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Biomedical subjects

H Liu

Publications and source records attributed to H Liu.

At least 1,135 records · Page 63Linked to original sources
PubMed1993

[Pathogenic factors of postischemic ventricular dysfunction and effects of magnesium].

To investigate the mechanism of myocardial; tunning, a Langendorff model of rat hearts (n = 18) underwent 15 min ischemia with coronary flow at 0.2 ml/min and 10 min reperfusion with Ringer's solution of 1.06 mmol/L Mg2+. Histological exam revealed no myocardial necrosis. However, the recovery of pressure product (RPP) was only 77% compared with control period. The myocardial Ca2+ content and water content were significantly increased (P < 0.01, vs control hearts). Pretreatment with high concentration of Mg2+ (2.4 mmol/L) improved the recovery of postischemic ventricular function, attenuated the Ca2+ overload and myocardial edema. The results indicated that a brief period of low-flow ischemia could produce a postischemic ventricular dysfunction-the myocardial stunning. Calcium overload and myocardial edema might be two pathogenic factors. An increased Mg2+ had a protective effects on postischemic ventricular dysfunction, which may involve the following mechanisms: reduced Ca2+ overload and attenuated myocardial edema.

Animals↗
PubMed1993

[Capillary blood viscosimeter of the microcomputer].

On the basis of specific property of non-Newtonian fluid (blood) we have worked out the formula of capillary blood viscosimeter:sheat stress tau alpha = alpha rho gh/2L shear rate f (tau alpha) = 1/pi alpha 3 [3q + h(dq/dh)] and designed and produced the prototype. Repetition experiments have indicated that the property of the instrument is stable, and a comparison of the prototype with the cone and plate viscosimeter has demonstrated the reliability of the measurements.

Blood Viscosity↗
PubMed1993

[Nilestriol prevents osteoporosis in ovariectomized rats].

In order to determine the effects and mechanism of Nilestriol upon bone metabolism, 4-month aged female SD rats were divided randomly into three groups: The OVX group subjected to bilateral ovariectomy, the SHAM group to sham operation, the Nilestriol (CEE3) group to bilateral ovariectomy and treated with CEE3 0.15 mg/100 g BW once a week for 10 weeks. The CEE3 was introduced directly into the stomach from the first day after operation. All rats were killed 10 weeks after operation and their right proximal tibiae were processed undercalcified for quantitative bone histomorphometry. The weights of bone and inorganic matter (ash content) and content of calcium, phosphorus of right humeral were measured. The results showed that in the OVX group the trabecular bone volume, the trabecular thickness, the content of calcium bone, and the ratios of bone weight and ash weight to body weight were all significantly reduced. The bone loss was associated with an increase in bone remodeling; the bone resorption appeared much more marked than the bone formation. In contrast, the ovariectomized animals treated with CEE3 had normalization of bone mass and a declined index of bone resorption and formation which recovered the balance of bone remodeling. It suggested that CEE3 is successful in prevention of bone loss in OVX rats. It is convinced of using Nilestriol to prevent postmenopausal osteoporosis.

Animals↗
PubMed1993

Production of anti-tumor human monoclonal antibodies using different approaches.

The production of anti-tumor human monoclonal antibodies (MAbs) by human-human or human-mouse hybridoma technology was studied. UC729-6, a human lymphoblastoid cell line, or NS-1, a mouse myeloma cell line, were fused with lymphocytes isolated from regional lymph modes of 26 patients with breast or gastrointestinal cancer, resulting in 130 immunoglobulin-secreting human-human hybrids and 21 human-mouse hybrids. The supernatants of 88 hybrids were screened against a panel of cancer cells. The supernatants of 37 human-human hybrids and 2 human-mouse hybrids reacted with cancer cell lines. After three times subcloning, only one anti-breast cancer hybrid human MAb, IgG(lambda) human-human hybridoma (MUBL-6), and one anti-gastric cancer human MAb, IgM(lambda) human-mouse hybridoma (HMG-1), were obtained. The antibody-secreting level was 1-4 micrograms/ml/24 h. Production of anti-breast cancer human MAbs by Epstein-Barr virus (EBV) hybridoma was also studied. Human lymphocytes were derived from draining lymph nodes of a breast cancer patient, whose serum antibody strongly reacted with tumor associated antigen (TAA). The enriched B cells were transformed with EBV in vitro. Positive antibody-secreting B cells were selected, expanded, and fused with heteromyeloma SHMD-33. The fusion frequency was 28/10(7) lymphocytes. Among them were 16 hybridomas secreting human immunoglobulin. After subcloning, 60% of the cloned hybridomas kept their antibody-secreting ability. Six observed hybridomas remained stable for more than 1 year in tissue cultures. The antibody-secreting level was 2.9-30 micrograms/ml/24 h. Supernatants from these hybridomas all reacted with breast cancer cell lines but not with gastric cancer cell lines.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1993

Health indicators of substance abuse problems in Baltimore.

