patients. PHF is also found in several animal models of hypertension, including spontaneously hypertensive rats (SHR), deoxycorticosterone acetate-salt hypertensive rats and salt-sensitive Dahl rats. The objective of the present study was to raise an antibody to PHF, and to use this antibody to study the effect of PHF in SHR. DESIGN: Plasma and parathyroid gland culture media collected from SHR were used in the present study as the antigen in the production and analysis of a polyclonal antiserum to PHF. METHODS: PHF is of low molecular weight (approximately 3000 daltons) and is sensitive to inactivation by trypsin. We used PHF partially purified from parathyroid gland culture media as the antigen to inoculate mice. The substance was bound to aminophenyl thioether paper discs to make it more antigenic. The discs were then emulsified in Freund's adjuvant (complete for first inoculation, incomplete for subsequent inoculations) for intraperitoneal implantation. Production of anti-PHF antisera was monitored by enzyme-linked immunosorbent assay. RESULTS: Antisera produced in mice reacted with purified PHF prepared from SHR plasma as well as with PHF prepared from parathyroid gland culture media. PHF treated with the PHF antiserum produced no characteristic hypertensive response in normotensive assay rats. The antisera did not crossreact with two forms of bovine parathyroid hormone, bPTH (1-84), bPTH (1-34) or with shorter parathyroid hormone fragments, or with any other vasoactive substance tested. Injection of an aliquot of the antiserum in anesthesized spontaneously hypertensive rats reduced mean arterial pressure to a normal range of approximately 110 mmHg. CONCLUSIONS: These results indicate that (1) polyclonal antisera to PHF can be raised in mice and (2) PHF may contribute significantly to the elevated blood pressure in SHR.

Animals↗
PubMed1993

Detection of hepatitis C virus RNA in the liver by in situ hybridization.

To examine HCV infection histologically, we attempted non-radioactive in situ hybridization of HCV-RNA in the liver. We amplified cDNA probe (360 base pairs) by PCR using the primers deduced from the core region of the HCV genome. The probe was labelled with digoxigenin by PCR and used for in situ hybridization on paraformaldehyde-fixed frozen liver sections. The hybrids were visualized immunohistochemically with alkaline-phosphatase-conjugated anti-digoxigenin and alkaline-phosphatase substrates. HCV-RNA-cDNA hybrids were detected in 21 of 24 patients with positive serum HCV markers, whereas there were no positive signals in the liver of 12 cases without HCV infection. The signal intensity of HCV-RNA-cDNA hybrids was abolished after RNase treatment. Various other specificity experiments also verified specific hybridization of HCV-RNA-cDNA. HCV-RNA was visualized in liver cells and most of them were regarded as hepatocytes from their characteristic features. The infected hepatocytes were frequently associated with mononuclear cell infiltration. Hepatocytes positive for HCV-RNA were sometimes binuclear and distributed in various patterns among cases tested. The present in situ hybridization of HCV RNA is highly sensitive and specific and the results suggest the host immune response to HCV-infected cells.

Hepacivirus↗
PubMed1993

Sequence, transcriptional, and functional analyses of the valine (branched-chain amino acid) dehydrogenase gene of Streptomyces coelicolor.

The gene encoding the valine (branched-chain amino acid) dehydrogenase (Vdh) from Streptomyces coelicolor has been characterized as follows. The vdh gene was identified by hybridization to a specific oligodeoxynucleotide that was synthesized on the basis of the N-terminal amino acid sequence of purified Vdh. Nucleotide sequence analysis predicts that the vdh gene contains a 364-amino-acid open reading frame that should produce a 38,305-M(r) protein. The deduced amino acid sequence of the Vdh protein is significantly similar to those of several other amino acid dehydrogenases, especially the leucine and phenylalanine dehydrogenases from Bacillus spp. The vdh gene is apparently transcribed from a single major transcriptional start point, separated by only 8 bp from the 5' end of a divergent transcript and located 63 bp upstream from the vdh translational start point. Mutants with a disrupted vdh gene have no detectable Vdh activity and have lost the ability to grow on valine, leucine, or isoleucine as the sole nitrogen source. This vdh mutation does not significantly affect growth or actinorhodin production in a minimal medium, yet the addition of 0.2% L-valine to the medium provokes approximately 32 and 80% increases in actinorhodin production in vdh+ and vdh strains, respectively.

