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Biomedical subjects

Z Wang

Publications and source records attributed to Z Wang.

At least 685 records · Page 38Linked to original sources
PubMed2000

Mycotic aneurysm of the abdominal aorta in a patient undergoing hemodialysis: an unusual complication of Staphylococcus aureus bacteremia.

When Staphylococcus aureus is repeatedly positive in blood cultures even under effective antibiotics therapy (vancomycin, teicoplanin, or rifampin), computed tomography scan and sonography should be performed early to exclude mycotic aneurysm of the deeply seated arteries, especially in patients with abdominal aortic calcification. Before 1990, the most common causative organism of suprarenal aortic mycotic aneurysm was Salmonella; since 1990, it has been gram-positive cocci (i.e., Streptococcus and Staphylococcus) rather than gram-negative bacilli (i.e., Salmonella), possibly because of the more invasive procedures performed in clinical settings, but this hypothesis needs further investigation.

Aged↗
PubMed2000

Selection and determination of beam weights based on genetic algorithms for conformal radiotherapy treatment planning.

A genetic algorithm has been used to optimize the selection of beam weights for external beam three-dimensional conformal radiotherapy treatment planning. A fitness function is defined, which includes a difference function to achieve a least-square fit to doses at preselected points in a planning target volume, and a penalty item to constrain the maximum allowable doses delivered to critical organs. Adjustment between the dose uniformity within the target volume and the dose constraint to the critical structures can be achieved by varying the beam weight variables in the fitness function. A floating-point encoding schema and several operators, like uniform crossover, arithmetical crossover, geometrical crossover, Gaussian mutation and uniform mutation, have been used to evolve the population. Three different cases were used to verify the correctness of the algorithm and quality assessment based on dose-volume histograms and three-dimensional dose distributions were given. The results indicate that the genetic algorithm presented here has considerable potential.

Adolescent↗
PubMed2000

Time-frequency analysis of heart rate variability using short-time fourier analysis.

This study was done to introduce new parameters derived by time frequency analysis of heart rate variability data. Four simulation experiments were carried out to compare the short-time Fourier transform (STFT) analysis method to the traditional overall spectral analysis method. Sinusoidal signals were generated with identical total power in the high-frequency band, but varying time-frequency and time-amplitude information. The STFT method was also applied to heart rate variability data from the stages of normal human sleep. Data analysis included computation of the power in the high-frequency band by overall spectral analysis. The instability coefficients (ICs) of the frequency and power in the high-frequency band were derived by STFT analysis. The ICs derived by the STFT method were able to describe time-frequency and time-amplitude variations in sinusoidal signals which contained identical total power in a specified frequency range. The ICs of the frequency and power were able to differentiate variations in vagal activity between the stages of human sleep and waking. The ICs represent new parameters derived by the STFT method, and allow the detection and quantification of short-lasting time-frequency and time-amplitude variations that remain obscured by overall spectral analysis.

Adult↗
PubMed2000

Total-body skeletal muscle mass: development and cross-validation of anthropometric prediction models.

BACKGROUND: Skeletal muscle (SM) is a large body compartment of biological importance, but it remains difficult to quantify SM with affordable and practical methods that can be applied in clinical and field settings. OBJECTIVE: The objective of this study was to develop and cross-validate anthropometric SM mass prediction models in healthy adults. DESIGN: SM mass, measured by using whole-body multislice magnetic resonance imaging, was set as the dependent variable in prediction models. Independent variables were organized into 2 separate formulas. One formula included mainly limb circumferences and skinfold thicknesses [model 1: height (in m) and skinfold-corrected upperarm, thigh, and calf girths (CAG, CTG, and CCG, respectively; in cm)]. The other formula included mainly body weight (in kg) and height (model 2). The models were developed and cross-validated in nonobese adults [body mass index (in kg/m(2)) < 30]. RESULTS: Two SM (in kg) models for nonobese subjects (n = 244) were developed as follows: SM = Ht x (0.00744 x CAG(2) + 0.00088 x CTG(2) + 0.00441 x CCG(2)) + 2.4 x sex - 0.048 x age + race + 7.8, where R:(2) = 0.91, P: < 0.0001, and SEE = 2.2 kg; sex = 0 for female and 1 for male, race = -2.0 for Asian, 1.1 for African American, and 0 for white and Hispanic, and SM = 0.244 x BW + 7.80 x Ht + 6.6 x sex - 0.098 x age + race - 3.3, where R:(2) = 0.86, P: < 0.0001, and SEE = 2.8 kg; sex = 0 for female and 1 for male, race = -1.2 for Asian, 1.4 for African American, and 0 for white and Hispanic. CONCLUSION: These 2 anthropometric prediction models, the first developed in vivo by using state-of-the-art body-composition methods, are likely to prove useful in clinical evaluations and field studies of SM mass in nonobese adults.

