Biomedical subjects

G Xu

Publications and source records attributed to G Xu.

At least 217 records · Page 12Linked to original sources

PubMed1999

A maize map standard with sequenced core markers, grass genome reference points and 932 expressed sequence tagged sites (ESTs) in a 1736-locus map.

We have constructed a 1736-locus maize genome map containing1156 loci probed by cDNAs, 545 probed by random genomic clones, 16 by simple sequence repeats (SSRs), 14 by isozymes, and 5 by anonymous clones. Sequence information is available for 56% of the loci with 66% of the sequenced loci assigned functions. A total of 596 new ESTs were mapped from a B73 library of 5-wk-old shoots. The map contains 237 loci probed by barley, oat, wheat, rice, or tripsacum clones, which serve as grass genome reference points in comparisons between maize and other grass maps. Ninety core markers selected for low copy number, high polymorphism, and even spacing along the chromosome delineate the 100 bins on the map. The average bin size is 17 cM. Use of bin assignments enables comparison among different maize mapping populations and experiments including those involving cytogenetic stocks, mutants, or quantitative trait loci. Integration of nonmaize markers in the map extends the resources available for gene discovery beyond the boundaries of maize mapping information into the expanse of map, sequence, and phenotype information from other grass species. This map provides a foundation for numerous basic and applied investigations including studies of gene organization, gene and genome evolution, targeted cloning, and dissection of complex traits.

Chromosome Mapping↗

PubMed1999

A statewide system to track medical students' careers: the Pennsylvania model.

In 1994 the Commonwealth of Pennsylvania announced a statewide Generalist Physician Initiative (GPI) modeled after The Robert Wood Johnson Foundation's GPI. Three-year grants totaling more than $9 million were awarded to seven of Pennsylvania's medical schools, including two that had already received GPI grants from the foundation. Stimulated by these initiatives, the state's six allopathic and two osteopathic medical schools decided to work together to develop a collaborative longitudinal tracking system to follow the careers of all their students from matriculation into their professional careers. This statewide data system, which includes information for more than 18,000 students and graduates beginning with the entering class of 1982, can be used to evaluate the impact of the Pennsylvania GPI, and it also yielded a local longitudinal tracking system for each medical school. This paper outlines the concept of the system, its technical implementation, and the corresponding implications for other medical schools considering the development of similar outcomes assessment systems.

Career Choice↗

PubMed1999

Factors associated with changing levels of interest in primary care during medical school.

PURPOSE: To examine changing levels of interest in primary care as related to clinical experiences during medical school, and to other variables. METHOD: A total of 1,911 (74%) allopathic medical school graduates responded to a national survey in early 1993. Respondents' reported changes of interest in primary care during medical school were cross-tabulated with their clinical experiences in medical school, their demographics, their interests prior to medical school, and their future practice plans. RESULTS: Increased interest in primary care during medical school was strongly associated with the electives taken in primary care. This positive change of interest in primary care was found to be associated with interest prior to medical school and with primary care career plans. CONCLUSION: Schools wishing to graduate more students who enter primary care specialties may want to raise the number of primary care elective courses to increase students' interests, and to help them choose to enter and remain in primary care specialties.

Adult↗

PubMed1999

Mild hypothermia improves recovery of cortical extracellular potassium ion activity and excitability after middle cerebral artery occlusion in the rat.

BACKGROUND AND PURPOSE: Mild brain hypothermia significantly alleviates damage after focal ischemia, although the mechanism of this protection remains poorly defined. In the present study, we tested the hypothesis that mild hypothermia would protect cortex from early deterioration of ion homeostasis and loss of excitability associated with reperfusion after focal ischemia. METHODS: Cortical extracellular potassium ion activity ([K+]o) and the response of [K+]o to direct cortical stimulation was measured both in the ischemic core and in the ischemic penumbra of normothermic and mildly hypothermic (31.5 degrees C to 32 degrees C) rats after distal middle cerebral artery occlusion (MCAO) and reperfusion. RESULTS: The response of [K+]o during MCAO was similar in normothermic and hypothermic animals. However, within 1 hour of reperfusion, [K+]o in the ischemic core region of normothermic animals showed incomplete recovery and was refractory to direct cortical stimulation. [K+]o in hypothermic animals returned to preischemic levels on reperfusion and continued to respond to direct cortical stimulation. Mild hypothermia prevented extensive infarction 24 hours after transient MCAO. CONCLUSIONS: The data suggest that transient focal ischemia is accompanied by early disturbances of potassium ion homeostasis during reperfusion, which are accompanied by loss of excitability and which may contribute ultimately to cortical infarction.

