Search PubMed⌕ Search

Biomedical subjects

W Shi

Publications and source records attributed to W Shi.

At least 181 records · Page 10Linked to original sources
PubMed1997

Differential relaxant responses of pulmonary arteries and veins in lung explants of guinea pigs.

The endothelium regulates vascular tone through release of relaxing or contracting factors, with nitric oxide (NO) being a major endothelium-derived relaxing factor. In the present study, we used a lung explant technique to determine the differential abilities and mechanisms of pulmonary arteries and veins of normal guinea pigs to relax after precontraction. Excised lungs of 15 guinea pigs were filled through the airways with 1% agarose, cut into 1-mm-thick slices, and cultured overnight. Luminal areas of vascular cross sections were measured with an image-analysis system. Vessels were precontracted with U-46619, and responses to histamine, acetylcholine (ACh), sodium nitroprusside, and papaverine were examined. We also determined the effects of N omega-nitro-L-arginine and of indomethacin on ACh-induced responses. We found that histamine relaxed arteries more than veins and that ACh relaxed only arteries. N omega-nitro-L-arginine pretreatment abolished ACh-induced relaxation of arteries and caused ACh-induced contraction of veins, whereas indomethacin markedly augmented ACh-induced relaxation of arteries (maximal relaxation: 48.5 +/- 4.7 vs. 19.2 +/- 5.1% without it) and induced a dose-dependent relaxation of veins (maximal relaxation: 17.0 +/- 4.1%). Sodium nitroprusside induced a significantly greater relaxation of arteries than veins, whereas papaverine relaxed them equally. We conclude that in guinea pigs endothelial NO-mediated relaxation is greater in pulmonary arteries than in veins and that ACh-induced NO-mediated relaxation is reduced by the simultaneous production of cyclooxygenase-derived vasoconstrictors.

15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5↗
PubMed1997

Effects of reduced maternal lipoprotein-cholesterol availability on placental progesterone biosynthesis in the baboon.

Maternal low density lipoprotein (LDL) is the principal source of cholesterol substrate for progesterone biosynthesis in the primate placental syncytiotrophoblast. The relationship of LDL-cholesterol availability and other potential cholesterol-yielding pathways to placental progesterone production have not, however, been demonstrated in vivo in a nonhuman primate. Therefore, maternal peripheral lipoprotein-cholesterol and progesterone concentrations were determined in blood samples obtained by venipuncture, from day 72 until day 100, from pregnant baboons (Papio sp) that were either untreated (n = 4) or treated (n = 3) with the inhibitor of hepatic lipoprotein production, 4-aminopyrazolo [3-4-d]pyrimidine (4-APP, 10 mg/kg BW) on days 98-99 of pregnancy (term = 184 days). Although LDL-cholesterol and progesterone levels remained unchanged in untreated animals, LDL-cholesterol concentrations were 9-fold lower (P < 0.005) in baboons receiving 4-APP than in untreated baboons 2 days following initial administration. Commensurate progesterone levels were 3.5-fold lower (P < 0.03) in 4-APP-treated baboons than in untreated baboons. RT-PCR was used to approximate relative changes in transcription of messengers RNAs (mRNAs) for selected cholesterol-sensitive pathways in placental tissue collected on day 100. Thus, expression of mRNAs for LDL receptor and 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase appeared enhanced, whereas acyl-coenzyme A:cholesterol acyl transferase (ACAT) mRNA was diminished in syncytiotrophoblast-enriched cell fractions as a result of 4-APP administration. No relative differences in mRNAs were apparent in whole placental villous tissue, however, as a result of 4-APP treatment. In summary, this experiment demonstrates a significant decline in progesterone production elicited by maternal LDL-cholesterol withdrawal, and attests to the efficacy of 4-APP administration during baboon pregnancy. These results also suggest a commensurate regulation of cholesterol-sensitive pathways in primate syncytiotrophoblast. However, no relative differences were apparent in mRNA levels for LDL receptor, HMG-CoA and ACAT in whole placental villous tissue as a result of LDL-cholesterol withdrawal, which may suggest potential disparities in the mechanisms regulating cholesterol homeostasis in steroidogenically active syncytiotrophoblasts vs. those in proliferative nonendocrine placental constituents.

