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Biomedical subjects

Y L Liu

Publications and source records attributed to Y L Liu.

At least 73 records · Page 4Linked to original sources
PubMed1996

Biphasic effects of the beta-adrenoceptor agonist, BRL 37344, on glucose utilization in rat isolated skeletal muscle.

1. The effects of the selective beta 3-adrenoceptor agonist, BRL 37344 (BRL) on glucose uptake and phosphorylation (i.e. glucose utilization; GU) and glycogen synthesis in rat isolated soleus and extensor digitorium longus (EDL) muscle preparations in vitro were investigated by use of 2-deoxy-[3H]-glucose (GU) and [U-14C]-glucose (glycogen synthesis). 2. Low concentrations of BRL (10(-11)-10(-9) M) significantly increased GU, with maximal increases of 30% in soleus and 24% in EDL at 10(-11) M. Neither the selective beta 1-adrenoceptor antagonist, atenolol (10(-8)-10(-6) M), nor the selective beta 2-adrenoceptor antagonist, ICI 118551 (10(-8)-10(-6) M) had any effect on the stimulation of GU induced by 10(-11) M BRL. 3. High concentrations of BRL (10(-6)-10(-5) M) caused significant inhibition (up to 30%) of GU in both soleus and EDL muscles. The inhibition of 10(-6) M BRL was blocked completely by 10(-6) and 10(-7) M ICI 118551 in soleus, and by 10(-6)-10(-8) M ICI 118551 in EDL; atenolol (10(-8)-10(6) M) had no effect. 4. Another selective beta 3-adrenoceptor agonist, CL 316,243, also caused a significant stimulation of muscle GU, with maximal increases of 43% at 10(-9) M in soleus and 45% at 10(-10) M in EDL. The stimulation of GU declined with further increases in the concentration of CL 316,243, but no inhibition of GU was seen, even at the highest concentration (10(-5) M) tested. 5. BRL at 10(-5) M inhibited completely insulin-stimulated glycogen synthesis in both soleus and EDL, but this inhibitory effect of BRL was abolished by 10(-6) M ICI 118551. BRL at 10(-11) M (with or without 10(-6) M ICI 118551) had no effect on insulin-stimulated glycogen synthesis. 6. It is concluded that: (i) low (< nM) concentrations of BRL stimulate GU via an atypical beta-adrenoceptor that is resistant to conventional beta 1-adrenoceptor and beta 2-adrenoceptor antagonists; (ii) the stimulation of GU is negated by the activation of beta 2-adrenoceptors that occurs at higher (> nM) concentrations of BRL; (iii) inhibition of GU via beta 2-adrenoceptor activation is associated with inhibition of glycogen synthesis, possibly due to activation of glycogenolysis; (iv) the opposing effects of beta 2-adrenoceptor and atypical beta-adrenoceptor activation on GU suggest that in skeletal muscle these adrenoceptors are linked to different post-receptor pathways.

Adrenergic beta-Agonists↗
PubMed1996

[Influence of green tea polyphenols varnish on saliva]

This study observed the inhibitory effect of green tea polyphenols varnish on the activity of humman saliva.We found 0.78 and 1.56mg/ml green tea polyphenols varnish is the best.We also observed the release of green tea polyphenols from liquid varnish is more than that from membraniform vanish.The release quantities of green tea polyphenols from membraniform is limited,suggest the influence of green tea polyphenols varnish on the activity of human saliva is small.

Journal Article↗
PubMed1995

Acute effects of the beta 3-adrenoceptor agonist, BRL 35135, on tissue glucose utilisation.

