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Biomedical subjects

J Tan

Publications and source records attributed to J Tan.

At least 253 records · Page 14Linked to original sources
PubMed1993

Excimer laser photorefractive keratectomy in Singapore--a new treatment modality for myopia.

BACKGROUND: Myopia is a national epidemic in Singapore. Photorefractive Keratectomy (PRK) for the treatment of myopia using the Argon Fluoride Excimer Laser commenced in January 1992 at the Singapore National Eye Centre. METHODS: An open, prospective, non randomised clinical trial to assess the efficacy, predictability, stability, and safety of PRK for the correction of myopia between -2.0 to -6.0 dioptres. RESULTS: One hundred and fifty-five eyes of one hundred and thirty-five patients underwent PRK between January and September 1992, of which thirty-one had completed at least six months of follow-up. Twenty-nine of the thirty-one patients (93.5%) achieved an unaided visual acuity of at least 6/12. Twenty-six patients (83.9%) were within 1 dioptre of emmetropia. There was an initial over-correction in all patients which regressed to a plateau at around three or four months. Corneal haze did not pose a significant problem. Three patients had ocular hypertension, and another developed a mild allergic reaction to the antibiotic-steroid ointment. CONCLUSIONS: Excimer Laser Photorefractive Keratectomy is a very effective, fairly predictable, stable and safe surgical method for the treatment of myopia.

Adult↗
PubMed1993

[A histological study on peripheral iris in primary angle closure glaucoma].

Iris specimens obtained during the peripheral iridectomy in 12 cases (18 eyes) of primary angle closure glaucoma were studied histologically. The iris specimens taken during the senile cataract extraction in otherwise normal eyes were used as controls. The remarkable differences of the two groups are the changes of the quality and quantity of the mitochondria in the cells of iris tissue. The changes in primary glaucoma, especially in the intermittent stage of the angle closure glaucoma, were found in the mitochondria of the cells.

Glaucoma, Angle-Closure↗
PubMed1993

[Nilestriol prevents osteoporosis in ovariectomized rats].

In order to determine the effects and mechanism of Nilestriol upon bone metabolism, 4-month aged female SD rats were divided randomly into three groups: The OVX group subjected to bilateral ovariectomy, the SHAM group to sham operation, the Nilestriol (CEE3) group to bilateral ovariectomy and treated with CEE3 0.15 mg/100 g BW once a week for 10 weeks. The CEE3 was introduced directly into the stomach from the first day after operation. All rats were killed 10 weeks after operation and their right proximal tibiae were processed undercalcified for quantitative bone histomorphometry. The weights of bone and inorganic matter (ash content) and content of calcium, phosphorus of right humeral were measured. The results showed that in the OVX group the trabecular bone volume, the trabecular thickness, the content of calcium bone, and the ratios of bone weight and ash weight to body weight were all significantly reduced. The bone loss was associated with an increase in bone remodeling; the bone resorption appeared much more marked than the bone formation. In contrast, the ovariectomized animals treated with CEE3 had normalization of bone mass and a declined index of bone resorption and formation which recovered the balance of bone remodeling. It suggested that CEE3 is successful in prevention of bone loss in OVX rats. It is convinced of using Nilestriol to prevent postmenopausal osteoporosis.

Animals↗
PubMed1993

Heterotopic ossification. The utility of osteocalcin in diagnosis and management.

The status of 12 patients after severe traumatic brain injury was investigated to determine the clinical significance of serum osteocalcin levels during the active phase of neurogenic heterotopic ossification. The diagnosis of heterotopic ossification was confirmed on the basis of radiologic findings. The mean interval between the initial injury and diagnosis of heterotopic ossification was 29 weeks. At the time of diagnosis, serum osteocalcin and total alkaline phosphatase levels were determined along with 24-hour urinary calcium and hydroxyproline excretion. The mean serum osteocalcin level was normal at 4.3 ng/ml (normal range 1.6-6.6 ng/ml) in contrast to the elevated mean values for serum alkaline phosphatase (mean = 173 units/liter; normal range 0-105 units/liter) and urinary hydroxyproline concentration (mean = 39.6 mg/24 h; normal range 7-25 mg/24 hr). Only 17% of the subjects demonstrated an elevated serum osteocalcin level, whereas 58% of the patients had an elevated serum alkaline phosphatase level. Urinary calcium excretion and hydroxyproline excretion were elevated in 33% and 70% of subjects, respectively. These data did not reveal a significant correlation between serum osteocalcin and serum alkaline phosphatase, urinary calcium excretion or urinary hydroxyproline at the time of diagnosis or in serial measurements. Therefore, serum osteocalcin is not a valuable adjunct in confirming the diagnosis of neurogenic heterotopic ossification once the diagnosis has been suggested on the basis of clinical findings and it does not appear to play a role in assessing the maturation of heterotopic ossification.

