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Biomedical subjects

S Li

Publications and source records attributed to S Li.

At least 1,063 records · Page 59Linked to original sources
PubMed1997

Geometric analysis of light-field position of a multileaf collimator with curved ends.

The purpose of this work was to analyze the difference between the light-field edge and the radiation field edge produced by multileaf collimator (MLC) leaves that are constructed with rounded ends. A formula was derived using three-dimensional geometry predicting the location of the ideal point-source light-field edge relative to the geometric projection of the tip of the rounded leaf end. The theoretical edge of the radiation field for a point source was also calculated along the projection of a chord whose length was one Half-Value Thickness (HVT). Analytic solutions were found for the radiation-field edge and the transmission penumbra. The displacement of the light-field edge relative to the projection of the leaf tip varied from 0 mm for the leaf tip projected onto the central axis to approximately 3.2 mm for the leaf tip projected to 20 cm off the central axis. The light-field edge was always displaced into the unblocked area. The location of the projection of the 1 HVT chord was displaced from the light-field edge by a small and essentially constant distance (approximately 0.3 mm) for all field sizes. The transmission penumbra (80%-20%) was about 1.2 mm for all leaf positions. The calibration of the leaf position must account for the nonlinear relationship between the leaf-tip projection and the light-field (or radiation-field) edge.

Evaluation Studies as Topic↗
PubMed1997

Analysis of the dose-surface histogram and dose-wall histogram for the rectum and bladder.

Dose distribution throughout a hollow organ is represented by either a dose-surface histogram (DSH) or a dose-wall histogram (DWH). A spherical shell model for the bladder and a cylindrical shell model for the rectum were introduced for quantifying the difference between the DWH and DSH. The difference was given by subtraction of the percent volume of the wall from the percent area of the surface for any specific dose level. Taking the dose-grid size and contour-delineation uncertainties into account, the DSH and DWH calculation errors were estimated by simplified formulas. The DSHs and DWHs for the rectum and bladder in patients undergoing four-field-prostate treatment and gynecological intracavitary brachytherapy were computed with a refined numerical algorithm. Results of the analytic models and the numerical calculations demonstrated that the difference between the DWH and DSH was small (about 5%) for a fully filled bladder or rectum but large (about 10%) for an empty rectum or a contracted bladder. The error of DSH was about 3%, which is smaller than that of DWH.

Humans↗
PubMed1997

Opioid regulation of the mouse delta-opioid receptor expressed in human embryonic kidney 293 cells.

Opioid analgesics are used extensively in the management of pain. Although the clinically effective opioids bind with high affinity to the mu-opioid receptor, studies have suggested that the delta-opioid agonists might represent more ideal analgesic agents, with fewer side effects. A limitation to opiate effectiveness is the development of tolerance, an event that has been linked to opioid receptor desensitization. To gain a better understanding of delta-receptor agonist regulation, the cloned mouse delta receptor was stably expressed in human embryonic kidney 293 cells, and the functional effects of agonist pretreatment were examined. With a 3-hr pretreatment protocol, the delta-selective agonists [D-Pen2,D-Pen5]enkephalin, [D-Ala2,D-Leu5]enkephalin, and [D-Ser2,Leu5]enkephalin-Thr and the nonselective opioids levorphanol, etorphine, and ethylketocyclazocine were found to desensitize delta receptors. [D-Pen2,D-Pen5]enkephalin, [D-Ser2,Leu5]enkephalin-Thr, [D-Ala2,D-Leu5]enkephalin, and etorphine treatments also caused a pronounced internalization of the epitope-tagged delta receptor, suggesting that the desensitization and internalization may be related. In contrast, levorphanol pretreatment did not internalize the receptor but still resulted in a 400-fold reduction in potency, suggesting that prolonged treatment with levorphanol only uncoupled the delta receptor from adenylyl cyclase. In contrast to the desensitization induced by peptide-selective delta agonists, pretreatment with the delta-selective nonpeptide agonist 7-spiroindanyloxymorphone and morphine sensitized the opioid inhibition of forskolin-stimulated cAMP accumulation. This differential regulation of the delta receptor may be due to variations in the ability of agonists to bind to the receptor. This hypothesis was supported by the finding that a point mutation that converted Asp128 to Asn128 (D128N) diminished the ability of delta-selective agonists to inhibit cAMP accumulation while increasing the potency of morphine to reduce cAMP accumulation. In particular, a lack of desensitization of the delta receptor by morphine may contribute to our understanding of the molecular basis of development of morphine-induced tolerance and dependence.

