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Biomedical subjects

M Cheng

Publications and source records attributed to M Cheng.

At least 91 records · Page 5Linked to original sources
PubMed1991

Biomechanical properties and collagen fiber orientation of temporomandibular joint discs in dogs: 2. Tensile mechanical properties of the discs.

The tensile properties of TMJ discs in dogs were investigated using soft-tissue tensile and stress-relaxation tests. The data obtained suggested that (1) the mediolateral tensile stiffness (199.7 and 234.0 MPa), tensile strength (46.73 and 69.99 MPa), and equilibrium moduli (30.0 and 30.1 MPa) of anterior and posterior bands of the disc, respectively, were much greater than those of the middle part (46.6, 14.71, and 18.4 MPa, respectively); (2) the difference in fracture strain of various parts was not significant; (3) the physiologic strain region of the discs was about 4%; and (4) the properties of low stress/relaxation rate and nonlinear relationship of the instantaneous elastic response to various strains may represent lower permeability of TMJ discs.

Analysis of Variance↗
PubMed1990

Effect of lateral mobility of fluorescent probes in lipid mixing assays of cell fusion.

Monolayers of human erythrocytes, immobilized on a cover slip, were induced to fuse by polyethylene glycol (mol wt 8,000). The mobility of fluorescent probes, 1-oleoyl-2-[12-[(7-nitro-2,1,3-benzoxadizol-4-yl)amino]dodecanoyl] phosphatidyl-choline (C12-NBD-PC), from labeled cells to unlabeled cells was monitored by video-enhanced fluorescence microscopy. A dequenching curve was obtained from the measurement of fluorescence intensities of pairs of fused cells over time. The dequenching curve and the curve obtained from macroscopic measurements of a cell monolayer (described in the preceding article) were compared and discussed. The slow probe transfer rate between a pair of fused cells was explained by a diffusion model based on membrane area conservation and the geometry of the fusion lumen. An equivalent lumen between two fused cells, thought to be the main rate limitation of probe mobility after fusion, was calculated to be approximately 130 nm in diameter. Lumens of 75 nm in diameter were observed by electron microscopy. Thus, the rate of macroscopic fluorescence dequenching depends not only upon the fusion efficiency, but also upon the number of simultaneous fusion partners, the geometry of their contact points, and the lateral mobility of the fluorescent probes through these points. The relative fusion efficiency can be derived only from the saturation dequenching values.

4-Chloro-7-nitrobenzofurazan↗
PubMed1990

[Content of histoamine in processed Phytolacca americana L].

The contents of histamine in processed Phytolacca americana has been determined by colorimetry. The result shows that the contents tend to decrease by 23.3% when the herb is shredded, but get a bit higher again when fried with vinegar. The method may be useful in the quality control of the herb.

Colorimetry↗
PubMed1990

Total and direct-reacting bilirubin values by automated methods compared with liquid chromatography and with manual methods for determining delta bilirubin.

This study compares total and direct-reacting bilirubin values in 40 serum samples from patients with various diagnoses, as measured by automated methods (Beckman Synchron CX-5, Beckman Astra 8, Kodak Ektachem 700) and HPLC and by a manual method for delta bilirubin. For total bilirubin, within-run CVs were less than 6%. The Ektachem 700 method underestimated bilirubin with serum samples from patients with Crigler-Najjar syndrome and from newborns in whom unconjugated bilirubin concentrations were increased but conjugated bilirubins were not present or were present only in small amounts. The Astra 8 and Synchron CX-5 methods were inaccurate with cholestatic serum samples, in which conjugated bilirubin concentrations were increased and other compounds such as bile acids could be expected to interfere. We conclude that each automated method examined provides reasonable estimates for total and direct-reacting bilirubin values for routine clinical use. The need for each laboratory to select the appropriate bilirubin method for its particular situation is obvious.

Autoanalysis↗
PubMed1989

Selection of therapeutic agents for intraocular proliferative disease 3. Effects of fluoropyrimidines on cell-mediated contraction of human fibroblasts.

