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Biomedical subjects

T T Nguyen

Publications and source records attributed to T T Nguyen.

At least 253 records · Page 14Linked to original sources
PubMed1984

Specific receptor-mediated inhibition by synthetic atrial natriuretic factor of hormone-stimulated steroidogenesis in cultured bovine adrenal cells.

The effect of synthetic atrial natriuretic factor (ANF) on adrenal steroidogenesis has been studied in primary culture of bovine adrenal cells. ANF-(8-33) produced a potent 40-70% inhibition of angiotensin II-, ACTH-, PGE1-, and forskolin-stimulated secretion of aldosterone production from zona glomerulosa cells with an ED50 of 120 pM. An equipotent inhibitory effect of the natriuretic factor on cortisol production was also observed in cultured zona fasciculata cells. Nicotine-stimulated secretion of catecholamines from medullary cells was only slightly inhibited by the factor at doses above 10 nM. [125I]iodo-ANF-(8-33) binding to glomerulosa membranes displayed an apparent affinity of 100-150 pM for specific receptor sites and was not inhibited by angiotensin II or ACTH. Conversely, the natriuretic factor had no affinity for angiotensin II receptor sites. The results demonstrate that part of the natriuretic effect of this new factor might be due to inhibition of adrenal steroidogenesis by action through a distinct receptor.

Adrenal Cortex↗
PubMed1983

Sequence homology between the tetracycline-resistance determinants of Tn10 and pBR322.

The Tn10 tetracycline resistance gene, tetA, encodes a tetracycline-inducible protein with an apparent Mr of 36 X 10(3). We have determined the nucleotide sequence of the Tn10 tetA gene. The extent of the tetA gene was determined by analysis of amino-terminal and carboxy-terminal deletion mutants. We conclude that a single Tn10 gene, the tetA gene, is sufficient to confer tetracycline resistance. The predicted Mr of the tetA protein is 43.2 X 10(3). The sequence homology between the Tn10 tetA gene and the pBR322 tetracycline resistance determinant (49% nucleotide homology, 44% amino acid homology) indicates that these phenotypically distinct tetracycline-resistance determinants must have evolved from a common ancestral sequence. The markedly hydrophobic character of the predicted amino acid sequences of the Tn10 tetA and pBR322 tet-coded proteins suggests that a substantial portion of these proteins may be embedded within the cytoplasmic membrane.

Bacterial Proteins↗
PubMed1983

Multicopy Tn10 tet plasmids confer sensitivity to induction of tet gene expression.

We inserted the Tn10 tetracycline resistance determinant (tet) into the multicopy plasmid pACYC177, and we examined the phenotype of Escherichia coli K-12 strains harboring these plasmids. In agreement with others, we find that Tn10 tet exhibits a negative gene dosage effect. Strains carrying multicopy Tn10 tet plasmids are 4- to 12-fold less resistant to tetracycline than are strains with a single copy of Tn10 in the bacterial chromosome. In addition, we find that multicopy tet strains are 30- to 100-fold less resistant to the tetracycline derivative 5a,6-anhydrotetracycline than are single-copy tet strains. Multicopy tet strains are, in fact, 10- to 25-fold more sensitive to anhydrotetracycline than are strains that lack tet altogether. The hypersensitivity of multi-copy strains to anhydrotetracycline is correlated with the effectiveness of anhydrotetracycline as an inducer of tet gene expression, rather than its effectiveness as an inhibitor of protein synthesis. Anhydrotetracycline is 50- to 100-fold more effective than tetracycline as an inducer of tetracycline resistance and as an inducer of beta-galactosidase in strains that harbor tet-lac gene fusions. In contrast, anhydrotetracycline appears to be two- to fourfold less effective than tetracycline as an inhibitor of protein synthesis. Both anhydrotetracycline and tetracycline induce synthesis of tet polypeptides in minicells harboring multicopy tet plasmids. Differences between E. coli K-12 backgrounds influence the tetracycline and anhydrotetracycline sensitivity of multicopy strains; ZnCl2 enhances the tetracycline and anhydrotetracycline sensitivity of these strains two- to threefold. We propose that the overexpression of one or more Tn10 tet gene products inhibits the growth of multicopy tet strains and accounts for their relative sensitivity to inducers of tet gene expression.