Selected health indicators were examined for which Baltimore-specific data were available, including substance abuse treatment admissions, AIDS (acquired immunodeficiency syndrome) case reports, and drug-related emergency room visits and deaths. All indicators reflected high levels and increasing rates of substance abuse problems in Baltimore. Drugs of choice most likely to result in adverse effects were heroin, cocaine, and alcohol--often in combination. The African-American population in Baltimore is disproportionately affected by substance abuse. Emerging drug use patterns are examined, and health service and policy issues are discussed.

Adolescent↗
PubMed1992

Protein tyrosine phosphorylation and regulation of the receptor for platelet-activating factor in rat Kupffer cells. Effect of sodium vanadate.

Platelet-activating factor (1-O-alkyl-2-acetyl-sn-glycero-3-phosphocholine, AGEPC) and sodium vanadate (a phosphotyrosine phosphatase inhibitor) induced a time- and concentration-dependent increase in phosphotyrosine in several proteins and stimulated prostaglandin (PG) E2 production in cultured rat Kupffer cells. In addition, vanadate induced a decrease in the surface expression of AGEPC receptors and, as a consequence, inhibited AGEPC-stimulated PGE2 production. The vanadate-induced decrease in the surface expression of AGEPC receptors was time- and concentration-dependent and was partially prevented by genistein, a putative tyrosine kinase inhibitor. Upon removal of vanadate from the culture medium and re-incubation of cells in vanadate-free medium, the surface AGEPC receptors were restored within 7 h after the removal of vanadate. Both AGEPC- and vanadate-stimulated PGE2 formation was attenuated by genistein. Thus the present investigation demonstrates that both AGEPC and sodium vanadate stimulate tyrosine phosphorylation of cellular proteins, and vanadate induces a decrease in the number of the surface AGEPC receptors. These results suggest that protein tyrosine phosphorylation may play a role, directly or indirectly, in the regulation of surface expression of AGEPC receptors as well as in PGE2 production in response to vanadate and AGEPC.

Animals↗
PubMed1992

Regulation of the surface expression of the platelet-activating factor receptor in IC-21 peritoneal macrophages. Effects of lipopolysaccharide.

The effect of bacterial lipopolysaccharide (LPS) on the expression of the receptor for platelet-activating factor (1-O-alkyl-2-acetyl-sn-glycero-3-phosphocholine; AGEPC) was examined in cultured IC-21 peritoneal macrophages. AGEPC binding to its receptors reached saturation within 20 min at 25 degrees C and was reversible. Scatchard analysis revealed a single class of AGEPC receptors with a Bmax of approximately 170 fmol/mg cellular protein and a Kd of 0.25 nM. Preincubation of IC-21 cells with LPS (0.01-1,000 ng/ml) induced an increase in the surface expression of AGEPC receptors in a time- and concentration-dependent fashion. The maximal effect of LPS on the AGEPC receptor was observed between 5 and 8 h, with a typical increase between 150 and 200%. Scatchard analysis indicated that LPS treatment of IC-21 cells increased the number of AGEPC receptors on the cell surface without any apparent change in the affinity of the receptor for the ligand. The effect of LPS on the surface expression of the AGEPC receptor was nearly abolished by cycloheximide (0.1 mM) and by actinomycin D (3 microM), suggesting the involvement of enhanced receptor protein synthesis and mRNA production in this event. Moreover, LPS treatment increased the capability of the IC-21 cell to respond to AGEPC addition by elevating intracellular free Ca2+ without causing an increase in the basal level of intracellular Ca2+. The present study demonstrates that IC-21 peritoneal macrophages possess high affinity AGEPC receptors and provides the evidence that the number of functional AGEPC receptors on a cell can be increased significantly upon exposure to LPS.

