GLORIA

GEOMAR Library Ocean Research Information Access

X
feed icon rss

Your email was sent successfully. Check your inbox.

An error occurred while sending the email. Please try again.

Proceed reservation?

Export
  • 1
    Electronic Resource
    Electronic Resource
    Androgen-induced changes in Leydig cell ultrastructure and steroidogenesis in juvenile African catfish, Clarias gariepinus (1999)
    Springer
    Cell & tissue research 297 (1999), S. 291-299 
    Details
    ISSN: 1432-0878
    Keywords: Key words Teleost fish ; Puberty ; Testes ; Sex steroids ; Ultrastructure ; Steroidogenesis ; Clarias gariepinus (Teleostei)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract  The present report focuses on the mechanism(s) involved in the steroid-induced decrease of androgen production in immature African catfish testes that was observed in previous studies. Juvenile animals were implanted with Silastic pellets containing different 11-oxygenated androgens (11-ketotestosterone, KT; 11β- hydroxyandrostenedione, OHA; 11-ketoandrostenedione, KA), testosterone (T) or estradiol-17β (E2). Control groups received steroid-free pellets. Two weeks later, testis tissue fragments were either incubated with increasing concentrations of catfish luteinizing hormone (LH), or incubated with [3H]-pregnenolone ([3H]-P5) or [3H]-androstenedione ([3H]-A). Tissue fragments were also prepared for the quantitative assessment of Leydig cell morphology. Most of the parameters studied were not affected significantly by implantation of E2. Implantation of all androgens inhibited both the basal and the LH-stimulated androgen secretory capacity in vitro. This was associated with a reduced size of the Leydig cells and loss of half of their mitochondria. The studies on the metabolism of tritiated steroid hormones indicated that steroidogenic steps prior to 11β-hydroxylation, probably C17–20 lyase activity, were affected by all androgens. Although the effects of 11-oxygenated androgens and T on Leydig cells were mostly similar, previous work showed that only the 11-oxygenated androgens stimulated spermatogenesis, suggesting that distinct mechanisms of action are used by 11-oxygenated androgens and T. These mechanisms, however, seem to merge on the same target(s) to impair Leydig cell androgen production. Such a negative feedback mechanism may be of relevance in the context of the decline in androgen secretion per milligram testis tissue that accompanies the first wave of spermatogenesis in pubertal African catfish.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004410051357
    Location Call Number Limitation Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 2
    Electronic Resource
    Electronic Resource
    Sexual steroids during puberty in male African catfish (Clarias gariepinus): serum levels and gonadotropin-stimulated testicular secretion in vitro (1994)
    Springer
    Journal of comparative physiology 164 (1994), S. 195-205 
    Details
    ISSN: 1432-136X
    Keywords: Sex steroids ; Blood levels ; Testicular in vitro secretion ; Pubertal development ; African catfish (Clarias gariepinus)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract Blood serum and testicular tissue samples were collected from 3 to 13-month-old African catfish (groups A-G) in order to study their pubertal development. The sampling covered the period from before the beginning of spermatogenesis until full maturity. Testes of fish in group A contained spermatogonia alone. In testes of group B, spermatogonia, spermatocytes and spermatids were present. Spermatozoa were first observed in group C and became predominant as the fish attained full maturity (group G). Several sex steroids were determined in the blood samples. Testosterone was the quantitatively dominating androgen in the blood serum (3–5 ng·ml-1) in groups B and C (fish in group A were too small to collect blood samples). In group D, the concentrations of 11-ketotestosterone and 11β-hydroxyandrostenedione increased to levels similar to those of testosterone. Androstenedione that was undetectable before (below 0.4 ng·ml serum-1), also increased to 3–5 ng·ml-1 in group D. The levels of androgens kept increasing until the fish attained full maturity (group G). In order to monitor the responsiveness to gonadotropic hormone and the steroid secretion capacity, the in vitro secretion of two steroids (11β-hydroxyandrostenedione and 17α,20β-dihydroxy-4-pregnen-3-one) by testicular tissue was quantified at the different stages of development. Testicular maturation was accompanied by changes of both the steroid secretion capacities and of the sensitivity to gonadotropic hormone. The most important changes occurred just after the initiation of spermatogenesis, as spermatocyte/spermatid formation was associated with a drop of the secretory capacity (amount of steroid secreted per milligram of tissue incubated) and with a reduced sensitivity to gonadotropic hormone. At later stages, when the testicular weight substantially increased concurrently with the formation of numerous spermatozoa, both the secretory capacity and the responsiveness to gonadotropic hormone increased again to reach the levels typical of adult fish. The blood levels of androgens appeared to be positively related to the increasing testicular weight in the later phases of development.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00354080
    Location Call Number Limitation Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 3
    Electronic Resource
    Electronic Resource