Adolescent↗
PubMed1992

Cardiac dimensions determined by cross-sectional echocardiography in the normal human fetus from 18 weeks to term.

Assessment of cardiac dimensions of the chambers, great arteries and veins in the human fetus is important to distinguish abnormal dimensions from normal. This study establishes normal values based on cross-sectional echocardiographic measurements over the gestational period where these measurements may be clinically useful. Ventricular and atrial dimensions were measured from the 4-chamber view, the short-axis dimension immediately below the mitral and tricuspid valve leaflets in diastole, and the long axis from the closed apposed atrioventricular valves to their respective apices. The ventricular walls and septum were measured at the level at which cavity dimensions in diastole were measured, defining both the left and right ventricular wall thickness, as well as that of the ventricular septum. Furthermore, the long axis of the right and left atria was measured from the center of the apposed atrioventricular valve leaflets to the posterior atrial wall, and the sizes of the atrial chambers were defined using their widths at the prospective broadest points through the area of foramen ovale. From a variety of views, diameters were measured at maximal expansion of the main, left and right pulmonary arteries, the ductus arteriosus, and the superior and inferior venae cavae. The data were evaluated longitudinally from 18 weeks to term, and regression analysis was performed using the best fit of a linear or polynomial equation. The data provide a means for evaluating the normal sizes and dimensions of the fetal heart chambers, as well as the thickness of the ventricular walls and septum.

Aorta↗
PubMed1992

Detection of genital human papillomavirus (HPV) DNA by PCR and other conventional hybridisation techniques in male partners of women with abnormal Papanicolaou smears.

OBJECTIVE: To study the prevalence of human papillomavirus (HPV) infection, using several different hybridisation techniques, in men whose female sexual partners had cervical HPV and/or cervical intraepithelial neoplasia (CIN). METHODS: The male genital area was examined colposcopically and areas suspicious of HPV changes were biopsied. Each biopsy was subjected to histological examination and HPV DNA analysis by conventional DNA analysis such as Southern, reverse and dot blot as well as with polymerase chain reaction (PCR). RESULTS: Colposcopic examination of men showed 133 to be normal whilst 82 (38%) had clinical or subclinical lesions. Of 55 colposcopically directed biopsies from the male lesions taken, detection of HPV DNA by hybridisation with conventional techniques and by PCR showed HPV DNA in 29 (53%) and 47 (85%) of biopsies respectively. Overall HPV types 6/11 were the predominant types. In 18 (33%) biopsies positive by PCR, multiple types were found. CONCLUSION: HPV DNA was present in the majority of biopsy specimens taken, with HPV 6/11 being the predominant type. Among methods for HPV DNA detection, PCR was the most sensitive and useful technique.

DNA Probes, HPV↗
PubMed1992

[Ultrastructure identification of raphe-spinal serotonergic pain modulating system in rats].

5,6-dihydroxytryptamine was microinjected into the nucleus raphe magus (NRM) of rats. The sections of upper cervical segments were processed for immunoreactive substance P (SP). The degenerated axon terminals and immunoreactive fibers were identified by electron microscopy. The results show that the degenerated axon terminals and immunoreactive positive dendrites and axons were found in the laminae I and II of the dorsal horn. The electron-dense axon terminals were in contact with unlabelled dendrites, some also in contract with immunoreactive dendrites. In lamina II, one of degenerated axon terminals as a center was contacted by several unlabelled axonal boutons. SP labelled terminals were synapsed with unlabelled dendrites and dendritic spine; in addition, unlabelled axo-axonal synapse was found in lamina II. These results suggest that 5-HT axon terminals from NRM directly innervate SP and non-SP neurons in the laminae I and II.

Animals↗
PubMed1992

[Changes in glomerular polyanions and ultrastructure induced by protamine in rats].