Action Potentials↗

PubMed1999

Increasing dietary cholesterol induces different regulation of classic and alternative bile acid synthesis.

We investigated the effect of increasing dietary cholesterol on bile acid pool sizes and the regulation of the two bile acid synthetic pathways (classic, via cholesterol 7alpha-hydroxylase, and alternative, via sterol 27-hydroxylase) in New Zealand white rabbits fed 3 g cholesterol/per day for up to 15 days. Feeding cholesterol for one day increased hepatic cholesterol 75% and cholesterol 7alpha-hydroxylase activity 1.6 times without significant change of bile acid pool size or sterol 27-hydroxylase activity. After three days of cholesterol feeding, the bile acid pool size increased 83% (P < 0.01), and further feeding produced 10%-20% increments, whereas cholesterol 7alpha-hydroxylase activity declined progressively to 60% below baseline. In contrast, sterol 27-hydroxylase activity rose 58% after three days of cholesterol feeding and remained elevated with continued intake. Bile drainage depleted the bile acid pool and stimulated downregulated cholesterol 7alpha-hydroxylase activity but did not affect sterol 27-hydroxylase activity. Thus, increasing hepatic cholesterol does not directly inhibit cholesterol 7alpha-hydroxylase and initially favors enzyme induction, whereas increased bile acid pool is the most powerful inhibitor of cholesterol 7alpha-hydroxylase. Sterol 27-hydroxylase is insensitive to the bile acid flux but is upregulated by increasing hepatic cholesterol.

Animals↗

PubMed1999

Who is a generalist? An analysis of whether physicians trained as generalists practice as generalists.

Accurate data on the number of generalist physicians are needed to monitor the physician workforce and to plan for future requirements in the changing health care system. This study assessed the relationship between two frequently used definitions of a generalist physician: completion of graduate medical education (GME) in only a generalist discipline and physician's self-report of practicing as a generalist. Data for 4,808 physician graduates from six Pennsylvania medical schools from 1986 to 1991 were analyzed using information from the GME tracking census of the Association of American Medical Colleges and the Physician Masterfile of the American Medical Association. Of 1,291 physicians trained in a generalist discipline, 1,205 (93%) reported practicing as generalists. Conversely, of the 3,517 not trained in a generalist discipline, 3,358 (95%) were not practicing as generalists. These results indicate GME training is a valid predictor of self-reported practice and provide baseline data to monitor future changes.

Attitude of Health Personnel↗

PubMed1999

The changing health care system. A research agenda for medical education.

The volatility in the U.S. health care system due to unprecedented changes in its organization, financing, and delivery, coupled with a growing physician surplus in certain areas, suggests the need for a research agenda to investigate the impact of these forces on the educational programs of medical schools. This article discusses the potential impact of trends in the health care environment on the following key aspects of undergraduate medical education: admissions, faculty, curriculum, and educational outcomes. A representative set of research questions intended to stimulate inquiry and guide empirical studies in each of the four domains is proposed.

Curriculum↗

PubMed1999

Perceptions of medical school seniors of the current changes in the U.S. health care system.

Perceptions of medical school seniors about changes occurring in the health care environment were investigated. A survey was completed by 196 Jefferson Medical College seniors in the class of 1997. Of the respondents, 79% believed that cost reduction rather than quality of care is the primary consideration behind recent changes, 78% felt that managed care organizations hamper physicians' abilities to render optimal care, 83% maintained that the control of health care by insurance companies would lead to lower quality of care, 69% agreed that patients should have the freedom to seek a specialist's care without being referred by a primary care physician, 82% recommended that mentally ill patients should be referred to a mental health professional, and 82% believed that learning to work in a managed care environment should be an essential component of medical education. Assessment of student perceptions can assist in the development and implementation of appropriate curricular changes.