Adult↗
PubMed2000

A novel Drosophila alkaline phosphatase specific to the ellipsoid body of the adult brain and the lower Malpighian (renal) tubule.

Two independent Drosophila melanogaster P(GAL4) enhancer-trap lines revealed identical GAL4-directed expression patterns in the ellipsoid body of the brain and in the Malpighian (renal) tubules in the abdomen. Both P-element insertions mapped to the same chromosomal site (100B2). The genomic locus, as characterized by plasmid rescue of flanking DNA, restriction mapping, and DNA sequencing, revealed the two P(GAL4) elements to be inserted in opposite orientations, only 46 bp apart. Three genes flanking the insertions have been identified. Calcineurin A1 (previously mapped to 21E-F) lies to one side, and two very closely linked genes lie to the other. The nearer encodes Aph-4, the first Drosophila alkaline phosphatase gene to be identified; the more distant gene [l(3)96601] is novel, with a head-elevated expression, and with distant similarity to transcription regulatory elements. Both in situ hybridization with Aph-4 probes and direct histochemical determination of alkaline phosphatase activity precisely matches the enhancer-trap pattern reported by the original lines. Although the P-element insertions are not recessive lethals, they display tubule phenotypes in both heterozygotes and homozygotes. Rates of fluid secretion in tubules from c507 homozygotes are reduced, both basally, and after stimulation by CAP(2b), cAMP, or Drosophila leucokinin. The P-element insertions also disrupt the expression of Aph-4, causing misexpression in the tubule main segment. This disruption extends to tubule pigmentation, with c507 homozygotes displaying white-like transparent main segments. These results suggest that Aph-4, while possessing a very narrow range of expression, nonetheless plays an important role in epithelial function.

Alkaline Phosphatase↗
PubMed2000

Stimulation of beta-adrenergic receptors inhibits the release of tumor necrosis factor-alpha from the isolated rat heart.

OBJECTIVES: Beta-adrenergic receptor agonists such as isoproterenol inhibit production of tumor necrosis factor (TNF)-alpha in a number of cell types. Because the heart is a source of TNF-alpha, we hypothesized that isoproterenol would inhibit cardiac production of the cytokine. DESIGN: Analysis of cardiac release of TNF-alpha. SETTING: Medical research laboratory. SUBJECTS: Rats. INTERVENTIONS: None. MEASUREMENTS AND MAIN RESULTS: With the approval of the Institutional Animal Care and Use Committee, rats were anesthetized and hearts were removed and perfused. After 30 mins, bacterial lipopolysaccharide (LPS) with or without isoproterenol was infused for 60 mins. At 30, 60, 90, 120, and 150 mins, coronary flow was measured and coronary effluent was analyzed for TNF-alpha. Cardiac production of TNF-alpha was expressed as pg/min. Cyclic adenosine monophosphate (AMP) in the coronary effluent was measured. TNF-alpha messenger RNA was determined in ventricular tissue. After 30 mins, TNF-alpha was undetectable in the coronary effluent However, 60 mins after the initiation of LPS infusion, TNF-alpha release was 875+/-255 pg/min and increased to 2164+/-721 pg/min at 150 mins. Simultaneous infusion of isoproterenol with LPS stimulated cyclic AMP release and inhibited TNF-alpha production. For instance, at 60 and 150 mins, TNF-alpha release was 75+/-38 and 58+/-29 pg/min, respectively (p < .05 vs. LPS alone). Simultaneous infusion of isoproterenol with LPS blocked the induction of TNF-alpha messenger RNA by LPS. Isoproterenol, begun 30 mins after the initiation of LPS infusion, still suppressed LPS-stimulated TNF-alpha release by 95% at 150 mins. Similar results were obtained with norepinephrine. CONCLUSIONS: Activation of beta-adrenergic receptors inhibits cardiac TNF-alpha release. This implies that cytokine production by the heart is inhibited by the sympathetic nervous system. In heart failure, the cardiac response to the sympathetic nervous system is impaired. This impairment may play a role in the high plasma levels of TNF-alpha found in heart failure.

