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  • Disturbances  (1)
  • Glucocorticoids  (1)
  • 1
    Digitale Medien
    Digitale Medien
    Springer
    Calcified tissue international 57 (1995), S. 120-126 
    ISSN: 1432-0827
    Schlagwort(e): Glucocorticoids ; Osteoblasts ; Bone ; Osteoporosis
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Medizin , Physik
    Notizen: Abstract Clinical observations suggest that the onset and severity of glucocorticoid (GC) induced osteoporosis is dependent on the duration of the GC treatment and the applied GC compound. To test whether these in vivo observations are reflected by different in vitro effects of various synthetic GCs on human bone cell metabolism we isolated human osteoblast-like cells (HOC) from bone biopsies of healthy (no clinical symptoms of arthritis or arthrosis) adults who underwent selective orthopedic surgery. HOC were identified as bone cells by 1,25-vitamin D3-stimulated increase of specific alkaline phosphatase (ALP) activity, secretion of osteocalcin and type-I procollagen peptide, and the ability to form mineral in vitro. We investigated the effects of dexamethasone (dexa), methylprednisolone (mpred), prednisolone (pred), and deflazacort (defla) on DNA-synthesis, ALP, and osteocalcin (OC)- and type-I procollagen peptide secretion of HOC in vitro. In summary, (1) GC exposure stimulates DNA synthesis after 6–12-hour treatment periods; (2) dex and mpred strongly inhibit DNA (48-hour treatment) and collagen synthesis but stimulate ALP, whereas pred and defla exhibit smaller effects on DNA synthesis, ALP, and collagen production; and (3) all tested glucocorticoids inhibit OC secretion by HOC in vitro. Thus, the effect of GC on DNA synthesis of HOC varies with the duration of GC exposure, and dex and mpred more potently affect HOC metabolism in vitro than pred and defla.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 2
    Digitale Medien
    Digitale Medien
    Springer
    Oecologia 71 (1986), S. 25-28 
    ISSN: 1432-1939
    Schlagwort(e): Diversity ; Disturbances ; Nutrient pulses ; Population reductions ; Varying frequency and intensity ; Growth strategies
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract The influence of periodic disturbances of various frequency on the maintenance of the phytoplankton diversity was studied by semicontinuous competition experiments. Disturbances consisted of dilution events, which meant both addition of fresh nutrients and elimination of organisms. The intervals between dilution events varied from 1 to 14 days. Diversity was found to increase with increasing intervals between disturbances. coexisting species belonged to different strategy types: (a) species with rapid growth under enriched conditions, (b) species with good competitive abilities under impoverished conditions, (c) species with the ability to build up storage pools of the limiting nutrient. An increase of the number of coexisting species over the number that would have coexisted in steady state was only found when the interval exceeded one generation time.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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