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Biomedical subjects

X G Liu

Publications and source records attributed to X G Liu.

At least 37 records · Page 2Linked to original sources
PubMed1995

Synthesis of oligosaccharide substrates for N-linked glycoprotein processing enzymes.

The stereoselective syntheses of one pentasaccharide and one tetrasaccharide containing the Glc-alpha-(1-->3)-Man-alpha moiety as their terminal unit, as well as one tetrasaccharide and one trisaccharide containing the Man-alpha-(1-->2)-Man-alpha terminal unit were accomplished through the utilization of two key glycosyl donors, namely, 4-pentenyl 3-O-acetyl-2,4,6-tri-O-benzyl-alpha-D-mannopyranoside and ethyl 2-O-acetyl-3,4,6-tri-O-benzyl-1-thio-alpha-D-mannopyranoside.

Carbohydrate Conformation↗
PubMed1995

Long-term potentiation of C-fiber-evoked potentials in the rat spinal dorsal horn is prevented by spinal N-methyl-D-aspartic acid receptor blockage.

Long-term potentiation (LTP) of synaptic potentials is a fundamental mechanism of memory formation in the hippocampus. Here, we have characterized long-term changes of field potentials which were evoked in the lumbar spinal dorsal horn by supramaximal electrical stimulation of the sciatic nerve in urethane anesthetized rats. The field potentials had high thresholds (> or = 7 V), long latencies (90-130 ms, corresponding to conduction velocities between 1.2 and 0.85 m/s) and were not affected by spinalization (at C5-C6) or muscle relaxation (with pancuronium), i.e. the potentials were probably evoked by afferent C-fibers. Tetanic electrical stimulation (0.5 ms pulses, 30-40 V, 100 Hz, given in 4 trains of 1 s duration at 10 s intervals) of sciatic nerve induced in all 9 rats tested a LTP of amplitude of the C-fiber-evoked potential throughout recording periods which lasted between 4 and 9 h. Mean potentiation ranged from +71% to +174%. Superfusion of spinal cord with N-methyl-D-aspartic acid (NMDA) receptor antagonist D-(-)-4-(3-phosphonopropyl)piperazine-2-carboxylic (500 nM), which has little effect on the amplitude of C-fiber-evoked potentials, completely blocked LTP induced by tetanic stimulation in all five rats tested. Superfusion of spinal cord with NMDA (1 microM, 10 microM or 50 microM) induced LTP in only 2 out of 8 rats. This is the first report showing that LTP of C-fiber-evoked field potentials in the spinal dorsal horn in vivo may last for more than 8 h. This LTP in the spinal dorsal horn may underlie plastic changes of spinal nociception.

Animals↗
PubMed1995

Cloning and chromosomal localization of the human TRK-B tyrosine kinase receptor gene (NTRK2).

There is increasing evidence that neutrophins and their receptors play an important role in regulating development of both the central and the peripheral nervous systems. Human TRK-A (NTRK1) and TRK-C (NTRK3) have been cloned and sequenced, but only a truncated form of human TRK-B has been published. Therefore, we isolated complementary DNAs spanning the entire coding region of both human full-length and truncated forms of TRK-B from human brain cDNA libraries. Human full-length TRK-B codes for a protein of 822 amino acid residues. The putative mature peptide sequence is 49% homologous to human TRK-A and 55% to full-length human TRK-C, with 40% amino acid identify among TRK-A, -B, and -C. Nine of 13 cysteine residues, 4 of 12N-glycosylation sites in the extracellular domain, and 10 of 13 tyrosine residues in the intracellular domain are conserved among human TRK-A, -B, and -C. There is a cluster of 10 serine residues in the juxtamembrane region of TRK-B that is absent in TRK-A. Two major sizes of TRK-B transcripts were expressed in human brain. Northern blot analysis using probes specific for the extracellular or the tyrosine kinase domain revealed that the 9.5-kb band encodes the full-length TRK-B mRNA and the 8.0-kb band encodes the truncated form of TRK-B mRNA. By fluorescence in situ hybridization and somatic cell hybrid mapping, the human TRK-B gene was localized to chromosome 9q22.1.

Amino Acid Sequence↗
PubMed1995

Intrinsic factors of apatite influencing its amorphization during plasma-spray coating.

