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Biomedical subjects

F Chen

Publications and source records attributed to F Chen.

At least 523 records · Page 29Linked to original sources
PubMed1994

Cooling responses of finger in contact with an aluminum surface.

Skin temperature (T sk) changes and subjective sensations of bare fingers touching a cold aluminum surface were determined in 25 subjects (12 female and 13 male). An 11-cm aluminum cube was placed in a mini-chamber, where chamber air and an aluminum cube were simultaneously cooled to -14, -5, and -1 degrees C, respectively. Subjects inserted their right hands into the chamber and pressed on the cube surface with three fingers with a force of 9.81 N (1 Kp). Exposure lasted until finger-skin temperature reached 0 degree C or was voluntarily ended by the subject. Regression equations with two exponential components were used to describe the relationship between T sk and exposure time. The short time constant (< 1 second) for the first part of the cooling curve is assumed to represent primarily thermocouple dynamics. The long time constant (> 20 seconds) for the second part of the cooling curve is interpreted as representing the rate of heat transfer from the tissues of the finger itself. Gender and cube-surface temperature had no significant effect on any of the time constants. Thermal sensation and pain sensation lacked a good correlation with the contact and T sk and T sk change.

Adult↗
PubMed1994

Estimates of trace element intakes in Chinese farmers.

Epidemiologic data on the average daily human dietary intake of the trace elements nickel, cadmium, molybdenum and silicon are scarce, worldwide, primarily because foods consumed vary widely over days and seasons. Available full year food allocation records for farmers in rural areas of China provide an unique opportunity to estimate dietary trace elements. In 1988, we measured the concentration of zinc, copper, iron, cadmium, nickel, molybdenum, silicon and selenium in different foods by using food samples collected from 232 villages (distributed among 21 communes). These measurements, combined with the food consumption information from existing food allocation records in each commune for an entire year, allowed us to estimate the average daily consumption of these trace elements by Chinese farmers. With one exception (an association of zinc and esophageal cancer), the variation of dietary trace elements did not show any association with mortality from several common diseases. The estimates for some of the dietary trace elements from some subpopulations were either less or more than current recommendations. No increases in mortality were found, however, from diseases normally associated with either dietary deficiencies or excesses of these elements.

Adult↗
PubMed1994

Identification and characterization of cDNA clones encoding plant calreticulin in barley.

Two cDNA clones (CRH1 and CRH2) homologous to animal calreticulin, a major calcium storage protein in the lumen of the endoplasmic reticulum, were isolated from an ovary cDNA library of barley through differential screening. The two clones differ in the 3' untranslated region and the 5' region that encodes a putative N-terminal signal sequence. CRH1 was mapped to the minus arm of chromosome 1. CRH2 was mapped to the minus arm of chromosome 2. The deduced amino acid sequences share 50 to 55% identity with animal calreticulins and exhibit the same three-zone characteristic. Recombinant protein stained blue with Stains-all and bound 45Ca2+ when transferred to nitrocellulose membranes. A native protein of approximately 55 kD was identified in ovary extract. Elevated gene expression was observed in ovaries 1 day after pollination and during early embryogenesis. CRH1 was expressed at a higher level than CRH2. These studies demonstrate the presence of calreticulin in plant cells and its developmental regulation in fertilization.

Amino Acid Sequence↗
PubMed1994

Excessive production of insulin-like growth factor-I by silicotic rat alveolar macrophages.

The supernatant of silicotic rat alveolar macrophages can stimulate fibroblast growth. The present study demonstrates that this activity is mainly attributed to insulin-like growth factor-I. Partial purification of the supernatant of alveolar macrophages, which were from silica-exposed 5 to 6-week-old rats, revealed a protein peak (peak 5) eluted from a molecular-sieve HPLC column, corresponding to a MW of 6-9 kDa. Activity assay and radioimmunoassay indicated that this peak is more potent with regard to stimulation of fibroblast growth and has higher insulin-like growth factor-I immunoreactivity, but there was no detectable activity of interleukin-1 or tumor necrosis factor. Quantification of insulin-like growth factor-I also manifests elevated insulin-like growth factor-I levels in silicotic rat bronchoalveolar lavage fluids which tend to increase with prolongation of silica exposure in vivo, but no alteration in insulin-like growth factor-I level can be found in sera. These findings suggest that excessive production of insulin-like growth factor-I by alveolar macrophages locally may play a pivotal role in silica-induced pulmonary interstitial fibrosis.