Adenylyl Cyclases↗
PubMed1997

Quantitative fluorescence in situ hybridization of Aureobasidium pullulans on microscope slides and leaf surfaces.

A 21-mer oligonucleotide probe designated Ap665, directed at the 18S rRNA of Aureobasidium pullulans and labelled with five molecules of fluorescein isothiocyanate, was applied by fluorescence in situ hybridization (FISH) to populations of the fungus on slides and apple leaves from growth chamber seedlings and orchard trees. In specificity tests that included Ap665 and a similarly labelled universal probe and the respective complementary probes as controls, the hybridization signal was strong for Ap665 reactions with 12 A. pullulans strains but at or below background level for 98 other fungi including 82 phylloplane isolates. Scanning confocal laser microscopy was used to confirm that the fluorescence originated from the cytoplasmic matrix and to overcome limitations imposed on conventional microscopy by leaf topography. Images were recorded with a cooled charge-coupled device video camera and digitized for storage and manipulation. Image analysis was used to verify semiquantitative fluorescence ratings and to demonstrate how the distribution of the fluorescence signal in specific interactions (e.g., Ap665 with A. pullulans cells) could be separated at a given probability level from nonspecific fluorescence (e.g., in interactions of Ap665 with Cryptococcus laurentii cells) of an overlapping population. Image analysis methods were used also to quantify epiphytic A. pullulans populations based on cell number or percent coverage of the leaf surface. Under some conditions, leaf autofluorescence and the release of fluorescent compounds by leaves during the processing for hybridization decreased the signal-to-noise ratio. These effects were reduced by the use of appropriate excitation filter sets and fixation conditions. We conclude that FISH can be used to detect and quantify A. pullulans cells in the phyllosphere.

Antibiosis↗
PubMed1997

Induction of CD4 expression and human immunodeficiency virus type 1 replication by mutants of the interferon-inducible protein kinase PKR.

Replication of the human immunodeficiency virus type 1 (HIV-1) is inhibited by interferons (IFNs), and the IFN-inducible protein kinase PKR is thought to mediate this effect by regulating protein synthesis. Here we report that ectopic expression of dominant negative PKR mutants in Jurkat cells induces HIV-1 replication. Specifically, expression of CD4 is upregulated by the PKR mutants, and this correlates with an induction of HIV-1 binding and proviral DNA synthesis upon HIV-1 infection. Moreover, activation of NF-kappaB was induced by an RNA binding-defective mutant of PKR. Thus, it appears that PKR, in addition to translational control, is involved in HIV-1 replication by modulating virus binding through the regulation of CD4 expression and virus gene expression through the activation of NF-kappaB.

CD4 Antigens↗
PubMed1997

Spatial variation of T2 in human articular cartilage.

PURPOSE: To determine the spatial variation of in vivo cartilage T2 in young asymptomatic adults. MATERIALS AND METHODS: Quantitative T2 maps of seven asymptomatic young male adults and one male volunteer with a history of previous intraarticular chondroid fragments were calculated by using a multiecho, spin-echo magnetic resonance imaging sequence at 3.0 T. The T2 maps were bilinearly interpolated to generate T2 profiles across the thickness of cartilage. RESULTS: All seven asymptomatic volunteers demonstrated a monotonic increase in T2, which increased from 32 msec +/- 1 in the deep radial zone and 48 msec +/- 1 in the deep transitional zone to 67 msec +/- 2 in the outer transitional superficial zone. The T2 profile of the volunteer with superficial fibrillation observed at arthroscopy demonstrated marked spatial heterogeneity and a statistically significant increase in cartilage T2. CONCLUSION: There is a reproducible pattern of increasing T2 that is proportional to the known spatial variation in cartilage water and is inversely proportional to the distribution of proteoglycans. The authors postulate that these regional T2 differences are secondary to the restricted mobility of cartilage water within an anisotropic solid matrix.

Adult↗
PubMed1997

Vascular smooth muscle cells on Matrigel as a model for LPS-induced hypocontractility and NO formation.