Attitude of Health Personnel↗

PubMed1999

Exendin-4 stimulates both beta-cell replication and neogenesis, resulting in increased beta-cell mass and improved glucose tolerance in diabetic rats.

Diabetes is a disease of increasing prevalence in the general population and of unknown cause. Diabetes is manifested as hyperglycemia due to a relative deficiency of the production of insulin by the pancreatic beta-cells. One determinant in the development of diabetes is an inadequate mass of beta-cells, either absolute (type 1, juvenile diabetes) or relative (type 2, maturity-onset diabetes). Earlier, we reported that the intestinal hormone glucagon-like peptide I (GLP-I) effectively augments glucose-stimulated insulin secretion. Here we report that exendin-4, a long-acting GLP-I agonist, stimulates both the differentiation of beta-cells from ductal progenitor cells (neogenesis) and proliferation of beta-cells when administered to rats. In a partial pancreatectomy rat model of type 2 diabetes, the daily administration of exendin-4 for 10 days post-pancreatectomy attenuates the development of diabetes. We show that exendin-4 stimulates the regeneration of the pancreas and expansion of beta-cell mass by processes of both neogenesis and proliferation of beta-cells. Thus, GLP-I and analogs thereof hold promise as a novel therapy to stimulate beta-cell growth and differentiation when administered to diabetic individuals with reduced beta-cell mass.

Animals↗

PubMed1999

Bile acid synthesis in the Smith-Lemli-Opitz syndrome: effects of dehydrocholesterols on cholesterol 7alpha-hydroxylase and 27-hydroxylase activities in rat liver.

The Smith-Lemli-Opitz syndrome (SLOS) is a congenital birth defect syndrome caused by a deficiency of 3beta-hydroxysterol Delta(7)-reductase, the final enzyme in the cholesterol biosynthetic pathway. The patients have reduced plasma and tissue cholesterol concentrations with the accumulation of 7-dehydrocholesterol and 8-dehydrocholesterol. Bile acid synthesis is reduced and unnatural cholenoic and cholestenoic acids have been identified in some SLOS patients. To explore the mechanism of the abnormal bile acid production, the activities of key enzymes in classic and alternative bile acid biosynthetic pathways (microsomal cholesterol 7alpha-hydroxylase and mitochondrial sterol 27-hydroxylase) were measured in liver biopsy specimens from two mildly affected SLOS patients. The effects of 7- and 8-dehydrocholesterols on these two enzyme activities were studied by using liver from SLOS model rats that were treated with the Delta(7)-reductase inhibitor (BM15.766) for 4 months and were comparable with more severe SLOS phenotype in plasma and hepatic sterol compositions. In the SLOS patients, cholesterol 7alpha-hydroxylase and sterol 27-hydroxylase were not defective. In BM15.766-treated rats, both enzyme activities were lower than those in control rats and they were competitively inhibited by 7- and 8-dehydrocholesterols. Rat microsomal cholesterol 7alpha-hydroxylase did not transform 7-dehydrocholesterol or 8-dehydrocholesterol into 7alpha-hydroxylated sterols. In contrast, rat mitochondrial sterol 27-hydroxylase catalyzed 27-hydroxylation of 7- and 8-dehydrocholesterols, which were partially converted to 3beta-hydroxycholestadienoic acids. Addition of microsomes to the mitochondrial 27-hydroxylase assay mixture reduced 27-hydroxydehydrocholesterol concentrations, which suggested that 27-hydroxydehydrocholesterols were further metabolized by microsomal enzymes. These results suggest that reduced normal bile acid production is characteristic of severe SLOS phenotype and is caused not only by depletion of hepatic cholesterol but also by competitive inhibition of cholesterol 7alpha-hydroxylase and sterol 27-hydroxylase activities by accumulated 7- and 8-dehydrocholesterols. Unnatural bile acids are synthesized mainly by the alternative pathway via mitochondrial sterol 27-hydroxylase in SLOS.

Animals↗

PubMed1999

[nm23-H1 protein expression and its clinical significance in human laryngeal carcinoma].