1. The acute effects of BRL 35135 (BRL) on tissue glucose utilisation index (GUI) in vivo were investigated in anaesthetized rats by use of 2-deoxy-[3H]-glucose. 2. Intravenous injection of BRL caused a dose-dependent increase in GUI in skeletal muscle, and white and brown adipose tissue; plasma insulin and fatty acid concentrations were also increased. Chronic treatment with BRL added to the diet caused a 34 fold increase in basal GUI of brown adipose tissue (BAT), but had no effect on GUI in other tissues. After chronic treatment, the acute tissue response to an intravenous maximal dose of BRL had disappeared completely in all tissues apart from the soleus muscle. 3. A high dose (20 mg kg-1) of the non-selective beta-antagonist, propranolol, inhibited the acute effect of BRL on GUI in BAT, but failed to affect GUI in muscle. A lower dose (1 mg kg-1) of the antagonist also inhibited the BAT response, but had little or no effect on the response in Type I (working) muscles such as soleus and adductor longus (ADL), and potentiated the response in Type II (non-working) muscles such as tibialis and extensor digitorium longus (EDL). 4. A low dose (1 mg kg-1) of the selective beta 1-antagonist, atenolol, had no effect on the BRL response but the same dose of the selective beta 2-antagonist, ICI 118551, potentiated significantly the effect of BRL on GUI in most muscles without altering plasma insulin levels. 5. It is concluded that: (i) the heterogeneous tissue responses of different muscle fibre types in the presence of P-antagonists indicates that BRL affects muscle GUI directly, in addition to effects mediated by increases in plasma insulin concentration; (ii) the resistance of the BRL response to conventional P-adrenoceptor antagonists implicates an atypical adrenoceptor mediating the GUI response in skeletal muscle, but this may not be identical to the adipose tissue P3-adrenoceptor; (iii) the potentiation of BRL responses by ICI 118551 indicates an inhibitory P2-adrenoceptor-mediated component in the muscle GUI response to BRL.

Adipose Tissue↗
PubMed1995

[Inhibitory effect of green tea polyphenols varnish on oral main cariogenic bacteria.].

This study observed the bacteriostatic effect of green tea polyphenols varnish,found green tea polyphenols varnish had significant inhibitory action on Streptococcus mutans,Streptococcus sobrinus and Lactobacilli.growth test showed the growth inhibitory rate of S.mutans and S.sobrinus was positive proportion with the concentration of green tea polyphenols varnish,demonstrated green tea polyphenols varnish possess certain anticariogenic effect.

English Abstract↗
PubMed1995

Contribution of beta 3-adrenoceptor activation to ephedrine-induced thermogenesis in humans.

OBJECTIVE: To investigate the contribution of beta 3-adrenoceptor activation to sympathetic stimulation of thermogenesis in humans using a sympathomimetic (ephedrine) in combination with a non-selective beta-adrenoceptor antagonist (nadolol). DESIGN: Three doses (2.5, 5 and 10 mg) of nadolol were used to estimate what fraction of the thermogenic response to ephedrine (30 mg) remained after inhibition of beta 1- and beta 2-adrenoceptor mediated responses. SUBJECTS: Nine healthy, young male volunteers at rest after an overnight fast. MEASUREMENTS: Energy expenditure, respiratory quotient, heart rate, blood pressure and plasma potassium, glucose, lactate, glycerol, NEFA and triglycerides were measured before, and for 3 h after treatment with placebo, ephedrine and ephedrine plus three doses of nadolol. RESULTS: Ephedrine produced significant increases in energy expenditure (thermogenesis), heart rate, systolic blood pressure and plasma glucose; the other parameters measured did not change significantly. Nadolol caused significant inhibition of all responses, but 43% of the thermogenic response to ephedrine remained after the 2.5 mg dose of nadolol, whereas the same dose completely inhibited the heart rate and plasma glucose responses. CONCLUSION: All three beta-adrenoceptor subtypes (beta 1, beta 2 and beta 3) may be involved in ephedrine-induced thermogenesis, but the resistance to complete inhibition by the non-selective antagonist nadolol indicates that at least 40% of the response is mediated by an atypical receptor, which is presumed to be the beta 3-adrenoceptor.

Adrenergic beta-Antagonists↗
PubMed1994

Phospholipase C-gamma 1 can induce DNA synthesis by a mechanism independent of its lipase activity.