Adenine↗
PubMed1997

Tyrosyl radicals in enzyme catalysis: some properties and a focus on photosynthetic water oxidation.

Enzymes that require a redox-active amino acid for catalysis or function have emerged as a distinct class of proteins. For the tyrosine-based radical enzymes, we show that the spin-density distribution in the radical follows an odd alternate pattern that is invariant to within 10% across the class. General properties of the radical enzymes are summarized from which we conclude that their essential role in catalysis is to initiate substrate metabolism by hydrogen-atom abstraction. These ideas are extended to the YZ and YD tyrosines in Photosystem II and a radical-based hydrogen-atom abstraction model for water oxidation is discussed. Differences in rates of oxidation of YZ and YD by the reaction-center chlorophyll, P680+, under various conditions, are considered and rationalized on the basis of changes in reorganization energy induced by the local protein structure and by the presence or absence of the (Mn)4 cluster that binds substrate water.

Free Radicals↗
PubMed1997

[The role of periaqueductal gray neurotensin in electroacupuncture analgesia].

The effect of periaqueductal gray (PAG) injection of neurotensin (NT), anti-NT serum (ANTS), and naloxone (Nx) on both the pain threshold and electroacupuncture (EA) analgesia in rat was investigated in this study. The potassium iontophoresis-induced tail-flick was used to measure the pain threshold. NT administration induced an increase in pain threshold and enhanced EA analgesia. Injection of ANTS reduced the pain threshold significantly and diminished the effect of EA analgesia. Furthermore, pre-injection of Nx into PAG could weaken analgesia effect of NT and NT-EA analgesia. These results indicate that NT in PAG is involved in pain modulation and plays a role in EA analgesia. The effect of NT may be partly conducted by endogenous opiate peptides.

Acupuncture Analgesia↗
PubMed1997

[Expression of epidermal growth factor receptor in human duodenal ulcer].

Expression of epidermal growth factor receptor (EGFR) was studied immunohistochemically in 111 cases of human duodenal bulb biopsy. The results showed that the expression of EGFR was strong on the luminal side of epithelial cell membrane, moderate in the basolateral membrane of epithilial cells and the cells of muscularis mucosae, low in the cytoplasm of the epithelial cells, and lower in the mesenchyma and Brunner's gland. No expression of EGFR was found in lymphoid aggregates. The expression was evidently stronger in duodenal ulcer and duodenal ulcer scar. EGFR expression was correlated with the severity of inflammation, but was not related to sex and age. In conclusion, the result suggests that EGFR is correlated with mucosal adaptation to inflammation, ulcer healing and tissue reconstruction.

Adult↗
PubMed1997

[Histological study of experimental reconstructive materials for lateral skull base and dural defect in dogs].

In order to observe the reconstructive effects of fascia lata, superficial fascia and bone morphogenic protein (BMP) in skull base surgery, a lateral skull base bone and dural defect model in dogs was established. Fascia was selected alone or combined with BMP as repairing materials and BMP was evaluated in reconstructing large cranial defect model. Forty dogs underwent a 3.0 x 4.0 cm full-thickness excision of the parietal bone were divided into different groups of five dogs each, and were reconstructed by 1. fascia lata; 2. fascia lata plus BMP; 3. nonreconstructed controls; 4. fascia lata plus BMP and exposed. The implants were harvested at 2-15 weeks and examined histologically. The new bone was found in the BMP. Implants treated and untreated were quite different. The unreconstructed controls demonstrated only a bridge of fibrovascular connective tissue. BMP are defined as osteoinductive by their ability to produce bone formation by stimulating mesenchymal cells to transform into bone-producing osteo-blasts. The results suggested the combination of BMP and reconstructive material in the treatment of bone defects.

Animals↗
PubMed1997

[A further study on the correlation between molar response value and molecular connectivity indices].

