Search PubMed⌕ Search

Biomedical subjects

S Chen

Publications and source records attributed to S Chen.

At least 1,225 records · Page 68Linked to original sources
PubMed1993

Patch length of localized repair events: role of DNA polymerase I in mutY-dependent mismatch repair.

In vivo experiments with heteroduplex lambda genomes show that the MutY mismatch repair system of Escherichia coli defines an average repair tract that is shorter than 27 nucleotides and longer than 9 nucleotides and extends 3' from the corrected adenine. The phenotype of a mutant defective in DNA polymerase I shows that this enzyme plays a significant, though not an essential, role in the in vivo repair of apurinic sites generated by this system. Evidence is presented that in the absence of polymerase I the repair tracts are modestly longer than in the polA+ extending in the 5' direction from the corrected adenine, suggesting a role for another DNA polymerase.

Adenosine Triphosphatases↗
PubMed1993

TSF3, a global regulatory protein that silences transcription of yeast GAL genes, also mediates repression by alpha 2 repressor and is identical to SIN4.

TSF3 encodes one of six (TSF1 to TSF6) recently identified global negative regulators of transcription in Saccharomyces cerevisiae. Mutant tsf3 strains exhibit defects in transcriptional silencing of the GAL1 promoter, allow expression from upstream activation sequence-less promoters, and exhibit pleiotropic defects in cell growth and development. Here we show that TSF3 is involved in transcriptional silencing mediated by the alpha 2 repressor and demonstrate that specific systems of transcriptional silencing may depend on the more global role of TSF3. Cloning and sequencing of TSF3 allowed us to predict a 974-amino-acid gene product identical to SIN4, a negative regulator of transcription of the HO (homothallism) mating type switching endonuclease. TSF3 disruptions are not lethal but result in phenotypes similar to those of the originally isolated alleles. Our results, together with those of Y. W. Jiang and D. J. Stillman (Mol. Cell. Biol. 12:4503-4514, 1992), suggest that TSF3 (SIN4) affects the function of the basal transcription apparatus, and this effect in turn alters the manner in which the latter responds to upstream regulatory proteins.

Amino Acid Sequence↗
PubMed1993

Effects of feeding premature infants with Lactobacillus GG on gut fermentation.

The study aimed to find out whether gut colonisation of premature babies with a probiotic, Lactobacillus GG, modified enteric carbohydrate fermentation. Twenty preterm infants were randomised to receive Lactobacillus GG 10(8) colony forming units twice a day for two weeks or to a control group. Faecal short chain fatty acids (SCFAs), ethanol, and urinary 2,3-butanediol, were measured in parallel with microbiological studies. Lactobacillus GG colonised nine babies. From 1-28 days of age faecal SCFAs did not differ significantly from controls. Median and ranges were (treated and controls, respectively): acetic acid: 173 (trace-799), 166 (trace-700); propionic acid: 44 (trace-169), 37 (11-229); butyric acid: 31 (5-107), 37 (2-118) mumol/g dry weight. Ethanol was detected in more faecal samples from treated babies (65% v 37%), and at higher concentration (6.3 (trace-40) v 3.3 (0.6-8.8; one 229) mumol/g). 2,3-Butanediol was found in 66% of urine samples from treated babies and 58% from controls. On 83% of these occasions Klebsiella sp, Enterobacter sp, or Serratia sp were cultured from faeces. Lactobacillus GG had no obvious adverse effects on nutritionally important SCFAs. The small increase in ethanol excretion is unlikely to have clinical significance.

Anti-Bacterial Agents↗
PubMed1993

Molecular analysis of HLA-DR beta and DQ beta polymorphism in Chinese with rheumatoid arthritis.

OBJECTIVES: Several studies have suggested that genetic predisposition to rheumatoid arthritis may be related to the presence of specific polymorphic HLA sequences that are often associated with HLA-DR4 haplotypes. This study was performed to determine if an association exists between Chinese with rheumatoid arthritis and a particular HLA-DR beta or DQ beta subtype. METHODS: This study used the polymerase chain reaction to amplify HLA-DR beta and DQ beta genes, and oligonucleotide probe hybridisation to examine the association of certain polymorphic sequences with rheumatoid arthritis in 23 Chinese patients from Shanghai. RESULTS: An HLA-DR4 associated sequence was significantly increased in the Chinese patients (43%) compared with healthy controls (14%) from the same location (relative risk = 4.6, 95% confidence limits 1.1 to 19.3). Analysis of the third hyperpolymorphic region of DR4 positive samples was performed to detect polymorphic sequences associated with Dw4, Dw10, Dw13, Dw14, Dw15, and KT2 cellular specificities. Examination of this region showed that 91% of patients had sequences encoding amino acids QRRAA (associated with Dw14 and Dw15) or QKRAA (associated with Dw4) compared with 64% of the DR4 positive controls. CONCLUSIONS: Rheumatoid arthritis in the Chinese is associated with HLA-DR4. There is a possible relationship between sequences within the third hyperpolymorphic region of the DRB allele and rheumatoid arthritis in the Chinese.