Amino Acid Oxidoreductases↗
PubMed1993

Direct evidence that the hydroxyl radical plays a pathogenetic role in myocardial "stunning" in the conscious dog and demonstration that stunning can be markedly attenuated without subsequent adverse effects.

Recent studies suggest that the hydroxyl radical (.OH) plays a pathogenetic role in postischemic ventricular dysfunction (myocardial "stunning"). This concept, however, is predicated exclusively on results obtained in anesthetized open-chest preparations, which are subject to the confounding influence of many unphysiological conditions and in which both myocardial stunning and free radical generation are greatly exaggerated. The lack of supporting evidence in more physiological animal models represents a major limitation of the .OH hypothesis of stunning. Furthermore, concern has been raised that myocardial stunning may be a period of "rest" necessary for full recovery, so that attenuation of the early phase of stunning by antioxidant therapy may have subsequent detrimental effects on the resting function and/or on the return of myocardial contractile reserve. To address these issues, in phase 1 of this study conscious unsedated dogs undergoing a 15-minute coronary artery occlusion received an intravenous infusion of normal saline (n = 22), of the .OH scavenger N-2-mercaptopropionyl glycine (MPG, n = 17), or of the iron chelator desferrioxamine (DF, n = 14). Compared with control dogs, the dogs treated with MPG or DF exhibited significantly greater postischemic wall thickening throughout the first 6 hours of reperfusion; the total deficit of wall thickening during this time interval was reduced 50% by MPG and 50% by DF. The magnitude of this beneficial effect was a function of the severity of ischemia, so that the dogs with the lowest collateral flows had the greatest improvement of wall thickening. The accelerated recovery produced by MPG and DF in the first 6 hours was not followed by any deterioration of resting wall thickening at 24 or 48 hours. Furthermore, in dogs treated with MPG or DF, the increase in wall thickening elicited by maximal inotropic stimulation (isoproterenol or dopamine) was similar before stunning and shortly after resting wall thickening had normalized (24 or 48 hours after reflow); thus, despite the fact that most of the early postischemic dysfunction had been eliminated by antioxidant therapy, there was no subsequent impairment of either resting function or contractile reserve. In phase 2, production of free radicals (measured with the spin trap alpha-phenyl N-tert-butyl nitrone) was markedly (> 80%) inhibited by the same doses of MPG and DF that attenuated stunning in phase 1.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1993

Immunosuppression in murine brucellosis.

Brucellosis in mice results in a distinct immunosuppression which may be abrogated by immunomodulators, such as levamisole, bestatin, interleukin-2 (IL-2) and Polyporus umbellatus. The data presented here provide evidence that immunosuppression in addition to infection of target tissues and allergic reactions (including types 3 and 4) contributes to the pathogenesis of brucellosis. The present study also provides some basic data regarding the value of this animal model, and criteria for observing the effect of therapy on chronic brucellosis.

Animals↗
PubMed1993

[3-dimensional finite element stress analysis of the periodontal ligament of bridge abutments in mandibular posterior fixed bridge].

According to the measured data, the characters of all components of fixed bridge and the periodontal supporting tissues, and the dividing principals of finite element, the three-dimensional finite element model was developed on the basis of a try adult mandible. 6 vertical loadings and 1 horizontal loading were applied on the abutments and the pontic. The Emax and Emin of PDL were calculated and the resulting principal stresses were plotted for each loading.

Adult↗
PubMed1993

Inflammatory responses to implanted polymeric biomaterials: role of surface-adsorbed immunoglobulin G.

