Search PubMed⌕ Search

Biomedical subjects

Q Liu

Publications and source records attributed to Q Liu.

At least 217 records · Page 12Linked to original sources
PubMed2000

Interaction of the novel GH secretagogue hexarelin with GHRH in regulating the secretion of GH by cultured human pituitary somatotrophinomas in vitro.

The effects of the novel GH-releasing hexapeptide, Hexarelin, on the secretion of GH in cultured human pituitary somatotrophinomas was further investigated. Hexarelin (20 nmol/L) strongly stimulated GH secretion, which could be reduced by phloretin, but not by RP-cAMPS, an inhibitor of protein kinase A (PKA). (Ac-Tyr1,D-Arg2)-GRF(1-29)-NH2 failed to block the effects of Hexarelin but completely abolished the stimulation of GH secretion exerted by GHRH. When added alone to somatotrophinoma cell cultures, Hexarelin had no effect on cAMP levels, but it potentiated the stimulatory effects of GHRH. These results demonstrated that Hexarelin could directly stimulate GH secretion by human pituitary somatotrophs PKC-dependently, which might be contributed to the activation of the PI transduction system. In addition, Hexarelin could interact with GHRH on the adenylyl cyclase system.

Adenoma↗
PubMed2000

Double labeling immunoelectron microscopic study on the synaptic connections between glutamic acid neurons and GABA neurons in the hippocampus of rats.

In order to explore the roles of different neurotransmitters in epileptic pathogenesis, the synaptic connections between glutamic acid (Glu) neurons and GABA neurons in normal rat hippocampus were studied by pre-embedding double labeling immunoelectron microscopy. The GABA immunoreaction was first demonstrated by chromogen DAB, then the Glu immunoreaction was demonstrated by molybdic acid-TMB method. After being stabilized by DAB-cobalt chloride, the sections were processed for electron microscopic embedding. Under electron microscope, there were many Glu immunoreaction-positive neurons in the pyramidal layer of hippocampal CA1 area and some GABA immunoreaction-positive neurons with pyramidal or polygonal perikarya in the pyramidal, polymorphic and radiant layer of CA1 area. There were also symmetric dendro-axonic synapses formed by GABA-positive dendrites and Glu-positive axons in the polymorphic layer and symmetric axo-dendrites synapses formed by GABA-positive axons and Glu-positive dendritic in the radiant layer. In addition, there were symmetric autoregulatory axo-dendritic synapses between Glu-positive axons and dendrites and autoregulatory axo-axonic synapses (both symmetric and asymmetric) between GABA-positive axons. Above mentioned results, for the first time, showed that there were complex synaptic regulatory relationships between excitatory Glu neurons and inhibitory GABA neurons in the hippocampal CA1 area, thereby, providing ultrastructural evidence for different neurotransmitters participating in epileptic pathogenesis.

Animals↗
PubMed2000

The role of protein kinase C and its effect on GHRH in the regulation of hormone secretion by somatotrophinomas.

Phorbol ester-induced release of growth hormone (GH) and prolactin (PRL) from human somatotrophic tumors was examined in vitro. 12-O-tetradecanoyl-phorbol-13-acetate (TPA) strongly stimulated GH and PRL secretion and showed an additive effect on GH secretion if used in combination with GH releasing hormone (GHRH). In contrast, staurosporine exerted a variable inhibitory effect on GH release. There was no correlation between such effects and gsp mutations. The findings suggested that TPA doesn't act directly through cAMP signal transduction system.

GTP-Binding Protein alpha Subunits, Gs↗
PubMed2000

Restrictive effect of puerarin on myocardial infarct area in dogs and its possible mechanism.

To evaluate the protective effect of puerarin on ischemic myocardium in dogs with acute myocardial infarction (AMI) and to reveal its possible mechanism, 10 dogs were randomly divided into puerarin group (group G) and control group (group C). AMI model was established in all dogs. Puerarin or saline was administered over a period of 21 days. Coronary angiography was performed before and after ligation of coronary artery. Eight hemorheological parameters were examined before and 22 days after the operation. The infarct area and vessel density of myocardium were assessed. The infarct area in group G was smaller than that in group C. Angiography 2 h and 22 d after ligation of coronary artery revealed significant augmentation of collateral vessels in group G as compared with control group. The platelet aggregation and the blood viscosity were increased during AMI when compared with control phase, and the increased indexes during AMI would be inhibited when puerarin were given. Capillaries and distribution vessel density in ischemic zone on day 22 showed statistically significant augmentation in group G as compared with control group. Puerarin might improve the opening and formation of coronary collateral circulation, and might inhibit the increase of platelet aggregation and the blood viscosity during AMI, and thereby improve microcirculation and restrict myocardial infarct area.

