PubMed Health⌕ Search

SEARCH · PubMed Health

Results for “Continuous Evolution”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 577 records · Page 32Linked to original sources
PubMed1992

Thylakoids from pea seedlings grown under intermittent light: biochemical and flash-spectrophotometric properties.

Thylakoid membranes were isolated from pea seedlings grown under intermittent light (2-min light/118-min dark cycles). These preparations differed from controls (thylakoids from plants grown under 16-h light/8-h dark cycles) in the following respects: 15 times smaller chlorophyll/protein ratio, 10 times greater chlorophyll a/b ratio, absence of light-harvesting chlorophyll a/b binding proteins, and 2-3-fold greater ratio of photosystem II over photosystem I. In addition we found the following: (1) Electrogenic electron transfer around cytochrome b6/f under flashing light was greatly enhanced, probably as a consequence of the greater photosystem II/photosystem I ratio. (2) The rate of proton uptake from the medium at the acceptor side of photosystem II was enhanced, probably by unshielding of the quinone binding domain. (3) The N,N'-dicyclohexylcarbodiimide sensitivity of the proton-pumping activity of photosystem II was absent, which was consistent with the attribution of a N,N'-dicyclohexylcarbodiimide-induced protonic short circuit to chlorophyll a/b binding proteins. (4) The sensitivity of oxygen evolution under continuous light to variations of pH or the concentration of Ca2+ was altered. Chlorophyll a/b binding proteins serve as light-harvesting antennas. We found in addition that they modulated the activity of water oxidation and, in particular, the proteolytic reactions around photosystem II.

Cell Fractionation↗
PubMed2005

Molecular-level investigation of the structure, transformation, and bioactivity of single living fission yeast cells by time- and space-resolved Raman spectroscopy.

The structure, transformation, and bioactivity of single living Schizosaccharomyces pombe cells at the molecular level have been studied in vivo by time- and space-resolved Raman spectroscopy. A time resolution of 100 s and a space resolution of 250 nm have been achieved with the use of a confocal Raman microspectrometer. The space-resolved Raman spectra of living S. pombe cells at different cell cycle stages were recorded in an effort to elucidate the molecular compositions of organelles, including nuclei, cytoplasm, mitochondria, and septa. The time- and space-resolved measurement of the central part of a dividing yeast cell showed continuous spectral evolution from that of the nucleus to those of the cytoplasm and mitochondria and finally to that of the septum, in accordance with the transformation during the cell cycle. A strong Raman band was observed at 1602 cm(-)(1) only when cells were under good nutrient conditions. The effect of a respiration inhibitor, KCN, on a living yeast cell was studied by measuring the Raman spectra of its mitochondria. A sudden disappearance of the 1602 cm(-)(1) band followed by the change in the shape and intensity of the phospholipid bands was observed, indicating a strong relationship between the cell activity and the intensity of this band. We therefore call this band "the Raman spectroscopic signature of life". The Raman mapping of a living yeast cell was also carried out. Not only the distributions of molecular species but also those of active mitochondria in the cell were successfully visualized in vivo.

Cell Cycle↗
PubMed2005

Ethene adsorption, dehydrogenation and reaction with Pd(110): Pd as a carbon 'sponge'.

The interaction of ethene with the Pd(110) surface has been investigated, mainly with a view to understanding the dehydrogenation reactions of the molecule and mainly using a molecular beam reactor. Ethene adsorbs with a high probability over the temperature range 130 to 800 K with the low-coverage sticking probability dropping from 0.8 at 130 K to 0.35 at 800 K. The adsorption is of the precursor type, with a weakly held form of ethene being the intermediate between the gas phase and strong chemisorption. Dehydrogenation begins at approximately 300 K and is fast above 350 K. If adsorption is carried out at temperatures up to approximately 380 K, adsorption saturates after about 0.25 monolayer have adsorbed, but above approximately 450 K, adsorption continues at a high rate with continuous hydrogen evolution and C deposition onto the surface. It appears that, in the intermediate temperature range, the carbonaceous species formed is located in the top layer and thus interferes with adsorption, whereas the C goes subsurface above 450 K, the adsorption is almost unaffected, and the C signal is significantly attenuated in XPS. However, the deposited carbon can easily be removed again by reaction with oxygen, thus implying that the carbon remains in the selvedge, that is, in the immediate subsurface region probably consisting of a few atomic layers. No well-ordered structures are identified in either LEED or STM, though some evidence of a c(2 x 2) structure can be seen. The Pd surface, at least above 450 K, appears to act as a "sponge" for carbon atoms, and this effect is also seen for the adsorption of other hydrocarbons such as acetaldehyde and acetic acid.