Bacterial Proteins↗
PubMed1983

[New substances with high specific activity for nucleic acid sequences: oligodeoxynucleotides covalently linked to an intercalating agent].

New molecules are described in which an intercalating agent is covalently linked through a polymethylene chain to an oligodeoxynucleotide. Using an oligodT sequence covalently linked to an acridine dye, it is shown that these molecules bind in a specific way to their complementary sequence (poly (A] and that the stability is strongly enhanced by the intercalating agent as compared with the unmodified oligodT. Substitution of a phosphate group by a positively charged group strengthens complex formation and protects the neighboring phosphodiester bond against nuclease cleavage.

Intercalating Agents↗
PubMed1981

[Ischemic hepatitis. Clinico-pathological presentation of 2 cases].

Just before death, two female patients with congestive heart failure exhibited marked elevation of cytolytic hepatic enzymes, suggesting the diagnosis of viral hepatitis. Histologic examination of autopsy material led us to conclude in both cases on the presence of extensive and confluent ischemic centrizonal necrosis (shock liver). This picture probably reflected the consequences of liver perfusion failure. Ischemic hepatitis is the association of shock liver with marked elevation of transaminases.

Aged↗
PubMed1981

New model of a scaling dermatosis: induction of hyperproliferation in hairless mice with eicosa-5,8,11-trienoic acid.

The present studies have demonstrated that topical application of a low concentration of eicosa-5,8,11-trienoic acid (a 20:3,n9 fatty acid previously reported to inhibit competitively the activity of the sheep vesicular cyclooxygenase) to skin of normal fed hairless mice produced severe scaly dermatosis which is characterized by marked hyperplasia and acanthosis of the epidermal layer. The precise mechanism of this induction of scaly dermatosis is presently unclear. It is nonetheless interesting that the treatment of skin with similar concentrations of other unsaturated fatty acids produced no visible or histologic effects. Furthermore, endogenous levels of arachidonic acid in epidermal phospholipid and triglyceride fractions were shown to increase significantly (p < 0.01) in skin treated with the 20:3,n9 fatty acid while the endogenous level of PGE2 in the same tissue decreased markedly. This latter observation is consistent at least in part, with a previous report from this laboratory in which the 20:3,n9 fatty acid inhibited in vitro the activity of the sheep vesicular cyclooxygenase (the rate limiting enzyme in the transformation of arachidonic acid into the prostaglandin endoperoxides) although the increase in arachidonic acid may also reflect an increased incorporation of this fatty acid into the epidermal lipids by the hyperproliferative tissue. Evaluation of the proliferative status of 20:3,n9 fatty acid-treated skin showed a significant increase (p < 0.01) in labeling and mitotic indices. The use of this potentially endogenous fatty acid may be a useful tool for further investigations of hyperproliferative skin diseases where dietary deficiency of essential fatty acids does not exist.

8,11,14-Eicosatrienoic Acid↗
PubMed1980

Field-flow fractionation of alkali-liberated nuclear polyhedrosis virus from gypsy moth Lymantria dispar Linnaeus.