In many cases, evidently inert and nontoxic biomaterials may trigger procoagulant and inflammatory responses. Because most polymeric biomaterials accumulate a surface layer of protein immediately after implantation, these adverse reactions may stem from secondary interactions between the host and this surface layer of adsorbed proteins. Using polyester terephthalate (the polymer from which both Dacron and Mylar are produced) as a model, we have explored the hypothesis that surface-adsorbed immunoglobulin might mediate subsequent inflammatory responses. We find, as have others, that immunoglobulin G (IgG) does spontaneously adsorb to polymer surfaces, both in vitro and in vivo. Furthermore, polymer implants precoated with IgG do activate human polymorphonuclear neutrophils in vitro and also attract substantial numbers of phagocytes (especially polymorphonuclear neutrophils and macrophages) when implanted in mice. However, when implants are placed in mice having a form of severe combined immunodeficiency (and, consequently, almost undetectable levels of serum IgG), a near-normal influx of phagocytic cells ensues. Thus, spontaneously-adsorbed surface IgG does not appear to be a necessary precedent to inflammatory responses directed against implanted biomaterials.

Adsorption↗
PubMed1992

Possible involvement of protein kinase C and calcium in GSH efflux from Hep G2 cells.

We investigated the effects of protein kinase C modulations and calcium mobilization on GSH efflux in Hep G2 cells. GSH efflux from Hep G2 cells was increased by a phorbol ester. Staurosporine, an inhibitor of protein kinase C, diminished phorbol ester-stimulated GSH efflux from the cells. GSH efflux was negatively correlated with extracellular calcium concentrations. Verapamil enhanced GSH efflux, whereas ATP decreased GSH efflux. The latter effect was diminished in the absence of extracellular calcium. Protein kinase C and calcium mobilization may be crucial factors in GSH efflux from human hepatocytes.

Adenosine Triphosphate↗
PubMed1992

Three beta-tubulin cDNAs from the parasitic nematode Haemonchus contortus.

Experimental evidence indicates that tubulin is the site of action of the anthelmintic benzimidazoles. Furthermore, certain residues of beta-tubulin seem to be critical for this mechanism. Although the benzimidazoles selectively affect nematode vs. mammalian beta-tubulin, the molecular basis for this differential action is not known. To enhance our understanding of this phenomenon, and to provide the basis for investigating benzimidazole resistance in parasitic nematodes, we undertook the cloning of beta-tubulin cDNAs from the ruminant parasite, Haemonchus contortus. We have cloned and sequenced three beta-tubulin cDNAs from this organism, beta 12-16, beta 12-164, and beta 8-9. The first 2 differ at only 23 nucleotides, which give rise to 4 amino acid changes. beta 8-9 represents a different isotype class from the other two, since it differs extensively in the carboxyterminus. By comparing the sequences of these and other nematode beta-tubulins with mammalian beta-tubulins, several regions of consistent difference can be recognized; the functional significance of these regional differences has not been defined. Sequences very similar or identical to beta 8-9 and beta 12-16 are present in both benzimidazole-sensitive and benzimidazole-resistant populations of H. contortus. However, it appears that drug-resistant organisms may differ in the presence of a gene product which is closely related to beta 8-9.

Amino Acid Sequence↗
PubMed1992

The rat dopamine D4 receptor: sequence, gene structure, and demonstration of expression in the cardiovascular system.

Dopamine receptors have been implicated in a variety of neurological and neuropsychiatric disorders. Here we describe the use of the polymerase chain reaction and low stringency library screening to isolate a rat genomic clone encoding a novel dopamine receptor. Sequence data and pharmacological analysis reveal this clone to be the rat analog of the human D4 receptor, which exhibits a high affinity for the antipsychotic drug clozapine. The mRNA for this receptor shows a restricted pattern of expression in the central nervous system. Significant levels of expression were found in the hypothalamus, thalamus, olfactory bulb, and frontal cortex. However, 20-fold higher levels of D4 mRNA expression were observed in the cardiovascular system. Thus, this receptor appears to mediate dopamine function in the cardiovascular system as well as the central nervous system.

Amino Acid Sequence↗