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Biomedical subjects

T H Chen

Publications and source records attributed to T H Chen.

At least 145 records · Page 8Linked to original sources
PubMed1992

[Extent of surgical resection for early carcinoma of the uterine cervix].

124 patients suffering from early carcinoma of uterine cervix treated by total hysterectomy are reported. Fifty-five (44%) patients had carcinoma in situ (Stage 0), 62 (50%) had Stage Ia and 7 (5.6%) Stage Ib lesions. All were treated by total hysterectomy. The 5-year survival rate was 97.6%. The authors believe that early lesion of carcinoma of uterine cervix having involvement within 2 cm and invasion to a depth of not more than 5 mm are curable by total hysterectomy without lymphatic dissection.

Adult↗
PubMed1992

Placement practices in specialized foster homes and small group homes for persons with mental retardation.

Resident functional and personal characteristics (e.g., gender, race, age, and level of mental retardation), placement histories, and projected placements of a nationally representative sample of 336 persons with mental retardation living in a total of 181 small, specialized foster care homes and group homes with 6 or fewer residents were compared. In addition, the extent to which resident characteristics differentiate between persons placed in specialized foster care homes or small group homes was assessed. Results indicate that there are some differences in resident characteristics across facility type, including communication and toileting skills, age, and mobility. Overall, results showed that small foster and group homes successfully serve a variety of people and that placement generally lasts for several years.

Activities of Daily Living↗
PubMed1991

Unlabeled hemoglobin adducts of 4,4'-methylenebis (2-chloroaniline) in rats and guinea pigs.

The capacity of N-oxidized metabolites of 4,4'-methylenebis(2-chloroaniline) (MBOCA) to form hemoglobin (Hb) adducts was determined in vitro, and the formation of Hb adducts following in vivo administration of MBOCA was assessed with or without prior induction of cytochrome P-450 enzymes with phenobarbital or beta-naphthoflavone. Hb adduct formation was determined by electron-capture GLC of MBOCA as the heptafluorobutyryl derivative following mild acid hydrolysis of protein-bound MBOCA. The method was confirmed by gas chromatography-mass spectrometry with selected ion monitoring. N-hydroxy- and mononitroso-MBOCA, but not MBOCA itself, formed adducts to rat and human Hb in vitro in a dose-related manner. Binding was inhibited by cysteine and glutathione but not oxidized glutathione or methionine. Intravenous administration of as little as 0.04 mumol/kg N-hydroxy-MBOCA to rats resulted in measurable formation of MBOCA-Hb adducts (0.9 ng/50 mg Hb). Intraperitoneal administration of 0.5-50 mg/kg MBOCA to rats, and subcutaneous administration of 5-500 mg/kg MBOCA to rats and 4-100 mg/kg to guinea pigs resulted in dose-related formation of Hb adducts. MBOCA-Hb remained elevated in blood for greater than 10 weeks following a single subcutaneous dose in guinea pigs. Pretreatment of rats with phenobarbital induced microsomal benzphetamine N-demethylase (BND) activity and resulted in a small increase in in vitro N- and ortho-hydroxylation of MBOCA, but did not increase in vivo Hb adducts.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1991

Photoperiod control of poplar bark storage protein accumulation.

Bark storage proteins (BSPs) accumulate in the inner bark parenchyma of many woody plants during autumn and winter. We investigated the effect of a short-day (SD) photoperiod on the accumulation of the 32-kilodalton bark storage protein of poplar (Populus deltoides Bart. ex Marsh.) under controlled environmental and natural growing conditions. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis and protein gel blot analysis revealed that 10 days of SD exposure (8 hours of light) resulted in a 20% increase in the relative abundance of the 32-kilodalton bark storage protein of poplar. After 17 days of SD exposure, the 32-kilodalton bark storage protein accounted for nearly one-half of the soluble bark proteins. In natural field conditions, accumulation of the 32-kilodalton bark storage protein was observed to start by August 18 (daylength 14.1 hours). Immunoprecipitation of in vitro translation products with anti-BSP serum revealed that the SD protein accumulation was correlated with changes in the pool of translatable mRNA. A survey of poplar clones from different geographic origins revealed the presence of the 32-kilodalton BSP in the dormant bark of all the clones tested. These results demonstrate that a SD photoperiod induces, whether directly or indirectly, rapid changes in woody plant gene expression, leading to the accumulation of BSP.

Journal Article↗
PubMed1991

Circadian Rhythm in Amino Acid Uptake by Synechococcus RF-1.

