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Biomedical subjects

T Nguyen

Publications and source records attributed to T Nguyen.

At least 415 records · Page 23Linked to original sources
PubMed1985

Analyses of vegetables from the highlands of Papua New Guinea.

Ten vegetable foods of the highlands were analysed for crude protein, amino acids and trypsin inhibitor. Pandanus nut, lima bean, fern, greens, pitpit and choko had good to acceptable crude protein contents and the proteins of fern, pitpit, Rungia klossii and Indian mustard were of good quality. Lima beans had a very high content of trypsin inhibitor and all others had small or zero amounts, including fern, which is used at pig feasts and hence does not contribute to pig bel.

Amino Acids↗
PubMed1984

Mechanisms of glucocorticoid hormone action.

This work summarizes some of our studies of the mechanisms of glucocorticoid action, including aspects of steroid binding to receptors, the activation of glucocorticoid-receptor complexes and the regulation of expression of endogenous and transferred glucocorticoid-responsive genes. Studies of the receptor-steroid interaction support the notion that steroid entry is passive. A comparative analysis of binding in isolated cytosol and intact cells suggests that the initial receptor-steroid binding reaction and not subsequent steps such as activation and nuclear binding, is predominantly responsible for the high-affinity state that is generated. The binding is driven by entropy and enthalpy changes at low temperature; at higher temperatures it is driven by entropy changes, with enthalpy working against it. Studies of the activation of the receptor-glucocorticoid complex with the use of highly purified receptors suggest that this step is associated with a change in charge of the receptor-glucocorticoid complex (such as would occur with a dephosphorylation reaction), whereas the data do not support the notion that dissociation of a bound RNA or of receptor oligomers is responsible for generating the nuclear- and DNA-binding activity of the complex. Studies of the regulation by glucocorticoids of expression of the endogenous rat growth hormone (rGH) gene in cultured rat pituitary tumor (GC, GH3D6) cells suggest that glucocorticoids increase the expression of this gene by multiple mechanisms. First, there is a modest direct stimulation of transcription by a mechanism(s) that does not depend on protein synthesis; however, if the cells have been exposed to thyroid hormone for several hours, the steroid exerts a much greater increase in rGH pre-mRNA levels. Secondly, the steroid appears to stimulate some relatively stable function or functions that increase the ability of thyroid hormone to increase rGH levels. Thirdly, the steroid probably increases rGH mRNA stability, since the fold-increases in rGH mRNA exceed those of transcription. Finally, the steroid may, by unknown mechanisms, affect rGH mRNA polyadenylation. The gene transfer experiments utilized the rat and human (h) GH genes and hybrid genes containing either rGH and Herpes Simplex virus thymidine kinase (TK) gene sequences or the human metallothionein-IIA (hMT-IIA) and TK gene sequences. The steroid was found to regulate hMT-IIA gene expression in all glucocorticoid-responsive cell types tested by actions on its 5'-flanking DNA. By contrast, the glucocorticoid regulated GH gene expression in some but not all glucocorticoid-responsive cell types.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1984

Drug distribution in solid tissue of the brain following chronic local perfusion utilizing implanted osmotic minipumps.

Surgically implanted osmotic minipumps were used to apply dye or [3H]-muscimol locally to the nucleus ventralis lateralis or globus pallidus of the cat. Extent of distribution of dye or radioactivity was measured from the site of application. A uniform distribution (1.2-2.5 mm) of dye or radioactivity was found lateral, ventral, and posterior to the perfusion site. Distribution dorsal to the perfusion site (2.5-7.5 mm) is complicated by infiltration into areas damaged by the implanted cannula. Anterior distribution (approximately 5 mm) was extensive, apparently as a result of the dye or labeled compound entering major tracts or projection pathways. This study demonstrates that with the appropriate precautions, distribution of drug following perfusion into solid tissue of the brain can be restricted to a localized area. However, our results also suggest that the neuroanatomical features of the chosen area (and surrounding area) may play a significant role in altering the pattern and extent of drug distribution.

Animals↗
PubMed1983

Modulation of myocardial cyclic AMP and vulnerability to fibrillation in the rat heart.

In the isolated rat heart, changes in the ventricular fibrillation threshold (VFT) relate to the myocardial cyclic AMP content rather than to the high-energy phosphate content. After coronary ligation the reduction in VFT correlates with the increase in ischemic tissue cyclic AMP. Agents that reduce the myocardial cyclic AMP (propranolol, 16 microM in perfusate, or amiodarone, 42 microM/kg pretreatment) prevent the postligation fall of the VFT without altering high-energy phosphate depletion. Conversely, theophylline (500 microM), which increases cyclic AMP in ischemic myocardium, causes a greater reduction of VFT without increasing high-energy phosphate depletion. Spontaneous ventricular tachycardia and fibrillation are uncommon in coronary ligated hearts in the first 15 min after ligation (10-20%); these arrhythmias are greatly increased either by reducing the perfusate potassium from 5.9 to 3.0 mM or by pretreating hearts with 1-methyl-3-isobutyl xanthine (10 microM), a cyclic-AMP phosphodiesterase inhibitor. Adenosine (100 microM) antagonizes the increased arrhythmogenesis in both low perfusate potassium and cyclic-AMP phosphodiesterase-inhibited hearts, in the latter without reducing the ischemic tissue cyclic AMP levels. The antiarrhythmic action of adenosine in these hearts is independent of reducing tissue cyclic AMP. Adenosine generated in ischemic myocardium may serve as an endogenous antagonist to the arrhythmogenic action of cyclic AMP.

