1,721,193 research outputs found
Microgravity as a model of ageing.
No full textPurpose of review: Longevity with good health and long-term survival in space are two of the many challenges that scientists face in the twenty-first century. Ageing and life in space are both associated with undesirable effects on normal physiological processes. This review will outline how the endocrine, metabolic, immune and musculoskeletal systems are affected by microgravity and ageing, drawing analogies between the observed changes in an attempt to highlight common mechanisms. Recent findings: Mild hypothyroidism, increased stress hormones (mainly catecholamines), decreased sex steroids, insulin resistance, impaired anabolic response to food intake, anorexia, altered mitochondrial function and systemic inflammatory response are common features of both ageing and microgravity. Both conditions lead to progressive bone and muscle atrophy, compromising mobility and the ability to perform essential daily tasks. In skeletal muscle, both ageing and space flight lead to weakness from whole muscle to single fibre level, accompanied by marked alterations in muscle architecture and in tendon mechanical properties. Summary: What makes microgravity an interesting and unique tool for gerontologists is that many space-related physiological changes resemble those observed during ageing, but are more or less quickly restored after re-entry, thus allowing the biology of ageing to be investigated both ways, not only during its development but also during recovery. © 2003 Lippincott Williams & Wilkins
Splanchnic versus whole-body production of alpha-ketoisocaproate from leucine in the fed state
No full textThe extent to which dietary branched-chain amino acids are deaminated by the splanchnic tissues (ie, the liver and gut) in the fed state and released as ketoacids into the systemic circulation is not known. To determine this, we combined the oral (L-[1-13C]-leucine, [13C]-Leu) and intravenous (L-[5,5,5-2H3]leucine, [2H3]-Leu) leucine tracer infusion with the intravenous administration of an independent isotope of the leucine ketoanalog alpha-ketoisocaproic acid (KIC) ([4,5-3H]KIC). The study was conducted during constant administration of a complete mixed meal. We found that 26% +/- 5% of the orally administered leucine was taken up by the splanchnic organs at first pass, whereas 74% +/- 5% appeared in the systemic circulation. The rate of splanchnic KIC release from deamination of dietary leucine accounted for 3% +/- 0.2% of the oral leucine administration rate and 13% +/- 2% of leucine splanchnic uptake (fractional splanchnic deamination). The fraction of whole-body total leucine uptake that was deaminated to KIC was 41% +/- 5% (P < .05 v fractional splanchnic deamination of dietary leucine uptake). We conclude that (1) the release of KIC from leucine deamination within splanchnic tissues constitutes a minimal fraction of first-pass dietary leucine uptake, and (2) splanchnic tissues are relatively less efficient than the whole body in KIC production from leucine deamination
A fast high-performance liquid chromatographic method for the measurement of plasma concentration and specific activity of phenylalanine.
No full textA fast high-performance liquid chromatographic (HPLC) method for the measurement in plasma of phenylalanine concentration and specific activity is reported. One-to-two mL of acidified plasma are applied to an ion-exchange resin. The eluted amino acids are enzymatically converted into the corresponding alpha-ketoacids, i.e. phenylalanine is converted into phenylpyruvic acid. After a two-step extraction, phenylpyruvic acid is separated by reverse phase chromatography within 8-10 min. The use of an internal standard allows precise quantitation of plasma concentrations. The radioactivity eluted from the HPLC is divided by the amount injected to yield the specific activity. Concentration and rate of appearance of phenylalanine in man, calculated with the L-[2,6-H-3]phenylalanine tracer, are in the range of published data
Regulation of postprandial whole-body proteolysis in insulin-deprived IDDM.
No full textSuppression of tissue proteolysis is an important mechanism of postprandial protein anabolism, and it may be mediated by insulin, hyperaminoacidemia, or both. To evaluate whether insulin is essential in the regulation of this process, we have investigated the effect of mixed-meal ingestion on whole-body protein breakdown in insulin-deprived insulin-dependent diabetes mellitus (IDDM) patients and normal control subjects. Endogenous phenylalanine and leucine rate of appearance (Ra) from proteolysis were measured at steady-state conditions using a multiple stable isotope technique before and after the constant administration of a synthetic mixed meal. In the postabsorptive state, the IDDM patients exhibited accelerated intracellular leucine Ra (IDDM, 2.64 +/- 0.19 mumol.min-1.kg-1; control, 2.02 +/- 0.08 mumol.min-1.kg-1; P < 0.05) and plasma phenylalanine Ra (IDDM, 0.73 +/- 0.03 mumol.min-1.kg-1; control, 0.61 +/- 0.04 mumol.min-1.kg-1; P < 0.05). During meal ingestion, endogenous phenylalanine and leucine Ra values were suppressed in both the insulin-deficient IDDM (P < 0.05) and control subjects (P < 0.05). Although postmeal endogenous leucine and phenylalanine Ra values remained greater (P < 0.05) in IDDM, the delta changes from the basal endogenous leucine Ra (IDDM, -0.56 +/- 0.11 mumol.min-1.kg-1; control, -0.56 +/- 0.09 mumol.min-1.kg-1) and phenylalanine Ra (IDDM, -0.13 +/- 0.01 mumol.min-1.kg-1; control, -0.14 +/- 0.02 mumol.min-1.kg-1) were similar in both groups. In the IDDM patients, the postmeal increases from the basal leucine concentration were onefold greater (P < 0.05) than in the control-subject
Effects of acute systemic hyperinsulinemia on forearm muscle proteolysis in healthy man.
No full textTo investigate the mechanism(s) of insulin-induced suppression of plasma amino acid concentration and release, we studied forearm as well as whole-body leucine and phenylalanine uptake and release during a peripheral insulin infusion in postabsorptive normal subjects using isotope-dilution methods. Before insulin, leucine and phenylalanine release exceeded uptake (P < 0.01 and P < 0.07, respectively). A net output of alpha-ketoisocaproate (KIC) was also observed. During insulin, arterial plasma leucine, KIC and phenylalanine concentrations decreased (P < 0.05 or less vs. basal), despite ongoing net output of these substrates by the forearm, that persisted after correction for the mean transit time spent through the extracellular muscular space. By the end of insulin, whole-body leucine and phenylalanine concentrations and rate of appearance were decreased (P < 0.01 vs. basal). However, release and uptake of both amino acids by the forearm were not significantly decreased vs. the preinsulin values. These data indicate that systemic hyperinsulinemia acutely decreases plasma amino acid concentrations by acting primarily at sites other than skeletal muscle
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
- …
