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Biomedical subjects

C Y Hwang

Publications and source records attributed to C Y Hwang.

24 records · Page 2Linked to original sources
PubMed1989

In vivo and in vitro studies on the release of thyrotropin in aging rats.

Effects of aging on the concentration of serum thyrotropin (TSH) and the release of TSH in vitro from anterior pituitary glands (APs) of male and female rats were investigated. Rats with 3-5 (young) and 24-26 (old) months of age were used. Some female rats were ovariectomized (Ovx) 10 weeks before use. After decapitation, trunk blood was collected. APs were bisected and preincubated with Krebs-Ringer phosphate buffer (KRB) at 37 degrees C for 60 min. They were then incubated with or without 10 nM thyrotropin-releasing hormone (TRH) for 30 min. The media were collected and replaced by fresh KRB. Incubations were continued and KRB media were changed three times, once every 30 min. One hemi-AP per flask and 7 or 8 flasks per group were used. The concentration of TSH in the medium and serum samples was measured by radioimmunoassay. The level of serum TSH in the diestrous, estrous and Ovx rats was reduced by aging. Thirty min after incubation with TRH, the release of TSH from APs of old intact female or Ovx rats was significantly (P less than 0.01) less than that of corresponding young rats. The concentration of serum TSH and TRH-stimulated release of TSH from APs of male rats was not altered by aging. There was no difference in the basal release of TSH from APs between old and young animals. These data suggest that the release of TSH from APs in response to TRH is decreased by aging in female but not in male rats.

Aging↗
PubMed1983

Size and shape of airborne asbestos fibres in mines and mills.

There is increasing evidence that fibre size and shape play an important part in the production of health effects related to asbestos. The dimensions of airborne fibres collected at various stages of fibre processing in three mines and six mills producing three types of asbestos were measured using phase contrast light microscopy and transmission electron microscopy. Airborne fibres of different asbestos types had appreciably different size and shape distributions. For a given asbestos type, fibres collected at different stages of processing differed in their size distributions but the differences were considerably less than between fibre types. Most of the airborne fibres to which miners and millers were exposed were short and thin and thus respirable. The physical properties which best differentiated crocidolite fibres from other types of asbestos and which had higher values determined for crocidolite fibres than those obtained for the other types, were median aspect ratio and the proportion of long thin fibres--that is, fibres less than or equal to 0.2 micron in diameter and greater than 5 micron in length as the percentage of total fibres. The median true diameter of amosite fibres was about four and three times higher than the median true diameters of chrysotile and crocidolite fibers respectively. The median true length of amosite fibres was more than four and two times higher than the median true lengths of chrysotile and crocidolite fibres respectively. The observed differences in size and shape of airborne fibres have important implications for the setting of work environmental standards and in explaining differences in health risks associated with different types of fibre.

Air↗
PubMed1980

Dimensions of airborne asbestos fibres.

Systematic measurements were made of the dimensions of fibres found in the air in mines and mills for crocidolite, amosite and chrysotile. Samples were collected on membrane filters and examined in light, transmission electron and scanning electron microscopes. The proportion of short fibres was shown to decrease with extent of processing, especially for amosite. No airborne fibres had a diameter greater than 3 micrometers, and all would therefore be capable of reaching the pulmonary alveoli. It was shown that for the same airborne mss of the different varieties of asbestos, fewer amosite fibres would be present than crocidolite or chrysotile fibres. Most of the fibres to which workers are exposed are short and thin. It was also shown that the choice of analytical method and the limits of fibre dimension that can be observed are critical. Thus, fibres greater than 5 micrometers which are visible in the light microscope represent only a small proportion of the total fibre count, and transmission electron microscopic methods can lead to under-reporting of long fibres.

Air Pollutants↗
PubMed1975

Physical parameters of airborne asbestos fibres in various work environments-preliminary findings.

The results of a pilot investigation to describe the physical parameters, length, aspect ratio, mass and shape of airborne fibres in a variety of industries producing processing and handling chrysotile, amosite and crocidolite are described. Samples of airborne dust were collected on nucleopore membrane filters and examined by scanning electron microscopy. The diameters and lengths of airborne fibres collected during the dumping of raw amosite at an asbestos products plant were greater than those of fibres collected during the application of amosite insulation. Chrysotile fibres collected in the carding area of an asbestos textile plant also tended to have smaller diameters than fibres collected in the dryer and bagging areas of an asbestos mill. The measurements of fibre dimensions indicate that the degree of protection afforded a worker by optical counts using the membrane filter technique is likely to depend on variety of asbestos and stage of processing. Preliminary results are not in conflict with experimental data suggesting that asbestosis might be related to the mass of airborne dust and primary malignant mesothelial tumors to exposure to fibres in a specific range of fibre diameter and length.

Air Pollutants↗
PubMedDate not supplied

Comparison of methods of assessing asbestos fiber concentrations.

Dimensional measurement of the counted fibers has important implications for setting of environmental standards to protect workers' health. Results of fiber concentrations as determined by different methods were compared. Each method was used to determine concentration by examining one sector of membrane filter on which fibrous dust was collected in various workplaces. The concentrations measured by the Asbestos International Association (AIA) method for 35 samples were, on the average, greater than the concentrations determined by the modified British Occupational Hygiene Society--Asbestosis Research Council (BOHS-ARC) method. The AIA and modified BOHS-ARC methods were found to be linearly correlated (r = 0.82). The mean of total fiber concentrations obtained by using the indirect transmission electron microscopy (TEM) method was 15.5 times the mean obtained by using the direct TEM method. The difference in concentrations determined by the two TEM methods resulted from disintegration of fiber bundles into single fibers during the ashing and ultrasonifying processes used in the indirect method. At least 83.5% of total fibers observed by TEM escaped detection by phase contrast microscopy.

Air Pollutants, Occupational↗