It has been shown that there exists very good correlation between molar response values and corresponding molecular connectivity indices for alkane, benzene series and alkanol on both TCD and FID and for ketone on TCD. The results of multivariate linear regression are as follows. Molar response values (SM) on TCD: alkanes SM = 32.55 + 32.71 1X + 1.20 2X - 7.33 3X, r = 0.9951, S = 1.6313, N = 32 (1) benzene series SM = 30.00 + 20.30 1Xv + 13.32 2X, r = 0.9880, S = 2.7689, N = 13 (3) alkanols SM =42.22 + 23.71 1Xv + 4.52 2X, r = 0.9914, S = 3.9610, N = 17 (5) ketones SM = 55.10 + 21.46 1Xv + 4.82 2Xv, r = 0.9914, S = 3.1361, N = 11 (7) Molar response values (SM) on FID: alkanes SM = 14.58 + 23.76 1X + 7.77 2X + 2.52 3X, r = 0.9967, S = 2.1762, N = 50 (2) benzene series SM = 39.45 + 22.25 1Xv + 6.63 2X, r = 0.9880, S = 2.4137, N = 20 (4) alkanols SM = -5.31 + 25.48 1Xv + 8.92 2Xv r = 0.9930, S = 4.8979, N = 14 (6) where r and S are regression coefficient and residual standard deviation, respectively; N is the data number; 1X, 2X and 3X are the first, second and third order molecular connectivity indices, respectively. 1Xv and 2Xv are the first and second order molecular connectivity indices for which the oxygen atom and the degree of unsaturation has been revised, respectively.

Alkanes↗
PubMed1997

[Research on the variation of peak shape in capillary zone electrophoresis].

The influence of operation conditions, such as, injection time, applied voltage and effective length of capillary column, on parameters of peak shape in capillary zone electrophoresis (CZE) was investigated by using exponential-modified Gaussian (EMG) equation. The CE experiments were carried out by using the sample of derivatives of benzoic acid and small peptides. The experimens indicated that there was a significant effect of injection time on W1/2 and that the peaks changed from tailing to leading when the injection time was over 3 seconds in the case of pressure injection. It is recommended that an injection time less than 3 seconds can lead to a good column efficiency. The good linear relationships between tm and tau, sigma, W1/2 (t) with different separation voltages were observed. In the range of experimental conditions (11-27kV), higher voltage could lead to smaller zone dispersion, giving rapid and high efficient separation, and the voltage was insignificant on peak tailing. It was also shown that sigma, tau and W1/2 increased slightly with increasing the effective length of capillary column.

Electrophoresis, Capillary↗
PubMed1997

[Research on the reproducibility and selection of experimental conditions of capillary electrochromatography].

In this work, we prepared the packed columns for capillary electrochromatography (CEC) with 75microm and 100microm i.d., both of coupled mode and uncoupled mode. A mixture of thiourea and other three aromatic compounds was employed to evaluate the efficiency of the CEC columns. RSD values of retention times smaller than 2.12% was obtained on the home-made CEC system. The influence of pH value and the concentration of the organic solvent in the buffer on the retention behavior was investigated, giving a guide to the selection of experimental conditions. High speed analysis can be achieved by using high pH value buffers. Higher concentration of acetonitrile will improve the elution ability, while lower ocncentration of acetonitrile would improve the resolution. Seven kinds of neutral molecules were separated efficiently within 25 minutes. The results from the two modes of CEC columns were compared.

English Abstract↗
PubMed1997

[Empirical expressions for the chromatographic peak width at inflection points and base].

From EMG function and linear regression, the projective distances on abscissa between inflection points in the left side (TL) or in the right side (TR) and the apex of a chromatographic peak which the asymmetry at 0.1 height fraction is within 1.09-3.00 can be expressed as: TL = -0.7898 + 0.8219 W(0.1,L), TR = 0.03536 + 0.4582 W(0.1,L), where W(0.1,L) is the projective distance on abscissa between the point at 1/10 height fraction in the left side and the apex. The correlation coefficients are all over 0.998 and the relative error limits are within -0.65%-0.40% and -0.39%-0.67%, respectively. The relationship between the peak width at base Wb and the peak width at half height W(0.5) or the peak width at 1/10 height fraction W(0.1) can be expressed as: Wb = 0.04827 + 1.6907 W(0.5), Wb = 1.9066 + 0.5300 W(0.1). The correlation coefficients are all over 0.999 and the relative error limits are within -0.54%-0.69% and -1.05%-1.40%, respectively.