Treatment of vascular tissue with low levels of lipopolysaccharide (LPS) induces nitric oxide synthase (NOS) activity and diminishes vascular contractility. However, in cultured vascular smooth muscle cells (VSMC), very high doses of LPS or the combination of LPS with cytokines are required for the induction of nitric oxide (NO) formation. The aims of this study were to establish a cell model to investigate LPS-induced hypocontractility and NO production and to test the hypothesis that responses of VSMC to LPS are differentiation regulated. We used Matrigel basement membrane matrix to maintain VSMC differentiation and found that VSMC cultured on Matrigel retained significant contractility in response to KCl stimulation. Incubation of VSMC with low levels of LPS(1-100 ng/ml) induced NOS mRNA and protein, induced NO production, and decreased cell contractility in a time- and dose-dependent fashion. The NOS inhibitor NG-nitro-L-arginine methyl ester (L-NAME) partially restored LPS-treated VSMC contractility, whereas L-arginine reversed the contractility-restoring effect of L-NAME. These results suggest that VSMC grown on Matrigel are a useful experimental model for investigations into signal transduction mechanisms responsible for LPS-induced vascular hypocontractility.

Animals↗
PubMed1997

Blunted serotonin response to fenfluramine challenge in premenstrual dysphoric disorder.

OBJECTIVE: Indirect evidence suggests that abnormalities in serotonergic function may be involved in the pathogenesis of premenstrual dysphoric disorder. The goal of this study was to test the hypothesis of serotonergic deficiency in premenstrual dysphoric disorder by measuring the prolactin response to fenfluramine. METHOD: The authors administered the serotonin-releasing drug dl-fenfluramine in a placebo-controlled protocol to nine women with premenstrual dysphoric disorder and 11 healthy female volunteers in the luteal phase of the menstrual cycle. RESULTS: Compared to the normal subjects, the women with premenstrual dysphoric disorder had a significantly blunted prolactin response to fenfluramine. CONCLUSIONS: Premenstrual dysphoric disorder appears to be associated with serotonergic deficiency.

Adult↗
PubMed1997

Drug policy in China. Transformations, current status and future prospects.

The pharmaceutical sector in China developed rapidly with the implementation of the market-oriented economic reforms, which began at the end of the 1970s. From 1980 to 1988 the production of drugs quadrupled, subsequently increasing at an annual rate of 20%, and consumption of drugs correspondingly increased. The increase in drug production was largely a result of the increase in the number of pharmaceutical companies, particularly the number of private joint ventures, of which there were none in 1980 and 1900 in 1994, accounting for 37% of the total number of pharmaceutical companies. With the transformation of the Chinese pharmaceutical market, some new problems have appeared. The low efficiency of pharmaceutical companies, poor-quality drugs, unfair competition and misuse of drugs have been of great concern to the Chinese government. Some countermeasures have been taken, but the problems remain. Increases in the age of the Chinese population, increases in income and changes in disease patterns, together with membership of the World Trade Organization will promote the development of the pharmaceutical market. However, health-insurance reform, an essential drug list, the separation of drugs from services, and controls on the increases in hospital revenue will reduce the demand for drugs. Pharmaceutical companies in China face both opportunities and challenges. The trend in development of the pharmaceutical market depends on the outcome of the interaction between the factors that increase, and those that decrease, the demand for drugs. While the general trend is towards an increase in the demand for drugs and the expansion of the pharmaceutical market, downward fluctuation is inevitable if effective health reforms of cost control are introduced nationwide.

China↗
PubMed1997

[Relationship of mdr1 gene expression and multidrug resistance of primary lung cancer].

OBJECTIVE: To evaluate the expression of mdr1 gene in various type of primary lung cancer. METHOD: A serious of 48 resected primary lung cancer tissues from 5 post-chemotherapy and 43 untreated patients and 33 adjacent normal lung tissues were analyzed for mdr1 gene by RT-PCR method. RESULTS: Fifteen of 48 tumor tissues were found to have overexpression of mdr1 gene, comprising 6 of 12 adenocarcinomas, 7 of 22 squamous cell carcinomas, 1 of 2 sarcocarcinomas, 1 of 12 small cell carcinomas. Of 5 post-chemotherapy specimens, only one case showed positive. In addition, 3 of 33 adjacent normal tissues also showed mdr1-positive. Overexpression of mdr1 gene did not be associated with tumor size, metastasis and stage of lung cancer. The relapse rate with mdr1-positive cases was higher (80%) than that with mdr1-negative (58%) by one year follow-up of these patients. CONCLUSION: Overexpression of mdr1 gene can be detected in untreated primary lung cancer, specially in non-small cell lung cancer and may be regarded as one poorly prognostic marker.