Animals↗
PubMed1994

Comparison of Western immunoblots and gene detection assays for identification of potentially enterotoxigenic isolates of Clostridium perfringens.

Clostridium perfringens enterotoxin (CPE) is an important sporulation-associated virulence factor in several illnesses of humans and domestic animals, including C. perfringens type A food poisoning. Therefore, the ability to determine the enterotoxigenicity of food or fecal C. perfringens isolates with simple, rapid assays should be helpful for epidemiologic investigations. In this study, Western immunoblotting (to detect CPE production in vitro) was compared with PCR assays and digoxigenin-labeled probe assays (to detect all or part of the cpe gene) as a method for determining the enterotoxigenicity of C. perfringens isolates. The cpe detection assays yielded reliable results with DNA purified from vegetative C. perfringens cultures, while Western immunoblots required in vitro sporulation of C. perfringens isolates to detect CPE production. Several cpe-positive C. perfringens isolates from diarrheic animals did not sporulate in vitro under commonly used sporulation-inducing conditions and consequently tested CPE negative. This result indicates that cpe gene detection and serologic CPE assays do not necessarily yield similar conclusions about the enterotoxigenicity of a C. perfringens isolate. Until further studies resolve whether these cpe-positive isolates which do not sporulate in vitro can or cannot sporulate and produce CPE in vivo, it may be preferable to use cpe detection assays for evaluating C. perfringens isolate enterotoxigenicity and thereby avoid potential false-negative conclusions which may occur with serologic assays.

Base Sequence↗
PubMed1994

Use of an ATP bioluminescent assay to evaluate viability of Pneumocystis carinii from rats.

A bioluminescent assay which employs the luciferin-luciferase ATP-dependent reaction was used to evaluate the viability of populations of Pneumocystis carinii derived from infected rat lungs. Contamination with host cells was reduced by a purification method which involved a combination of low- and high-speed centrifugations resulting in a 1,000-fold reduction of the rat cells while enriching for the trophic form of P. carinii. A linear correlation for the number of P. carinii nuclei versus the amount of ATP was observed. The ATP content of the organism populations could be maintained at inoculum levels for one week, although the number of organisms did not increase. Addition of respiratory chain inhibitors dramatically decreased the ATP content of the P. carinii after 24 h of incubation, with the exception of the antibiotic oligomycin B. Low concentrations of trimethoprim-sulfamethoxazole and pentamidine isethionate reduced the organism ATP content by over 50% after 24 h of exposure, while no effect was observed with 100-fold greater concentrations of ampicillin. The bioluminescent assay was found to be a more sensitive indicator of viability than a dual fluorescent staining technique. This assay does not require replication of P. carinii and should be a useful method for in vitro drug screening and viability assessment of P. carinii populations.

Adenosine Triphosphate↗
PubMed1994

Characterization of cell lines that inducibly express the adeno-associated virus Rep proteins.

The replication (rep) gene of adeno-associated virus (AAV) is involved in AAV DNA replication, gene regulation, and inhibition of cellular transformation induced by various oncogenes. To study the rep gene's antiproliferative effects, we have developed cell lines which express the replication proteins under the control of an inducible mouse metallothionein transcription promoter. The Rep78 protein produced in these cell lines binds to the AAV terminal repeat sequences in vitro and supports AAV DNA replication and trans activation of the AAV p40 transcription promoter in vivo. These cell lines are capable of assembling infectious viruses containing a mutant rep gene or a vector bearing a heterologous gene. Growth rate and colony formation efficiency assays indicated that rep gene expression substantially altered cellular proliferation. Long-term induction of the cell lines followed by removal of the inducing agent suggested that constitutive expression of the Rep proteins does not necessarily result in cell death and that the cells can recover from the cytostatic effects. Flow cytometry analysis indicated that the presence of the Rep proteins increased the population of cells in the S phase of the cell cycle. Thus the rep gene's antiproliferative effects may be realized by interference with cellular DNA replication.