In the prokaryote Synechococcus RF-1, circadian changes in the uptake of l-leucine and 2-amino isobutyric acid were observed. Uptake rates in the light period were higher than in the dark period for cultures entrained by 12/12 hour light/dark cycles. The periodic changes in l-leucine uptake persisted for at least 72 hours into continuous light (L/L). The rhythm had a free-running period of about 24 hours in L/L at 29 degrees C. A single dark treatment of 12 hours could initiate rhythmic leucine uptake in an L/L culture. The phase of rhythm could be shifted by a pulse of low temperature (0 degrees C). The free-running periodicity was "temperature-compensated" from 21 to 37 degrees C. A 24 hour depletion of extracellular Ca(2+) before the free-running L/L condition reduced the variation in uptake rate but had little effect on the periodicity of the rhythm. The periodicity was also not affected by the introduction of 25 mm NaNO(3). The uptake rates for 20 natural amino acids were studied at 12 hour intervals in cultures exposed to 12/12 hour light/dark cycles. For eight of these amino acids (l-Val, l-Leu, l-Ile, l-Pro, l-Phe, l-Trp, l-Met, and l-Tyr), the light/dark uptake rate ratios had values greater than 3 and the rhythm persisted in L/L.

Journal Article↗
PubMed1990

Circadian Rhythm of the Prokaryote Synechococcus sp. RF-1.

The prokaryotic Synechococcus sp. RF-1 exhibited a nitrogen fixation circadian rhythm with characteristics remarkably similar to the circadian rhythm of eukaryotes. The rhythm had a free-running period of about 24 hours when the length of the preen-trained cycle did not differ too much from 24 hours, and it was insensitive to changes in temperature from 22 degrees C to 33 degrees C. Because the endogenous rhythm of nitrogen fixation was not affected by a phase-shift of its previous cycles, the circadian rhythm in Synechococcus sp. RF-1 was not considered to be controlled simply by a feedback mechanism.

Journal Article↗
PubMed1990

Water Content during Abscisic Acid Induced Freezing Tolerance in Bromegrass Cells.

Changes in water content and dry weight were determined in control cells and those induced to cold harden in response to abscisic acid (ABA) treatment (7.5 x 10(-5) molar). Bromegrass (Bromus inermis Leyss cv Manchar) cells grown in suspension culture at room temperature (23 degrees C) for 7 days acclimated to -28 degrees C (LT(50)) when treated with ABA, or to -5 degrees C when untreated. ABA significantly reduced cell growth rates at 5 and 7 days after treatment. Growth reduction was due to a decrease in cell number rather than cell size. When the cell water content was expressed as percent water (percent H(2)O) or as grams water per gram dry weight (gram H(2)O/gram dry weight [g DW]), the water content of hardy, ABA-treated cells decreased from 85% to 77% or from 6.4 to 3.3 g H(2)O/g DW in 7 days. Control cell water content remained static at approximately 87% and 7.5 g H(2)O/g DW. However, cell water content, expressed as milligrams water per million cells (milligram H(2)O/10(6) cells), did not differ in ABA-treated or control cells. The dry matter content of ABA-treated cells, expressed as milligram DW/10(6) cells increased to 3.3 milligram/10(6) cells in 7 days, whereas the dry weight of the control cells remained between 1.4 to 2.1 milligrams/10(6) cells. The osmotic potential of ABA-treated cells decreased by the fifth day while that of control cells increased significantly and then decreased by day 7. Elevated osmotic potentials were not associated with increased ion uptake. In contrast to much published literature, these results suggest that cell water content does not decrease in ABA-treated cells during the induction of freezing tolerance, rather the dry matter mass per cell increased. Cell water content may be more accurately expressed as a function of cell number when accompanying changes to dry cell matter occur.

Journal Article↗
PubMed1990

Regeneration of Freezing-Tolerant Spring Wheat (Triticum aestivum L.) Plants from Cryoselected Callus.