Animals↗
PubMed2000

Detection of congenital malaria by polymerase-chain-reaction methodology in Dar es Salaam, Tanzania.

The examination of congenital malaria was performed by Giemsa staining and polymerase-chain-reaction (PCR) methodology. We randomly selected 298 neonates who had been admitted to Muhimbili Medical Center (MMC) at Dar es Salaam, Tanzania. One baby among all the enrolled neonates was recognized as having a congenital malaria infection, which gave a prevalence of 0.33%. The present result was 5-fold the clinically recognized prevalence of congenital infection with malaria in the ward. The PCR method identified two cases, one of which was negative as determined by the Giemsa-staining method. Therefore, the PCR method was useful for the detection of scant amounts of malarial parasites in numerous blood samples. The screening of malaria by a sensitive PCR method contributes to reduce the mortality of asymptotic neonates in particular.

Gestational Age↗
PubMed2000

Important role of CD18 in TNF-alpha-induced leukocyte adhesion in muscle and skin venules in vivo.

OBJECTIVE: To examine the role of CD 18 in tumor necrosis factor-alpha (TNF-alpha)-induced leukocyte adhesion and extravasation in vivo. MATERIAL: Male wild-type (WT) and mutated mice with hypomorphic expression of CD 18. METHODS: Intravital microscopy was used to quantitate leukocyte-endothelium interactions provoked by TNF-alpha (0.5 microg) in the cremaster muscle and dorsal skin microcirculation. Tissue recruitment of leukocytes was evaluated in wholemounts of the cremaster muscle and in air pouches in the dorsal skin after TNF-alpha stimulation. RESULTS: TNF-alpha markedly increased venular leukocyte adhesion and recruitment in the cremaster muscle and skin in WT. Notably, in CD 18-targeted animals, leukocyte adhesion triggered by TNF-alpha challenge was significantly reduced by 58% and 72% in venules of the cremaster muscle and skin, respectively. Moreover, in CD18-mutants, tissue accumulation of polymorphonuclear leukocytes (PMNLs) provoked by TNF-alpha in the muscle and skin was decreased by 84% and 70%, respectively. Interestingly, the observed level of reduction in TNF-alpha-induced neutrophil adhesion and recruitment in CD18 gene-targeted animals corresponded well with the decrease in CD 18 expression on neutrophils from these mice, i.e. the surface density of CD18 was reduced by 77% in mutants compared to WT. Differential analysis revealed that the extravascular leukocytes comprised more than 90% PMNLs, indicating that neutrophils were the main inflammatory cell responding to TNF-alpha activation. Notably, the expression of CD18 increased by more than two-fold on extravasated neutrophils compared to circulating neutrophils in the peripheral blood both in WT and mutant animals. CONCLUSIONS: These findings suggest that CD18 is a dominant mediator of firm neutrophil adhesion to venular endothelial cells in the muscle and skin stimulated by TNF-alpha in vivo. In addition, this decreased adhesion in CD18-mutants attenuates leukocyte extravasation in response to TNF-alpha activation. Thus, inhibition of CD 18-function may provide an important strategy to inhibit leukocyte recruitment in cytokine-dependent diseases.

Animals↗
PubMed2000

Circulating cytokines and hormones with immunosuppressive but neutrophil-priming potentials rise after endurance exercise in humans.