Amino Acid Sequence↗
PubMed1993

The absence of HPV DNA in genital specimens from infants.

OBJECTIVE: To identify the prevalence of HPV DNA using the polymerase chain reaction (PCR) in neonatal foreskin and cervical specimens obtained at necropsy. MATERIALS: Foreskin and cervical specimens were obtained from consecutive neonates who had autopsies performed at The Royal Women's Hospital, Melbourne, from June 1991 to February 1992. Specimens were analysed for HPV DNA using the polymerase chain reaction and the L1 consensus primers and generic probes. RESULTS: Specimens were obtained from 98 neonates, 52 males and 46 female. The mean gestational age of the neonates was 29 weeks (range 20-42). Eighty neonates died in utero, three during labour and 15 following delivery. Ninety four were delivered vaginally whilst four were delivered by caesarean section. Samples were collected a mean of 20 hours (range 2-48) from the time of delivery. In 30 cases there was evidence of autolytic change while in the remaining cases, the histology was well preserved. No evidence of HPV DNA was found in any of the samples using the L1 general primers (95% confidence interval 0-3.6%). Recent cervical cytology was available on 70 of the infant's mothers. Six had cytological evidence of HPV infection while the remainder were normal. CONCLUSIONS: HPV DNA is uncommonly detected (by PCR) in foreskin and cervical specimens obtained from neonates.

Cervix Uteri↗
PubMed1993

Long-term ouabain administration produces hypertension in rats.

Ouabain has recently been identified as an endogenous Na(+)-K+ pump inhibitor. We administered ouabain chronically to normotensive rats with varying degrees of reduced renal mass (RRM) and to normal two-kidney rats to see whether hypertension could be produced. Normal male Wistar rats and rats with 25%, 60%, and 70% RRM received ouabain (13.9 micrograms/kg per day IP) in normal saline for 4 weeks followed by ouabain (27.8 micrograms/kg per day IP) for 3 to 4 more weeks. Respective control animals received vehicle only. Blood pressure was recorded weekly by tail plethysmography. Animals received tap water and standard rat chow, except for 70% RRM rats, which received distilled water and sodium-free chow. After 6 to 8 weeks of treatment, with rats under thiobutabarbital anesthesia, direct blood pressure was determined. Plasma, tissue, and urinary ouabain levels were measured with a specific radioimmunoassay. Animals receiving ouabain developed significant increases in mean blood pressure compared with control animals (70% RRM, 147 +/- 4 vs 116 +/- 4 mm Hg; 60% RRM, 140 +/- 4 vs 107 +/- 3 mm Hg; 25% RRM, 131 +/- 5 vs 100 +/- 2 mm Hg; no RRM, 116 +/- 4 vs 98 +/- 5 mm Hg). Plasma ouabain levels measured 24 hours after the last ouabain dose were not different in animals receiving ouabain vs those receiving vehicle. However, kidney tissue ouabain levels were significantly greater (6.39 +/- 1.17 vs 2.36 +/- 0.52 micrograms/kg, P < .05) in animals receiving ouabain. In conclusion, ouabain, given chronically, is associated with the development of hypertension in RRM rats as well as in normal rats. Blood pressure was greater in animals with greater degrees of RRM for a given ouabain dose.

Animals↗
PubMed1993

Pharmacokinetic profile of recombinant human (rh) inhibin A and activin A in the immature rat. I. Serum profile of rh-inhibin A and rh-activin A in the immature female rat.

The serum pharmacokinetics of recombinant human inhibin A (rh-inhibin A) and rh-activin A were examined in immature female Sprague Dawley-derived rats after iv and sc injection of the drugs. After iv administration of rh-inhibin A (120 micrograms/kg), the serum concentrations were described by a biexponential equation. The weight-normalized clearance was 21.3 ml/min.kg, and the initial (t1/2 alpha) and terminal (t1/2 beta) half-lives were 2.9 min and 37.9 min, respectively. Subcutaneous administration of 120 micrograms/kg rh-inhibin A resulted in a peak serum concentration of 10.6 ng/ml at 30.8 min after injection. Approximately 24% of the sc administered material was absorbed. Serum concentrations of rh-activin A also declined biexponentially after iv injection of the drug (120 micrograms/kg). The clearance of rh-activin A was 5.1 ml/min.kg, the t1/2 alpha was 6.1 min, and the t1/2 beta was 46.3 min. The peak serum concentration of rh-activin A (104.7 ng/ml) was achieved 24.7 min after sc delivery of the drug. The bioavailability of the sc dose was 38%. Iodinated rh-inhibin A and rh-activin A were used to examine the serum forms and metabolites of the drugs. [125I]rh-inhibin A and [125I]rh-activin A associated with two serum-binding proteins. Within 2 min of iv injection, the labeled hormones bound follistatin and alpha-2-macroglobulin. Even though rh-inhibin A and rh-activin A are structurally similar and appear to bind to the same serum proteins, their disposition in the immature rat differ.