Acetates↗
PubMed1992

31P-NMR study of the phospholipid moiety of lipophorin subspecies.

31P-NMR spectra of four distinct subspecies of Manduca sexta hemolymph lipophorin revealed the presence of two resonances separated by 0.6 ppm. Phospholipid analysis of the lipoproteins showed that phosphatidylcholine (PC) and phosphatidylethanolamine (PE) were present and their mass ratio correlated well to the intensity of the two resonances in each of the different subspecies. The two resonances persisted in 31P-NMR spectra of organic solvent extracts of lipophorin. These results, together with the fact that PE, but not PC, can form an intramolecular hydrogen bond between the phosphate oxygen and the amino group of ethanolamine, resulting in deshielding of the phosphorus nucleus (and a 0.6 ppm downfield shift), strongly suggest the resonances observed represent the PC and PE components of these lipoproteins. 31P-NMR line-width data obtained as a function of temperature and solvent viscosity were used to calculate the chemical shift anisotropy (delta sigma), intrinsic viscosity (eta'), and lateral diffusion coefficients (DT) of PC and PE in different lipophorin subspecies. eta' and DT for PC and PE were similar among high-density lipophorins but differed in low-density lipophorin (LDLp). These differences may be related to the large increase in diacylglycerol content in this particle and/or the association of up to 16 molecules of apolipophorin III. On the basis of the known lipid compositional differences between LDLp and high-density lipophorin subspecies, we propose that uptake of large amounts of diacylglycerol during LDLp formation results in partitioning of this lipid to the surface monolayer where it intercalates between phospholipid molecules. Diacylglycerol intercalation creates gaps between phospholipid head groups that expose the hydrophobic surface.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1992

Effects of insulin on steady state kinetics of GLUT4 subcellular distribution in rat adipocytes. Evidence of constitutive GLUT4 recycling.

We labeled rat adipocyte cell surface glucose transporters with an impermeable, photoreactive glucose analogue, 1,3-bis-(3-deoxy-D-glucopyranose-3-yloxy)-2-propyl 4-benzoylbenzoate (B3GL) and its radioactive tracer [3H]B3GL. The labeling did not affect glucose transporter subcellular distribution in basal and insulin-stimulated adipocytes. When basal or insulin-stimulated adipocytes were labeled with [3H]B3GL and incubated at 37 degrees C in steady state, labeled GLUT4 was rapidly reduced at the cell surface and stoichiometrically recovered in microsomes without any change in GLUT4 protein levels in either pool. The labeled GLUT4 equilibrium exchange was found to be a simple first order process describable by two first order rate constants, one for internalization (k(in)) and the other for externalization (kex). Insulin affected both rate constants, reducing k(in) by 2.8-fold and increasing kex by 3.3-fold. It is concluded that GLUT4 constantly and rapidly recycles in adipocytes between the cell surface and its storage pool, and insulin increases the cell surface GLUT4 level in rat adipocytes by modulating both the internalization and the externalization steps of constitutively recycling GLUT4.

3-O-Methylglucose↗
PubMed1992

Measurement of free amino acid levels in ultrafiltrates of blood plasma by high-performance liquid chromatography with automatic pre-column derivatization.

Although there are many techniques available for the analysis of amino acids, deproteinization is still one of the major problems in the analysis of amino acids in physiological fluids. The method used to prepare the plasma and to remove the plasma protein has a marked effect on the final results. The most widely used method of deproteinization is precipitation with 5-sulphosalicyclic acid followed by centrifugation to remove the precipitated protein. We have not had success in using this deproteinization agent for the analysis of plasma amino acids by a high-performance liquid chromatographic method with automatic pre-column o-phthaldialdehyde-3-mercaptopropionic acid and 9-fluorenylmethyl chloroformate derivatization because of the adverse effect of the sulphosalicyclic acid supernatant on the quantitation and separation. Ultrafiltration was used as an alternative method for the preparation of plasma samples in this experiment. The results were satisfactory for the analysis of plasma amino acids in 1500 samples during a period of four years. Some factors that might influence the results of the ultrafiltration were investigated.

Amino Acids↗
PubMed1992

Solid-phase extraction with supercritical fluid elution as a sample preparation technique for the ultratrace analysis of flavone in blood plasma.