Journal Article↗
PubMed1986

A microcalorimetric study of heat production in resting skeletal muscle from human subjects.

Different microcalorimetric techniques have been compared for the assessment in vitro of the total metabolic activity of resting skeletal muscle. Human fibre bundles were suspended in Krebs-Ringer-phosphate buffer containing glucose and insulin and the heat evolution was continuously monitored for 2-6 h. Palmitate as substrate was also tested. The power signals declined rapidly when a static calorimetric method (A) was used. Two different perfusion methods (B, C) gave higher power values. Long-lasting steady states were observed with method C, where the sample was contained in a cage acting as a stirrer. Significant differences were found for fibre bundles from different human muscles as well as age- and sex-related differences. The heat production in samples from the rectus abdominis muscle (method B), 0.73 mW/g muscle wet wt., was significantly higher than for the obliquus internus muscle, 0.44 mW/g, and the vastus lateralis muscle, 0.55 mW/g, but not different from the heat production value of vastus medialis, 0.66 mW/g. In method C particularly, the fibre bundles are believed to be in adequate contact with the surrounding medium. With the use of a multi-channel calorimeter it is possible to perform up to four experiments simultaneously, e.g. involving the calorigenic effects of pharmacological substances. The technique provides a new approach for detailed studies of muscle metabolism in physiological and pathological conditions.

Adolescent↗
PubMed1999

Graves-Basedow disease goiter: a model of Bax-Bcl2 regulated apoptosis.

This study demonstrates the involvement of a Bax-Bcl2-dependent apoptotic process in Graves-Basedow thyroid disease, a pathological condition known for its spontaneously oscillating evolution. A continuous series of 86 cases of surgically treated Graves' thyroid was evaluated for apoptotic cell content identified by histological criteria and confirmed by terminal desoxynucleotidyl transferase-mediated desoxyuridine triphosphate nick end-labeling (TUNEL). A significant correlation was found between tissue features of Graves' disease (epithelial hyperplasia, cellular hypertrophy, colloid content) and the amount of apoptotic cells. No correlation was found with lymphocytic infiltrates. Significantly, 11 cases (about 12% of the series) with high-level apoptosis displayed the typical features of active Graves' disease over all tissue sections. In contrast, cases with no detectable apoptosis exhibited regressive tissue features of Graves' disease. An intermediate group of cases was characterized by tissue heterogeneity with hyperactive foci, rich in apoptosis, alternating with regressive areas lacking apoptosis. In this group the participation of apoptosis to the remodeling of Graves' thyroid parenchyma, in a tight balance with cell proliferation, was best illustrated. Moreover, the thyroid follicle by accumulating apoptotic cells and bodies, allowed a tentative chronological ordering of apoptosis steps in correlation with Bax-Bcl2 tissue distribution and cellular pattern. Our observations suggest that the initiation of apoptosis corresponds to a loss of cellular cohesion, a drop in Bcl2 expression, and a delocalization of Bax from a putative Golgi storage location to a mitochondrial distribution.

Adult↗
PubMed2003

Extended lifespan of Barrett's esophagus epithelium transduced with the human telomerase catalytic subunit: a useful in vitro model.