We evaluated the efficacy of 5-fluorouracil (5-FU) and 5-fluorouridine (5-FUR) as anticontractile agents in an in vitro model that measures the ability of human and rabbit fibroblasts to contract a collagen gel. Human fibroblasts were more contractile than rabbit fibroblasts, required higher concentrations of 5-FUR for inhibition of contraction, and were able to tolerate higher doses of the drug. 5-FU failed to inhibit contraction of human fibroblasts at concentrations up to 1.5 mM (200 micrograms ml-1), but significantly inhibited rabbit fibroblast contraction, although to a lesser degree than 5-FUR under similar conditions. 5-Fluorouridine (100 microM, 26 micrograms ml-1) inhibited contraction of human fibroblasts by more than 80%, whereas only 10 microM (2.6 micrograms ml-1) 5-FUR was required for 90% inhibition of rabbit fibroblast contraction. 5-FUR was cytotoxic to rabbit fibroblasts at concentrations of 200 microM (52 micrograms ml-1) or greater, but 800 microM was non-toxic to human fibroblasts after 96 hr exposure. At concentrations of 1.5 mM, 5-FU had no significant effects on the viability of either human or rabbit fibroblasts. These results suggest that 5-FUR may prove useful for the treatment of human ocular proliferative disorders in which contraction of fibrocellular elements is thought to play a part. They also suggest that fluoropyrimidine dosages found to be effective in a rabbit model of proliferative vitreoretinopathy may be less effective in humans and that 5-FUR levels shown to be toxic to rabbit-derived cells may be tolerated by humans cells.

Cells, Cultured↗
PubMed1989

Oxygenation during chest physiotherapy of very-low-birth-weight infants: relations among fraction of inspired oxygen levels, number of hand ventilations, and transcutaneous oxygen pressure.

Chest physiotherapy (CPT) to clear the airway of infants requiring assisted ventilation is a routine procedure in neonatal intensive care units. This study was done to describe the relationships between fraction of inspired oxygen (FiO2) levels and the number of hand ventilations (independent variables) and variations of transcutaneous oxygen pressure (TcPO2) from baseline among intubated very-low-birth-weight (VLBW) infants receiving CPT. The study consisted of 30 observations of 13 intubated VLBW infants receiving CPT. Data were obtained by observations during routine CPT procedures performed by the nurses in charge of the infants. Stepwise multiple regression showed that hand ventilations and FiO2 levels significantly accounted for the variability in TcPO2 levels during CPT. Pearson correlation analysis showed that there was a negative correlation between FiO2 and TcPO2 and between the number of hand ventilations and TcPO2.

Blood Gas Monitoring, Transcutaneous↗
PubMed1988

Effects of carbon monoxide on cardiac muscle cells in culture.

Embryonic rat cardiac muscle cells grown in the presence of various tensions of CO (5-95%) without the presence of O2 survived and exhibited reduced cell growth, which was concentration dependent. When cardiac muscle cells were grown in the presence of a mixture of CO (10-20%) and O2 (10-20%), the growth rate of these cells was comparable to that of the control cells. Cardiac myocytes continued to beat when exposed to varying tensions of CO, except in the case of 95% CO. The cells exposed to different concentrations of CO contained fewer myofibrils of different stages of differentiation compared with the control and the culture exposed to a mixture of 20% O2 and 20% CO, with cells that contained abundant, highly differentiated myofibrils. There was no significant difference in the structural organization of mitochondria between the control and the surviving experimental cells. It is evident from the present studies that O2 is required for the optimum in vitro cellular growth of cardiac muscle. Furthermore, CO in combination with O2 at a concentration of 10 or 20% can produce optimal growth of cardiac muscle cells in culture.

Animals↗
PubMed1988

Methotrexate: assessment of in vivo clastogenicity and carcinogenicity.

