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Biomedical subjects

X P Xu

Publications and source records attributed to X P Xu.

15 recordsLinked to original sources
PubMed1995

Prostaglandin-mediated inhibition of nitric oxide production by bovine aortic endothelium during hypoxia.

OBJECTIVE: The present study utilized a monoculture of vascular endothelium to: (1) determine if nitric oxide (NO) production was decreased during hypoxia, (2) ascertain if specific prostaglandins were released in response to hypoxia, and (3) determine if cyclo-oxygenase inhibition would modulate hypoxia-induced decreases in NO production. METHODS: Bovine aortic endothelial cells (BAE cells) were grown to confluence on microcarrier beads. NO released in response to the receptor-independent agonist, A23187 calcium ionophore, was directly and continuously measured using a sensitive and specific chemiluminescence method. Cells were exposed to either "hypoxia" (pO2 = 10 mmHg) or "normoxia" (pO2 = 160 mmHg) for 30 min. NO was quantitatively measured with and without indomethacin (1.7 microM) in the incubation medium, and also following incubation with the prostacyclin analog, iloprost. The prostaglandins PGI2 and PGE2 released in response to hypoxia were quantitated using an enzyme immunoassay. RESULTS: Hypoxia significantly decreased NO production, resulting in a 22.8(2.1)% reduction in NO from 94.3(5.3) nmol/micrograms protein (during normoxia) to 73.5(2) nmol/micrograms protein (during hypoxia). Hypoxia significantly stimulated the production of PGI2 and PGE2, in excess of that released in response to A23187 when compared with normoxia. Following cyclo-oxygenase inhibition, the hypoxia-induced decrease in NO production was abolished (0.13 [2.7] % change relative to controls). Furthermore, iloprost (10 nM) directly inhibited NO production. CONCLUSIONS: The results demonstrate that ionophore-stimulated NO production is sensitive to oxygen tension, decreasing in response to hypoxia. Inhibition of prostaglandin synthesis restores NO production during hypoxia, while iloprost directly suppresses NO production. Thus, endothelium-derived prostanoids produced in response to hypoxia may modulate NO production via an autocrine negative feedback mechanism.

Animals↗
PubMed1994

Effects of smoking and drinking habits on urinary o-cresol excretion after occupational exposure to toluene vapor among Chinese workers.

The relationship between the time-weighted average intensity of exposure to toluene and o-cresol concentration in shift-end urine was investigated in nearly 500 factory workers of both sexes in China, together with a similar number of nonexposed control subjects. Toluene concentration (25 ppm as geometric mean and 550 ppm as the maximum) was monitored by diffusive sampling using carbon cloth as adsorbent followed by gas chromatographic (GC) analysis. o-Cresol (up to 7 mg/l) was measured by GC after acid hydrolysis of samples. Urinary o-cresol levels correlated significantly (r = 0.69-0.77; p < 0.01) with toluene exposure in men, women and the two sexes in combination, regardless of correction for urine density. When compared with hippuric acid, however, o-cresol was less sensitive as an indicator of exposure to toluene and is not a suitable biological marker for detecting low level toluene exposure. Since urinary o-cresol level was significantly reduced by smoking, drinking, and the two habits combined, it cannot be considered reliable as an indicator of exposure to toluene.

Air Pollutants, Occupational↗
PubMed1994

[Effect of panaxadiol saponin (PDS) on phorbol ester induced change of protein kinase C activity in cardiomyocytes].

Partially purified protein kinase C and protein kinase A were separately incubated with various concentrations of PDS (1-1000 micrograms.ml-1) for 10 min in vitro. The results indicate that protein kinase C activity was inhibited in a dose-dependent manner by PDS, but type I and type II protein kinase A were not. In cardiomyocytes preincubated with PDS (250, 500, 1000 micrograms.ml-1) for 10 min, PMA-induced decrease of cytosol protein kinase C activity and increase of membrane protein kinase C activity were greatly inhibited in the same manner. These results suggest that PDS not only inhibited protein kinase C in vitro, but also inhibited activation of protein kinase C in cardiomyocytes.

Animals↗
PubMed1992

Toluene vapor exposure and urinary excretion of hippuric acid among workers in China.

A factory survey was conducted in three provinces in China from 1985 to 1989. The time-weighted average toluene concentrations in breathing zone air were monitored by diffusive sampling, whereas hippuric acid (HA) concentrations in shift-end urine samples were measured by high performance liquid chromatography (HPLC). Exposed workers (456 men and women) were those for whom toluene (up to 548 ppm toluene) accounted for greater than or equal to 90% of total exposure (by vapor concentration in ppm), whereas 517 nonexposed controls were recruited from the same factories or from factories of the same region. There was a linear correlation between the intensity of toluene exposure and HA concentration in the shift-end urine. Comparison of the results with findings in the literature shows that the toluene-induced increase in urinary HA concentration among workers in China is significantly smaller than the published values, whereas HA concentrations in urine samples from nonexposed controls are comparable to the levels previously reported.

