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Biomedical subjects

S Tan

Publications and source records attributed to S Tan.

At least 181 records · Page 10Linked to original sources
PubMed1992

[The operation treatment for the age-related macular degeneration wet-type eyes and its complications].

Age-related macular degeneration (AMD) is one of the important causes for blindness in elderly population. The effect of the treatments by laser and vitrectomy in AMD wet-type eyes, which subretinal neovascularization is existed in or have vitreous hemorrhage, is reported and discussed. Using laser photocoagulation, 65% of the affected eyes had marked cicatrization and 31% were partially improved. Among the 4 AMD eyes with vitreous hemorrhage, three cases were successful after vitrectomy. It has a certain significance for rescuing the vision and controlling the development in AMD wet-type eyes.

Aged↗
PubMed1992

The impact of HLA match transfusions and presensitization on renal transplantation in the cyclosporine era.

The successful engraftment of a renal transplant is dependent on multiple factors, immunological factors being of major importance. Specifically, histocompatibility, lymphocytotoxic antibodies and pretransplant blood transfusions have been shown to play a major role in determining graft outcome in renal transplant recipients receiving Azathioprine-Prednisolone immunosuppression. The impact of the immunosuppressive drug, Cyclosporine on graft outcome in relation to established risk factors were examined among 116 cadaveric and 34 living related renal allograft recipients from our center. Histoincompatibility and pretransplant blood transfusions did not significantly affect graft survival among cadaveric transplant recipients. Similarly, graft survival was not significantly different between two haplotype-matched and less well-matched living-related graft recipients (75% versus 96.5% respectively). On the other hand, lymphocytotoxic antibodies remained a major risk factor for immunologically mediated graft loss among cadaveric graft recipients (48.0% versus 92.2% four year graft survival among those with and without antibodies respectively). These results suggest that Cyclosporine has abrogated some immunological risk factors in renal transplantation.

Adult↗
PubMed1991

Hormone replacement therapy and survival after surgery for ovarian cancer.

OBJECTIVE: To evaluate whether hormone replacement therapy affects survival in women who have undergone bilateral salphingo-oophorectomy because of epithelial ovarian cancer. DESIGN: Retrospective analysis by review of patients' notes and questionnaires completed by general practitioners to compare the overall survival and disease free survival in patients with ovarian cancer who did or did not receive hormone replacement therapy after diagnosis. Data were analysed by Cox regression, with hormone replacement therapy as a time dependent covariate because patients who received hormone replacement did so at different times after diagnosis. SETTING: Gynaecological oncology unit of Royal Marsden Hospital. PATIENTS: 373 patients aged 50 years or younger who attended the hospital from 1972 to 1988. All of the women had undergone bilateral salpingoophorectomy for epithelial ovarian cancer. In all, 78 had received hormone replacement therapy, starting at a median of four months after diagnosis. INTERVENTION: A questionnaire was sent to the general practitioners of all patients who were not recorded as having received hormone replacement therapy. MAIN OUTCOME MEASURES: Overall survival and disease free survival. RESULTS: There was no significant difference in survival between women receiving hormone replacement therapy and those not receiving it after accounting for the effects of other known prognostic factors (stage of cancer, differentiation of tumour, histological results, and time to relapse). The relative risk of dying in those who received hormone replacement therapy was 0.73 (95% confidence interval 0.44 to 1.20). In addition, there was no significant difference in disease free survival (relative risk in those receiving hormone replacement therapy was 0.90; 95% confidence interval 0.52 to 1.54). CONCLUSIONS: This study shows that hormone replacement therapy is unlikely to have a detrimental effect on the prognosis of patients with ovarian cancer, but this would be shown conclusively only by a randomised controlled trial.

Adult↗
PubMed1991

[Studies on the chemical constituents of rutaceous plants. LXVII. The chemical constituents of Toddalia asiatica (L.) Lam. (T. aculeata Pers). Examination of coumarins using supercritical fluid and soxhlet extraction. Is toddalolactone a genuine natural coumarin?].