Perfusion of rat kidneys with polycation protamine, resulted in pathologic alterations of glomeruli very similar to those observed in minimal change nephrotic syndrome in human. In the experimental model, colloidal iron stained kidney tissue sections were analyzed quantitatively by image analyzer and stereology in combination with the observation of other glomerular ultrastructure. The mean thickness of foot processes and the foot processes making up the volume fraction of glomerular capillary were determined. The studies showed that there was a significant decrease in glomerular polyanions of kidneys perfused with protamine as compared with that of the control group (P < 0.01). The glomerular alterations included swelling and fusion of foot processes and narrowing or loss of filtration slits. Electron-dense particles formed by binding of protamine to polyanions were seen primarily in the lamina rara externa of glomerular basement membrane and also along the lamina rara interna and on the foot process surface, which showed the distribution feature of glomerular filter. These results suggest that the ultrastructure alterations of glomeruli may result from the neutralization of polyanions by perfusion with protamine.

Animals↗
PubMed1992

Detection and molecular analysis of alpha and beta thalassaemia genes--recent developments in screening protocols.

Molecular and non-molecular techniques have been utilized for the detection and characterisation of alpha- and beta-thalassaemia genes. Non-molecular techniques example, haematological indices and haemoglobin electrophoresis allow samples to be screened rapidly without the use of radionuclides but these techniques are unable to detect mutations at the gene level. Molecular analysis of alpha- and beta-globin genes either by Southern Blotting and radionuclides or DNA amplification using the polymerase chain reaction (PCR) allows detection of specific mutations and have enabled prenatal diagnosis of the thalassaemias.

Female↗
PubMed1992

[Antisteatotic effects of four kinds of dietary fibers in rats fed on high cholesterol diet: a preliminary morphometric analysis].

The hypolipidaemic and antisteatotic effects of the Konnyaku Powder (KP) have been reported before. In order to evaluate further the antisteatotic role played by KP, the effects of KP on the levels of liver lipid and on the hepatic histopathology and morphometry in comparison with those of pectin, algin and agar were studied. Sixty Wistar strain rats were divided into 6 groups: a normal diet group, a high cholesterol diet group (HC), and 4 test groups, in which the animals were fed on a diet similar to that of the high cholesterol diet group with addition of KP, pectin, algin or agar at a dosage of 5%, respectively. All the animals were killed at the end of the diet treatment for 9 weeks. The results showed that relative liver weights were lower in four experimental groups than in the HC group. The levels of total and free cholesterol, and triglyceride in the liver were lower in KP group than in HC group and in the other three experimental groups. Hepatic histopathology and morphometric examination indicated that antisteatotic effects of KP appeared to be much more significant than those of the other fibers.

Agar↗
PubMed1992

[A study of genetic polymorphism of isozymes in natural populations of Drosophila virilis in east China].

A study of genetic variation at Est-alpha, Est-beta, A my, Acph and alpha-Gpdh loci in local samples of Hefei, Wuhu, Jiujiang, Nanchang, Changzhou, Fuzhou and Quanzhou Drosophila virilis population is presented. The employment of standard techniques of polyacrylamide electrophoresis and agarose electrophoresis reveals that the former three loci are highly polymorphic in all these populations. According to the allelic frequency of the 5 loci, a genetic distance between the above-mentioned populations was calculated. Along with the results obtained by Mr He Chaozheng from Hongze, Nanjing, Hangzhou and Ningbo populations, a dendrogram was made. It was found that Quanzhou and Fuzhou populations differed from the others in allelic frequencies and genetic distances which suggests that this difference is related to the extent of geographic isolation among them.

Animals↗
PubMed1992

Retinal artery occlusion in a diver.

The clinical manifestation of decompression disorders is highly variable, ranging from mild rashes or joint pains to central nervous system symptoms like scotomata, paralysis and death. The diagnosis is easily overlooked, especially if an occupational history is not obtained. Recompression treatment with hyperbaric oxygen is the specific treatment for decompression sickness and air embolism. Prompt recognition and treatment are vital to recovery. However, there is a place for treatment of decompression disorders and embolism even when significant delay of up to 14 days has occurred. This case report discusses decompression disorders in relation to an unskilled fisherman diver who present with retinal artery occlusion. Decompression disorder leading to retinal artery occlusion is a very rare presentation. The difficulty of diagnosis is discussed as well as the result of delayed hyperbaric treatment.

Adult↗
PubMed1991

Primary structure of the assimilatory-type sulfite reductase from Desulfovibrio vulgaris (Hildenborough): cloning and nucleotide sequence of the reductase gene.

