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Biomedical subjects

H T Nguyen

Publications and source records attributed to H T Nguyen.

194 records · Page 11Linked to original sources
PubMed1980

Cytoplasmic processing of myosin heavy chain messenger RNA: evidence provided by using a recombinant DNA plasmid.

A recombinant DNA plasmid, designated pMHC25, has been constructed that contains structural gene sequences for rat skeletal muscle myosin heavy chain (MHC). The identity of the MHC sequence insert in pMHC25 was determined by muscle-tissue specificity, inhibition of MHC protein synthesis in vitro by hybrid-arrested translation, purification of mRNA that directs the synthesis of MHC protein in vitro, and hybridization to a 33S cytoplasmic mRNA found only in differentiated muscle cells. pMHC25-DNA-excess filter hybridizations were used to show that more than 90% of the newly synthesized MHC mRNA that appears in the cytoplasm of differentiated L6E9 myotubes contains a long 3' poly(A) tail. In contrast, 90% of the MHC mRNA that accumulates in the cytoplasm of these same cells during myogenic differentiation lacks this long 3' poly(A) tail. These results suggest the occurrence of a posttranscriptional event in differentiated L6E9 myotubes that involves the cytoplasmic processing of poly(A)+ MHC mRNA to poly(A)- or poly(A)-short MHC mRNA.

Animals↗
PubMed1980

Intranephronic calculosis in rats: an ultrastructural study.

Female Sprague-Dawley rats weighing 45-55 g fed a purified diet for 18 days developed hydroxyapatite intratubular lithiasis, the earliest calcific lesions being detectable by light microscopy on Day 12. The kidneys from these rats revealed ultrastructural changes in proximal tubular cells prior to intraluminal microlith formation. These changes included evidence for increased intracellular calcium, accumulation of electron-dense cytoplasmic granules, and vesiculation and shedding of brush border microvilli within Segment I of the proximal tubule. It was concluded, on the basis of ultrastructural observation, that microvesicles were formed by the shedding of vesiculated microvilli and microvesicles initiated the formation of an intraluminal microurolith in Segment I of the proximal tubule. The initially formed microurolith grew, as it traveled down the nephron, to a size large enough to be visualized by light microscopy. When it reached Segment III (straight segment) of the proximal tubule, the microurolith reached a size so large that it became difficult for it to pass the loop of Henle.

Absorption↗
PubMed1979

Circular dichroism and magnetic circular dichroism of nitrogenase proteins.

Circular dichroism (CD) and magnetic circular dichroism (MCD) spectra of nitrogenase components (MoFe protein and Fe protein) from Azotobacter vinelandii (Av) and Klebsiella pneumoniae (Kp) have been obtained in the near infrared-visible-near ultraviolet spectral region. Previously, visible CD was reported to be absent or barely detectable in nitrogenase proteins; MCD spectra have not been reported. The chiroptical spectra can be measured in solution at room temperature, an advantage relative to spectroscopic methods requiring cryogenic sample temperatures. Absorption spectra were also obtained. The CD and MCD are markedly more structured, and thus interpretively more useful, than the corresponding absorption spectra. The dithionite-reduced MoFe proteins (Av1, Kp1) have nearly identical CD and MCD, demonstrating identical numbers and types of metal centers in similar protein environments. The CD and MCD cannot be explained solely in terms of contributions from known 4-Fe or 2-Fe clusters; the near-infrared MCD is inconsistent with the presence of known 4-Fe clusters. CD and MCD spectra of Lauth's violet-oxidized Kp1 are also reported. The reduced Fe proteins (Av2, Kp2) have similar CD and MCD, again indicating significant conservation of chromophore environment. The spectra clearly demonstrate the presence of a reduced bacterial ferredoxin-like (C(3-)) 4-Fe cluster. No obvious evidence of additional chromophores is observed. CD, MCD, and absorption spectra of Av1-oxidized Av2 are reported. The absorption spectrum shows the expected shoulder near 390 nm. The CD and MCD are characteristic of a C(2-) 4-Fe cluster; in particular, the diagnostic near-infrared MCD peak is observed at approximately 8300 cm(-1). The CD of Av2 oxidized in the presence and absence of MgATP are radically different, providing the first direct evidence for MgATP interaction with Fe protein in this oxidation state.

Azotobacter↗
PubMed1979

Comparative ultrastructure of Mycobacterium leprae and Mycobacterium lepraemurium cell envelopes.

The structural properties of the cell envelopes of Mycobacterium leprae and Mycobacterium lepraemurium were investigated by freeze-fracture, freeze-etching, and negative-staining techniques. Freeze-fracture split the cell wall and exposed the internal features of the peptidoglycolipid mycosidic filamentous network. The cell membrane was also split into two asymmetric faces. The external fracture face was characterized by linear arrays of intramembranous particles, whereas the protoplasmic fracture face showed randomly distributed clusters of particulate entities. Comparative analysis of the ultrastructural features observed in M. leprae and M. lepraemurium indicated that the organization of the cell envelope in these two species differed particularly with respect to the amount and complexity of the superficial peptidoglycolipid and mycosidic integument, which is poorly developed in the mycobacterium responsible for human disease.

Animals↗
PubMed1979

Urolithiasis in ferrets (Mustela putorius).

Urinary calculi was observed frequently in ferrets which were from a group used for influenza research. They were submitted for necropsy with various clinical signs. The calculi were composed of magnesium ammonium phosphate hexahydrate and were found in the pelvis of the kidney, urinary bladder and urethra. Crystals of undetermined nature occasionally were observed in the kidneys.