Adenosine↗
PubMed1983

Antiarrhythmic action of labetalol and its effect on adenine metabolism in the isolated rat heart.

Labetalol, a combined alpha- and beta-adrenergic antagonist, was assessed for antiarrhythmic activity in the isolated perfused rat heart. Inclusion of 5.0 and 7.5 mumol/liter labetalol in the perfusate reduced the fall in ventricular fibrillation threshold and eliminated ventricular arrhythmias during the coronary occlusion period of 15 minutes. In treated hearts, levels of high energy phosphates were significantly higher and lactate, adenosine and hypoxanthine levels were lower in ischemic myocardium. Cyclic adenosine monophosphate levels were reduced in uninvolved myocardium (0.31 +/- 0.01 and 0.24 +/- 0.02 versus 0.43 +/- 0.02 nmol/g fresh weight) and in the ischemic myocardium (0.38 +/- 0.02 and 0.34 +/- 0.04 versus 0.65 +/- 0.05 nmol/g) in hearts treated respectively with 5.0 and 7.5 mumol/liter labetalol versus control hearts. When untreated hearts were perfused with 3.0 mmol/liter potassium in perfusate, all had ventricular tachycardia or fibrillation during coronary ligation and developed ventricular fibrillation after reperfusion. Labetalol, 5.0 mumol/liter, reduced ventricular tachyarrhythmias during coronary occlusion and after reperfusion, whereas labetalol, 7.5 mumol/liter, eliminated tachyarrhythmias during occlusion and reperfusion. Labetalol had potent antiarrhythmic activity in the hearts rendered uniformly prone to arrhythmias by perfusion with a low potassium solution.

Adenine↗
PubMed1983

Soybean nodulin genes: Analysis of cDNA clones reveals several major tissue-specific sequences in nitrogen-fixing root nodules.

Plant gene products that could play a role in the process of symbiotic nitrogen fixation in leguminous plants were detected by screening a cDNA library prepared from soybean nodule poly(A)(+) RNA. About 13% of the 5,700 clones screened contained sequences detectable with a root cDNA probe while about 2,100 clones (37% of the library) contained sequences that were detectable only with nodule cDNA. Five unique sequence species, accounting for more than half of the 2,100 nodule-specific clones, were identified by cross-hybridization experiments. The most abundant species, represented by 860 clones, encodes the well-characterized protein, leghemoglobin (Lb). The other four species, designated NodA, NodB, NodC, and NodD, are represented by 350, 55, 61, and 6 clones, respectively. Each of these four species was found to be encoded by the plant nuclear genome at low copy number. The transcripts corresponding to the nodule-specific clones represented 12-15% (Lb), 6% (NodA), and 0.5-1.1% (NodB, NodC, and NodD) mole fraction of nodule polysomal mRNAs but could not be detected in root polysomal RNA. Hybrid-selection of nodule mRNAs by representative clones and in vitro translation indicated that polypeptides of M(r) 44,000, 27,000, 24,000, and 100,000-120,000 are encoded by NodA, NodB, NodC, and NodD sequences, respectively. These polypeptides reacted with antiserum prepared against total soluble nodule proteins suggesting that the cloned sequences encode nodule-specific proteins, nodulins.

Journal Article↗
PubMed1983

Dopamine stimulates somatostatin release from perifused hypothalamic cells.

We studied the release of immunoreactive somatostatin (IR-SRIF) from hypothalamic cells that were obtained from rats and dispersed with the aid of collagenase. Twenty-four hours after dispersion, cells were placed in a column supported by a matrix of preswollen Biogel P2 and perifused. Fractions were collected on ice and subsequently assayed for SRIF. SRIF release was stimulated markedly by potassium depolarization (KCl, 56 mM), by the Na+-K+-ATPase inhibitor ouabain (10(-4) M), and by dopamine at concentrations as low as 10(-11) M. The stimulatory effects of membrane depolarization were calcium dependent and were not observed in the absence of exogenous calcium in the perifusion medium or in the presence of EDTA (0.05 M). Metoclopramide, the dopamine antagonist, abolished the stimulatory effect of dopamine. In conclusion, release of IR-SRIF by dispersed rat hypothalamic cells can be studied in a simple perifusion apparatus. Release is stimulated by membrane depolarization in a calcium-dependent manner and by dopamine at physiological concentrations.