Hydroxyapatite coatings were prepared from differently treated starting powders to investigate the intrinsic factors of apatite influencing its amorphization during plasma-spray coating. The joint analyses of X-ray diffraction and infrared spectra show that the vacancies located on missing hydroxyl sites retard the amorphous/crystalline conversion and enforce retention of the amorphous component; the absorbed water molecules that pre-exist in the starting powder can be incorporated into the vacancies in the hydroxyapatite lattice during plasma-spray coating and compensate for the missing hydroxyls so as to promote the transformation of amorphous into crystalline apatite in the coating process. The more vacancies there are in the apatite structure due to missing hydroxyl sites, the more amorphous the component in the resultant coatings. Moreover, the amorphous phase formed in this way is stable in room conditions.

Biodegradation, Environmental↗
PubMed1995

The effects of extrasynaptic substance P on nociceptive neurons in laminae I and II in rat lumbar spinal dorsal horn.

Inflammation of the skin induces release and extrasynaptic spread of neuropeptides such as substance P mainly in spinal laminae I and II and causes changes in discharge properties of nociceptive neurons in spinal dorsal horn. To evaluate the role of extrasynaptic substance P we have superfused the spinal cord at recording segment with artificial cerebrospinal fluid or with substance P. A total of 102 multireceptive neurons responding to both noxious and innocuous skin stimulation were recorded in laminae I or II of lumbar spinal dorsal horn in pentobarbital anaesthetized rats. During superfusion with substance P (10 or 100 microM) significant increases of background activities (from 2.2 +/- 0.6 to 8.4 +/- 3.2 imp./s, mean +/- S.E.M.), enlargement of cutaneous receptive fields (from 359.9 +/- 60.4 to 465.5 +/- 77.3 mm2) and enhanced responses to mechanical (from 89.1 +/- 22.7 to 147.0 +/- 27.5 imp./5 s) but not thermal noxious skin stimuli were observed in the 22 neurons tested. Noxious heat-evoked responses and C-fibre-evoked responses were changed in both directions. In 50 other neurons, the coefficients of dispersion of interspike intervals, which is an indicator of burst-like discharges, were significantly reduced (from 60.4 +/- 5.5 to 52.7 +/- 5.3) after application of substance P. Substance P induced oscillations in background activities in 13 of 40 non-rhythmic neurons and depressed oscillations in 2 of 11 neurons. Cross-correlations of discharges of pairs simultaneously recorded neurons were flat (n = 4), or had a central peak (n = 19) or a central trough (n = 2) and were not changed qualitatively by extrasynaptic substance P. Thus, extrasynaptic substance P can modify not only discharge patterns in the spinal dorsal horn.

Analgesics↗
PubMed1995

Molecular characterization and chromosomal localization of DRT (EPHT3): a developmentally regulated human protein-tyrosine kinase gene of the EPH family.

By screening a human fetal brain cDNA expression library using a monoclonal antiphosphotyrosine antibody and by 5' RACE procedures, we have isolated overlapping cDNAs encoding a receptor-type tyrosine kinase belonging to the EPH family, DRT (Developmentally Regulated EPH-related Tyrosine kinase gene). The DRT gene is expressed in three different size transcripts (i.e. 4, 5 and 11 kb). DRT transcripts are expressed in human brain and several other tissues, including heart, lung, kidney, placenta, pancreas, liver and skeletal muscle, but the 11 kb DRT transcript is preferentially expressed in fetal brain. Steady-state levels of DRT mRNA in several tissues, including brain, heart, lung and kidney, are greater in the midterm fetus than those in the adult. DRT transcripts are detectable at low levels in a human teratocarcinoma cell line (NTera-2), but its expression is greatly increased after the NTera-2 cells are induced to become postmitotic neurons (NTera-2N) by retinoic acid treatment. These data suggest that DRT plays a part in human neurogenesis. A large number of tumor cell lines derived from neuroectoderm express DRT transcripts, including 12 neuroblastomas, two medulloblastomas, one primitive neuroectodermal tumor and six small cell lung carcinomas (SCLC). Interestingly, several neuroblastoma cell lines with 1p deletion and one SCLC cell line express DRT transcripts of aberrant size (i.e. 3, 6 and 8 kb) in addition to those found in normal tissues. We mapped the DRT gene to human chromosome 1p35-1p36.1 by PCR screening of human-rodent somatic cell hybrid panels and by fluorescence in situ hybridization. As the distal end of chromosome 1p is often deleted in neuroblastomas and altered in some cases in SCLCs, these chromosomal abnormalities may have resulted in the generation of aberrant size transcripts. Thus, the DRT gene may play a part in neuroblastoma and SCLC tumorigenesis.