As there has been no previous information on the consequences of telomerase expression in genetically altered, mortal cells derived from pre-malignant tissue, we sought to determine the effect of hTERT (human catalytic subunit of telomerase reverse transcriptase) transduction of pre-malignant cell strains from Barrett's esophagus that do not contain telomerase activity and possess a finite lifespan. Primary cultures of Barrett's esophageal epithelium transduced with a retrovirus containing hTERT were characterized by growth factor requirements, cytogenetics and flow cytometry. Expression of telomerase lengthened telomeres and greatly extended the lifespan of hTERT transduced (hTERT+) Barrett's esophagus cells. Growth factor dependency of the hTERT+ cultures remained largely similar to the parental cultures, although there was a modest increase in the ability to grow in agar. Chromosomal instability, measured by both karyotypic and FISH (fluorescence in situ hybridization) analyses, was reduced but not abrogated by hTERT transduction, suggesting that telomerase expression can enhance genomic stability. However, the persistence of residual instability gave rise to new clonal and non-clonal genetic variants, and in one hTERT+ culture a new DNA aneuploid population was observed, the only time such a ploidy shift has been seen in Barrett's cell strains in vitro. These in vitro observations are analogous to the clinical progression to aneuploidy that often precedes cancer in Barrett's esophagus, and suggest that reactivation of telomerase may be permissive for continued genetic evolution to cancer. Long-lived Barrett's esophagus epithelial cultures should provide a useful in vitro model for studies of neoplastic evolution and chemopreventive therapies.

Barrett Esophagus↗
PubMed1997

Potential role of TNFalpha and lipoprotein lipase as candidate genes for obesity.

To maintain body weight, metabolic efficiency was promoted during evolution; two candidate genes for body weight regulation are lipoprotein lipase (LPL) and tumor necrosis factor-alpha (TNFalpha). Human fat cells do not synthesize lipid, but rely on LPL-mediated plasma triglyceride hydrolysis. Adipose LPL is elevated in obesity. Following weight loss, LPL is elevated further, suggesting attempts to maintain lipid stores during fasting and to replenish lipid stores during refeeding. Muscle LPL is regulated inversely to adipose LPL. Thus, an increased adipose/muscle LPL ratio would partition dietary lipid into adipose tissue and would explain some of the variability in weight gain when humans are exposed to excess calories. Adipose tissue TNFalpha expression is increased in obese rodents and humans and may be important in obesity. When insulin-resistant rodents were injected with anti-TNF binding protein, insulin action improved, suggesting a link between insulin resistance and TNF. TNF is expressed at higher levels in muscle cells of insulin-resistant subjects, and TNF may inhibit LPL expression. Overall, TNF may function to make the subject less obese by inhibiting LPL and rendering the animal more insulin resistant. Obesity has many components, both metabolic and behavioral. However, the metabolic changes resulting from LPL and TNF likely played a role in regulating body adipose tissue during much of human evolution and continue to affect human obesity today.

Adipose Tissue↗
PubMed2007

In vitro gamete derivation from pluripotent stem cells: progress and perspective.

Germ cells constitute a highly specialized cell population that is indispensable for the continuation and evolution of the species. Recently, several research groups have shown that these unique cells can be produced in vitro from pluripotent stem cells. Furthermore, live births of offspring using induced germ cells have been reported in one study. These results suggest that it may be possible to investigate germ cell development ex vivo and to establish novel reproductive technologies. To this end, it is critical to assess if gamete induction processes in vitro faithfully recapitulate normal germ cell development in vivo. Here, this issue is discussed with a focus on the germ line specification and the sex-specific development of pre- and postnatal germ cells. The aim of this paper is to concisely summarize the past progress and to present some future issues for the investigation into in vitro gamete production from pluripotent stem cells.

Animals↗
PubMed2003

Calicivirus infections in children.

PURPOSE OF REVIEW: Caliciviruses are a major cause of human illness, and are listed as category B pathogens according to the National Institute of Allergy and Infectious Diseases classification of pathogens important for biodefense. Caliciviruses are commonly encountered in contaminated food and water, and a large variety has been implicated as sources of infection during outbreak investigations. RECENT FINDINGS: New names for two of the four genera of the Caliciviridae were approved in 2002. They are Norovirus, for what were previously called Norwalk-like viruses or small, round-structured viruses, and Sapovirus, for what were previously called Sapporo-like viruses. Caliciviruses are highly diverse genetically and antigenically. This diversity complicates the design of diagnostic assays, yet can be used to discriminate contaminating and infecting strains during outbreak investigations. Of particular interest is the recent finding of naturally occurring recombinant Norovirus strains, all of which have been virulent and are widely dispersed and apparently ecologically indistinguishable from other calicivirus strains. This finding is considered in light of the evidence for recombination between caliciviruses and picornaviruses, and recombination as a more general phenomenon for virus evolution. SUMMARY: Continued investigations of calicivirus outbreaks are now focusing on the implicated sources of infection. While many foods and environmental waters have long been implicated as outbreak sources, the methods for detecting caliciviruses are being developed and refined. Recognition is now turning to unexpected sources of contamination, such as presumably clean foods and waters, including bottled water and minimally handled foods. Parallels between Norovirus and Salmonella ecology and epidemiology are noted, as a guide to understanding evolving new information about caliciviruses.