English Abstract↗
PubMed1997

[Histomorphometric study of the effect of nylestriol on bone turnover in ovariectomized rabbits].

OBJECTIVE: To assess the effect of Nylestriol on postmenopausal osteoporosis in an attempt to reveal its mechanism. METHODS: Thirty-seven month-old female New Zealand white rabbits were randomized into 3 groups (10 rabbits per group): treatment group [ovariectomized (OVX) + nylestriol (2 mg, monthly)], OVX control group (OVX + vehicle) and normal control group (sham operation + vehicle). Six months later, all rabbits were subjected to tetracycline labelling and then were killed. Under VIDAS system, bone turnover was assessed by bone histomorphometry. RESULTS: Bone volume trabecular (BV/TV), relative osteoid volume (OV/BV), osteoblastic index (OBI) and bone formation rate at tissue level [BFR(T)] increased in treatment group compared with OVX control group and (or) sham control group. CONCLUSIONS: Nylestriol can increase the number of osteoblast, which resulted in more bone matrix production and consequently converted the bone turnover of OVX rabbits to a positive balance situation. It indicated that Nylestriol was probably a stimulator for osteoblast recruitment and (or) proliferation.

Animals↗
PubMed1996

Cell density regulates cellular reversal frequency in Myxococcus xanthus.

Myxococcus xanthus is a Gram-negative bacterium that aggregates to form fruiting bodies when nutrients are limiting. Previous studies showed that the frz mutants that are defective in chemotaxis exhibited irregular and infrequent patterns of cellular reversal. In contrast, wild-type cells, when examined individually, reverse relatively frequently, about once every 6 min. It is not known how the change of reversal frequency effects cellular aggregation during fruiting body formation in M. xanthus. In this study, we stained cells with a tetrazolium dye so that we could track the reversal frequencies of single cells and cells in groups. We found that developmental cells in large groups reverse much less than cells in small groups or as single cells. This reduced cellular reversal frequency is related to the frz signal transduction system and correlated with the methylation of FrzCD (a methyl-accepting chemotaxis protein). Cells containing a mutation in the frz genes or in the genes required for social motility do not respond in this way. The reduction in cellular reversals as developmental cells accumulate in groups suggests a simple hypothesis for the aggregation of cells into discrete mounds during fruiting body formation. We also found that M. xanthus cells glide with equal frequency in the forward or reverse directions, indicating that cells do not contain a "head" or "tail."

Bacterial Proteins↗
PubMed1996

The role of arsenic-thiol interactions in metalloregulation of the ars operon.

The ars operon of the Escherichia coli plasmid R773 that confers arsenical and antimonial resistance is negatively regulated by the ArsR repressor. ArsR residues Cys-32 and Cys-34 were previously identified as involved in induction by arsenite and antimonite, suggesting coordination between As(III) and the two cysteine thiolates. However, in small molecule thiolate-As(III) complexes, arsenic is frequently three-coordinate. A site-directed mutagenic approach was employed in a search for a third arsenic ligand. ArsR proteins with C32G, C34G, and C32G/C34G substitutions were active repressors, but were not inducible in vivo. In vitro, the altered repressor-ars DNA complexes could not be dissociated by inducers. Alteration of Cys-37 and Ser-43, residues located in or near the putative helix-turn-helix DNA-binding region of the protein, had no effect on the inducibility of the operon. While these results indicated that neither the thiolate of Cys-37 nor the hydroxyl oxygen of Ser-43 is required for induction, they did not eliminate either atom as a potential arsenic ligand. Another approach involved reaction with an alternative inducer, phenylarsine oxide, which can form only two coordinations. Phenylarsine oxide was shown to be as effective as or more effective than arsenite or antimonite in induction in vivo. In vitro, the organic arsenical was more effective than either arsenite or antimonite in dissociating the repressor-promoter complex. Thus, two ArsR-arsenic bonds are sufficient for induction. The interaction of ArsR proteins with As(III) was examined using a phenylarsine oxide affinity resin. ArsR proteins containing any two of the three cysteine residues Cys-32, Cys-34, and Cys-37 bound to the resin. Alteration of any two of the three resulted in loss of binding. Arsenic X-ray absorption spectroscopy of ArsR treated stoichiometrically with arsenite confirmed the average arsenic coordination as AsS3 These results suggest that all three cysteine thiolates are arsenic ligands, but binding to only two, the Cys-32 and Cys-34 thiolates, is required to produce the conformational change that results in release of the repressor from the DNA and induction.