A cryoselection protocol has been developed that provides freezing-tolerant callus that, in turn, can regenerate plants with enhanced cold hardiness. Tolerant calli were selected from spring wheat (Triticum aestivum L.) callus by immersion in liquid nitrogen without addition of cryoprotectants. Less than 15% of the calli survived the initial challenge, whereas 30 to 40% of previously selected calli survived subsequent exposure. Seed progeny from five of 11 regenerant (R2) lines tested exhibited significantly enhanced tolerance to freezing at -12 degrees C. Thus, cryoselection appears to involve at least in part, selection for genetic rather than epigenetic variants. Analysis of one callus line indicated that cryoselection did not induce significant alterations in lipid composition, adenylate energy charge, or freezing point. An increase in the soluble sugar component was detected. Changes were also detected in the protein complement of microsomal membrane and soluble protein extracts of cryoselected callus. In all, seven unique proteins ranging from 79 to 149 kilodaltons were identified. The results demonstrate that freezing tolerant callus can be isolated from a heterogeneous population by cryoselection, and factors that contribute to hardiness at the callus level are biologically stable and can contribute to tolerance at the whole plant level.

Journal Article↗
PubMed1990

Effects of protein kinase C activation on inositol phosphate generation and intracellular Ca2+ mobilization in bovine parathyroid cells.

Activators of protein kinase C, such as phorbol myristate acetate (PMA) and the synthetic diacylglycerol dioctanoylglycerol (diC8), either stimulate or inhibit PTH release depending on the extracellular Ca2+ concentration. By increasing PTH release at high extracellular Ca2+, these agents, in effect, block high Ca2(+)-induced inhibition of secretion. Since raising extracellular Ca2+ increases intracellular free Ca2+ ([Ca2+]i) and inositol trisphosphate (InsP3) formation in parathyroid cells, we assessed the effects of PMA pretreatment on [Ca2+]i and InsP3 to ascertain whether these second messengers might be altered by protein kinase C activation. Preincubation of parathyroid cells with PMA (10(-6) M) significantly lowered the intracellular Ca2+ response to raising extracellular Ca2+ from 0.5-2.0 mM. The peak increase in [Ca2+]i averaged 475 +/- 11 nM in PMA-treated cells compared to 703 +/- 44 nM in control cells. High extracellular Ca2(+)-induced InsP3 accumulation was also reduced after incubating the cells with PMA. To determine whether intracellular Ca2+ stores and/or transmembrane Ca2+ uptake were affected by activating protein kinase C, we examined intracellular Ca2+ responses to the Ca2+ ionophore ionomycin after PMA pretreatment. At 0.5 mM Ca2+, ionomycin (10(-6) M) increased [Ca2+]i to an initial peak of 738 +/- 49 nM followed by a sustained increase to 501 +/- 30 nM in control cells (n = 15). After exposure to PMA (greater than or equal to 20 min), however, peak and sustained increments in [Ca2+]i were significantly lower at 550 +/- 32 and 394 +/- 16 nM, respectively (P less than 0.02, n = 8). In the absence of extracellular Ca2+, basal [Ca2+]i was 197 +/- 5 and peaked at 323 +/- 15 nM with ionomycin (10(-6) M) in PMA-treated cells (n = 16). The latter value was significantly less than the peak increase in [Ca2+]i to 461 +/- 19 nM observed with ionomycin (10(-6) M) in control cells (P less than 0.001, n = 15). With respect to secretion, either of the protein kinase C agonists (i.e. PMA or diC8) or the Ca2+ ionophore ionomycin inhibited PTH release at 0.5 mM Ca2+. To determine whether the concomitant activation of protein kinase C- and Ca2(+)-dependent pathways could additively suppress PTH release, we assessed the effects of ionomycin and either PMA or diC8 on secretion. PTH release at 0.5 mM Ca2+ was reduced in an additive manner by either of these protein kinase C agonists plus ionomycin. At 2 mM Ca2+, protein kinase C agonists stimulated PTH release.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1990

Dynamic modelling of the growth of a surface fungal colony.

The growth of a surface fungal colony in the three-dimensional space was modeled kinetically. The present analysis led to the conclusion that the radius of a fungal colony increases exponentially in the initial period followed by a constant increase in its radius at large times. This is justified by analyzing the available experimental data. The elevation of a fungal colony was limited by a balance of the transport of protoplasm inside a growing hyphae and a maintenance factor. A numerical simulation revealed that a typical fungal colony had a disk-shaped base with a flat top and a side face generated by rotating a concave upward curve about a vertical axis.

Fungi↗
PubMed1990

The role of atrial natriuretic factor in dehydration and schedule-induced drinking behaviour.