Caliciviridae↗
PubMed2003

Magnetic resonance imaging and spectroscopic imaging of prostate cancer.

PURPOSE: We describe the practical technical aspects of magnetic resonance spectroscopic imaging (MRSI), and summarize the current and potential future status of magnetic resonance imaging (MRI) and MRSI in the diagnosis, localization, staging, treatment planning and post-treatment followup of prostate cancer. MATERIALS AND METHODS: Contemporary series of patients with prostate cancer evaluated by MRI and MRSI were reviewed, with particular respect to imaging accuracy as evaluated by histopathological correlation, and the relationship between MRI and MRSI and outcome. RESULTS: MRI and MRSI have a limited role in prostate cancer diagnosis but may be helpful for patients with a high index of suspicion and negative initial biopsy. High specificity can be achieved for sextant localization of cancer when sextant biopsy, MRI and MRSI are all positive. Volumetric localization is of limited accuracy for tumors less than 0.5 cc. Staging by MRI, which is improved by the addition of MRSI, is of incremental prognostic significance for patients with moderate and high risk tumors. MRI and MRSI may assist in surgical and radiation treatment planning, and posttreatment followup. In particular, the use of MRI to assist radiation treatment planning has been shown to improve outcome. Interventional MRI guided biopsy and therapy remain under investigation. CONCLUSIONS: Only MRI and MRSI allow combined structural and metabolic evaluation of prostate cancer location, aggressiveness and stage. MRI provides clinically and therapeutically relevant anatomical information. The technology remains in evolution, and continued advances in accuracy and use are likely.

Humans↗
PubMed2002

Abrasive wear on the atomic scale.

A scanning force microscope in ultrahigh vacuum has been used to realize and detect atomic-scale abrasion on KBr(001). The continuous time evolution of the lateral force under scratching reveals that the wear mechanism is due to the removal and the rearrangement of single ion pairs. The debris is reorganized in regular terraces with the same periodicity and orientation as the unscratched surface, as in local epitaxial growth. The applied load has a strong influence on the abrasive process, whereas the scan velocity is less relevant.

Journal Article↗
PubMed2003

Lattice parameters and structural phase transition of lanthanum titanate perovskite, La0.68(Ti0.95,Al0.05)O3.

Lattice parameters and the structural phase transition of La(0.68)(Ti(0.95),Al(0.05))O(3) have been investigated in situ in the temperature range 301-689 K by the synchrotron radiation powder diffraction (SR-PD) technique. High-angular-resolution SR-PD is confirmed to be a powerful technique for determining precise lattice parameters around a phase-transition temperature. The title compound exhibits a reversible phase transition between orthorhombic and tetragonal phases at 622.3 +/- 0.6 K. The following results were obtained: (i) the lattice parameters increased continuously with temperature, while the b/a ratio decreased continuously with temperature and became unity at the orthorhombic-tetragonal transition point; (ii) no hysteresis was observed between the lattice-parameter values measured on heating and on cooling. Results (i) and (ii) indicate that the orthorhombic-tetragonal phase transition is continuous and reversible. The b/a ratio is found to exhibit a more continuous temperature evolution than does the order parameter for a typical second-order phase transition based on Landau theory.

Journal Article↗
PubMed2006

A nonlinear model with latent process for cognitive evolution using multivariate longitudinal data.

