Library

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
    Free radical additions. Part II. Kinetics of free radical additions of bromomalononitrile to alkenes and PMO treatment of the reactivity and regioselectivity (1987)
    s.l. : American Chemical Society
    The @journal of organic chemistry 52 (1987), S. 205-212 
    Details
    ISSN: 1520-6904
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/jo00378a009
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 2
    Electronic Resource
    Electronic Resource
    Daytime changes in oocyte development with relation to the tide for the Hawaiian saddleback wrasse, Thalassoma duperrey (1989)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of fish biology 34 (1989), S. 0 
    Details
    ISSN: 1095-8649
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Hourly variations in oocyte stages were characterized by size class and histological examination inassociation to the daytime tidal cycle for the Hawaiian saddleback wrasse, Thalassoma duperrey. Stage I (previtellogenic), stage II (vitellogenic) and stage III (hydrated) oocytes were identified as distinct clutches. During the autumn the profiles of oocytes stages showed rapid, group-synchronous development from stage I to stage III. Concurrent increases in percentages of both stage III oocytes and the gonadosomatic index (GSI) were positively correlated to and occurred I h before the high tide. Increases in stage I and stage II oocytes 1 h after high tide indicated development of new clutches following a decline in stage III oocytes, and the appearance of post-ovulatory follicles. The profile of stage II oocytes always exceeded 30% of the ovary. Lower GSI and percentages of stage III oocytes reflect significantly reduced reproduction in the summer: as in the autumn, both factors were significantly correlated, but neither variable showed a statistical relationship to the tide. Nevertheless, hydrated oocytes were found almost exclusively within 2 h of the high tide. The association of developmental changes with changes in tidal heights points to the importance of the tidal cycle or its underlying lunar influence as a predominant reproductive cue. These data show that developmental changes in oocytes occur more rapidly than observed in some more commonly studied temperate species which reproduce annually.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1095-8649.1989.tb03333.x
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 3
    Electronic Resource
    Electronic Resource
    Histological and ultrastructural evidence for the role of gonadal steroid hormones in sex change in the protogynous wrasse Thalassoma duperrey (1989)
    Springer
    Environmental biology of fishes 24 (1989), S. 117-136 
    Details
    ISSN: 1573-5133
    Keywords: Behavior ; Coral reef fish ; Hermaphroditism ; Initial-phase ; Labridae ; Leydig cells ; Oocytes ; Protogyny ; Reproduction ; Spermatogonia ; Terminal-phase
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Synopsis The process of sex change in the protogynous wrasse, Thalassoma duperrey, was investigated through histological and ultrastructural observations on the gonads of females changing sex to male. Changes in plasma steroid levels concomitant with structural changes were measured by radioimmunoassay. The process of sex change from ovary to testis was divided into six stages on the basis of changes in the structure of the germinal and somatic elements. Ovaries of females were filled with vitellogenic oocytes during the breeding season, but contained no spermatogenic tissue (Stage 1). At the commencement of sex change (Stage 2), vitellogenic oocytes began to degenerate, and were ingested by macrophagous cells. This stage was accompanied by a rapid drop in plasma levels of estradiol-17β. Thereafter, previtellogenic oocytes (Stage 3) also began to degenerate, and aggregations of stromal tissue, and loose connective tissue were observed in the central region of the lamellae. Steroid producing cells (Leydig cells), developed at the border of this loose connective tissue. Presumed spermatogonia proliferated on the periphery of the lamellae, and Leydig cells increased in size and number (Stage 4). Spermatogonia formed cysts, and underwent spermatogenesis (Stage 5). Finally, sex change to male was considered complete, with the beginning of active spermatogenesis and spermiation (Stage 6). Plasma levels of testosterone remained low throughout the sex change, but a second androgen, 11-ketotestosterone increased gradually in parallel to the increased numbers of Leydig cells and spermatogonia. Preliminary in vitro incubation of gonads with salmon gonadotropin, revealed that sex-changed males had higher levels of 11-ketotestosterone production than did females, while females had higher levels of estradiol-17β production than did males. Production of both these steroids increased in a dose-related fashion with increasing doses of gonadotropin.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00001282
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 4
    Electronic Resource
    Electronic Resource
    Effect of thyroid-stimulating hormone on the physiology and morphology of the thyroid gland in coho salmon,Oncorhynchus kisutch (1987)
    Springer
    Fish physiology and biochemistry 3 (1987), S. 63-71 
    Details
    ISSN: 1573-5168
    Keywords: thyroid physiology and morphology ; coho salmon ; thyrotropin