To investigate the mechanisms of exercise-induced immune perturbations, we measured promising immunomodulatory hormones and cytokines in plasma of 16 male marathon runners before and after a competitive 42.195-km race. Interleukin 1-beta (IL-1beta) and interferon gamma (IFN-gamma) concentrations remained unchanged after the marathon. The cytokines IL-12, IFN-alpha and tumour necrosis factor alpha (TNF-alpha) could not be detected even using highly sensitive specific immunoassays, indicating at least that overshooting responses of these cytokines had not occurred after exercise. As mechanisms for the small changes in these cytokines, we demonstrated for the first time a significant rise in concentrations of inhibitory cytokine IL-10 in addition to the immunosuppressive hormone cortisol, although concentrations of IL-4 and transforming growth factor-beta (TGF-beta) were unaffected by the race. Furthermore, concentrations of IL-1 receptor antagonist (IL-1ra) and IL-6, which are negative-feedback inhibitors of cytokine production, increased by more than 100 times. As for humoral mediators of neutrophil mobilization, concentrations of growth hormone (GH), cortisol and granulocyte colony-stimulating factor (G-CSF) increased significantly. In addition, concentrations of neutrophil-priming substances (IL-6, IL-8, G-CSF, GH and prolactin) also increased significantly and the induction of IL-8 and G-CSF with exercise was demonstrated for the first time in the present study. In contrast, IL-2 concentration decreased, by 32%, and this was correlated with the induction of nitric oxide (NO) production. Muscle damage, monitored using changes in concentrations of creatine kinase and myoglobin, was also observed. These results suggested that exercise-induced pathogenesis including previously reported immunosuppression and neutrophil hyper-reactivity might be attributed, at least partly, to the systemic dynamics of the above bioactive substances.

Adult↗
PubMed2000

Evidence for translation of VP3 of avian polyomavirus BFDV by leaky ribosomal scanning.

Due to several incomplete splicing reactions, budgerigar fledgling disease virus (BFDV) late mature mRNAs are either bicistronic or polycistronic with an agnogene located upstream of viral protein (VP) genes. While the bicistronic mRNAs code for the vast majority of VP1, the polycistronic mRNAs contain the coding sequences of VP2, VP3, and VP1 (as the most distal cistron relative to VP2 and VP3). In this work, the translation initiation mechanism of VP3 was investigated in chicken embryo fibroblast cells by transfection of a series of BFDV mutant clones and transient reporter gene chloramphenicol acetyltransferase (CAT) expression assay, leading to the conclusion that BFDV VP3 was translated by leaky ribosomal scanning. Furthermore, thanks to the high sensitivity of CAT assay experiment, we were able to demonstrate that ribosomes could reach VP1-AUG and initiate translation after scanning through 900 nucleotides on the unspliced polycistronic mRNA.

Animals↗
PubMed2000

Recombinant expression and modification analysis of protein agno-1b encoded by avian polyomavirus BFDV.

Among two pairs of agnoproteins encoded in upstream positions in the late mRNAs of avian polyomavirus BFDV, either agno-1a or its splice derivative agno-1b are required for viral propagation. Out of the two proteins both of which consist of multiple electrophoretic subspecies, the smaller and less complex agno-1b has been cDNA-cloned into an influenza-virus /RNA-polymerase I expression system for production of higher amounts of this protein in infected chicken embryo fibroblasts. Fractional modification of agno-1b by phosphorylation at residues serine 51, serine 53, and threonine 73 is demonstrated through dephosphorylation by alkaline phosphatase, mass spectrometry of individual protein species isolated by strong anion exchange chromatography, and single or multiple alanine substitutions of serine or threonine residues in site-directed mutagenesis.

Amino Acid Sequence↗
PubMed2000

Efficiency of platelet adhesion to fibrinogen depends on both cell activation and flow.

The kinetics of adhesion of platelets to fibrinogen (Fg) immobilized on polystyrene latex beads (Fg-beads) was determined in suspensions undergoing Couette flow at well-defined homogeneous shear rates. The efficiency of platelet adhesion to Fg-beads was compared for ADP-activated versus "resting" platelets. The effects of the shear rate (100-2000 s(-1)), Fg density on the beads (24-2882 Fg/microm(2)), the concentration of ADP used to activate the platelets, and the presence of soluble fibrinogen were assessed. "Resting" platelets did not specifically adhere to Fg-beads at levels detectable with our methodology. The apparent efficiency of platelet adhesion to Fg-beads readily correlated with the proportion of platelets "quantally" activated by doses of ADP, i.e., only ADP-activated platelets appeared to adhere to Fg-beads, with a maximal adhesion efficiency of 6-10% at shear rates of 100-300 s(-1), decreasing with increasing shear rates up to 2000 s(-1). The adhesion efficiency was found to decrease by only threefold when decreasing the density of Fg at the surface of the beads by 100-fold, with only moderate decreases in the presence of physiologic concentrations of soluble Fg. These adhesive interactions were also compared using activated GPIIbIIIa-coated beads. Our studies provide novel model particles for studying platelet adhesion relevant to hemostasis and thrombosis, and show how the state of activation of the platelet and the local flow conditions regulate Fg-dependent adhesion.