Cognition is not directly measurable. It is assessed using psychometric tests, which can be viewed as quantitative measures of cognition with error. The aim of this article is to propose a model to describe the evolution in continuous time of unobserved cognition in the elderly and assess the impact of covariates directly on it. The latent cognitive process is defined using a linear mixed model including a Brownian motion and time-dependent covariates. The observed psychometric tests are considered as the results of parameterized nonlinear transformations of the latent cognitive process at discrete occasions. Estimation of the parameters contained both in the transformations and in the linear mixed model is achieved by maximizing the observed likelihood and graphical methods are performed to assess the goodness of fit of the model. The method is applied to data from PAQUID, a French prospective cohort study of ageing.

Aged↗
PubMed2006

Evolution of technology for automated peritoneal dialysis.

Automated peritoneal dialysis (APD) is important for the further penetration of PD in the dialysis marketplace. Long dwell, equilibration PD (CAPD) has limited applicability in many patients due to inadequate solute clearance or fast membrane transport characteristics. Providing large volumes of dialysate over circumscribed hours is highly labor intensive without an automated system. Early attempts at APD were crude but effective in reducing labor, which was generally provided by nursing staff. Later evolution of PD technology has been greatly accelerated by the microchip, and by miniaturization of components. Current generation machines allow individualized fill volumes, variable tidal volumes and additional daytime automated exchanges, teledialysis, memorized delivery control, and full portability. The ideal machine should not only be able to perform all treatment schedules, but it should also optimize the performance of a selected treatment strategy. Biocompatible solutions, improved osmotic agents, and sorbent technology are all adaptable to APD. The eventual evolution toward continuous flow PD will resolve many of the current problems with both CAPD and APD.

Humans↗
PubMedDate not supplied

Indications, benefits and outcome of laparoscopic Nissen fundoplication.

The advent of laparoscopic fundoplication has catalyzed renewed interest in the surgical treatment of gastroesophageal reflux disease (GERD), and continues the evolution of surgical treatment begun by Phillip Allison in the early 1950s. Clinical observations of the natural history of GERD suggest a high risk group of approximately 25% of patients who develop recurrent and progressive disease, often despite medical therapy. These patients should be considered candidates for early surgical intervention. Early clinical studies of laparoscopic fundoplication document successful relief of reflux symptoms in nearly 90% of patients, results nearly identical to its open counterpart. This review focuses on the indications and patient selection for, as well as the technique and outcome of laparoscopic Nissen fundoplication.

Esophagitis, Peptic↗
PubMed1992

Clinical pathology in the National Toxicology Program.

The National Toxicology Program (NTP) developed a standard approach for clinical pathology investigations that was integrated into most toxicity studies designed and conducted after 1986. Protocols for these studies include specific hematology and clinical chemistry analyses at 3 selected time points in 13-wk studies. Requirements concerning the anesthetization of animals, collection and analysis of samples, and reporting of results have been established to control sources of variability within and between contract laboratories that perform these studies for the NTP. Laboratories must meet minimum standards to be approved for participation in the Program. Important areas of consideration for these laboratories to perform clinical pathology investigations include the facility, equipment, personnel, performance, and quality control procedures. Clinical pathology results from approximately 60 13-wk studies that have been conducted by the NTP in 7 laboratories since 1987 are being analyzed to generate a database of control values for the Fischer rat and B6C3F1 mouse and to identify sources of variability. Experimental data from these studies are being analyzed and correlated with histopathologic findings to evaluate the contribution of clinical pathology to the characterization of toxicity and to examine the appropriateness of the current approach. Efforts such as these will provide for the evolution and continued relevance of clinical pathology in toxicity testing.

Animals↗
PubMed1993

Clinical quality improvement in a multihospital system: the voluntary hospitals of America/Pennsylvania experience.

Sharing of patient outcome data among hospitals hastened the evolution of continuous quality improvement at Voluntary Hospitals of American/Pennsylvania (VHA/PA) to a focus on learning from the best: clinical benchmarking. Analysis of VHA/PA MedisGroups comparative outcome data showed significant variation. In the first study, variations from 3 to 25% normal appendectomy rates were noted. A second study on primary and secondary cesarean section rates again showed variation in outcomes. A study of the benchmark hospitals showed characteristics, specific to those institutions, that resulted in excellent outcomes. To quantify best processes, VHA/PA has embarked on a clinical benchmarking project with the assistance of MediQual Systems, Inc.

Adolescent↗