Air Pollutants, Occupational↗
PubMed1992

Sequencing and population analysis of four novel HLA-DPA1 alleles.

We determined the base sequences of the HLA-DPA1 gene from four B-lymphoblastoid cell lines (CB6B, LKT3, AMAI, and T7526) that showed distinct electrophoretic patterns of single-stranded polymerase chain reaction products of the HLA-DPA1 gene. The novel HLA-DPA1 alleles of CB6B, LKT3, AMAI, and T7526 were designated DPA1*02021, DPA1*02022, DPA1*0301, and DPA1*0401, respectively. Although there was only one base substitution between DPA1*02021 and DPA1*02022, the single-strand conformation polymorphism of these two alleles was clearly demonstrated by electrophoresis in a nondenaturing polyacrylamide gel containing 10% glycerol. In addition, we genotyped for the HLA-DPA1 gene of healthy unrelated Oriental individuals--i.e., 227 Japanese, 88 Papua New Guineans, and 41 Buyi-Chinese--to demonstrate the ethnic distribution of the HLA-DPA1 alleles.

Alleles↗
PubMed1991

Decreased transient outward K+ current in ventricular myocytes from acromegalic rats.

Cardiac hypertrophy and heart failure are common to acromegalic patients who have abnormally high serum growth hormone (GH). While the function of cardiac muscle is clearly affected by chronically elevated GH, the electrical activity of myocytes from hearts with GH-dependent hypertrophy has not been studied. We used adult, female Wistar-Furth rats with induced GH-secreting tumors to study the effect of excessive GH on ion channels of cardiac myocytes. GH-secreting tumors were induced by subcutaneous inoculation of GH3 cells. Eight weeks after inoculation, the rats had doubled their body weight and heart size compared with age-matched controls. There were no differences in either action potential amplitude or resting potential of right ventricular myocytes from control and tumor-bearing rats. However, action potential duration increased significantly in tumor-bearing rats; the time to 50% repolarization was 23 +/- 14 ms (n = 10) compared with 6.6 +/- 1.5 ms (n = 14) in controls. The prolongation of the action potential was mainly due to a decrease in density of a transient outward current (It,o) carried by K+. The normalized conductance for It,o decreased from 0.53 +/- 0.10 nS/pF (n = 25) in controls to 0.33 +/- 0.09 nS/pF (n = 26) in tumor-bearing rats. The decrease in It,o) and increase in heart weight occurred with a similar time course. The increased action potential duration prolongs Ca2+ influx through L-type Ca2+ channels in the tumor-bearing animals; this may be important in cardiovascular adaptation.

Acromegaly↗
PubMed1991

Prevalence of hepatitis B virus infection markers among factory workers in Beijing, China.

Nearly 1,000 serum samples were obtained from apparently healthy workers of both sexes in various factories in Beijing during 1988-1989 and were examined for hepatitis B virus infection markers by radioimmunoassay. The overall prevalence (all ages and both sexes combined) of cases positive for HBsAg, anti-HBs and anti-HBc were 3.7%, 36.6% and 37.7%, respectively and the rate of those negative to any of the three markers studied was 56.1%. The infection rate was lower than the values reported early in the 1980s for Beijing populations or the values for populations in other parts of China.

Adolescent↗
PubMed1990

Increase in T-type calcium current in atrial myocytes from adult rats with growth hormone-secreting tumors.

Growth hormone (GH) has pronounced effects on protein synthesis and cell growth in cardiac muscle from adult animals, although the mechanism of its action is not understood. Because Ca2+ has been implicated as a regulator of mitogenic processes in a number of tissues, we investigated whether GH affects the transmembrane movement of Ca2+ through voltage-activated channels of cardiac myocytes. Atrial and ventricular myocytes were isolated from adult rats with GH-secreting tumors and studied electrophysiologically by using patch-clamp techniques. Tumor-bearing rats re-enter an active growth phase and double their body weight over age-matched controls 8 weeks after introduction of the tumor. Atrial myocytes from tumor-bearing animals showed a 3-fold increase in the density of T-type Ca2+ current compared with cells from control animals, although the voltage dependency of activation and inactivation of T-type current was not altered. The increase in T-current density of atrial myocytes preceded by at least a week any measurable change in heart weight, body weight, or myocyte size. L-type Ca2+ currents in atrial and ventricular cells were not affected. The results suggest that a tumor-derived growth factor, most likely GH, can cause a specific enhancement of T-type Ca2+ current in atrial myocytes.

Animals↗
PubMed1990

Longitudinal and cross-sectional estimates of pulmonary function decline in never-smoking adults.