Animals↗
PubMed1982

Lipoprotein quantification: an electrophoretic method compared with the Lipid Research Clinics method.

We compared a turbidimetric electrophoretic method (Lipidophor) for lipoprotein quantification with the standardized Lipid Research Clinics (LRC) method. In the Lipidophor procedure, major lipoproteins are separated by electrophoresis on agarose gels, precipitated on the gels with phosphotungstate-Mg2+ reagent, and the resulting turbidity is measured densitometrically. Measurements of relative turbidity were converted into lipoprotein cholesterol values by the use of numeric constants provided by the manufacturer. Among-day CVs (n = 46) for the Lipidophor method were 6.0%, 3.6%, and 9.9% for cholesterol in the alpha-, beta-, and pre-beta lipoproteins, respectively. The Lipidophor alpha-cholesterol was significantly lower (n = 171 specimens) than the LRC high-density lipoprotein (HDL) cholesterol (514 vs 586 mg/L), and beta-cholesterol was significantly higher than the corresponding LRC low-density lipoprotein (LDL) cholesterol values (1505 vs 1409 mg/L). The linear relation between the two methods for lipoprotein cholesterol quantification is as follows: Lipidophor alpha = 0.77 LRC HDL + 63 mg/L with correlation coefficient (r) of 0.87; Lipidophor beta = 0.95 LRC LDL + 166 mg/L (r = 0.96); Lipidophor pre-beta = 0.57 LRC very-low-density lipoprotein + 39 mg/L (r = 0.82). We derived a revised algorithm for estimating lipoprotein cholesterol from turbidity measurements. Lipoprotein cholesterol values by the Lipidophor method agree well with those obtained by the LRC method when these constants are used.

Adult↗
PubMed1978

An insect cell line persistently infected with a baculovirus-like particle.

A persistent infection by a baculovirus-like particle was found in the established lepidopteran (Heliothis zea) cell line, IMC-HZ-1. The virus caused CPE in less than 1% of the IMC-HZ-1 cells, as measured by phase-contrast and electron microscopy. Transmission tests showed that four lepidopteran cell lines were susceptible to the persistent virus (designated as IMC-HZ-I-NOV). In inoculated TN-368 cell cultures, 90--100% infection was achieved. The ultrastructure and development of IMC-HZ-I-NOV in cell cultures were similar to known baculoviruses, and it is probable that this persistent virus is a member of the family Baculoviridae. Two lepidopterous species (Estigmene acrea and H. zea) inoculated with IMC-HZ-1-NOV by intrahemocoelic injection and/or per os feeding of larvae were not susceptible.

Cell Line↗
PubMedDate not supplied

Effects of smoking, alcohol, and drugs of abuse on the outcome of "expectantly" managed cases of preterm premature rupture of membranes.

We evaluated the outcome of pregnancies complicated by preterm premature rupture of membrane (PROM) in order to determine if tobacco, alcohol, or illicit drug usage were associated with alterations in pregnancy or neonatal outcome. Comparisons in outcome were made with respect to tobacco, alcohol, and/or illicit drug usage. Comparisons were made with gestational age (GA) of PROM, GA of delivery, latency period (LP), maternal age, initial cervical exam (by speculum), age, race, tocolytic use, chorioamnionitis, and birthweight. Student's t-test, Mann-Whitney test, and Chi-square analysis were used to evaluate for significant differences (significance set at P < 0.05). A total of 119 charts were evaluated. Differences were noted with respect to smokers vs. nonsmokers for latency period (6.0 days vs. 9.4 days, P < 0.03), age (29.1 years vs. 24.8, P < 0.001), and gravidity (4.2 vs. 2.8, P < 0.005). Differences were noted for use of alcohol and age (29.9 vs. 25.2, P < 0.006). Differences were also noted for the use of illicit drugs and the following variables: age (30.0 vs. 24.9, P < 0.001), gravidity (4.7 vs. 2.5, P < 0.006), latency (6.2 vs. 9.0, P < 0.009), and parity (2.6 vs. 1.2, P < 0.01). A difference was noted with respect to cocaine and latency period (5.8 vs. 9.0, P < 0.01), age (31.2 vs. 24.8, P < 0.001), gravidity (4.8 vs. 2.9, P < 0.01), and parity (2.6 vs. 1.2, P < 0.03), and the use of tocolytics (22% vs. 55.4%, P < 0.02). These relationships held after multivariate analysis was performed. There were no associations among use of tobacco, alcohol, drugs of abuse, or cocaine and respiratory distress syndrome, intraventricular hemorrhage, or necrotizing enterocolitis. The use of tobacco during pregnancy appears to shorten the latency period in pregnancies complicated by PROM. Cocaine abuse also appears to shorten the latency period. These shortened latency periods could potentially contribute to increased neonatal morbidity. Larger studies evaluating this are needed.

Adult↗