The Objective of the study on the expression of nm23-H1 protein in human laryngeal carcinoma, was to explore the role of nm23 gene in lymph node metastasis and invasion. The expression of nm23-H1 protein was immunohistochemically examined in 86 resected human laryngeal carcinomas. Anti-nm23-H1 monoclonal antibody was used. The results showed that 66.3%(57/86) of the cases were positive for nm23-H1 protein expression in the primary lesions. The positive staining rate (90.5%, 38/42) of the patients without regional lymph node metastasis, was significantly higher than that of patients with nodal involvement (43.2%, 19/44). Inverse relationship were found between the nm23-H1 protein expression in the primary lesions and the depth of tumor invasion or the advance of clinical stage. Expression of nm23-H1 protein was positively associated with the ascending histological grade of the lesion, and the relationship was significant. The above data suggest that nm23 gene plays an important role in the control of lymph node metastasis and invasion in laryngeal carcinomas.

Adult↗

PubMed1999

[A study of the relationship between dynamic blood rheologic changes and the fluid resuscitation in burn patients].

OBJECTIVE: To further study the relationship between hemor rheologic changes and fluid resuscitation in patients with burn and treatment of anemia after burns. METHODS: 238 case of burn patients were divided into four groups. In which patients with major burn were allocated to group C and D according to different methods of fluid resuscitation and treatment of anemia. RESULTS: Abnormal hemorrheologic parameters could be corrected when transfusion of fresh whole blood and traditional herb medicines were given within 24-48 hours after burn injury. CONCLUSION: Dynamic observation of hemorrheologic changes is one of important index in monitoring burn shock and guiding fluid resuscitation. Blood transfusion and traditional medicine can improve abnormal blood rheologic parameters, effectively correct anemia when given early.

Adolescent↗

PubMed1999

[Transfection of Fas(CD95) gene into HL-60 cell and its role in rhG-CSF-induced apoptosis].

OBJECTIVE: To explore the role of Fas gene in rhG-CSF-induced apoptosis. METHODS: Mediated by lipofection (DOTAP), Fas cDNA was transferred into HL-60 cells. In situ hybridization, Western blotting and FCM analysis were used to demonstrate the successful transfection. The apoptosis percentages of HL-60 and Fas transfected HL-60 cells were compared after coculturing with rhG-CSF at the same final concentration. RESULTS: After cocultured with rhG-CSF (10 ng/ml) for 96 hours, the apoptosis percentage of Fas transferred HL-60 cells was significantly higher than that of HL-60 cells, and the Fas expressions could be up-regulated by rhG-CSF. CONCLUSIONS: Fas is an apoptosis-induction oncogene, and rhG-CSF induces apoptosis of HL-60 cells through Fas signalling pathway.

Apoptosis↗

PubMed1999

[Reconstitution and protection of murine hematopoiesis by second transplantation with bone marrow cells containing mutant human DHFR gene from primary generation murine].

OBJECTIVE: To observe the effect of donor murine bone marrow, which was transfected in vivo with mutant hDHFR gene, on the reconstitution and protection of hematopoiesis of lethally irradiated recipient mice. METHODS: Mice bone marrow transduced in vivo with mutant hDHFR gene were used for transplantation. After whole bodily irradiated (8.5-9.0 Gy) and then transplanted with the transduced marrow, the recipients were treated with methotrexate (4 mg/kg twice a week for the first week; and then 10 mg/kg twice a week). The survival rate and blood picture of the recipients as well as the integration and expression of hDHFR gene were studied by using PCR and Southern blotting. RESULTS: The hematopoiesis of the recipient mice could be reconstituted and protected from lethal toxicity of high dose methotrexate. It was confirmed that hDHFR gene was integrated into hematopoietic cell as well as some tissues genomic DNA and expressed successfully in the recipients. CONCLUSION: Donor mice bone marrow transfected with mutant hDHFR gene can effectively reconstitute and protect hematopoiesis in lethally irradiated recipient mice.

Animals↗

PubMed1999

The diagnostic criteria for classic parasystole.