Amino Acid Sequence↗
PubMed1995

Felodipine- and ethanol-induced gastric mucosal damage in rats.

Calcium channel blockers like verapamil have been shown to potentiate ethanol-induced gastric mucosal damage. However, the exact mechanism for this adverse drug interaction is still unknown. We used felodipine to study the ulcerogenic mechanisms of calcium channel blockers and the pathogenesis of ethanol-induced ulceration. The experiment was conducted in an ex vivo gastric chamber prepared in anesthetized animals. Felodipine (0.25, 0.5, 1.0, or 2.0 mg/kg s.c.) dose-dependently reduced the systemic blood pressure which was accompanied by a decrease in gastric mucosal blood flow (GMBF), with an insignificant change in heart rate. Ethanol lowered the GMBF and produced gastric mucosal lesions, and these actions were potentiated by felodipine. Preincubation with calcium gluconate but not the sodium salt attenuated the adverse effects of ethanol on GMBF and lesion formation; it also significantly prevented the gastric effects of felodipine but not the decrease of the systemic blood pressure. It is concluded that felodipine aggravates ethanol ulceration through a depressive action on the GMBF. These actions were attenuated by the supplementation with calcium ions in the gastric mucosa. Therefore, maintenance of calcium homeostasis in the gastric wall could play a significant role in the prevention of ethanol ulceration in rats.

Analysis of Variance↗
PubMed1995

[A rat middle cerebral artery thrombosis model for evaluation of thrombolytic and antithrombotic agents].

The purpose of this study was to develope a rat model of cerebral artery thrombosis by adding FeCl3 to the surface of right middle cerebral artery (MCA) for 30 min. After 4 h, 8 h, 24 h, 48 h, 72 h, 1 week and 2 week, the extent of neurologic deficits of rats was evaluated and after 24 h and 48 h the size of cerebral infarction was measured. The results indicate that the features of neurologic deficits and infarction were similar to those of the rat focal cerebral ischemia model established by Tamura et al (1981). The nature of thrombus formed in our experiment is combined-thrombus. The antithrombotic effect of aspirin and the thrombolytic effect of urokinase were also examined. Aspirin (50 mg.kg-1) was given by duodenum 30 min before adding FeCl3 to the surface of the right MCA and urokinase (4000 U.kg-1, iv) was given 30 min after thrombosis. After operation, the behavior of rats were observed. The cerebral infarction was evaluated 24 h after thrombosis. The infarcted areas in the aspirin and the urokinase groups were reduced to 20% and 11% those of the control group, respectively. The neurologic deficits were also attenuated. These studies suggest that this rat model may be used for testing not only antithrombotic but also thrombolytic agents.

Animals↗
PubMed1995

[Protective effect of dl-3-n-butylphthalide on ischemic neurological damage and abnormal behavior in rats subjected to focal ischemia].

dl-3-n-Butylphthalide (NBP) was known to have improving effect on brain energy metabolism after ischemia insult. The purpose of this study is to determine if the drug has protective action against ischemic neuronal damage. In the present study, the effect of NBP on cerebral infarction and neurological deficits after middle cerebral artery occlusion (MCAO) in rats was investigated. Focal cerebral ischemia was produced by permanent occlusion of the proximal portion of the right middle cerebral artery (MCA) according to the technique of Tamura. The infarct area was measured by 2,3,5-triphenyltetrazolium chloride (TTC) staining technique. The extent of neurological deficits was evaluated by the method of Bederson. The histological changes in neuronal change after MCAO in rats were also studied. The results indicate that the infarct area and the score of neurological deficits after MCAO were reduced significantly following intraperitoneal pretreatment or pre- and post-treatment with NBP 20 mg . kg-1. The treatment with NBP 10 or 20 mg . kg-1(i.p.), or 20,40 or 80 mg . kg-1 (po) 15 min and even 2 h (20 mg . kg-1, i.p.) after MCAO also markedly reduced the infarct area and the score of neurological deficits. However, no effect was found when NBP (20 mg . kg-1) was injected intraperitoneally 4 h after MCAO. MK-801 (0.5 mg . kg-1, i.p.), a non-competitive antagonist of NMDA receptor, significantly reduced the size of infarction and the score of neurological deficits in rats subjected to MCAO. The potency of NBP in reducing the infarct area and neurological deficits was found to be quite similar to that of MK-801 (0.5 mg . kg-1, i.p.). No neuroprotective effect of nimodipine (1.0 mg . kg-1, sc) was found. Generally, the potency of NBP in protecting rats from ischemic neurological damage is equal to that of MK-801 and is more powerful than that of Nimodipine. Side effects of NBP in behavior was not found. Therefore, NBP seems to be a hopeful drug for the treatment of stroke.