Amino Acid Sequence↗
PubMed1996

Essential role of Stat6 in IL-4 signalling.

Interleukin-4 (IL-4) is a pleiotropic lymphokine which plays an important role in the immune system. IL-4 activates two distinct signalling pathways through tyrosine phosphorylation of Stat6, a signal transducer and activator of transcription, and of a 170K protein called 4PS. To investigate the functional role of Stat6 in IL-4 signalling, we generated mice deficient in Stat6 by gene targeting. We report here that in the mutant mice, expression of CD23 and major histocompatibility complex (MHC) class II in resting B cells was not enhanced in response to IL-4. IL-4 induced B-cell proliferation costimulated by anti-IgM antibody was abolished. The T-cell proliferative response was also notably reduced. Furthermore, production of Th2 cytokines from T cells as well as IgE and IgG1 responses after nematode infection were profoundly reduced. These findings agreed with those obtained in IL-4 deficient mice or using antibodies to IL-4 and the IL-4 receptor. We conclude that Stat6 plays a central role in exerting IL-4 mediated biological responses.

Animals↗
PubMed1996

Direct association of STAT3 with the IFNAR-1 chain of the human type I interferon receptor.

Based on the reports of the activation of the transcription factor known as STAT3 (for signal transducers and activators of transcription) or APRF (for acute phase response factor) by various cytokines, we investigated the possible role of STAT3 in type I interferon (IFN) receptor signaling. We show that STAT3 undergoes IFNalpha-dependent tyrosine phosphorylation and IFNalpha treatment induces protein-DNA complexes that contain STAT3. In addition, STAT3 associates with the IFNAR-1 chain of the type I receptor in a tyrosine phosphorylation-dependent manner upon IFNalpha addition. The binding of STAT3 to the IFNAR-1 chain occurs through a direct interaction between the SH2 domain-containing portion of STAT3 and the tyrosine-phosphorylated IFNAR-1 chain. Furthermore, tyrosine-phosphorylated STAT3 bound to the IFNAR-1 chain also undergoes a secondary modification involving serine phosphorylation. This phosphorylation event is apparently mediated by protein kinase C, since it was blocked by low concentrations of the protein kinase inhibitor H-7. The biological relevance of IFN activation of STAT3 is further illustrated by the finding that STAT3 is not activated by IFN in a cell line resistant to the antiviral and antiproliferative actions of IFN alpha but in which other components of the JAK-STAT pathway are activated by IFNalpha.

Base Sequence↗
PubMed1996

The chromosomal arsR gene of Escherichia coli encodes a trans-acting metalloregulatory protein.

Plasmid-encoded arsenical resistance (ars) operons confer high level resistance to arsenicals and antimonials, while the chromosomally encoded ars operon of Escherichia coli bestows low level resistance. The transcriptional start site of the chromosomal ars mRNA was mapped by primer extension, and putative -10 and -35 promoter recognition sites were identified. The arsR gene, the first gene in this operon, was cloned using polymerase chain reaction. The arsR gene product, the ArsR repressor, was expressed and purified. The results of gel mobility shift assays indicated that the repressor is a DNA binding protein that binds to a fragment of DNA containing the chromosomal ars promoter. The specific binding site, as determined by DNase I footprint analysis, spans 33 nucleotides in the promoter region, including the putative -35 promoter element. By construction and expression of a series of in-frame fusions between truncated arsR genes and the coding region for the mature form of beta-lactamase (blaM'), it was shown that ArsR is a trans-acting repressor that regulates expression of the chromosomal ars operon. In addition, the chromosomally-encoded repressor can regulate expression of the ars operon of plasmid R773, and the R773 repressor can cross-regulate expression from the chromosomal operon.

Amino Acid Sequence↗