It is well known that toddalolactone (1) is a main component of Toddalia asiatica (L.) Lam. (T. aculeata Pers.) (Rutaceae). However, supercritical fluid (SCF) extraction of the plant by using CO2 showed that a main component of the extract was not 1, but aculeatin (2), a coumarin having an epoxy ring on the side chain. The same result was obtained from Soxhlet extraction by using aprotic solvents. On the other hand, Soxhlet extraction by using methanol yielded 13, corresponding to a methanol adduct of 2, as an additional component, which was able to be also produced in 50.2% yield only by heating pure 2 in methanol, indicating that the epoxy ring in 2 can be easily attacked by a weak nucleophile like methanol. These facts strongly suggested that 1, corresponding to the hydrate of 2, was an artefact derived from 2 during extraction. SCF extraction under various conditions was examined in detail by quantitative analyses of 1 and 2 by high performance liquid chromatography and the optimum condition extracting the both components was found to be at 40 degrees C and at 300 kg/cm2. The condition was applied to the plant treated with aqueous sodium hydrogen carbonate in order to remove any acidic substances and 1 was still detected in the extract. Thus, it is conclude that 1 should be a genuine natural coumarin but that previous isolation of 1 as a main component resulted in an isolation of an artefact derived from 2. SCF extraction was suggested to be a useful extraction method.

Chemical Fractionation↗
PubMed1991

[Rational close planting in raising the seedlings of Panax quinguefolium linn].

It has been found that the effect of planting density is hardly noticeable for one-year-old seedlings, but very apparent for 2-year-old ones. With the increase of planting density, the leaf area gets smaller, stem higher, and root thinner and shorter. The larger the planting density. The smaller the dry weights of canopy and root and the root-canopy ratio. It is thus advocated that rational planting densities be selected according to the proper cultivation systems.

Panax↗
PubMed1991

[Biological assay, reliability test, error analysis and pooled calculation for assessing leucomycin yield].

A biological assay for determining leucomycin yield was established by using a curillinear protocol (Sarcina lutea) and (2.2) dosage or (3.3) dosage protocol (Bacillus subtillis 63501). At the same time, according to the principles of biostatistics and the methods of variance analysis, reliability tests, error analysis and pooled calculations were carried out, so as to hold the confidence limit below the internationally accepted level of 5%.

Biological Assay↗
PubMed1990

DNA binding-induced conformational change of the yeast transcriptional activator PRTF.

Our studies using proteases to probe protein structure establish that binding to the upstream activating sequences (UASs) of two different yeast a-specific genes induces a conformational change in the pheromone/receptor transcription factor (PRTF), which is not observed upon binding to the UASs of either of two alpha-specific genes. We propose that this selective structural alteration exposes an activation region of PRTF when it binds a-specific genes, switching these genes on. The transcriptional activator MAT alpha 1 may activate alpha-specific genes by binding to the PRTF-alpha-specific UAS complex and unmasking the otherwise hidden activation surface of PRTF. We also show that the N-terminal third of PRTF is sufficient for specific DNA binding, while the middle third of the protein interacts with MAT alpha 1.

Affinity Labels↗
PubMed1990

Chlordiazepoxide reduces discriminability but not rate of forgetting in delayed conditional discrimination.

Benzodiazepine and anticholinergic drugs interfere with septo-hippocampal function in similar but not identical ways. They also share a number of common behavioural effects and, in particular, both classes of drug interfere with spatial memory in the Morris Water Maze--a test which is very sensitive to hippocampal dysfunction. We have previously shown that the anticholinergic drug scopolamine impairs discriminability, but not rate of forgetting, in delayed conditional discrimination. In the present study forgetting was quantified by fitting a negative exponential function to estimates of discriminability derived from a signal detection analysis of data from an auditory delayed conditional discrimination task. Chlordiazepoxide produced a highly significant decrease in discriminability which was monotonically related to the logarithm of dose in the range 0.67-18.0 mg/kg IP. The rate of forgetting was not increased. These data confirm the pharmacological independence of changes in discriminability and rate of forgetting; demonstrate that in this task chlordiazepoxide has similar effects to scopolamine; and suggest that the effects of chlordiazepoxide in other working memory tasks could be more a result of changed stimulus processing than impairment of memorial processes.

Animals↗
PubMed1990

The magnetic field of cortical current sources: the application of a spatial filtering model to the forward and inverse problems.

We extend our theoretical model based on spatial filtering to determine the ability of a SQUID magnetometer to resolve 2 localized current sources in the brain. We find that in order to resolve 2 separated but coaxial cortical sources, the source-to-pickup coil distance must be comparable to the distance between the 2 sources. The size of the current sources affects the resolving power of a magnetometer, but an anisotropy of 3 in the cortical tissue does not produce a significant effect. The model also provides a solution of the inverse calculation, either to reconstruct the original current source distribution from the measured magnetic field, or to continue the field at the magnetometer inward towards the sources. Both the inverse and inward calculations are limited by the fact that the inverse filter function serves as a high-pass filter, which leads to instabilities at high spatial frequencies, particularly in the presence of noise. The instabilities can be minimized by choosing an appropriate window to attenuate the noise, but this in turn reduces the spatial resolution.

