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Biomedical subjects

W J Yu

Publications and source records attributed to W J Yu.

17 recordsLinked to original sources
PubMed2006

An evaluation of localized debonding between fibre post and root canal wall by finite element simulation.

AIM: To investigate the effect of localized bonding defects between fibre post and root canal wall on the stress distribution in the radicular dentine. METHODOLOGY: A tooth restored with a fibre post together with the alveolar bone were axisymmetrically modelled. A total of four models with localized debonding at the post to canal wall interface in different locations were analysed: Model A: perfect bonding layer over the entire interface; Model B: debonding at the cervical 1/3 of the interface; Model C: debonding at the mid 1/3; and Model D: debonding at the apical 1/3. A tooth restored without using a post was also included as the control (Model E). A load of 50 N was applied to the top of the full veneer cast crown at angles of 0, 15, 30, and 45 degrees with the tooth's longitudinal axis. The stress distribution across the fibre post and root dentine was compared. RESULTS: Higher stresses were generated in the radicular dentine as a function of the load angle. The differences in the stress distribution were negligible between the four models and virtually the same as that for model E (control). CONCLUSIONS: In this simulation, localized debonding at the fibre post to root canal wall interface, regardless of its location along the post, had little effect on the stress distribution in the root dentine.

Dental Bonding↗
PubMed2005

Centrifugal force model for pedestrian dynamics.

In this paper, a centrifugal force model is developed for pedestrian dynamics. The effects of both the headway and the relative velocity among pedestrians are taken into account, which can be expressed by a "centrifugal force" term in dynamic equation. The jamming probability due to the arching at exits for crowd flows is provided. A quantitative analysis of the crowd flowing out of a hall shows that the average leaving time T is a function of the exit width W in negative power. The related simulation indicates that the proposed model is able to reproduce the self-organization phenomena of lane formation for sparse flows.

Behavior↗
PubMed2002

A capsule review of recent studies on the application of mass spectrometry in the analysis of Chinese medicinal herbs.

Chinese herbal medicine is gaining increasing popularity worldwide as an alternative approach to the development of pharmaceuticals in therapeutic applications. Chemical characterization and compositional analysis of Chinese medicines provide the necessary scientific basis for the discovery and development of new drugs of natural origin. Applications of mass spectrometry in the analysis of Chinese herbal medicines have been growing rapidly in recent years owing to the rapid technical advances and increasing availability of the instrumentation. This paper reviews the current status of how different mass spectrometric techniques are being used to support research studies of Chinese medicines. The focus is on crude herbal medicines and their derived products. The review is not meant to be exhaustive, but rather to provide a general overview of the various research activities in this rapidly expanding field. In the discussion of specific herbs, the emphasis is placed on ginseng and Danshen, two of the herbs for which active experimental work is on-going in the authors' laboratories. Other selected herbs will be discussed only briefly, aiming primarily to illustrate the current status of research in the area.

DNA Fingerprinting↗
PubMed2001

Poly[cadmium(II)-mu-4,4'-oxydianiline-N:N'-di-mu-thiocyanato-N:S].

The title polymeric complex, [Cd(SCN)(2)(C(12)H(12)N(2)O)], exhibits a three-dimensional framework in which each Cd(II) atom is bridged by two eta-1,3-(SCN)(-) groups, forming a double-stranded chain. The unique Cd(II) atom lies on an inversion centre and the coordination sphere is completed by two terminal N atoms from two different 4,4'-oxydianiline (4,4'-Oda) ligands, furnishing a CdS(2)N(4) octahedral geometry. Adjacent polymeric double-stranded chains are linked via the 4,4'-Oda ligands, which lie across twofold rotation axes.

Journal Article↗
PubMed2000

Insulin restores neuronal nitric oxide synthase expression in streptozotocin-induced diabetic rats.

Nitric oxide (NO) is known to play an important role in the pathophysiology of insulin-dependent diabetic mellitus (IDDM). In an attempt to investigate the relation between insulin and NO in IDDM, the present study employed male Wistar rats to induce IDDM by intravenous injection of streptozotocin (STZ). Four groups of rats were used; untreated normal control group, insulin treated STZ group, vehicle-treated STZ control, and one group of age-matched rats which were orally supplied with glucose to increase plasma glucose (glucose-challenged rats). Changes of the activity and gene expression of neuronal nitric oxide synthase (nNOS) were examined in cerebellum and kidney of these groups. The activity of nNOS in cerebellum, determined by conversion of [3H] L-arginine to [3H] L-citrulline, in STZ-induced diabetic rats was markedly lower than normal rats. Insulin treatment reversed the nNOS activity. Similar reversion by insulin treatment was also obtained in the gene expression of nNOS. However, the activity and gene expression of nNOS in glucose-challenged rats were not different from those in normal rats. The role of hyperglycemia can thus be ruled out. These findings indicated that an impairment of nNOS in the brain of rats with IDDM is mainly due to the absence of insulin.