The genotoxic and oncogenic potentials of methotrexate were studied in Sprague-Dawley rats. The rats received 0.1, 0.2, or 0.4 mg/kg of methotrexate as dietary admixtures on a 5 days on, 9 days off, regimen for 23 months. In the females of the high-dose group, there was a significant increase in mortality starting at 18 months. Significant increases in the number of rats with focal pulmonary interstitial fibrosis were seen in both sexes at the high-dose level. At the mid- and high-dose levels of both sexes, there was a significantly increased number of rats with myeloid and erythroid bone marrow hypoplasia. There was no evidence of either early onset or increased incidence of any tumor type in the treatment groups. Therefore, it is concluded that methotrexate does not have oncogenic potential. Also, at terminal sacrifice, bone marrow cells were harvested from selected animals on the last day of the 5-day dosing cycle and cytogenetic evaluation was performed. No significant increase in chromosomal aberrations was seen in any dose group relative to the control group. This observation further substantiates the absence of oncogenic potential due to methotrexate in rats.

Animals↗
PubMed1988

Effect of total-body irradiation with bone marrow transplantation on toxicity of cisplatin.

In defined-flora, barrier-maintained rats (WAG/RijMCW males), radiation nephritis is the principal late toxicity seen after high-dose-rate, total-body irradiation (TBI) when hematologic toxicity is prevented by bone marrow transplantation. Pneumonitis develops only if rats are exposed to a conventional environment during and after bone marrow transplantation. Low-dose-rate TBI gives similar toxicity at doses twice as large. Rats surviving for 9 months after TBI show decreased tolerance for cisplatin. This decreased tolerance is related to dose and dose rate and is seen for radiation doses that show little or no renal toxicity. Evidence suggests that the decrease in renal tolerance is due to decreased renal platinum clearance in the irradiated kidneys.

Animals↗
PubMed1988

Trace element status of children with PKU and normal children.

The trace mineral (chromium, copper, iron, selenium, and zinc) status of 10 children (4 to 13.8 years) with phenylketonuria (PKU) and 9 normal children (6.5 to 15.9 years) was assessed. The children with PKU were treated with a phenylalanine-free L-amino acid mix that supplied the following percentages (mean +/- standard deviation) of total daily intake: energy, 45 +/- 13; protein, 75 +/- 11; copper (Cu), 62 +/- 10; iron (Fe), 82 +/- 7; selenium (Se), 40 +/- 20; and zinc (Zn) 87 +/- 8. Diet records and blood samples were collected from each subject. Children with PKU had significantly greater mean intakes of Cu, Fe, and Zn than normal children. Mean serum Cu, Fe, and Zn concentrations of the children with PKU and normal children were not different despite significantly greater intakes by the children with PKU. Normal children had a significantly greater mean serum Se concentration and a mean blood chromium concentration 1.6 times that of children with PKU. Individuals whose primary source of protein is an elemental diet are especially at risk for multiple trace mineral deficiencies. Manufacturers of chemically defined medical foods should evaluate composition, specifically molar ratios between minerals, as a basis for product formulation.

Child↗
PubMed1987

Effects of extinction, pimozide, SCH 23390, and metoclopramide on food-rewarded operant responding of rats.

The similarity in the pattern of responding produced by extinction and dopamine (DA) receptor blockers has led to the suggestion that DA neurons may participate in the usual effects of reward on behaviour. The purpose of the present study was to evaluate the effect of receptor-subtype specific DA antagonists on food-rewarded operant responding. Rats were trained to lever press for food on a variable interval 30-s schedule. They then received one of the following treatments prior to testing on the next 5 days: saline, nonreinforcement, the DA receptor blocker pimozide (0.5 or 1.0 mg/kg), the D1 receptor blocker SCH 23390 (0.01, 0.05, 0.1 mg/kg), and the D2 receptor blocker metoclopramide (1.0, 5.0, 10.0 mg/kg). Nonreinforcement resulted in both intra- and intersession declines in responding. The drugs produced dose-dependent decreases in overall responding. Additionally, both doses of pimozide and the higher doses of SCH 23390 and metoclopramide altered intrasession patterns of responding when compared to saline, with their greatest effect being in the latter portion of the session. Intersession declines were seen with the highest doses of SCH 23390 and metoclopramide and control studies showed that these declines could not be attributed to a buildup of the drug with repeated dosing. It was concluded that both D1 and D2 receptors participate in the control of behaviour by reward.

Animals↗