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Biomedical subjects

S W Chan

Publications and source records attributed to S W Chan.

At least 73 records · Page 4Linked to original sources
PubMed1981

Specific anti-thyroxine antisera induced by thyroxine sensitized liposomes.

Specific anti-thyroxine rabbit antisera were generated from complete Freund's adjuvant with liposomes consisting of sphingomyelin, cholesterol, dicetylphosphate and 5-N-thyroxine-2,4-dinitrophenyl-phosphatidylethanolamine (T4-Dnp-PE). Spin membrane immunoassay technique was used to measure the sensitivity and specificity of these antisera. Addition of 10 to 70 ng of L-thyroxine produced significant inhibition of immune lysis. Addition of L-3,3',5-triiodothyronine (T3) up to 800 ng showed no cross reaction.

Amines↗
PubMed1980

The effects of egg yolk diet on serum lipids, aortic atherosclerosis and connective tissue in male miniature pigs.

The effects of feeding an experimental diet consisting of 16.25% (w/w) dry powdered egg yolk and 30.8% total fat (20% from lard) was compared with an isocaloric amount of control (stock) regimen in male Hormel miniature pigs. The experimental diet was started at 30 weeks of age. The serum lipids (cholesterol and triglycerides) were determined at 5- week intervals until 55 weeks of age. At 55 weeks, the pigs were sacrificed and aortae evaluated for fatty streaks and atherosclerotic lesions. The ingestion of egg yolk diet resulted in hypercholesterolemia as the final serum fold over its initial value. Initial and final serum cholesterol levels of the controls were not statistically different. Triglyceride concentrations were nof influenced by an egg yolk regimen. It was observed that thoracic and abdominal atherogenesis was markedly increased in pigs fed the experimental diet as compared to the controls. No lesions were observed in the coronary arteries. There were no significant changes in the percent of collagen, elastin or C/E ratio in the thoracic and abdominal aortae as well as the coronary arteries. These results indicate that feeding miniature pigs an egg yolk : larg diet produced hypercholesterolemia, increased fatty streaking and atherosclerosis in the aortae.

Animals↗
PubMed1978

Spin membrane immunoassay: simplicity and specificity.

The many disadvantages of radioimmunoassay (RIA) have stimulated attempts to develop non-radioactive assays. These include spin immunoassay (SIA), which is simple, specific, and requires no separation procedures but is much less sensitive than RIA. The membrane immunoassay (MIA) described here is more sensitive than the SIA. Serum is prepared as for RIA. The MIA employs liposomes sensitized with epsilon-dinitrophenylated aminocaproyl phosphatidylethanolamine. It records liposome lysis induced by specific anti-Dnp antibodies, and complement which is monitored by the release of trapped spin labels (N-(2,2,6,6-tetramethylpiperidinyl-1-oxyl)-choline chloride). The sensitized liposomes are stable and give reproducible results for up to 4 weeks. The system's sensitivity is limited by the antibody's affinity (Ka approximately 10(8) M-1) rather than the sensitivity of the electron spin resonance spectrometer (approximately 1 X 10(-7) M). The inhibition of liposome lysis is hapten specific: (epsilon-Dnp-aminocaproic acid,epsilon-Dnp-lysine) greater than alpha-Dnp-glycine; o-nitroaniline and epsilon-dansyl-lysine are ineffective. Inhibition is quantitative without augmentation.

Animals↗
PubMed1977

Studies on the adrenal cortex of hypophysectomized rats: a model for abnormal cellular atrophy and death.

Biochemical and ultrastructural studies indicate that the atrophy of adrenal cortex in hypoyhysectomized rats involves the following changes: (1) One to two days after hypophysectomy, there is loss of "template activity" resulting from cumulative DNA-damage and heterochromatinization. In vivo ACTH-administration led to recuperation of these cells, indicating damage during hypophysectomized state to be reversible. (2) If the duration of hypophysectomy is prolonged, some of the cells become irreversibly damaged and can no longer recuperate after in vivo ACTH administration. (3) The period of most rapid cell death is from the third to seventh day after hypophysectomy. The cause of cell death is probably due to membrane damage in the absence of protein synthesis, leading to lysis of the cells. Lysozomes and macrophages are apparently not involved.