A new sample preparation technique, solid-phase extraction with supercritical fluid elution, was developed for the selective isolation of ultratrace levels of drugs from plasma. Plasma samples spiked with a drug were applied to octadecylsilane cartridges and the cartridges were then washed, briefly dried and directly fitted into cells for subsequent supercritical fluid elution. The absolute recovery was studied by using a radiolabeled model compound. The extraction selectivity was examined by chromatographing the extracts with a reversed-phase high-performance liquid chromatographic method with ultraviolet detection. The effects of extraction pressure and the length of capillary restrictors on drug recovery were examined in order to determine the optimal conditions for supercritical fluid elution. The performance of the method was compared to that of conventional solid-phase extraction in terms of recovery, selectivity, precision and accuracy of analysis. Flavone was used as the model compound and dog plasma as the biological matrix for these studies.

Animals↗
PubMed1992

Human apolipoprotein A-I liberated from high-density lipoprotein without denaturation.

Apolipoprotein A-I (apoA-I) was liberated from human high-density lipoprotein (HDL) without exposure to organic solvents or chaotropic salts by the action of isolated insect hemolymph lipid transfer particle (LTP). LTP-catalyzed lipid redistribution results in transformation of HDL into larger, less dense particles accompanied by an overall decrease in HDL particle surface area:core volume ratio, giving rise to an excess of amphiphilic surface components. Preferential dissociation of apolipoprotein versus phospholipid and unesterified cholesterol from the particle surface results in apolipoprotein recovery in the bottom fraction following ultracentrifugation at a density = 1.23 g/mL. ApoA-I was then isolated from other contaminating HDL apolipoproteins by incubation with additional HDL in the absence of LTP, whereupon apolipoprotein A-II and the C apolipoproteins reassociate with the HDL surface by displacement of apoA-I. After a second density gradient ultracentrifugation, electrophoretically pure apoA-I was obtained. Sedimentation equilibrium experiments revealed that apoA-I isolated via this method exhibits a tendency to self-associate in an aqueous solution while its circular dichroism spectrum was indicative of a significant amount of alpha-helix. Both measurements are consistent with that observed on material prepared by denaturation/renaturation. The ability of apoA-I to activate lecithin:cholesterol acyltransferase was found to be similar to that of apoA-I isolated by conventional methods. The present results illustrate that LTP-mediated alteration in lipoprotein particle surface area leads to dissociation of substantial amounts of surface active apoprotein components, thus providing the opportunity to isolate apoA-I without the denaturation/renaturation steps common to all previous isolation procedures.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1992

Determination of valproic acid by high-performance liquid chromatography with photodiode-array and fluorescence detection.

The derivatization of valproic acid and undecylenic acid with 4-bromomethyl-7-methoxycoumarin is described. The derivatives were detected by photodiode-array and fluorescence detectors. The optimum monitoring conditions and the stability of the suspension solution and derivatives were investigated. A high-performance liquid chromatographic (HPLC) method with isocratic or gradient elution has been established for the analysis. This method has been used for the determination of total and free valproic acid in serum. There is a satisfactory correlation between the results obtained by this HPLC method and those measured by the enzyme immunoassay. Some other common anti-epileptic drugs did not interfere with the analysis. The method is simple and fast and has better sensitivity and linearity than enzyme immunoassay. It is suited for routine therapeutic drug monitoring.

Chromatography, High Pressure Liquid↗
PubMed1992

Ultrastructural evidence for GABA-mediated disinhibitory circuits in the spinal cord of the cat.

The synaptic relationships between gamma-aminobutyric acid (GABA)-immunoreactive and enkephalin-immunoreactive profiles in the cat spinal cord were examined using combined pre-embedding immunoperoxidase and post-embedding immunogold electron microscopic immunocytochemistry. Although colchicine was not used, enkephalin-immunoreactive somata and dendrites were detected in regions associated with nociceptive transmission, including laminae I, II, V and X. In each of these laminae, many GABA-immunoreactive terminals were found presynaptic to enkephalin-immunoreactive cell bodies and dendrites. We propose that disinhibition of opioid-containing neurons may be a common feature of pain-related circuits in the cat spinal cord.

Animals↗
PubMed1992

Platelet-activating factor-stimulated protein tyrosine phosphorylation and eicosanoid synthesis in rat Kupffer cells. Evidence for calcium-dependent and protein kinase C-dependent and -independent pathways.