Animals↗
PubMed2000

Systemic mononuclear inflammatory vasculopathy associated with Sjögren's syndrome in a patient with primary biliary cirrhosis.

We report a 46-year-old woman with primary biliary cirrhosis (PBC) presenting with Sjögren's syndrome and systemic mononuclear inflammatory vasculopathy. Biopsy specimens of sural nerve showed findings consistent with vasculitic neuropathy. Perivascular inflammatory mononuclear cell infiltration was observed on muscle biopsy specimen. The findings of abdominal computed tomography and brain magnetic resonance imaging were suggestive of vasculitis. Clinical manifestations and radiologic findings were improved after high dose prednisolone therapy.

Biopsy, Needle↗
PubMed1999

Decrease of nitric oxide synthase in the cerebrocortex of streptozotocin-induced diabetic rats.

In an attempt to know the role of nitric oxide in the disease of insulin-dependent diabetic mellitus (IDDM), the present study examined the change of nitric oxide synthase (NOS) both the activity and gene expression in cerebrocortex of streptozotocin-induced diabetic rats (STZ-diabetic rats). The activity of NOS determined by conversion of [3H] L-arginine to [3H] L-citrulline was markedly decreased in STZ-diabetic rats. Northern blot showed that STZ-diabetic rats expressed a lower mRNA level of neuronal NOS (nNOS). Western blot showed a similar decrease of nNOS in STZ-diabetic rats. However, the NOS activity was increased in rats receiving repeated supply of glucose named glucose-challenged rats. Although the mRNA level of nNOS was not changed in the glucose-challenged rats, the immunoblot of nNOS was also decreased in glucose-challenged rats. These findings suggested that NOS was lowered in the brain of STZ-diabetic rats in a way unrelated to the increase of glucose.

Animals↗
PubMed1999

Effect of serum in medium on the expression of inducible nitric oxide synthase and superoxide dismutases in cultured C6 glioma cells.

It has been documented that C6 glioma cells can be changed into normal glial cells when they were cultured in serum free medium. In the present study, the expressions of inducible nitric oxide synthase (iNOS) and superoxide dismutase (SOD) were investigated. The mRNA level of iNOS was markedly increased by lipopolysaccharide (LPS) in cultured rat brain astrocytes (RBA-1) but not in C6 glioma cells. However, increase of mRNA for iNOS by LPS can be obtained in C6 glioma cells when they were cultured in serum free medium. The mRNA level of magnesium-SOD (Mn-SOD) was increased by LPS in both cells while the expression of constituted SOD (Cu,Zn-SOD) was not stimulated by LPS. Western blotting analysis indicating the amount of protein showed a similar change. After serum deprivation, the protein of iNOS or Mn-SOD was increased by LPS in C6 glioma cells in a way similar as that in RBA-1 cells. These results suggest that serum free conditioned C6 glioma cells were adapted to astroglial cell-like properties which may express more iNOS and Mn-SOD mRNA in the presence of LPS.

Animals↗
PubMed1997

[Effects of hypoxia/reoxygenation on mitogen-activated protein kinase activity in cultured neonatal rabbit cardiac myocytes].

Cardiomyocytes subjected to brief episode of hypoxia possess a resistance to serious damaging effect exerted by a subsequent long-time hypoxia on these cells, which is called hypoxic preconditioning (PC). The pathway of intracellular signal transduction during hypoxia PC has not yet been validated. On a model of hypoxia/reoxygenation (H/R) of cultured neonatal rabbit cardiomyocytes, the present study is taken to investigate the changes of mitogen-activated protein kinase (MAPK) and ribosomal S6 kinase (S6K) activity. It was found that intracellular total MAPK and nuclear MAPK, after a 15-min period of reoxygenation preceded by a single 60-min period of hypoxia, were increased by 95% and 230%, respectively. Intracellular S6K activity increased by 142% at 30 min of H/R vs the control group (P < 0.01). Phosphatase 1 (PPase 1) inhibitor (ocadaic acid, OA 1 mumol/L) augmented the increase of MAPK and S6K activity induced by H/R. However, tyrosine kinase (Tyr K) inhibitor (genistein), protein kinase C (PKC) inhibitor (H7) and preincubation of cardiomyocytes with PKC activator PMA all reduced MAPK activation by H/R. Protein kinase A (PKA) inhibitor (H89), Ca2+/Calmodulin-dependent protein kinase (PKM) inhibitor (W7) or PPase 2a inhibitor (OA 10 nmol/L) had no significant effect on MAPK and S6K activity. The above results suggested that activation of MAPK and S6K activity during hypoxia/reoxygenation there might require participation of PKC, Tyr K and PPase 1, while PKA, PKM and PPase 2a were not involved.

Animals↗
PubMed1996

Electrophysiologic characteristics and anatomical complexities of accessory atrioventricular pathways with successful ablation of anterograde and retrograde conduction at different sites.