Cell Division↗
PubMed1994

Subcellular distribution of dystrophin in isolated adult and neonatal cardiac myocytes.

The subcellular localization of dystrophin was examined in adult rabbit and rat cardiac myocytes with immunofluorescence and at higher resolution with immunogold. The aim was to resolve the conflicting reports on the presence of dystrophin in the transverse tubules (T tubules) of cardiac muscle and to determine its distribution in neonatal myocytes before and during the development of the T tubules. Dystrophin was localized to the peripheral sarcolemma and the T-tubular membrane and was absent from the intercalated disk membranes. In addition, dystrophin localization was followed with immunofluorescence in developing rabbit myocytes at 4 days, 1 wk, and 1 mo after birth. At 4 days of age, T tubules are absent and dystrophin was localized only in the peripheral sarcolemma. Dystrophin was present in the developing T tubules at 1 wk and 1 mo. These results imply that dystrophin is expressed in the T tubules as soon as they develop and confirm the different distribution of dystrophin in the T tubules of cardiac and skeletal muscle.

Amino Acid Sequence↗
PubMed1994

A region in the human glycoprotein hormone alpha-subunit important in holoprotein formation and receptor binding.

Using site-directed mutagenesis of the human glycoprotein hormone alpha-subunit, we have shown that single replacements of Ala36 and Pro38 with Glu and Asp, respectively, result in mutant subunits that do not bind significantly to hCG beta. In contrast, the replacement of Lys44 with Ala did not interfere with hCG beta binding, but the resulting holoprotein failed to exhibit high affinity binding to the LH/CG receptor. These results in conjunction with other data suggest that the region of human alpha between positions 33-45 contains several amino acid residues that participate in subunit binding and others that function in receptor binding.

Amino Acid Sequence↗
PubMed1994

Cloning of a novel orphan receptor (GCNF) expressed during germ cell development.

We have cloned a novel member of the nuclear receptor superfamily that has been identified from complementary DNA libraries derived from mouse tissues using a low stringency cross hybridization strategy. The deduced protein sequence contains 495 amino acids and consists of the characteristic DNA-binding and ligand-binding domains of the nuclear receptor superfamily. The primary sequence of this new orphan is distinct from those of previously cloned members and subgroups. Analysis of the DNA-binding properties of the in vitro synthesized protein revealed that this new orphan receptor binds to the sequence TCAAGGTCA that includes the steroidogenic factor-1 half-site and direct repeat with 0 bp spacing elements. Northern blot and ribonuclease protection assays showed that the receptor was predominantly expressed in the testis. Results from in situ hybridization experiments confirmed this observation and showed it to be located in the spermatogenic cells. High level expression was also detected in developing oocytes in the ovary. Thus, high level expression of this gene is restricted to developing germ cells, the oocytes and spermatogenic cells. We speculate that this orphan receptor may be a molecule involved in regulating some aspect of meiosis, and that the major function of this factor is likely to be involved in the regulation of gene expression in germ cell development during gametogenesis. It has been designated germ cell nuclear factor.

Amino Acid Sequence↗
PubMed1994

Dietary biotin and turkey breeder performance.

The effect of biotin supplementation on turkey breeder hen performance was examined in two experiments. A corn-soybean meal-based breeder diet was supplemented with biotin to provide a low (.178 mg/kg) and high (.75 mg/kg) level of dietary biotin. The diets were fed to female-line hens (Nicholas strain) starting at time of light stimulation (31 and 30 wk of age for Experiments 1 and 2, respectively) for 27 wk. Each diet was fed to four replicate pens of 25 hens each. In Experiment 1, egg production and hatchability of fertile eggs from hens fed the high level of biotin was significantly greater (P < .05) during 50 to 54 wk of age. Egg production and hatchability were improved by 22 and 10%, respectively, from 50 to 54 wk of age. In Experiment 2, reproductive performance was unaffected by biotin level during 33 to 57 wk of age. The higher level of dietary biotin seemed beneficial in supporting later reproductive performance in one of two experiments.

Animals↗
PubMed1994

[On the method of hyperthermic chemotherapy by regional isolated perfusion for tumors of lower extremities].