Inositol phospholipid-specific phospholipase C (PLC) is involved in several signaling pathways leading to cellular growth and differentiation. Our previous studies reported the induction of DNA synthesis in quiescent NIH 3T3 cells after microinjection of PLC and the inhibition of serum- or Ras-stimulated DNA synthesis by a mixture of monoclonal antibodies to PLC-gamma 1. In the course of our investigation of anti-PLC-gamma 1 monoclonal antibodies, we found that each antibody exerts different inhibitory effects on the phosphatidylinositol-hydrolyzing activity of PLC-gamma 1 and that the inhibition of enzymatic activity does not correlate with the inhibition of DNA synthesis observed in the microinjection assay. PLC-gamma 1 with defective enzymatic activity was synthesized by substituting phenylalanine for histidine within the PLC-gamma 1 catalytic domain at amino acids 335 and 380, and mutant enzymes were expressed using a vaccinia expression system. The mutant enzymes were purified and microinjected into quiescent NIH 3T3 cells to evaluate their mitogenic activity. A moderate induction of DNA synthesis occurred after injection of mutant PLC-gamma 1. This mitogenic activity was inhibited by an antibody (alpha E 8-4) that does not significantly inhibit PLC-gamma 1 enzyme activity, which indicates that something else has to be inhibited. Furthermore, the partial induction of DNA synthesis observed with mutant PLC-gamma 1 was increased to levels seen with wild-type PLC-gamma 1 by coinjection of mutant PLC-gamma 1 with two second messengers, diacylglycerol and inositol trisphosphate. These results suggest that the mitogenic activity of PLC-gamma 1 does not exclusively result from the enzymatic activity of the lipase and that another activity inherent to the PLC-gamma 1 molecule can also induce DNA synthesis in quiescent cells.

3T3 Cells↗
PubMed1994

An acylated flavone C-glycoside from Glycyrrhiza eurycarpa.

A new acylated flavone C-glycoside, apigenin 6-C-alpha-L-rhamnopyranoside-8-C-[6"-(3-hydroxy-3-methyl-glutaroyl )-beta-D-glucopyranoside], was isolated from rhizomes of Glycyrrhiza eurycarpa and its structure was established on the basis of spectroscopic data.

Apigenin↗
PubMed1994

A comparison of proteins and peptides as substrates for microsomal and solubilized oligosaccharyltransferase.

A chemoenzymatic synthesis of homogeneous neoglycoproteins and glycopeptides was explored using oligosaccharyltransferase isolated from yeast. Neither the microsomal form nor the solubilized form of the enzyme catalyzed the transfer of the core Glc3Man9(GlcNAc)2 oligosaccharide to chemically modified ribonuclease A or alpha-lactalbumin. Similarly, no transfer was observed to the 32-amino acid peptide hormone, calcitonin, by either the membrane-bound or soluble form of oligosaccharyltransferase. However, a 17-amino acid fragment of yeast invertase with the unusual sequence containing two overlapping glycosylation sequons proved to be a good substrate, slightly less effective than the well studied tripeptide, Bz-Asn-Leu-Thr-NH2. Product analysis using gel permeation chromatography showed that the expected glycopeptides were formed and endo H-catalyzed cleavage of the oligosaccharide portion from the glycopeptides demonstrated that the glycopeptides contained the same carbohydrate moiety.

Amino Acid Sequence↗
PubMed1994

Swertifrancheside, an HIV-reverse transcriptase inhibitor and the first flavone-xanthone dimer, from Swertia franchetiana.

The first flavone-xanthone C-glucoside, swertifrancheside, was isolated from Swertia franchetiana, and its structure was elucidated on the basis of spectroscopic analysis as 1,5,8-trihydroxy-3-methoxy-7-(5',7',3'',4''- tetrahydroxy-6'-C-beta-D-glucopyranosyl-4'-oxy-8'-flavyl)-xanthone . This compound was a moderately potent inhibitor of HIV reverse transcriptase.

Antimalarials↗
PubMed1994

[Anti-proliferative effects of tumor necrosis factor and gamma interferon on human ovarian cancer cell lines].

