Search PubMed⌕ Search

Biomedical subjects

A S Chan

Publications and source records attributed to A S Chan.

108 records · Page 6Linked to original sources
PubMed1978

Ultrastructure of the ultimobranchial follicles of the laying chicken.

The ultimobranchial gland of the laying chicken consists of groups of C cells interspersed among a collection of intercommunicating follicles and ducts of variable size and shape. The epithelium lining this system ranges from squamous to columnar and includes stratified squamous and pseudostratified columnar elements. Four cell types are distinguished in this epithelium: F, mucous, C, and basal cells. F cells show microvilli and microfilaments. Pinocytotic activity and images of fusion of coated vesicles with the plasma membrane are evident. The rough-surfaced endoplasmic reticulum (RER) and the Golgi complex are moderately developed. Dense bodies are encountered apically in some cells. Mucous cells possess microvilli and secretory material in the typical form of partially fused droplets. C cells contain secretory granules and are invariably separated from the follicular lumen by other cell types. The smaller, pyramidal basal cells contain filaments, RER, small Golgi complexes, free ribosomes and hemidesmosomes. The lumina contain flocculent or granular material, cellular debris and desquamated cells. Morphological evidence demonstrates that features of the pharyngeal epithelium are retained and that the majority of the cell types, with the exception of C cells, are presumably nonendocrine.

Animals↗
PubMed1977

Signal to noise enhancement in dark field electron micrographs of vasopressin: filtering of arrays of images in reciprocal space.

A technique for filtering arrays of images of dispersed molecules is presented which takes advantage of the crystallographic properties of regular arrays and the rapidity of optical treatment. A filter in reciprocal space consisting of perforations in a square or rectangular lattice, as determined by the image arrrangement, reduces noise and averages the images simultaneously by transmitting only regularly recurring image structure. The filter is universal for all image contents and introduces no additional biases. The signal to noise improvement approaches square root N for N independent images of the same molecule in the same configuration. The procedure which is simple, rapid and inexpensive, is demonstrated with the aid of dark field electron micrographs of the protein vasopressin and combined with iodination of that molecule to elucidate its structure.

Crystallography↗
PubMed1977

Ultrastructure of the parathyroid glands in the chicks.

The ultrastructure of the parathyroid glands in 4-week-old white leghorn chicks has been examined. The gland consists of chief cells arranged in diffuse cords or solid masses. The chief cells vary in electron density. The rough-surfaced endoplasmic reticulum is invariably moderately to well developed and consists of cisternae arranged in well-ordered patterns or distributed randomly. The Golgi complex consists of cisternae arranged in concentric layers, smooth-surfaced and coated vesicles. Cisternae of the Golgi complex arranged in circular and tortuous profiles are also observed. The chief cells contain occasional membrane-limited secretory granules 150-350 nm in diameter and with contents which vary in electron density. Secretory granules are distributed randomly in the cytoplasm and along with the plasma membrane, Images of fusion of coated vesicles with the plasma membrane are sometimes observed. The cytoplasm also contains round- to rod-shaped mitochondria, lysosome-like structures and occasional lipid bodies. Dark cells with electron-dense cytoplasm and containing organelles in close proximity are also observed. Morphological evidence of synthetic and secretory activities in the chief cells suggests active parathyroid function in the rapidly growing chicks.

Animals↗
PubMed1977

Iodinated E. coli 70S ribosomes as a radiocolloid of uniform particle size for lymph-node and liver scanning.

As an example of the use of biologic particles as carriers for radioactive tracers, E. coli 70S ribosomes were labeled with I-125 using chloramine-T. The labeled ribosomes, after treatment with glutaraldehyde, were injected into rabbits either subcutaneously (through the dorsum of the foot) or intravenously (through the ear). After subcutaneous injection, 40% of the activity accumulated in the lymph nodes during the first 5 hr, and the 70S ribosomal particles were shown to remain within the lymphatic system for at least 8 hr. After intravenous injection, 71% of the activity was detected in the liver within minutes by scintigraphic techniques. The effective half-time of the label in the liver from glutaraldehyde-treated I-125-tagged 70S ribosomal colloidal particles is 4-5 hr. No pyrogenic response was observed. Barring any deleterious side effects, the results indicate that biologic cell components of definite dimensions (in this case E. coli 70S ribosomes about 20 nm in diam) could be considered as radiocolloids for lymph-node and liver imaging.