Animals↗
PubMed1993

[An urease enzyme linked immunosorbent assay for detection of Helicobacter pylori infection].

A sensitive and specific serological diagnostic test for Helicobacter pylori infection has been developed and validated in 120 patients with dyspeptic symptoms undergoing endoscopy. This test is to use urease, a protein unique to H. pylori, as the basis for the enzyme linked immunosorbent assay (ELISA) that detects serum H. pylori urease antibodies. The ELISA mean optical density (OD) in H. pylori-positive group is higher than that in H. pylori-negative group (0.57 +/- 0.23 vs 0.24 +/- 0.15, P < 0.001), a cut-off 0.3 OD yields a sensitivity of 95% and a specificity of 93%. Serum absorption test showed that Escherichia coli, Klebsiella pneumonia, Proteus mirabilis, Yersinia enterocolotica, Pseudomonas aeruginosa cell lysate do not influence serum H. pylori urease antibody level, though they all have urease except E. coli. The result implied that H. pylori urease can be a good antigen to detect serum H. pylori antibody and it would be useful for epidemiological survey and routine diagnostic approach. Nearly half of the blood donors showed positive result with H. pylori urease antibody. It is suggested that H. pylori infection is quite common in the asymptomatic population.

Adult↗
PubMed1992

Polyethylene glycol: its adverse gastric effects in rats.

The effects of polyethylene glycol (PEG) on gastric function and on lesion formation, evoked by topical applications of absolute ethanol to an ex-vivo stomach chamber preparation have been examined. Parenteral injection (i.p. or s.c.) of PEG with different molecular weights (PEG 300, 400 or 4000), dose-dependently reduced the gastric mucosal blood flow and volume of gastric secretion; these effects were greater in rats given PEG by the i.p. route, which also lowered acid output. Topical application of 1.5 mL absolute ethanol produced severe gastric mucosal injury, which was exacerbated by PEG; this lesion-aggravating effect was higher in the i.p.-injected groups. These findings indicate that when PEG is given by injection, it can adversely affect gastric function and increase the damaging action of alcohol. It is suggested that the use of PEG as a vehicle for injection should be re-assessed.

Animals↗
PubMed1992

A model of acute focal ischemia in the territory of the anterior cerebral artery in baboons.

BACKGROUND AND PURPOSE: We developed a model of acute focal ischemia in the territory of the anterior cerebral artery in baboons to study the ischemic pattern following occlusion and changes in regional cerebral blood flow. METHODS: In nine anesthetized animals, a Scoville clip was placed on the proximal segment of the common anterior cerebral artery via a unilateral transorbital approach. Regional cerebral blood flow was measured by hydrogen clearance in the cortex and corpus callosum. Postexperimentally, arteries were selectively injected. RESULTS: The resulting ischemia involved both hemispheres symmetrically and the corpus callosum. Cortical flows were significantly reduced within a region 15 mm from the midline on each side (p less than 0.01). A gradient of cortical flow reduction was produced between 10 and 25 mm from the midline. This area defines the boundary region between the territories of the anterior and middle cerebral arteries, and is identified as the "penumbra" of the ischemic core, which itself lies within 10 mm of the midline. Blood flows in the corpus callosum decreased from an average of 21.0 to 6.7 ml/100 g/min in the body (p less than 0.01) and from 22.5 to 10.7 ml/100 g/min in the genu (p less than 0.05). CONCLUSIONS: This ischemic model has close physiological and morphological relevance to stroke-related clinical circumstances, in particular the acute conditions of focal cerebral ischemia associated with vascular surgery. It also provides a new framework for experimental investigation of the ischemic penumbra.

Animals↗
PubMed1992

Growth promoting effect of zinc supplementation in infants of high-risk pregnancies.