Adenosine Diphosphate↗
PubMed2000

Impact severity in self-initiated sits and falls associates with center-of-gravity excursion during descent.

Although the energy available during a fall from standing greatly exceeds that required to produce hip fracture, this occurs in only about 2% of falls in the elderly. This is thought to be due in part to one's ability to reduce the vertical impact velocity (nu(nu)) and kinetic energy (KE(nu)) of the body through energy absorption in the lower extremity muscles during descent. The present study tested the hypothesis that the magnitude and percent attenuation in nu(nu) and KE(nu) associate with the horizontal and vertical excursion of the body's center-of-gravity during descent. Measures were acquired of whole-body kinematics and lower extremity kinetics as young subjects underwent backward descents involving vertical drops of either thigh length (SIT) or lower extremity length (FALL), and horizontal pelvis excursions of either 33 or 66% of lower extremity length. In all trials, subjects attempted to "land as softly as possible." While attenuation in nu(nu) and KE(nu) (which averaged 62 and 92% respectively), did not associate with trial type, raw magnitudes of these parameters did, with nu(nu) averaging 2-fold greater, and KE(nu) averaging 6-fold greater, in 66% FALL than in 33% SIT or 66% SIT trials. This was due to a rapid increase in downward velocity accompanying the final stage of descent in 66% SIT and 66% FALL trials, which coincided with the knee moving posterior to the ankle. Accordingly, severe impacts likely accompany not only large fall heights, but also falls where the feet are thrown rapidly forward, as during a backward slip.

Accidental Falls↗
PubMed2000

Purification and characterization of anticoagulation factors from the venom of Agkistrodon acutus.

Two anticoagulants from five-pace snake (Agkistrodon acutus) venom, anticoagulation factor I (ACF I) and anticoagulation factor II (ACF II), have been purified by a multiple-step chromatography procedure of anion-exchange chromatography, gel permeation chromatography and cation-exchange chromatography. Each of them is shown to be homogeneous as judged by PAGE, SDS-PAGE and mass spectrometry. In vitro, both proteins show equivalent anticoagulant activity, and are devoid of proteolytic, esterolytic, L-amino acid oxidase, phospholipase A, thrombin-like, fibrinolytic, hemorrhagic and lethal activities. They have similar amino acid compositions with similar absorption coeffecients (A(1%)(280)) (30.5 for ACF I and 30.0 for ACF II). Both are disulfide-linked consisting of two 14.7 kD chains for ACF I and two 14.6 kD chains for ACFII. ACF I has a molecular mass of 29,604+/-8 atomic mass units (amu) compared to 29,468+/-6 amu for ACF II, determined by mass spectrometry. The isoelectric points of ACF I and ACF II are 5.7 and 7.0, respectively. We conclude that the two isoforms possess equivalent biological activities with similar amino acid compositions and molecular masses, but different isoelectric points.

Agkistrodon↗
PubMed2000

Preparation of macroporous poly(2-hydroxyethyl methacrylate) hydrogels by enhanced phase separation.

Macroporous poly(2-hydroxyethyl methacrylate) (p(HEMA)) hydrogels were prepared in the presence of a 0.3-0.7 M NaCl solution. The pore morphology of the p(HEMA) hydrogels was dependent on the concentration of NaCl for a constant monomer solution to aqueous solution ratio. Swelling studies showed an increase in equilibrium water content and hydrogel porosity as the NaCl concentration in the polymerization medium increased from 0 to 0.7 M. The equilibrium water content, however, decreased as the NaCl concentration in the swelling medium increased. The frozen water content increased and non-frozen water decreased with an increase in the NaCl concentration in the polymerization medium. Mechanical testing indicated that the elastic modulus of the hydrogels was not affected by the increased porosity until the pores became interconnected. These data suggest that the addition of NaCl to the polymerization medium results in a multi-phase separation during fabrication that produces macroporous hydrogels of controlled morphology.