Dehydration-induced drinking (DID) has been defined as a type of homeostatic behaviour controlled by factors related to water balance, whereas schedule-induced polydipsia (SIP) is considered to be a type of nonhomeostatic drinking subsequent to a general increase in motor excitability. In this study, we have attempted to assess the role of atrial natriuretic factor (ANF) in both models to elucidate the mechanisms controlling water intake. Intracerebroventricular injection of ANF (2-8 nmol) caused a dose related suppression of water intake in both DID and SIP, but intravenous injection with a higher dose of ANF (8 nmol) produced a significant suppression of water intake only in DID. Before drinking started, tissue ANF levels increased in atria in both models and decreased in hypothalamus in DID but not in SIP. After 1 hour of drinking, ANF levels decreased in atria in both models and increased in hypothalamus in SIP but not in DID. These results suggest that DID and SIP are different in their thirst regulation, and that the notion that peripheral ANF serves as a humoral factor sending signals to central in the fluid homeostatic control mechanism is questionable.

Animals↗
PubMed1989

Pediatric burns--2 year survey of cases admitted to the Chang Gung Memorial Hospital.

A total of 722 patients were admitted to the Burn Unit of Chang Gung Memorial Hospital over a 2-year period, of these 285 (39.5%) were under 15 years of age. The major cause of pediatric burns was scalding, 236 (82.8%). Most of the patients under age of 15 years had total burn surface under 20% (199 patients, 70%), and were discharged from the hospital within one month (263 patients, 91%). Treatments included debridement done in 98 patients (41.5%) and skin grafting in 81 patients (28%). Oxacillin-Resistant Staphylococcus Aureus infections were the most common complication (5.3%). The mortality rate was 5.3%.

Adolescent↗
PubMed1989

On the dissociation constants of BAPTA-type calcium buffers.

We have determined or redetermined the calcium dissociation constants of seven BAPTA-type buffers with KD's in the range from 0.4 microM to about 20 mM in 300 mM KCl. These include four newly synthesized ones: 5-nitro BAPTA; 5,5'-dinitro BAPTA; 5-methyl-5'-nitro BAPTA; and 5-methyl-5'-formyl BAPTA. Moreover, we tabulate dissociation constants or KD's for BAPTA and eleven BAPTA-type buffers, compare most of them with an empirical curve based upon so-called Hammett values, and predict KD's for several still unsynthesized but potentially valuable buffers.

Buffers↗
PubMed1989

Calcium buffer injections block fucoid egg development by facilitating calcium diffusion.

The polarity of fucoid eggs is fixed either when tip growth starts or a bit earlier. A steady flow of calcium ions into the incipient tip is thought to establish a high calcium zone that is needed for its localization and formation. To test this hypothesis, we have injected seven different 1,2-bis(o-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid (BAPTA)-type calcium buffers into Pelvetia eggs many hours before tip growth normally starts. Critical final cell concentrations of each buffer prove to block outgrowth (as well as cell division) for up to 2 weeks. This critical inhibitory concentration is lowest for two buffers with dissociation constants or Kd values of 4-5 x 10(-6) M and increases steadily as the buffers' Kd values shift either below or above this optimal value to ones as low as 4 x 10(-7) M or as high as 9.4 x 10(-5) M. To analyze these results, we have derived an equation (based on the concept of facilitated diffusion) for the effects of diffusable calcium buffers on steady-state calcium gradients. The data fit this equation quite well if it is assumed that cytosolic free calcium at the incipient tip is normally kept at about 7 microM and, thus, far above the general cytosolic level.

Buffers↗
PubMed1989

The effects of protein kinase-C agonists on parathyroid hormone release and intracellular free Ca2+ in bovine parathyroid cells.