Two ovarian cancer cell lines, 3AO and NIH: OVCAR-3, were used in this study to assess the synergistic effect of TNF and IFN gamma in combination. The result showed that these two ovarian cancer cell lines were all resistant to TNF and IFN gamma individually, but sensitive to the combined administration of TNF and IFN gamma. Concentration of 1 x 10(4) U/L of TNF and IFN gamma significantly inhibited 3AO and NIH: OVCAR-3 ovarian cancer cells (P < 0.05). Administration of 1 x 10(6) U/L TNF and IFN gamma could inhibit the growth of 3AO cells by 55% and NIH: OVCAR-3 cells by 75% (P < 0.01). It suggests that in some ovarian cancer cells which resistant to TNF could be changed to TNF sensitive cells by IFN gamma. anticancer treatment higher antitumor activity could be achieved by combined administration of TNF and IFN gamma.

Antineoplastic Agents↗
PubMed1994

[Clinical and experimental studies on analgesic effects of ipsilateral and contralateral stimulations with electro-acupuncture].

Through the treatment of 65 cases of painful diseases with electroacupuncture, in comparing with the analgesic effect of contralateral stimulation (CS) and ipsilateral stimulation (IS), it was verified that IS and CS had the similar effect on pain-relieving, while CS was better in improving motor impairment. By testing the rat's pain threshold and recording the neuronal activity in the D-PAG, it was found that neither IS nor CS could increase the pain threshold in the unilateral D-PAG lesioned rats, and the excited neuronal discharge was recorded in the unilateral D-PAG by stimulating rat's Zusanli (ST 36) at each side. It indicates that IS and CS might share the same high level afferent pathway in acupuncture analgesia in CNS.

Acupuncture Analgesia↗
PubMed1994

Peak oxygen deficit predicts sprint and middle-distance track performance.

The purpose of this study was to determine the value of the peak oxygen deficit (POD) as a predictor of sprint and middle-distance track performance. POD, peak blood lactate, VO2peak, lactate threshold, and running economy at 3.6 m.s-1 were measured during horizontal treadmill running in 22 male and 19 female competitive runners of different event specialties. Subjects also completed running performance trials at 100, 200, 400, 800, 1500, and 5000 m. Correlations of track performances with POD (ml.kg-1) (-0.66, -0.71, -0.71, -0.62, -0.52, and -0.40) were moderately strong at the sprint and middle distances, accounting for 44-50% of the performance variance at the three shortest distances. Correlations of track performances with peak blood lactate concentration were lower than with POD and accounted for approximately one-half as much of the performance variance (21-26%) at the three shortest distances. Multiple regression analyses indicated that the POD was the strongest metabolic predictor of 100-, 200- and 400-m performance, and that VO2peak was the strongest metabolic predictor of 800-, 1500-, and 5000-m performance. We conclude that the POD is a moderately strong predictor of sprint and middle-distance track performance.

Adolescent↗
PubMed1994

Expression of human hepatitis B virus surface antigen gene in transgenic tobacco.

Expression of Human hepatitis B virus surface antigen (HBsAg) gene in plant was reported for the first time. The recombinant plasmid pRoKII-HBsAg was constructed by inserting HBsAg gene into the downstream of CaMV 35S promoter of binary vector pRoKII and then introduced into Agrobacterium tumefaciens LBA4404. The kanamycin-resistant plants were obtained by Agrobacterium-mediated transformation system. It was shown that HBsAg gene was expressed in transgenic tobacco plants and their progenies by ELISA. The spherical particles of psi 22 nm is the leaf extract of transgenic tobacco were observed by immunosorbent electron microscopy.

Gene Expression↗
PubMed1994

A 5-year evaluation of NORPLANT contraceptive implants in China.