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Activity of the thyroid gland of the coho salmon,Oncorhynchus kisutch, was assessed by physiological, histological and ultrastructural criteria after treatment with graded doses of bovine thyrotropin (bTSH) in January and March. Average plasma thyroxine (T4) levels increased from about 0.8 ng/ml in saline-injected controls to about 15 ng/ml in fish treated with four intraperitoneal injections of 0.8 lU bTSH. Light-microscope observations of one μm-thick sections stained with methylene blue and azure II, showed that bTSH treatment increased epithelial height in both presmolts and smolts. Ultrastructural manifestations of increased activity owing to bTSH treatment were also seen, along with evidence of follicle proliferation. Cytoplasmic organelles and secretory granules increased in numbers with increased dosage of bTSH.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02183000
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 5
    Electronic Resource
    Electronic Resource
    The tilapia prolactin cell: A model for stimulus-secretion coupling (1989)
    Springer
    Fish physiology and biochemistry 7 (1989), S. 11-19 
    Details
    ISSN: 1573-5168
    Keywords: prolactin ; teleost fish ; stimulus-secretion coupling ; osmosensitive ; osmoreceptive ; Ca++ ; cAMP
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The tilapia prolactin (PRL) cell responds rapidly (10–20 min) to small physiological changes in medium osmotic pressure (OP), releasing increasing quantities of hormone as medium OP is reduced. This release is rapidly (≤ 10 min) inhibited by somatostatin (SRIF). There is now extensive evidence that tilapia PRL cell function is regulated through the second messengers Ca++ and cAMP. Our studies have shown that PRL release is augmented by treatments that lead to increased levels of intracellular Ca++ or cAMP. On the other hand, PRL release is blocked when tissues are incubated in Ca++-depleted medium or upon the addition of Co++, an inhibitor of Ca++-mediated processes. The use of45Ca++ to characterize the movement of Ca++ into PRL cells has provided evidence that an increase in the influx of extracellular Ca++ may participate in PRL release upon exposure to hyposmotic medium. Our studies have also shown that SRIF suppresses the increase in45Ca++ accumulation that is brought about when OP is reduced. We have also examined the effects of OP and SRIF on cAMP levels. The reduction of medium OP did not alter cAMP metabolism during 20 min of incubation. By contrast, cAMP accumulation in the presence of IBMX was enhanced at 1 hr of incubation in reduced OP. Thus, an increase in cAMP turnover may play a role in maintaining PRL release under sustained stimulation. SRIF reduced the accumulation of cAMP during 10 min of incubation with IBMX and also reduced the forskolin-stimulated increase in cAMP. Thus, SRIF may suppress adenylate cyclase activity. Finally, our studies have revealed that the forskolin-stimulated increase in cAMP levels is not dependent upon medium Ca++. The presence of Ca++ in the medium is required, however, for PRL release even when the cAMP messenger system has been activated. Moreover, cAMP accumulation was augmented when intracellular Ca++ was increased. This raises the possibility that reduced OP may stimulate an increase in cAMP turnover indirectly through its action(s) on cytosolic Ca++.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00004685
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 6
    Electronic Resource
    Electronic Resource
    Ultrastructural changes in the parrotfish thyroid afterin vitro stimulation with bovine thyrotropin (1986)
    Springer
    Fish physiology and biochemistry 1 (1986), S. 153-162 
    Details
    ISSN: 1573-5168
    Keywords: thyroid gland ; teleost ; ultrastructure ; thyrotropin ; thyroid hormone ; organelles ; morphology ; parrotfish (Scarus dubius) ; stereology
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Six groups of thyroid glands ofScarus dubius were examined and compared by electron microscopy after anin vitro culture for 4h with graded doses of bovine thyrotropin (bTSH). Five doses of bTSH were used encompassing the full range of the dose-response curve developed for this tissue. Upon electron microscopic examination, micrographs were taken randomly and at the same magnification, and three intracellular inclusions were quantified. The relative surface density of rough endoplasmic reticulum (rER) and the relative surface area of lysosomes and engulfed colloid droplets were recorded for each group. Three treatment groups, (1) control, no bTSH, (2) tissues exposed to 1 mIU/ml bTSH, and (3) tissues exposed to 2 mIU/ml bTSH, did not differ from each other in the quantified organelles nor in general appearance. Overall, these three groups were similar in appearance to the ultrastructure described in other teleosts except for a lack of flagellated cells. Compared to the first three groups, treatment with 5 mIU/ml bTSH, increased the density of rER, and the proportion of cell area occupied by lysosomes and engulfed colloid. This group also possessed either more microvilli or pseudopods at the lumenal surface of the follicular epithelium. After exposure to 10 mIU/ml bTSH there was an even greater increase in surface density of rER, and in surface area occupied by lysosomes and engulfed colloid droplets. The apical portion of this group was highly irregular, commonly displaying pseudopods. Group (6), (20 mIU/ml), showed a decline in cytoplasm in comparison to group (5) with many epithelial cells breaking apart. A few cells in this group were still intact but contained huge engulfed colloid droplets which extended from the basal to apical borders. This first detailed description suggests that the teleost thyroid gland undergoes ultrastructural changes with exogenous TSH stimulation in a manner similar to that seen in higher vertebrates.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02290256
    Library Location Call Number Volume/Issue/Year 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...