The lipid mediator platelet-activating factor (1-O-alkyl-2-acetyl-sn-glycero-3-phosphocholine, AGEPC) has been shown to elicit several important biochemical signaling responses in mammalian cells, including polyphosphoinositide hydrolysis, arachidonic acid release/eicosanoid production, and protein tyrosine phosphorylation. In the present study, the roles of Ca2+ and protein kinase C (PKC), two signaling components of the phospholipase C pathway, in AGEPC-stimulated eicosanoid production and protein tyrosine phosphorylation, were investigated in cultured rat Kupffer cells. AGEPC at nanomolar concentrations induced an increase in intracellular calcium concentration ([Ca2+]i), stimulated membrane PKC activity, and resulted in protein tyrosine phosphorylation. The maximal increase in [Ca2+]i and membrane PKC activity in response to AGEPC were observed within 30-50 s, whereas the AGEPC-induced protein tyrosine phosphorylation reached maximal levels within 2-5 min. [Ethylenebis(oxyethylenenitrilo)]tetraacetic acid (EGTA) but not 8-(N,N-diethylamino)-octyl-3,4,5-trimethoxybenzoate hydrochloride (TMB-8), an inhibitor of calcium release from intracellular compartments, nearly abolished the AGEPC-induced increase in [Ca2+]i suggesting involvement of extracellular calcium influx in this event. Both EGTA and TMB-8 abolished or inhibited AGEPC-stimulated protein tyrosine phosphorylation and eicosanoid formation, respectively. The calcium ionophore A23187 alone stimulated eicosanoid production and protein tyrosine phosphorylation with an identical pattern to that of AGEPC. Phorbol myristate acetate (PMA), an activator of PKC, which did not affect [Ca2+]i, mimicked the actions of AGEPC, stimulating eicosanoid production and promoting tyrosine phosphorylation of a set of proteins similar to those phosphorylated following AGEPC stimulation. AGEPC-enhanced tyrosine phosphorylation of some of the protein substrates and eicosanoid production were inhibited in cells "down-regulated" for PKC. Furthermore, both PMA- and AGEPC-stimulated eicosanoid production and protein tyrosine phosphorylation were attenuated or abolished by at least one of the PKC inhibitors, staurosporine, and calphostin C. Taken together, these results are consistent with the conclusions that: (a) AGEPC stimulates the phospholipase-mediated arachidonic acid release/eicosanoid synthesis cascade and protein tyrosine phosphorylation through extracellular Ca(2+)-dependent and PKC-dependent and -independent mechanism(s) and (b) the Ca(2+)-PKC interaction determines the efficacy of the AGEPC-stimulated cellular events.

Animals↗
PubMed1992

Combined supercritical fluid extraction/solid-phase extraction with octadecylsilane cartridges as a sample preparation technique for the ultratrace analysis of a drug metabolite in plasma.

Supercritical fluid extraction was coupled with solid-phase extraction using octadecylsilane cartridges for the selective isolation of ultratrace levels of a drug metabolite, mebeverine alcohol, from plasma. Plasma was directly applied to the extraction cartridge, the cartridge was washed to remove protein and then extracted under supercritical conditions using CO2/5% methanol. The effluent from the extraction cell was bubbled through a small volume of 2-propanol to trap the extracted mebeverine alcohol. The effects of extraction pressure and temperature on analyte recovery were examined. The absolute recovery, selectivity, precision, and accuracy of the combined supercritical fluid extraction/solid-phase extraction approach were compared to those of conventional solid-phase extraction using gas chromatography/mass spectrometry in the selected-ion monitoring mode. Mebeverine alcohol was used as a model compound, and dog plasma was employed as the biological matrix for these studies.

Animals↗
PubMed1992

Comparison of ampicillin/sulbactam and amoxicillin/clavulanic acid for detection of borderline oxacillin-resistant Staphylococcus aureus.

Borderline oxacillin-resistant Staphylococcus aureus (BORSA) may be misidentified as intrinsically methicillin-resistant Staphylococcus aureus (MRSA) in the clinical laboratory. Under disk diffusion testing conditions designed to maximize detection of MRSA (incubation at 32 degrees C, pre-induction with methicillin, or plating on 4% NaCl-supplemented agar), BORSA strains also tend to appear resistant to semisynthetic penicillins. Under these conditions, ampicillin/sulbactam appears to be more accurate than amoxicillin/clavulanic acid for differentiating BORSA from MRSA.

Amoxicillin↗