High extracellular Ca2+ stimulates the accumulation of inositol trisphosphate and diacylglycerol in parathyroid cells and suppresses PTH release. Since diacylglycerol is an endogenous activator of protein kinase-C, these observations would suggest that activation of protein kinase-C is associated with inhibition of PTH release. However, phorbol esters, which stimulate protein kinase-C activity, have been reported to enhance PTH release. To clarify the role of protein kinase-C in the regulation of PTH secretion, we studied the responses of parathyroid cells to phorbol myristate acetate (PMA), bryostatin-1, and 1,2-dioctanoylglycerol (diC8). PMA and bryostatin-1 translocated protein kinase-C activity from the soluble to particulate fractions of cell homogenates. Phosphotransferase activity in the particulate fractions increased from 21 +/- 4% to 93 +/- 6% of the total activity after 10 min of exposure to PMA (10(-6) M) and from 21 +/- 2% to 69 +/- 2% after 5 min of exposure to bryostatin-1 (10(-7) M). These three structurally different agonists of protein kinase-C also altered the typical secretory response to Ca2+ in parathyroid cells. At 2.0 mM extracellular Ca2+, PMA (10(-6) M) bryostatin-1 (10(-7) M), and 1,2-dioctanoylglycerol (3 x 10(-4) M) blunted the suppressive effects of high Ca2+ on secretion, thus stimulating PTH release 252 +/- 45%, 122 +/- 20%, and 485 +/- 95% over control levels, respectively. However, at low extracellular Ca2+, these agents inhibited maximal PTH release. Since changes in the intracellular free Ca2+ concentration ([Ca2+]i) may be important in the control of PTH release, we investigated whether protein kinase-C agonists changed the relationship between extracellular Ca2+ and PTH release by affecting [Ca2+]i. In PMA-treated cells, the intracellular Ca2+ response to raising extracellular Ca2+ from 0.5 to 1.5 and 2.0 mM was reduced to 50 +/- 1% and 63 +/- 3% of that in control cells, respectively (P less than 0.005; n = 7-11). Specifically, PMA preincubation reduced the initial intracellular Ca2+ transient with raising extracellular Ca2+ from 0.5 to 2.0 mM and with adding 4.0 mM Sr2+. The sustained phase response to high Ca2+, but not to Sr2+, was also attenuated after incubation with PMA. We conclude that protein kinase-C agonists suppress PTH release at low extracellular Ca2+ and enhance PTH release at high extracellular Ca2+. The effects on secretion at high extracellular Ca2+ may be related to the ability of protein kinase-C agonists to change the sensitivity of [Ca2+]i to high extracellular Ca2+ in these cells.

Animals↗
PubMed1988

Strain difference in galactokinase level and susceptibility to the teratogenic effect of dietary galactose in mice: I. Teratogenic and embryopathic effect.

Congenital cataracts have been noted to occur in infants when either the mother or the mother and infant have reduced activity of the enzymes galactokinase (GK) or galactose-1-phosphate uridyl transferase (GALT). Studies were undertaken to elucidate the possible genetic and dietary fetomaternal interactions leading to the presumptive galactose teratogenesis noted in two inbred strains of mice differing in GK activity. Pregnant A/J (high erythrocyte GK activity 134.18 +/- 17.89 mU/gm Hb) and C57BL/6J (low erythrocyte GK activity 55.05 +/- 11.39 mU/gm Hb) mice were treated with a diet containing either 25% or 50% galactose throughout gestation. A significantly higher percentage of C57BL offspring (92.3%) were observed to have lens opacities when their mothers were fed a high-galactose diet, whereas no increase in lens pathology was observed in the offspring of similarly treated A/J mothers. Additionally, reciprocal matings were carried out so that all offspring were genetically equivalent in terms of GK activity. However, when the mother had low GK activity, a significant incidence of lens opacities was present in their offspring; this was not found when the mother had high GK activity. After weaning, no difference in the incidence of lens opacities was observed when the 25% galactose diet was introduced to the offspring of these reciprocal crosses, providing additional support for a maternal dietary influence on the development of lens opacities.

Animals↗
PubMed1987

Streptococcal protein G-gold complex: comparison with staphylococcal protein A-gold complex for spot blotting and immunolabeling.

Protein G, a cell wall protein isolated from human group G streptococci strain G148, binds in a similar manner as protein A from Staphylococcus aureus to the Fc portion of IgG molecules. Indeed, protein G has been proposed as a superior Fc binding protein due to its broader species reactivity. Thus, we have prepared a complex of protein G with particles of colloidal gold and determined its applicability for spot-blot analysis and postembedding immunolabeling by comparing it with protein A-gold complex. By spot-blot analysis no difference in binding of protein G-gold or protein A-gold to IgG molecules from a whole spectrum of animal species was observed. Moreover, using rabbit, sheep, or goat anti-rat albumin antibodies to detect nitrocellulose-immobilized rat albumin or antigenic sites in paraffin and Lowicryl K4M thin sections from rat liver, no difference was found with protein G-gold or protein A-gold. Similarly, no difference in binding to protein G-gold or protein A-gold was observed with a battery of monoclonal antibodies. However, in contrast to expectations, protein A-gold reacted well with both sheep and goat IgG molecules; indeed, for the light and electron microscopic localization of albumin with sheep or goat antibodies it was as efficient as protein G-gold. These results demonstrate, therefore, that both protein G-gold and protein A-gold are useful second step reagents for immunolabeling and that protein G-gold was not a superior probe in the systems tested.

Albumins↗