Animals↗
PubMedDate not supplied

Dominant risk factors for retinopathy at clinical diagnosis in patients with type II diabetes mellitus.

A study of 270 newly presenting, previously untreated, type II diabetic patents revealed that 38 patients (14%) had already developed diabetic retinopathy (DR). Among this group, 26 patients had lesions of background diabetic retinopathy and 12 patients already had maculopathy or preproliferative changes. The aim of this study was to determine the risk factors influencing susceptibility to retinopathy, and to provide an accurate predictive value for diabetic retinopathy from a detailed multiple regression analysis that involved 27 demographic variables and the metabolic and hormonal responses during a meal tolerance test (MTT) at presentation. Compared to the nonretinopaths, the retinopaths had higher fasting plasma glucose levels (FPG) (mean +/- SD) (13.9 +/- 3.1 versus 11.6 +/- 3.2 mmol/L, p < 0.001), lower body-mass index values (BMI) (26.1 +/- 3.8 versus 29.3 +/- 5.0 kg/m2, p < 0.001) and higher plasma urea concentrations (6.0 +/- 1.9 versus 5.3 +/- 1.2 mmol/L, p 0.05). In contrast, gender and levels of blood pressure and other lipid levels did not influence the prevalence of diabetic retinopathy. A multiple regression formula for the prediction of diabetic retinopathy was derived and then used to categorize patients into high-risk and low-risk groups. The retinopaths also had higher HbA1c (p < 0.001), higher plasma glucose are under curve (0-2 h, p < 0.001), lower plasma insulin area under curve (0-22 h, p < 0.001), lower C-peptide area under curve (0-2 h, p < 0.01). They were also leaner (p < 0.001) and older (p < 0.05). However, these variables did not feature significantly in the multiple regression formula. The retinopaths were found to have higher risk probability values (25.1 +/- 11.5 versus 13.1 +/- 10.4%, p < 0.001). In the high risk group, 81.6% of retinopaths were identified. In the low-risk group, 63.8% of nonretinopaths were found. The incidence of diabetic retinopathy in type II diabetic patients at clinical diagnosis was found to be highly related to the degree of hyperglycemia, body-mass index, and to a lesser extent, renal impairment.

Adult↗
PubMedDate not supplied

Interexaminer reliability of activator methods' relative leg-length evaluation in the prone extended position.

OBJECTIVE: To investigate the interexaminer reliability of the prone extended relative leg-length check as described by Activator Methods, Inc. SUBJECTS: Thirty-four subjects were selected from a pool of 52 consecutive patients visiting a private chiropractic office. METHODS: Exclusion criteria included congenital or acquired conditions known to affect lower extremity length and inability to lie prone for a 10-minute period. Two experienced chiropractors who specialize in Activator Methods and are "advanced-proficiency rated" by Activator Methods, Inc. assessed each patient in random order for leg length inequality. Findings were recorded as left short leg, equal leg length, or right short leg. RESULTS: The data for 34 subjects were organized in a 3 x 3 contingency table. Total agreement was 85%. A simple, unweighted kappa value yielded kappa = 0.66. A disproportionately greater number of right short leg findings than left short leg findings were observed by both examiners. In only 2 instances were equal leg lengths observed, and both were detected by the same examiner. Because examiners found only 2 of 34 subjects with equal leg lengths, several secondary analyses involving data reductions were conducted. The resulting kappa values were similar to the 3 x 3 analysis. CONCLUSION: There was good reproducibility between 2 examiners by using the Activator Method to detect leg length inequality in the prone extended position. This study does not address the validity or clinical significance of the measurement method. Future studies should include larger numbers, a wider variety of subjects, and a diversity of examiners.

Adult↗
PubMedDate not supplied

Mapping QTLs associated with drought resistance in sorghum (Sorghum bicolor L. Moench).

Drought is a major abiotic stress factor limiting crop production. Identification of genetic factors involved in plant responses to drought stress will provide a solid foundation to improve drought resistance. Sorghum is well adapted to hot dry environments and regarded as a model for studying drought resistance among the grasses. Significant progress in genome mapping of this crop has also been made. In sorghum, rapid premature leaf death generally occurs when water is limited during the grain filling period. Premature leaf senescence, in turn, leads to charcoal rot, stalk lodging, and significant yield loss. More than 80% of commercial sorghum hybrids in the United States are grown under non-irrigated conditions and although most of them have pre-flowering drought resistance, many do not have any significant post-flowering drought resistance. Stay-green is one form of drought resistance mechanism, which gives sorghum resistance to premature senescence under soil moisture stress during the post-flowering period. Quantitative trait locus (QTL) studies with recombinant inbred lines (RILs) and near-isogenic lines (NILs) identified several genomic regions associated with resistance to pre-flowering and post-flowering drought stress. We have identified four genomic regions associated with the stay-green trait using a RIL population developed from B35 x Tx7000. These four major stay-green QTLs were consistently identified in all field trials and accounted for 53.5% of the phenotypic variance. We review the progress in mapping stay-green QTLs as a component of drought resistance in sorghum. The molecular genetic dissection of the QTLs affecting stay-green will provide further opportunities to elucidate the underlying physiological mechanisms involved in drought resistance in sorghum and other grasses.

Adaptation, Physiological↗
PubMedDate not supplied

[Effect of weightlessness on the water fern Azolla].

An exposure to 6-day weightlessness of the fern Azolla pinnata R. Br. symbiotically related to the nitrogen fixing alga Anabena azollae did not affect the main biological characteristics (growth, development and morphological structure) of both fern plants and algae. The exposure did not influence the growth rate or subsequent Azolla generations on the Earth.

Life Support Systems↗