Calorimetry, Differential Scanning↗
PubMed2000

Effect of decaglycerol monooleate on phagocytosis and respiratory burst activity of human neutrophils: an in vitro study.

Decaglycerol monooleate (DGMO), a type of polyglycerol esters of fatty acids (PGEF), was evaluated for its in vitro effect on phagocytosis and respiratory burst activity of isolated human neutrophils using flow cytometric assay. Opsonized zymosan particles labelled with FITC (FITC-OZ) were employed as an indicator of phagocytosis. Fluorescence of FITC-OZ attached on to the surface of neutrophils was quenched by addition of trypan blue solution. After 10 minutes of incubation with DGMO up to a concentration of 10 mg/ml, neutrophil phagocytosis was not affected markedly. At the same time, the DGMO emulsion left little influence on complement receptor type three (CR3) that is associated with phagocytosis. On the other hand, oxidation of hydroethidine, which was used as an indicator of intracellular generation of reactive oxygen species (mainly for superoxide anion), was significantly inhibited by DGMO over 1 mg/ml. However, this phenomenon was not seen in DGMO-treated neutrophils when DGMO was removed after incubation. The present data suggest that DGMO does not affect phagocytosis of human neutrophils but down-regulates respiratory burst activity.

Adult↗
PubMed2000

Adenovirus-mediated delivery of p53 results in substantial apoptosis to myeloma cells and is not cytotoxic to flow-sorted CD34(+) hematopoietic progenitor cells and normal lymphocytes.

Multiple myeloma (MM) is an incurable disease; therefore, there is a need for new modalities of treatment for this disease. We designed a study to test the sensitivity of MM cell lines, freshly isolated myeloma cells, and CD34(+) hematopoietic progenitor cells to adenovirus-mediated delivery of wild-type p53 (Ad-p53). Replication-deficient Ad-p53, previously used in phase I-II clinical trial for treatment of patients with solid tumors, was used in this study. Myeloma cells from seven MM cell lines with mutated or w.t. p53 and varying expression of bcl-2 were used. Fresh myeloma cells (CD38(bright)CD45(-)) and fresh CD34(+) hematopoietic stem cells and CD34(-) cells were purified by flow sorting of apheresis collections of MM patients undergoing high-dose chemotherapy and stem cell rescue. The effect of Ad-p53 on colony-forming unit granulocyte-macrophage (CFU-GM) and burst-forming unit erythroid (BFU-E) colony formation in methylcellulose was tested on purified CD34(+) and CD34(-) cells to evaluate bone marrow toxicity. Myeloma cells from cell lines, or freshly isolated myeloma cells, were sensitive to Ad-p53 only if they had mutated p53 and had low expression of bcl-2. CD34(+) cells were resistant to Ad-p53-mediated apoptosis, and CFU-GM and BFU-E colony formation was not affected by treatment with Ad-p53.Ad-p53 is a potent inducer of apoptosis in MM cell lines and in freshly isolated myeloma cells expressing low levels of bcl-2. Ad-p53 is not overtly cytotoxic to normal hematopoietic stem cells or normal lymphocytes; therefore, it could be considered for a phase I clinical trial of MM patients with mutated p53.

ADP-ribosyl Cyclase↗
PubMed2000

Fluorescent studies on the binding-Ca2 + in fibrinolytic principle separated from snake venom.

By using equilibrium dialysis, atomic absorption spectrometry, fluorescence titration and determination of fluorescence lifetime, it can be determined that each fibrinolytic principle (FP) molecule contains one Ca2+-binding site and one Ca2+ ion, which can be substituted by a Tb3+ ion completely. The intramolecular energy transfer between Tb3+ and the tryptophan (Trp) residue in FP has been investigated through fluorescence spectroscopy. In the FP molecule, the excited energy can transfer from the Trp residue as an energy donor to the Tb3+ ion substituted as an acceptor. The distance between Tb3+ and the Trp residue, approximately 0.38 nm, has been calculated with the experimental data and Forster theory.

Agkistrodon↗