1,720,958 research outputs found
In vivo chronic exposure to heroin or naltrexone selectively inhibits liver microsome formation of estradiol-3-glucuronide in the rat
No full textWe have previously found that repeated exposure to heroin reduces liver synthesis of morphine-3-glucuronicle (M3G) and increases the production of morphine-6-glucuronide (M6G), which normally is not formed in the rat. By contrast repeated exposure to naltrexone does not activate M6G synthesis but increases the V,a of M3G formation. M3G synthesis depends on the activity of two isoforms of the UDP-glucuronosyltransferase (UGT), UGT1A1 and UGT2B1. These isozymes also activate the formation of estradiol-3-glucuronide (E3G) and estradiol-17-glucuronide (E17G), respectively. The goal of the present study was to investigate the role of UGT1A1 and UGT2B1 in the effects of heroin and naltrexone by determining their influence on the synthesis of E3G and E17G. Estradiol glucuronidation was performed using microsomes of rats treated daily, for 10 days, with saline, heroin (10 mg/kg, i.p.), or naltrexone (40 mg/kg, i.p.). Moreover, liver expression of both UGT1A1 and UGT2B1 was studied in the same experimental conditions by polymerase chain reaction analysis. Kinetic analysis showed that the V-max for E3G formation was significantly reduced by both heroin (168.82 +/- 9.73 nmol/mg/min) and naltrexone (194.60 +/- 16.6) relative to saline (624.60 +/- 17.6). Moreover, homotropic kinetic of E3G formation (Hill coefficient: 1.8) was transformed in Michaelis-Menten kinetic by both heroin (0.88) and naltrexone (1.15). The synthesis of E17G was not affected by either opioid. The expression of liver UGT1A1 and UGT2B1 did not differ across groups. The present results suggest that heroin and naltrexone can reduce estradiol glucuronidation via a specific interaction with UGT1A1 isoform. (C) 2008 Elsevier Inc. All rights reserved
Non-opioid induction of morphine-6-glucuronide synthesis is elicited by prolonged exposure of rat hepatocytes to heroin
No full textBackground: Liver metabolism of morphine leads to the formation of morphine-3-glucuronide (M3G) and morphine-6-glucuronide (M6G), the latter possessing strong opioid activity that however differs from that of the parent compound. In previous studies conducted in rats we have shown that repeated in vivo exposure to phenanthrene class of mu opioid receptor (MOR) agonists or antagonists (heroin, morphine, and naltrexone), but not to non-phenanthrene class of MOR agonist methadone, affects morphine glucuronidation by liver microsomes. Methods: In the present study, we measured the in vitro formation of M3G and M6G by rat hepatocytes incubated for 120 min with morphine (0.1-1.0 mM) after 72 h pre-incubation with one of the following MOR agonists: heroin (3.3 or 6.6 mu M), morphine (7.8 mu M), or methadone (12 mu M). The MOR antagonist naltrexone (10 or 25 mu M) was also tested, alone or in combination with heroin. The amount of M3G and M6G synthesized was then measured by HPLC method. Results: Heroin inhibited M3G synthesis and induced the formation of M6G, which under basal conditions is not synthesized in rats. Heroin effects were not blocked by naltrexone. Morphine, but not methadone, produced effects similar to those of heroin but more modest in intensity. Pre-incubation with naltrexone alone slightly increased M3G synthesis, but had no effect on M6G formation. Conclusions: These results are in agreement with those of previous ex vivo studies and indicate that exposure to heroin or, to a lesser extent, morphine, can affect morphine glucuronidation via direct non-opioid actions on the hepatocytes. (C) 2008 Elsevier Ireland Ltd. All rights reserved
Repeated exposure to codeine alters morphine glucuronidation by affecting UGT gene expression in the rat
No full textWe have previously found that phenantrenic opioids, such as heroin or naltrexone, modulate morphine glucuronidation in the rat. Here we further investigated the effects of phenantrenic opioids on morphine glucuronidation comparing the effects of codeine and heroin. In particular, we measured the synthesis of morphine-3-glucuronide (M3G) and morphine-6-glucuronide (M6G) from morphine: in the liver microsomal preparations obtained from rats repeatedly treated with two different doses of codeine (ex vivo study); in primary cultures of rat hepatocytes previously incubated for 72 h with codeine, or heroin (in vitro study); in the latter conditions, the levels of expression of genes coding for uridine-5'-diphosphate-glucuronosyltransferases (UGTs) A1, A6, A7and 2B1 were also determined; finally, the levels of glucuronic acid in rat hepatocytes previously incubated for 72 h with codeine or heroin were assessed. The ex vivo study shows that codeine exposure in vivo stimulated liver microsomal M3G formation and de novo synthesis of M6G. Differently, in primary hepatocyte cultures both codeine and heroin inhibited M3G formation, whereas heroin only stimulated de novo synthesis of M6G; moreover, codeine significantly reduced UGT2B1 expression at 6 h and caused a trend toward inhibition of UGT1A1 expression at 72 h; heroin enhanced UGT2B1 expression and inhibited that of UGT1A1 at 72 h; finally, both codeine and heroin depleted UDPGA content of hepatocytes. In conclusion, codeine affects liver glucuronidation of morphine enlightening the possible contribution of changes in the spectrum of UGT gene expression and co-factor synthesis in this phenomenon. (c) 2012 Elsevier B.V. All rights reserved
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
Activity of Adenosine Receptors Type 1 Is Required for CX3CL1-Mediated Neuroprotection and Neuromodulation in Hippocampal Neurons.
Full text linkThe chemokine fractalkine (CX(3)CL1) is constitutively expressed by central neurons, regulating microglial responses including chemotaxis, activation, and toxicity. Through the activation of its own specific receptor, CX(3)CR1, CX(3)CL1 exerts both neuroprotection against glutamate (Glu) toxicity and neuromodulation of the glutamatergic synaptic transmission in hippocampal neurons. Using cultured hippocampal neuronal cell preparations, obtained from CX(3)CR1(-/-) (CX(3)CR1(GFP/GFP)) mice, we report that these same effects are mimicked by exposing neurons to a medium conditioned with CX(3)CL1-treated mouse microglial cell line BV2 (BV2-st medium). Furthermore, CX(3)CL1-induced neuroprotection from Glu toxicity is mediated through the adenosine receptor 1 (AR(1)), being blocked by neuronal cell preparations treatment with 1,3-dipropyl-8-cyclopentylxanthine (DPCPX), a specific inhibitor of AR(1), and mimicked by both adenosine and the specific AR(1) agonist 2-chloro-N(6)-cyclopentyladenosine. Similarly, experiments from whole-cell patch-clamped hippocampal neurons in culture, obtained from CX(3)CR1(+/+) mice, show that CX(3)CL1-induced depression of alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid- (AMPA-) type Glu receptor-mediated current (AMPA-current), is associated with AR(1) activity being blocked by DPCPX and mimicked by adenosine. Furthermore, BV2-st medium induced a similar AMPA-current depression in CX(3)CR1(GFP/GFP) hippocampal neurons and this depression was again blocked by DPCPX. We also report that CX(3)CL1 induced a significant release of adenosine from microglial BV2 cells, as measured by HPLC analysis. We demonstrate that (i) CX(3)CL1, along with AR(1), are critical players for counteracting Glu-mediated neurotoxicity in the brain and (ii) AR(1) mediates neuromodulatory action of CX(3)CL1 on hippocampal neurons
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
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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