From August 1990 to June 1993, 30 patients with osteosarcoma of lower extremities were treated with chemotherapy by hyperthermic regional isolated perfusion. There were 19 male and 11 female with a mean age of 21 (15-28) years. All of the tumors were located in the lower limbs: 20 on the femora, 9 on the tibiae and 1 on the fibula. Chemotherapy was going on for 60 minutes during hyperthermic regional isolated perfusion. Temperature was kept at 42 degrees C in deep soft tissue around the tumor during perfusion. The results showed that local edema of the limbs were reduced observably, tumors were shrunken and hardened after perfusion. Perimeter of the limbs were decreased and mobility of the limbs increased. Pathological examination indicated that all of the tumors responded well to the chemotherapy by perfusion and 90%-95% of the osteosarcoma cells were destroyed. Two cases were complicated with compression syndrome, and 1 with renal failure. The authors would suggest that hyperthermic regional isolated perfusion is an effective chemotherapeutic method in management of malignant tumors of limbs.

Adolescent↗
PubMed1994

[Experimental study of the evaluation of efficacy of fluid replacement based on Parkland formula for burn shock].

In order to investigate the effect of fluid resuscitation of burn shock according to Parkland formula and to find out whether it leaves any damage due to hypoxia, 22 male mongrel dogs with 50% III degrees burn were divided randomly into two groups. Group 1 (14 dogs) received no fluid replacement, whereas in group 2 (8 dogs) Ringer's lactate solution was given according to Parkland formula after the injury. Swan-Ganz catheter was inserted to the pulmonary artery before burn. FAP, CVP, PAP, cardiac output and blood gas analysis were measured preburn and at 2, 6, 12, 18, 24, 36 and 48 hours postburn. The results demonstrated that group 1 dogs all died within 12 hours postburn and group 2 dogs all survived over the shock period. However, even in these survived dogs, markedly decreased cardiac output and oxygen consumption were observed over the first 18 hours postburn. This indicated that fluid replacement according to Parkland formula can not completely correct the inadequacy of tissue perfusion, and it may leave certain damage of oxygen deficiency. Therefore, further improvement in fluid resuscitation and combined treatment for early burn shock to raise cardiac output and improve tissue oxygen delivery may be needed.

Animals↗
PubMed1994

Management of tibial defects in total knee arthroplasty. A biomechanical study.

Peripheral deficiencies of tibial bone stock must be appropriately addressed at total knee arthroplasty to help ensure stability of the tibial component. Conversion of the oblique shaped peripheral defects into defects with vertical and horizontal surfaces, before repair, should lead to improved stability of tibial component fixation. In vitro testing revealed that conversion of the oblique wedge defect into a stepped pattern resulted in improved rigidity of the system when testing five specimens with a 20 degrees peripheral defect (wedge stiffness 25.5 +/- 1.08 versus step stiffness 32.4 +/- 1.72; p < 0.01) and five specimens with a 35 degrees defect (wedge stiffness 18.7 +/- 0.74 versus step stiffness 25.6 +/- 0.85; p < 0.0001). Improved rigidity of the system was further illustrated when a fibrous interface was introduced between the bone and cement surfaces (wedge stiffness 4.8 +/- 0.6 versus step stiffness 29.9 +/- 1.4; p < 0.0001). One hundred percent of wedge shaped cement constructs failed and slipped off, while none of the step shaped constructs described herein failed at the cement to bone interface. There were no statistically significant differences in stiffness with the incorporation of a metal wedge or block into the system when compared with the cement repaired stepped pattern. These biomechanical studies suggest that alterations in the configuration of peripheral defects can create a more rigid system that should ultimately result in improved support to the tibial component overlying these defects.

Animals↗
PubMed1994

Evaluation of captopril renography with 99mTc-MAG3 in the diagnosis of renovascular hypertension.

Eighty-one patients with suspected renovascular hypertension (RVH) were studied using 99mTc-MAG3 renography before and after administration of 25 mg captopril (CAP). Among the 81 cases, 22 were proven by renal arteriography or DSA. The results showed that by using CAP, the sensitivity and specificity of renography in RVH diagnosis increased from 66% to 72% and from 33% to 100%, respectively. We conclude that renography is a simple, noninvasive, sensitive and specific method for screening RVH and is suitable for use in hospitals with no gamma-cameras.

Adolescent↗