Adenocarcinoma↗
PubMed1997

[Diagnosis and surgical treatment for tuberculous bronchostenosis].

OBJECTIVE: To explore the appropriate diagnosis and treatment for tuberculous bronchostenosis patients who failed in anti-tuberculosis chemotherapy. METHOD: The 46 patients with tuberculous bronchostenosis were treated with pneumonectomy and bronchoplasty. The latter included pulmonary lobectomy, wedge and sleeve resection of primary bronchus. RESULTS: All the patients showed sputum negative conversion and were cured without anastomotic fistulae, stenoses and other complications. CONCLUSIONS: Pneumonectomy is a routine treatment for tuberculous bronchostenosis, and bronchoplasty is a good method for treatment of the disease.

Adolescent↗
PubMed1997

[The effect of endurance training and exhaustive exercise on metallothionein in rats].

To understand physiological role of metallothionein (MT) during exercise, MT levels in liver, brain, heart, lung, blood vessel, skeletal muscle and serum were observed in rats. The results showed that the levels of MT were decreased by 13-34% in lung, liver, heart and skeletal muscle of rats trained by swimming for 10 weeks and were increased by 21%-75% in skeletal muscle, heart, brain, lung and liver of rats after exhaustive swimming respectively, compared with normal control rats. (P < 0.05 and P < 0.01). But the levels of MT in blood vessel and serum were not changed in two groups of rats by swimming for 10 weeks and acute exhaustive swimming (P > 0.05). It is suggested that the different changes of MT levels under physical training and acute exhaustive exercise may be of importance in protection against oxygen free radicals.

Animals↗
PubMed1997

[Improvement of operating method of repairing fistula of maxillary sinus].

5 cases of fistula of the maxillary sinus have been repaired by improved Teruo method, which uses flaps derived from submucous connective tissue of the palate and buccal mucous to repair the fistula. It has been satisfied after 4-13 years of follow-up observation. This article also discussed the difficulty of fistula repair and the advantage of the method. The authors thought that the method would be an ideal way to repair fistula of the maxillary sinus.

Adult↗
PubMed1997

[Molecular mechanism of mutagenesis induced by aflatoxin B1 using a shuttle vector pSP189/mammalian cell system].

AFB1 is one of the most potent carcinogenic mycotoxins, naturally occurred in foods. We applied a new SV40-based shuttle vector pSP189 and African Green kidney cells (VeroE6 cell line), which constitute shuttle vector/mammalian cell system to detect mutagenesis induced by AFB1 and to study the effects of AFB1 on the mutation site, type and sequence specificity of DNA molecular level through sequence analysis of pSP189 target gene SupF TRNA. The results indicated that through various time treatment of AFB1 and rat liver microsome, the mutants were obtained by transformation of E. Coli MBM 7070 with progeny of pSP189 generated during replication in veroE6 cells, which increased gradually with the lapse of time, and this experiment showed a significant dose-response relationship. Most detected mutants were point mutations evidenced by agarose gel electrophoresis analysis. The results of direct sequencing SupF TRNA of 53 independent mutants showed that most mutations (about 84.9%) were single base substitutions, among which 95.2% of base substitutions happened on the site of G:C base pair, the predominant mutation was G:C-->T:A transversion, accounting for 53.3%, followed by G:C-->A:T transition, accounting for 35.6%. AFB1-induced mutations did not distributed randomly, and had mutation hot spots and sequence specificity, which contained 5 base pair sequence 5'-NNTTC-3'. The mutations on the SupF shuttle vector were consistent with the results from studies of oncogene tumor suppressor genes and DNA adduct.

Aflatoxin B1↗
PubMed1997

[A study on the corrosion of desalinated drinking water from electrodialysis process and its control].

The stability index IR of desalinated drinking water from electrodialysis process was more than 9.0. Its corrosion rate P reached 0.59 mm/a. This is the main cause of "Red Water" and severe corrosion in network of pipes of water supply in an oil field. A large number of iron bacteria and sulfur bacteria in water are the biological causes of tubercles and block up. But the P becomes less than 0.05 mm/a, when the water is remineralized. It is an effective measurement to control the pipe corrosion and to provide good quality drinking water.

Corrosion↗