Activins↗
PubMed1993

Renal lymphatic obstruction in diabetic rats induces systemic hypotension.

We obstructed renal lymph drainage from a single kidney in diabetic rats who had received 65 mg/kg streptozotocin 6 months prior to the study. Lymphatic obstruction led to a progressive fall in systematic blood pressure from a mean arterial pressure of 101 +/- 5 (SEM) mm Hg (n = 7) to 62 +/- 4 mm Hg (n = 5) (p < .02) after 1.5 h. No change was seen in a sham-operated animal. Despite the decline in systemic blood pressure there was no significant change in the GFR of either kidney. Sodium excretion increased significantly in the experimental kidney. There was no change in the urinary excretion of cyclic GMP from either kidney, and plasma levels of atrial natriuretic peptide (ANP) did not change (55 +/- 21 pg/mL pre- to 64 +/- 18 postobstruction). The results are consistent with a systemic vasodilatation after lymphatic obstruction. The mechanism of this response is still under investigation, but apparently it does not involve ANP.

Animals↗
PubMed1993

[Effect of EA on the enzymes of microvasculature and CA fluorescence in acute myocardial ischemia].

It was aimed at observing the histochemical basis of physiological experiment about the effect of electroacupuncture (EA) on acute myocardial ischemia (AMI) in this paper. The capillaries of myocardium were reflected with both alkaline phosphatase (ALP) and Mg(2+)-ATPase. Thirty min after ligating the left ventricular branch (LVB), the capillaries stained by ALP were much decreased in the ischemic group without EA, while in EA group they were increased distinctly. The number and the total length of the capillaries in a 220 x 320 microns ischemic area of the posterior wall (section 10 microns) were measured and compared. In ischemic group the number was 17.2 +/- 1.65, the length was 634.62 +/- 66.24 microns, in EA group 22.5 +/- 1.44, 1187.57 +/- 103.69 microns, respectively. Both counts were significant differences (P < 0.05, P < 0.001). It reflected that EA could improve the microcirculation and metabolic function of AMI. Mg(2+)-ATPase was shown on the plasma membrane of endothelial cell of microvasculature and analysed quantitatively with a Univar scanning microspectrophotometer. After occluding LVB for 30 min its optic density of AMI was decreased to 106.83 +/- 14.06, while it was increased to 210.83 +/- 24.88 in EA group, P < 0.05. The activity of Mg(2+)-ATPase could increase in transporting Na+, k+ ions through the membrane of the endothelial cells of ischemic myocardium. The result was consistent with the physiological experiment, because EA could regulate the changes of mean repolarization rate induced by AMI and adjust the ion concentration of transmembrane. The catecholamine (CA) in myocardium was located at sympathetic adrenergic terminals with varicosities containing norepinephrine (NE).(ABSTRACT TRUNCATED AT 250 WORDS)

Alkaline Phosphatase↗
PubMed1993

[Influence of electroacupuncture on electrical activity of dorsal horn neurons of the thoracic spinal cord in the rabbit].

In the present paper, influence of electroacupuncture (EA) on electrical activity of neurons of dorsal horns of T2-T3 spinal segments was analysed in chloralose-urethane anesthetized rabbits. Results were: 1). after EA of "Neiguan" (PC 6), of the 31 dorsal horn neurons, 11 increased significantly in their firing rate, 4 decreased obviously and other 16 had no marked change; 2). after EA of "Zusanli" (ST 36), of the 28 neurons, only 2 increased significantly in firing rate, 14 decreased and other 12 had no clear change; 3). of the 6 neurons which all responded to EA of "Neiguan" (PC 6) and "Zusanli" (ST 36), 5 were excited by "Neiguan" (PC 6) and suppressed by "Zusanli (ST 36); the other one was inhibited by both; 4). the receptive field on the body surface and physiological types of 18 neurons were also examined. The results indicate that information from EA of "Neiguan" and "Zusanli" can converge to the neurons of dorsal horns of T2-T3 spinal cord, and different acupoints have a relative specificity.

Acupuncture Points↗
PubMed1993

[Influence of EA on the effective refractory period in rabbits with AMI].