Animals↗
PubMed2000

Age-related changes in contractile responses of rabbit lower urinary tract to endothelin.

PURPOSE: As there are significant amounts of endothelin (ET) receptors in the mammalian urinary tract, we investigated the pharmacological properties and localization of ET receptors in the rabbit lower urinary tract as a function of age. MATERIALS AND METHODS: The characteristics of ET receptors in bladder dome, trigone and urethra of 6 weeks and 6 months old male rabbits were determined using muscle bath and autoradiographic techniques. RESULTS: ET-1 produces significant contractile responses in smooth muscle strips from bladder dome, trigone, and urethra in both 6 weeks and 6 months old rabbits. Although there was no significant difference in the maximum contractile response of urethral muscle strips to ET-1 between 6 weeks and 6 months old rabbits, the maximum responses to ET-1 were higher in both bladder dome and trigone of 6 weeks than 6 months old rabbits. A selective ETA receptor antagonist, BQ 610, shifted the concentration response curve to ET-1 to the right without decreasing maximal contractile responses in all regions from both age groups, whereas a selective ETB receptor antagonist, IRL 1038, had no significant effect on the contractile response in these tissues. Autoradiographic studies indicate that both ET receptor subtypes are expressed in bladder dome, trigone, and urethra with the ETA subtype being located only in the smooth muscle layers and the ETB subtype being located in both the urothelial and smooth muscle layers. CONCLUSION: Our data indicate the presence of region- and age-dependent differences in the contractile properties of ET receptors in the male rabbit lower urinary tract. Although both ETA and ETB receptor subtypes are present in the smooth muscle layers, the ETA receptor is the sub-type that is primarily involved in the mediation of contractions.

Aging↗
PubMed2000

Nitrogen atom energy distributions in a hollow-cathode planar sputtering magnetron

Energy distributions of nitrogen atoms (N) in a hollow-cathode planar sputtering magnetron were obtained by use of optical emission spectroscopy. A characteristic line, N I 8216.3 A, well separated from molecular nitrogen emission bands, was identified. Jansson's nonlinear spectral deconvolution method, refined by minimization of chi(2)(w), was used to obtain the optimal deconvolved spectra. These showed nitrogen atom energies from 1 eV to beyond 500 eV. Based on comparisons with VFTRIM computer code results, it is proposed that the energetic N's are generated from N+2 ions after these ions are accelerated through the sheath and dissociatively reflect from the cathode.

Journal Article↗
PubMed2000

Simulation of field-induced structural formation and transition in electromagnetorheological suspensions.

A computer simulation method has been used to study the three-dimensional structural formation and transition of electromagnetorheological (EMR) suspensions under compatible electric and magnetic fields. When the fields are applied simultaneously and perpendicularly to each other, the particles rapidly arrange into single layer structures parallel to both fields. In each layer, there is a two-dimensional hexagonal lattice. The single layers then combine together to form thicker sheetlike structures. With the help of the thermal fluctuations, the thicker structures relax into three-dimensional close-packed structures, which may be face-centered cubic (fcc), hexagonal close-packed (hcp) lattices, or, more probably, the mixture of them, depending on the initial configurations and the thermal fluctuations. On the other hand, if the electric field is applied first to induce the body-centered tetragonal (bct) columns in the system, and then the magnetic field is applied in the perpendicular direction, the bct to fcc structure transition is observed in a very short time. Following that, the structure keeps on evolving due to the demagnetization effect and finally forms close-packed structures with fcc and hcp lattice character. The simulation results are in agreement with the theoretical and experimental results.

Journal Article↗
PubMed2000

Body mass index in aboriginal Australians in remote communities.