This study was made to determine whether zinc deficiency is one of the factors involved in growth retardation of infants of high-risk pregnancies. The high risk factors were hypertension of pregnancy, diabetes mellitus, congenital heart disease, chronic nephritis, rheumatic heart disease and hyperthyroidism. 102 neonatal infants were divided into 3 groups: breast fed group, 37 cases; test group, 32 cases formula-fed with supplementary zinc 1.14-2.28 mg/kg/d; and control group, 33 cases formula-fed and supplemented with Vitamin B complex as placebo. The groups were divided by double-blind and randomized method. There were no differences in the 3 groups in sex ratio, growth status and serum zinc concentration at the beginning of the study. Anthropometric data were obtained at 0, 3 and 6 months.

Double-Blind Method↗
PubMed1992

[Study on the response index of population--the prevalence degree of pneumoconiosis].

Comparison and analysis of the relationship between the prevalence and factors associated with CWP in five collieries, showed that the prevalence rate only reflected the rate of CWP in population and not the category construction of CWP; so, in certain circumstances, it is not suitable to estimate the risk of CWP in different collieries. A new index, the prevalence degree suggested by the authors, is a compound measure of risk of both the prevalence rate and the category construction of pneumoconiosis for population; so, it can reflect the risk of pneumoconiosis comprehensively and sensitively.

Adult↗
PubMed1991

Effects of adenosine on gastric and cardiovascular systems, and ethanol ulceration in male and female rats.

The time course of the effects of adenosine, a vasodilator, on the ulcerogenicity of ethanol was studied in male and female rats. Gastric secretory function and mucosal blood flow (GMBF), systemic blood pressure and heart rate were monitored during the 90-min experimental period. In the male rats, adenosine 7.5 mg/kg s.c. (injected at 30 min) increased the GMBF at 45 min and depressed it at 75 min. The mean blood pressure was decreased at 45 min and steadily recovered thereafter; the heart rate was unaffected throughout the experimental period. The gastric secretory volume was elevated at 60 min, with a significant drop in gastric acid output at the same time. Ethanol administration from 45 to 90 min produced haemorrhagic lesions in the glandular mucosa. The severity of gastric damage was markedly reduced by adenosine at 45 and 60 min when the GMBF and the secretory volume were increased respectively, but severity was increased at 75 min while the GMBF was significantly reduced. In the female rats, adenosine had no effect on the secretory function but still had a depressive action on GMBF at the 75th min. In these animals, adenosine exacerbated the gastric injury at 60 and 75 min. The blood pressure was also decreased at 45 min. In conclusion, adenosine produces a different pattern of effects on the ulcerogenic action of ethanol in male and in female rats. These differential effects depend on the states of GMBF and gastric secretory volume but not on the changes of systemic blood pressure and gastric acid secretion.

Adenosine↗
PubMed1991

[Serum and tissue copper, zinc and selenium levels in patients with gastric carcinoma].

Serum and tissue copper, zinc and selenium levels were measured in patients with gastric carcinoma. The mean level of serum copper in patients with gastric carcinoma (42 cases) was 950 +/- 130 ug/L, which was higher than 800 +/- 70 ug/L of the control (30 cases, P less than 0.05). The serum selenium level in patients with gastric carcinoma was lower than that in the control (63 +/- 15 ug/L vs 85 +/- 8 ug/L, P less than 0.05). No significant difference in serum zinc level was found between the patient and control groups. In cancer tissues, the mean concentration of copper was 13.5 +/- 2.6 micrograms/g dry weight, which was much higher than 7.1 +/- 1.6 micrograms/g dry weight in the intact gastric mucosa (P less than 0.01). The activity of superoxide dismutase (SOD) in cancer tissue was 95 +/- 10 u/mg-protein, which was lower than 124 +/- 12 u/mg-protein in the intact gastric mucosa (P less than 0.05). The above changes may facilitate production of free radicals, tissue damage and carcinogenesis.

Adenocarcinoma↗
PubMed1990

[Analysis of the high-resolution real-time sonographic images of the carotid bifurcations in normal adults].

The high-resolution real-time sonographic images in 186 carotid bifurcations (CB) of 93 selected normal persons were quantitatively analysed for 9 parameters including the diameters of the internal carotid arteries (CCA), the bifurcating angles of the ICA and ECA, and the angles between the ICA and ECA. The results of all the measurements were analysed with the relevant statistical methods. The normal field (99% limit) of CB in every age group was shown in this paper. The normal range of the measured values of the carotid bifurcations in each age group was calculated, and the laws governing their changing trends and their clinical significance were discussed.

Adult↗