Adrenal Cortex↗
PubMed1977

Aging and ovarian steroidogenesis in the rat.

Ovaries obtained from rats of 4 and 18 mo of age were incubated in vitro with 3H-pregnenolone as the added precursor. Incorporation of radioactivity into progesterone (P), 20alpha-dihydroprogesterone (20alpha-P), 17alpha-hydroxyprogesterone (17alpha-OHP), androstenedione, and testosterone were studied by serial paper and thin-layer chromatography. Significantly more P, 17alpha-OHP and androgen was produced by the older ovaries. Addition of hCG (100 I.U.) to the incubate increased 20alpha-P production in the ovaries of both age groups, depressed 17alpha-OHP and androgen formation in the ovaries of older rats, and had no effect on progesterone synthesis in either age group. Serum progesterone in 4-mo-old rats was 13.5 +/- 1.91 ng/ml at estrus and 3.69 +/- 0.9 ng/ml at diestrus, whereas serum progesterone in 18-mo-old rats was 0.85 +/- 0.15 ng/ml at constant estrus and 1.23 +/- 0.54 ng/ml at constant diestrus. Treatment with hCG for 20 days increased serum progesterone to 29.6 ng/ml in young rats and to 4.21 +/- 2.0 ng/ml in older rats. Shorter treatments were less effective. These data reveal a definite change in steroidogenic competence in older rat ovaries.

Age Factors↗
PubMed1977

Placental steriodogenesis in the rat: comparison of normal and giant placentae.

Placental hypertrophy was induced in pregnant rats by daily treatment with estrone (0.5 microng) and progesterone (4 mg) from day 3 through 19 combined with ovariectomy on day 12 of pregnancy. The ratio of basal zone to whole placenta was 47% by weight in these enlarged placentae on day 20 of pregnancy but only 34% in normal placentae. In each case, the basal zone tissue was homogenized and the 10,000 x g supernatant fraction was used for in vitro incubation with [7alpha-3H]pregnenolone as the added substrate. The normal placental tissue synthesized more progesterone and testosterone but less androstenedione and 5alpha-pregnane-3,20-dione than the giant placentae. Utilization of the pregnenolone substrate by the giant placentae was subnormal. Addition of 200 IU of human chorionic gonadotropin (hCG) in vitro to normal basal zone placentae sharply increased the production of progesterone, 17alpha-hydroxyprogesterone, androstenedione and 5alpha-pregnane-3,20-dione. The giant placentage failed to respond to hCG. Thus, steroid-induced hypertrophied placentae in rats do not participate in a compensatory mechanism for steroid hormone production toward pregnancy maintenance.

Androstenedione↗
PubMed1975

Placental steroidogenesis in the rat: progesterone production by tissue of the basal zone.

Previous reports suggested that the rat placenta had a rather limited capacity for steroidogenesis, particularly with respect to progesterone production. We found that the basal zone in the rat placenta, which contains the steroidogenic giant cells, can be isolated by simple surgical separation, and using them for in vitro incubations, significant conversion of pregnenolone-7 alpha-3H to progesterone-1H could be demonstrated. The 5alpha-reduced metabolites of progesterone, as well as compounds of the delta4 pathway, including 17alpha-hydroxyprogesterone, androstenedione and testosterone were also isolated and characterized. When progesterone-7alpha-3H was added as precursor, most of it remained unmetabolized, but qualitatively identical products were isolated as were found when pregnenolong-7alpha-3H was used as precursor. Incubations of the whole placenta and of labyrinth tissue yielded relatively much lower progesterone-3H from pregnenolone-7alpha-3H. Our results have thus established that the rat placenta is a steroidogenic organ, just as in many other species. Past difficulties in isolating progesterone from in vitro studies may possibly be due to the intense activity of the enzyme 5alpha-reductase when the whole placenta was used.

Androstenedione↗