OBJECTIVES: To describe the distribution of body mass index (BMI) and estimate the prevalence of potential chronic energy deficiency (CED) and obesity in Aborigines in remote communities (ARC) in the Top End of the Northern Territory, Australia. METHODS: Centile charts were constructed for BMI from 1,631 sets of measurements from 1,138 Aborigines, aged five to 77 years, in three remote communities on the Tiwi Islands, using Cole's LMS method. These were compared with European, American white and American black reference charts. The prevalences of CED and obesity were also compared to the corresponding values from a national Indigenous sample. RESULTS: The BMI centiles change with age. Compared with reference populations, BMIs are lower in ARC children and adult males. Young adult females have similar BMIs to American black and higher BMIs than American white and French counterparts up to 45 years. Aborigines older than 50 years are 'thinner'. Compared with a national sample of Indigenous Australians, our sample has a higher prevalence of CED and a lower prevalence of obesity. CONCLUSIONS: The BMI centile curves describe the contemporary nutritional status in the remote communities. Nutritional status measured by BMI is different in ARC than in other populations. IMPLICATIONS: The difference in nutritional status between ARC and other populations should be considered when planning nutritional intervention strategies. The centile charts will allow health workers to determine the relative ranking of BMI for individual Aborigines in the remote communities.

Adolescent↗
PubMed2000

Three 5'-variant mRNAs of anion exchanger AE2 in stomach and intestine of mouse, rabbit, and rat.

AE2 is one of three known isoforms of the anion exchanger (AE) gene family. The use of alternative promoters, resulting in a tissue-specific transcript pattern, was reported for all AE genes. Three N-terminal variant AE2 subtypes are described: AE2a, AE2b, and AE2c. Although the basolaterally located parietal cell anion exchanger is known to be an AE2, the molecular identity of the basolateral and apical anion exchangers throughout the gut are still unknown. This article summarizes functional, immunohistochemical, and Western blot data demonstrating the basolateral localization of the gastric and intestinal AE2 in rabbit, mouse, and rat, and showing the AE2 subtype mRNA expression pattern in the stomach and along the intestine of rabbit and mouse: AE2a is expressed in all studied tissues, but most strongly in the colon; AE2b is expressed mainly in the stomach; and AE2c is detected nearly exclusively in the stomach. Further investigation is necessary to characterize the apical anion transport protein involved in NaCl absorption and HCO3- secretion in the gut.

5' Untranslated Regions↗
PubMed2000

Body composition modeling. Application to exploration of the resting energy expenditure fat-free mass relationship.

There are now many published methods for predicting resting energy expenditure (REE) from measured body mass and composition. Although these published reports extend back almost a century, new related studies appear on a regular basis. It remains unclear what the similarities and differences are between these many methods and what, if any, advantages the newly introduced REE prediction models offer. These issues led us to develop an organizational system for REE prediction methods with the ultimate aim of clarifying prevailing ambiguities in the field. Our classification scheme is founded on the mathematical function type (descriptive and mechanistic) and body composition level (whole body-->molecular) used in REE prediction model development. The model is applied in an exploration of the well-established empirical relationship between REE and fat-free body mass (FFM). The developed relationships indicate that REE vs. FFM is a curvilinear relationship in mammals as a whole, that the relationship can be described as a linear function in humans, and that the simple linear regression line coefficients can be reconstructed from established tissue-system level component relationships. Our classification system, the first founded on a conceptual basis, highlights similarities and differences between the many diverse REE body composition prediction methods, provides a framework for teaching REE-body composition relationships to students, and suggests important future research opportunities.

Adipose Tissue↗
PubMed2000

Cellular-level body composition model. A new approach to studying fat-free mass hydration.

Fat-free mass hydration, the ratio of total body water (TBW) to fat-free mass (FFM), is stable at approximately 0.73 in mammals, and this constancy provides a means of estimating total body fat in vivo. As there is no mechanistic theory to explain the magnitude and variability in TBW/FFM, the present investigation describes a cellular-level model indicating that FFM hydration is determined by four factors: body cell mass hydration, extracellular fluid hydration, ratio of extracellular solids to TBW, and ratio of extracellular water to intracellular water. According to the model, TBW/FFM can be predicted for adult humans as a mean of 0.73, and a variation range 0.69-0.77. The suggested modeling approach provides a conceptual framework for TBW-fat estimation method and identifies important areas that remain to be studied.