A method of an incomplete ischemia of the lateral wall of the left ventricle produced by pulling the ventricular branch of the left coronary artery of rabbits was employed in this study and the dispersion of the effective refractoriness used as an index. It was noted that the effective refractory periods at the different sites in AMI region were mainly shortened and the dispersion of refractoriness increased obviously. Nevertheless, EA at Neiguan acupoint could inhibit reduction of the effective refractory of ischemic myocardium and improve the dispersion of refractoriness markedly, which would be beneficial to synchronization of the myocardial excitatory state. It suggests that EA have some effect of anti-arrhythmia.

Acupuncture Therapy↗
PubMed1993

Parkinsonism induced with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) in cats: behavioral, biochemical and pathological studies.

Intraperitoneal injection of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) in four cats produced akinesia, bradykinesia, crouched posture, feeding difficulty, and so on, lasting for two weeks. Madopar therapy ameliorated these motor impairments. Reduction of the concentration of dopamine and its metabolites was determined in the substantia nigra and putamen by high performance liquid chromatography (HPLC). Depletion of noradrenaline, serotonin and their metabolites was also seen. Loss of nerve cells and proliferation of glial cells in the substantia nigra were observed under the light microscope. The results indicate that MPTP-induced Parkinsonism in the cat provides an animal model that can be used for basic and therapeutic research on Parkinson's disease.

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine↗
PubMed1993

Melanocytoma with juxtapapillary nevus: premalignant or benign?

A melanocytoma is a benign heavily pigmented tumor that usually arises at the optic nerve. Originally thought to be a malignant neoplasm, currently, it is believed to be a variant of the melanocytic nevus. Recently, several cases of malignant transformation to malignant melanoma have been reported. We present the case of a 63-year-old man with a melanocytoma and juxtapapillary choroidal nevus that remained stable for more than six years. Although the overwhelming majority of such neoplasms are benign, regular follow-up examinations are recommended because there is a small risk of malignant transformation.

Choroid Neoplasms↗
PubMed1993

[Analysis of trace elements in scalp hair of healthy people, breast cancer and hyperplasia patients with XRF method].

The trace element analysis on the scalp hair of patients with breast cancer and hyperplasia was made using the XRF method and compared with that of healthy people. The hair samples from 42 breast cancer patients, 57 hyperplasia patients and 31 healthy people were collected respectively. The results showed that Mn, Cr and K content in the hair of the patients with cancer was much higher than that of the normal (P < 0.05). Significant differences were also found between patients with breast cancer and with hyperplasia in K and Fe content. The former was much higher than the latter (P < 0.05).

Adult↗
PubMed1993

[Molecular study of the mechanism of chromosomal translocation (15;17) in acute promyelocytic leukemia (APL)].

Molecular studies of chromosomal translocation (15;17) in acute promyelocytic leukemia (APL) have shown that retinoic acid receptor A (RARA) gene on chromosome 17 is juxtaposed to the PML gene on chromosome 15. This results in a PML-RARA chimeric gene. Our work has demonstrated that the PML breakpoints in APL patients are clustered in two limited regions, PML-bcr1 and PML-bcr2, separated from each other by about 10 kb. DNA sequence of PML-bcr1 and primary structure of the junctional region of reciprocal chromosomal translocation in a patient have been determined in this paper. Compared to those of two previously reported cases abroad, we found that the breakpoint may be situated in the topoisomerase II cleavage site. A working model has been proposed for the mechanism of DNA illegitimate recombination in t (15;17).

Base Sequence↗
PubMed1993

[A comparative analysis of current conditions of oral health between residents living in towns and those in countryside in Guangdong Province].

A sampling population of 23,665 in Guangdong Province including 4 towns and 4 countryside had been surveyed for the current situation of oral health. A comparative analysis of residents between towns and countryside had been conducted and the results indicated that the rural residents had a higher prevalence rate of dental caries (65.30%) than those who lived in towns (59.96%). The Decayed Missing Filling (DMF) of the population (4.62) and of the patients (7.08) in countryside were both significantly higher than those (2.86 and 4.78, respectively) of citizens (P < 0.001). Females had a higher rate of dental caries than males both in towns and in countryside. Citizens had a higher prevalence rate of periodontosis than rural residents. This paper also presents a comparison of jaw deformity and personal health behaviour, an age distribution of dental caries and a multiple regression analysis.

Adolescent↗
PubMed1993

[A study on a local epidemic of dengue fever in Shaxi district of Zhongshan city, 1991].

An epidemic of dengue fever occurred in Shengshi Village of Shaxi District in the last ten-day period of August, 1991. A wrong diagnosis was made on account of atypical clinical symptoms and careless investigation during early days. Effective measures had not been taken in time, so that the disease spread to neighbouring three villages and the town. The epidemic lasted for 64 days and 112 cases were found. It had been proven by etiologic studies that type 1 dengue virus caused this epidemic.

Adolescent↗