Rod-shaped viral particles of the gypsy moth nuclear polyhedrosis virus (NPV) were obtained through alkaline dissolution of inclusion bodies isolated and purified from infected hosts. The liberated viral fraction contains a wide assortment of enveloped aggregated forms as well as enveloped monomers. This complex mixture was separated by means of sedimentation field-flow fractionation (sedimentation FFF) to give a mass spectrum of the separated particles. From the elution pattern effective molecular weights could be assigned to the various resolved components. Through electron microscopy it was possible to characterize the components as monomers, dimers, etc. In parallel experiments the same viral mixture was separated by the more commonly used density gradient sedimentation technique. The two methods are compared as to time and convenience of manipulation, as well as to the amount of physicochemical information that can be extracted from each separation. The mixture of aggregate viral structures was dialyzed against a nonionic detergent solution. Sedimentation FFF of the dialysate revealed a uniform population of non-enveloped particles with no effective molecular weight which was lower than that of the initial monomer fraction. Electron microscopic observations confirmed that this lower molecular weight fraction did indeed contain rod-like structures which were thinner than the initial enveloped monomers indicating that most if not all of the enveloped material had been removed from the viral rod structures.

Animals↗
PubMed1980

Hepatic delta 9 and delta 6 desaturase activities during the recovery period following carbon tetrachloride poisoning.

The liver microsomal delta 9 and delta 6 desaturase activities have been studied in rats with carbon tetrachloride-induced hepatitis. Immediately after poisoning, significant decreases were observed for both types of desaturase activity. However, recovery kinetics were slower for the delta 6 desaturase than for the delta 9 desaturase. The activities of NADH-ferricyanide and NADH-cytochrome C reductases, proteins involved in the electron transfers associated with microsomal desaturation, were also measured. There was a fall in both activities after poisoning, but this decrease was less than that of the desaturase activities.

Acyl Coenzyme A↗
PubMed1975

Effect of renal microsomes and renal lysosomes on in vitro hepatic fatty acid synthesis.

An inhibitor and stimulator of in vitro hepatic fatty acid synthesis are present in renal microsomes. In addition, a stimulator of fatty acid synthesis is present in renal lysosomes. Renal microsomal inhibition of hepatic fatty acid synthesis is not due to the depletion of cofactors in the system. This inhibitor appears to be located exclusively in the kidney medullary microsomes. It is destroyed by Pronase and heat treatment suggesting it may be a protein. Its effects on fatty acid synthesis may be attributed in part to ATPase activity as well as a direct effect on the hepatic fatty acid synthesizing system. A stimulator of hepatic fatty acid synthesis is present in the buffer insoluble fraction of an acetone powder preparation of renal microsomes. This stimulator is relatively heat labile and does not appear to be a phospholipid. The lysosomal stimulator of hepatic fatty acid synthesis is associated with the contents of renal lysosomes and not with the lysosomal membranes. It acts at the acetyl-CoA carboxylase step and its activity is not affected by fasting or aminonucleoside induced nephrosis.

Adenosine Triphosphate↗
PubMedDate not supplied

Streaming potentials during the confined compression creep test of normal and proteoglycan-depleted cartilage.

The streaming potential response of cartilage in the confined compression creep configuration was assessed theoretically and measured experimentally in normal and proteoglycan-depleted tissue. The analytical solution, using the linear biphasic continuum model including electrokinetics and assuming homogeneous material properties, predicted that: (i) the peak streaming potential is delta V = ke x delta sigma, where ke is the electrokinetic coefficient and delta sigma is the change in compressive stress; (ii) the potential is maintained at 95 to 100% of the peak value for 0 < t < 0.10 tau, where tau is the gel diffusion time constant; and (iii) during short times, 0 < t < 0.01 tau, 90% of the peak streaming potential occurs over a region extending 23% into the tissue sample. Experimentally, adult bovine cartilage disks, 0.5 mm thick, were subjected to step changes of compressive stress. The measured changes in potential indicated a linear response for changes in stress up to 0.10 MPa. The ke of normal cartilage, estimated from the short time (0 < t < 2 sec) change in potential, was -1.65 +/- 1.25 mV/MPa. Digestion of cartilage by chondroitinase ABC resulted in an increased (less negative) ke of -0.75 +/- 0.70 mV/MPa and a 33 +/- 29% depletion of anionic glycosaminoglycan, whereas digestion with trypsin resulted in a further increase in ke to +1.74 +/- 0.95 mV/MPa and a 98 +/- 1 % depletion of glycosaminoglycan. The streaming potential measurement may be a useful addition to the widely used confined compression creep test to assess cartilage material properties.