    Effect of salmon gonadotropic hormone on sex steroids in male rainbow trout: plasma levels and testicular secretion in vitro (1992)
    Springer
    Journal of comparative physiology 162 (1992), S. 224-230 
    Details
    ISSN: 1432-136X
    Keywords: Gonadotropic hormone ; Sex steroids ; Reproductive cycle ; Testis ; Rainbow trout, Oncorhynchus mykiss
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary Male rainbow trout were treated with salmon gonadotropic hormone (GTH) at different stages of the circannual reproductive cycle; spawning fish were also treated with an antiserum against salmon GTH. Injection of GTH led to a several-fold increase of plasma sex steroid levels during spermatogenesis and in the spawning season but was without effect at early stages of testicular development. GTH neutralization during the spawning season was followed by a several-fold decrease of plasma sex steroid levels. During spermatogenesis and in the spawning season, both treatment regimes resulted in an increased sensitivity of testicular explants in response to a subsequent stimulation of steroid secretion in vitro. This up-regulatory response may facilitate and maintain the high sex steroid plasma levels observed during the spawning season. It may also be necessary to allow for concomitant peak values of plasma GTH and sex steroids in the spawning season, a situation difficult to understand within the negative feedback concept. The adaptive capacities of the testicular steroidogenic system indicate that it is not only an effector site for GTH but also an active part of the endocrine system controling reproduction.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00357528
    Location Call Number Limitation Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 4
    Electronic Resource
    Electronic Resource
    1 3C-NMR-Spektroskopie an Polyäthern (1974)
    Weinheim : Wiley-Blackwell
    Zeitschrift für die chemische Industrie 86 (1974), S. 450-450 
    Details
    ISSN: 0044-8249
    Keywords: Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/ange.19740861216
    Location Call Number Limitation Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 5
    Electronic Resource
    Electronic Resource
    Polymere mit atropisomeren Biphenyl-Grundbausteinen (1967)
    Weinheim : Wiley-Blackwell
    Zeitschrift für die chemische Industrie 79 (1967), S. 422-422 
    Details
    ISSN: 0044-8249
    Keywords: Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/ange.19670790936
    Location Call Number Limitation Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 6
    Electronic Resource
    Electronic Resource
    Synthetische makromolekulare Stoffe mit reaktiven Gruppen (1957)
    Weinheim : Wiley-Blackwell
    Zeitschrift für die chemische Industrie 69 (1957), S. 153-171 
    Details
    ISSN: 0044-8249
    Keywords: Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Es wird über Synthese, Eigenschaften und Reaktionen einiger makromolekularer Stoffe mit reaktiven Gruppen berichtet, und zwar über Derivate der Polyacrylsäure (Polyacrylsäure-hydrazid, Polyacrylhydroxamsäure, Polyacrylsäureamid), des Polyvinylalkohols, über Polyacrolein und Polymethacrolein, Polyvinylsulfonsäure und ihre Derivate sowie über Copolymere aus Styrol und Maleinsäureanhydrid. An den reaktiven Gruppen dieser polymeren Stoffe werden chemische Reaktionen ausgeführt. Dabei zeigt sich, daß unter Bedingungen, die dem makromolekularen Bau des Reaktionspartners angepaßt sind, eine Reihe von Reaktionen, die aus der niedermolekularen Chemie gut bekannt sind, auf solche Polymere übertragen werden können. Dadurch werden neue makromolekulare Stoffe zugänglich, die durch Polymerisation oder Polykondensation nicht zu erhalten sind.
    Additional Material: 10 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/ange.19570690502
    Location Call Number Limitation Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 7
    Electronic Resource
    Electronic Resource
    Neuere Untersuchungen über optisch aktive Polymere (1967)
    Weinheim : Wiley-Blackwell
    Zeitschrift für die chemische Industrie 79 (1967), S. 280-280 
    Details
    ISSN: 0044-8249
    Keywords: Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/ange.19670790621
    Location Call Number Limitation Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 8
    Electronic Resource
    Electronic Resource
    Recent Studies of Optically Active Polymers (1967)
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 6 (1967), S. 271-271 
    Details
    ISSN: 0570-0833
    Keywords: Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/anie.196702712
    Location Call Number Limitation Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 9
    Electronic Resource
    Electronic Resource
    Über den mit Säuren katalysierten Abbau von Poly-3,4-acrolein (1966)
    Weinheim : Wiley-Blackwell
    Zeitschrift für die chemische Industrie 78 (1966), S. 613-613 
    Details
    ISSN: 0044-8249
    Keywords: Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/ange.19660781156
    Location Call Number Limitation Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 10
    Electronic Resource
    Electronic Resource
    Methoden und Probleme beim Studium optisch aktiver Polymerer (1966)
    Weinheim : Wiley-Blackwell
    Zeitschrift für die chemische Industrie 78 (1966), S. 909-909 
    Details
    ISSN: 0044-8249
    Keywords: Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/ange.19660781821
    Location Call Number Limitation Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
Close ⊗
This website uses cookies and the analysis tool Matomo. More information can be found here...