Adipose Tissue↗
PubMed2000

Smaller organ tissue mass in the elderly fails to explain lower resting metabolic rate.

We previously reported our in vivo prediction of whole body resting energy expenditure (REE) using magnetic resonance imaging and echocardiography-derived organ volumes combined with published organ tissue metabolic rates. The models, developed in young healthy persons from predicted and measured variables, were highly correlated (e.g., calculated vs. measured REE, r = 0.92, p < 0.001), with no significant differences (p = NS) between them. This study employed the same approach to determine whether possible age-related decreases in organ tissue mass may account for the lower REE commonly reported in elderly persons. Measurements of REE (REEm) were acquired by indirect calorimetry. Calculated REE (REEc) models were developed from measured tissues and organs, and energy flux rates were assigned for each of the seven tissue/organ components, as reported by Elia. Older men (n = 6) and women (n = 7) had significantly lower REEm compared to REEc (p = 0.001). The magnitude of the differences were 13% and 9.5%, respectively, for men and women. These preliminary data suggest that factors other than organ atrophy may contribute to the lower metabolic rate of older persons. Further studies are required to investigate whether there is a reduction in the oxidative capacity of individual organs and tissues.

Absorptiometry, Photon↗
PubMed2000

A steroid derivative with paclitaxel-like effects on tubulin polymerization.

The endogenous estrogen metabolite 2-methoxyestradiol has modest antimitotic activity that may result from a weak interaction at the colchicine binding site of tubulin, but it nevertheless has in vivo antitumor activity. Synthetic efforts to improve activity led to compounds that increased inhibitory effects on cell growth, tubulin polymerization, and binding of colchicine to tubulin. This earlier work was directed at modifications in the steroid A ring, which is probably analogous to the colchicine tropolonic C ring. One of the most active analogs prepared was 2-ethoxyestradiol (2EE). We report here that different modifications in the steroid B ring of 2EE yield compounds with two apparently distinct modes of action. Simple expansion of the B ring to seven members resulted in a compound comparable to 2EE in its ability to inhibit tubulin polymerization and colchicine binding to tubulin. Acetylation of the hydroxyl groups in this analog and in 2EE essentially abolished these inhibitory properties. The introduction of a ketone functionality at C6, together with acetylation of the hydroxyls at positions 3 and 17, produced a compound with activity similar to that of paclitaxel, in that the agent enhanced tubulin polymerization into polymers that were partially stable at 0 degrees C. The acetyl group at C17, but not that at C3, was essential for this paclitaxel-like activity.

2-Methoxyestradiol↗
PubMed2000

Molecular cloning and characterization of a second human cysteinyl leukotriene receptor: discovery of a subtype selective agonist.

The cysteinyl leukotrienes (CysLTs) are potent biological mediators in the pathophysiology of inflammatory diseases, in particular of airway obstruction in asthma. Pharmacological studies have suggested the existence of at least two types of CysLT receptors, designated CysLT(1) and CysLT(2). The CysLT(1) receptor has been cloned recently. Here we report the molecular cloning, expression, localization, and functional characterization of a human G protein-coupled receptor that has the expected characteristics of a CysLT(2) receptor. This new receptor is selectively activated by nanomolar concentrations of CysLTs with a rank order potency of LTC(4) = LTD(4) >> LTE(4). The leukotriene analog BAY u9773, reported to be a dual CysLT(1)/CysLT(2) antagonist, was found to be an antagonist at CysLT(1) sites but acted as a partial agonist at this new receptor. The structurally different CysLT(1) receptor-selective antagonists zafirlukast, montelukast, and MK-571 did not inhibit the agonist-mediated calcium mobilization of CysLT(2) receptors at physiological concentrations. Localization studies indicate highest expression of CysLT(2) receptors in adrenal glands, heart, and placenta; moderate levels in spleen, peripheral blood leukocytes, and lymph nodes; and low levels in the central nervous system and pituitary. The human CysLT(2) receptor gene is located on chromosome 13q14.12-21.1. The new receptor exhibits all characteristics of the thus far poorly defined CysLT(2) receptor. Moreover, we have identified BAY u9773 as a CysLT(2) selective agonist, which could prove to be of immediate use in understanding the functional roles of the CysLT(2) receptor.

Amino Acid Sequence↗