Animals↗
PubMed1976

Effect of a low calcium diet on the ultrastructure of the parathyroid gland of chicks.

The effect of a low calcium diet on the ultrastructure of the parathyroid gland in the chick was examined. Two-week-old White Leghorn chicks were fed a low calcium diet (calcium content 0.63%) for two weeks. In these chicks, the parathyroid glands are grossly enlarged. Hypertrophy and hyperplasia of the chief cells are evident. The plasma membranes between adjacent cells are relatively straight but interdigitate in some places. Chief cells contain occasional membrane-limited secretory granules (150-350 mmu in diameter) and with contents of variable electron density. Secretory granules are distributed randomly but some are closely applied to the plasma membrane. There is an increase in the development of the rough-surfaced endoplasmic reticulum. The Golgi complex is enlarged and consists of cisternae arranged in concentric layers, smooth-surfaced and coated vesicles and condensing vacuoles. Dilatations of the cisternae at several points are observed. Mitochondria and filaments are also encountered. These morphological features suggest that low calcium intake stimulates the synthetic activity of the chief cells of the chick parathyroid.

Animals↗
PubMedDate not supplied

Comparison of the aesthetic facial proportions of southern Chinese and white women.

OBJECTIVE: To compare the aesthetic facial proportions of southern Chinese women with published average and ideal values for white women. DESIGN: One hundred Chinese women between the ages of 18 and 40 years who had not undergone previous facial surgery were chosen at random, and their aesthetic facial proportions were measured from 5 x 7-in photographs. Comparisons were made with similar reported measurements for the white face, and the surgical relevance of the differences observed is discussed. RESULTS: The major facial differences observed in the Chinese face were the wider intercanthal distance, the wider nasal base, a different profile of the lower face, and differences in the eyelids. The Chinese nose was less prominent, the alae were more flared, the nostrils were more horizontally oriented, the alar-columellar relationships were different, and the nasal tip was less defined. CONCLUSIONS: Although the general principles of facial plastic surgery apply to both white and Chinese faces, the aesthetic goals are different. The aim is to retain the ethnicity and natural appearance of the face.

Adolescent↗
PubMedDate not supplied

Variant EWS-WT1 chimeric product in the desmoplastic small round cell tumor.

Chromosome translocations found in neoplasms often result in the creation of hybrid genes encoding chimeric proteins. Desmoplastic small round cell tumor (DSRCT) is a recently described aggressive malignancy associated with a unique chromosomal translocation t(11;22)(p13;q12). This translocation has recently been characterized, revealing the rearrangement and fusion of the WT1 gene on chromosome 11 to the EWS gene on chromosome 22. Fusion of these two genes results in the production of a putative oncogenic protein composed of the zinc finger DNA-binding domains of WT1 linked to the potential transcriptional regulatory domains of EWS. The typical chimeric transcript consists of the first 7 exons of EWS and the last 3 exons of WT1. We report here the first case of DSRCT with a variant EWS-WT1 chimeric product that includes 9 exons of EWS and 3 exons of WT1.

Adolescent↗
PubMedDate not supplied

Results of treatment with quinolones of sexually transmitted diseases in the Far East: a brief summary.

The emergence of penicillinase-producing Neisseria gonorrhoeae (PPNG) strains in 1976 and the increasing frequency of chromosomally mediated resistance to penicillin has resulted in a decline in the effectiveness of penicillin for the treatment of gonorrhea. In Hong Kong, the emergence of bacterial resistance to kanamycin or tetracycline has also been observed. Quinolones were first introduced in Hong Kong in 1985, and since then the percentage of PPNG-related cases of gonorrhea has dropped dramatically. The use of quinolones for the treatment of nongonococcal urethritis has not been as successful as that for gonorrhea. Haemophilus ducreyi (the causative organism of chancroid) is sensitive to quinolones, and the occurrence of chancroid since 1985 has decreased from 628 to (in 1987) 184.

4-Quinolones↗
PubMedDate not supplied

Overexpression of p53 in hepatocellular carcinomas: a clinicopathological and prognostic correlation.