The nucleotide sequence encoding the structural gene (651 bp) and flanking regions for the assimilatory-type sulfite reductase from the sulfate-reducing bacterium Desulfovibrio vulgaris (Hildenborough) was determined after cloning a 1.4 kb HindIII/SalI genomic fragment possessing the gene into Bluescript pBS(+)KS. The primary structure of the protein was deduced, and the molecular mass of the apoprotein was estimated as 24 kDa. The amino acid sequence of the polypeptide shows some similarities at putative [Fe4S4] cluster binding sites in comparison with the heme protein subunit of the larger Escherichia coli and Salmonella typhimurium sulfite reductases and spinach nitrite reductase. This is the first reported sequence of a member of a new class of low molecular weight assimilatory sulfite-reducing enzymes recently identified in a number of anaerobic bacteria [Moura, I., Lina, A. R., Moura, J. J. G., Xavier, A. V., Fauque, G., Peck, H. D., & Le Gall, J. (1986) Biochem. Biophys. Res. Commun. 141, 1032-1041].

Amino Acid Sequence↗
PubMed1991

Enzymatic redox chemistry: a proposed reaction pathway for the six-electron reduction of SO3(2-) to S2- by the assimilatory-type sulfite reductase from Desulfovibrio vulgaris (Hildenborough).

A detailed reaction pathway for the six-electron reduction of SO3(2-) to S2- by the assimilatory-type sulfite reductase (SiR) from Desulfovibrio vulgaris (Hildenborough) has been deduced from experiments with 35S-labeled enzyme and the relative reaction rates of nitrogenous substrates. The ligand bridging the prosthetic [Fe4S4]-siroheme center is apparently exchanged by 35S2- in both oxidized and reduced enzyme. This 35S2- label was retained in the course of SO3(2-) reduction, implicating substrate binding to the nonbridging axial site of the siroheme. A reaction mechanism is proposed in which SO3(2-) binds to Fe2+ through the sulfur atom, followed by a series of two-electron reductive cleavages of S-O bonds. Protonation of oxygen facilitates bond cleavage, giving hydroxide as leaving group. The bridge remains intact throughout the course of the reaction, providing an efficient coupling pathway for electron transfer between the cluster and siroheme.

Binding Sites↗
PubMed1991

Efficient transformation and regeneration of rice small cell groups.

Transgenic plants have been regenerated from small cell groups of rice using a simpler, faster, and more efficient method than used previously (e.g., protoplast transformation and regeneration methods). Small cell groups of 50-100 cells were prepared from established suspension cultures of rice cell lines. Transformation of small cell groups with intact cell walls was carried out with a plasmid harboring the beta-glucuronidase gene and was mediated by polyethylene glycol. Assay of beta-glucuronidase activity indicated that the frequency of transformation was about 7%. beta-Glucuronidase activity was detected in the roots and leaves of plants regenerated from transformed calli. One or two copies of the beta-glucuronidase gene per cell were determined to be integrated into the rice chromosomal DNA isolated from transformed calli. This method of transformation and regeneration is widely applicable to both dicotyledonous and monocotyledonous plants, especially those varieties that are resistant to regeneration from protoplasts.

Journal Article↗
PubMed1991

Monovalent Fab fragments of D7.5 monoclonal antibody activate intracellular Ca2+ mobilization and secretion of cytolytic factors by thymus cells.

Previous studies have identified two mouse monoclonal antibodies, D7.5 and G1.4, that each can cause secretion of cytolytic factors from natural killer (NK) cells and resting T cells in humans, rats, and hamsters. Toward elucidation of the molecular identity and the transmembrane signaling mechanism of the antibody-defined trigger molecules, we investigated 1) their surface density, 2) the crosslinking requirement for signaling, and 3) their ability to mobilize intracellular calcium ions. Equilibrium binding studies using monovalent Fab fragments of D7.5 showed the presence of approximately 20,000 trigger molecules per thymus cell and an antibody dissociation constant of 1.8 x 10(-6) M. Thymus cells incubated in the presence of either intact or Fab fragments of D7.5 acquired the ability to lyse Yac-1 cells. Furthermore, the incubation media of thymocytes that were treated with either intact or Fab fragments of D7.5 contained effector-cell derived factors that could lyse Yac-1 cells. Flow cytometry measurements of changes in intracellular free calcium concentration ([Ca2+]i) in thymocytes. A significantly elevated level of [Ca2+]i was observed at 60s after antibody addition and this response, which required the external calcium source, increased continuously during the 30 min incubation. Furthermore, dbcAMP plus theophylline did not alter the ability of D7.5 to induce calcium mobilization suggesting that the antibody-defined trigger may not use the signaling pathway involving breakdown of phosphatidylinositol.

Animals↗