OBJECTIVE: To establish a diagnostic criteria of parasystole with high sensitivity and high specificity. METHODS: After excluded from nonparasystole and each variant parasystoles, based on the electrocardiographic data obtained from 61 patients with classic parasystole, we selected the quantitative indices which could reflect the features of ectopic focus with complete entrance block as the diagnostic criteria for parasystole. RESULTS: The common features of the electrocardiograms of this group were: 1) Take the earliest recorded eight interectopic intervals in which at least four intervals containing sinus beats or other beats having activated to the area within the ectopic focus. When in case of deficiency, it will fill up a vacancy in order. The ratios of the shortest coupling interval to the shortest ectopic cycle length (ECL) were all less than 80%; 2) The coefficients of variation of the eight ECLs were all less than 6%; 3) The maximal differences of coupling intervals were all equal to or more than 0.11 second. CONCLUSION: Three quantitative indices as necessary conditions have been used as diagnostic criteria for parasystole with high sensitivity and high specificity.

Electrocardiography↗

PubMed1999

[Symptomatic treatment versus combination chemotherapy in advanced non-small cell lung cancer].

OBJECTIVE: To evaluate the effects on survival of combination chemotherapy in patients with advanced non-small cell lung cancer (NSCLC). METHODS: Seventy patients with advanced NSCLC were pairingly divided into two equal groups: 35 patients who refused chemotherapy received symptomatic treatment; the other 35 patients received combined chemotherapy with mitomycin(8-10 mg/m2, dl), vindesine (3 mg/m2, dl, 8) cisplatin (20 mg/m2, dl-5), repeated every four weeks for 2-4 cycles and followed by oral administration of Ftorafur (FT-207) 200-300 mg tid, until recurrence or progression of disease. RESULTS: The overall median survival time in the chemotherapy group was 9 months, and 4.5 months in the symptomatically treated group. The one-year survival rate was 34.3% and 8.0% respectively. The major toxic effects of chemotherapy were gastrointestinal tract reactions and myelosuppression. CONCLUSION: Combination chemotherapy can prolong survival time in patients with advanced NSCLC.

Adult↗

PubMed1999

[Treatment and outcome of cervical lymph nodal metastases of unknown primary sites].

OBJECTIVE: To ascertain the optimal management of cervical nodal metasta of unknown primary sites. METHODS: The clinical data of 114 patients of cervical nodal metastases of unknown primary sites were retrospectively analyzed. RESULTS: For metatic masses of the upper and/or middle part of the neck, the optimal approach varied depnding on the histologic type. Poorly-differentiated carcinoma was treated with radiotherapy, squamous-cell carcinoma was treated with radiotherapy plus surgery, while papillary adenocarcinoma was treated by combined radical thyroidectomy. Their 5-year survival rate was 45.2%, 53.8% and 62.5%, respectively. For metastatic masses in the supraclavicular region, chemotherapy was the first treatment of choice in all patients. In only 12 of the 114 patients (11.2%) the primary sites were found in the follow-up period. CONCLUSION: For patients with cervical lymph node metastases from unknown primary sites, the management should be given according to the location of lymph node involved and histopathologic type of the tumor.

Adolescent↗

PubMed1999

[The role of detecting bile reflux in the diagnosis of gastroesophageal reflux disease].

OBJECTIVE: To investigate the incidence of esophageal bile reflux and its relationship with acid or alkaline reflux and to evaluate the significance of detecting bile reflux in the diagnosis of gastroesophageal reflux disease (GERD). METHODS: Using ambulatory 24-hour pH monitoring and bilirubin monitoring technique, the changes of 24-hour intraesophageal pH and bile reflux in 34 subjects (including healthy subjects, patients with reflux esophagitis and patients after gastrectomy) were simultaneously assessed. RESULTS: The time of esophageal acid exposure for reflux esophagitis (RE) patients was significantly longer than that in the controls and the patients after gastrectomy, but there was no difference between postgastrectomized patients and healthy controls. Total percent time of pH > 8 in each group was similar and were very low. Bile reflux [duodenogastroesophageal reflux (DGER)], represented by total time percentage of bilirubin absorbance >or=0.14, was greatest in postgastrectomized patients, and next in the patients with RE, but the value in both groups was significantly higher than that in the controls. There was a close association between DGER and total time percentage of pH < 4 (r = 0.75, P < 0.05) but a poor relationship (r = 0.17) with total time percentage pH > 8. 63.6% of the patients with RE had acid and bile reflux simultaneously. CONCLUSION: DGER is common in GERD and postgastrectomized patients. It can occur with acid reflux and may play a role in the development of GERD. It is very important to monitor acid and bile reflux at the same time in the diagnosis of GERD.

Adult↗