Overexpression of the p53 tumour suppressor gene is one of the most common abnormalities in primary human cancers and appears to be a result of point mutation within a highly conserved region of the gene with subsequent encoding for a mutant, more stable protein. In the study, 71 surgically resected hepatocellular carcinomas (HCC) were examined to study the expression of the p53 gene, its relation with clinicopathological parameters and its prognostic significance. Using immunohistochemical detection for mutant p53 protein with monoclonal antibody PAb1801, p53 overexpression was found in 22 tumours (31%) but in none of the non-tumorous liver specimens. Overexpression of p53 was more frequent in tumours with poor cellular differentiation (P = 0.01), in tumours > 5 cm in diameter (P = 0.05), and in those with giant cells present (P = 0.03) and, less significantly, of massive type of Eggel's classification (P = 0.06). It did not have any significant correlation with hepatitis B or C status, background liver disease or serum alpha-fetoprotein levels, nor was it related to tumour invasiveness (venous permeation, direct liver invasion and tumour microsatellite formation). In addition, the presence of p53 mutant protein did not influence tumour recurrence or patients' survival rates. The data suggested that p53 mutation in HCC was associated with a later stage of oncogenesis. However, it was not apparently related to tumour invasiveness/aggressiveness and prognosis.

Adult↗
PubMedDate not supplied

Methane oxidation and production activity in soils from natural and agricultural ecosystems.

Methane (CH4) flux from soil to the atmosphere is the result of two microbial processes, methanogenesis and CH4 oxidation. Land use may have a profound impact on the relative activities of these groups of organisms. In this study, the CH4 production and consumption potentials of soils from agricultural and nonagricultural ecosystems were assessed in laboratory incubations. Methane production potentials of most soils were low and in the range of 0.02 to 0.35 nmol CH4 g soil(-1) h(-1); however, soils from two of the agricultural sites that experience periodic water saturation had CH4 production potentials from 100 to 300 nmol CH4 g soil(-1) h(-1). The high methanogenic potential suggests that CH4 consumers may not be wholly dependent on atmospheric CH4 for their survival and maintenance. The prairie soils exhibited the highest CH4 oxidation under ambient atmospheric CH4 concentrations, and CH4 oxidation activity was markedly enhanced in incubations with an atmosphere enriched in CH4. This stimulated CH4 oxidation activity was generally greater in the agricultural soils as compared with the forest and prairie soils. Methane oxidation appeared to be related to soil nitrogen status. Under ambient atmospheric CH4 concentrations, CH4 oxidation was negatively related to soil mineral N (NO2- + NO3- + NH4+) concentration. However, a positive relationship between soil mineral N status and CH4 oxidation activity was observed in incubations with atmospheres enriched in CH4. This pattern suggests that the agricultural lands contain different populations of CH4 oxidizers than the natural systems.

Agriculture↗
PubMedDate not supplied

Effect of land use on methane flux from soil.

The precise effects of natural and disturbed terrestrial systems on the atmospheric CH4 pool are uncertain. This study was conducted to quantify and compare CH4 fluxes from a variety of ecosystems in central Iowa. We investigated agricultural systems under different management practices, a hardwood forest site, native and restored prairies, and a municipal landfill. Flux measurements were obtained using a closed-chamber method, and measurements were compiled by sampling over the 1993 and 1994 growing seasons. In 1993, most of the agricultural sites were net CH4 producers with cumulative CH4 fluxes ranging from -0.02 to 3.19 g m(-2) over the 258-d sampling season, while the natural ecosystems were net CH4 consumers, with cumulative seasonal fluxes ranging from -0.27 to -0.07 g m-2 258 d(-1). In 1994, only the landfill and the agricultural site treated with broadcast liquid swine manure (LSM) were net CH4 producers, while the remainder of the natural and agricultural ecosystems were net CH4 consumers, with mean seasonal flux rates ranging from -0.43 to -0.008 g m(-2) 271 d(-1). We hypothesize that the differences in CH4 fluxes between the two years are due to differences in rainfall. To illustrate the integration between land use and CH4 flux, we computed an area-weighted soil CH4 flux for the state of Iowa. Our calculations yielded a net average soil CH4 flux of 139,000 Mg CH4 for 1993 and 1994.

Agriculture↗