OBJECTIVE: To assess the efficacy, safety, and acceptability of NORPLANT implants when used by Chinese women. METHODS: In a prospective, multicenter clinical trial, 10,718 women selecting NORPLANT implants were monitored semiannually for the first 2 study years and then annually through 5 years. Life table rates of pregnancy and other terminations were calculated, as were incidence rates of serious conditions leading to termination. RESULTS: The 5-year average annual pregnancy rate was 0.3 per 100 and the ectopic pregnancy rate was minimal, 0.09 per 1000 woman-years. Pregnancy rates correlated significantly with weight, but regardless of weight group, annual average pregnancy rates were less than one per 100. Younger women experienced higher pregnancy rates than did older users. Headache, myoma, dizziness, and weight gain led more frequently to termination than did other adverse events apart from menstrual disturbances. Mortality during use was 2.0 per 10,000 years, based on 44,954 years of experience. There were no cardiovascular or cerebrovascular deaths, and no deaths were attributable to NORPLANT use. Seventy-two per 100 initial acceptors used the implants continuously for 5 years. CONCLUSION: NORPLANT implants proved highly effective, safe, and acceptable among Chinese women regardless of province, age, or weight at admission.

Adult↗
PubMed1993

A monitoring, feedback, and triggering system for reproducible breath-hold MR imaging.

A technique is described that provides improved reproducibility of breath-holding for MR image acquisition by monitoring the superior-inferior (S/I) position of the diaphragm. The method incorporates detection of the level of inspiration using an MR signal, rapid display to the patient of diaphragm position to enable breath-hold adjustment, and triggering of image data acquisition once appropriate position is attained. The response time of the system is short, approximately 10 ms. Studies in six volunteers using this method demonstrate a considerable decrease in the S/I range of diaphragm position over 10 consecutive periods of suspended respiration. The mean range is 1.3 mm with the system, while it is 8.3 mm without using it. It is expected that this method will be of assistance in many abdominal and cardiothoracic studies that use breath-hold techniques.

Feedback↗
PubMed1993

[Swertiapunimarin from Swertia punicea Hemsl].

A new secoiridoid glycoside, swertiapunimarin (I), was isolated from the whole plant of Swertia punicea Hemsl. The structure was elucidated as 6'-O-beta-D-glucopyranosylsweroside on the basis of chemical and spectroscopic analysis. The other seven known compounds were identified as sweroside (II), swertiamarin (III), oleanolic acid (IV), daucosterol (V), beta-sitosterol (VI), 2,3-dihydroxy-1,4-benzodicarboxylic acid (VII) and methylswertianin (VIII).

Drugs, Chinese Herbal↗
PubMed1992

Characterization and purification of a novel transcriptional repressor from HeLa cell nuclear extracts recognizing the negative regulatory element region of human immunodeficiency virus-1 long terminal repeat.

Cellular transcription factors play critical roles in regulating human immunodeficiency virus (HIV) gene transcription, although the precise mechanism(s) defining their roles are not well established. Primarily it has been suggested that sequence-specific interaction of trans-activating proteins with cis-acting DNA elements plays a crucial role in regulating the target genes. The negative regulatory element (NRE) of HIV-1 long terminal repeat (LTR) is one such defined region that has been reported to down-regulate LTR-directed HIV gene expression. Information regarding the role of this region in the regulation of HIV expression is lacking. Here we describe an attempt to further characterize the role of NRE cis-elements and define any sequence-specific interaction with cellular factors. Using gel mobility shift DNA-binding and Southwestern blot assays, we have mapped a distinct region of NRE (-290 to -260, a 30-base pair (bp) domain of NRE-A) sequences of HIV-1 LTR, which recognizes a specific DNA-binding protein from HeLa cell nuclear extracts. This factor is a 38-kDa polypeptide which can be affinity-purified to near homogeneity by this 30-bp specific oligonucleotide in affinity chromatography. The cellular factor from HeLa cell nuclear extract exhibits specific interaction only with the 30-bp NRE-A domain of HIV-1 LTR and acts as a strong transcriptional repressor/inhibitor molecule in the DNA-protein gel binding, as well as in vitro transcriptional studies with the nuclear extracts from cells with productive HIV-1 infection. To our knowledge, this is the first report of a factor recognizing a distinct segment within NRE that has been shown to exert an inhibitory effect on transcriptionally active DNA-protein "pre-initiation" complex formation, suggesting a possible role in HIV-1 gene regulation.

Base Sequence↗