INTRODUCTION: Catheter ablation may eliminate anterograde and retrograde accessory pathway conduction at closely adjacent but anatomically discrete sites. However, the mechanisms of this discrepancy, the electrophysiologic and anatomical characteristics, and information about systematic study from a large patient population are not available. The purpose of this study was to investigate the electrophysiologic characteristics and anatomical complexities of the accessory pathway in which anterograde and retrograde conduction was successfully ablated at different sites. METHODS AND RESULTS: Thirty-eight (10.9%) patients (19 men and 19 women; mean age 37 +/- 2.4 years) fulfilling the criteria of having separate ablation sites for anterograde and retrograde conduction were designated as group I, and the other 310 patients (215 men and 95 women; mean age 47 +/- 0.6 years) were designated as group II. The patients with right-sided free-wall pathways had the highest incidence (18.6%) of separate ablation sites. The anatomical distance between anterograde and retrograde directions (left anterior oblique view, 13 +/- 0.6 vs 8 +/- 0.9 mm, P < 0.01; right anterior oblique view, 17 +/- 0.6 vs 5 +/- 0.7 mm, P < 0.01), and incidence of conduction impairment in one direction after successful ablation of another direction (15% vs 78%, P < 0.05) differed significantly between left and right free-wall pathways. The mean distances obtained from left (7 +/- 0.4 vs 14 +/- 0.4 mm, P < 0.05) and right (7 +/- 1.1 vs 15 +/- 0.9 mm, P < 0.05) anterior oblique views were shorter in patients who had impairment of conduction properties than those in patients without impaired conduction after successful ablation of one direction. CONCLUSIONS: This study showed that anatomical and functional dissociation of the accessory pathway into anterograde and retrograde components was possible. Further study on the relation between electrophysiologic and pathologic characteristics would be helpful to confirm these findings.

Adolescent↗
PubMed1989

[Changes in populations of T lymphocytes in mice infected with Trichinella spiralis].

Acid alpha-naphthyl acetate esterase (ANAE), a cytoplasmic marker was used to identify the T lymphocytes and their subpopulations in peripheral blood of mice experimentally infected with T. spiralis. The results showed that the absolute number of lymphocytes and T lymphocytes increased in parallel on d3 after infection, reaching the peak on d14, and remaining above normal level on d60. The spotted granular ANAE positive cells (Helper T cells, Th) were decreasing and the scattered granular ANAE positive cells (suppressor T cells, Ts) were increasing, leading to a lowering of the Th/Ts ratio which was most marked on d14 and returned to normal on d60. The depression of host immune function during T. spiralis infection might be related to the lowering of Th/Ts ratio.

Animals↗
PubMed1986

Regulatory role of calcium on histamine secretion.

Calcium seems to have two opposing effects on histamine secretion from mast cells. A rise in the cytosol calcium concentration initiates the chain of reactions leading to histamine secretion. On the other hand, calcium appears to have a regulatory role, limiting the secretion. Removal of cell surface calcium enhances histamine secretion. The present work demonstrates an inhibitory effect of calcium in the medium, using low concentrations of compound 48/80 as the secretagogue. Histamine secretion in response to compound 48/80 primarily utilizes intracellular calcium. When low concentrations of compound 48/80 were used (usually 20-50 ng/ml), calcium (1 mM) inhibited the secretion, the inhibition being more pronounced as the pH was increased from 6.5 to 8.5. The higher pH conceivably promotes the binding of calcium to the phospholipids in the cell membrane. Calcium at this site seems to depress the efflux of calcium from the intracellular stores to the cytosol. The possibility that the removal of calcium from the cell surface causes increased sodium permeability was considered. However, the sodium channel blocker tetrodotoxin (10(-5) M) was equally ineffective in influencing histamine release in the presence and absence of calcium, indicating that a change of sodium permeability was not involved. Antigen-induced (anaphylactic) histamine secretion depends mainly on extracellular calcium, although some secretion occurs in a calcium-free medium. Addition of calcium alone to the medium caused only slight increase in the secretion, but when both phosphatidylserine and calcium were added histamine secretion was remarkably stimulated, apparently through the effect of phosphatidylserine on calcium transport across the plasma membrane.

Anaphylaxis↗
PubMed1984

Role of intracellular calcium in histamine release from rat mast cells.

Compound 48/80-induced histamine release may utilize both intracellular and extracellular calcium. The release is inhibited by La3+ and TMB-8 both in the presence and absence of calcium. The observations are consistent with a mobilization of calcium from the inner surface of the plasma membrane supporting the release. TMB-8 probably acts at more than one site. It has been shown to inhibit skeletal muscle contraction and this has been correlated to its inhibitory effect on the release of Ca2+ from the sarcoplasmic reticulum. TMB-8 also inhibits resting cellular influx and efflux of calcium in the ileum. Anaphylactic and dextran-induced histamine release is dependent on extracellular calcium; the inhibition of the release by TMB-8 seems to be primarily due to an interference with calcium transport across the plasma membrane. In the absence of extracellular calcium the inhibition of compound 48/80-induced histamine release by TMB-8 seems to be due to stabilization of Ca2+ binding to cellular stores.

Animals↗