Cerebral Cortex↗
PubMed1990

Asymmetries in face perception: component processes, face specificity and expertise effects.

Three experiments were carried out to analyze the component processes contributing to observed asymmetries in face perception, to determine whether these asymmetries occur for complex visuospatial stimuli other than human faces, and to investigate the effects of expertise on the asymmetries. Two component processes contributed to the observed asymmetries: perceptual bias (PB) in the observer and face asymmetries (FA). There was no PB effect for complex visuospatial stimuli other than human faces (landscapes, abstract paintings and animal faces). Expertise effects were investigated by examining the judgments of Chinese and Caucasian subjects for own-race and other-race faces. A PB was found for both Caucasian and Chinese faces, but the size of the effect was not related unequivocally to expertise. Caucasian subjects showed a PB for own-race faces only, but Chinese subjects showed a PB for both Chinese and Caucasian faces. There was no FA effect for Chinese faces, even when the composites were perceived as more dissimilar than the Caucasian composites, for which there was an FA effect. The implications of these results for the theoretical interpretation of perceptual asymmetries are discussed.

Analysis of Variance↗
PubMed1990

Selectivity for omega-receptor subtypes as a strategy for the development of anxiolytic drugs.

The names omega 1-, omega 2-, and omega 3-receptor subtypes have recently been proposed to replace the nomenclature of BZ1, BZ2 and BZp receptors in order to avoid a nomenclature exclusively linked to the benzodiazepine (BZ) structure or to a regional localization. The multiplicity of pharmacological actions of currently available anxiolytics may be due to their lack of selectivity for omega-receptor subtypes. The idea that a receptor-subtype selective drug will offer a more specific therapeutic profile is widely accepted. In the field of preferential anxiolytic or hypnotic drugs, imidazopyridines represent a new chemical and therapeutic class possessing selectivity for omega-receptor subtypes. Of these, alpidem (6-chloro-2-(4-chloro-phenyl)-N,N-dipropylimid-azo[1,2-a] pyridine-3-acetamide) behaves preferentially as an anxiolytic drug in both animal models and man. Receptor-binding studies using alpidem either as a displacer or as a radioligand indicate that the compound has a high affinity for omega 1- and for omega 3- but not for omega 2-receptors. In the human brain, the binding of [3H]-alpidem to omega 1- and omega 3-receptors occurs with a Kd of 1.67 nM and 0.33 nM respectively. The binding of [3H]-alpidem to omega 1-receptors in the rat cerebral cortex with a Kd of 1.5 nM is enhanced by GABA, and in contrast to anxiolytics of the benzodiazepine type, is unaffected by chloride ions and pentobarbital. In conclusion, the affinity of alpidem for the omega 1-receptor is allosterically influenced by the activation of the GABAA receptor but not by other components of the same receptor complex.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1990

Lithium and imipramin effects on paw preference in cats.

The effect of lithium and imipramin on paw preference was studied in cats. Paw preference was assessed by the food-reaching test. It was found that lithium decreased, and imipramin increased the asymmetry of paw use. The lithium effect was antagonized by imipramin. It was concluded that paw preference may reflect a biochemical asymmetry in the brain. These effects of these psychoactive drugs may be of importance for the origin and treatment of affective disorders.

Animals↗
PubMed1990

[The relations between acupuncture analgesia and changes of concentration of serum metallic ion].

Forty patients treated by thyroidectomy received superficial cervical plexus block or electric acupuncture stimulation of acupoint Hegu and Neiguan bilaterally. All patients were random divided into groups of C, A1, A2 and A3 on the basis of anesthetic method. Every patients were measured their serum concentration of Na+, K+, Ca++, Cu++, Mg++ and Zn++ before and during anesthesia or electric acupuncture stimulation and postoperation. There was no difference about analgesic effect of four groups (P greater than 0.05). Serum Ca++ concentration reduced various level during electric acupuncture stimulation (P less than 0.05-0.01), but no difference between group A1 and group A2 (P greater than 0.05). The results showed: 1. It made level of serum Ca++ reduced because internal environment of patients were affected by the signal of acupuncture. 2. There was no addition effect for the influence of serum Ca++ when electric acupuncture stimulated points Hegu and Neiguan at the same time intravenous injected Pethedine (1.3 mg/kg). 3. It probably disturbed the value of serum Ca++ concentration when intravenous injected 5% Glucose during the operation, but it had not influence on analgesic effect. 4. Acupuncture probably made concentration of serum Na+, Cu++, Mg++ and Zn++ changed which had statistical difference but with marked irregular figure, the real causes are worth going further into research in future.

Acupuncture Analgesia↗