1,720,976 research outputs found
Specific linkages among luteinizing hormone, follicle-stimulating hormone, and testosterone release in the peripheral blood and human spermatic vein: evidence for both positive (feed-forward) and negative (feedback) within-axis regulation.
No full textWe have investigated possible (negative) feedback and (positive) feed-forward activity within the human male gonadotropic axis by measuring serum concentrations of LH, FSH, and testosterone in blood sampled frequently and for a prolonged interval (every 20 min for 19 h) simultaneously from the peripheral circulation and the left spermatic vein. Cross-correlation analysis with time lag was used to evaluate relationships among serial serum LH, FSH, and/or testosterone concentrations over time (i.e. consistency or dissociation of trends in concentrations). Separately, Cluster analysis was applied to identify discrete LH, FSH, and testosterone pulses, which were cataloged for possible peak coincidence. The hypergeometric probability distribution was then used to test the null hypothesis that LH, FSH, and testosterone pulses are randomly associated. Cross-correlation analysis revealed: 1) peripheral blood LH and testosterone concentrations correlate positively at lags of 40-120 min with LH increases preceding testosterone increases, viz., feed-forward (P < 0.001); 2) LH and FSH concentrations in peripheral blood are positively correlated in simultaneous blood samples, as well as when FSH lags LH by 20 min (P < 0.01); 3) unexpectedly, LH and FSH concentrations in peripheral blood are inversely related at a lag of 80-100 min (P = 0.002) and 0.004, respectively) where LH lags FSH; 4) LH and testosterone concentrations in the spermatic vein show strongly positive correlations at lags of 80, 100, and 120 min (P = 0.002, 0.004, and 0.021, respectively); 5) spermatic vein testosterone concentrations correlate negatively with peripheral blood LH concentrations 20 or 40 min later (P = 0.012 and 0.05, respectively), which indicates autonegative feedback; and 6) in contrast, testosterone levels in the spermatic vein correlate negatively with FSH values in the periphery 100 and 120 min later (P < 0.01), indicating more delayed negative feedback of testosterone on serum FSH concentrations. Discrete pulse coincidence analysis disclosed: 1) a total of 30 testosterone pulses in the spermatic vein and 25 testosterone pulses in peripheral blood, with 28 LH and 29 FSH pulses in the periphery; 2) individual LH and FSH peak concordance was significantly nonrandom for FSH pulse maxima lagging LH pulse maxima by 20 min (P < 0.05 vs. randomness), with 6 observed coincidences vs. 2.9 +/- 1.5 (SD) expected; 3) peripheral LH pulses and spermatic vein testosterone pulses were strongly nonrandomly coupled at an 80-min lag, with 8 events observed vs. 3.0 +/- 1.5 events expected (P = 0.004); and 4) LH peaks in peripheral blood followed testosterone peaks in the spermatic vein by 40 min in a nonrandom manner, specifically, n = 11 observed vs. 3.0 +/- 1.5 expected (P < 0.001), indicating possible LH escape from testosterone's negative feedback. In summary, physiological regulation of the human male LH, FSH, and testosterone axis comprises multidirectional interactions, consisting of both (positive) feed-forward and (negative) feedback coupling. Based on a concept of network integration, we propose that age and other pathophysiological factors might modulate and/or disrupt these dynamic within-axis multihormonal linkage
Extracellular ATP stimulates estradiol secretion in rat Sertoli cells in vitro: modulation by external sodium
No full textpituitary adenylate cyclase activating polypeptide stimulates rat Leydig cell steroidogenesis through a novel transduction pathway
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Evidence for specific binding and stimulatory effects of recombinant human erythropoietin on isolated adult rat Leydig cells.
No full textThe presence of specific binding of recombinant human erythropoietin and its effect on testosterone production were evaluated in isolated intact adult rat Leydig cells. Maximal specific binding was observed after 135 min incubation at 34°C. Scatchard analysis of the binding data revealed two distinct classes of binding sites for [125I]-recombinant human erythropoietin with dissociation constants of (Kd1) 1.9 x 10-10 mol/l and (Kd2) 1.37 x 10-8 mol/l respectively and binding capacity of (Bmax1) 12.3 fmol/106 cells and (Bmax2) 42.8 fmol/106 cells, respectively. GnRH, hCG, IGF-1 and EGF did not induce any modification of recombinant human erythropoietin-specific binding. Recombinant human erythropoietin added to isolated adult rat Leydig cells exerted a stimulatory effect on testosterone production reaching its maximal effect at the dose of 10-10 mol/l (testosterone production from 14.9 ± 1.7 to 45.1 ± 6.2 pmol/106 cells/3 h). Addition of anti-recombinant human erythropoietin serum completely blocked the recombinant human erythropoietin-stimulated testosterone production. These results show that purified adult rat Leydig cells possess recombinant human erythropoietin specific binding, and suggest that this glycoprotein directly influences rat Leydig steroidogenesis
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
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