This paper describes methods for simultaneous cross-sectional and longitudinal analysis of repeated measurements obtained in cohort studies with regular examination schedules, then uses these methods to describe age-related changes in pulmonary function level among nonsmoking participants in the Six Cities Study, a longitudinal study of air pollution and respiratory health conducted between 1974 and 1983 in Watertown, Massachusetts; Kingston and Harriman, Tennessee; St. Louis, Missouri; Steubenville, Ohio; Portage, Wisconsin; and Topeka, Kansas. The subjects, initially aged 25-74, were examined on three occasions at 3-year intervals. Individual rates of loss increased more rapidly with age than predicted from the cross-sectional model. For example, for a male of height 1.75 m, the cross-sectional model predicted an increase in the annual rate of loss of FEV1 from 23.7 ml/yr at age 25 to 39.0 ml/yr at age 75, while the longitudinal model gave rates of loss increasing from 12.9 ml/yr at age 25 to 58.2 ml/yr at age 75. These results contrast with those of other studies comparing longitudinal and cross-sectional estimates of pulmonary function loss.

Adult↗
PubMed1989

Risk factors in chronic obstructive pulmonary malfunction and "chronic bronchitis" symptoms in Beijing district: a joint study between Japan and China.

A cross sectional study of risk factors in respiratory diseases was carried out in August 1986, in Beijing, China. Inhabitants greater than or equal to 40 years old were selected at random from a rural area, a residential area and an industrial area, using a two stage sampling method. The analysis presented here is based on the sample population of adults who (1) were prepared to be interviewed, using the British Medical Research Council's questionnaire translated into Chinese (n = 3423) and (2) had lung function measurements at the same time (n = 3373). Obstructive lung disease was defined as forced expiratory volume in 1s (FEV1) less than 68% of forced vital capacity (FVC). Seven variables were considered as potential risk factors or confounding factors: area of residence, sex, age, cigarette smoking, history of respiratory disease, socio-economic status and familial component. A modified binary variable regression method developed by Feldstein was used for the adjustment of rate ratios. The adjusted prevalence of obstructive lung disease was highest in the rural area and lowest in the residential area(s). An increase in age, cigarette smoking, low socio-economic status and positive history of respiratory diseases were associated with significantly higher rates of impaired pulmonary function. The other measured factors did not appear to be related to impaired pulmonary function.

Adult↗
PubMed1986

Study on the association of HLA with malignant lymphoma.

The association of HLA with malignant lymphomas in 50 Chinese patients of the HAN nationality was investigated. The frequencies of antigens HLA-A and -C and the majority of HLA-B phenotypes were not significantly different between the patient and control groups, whereas the antigen frequency of HLA-B16 was increased significantly (P less than 0.025) in the patient group. The relative risk associated with HLA-B16 was 2.5694. The association of this antigen with malignant lymphoma might be unique for Oriental patients.

Antigens, Neoplasm↗
PubMed1986

Study on the association of HLA with pulmonary tuberculosis.

The association between HLA and pulmonary tuberculosis was investigated in 50 Chinese patients. The frequencies of the HLA-A11 and -B15 antigens were increased (P less than 0.025) in patient group. Relative risks (R.R.) were 2.13 and 2.39, respectively. In contrast, the frequency of the HLA-Cw3 antigen and the R.R. (0.29) were decreased (P less than 0.005) in the patient group. These results are different from those reported by other researchers for Caucasian and Chinese tuberculosis patients. Moreover, it was found that the frequency of the A11-B15 haplotype in all patients with cavitation was 3-4 times higher (P less than 0.01) than in control individuals. The R.R. was 3.57.

Cytotoxicity, Immunologic↗
PubMedDate not supplied

Effects of air pollution on adult pulmonary function.

We conducted a study in three representative areas of Beijing to determine respiratory health effects of indoor and outdoor air pollution. In August 1986, we measured the lung function of 1,440 adults who were 40-69 y of age and who had never smoked. Forced vital capacity (FVC) and forced expiratory volume in 1 s (FEV1.0) were adjusted for height, sex, and age. Outdoor ambient air pollution measurements from the World Health Organization Global Air Pollution Monitoring Station were very different in the three study areas; the annual mean concentrations of sulfur dioxide (SO2) in residential, suburban, and industrial areas were 128, 18, and 57 micrograms/m3, respectively, and annual mean concentrations of total suspended particulate matter (TSPM) were 389, 261, and 449 micrograms/m3, respectively. Coal was most frequently used for domestic heating in the residential (92%) and suburban (96%) areas compared with the industrial area (17%). Heating with coal was associated with a reduced FEV1.0 (-91 +/- 36 ml) and FVC (-84 +/- 41 ml). Living in the residential area was associated with an additional reduction in FEV1.0 (-69 +/- 34 ml) and FVC (-257 +/- 37 ml). After we adjusted for age, height, and sex, an inverse linear association was found between In outdoor SO2 (or TSPM) concentration and FEV1.0 and FVC in subjects who had and had not used coal stove heating. Regression analysis results showed that a per-unit increase in In SO2 (TSPM) concentration (microgram/m3) could result in a 35.6 (131.4) ml reduction in FEV1.0 and a 142.2 (478.7) ml reduction in FVC.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