Analysis of Variance↗
PubMedDate not supplied

Differential regulation of natriuretic peptide biosynthesis in bovine adrenal chromaffin cells.

Chromaffin cells synthesize and secrete two forms of natriuretic peptides which are also found in the heart and in the central nervous system. While atrial tissue predominantly contains atrial natriuretic factor (ANF), brain tissue appears to produce relatively larger amounts of brain natriuretic peptide (BNP) also identified as aldosterone secretion inhibitory factor (ASIF), suggesting tissue-specific differential regulation of these two peptides. This report compares the modulation of the biosynthesis and secretion of ASIF with that of ANF using cultured chromaffin cells as a model system. Cholinergic nicotinic activation and KCl depolarization induce a 5-fold increase of the corelease of ASIF and pro-ASIF in cell culture medium concomitantly with a 3-fold stimulation of ANF and pro-ANF cosecretion. While the combined treatment with phorbol ester and forskolin produces a 2-fold increase in total ANF level, it induces a synergistic 20-fold elevation of total ASIF level. These results indicate that chromaffin cell secretagogues induce the cosecretion of both the precursor and mature forms of ASIF and ANF. The preferential stimulation of ASIF production is revealed by the combined treatment rendering the ASIF to ANF proportion similar to that in brain.

Adrenal Medulla↗
PubMedDate not supplied

Fluoride profiles in dental calculus from Japanese, Chinese and British residents.

Whether the fluoride concentrations and profiles differ in human dental calculus obtained from different countries was investigated. A total of 203 dental calculus deposits on 203 permanent teeth from residents (mean age, 52.1 years) of Nagoya (Japan), Shanghai (China), Leeds (Great Britain) and the Wuhan mountainous area (China, fluoridated area) were analysed. An abrasive microsampling procedure was used to examine fluoride distribution. There were five types of fluoride profiles in dental calculus in each area/country (designated types L, J, U, T, W). In supragingival calculus, type L (highest in the outermost layers) and type J (highest in the innermost layers) both had significantly higher values than type U (high in the surface and innermost layers) but were relatively identical. In subgingival calculus, type W (high in the outermost, mid and innermost layers) was characteristics. Calculus from the Wuhan mountainous area (fluoridated) had the highest fluoride concentration, followed by Leeds (non-fluoridated), and Nagoya and Shanghai (non-fluoridated) calculus had the lowest. Fluoride concentrations in supragingival calculus were higher in teeth extracted because of periodontal diseases than dental caries. It is concluded that fluoride concentrations and distribution in dental calculus differ from country to country, probably due to different fluoride environments.

Adult↗
PubMedDate not supplied

Risk factors for typhoid fever in the Mekong delta, southern Viet Nam: a case-control study.

In order to identify risk factors for typhoid fever in a highly endemic area, we undertook a case-control study in the Mekong delta, Viet Nam. Cases were 144 consecutive patients admitted to hospital with blood culture-confirmed typhoid fever. Two controls (1 in the hospital and 1 in the community) were chosen for each case. Standardized interviews were conducted with questions regarding recent contact with a typhoid fever patient, eating habits, hygiene and socio-economic level. Cases were more likely to have been in contact with a patient with typhoid fever than hospital controls (adjusted odds ratio (OR) = 5.2, 95% confidence interval (95% CI) 1.7-15.9) or community controls (adjusted OR = 11.9, 95% CI 2.3-60.7); 11% and 14% of typhoid fever cases (compared to hospital or community controls, respectively) were attributable to recent contact with a patient with this disease. These findings suggest that strategies directed towards the persons in contact with a patient might reduce the incidence of secondary cases of typhoid fever.

Adolescent↗