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  • Articles: DFG German National Licenses  (3)
  • Protein kinase C  (2)
  • Isolated islets  (1)
  • 1
    Electronic Resource
    Electronic Resource
    Direct effects of progesterone on rat islets of Langerhans in vivo and in tissue culture (1977)
    Springer
    Diabetologia 13 (1977), S. 579-583 
    Details
    ISSN: 1432-0428
    Keywords: Isolated islets ; tissue culture ; insulin secretion ; progesterone ; oestradiol ; adenylate cyclase
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Progesterone and oestradiol did not alter rates of insulin secretion from isolated rat islets of Langerhans during a 60 min period of incubation in vitro. However, islets isolated from rats which had been injected daily for 15 days with progesterone (5 mg) and oestradiol (5 μg) showed enhanced rates of insulin secretion in response to stimulation by 20 mmol/l glucose or 6 and 20 mmol/l glucose plus 5 mmol/l theophylline. Islets from rats which had been injected with the slow-releasing depot progesterone derivative, hydroxyprogesterone hexanoate, 3 times in 15 days, also showed enhanced rates of insulin release in the absence of any alteration in adenylate cyclase activity. In neither experiment could increased food intake, blood glucose levels or islet insulin content account for the observed changes. The possibility of a direct effect of progesterone on the secretory process was investigated in islets which had been cultured for 20 h with progesterone and oestradiol; these islets were then subjected to a variety of stimuli for secretion. They responded significantly more to glucose (6 or 20 mmol/l) in the presence of theophylline (5 mmol/l), while their insulin content was not significantly different from control islets cultured for a similar period. Islets cultured for 20 h in the presence of progesterone and oestradiol did not show any change in their adenylate cyclase activities. Similarly, direct addition of progesterone and oestradiol to islet homogenates did not alter the adenylate cyclase activity during a 30 minute incubation. These results suggest that progesterone and oestradiol affect insulin secretion directly, by a mechanism which does not involve activation of adenylate cyclase.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01236310
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    The role of protein kinase C in insulin biosynthesis (1993)
    Springer
    Acta diabetologica 30 (1993), S. 99-104 
    Details
    ISSN: 1432-5233
    Keywords: Insulin synthesis ; Islet of Langerhans ; Northern blotting ; Phorbol ester ; Protein kinase C
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Activation of protein kinase C (PKC) by the phorbol ester 4β-phorbol myristate acetate (4β-PMA) stimulated (pro)insulin biosynthesis in collagenase-isolated rat islets of Langerhans, as assessed by measuring the incorporation of [35S]cysteine into proinsulin and insulin after fractionation by high performance liquid chromatography. The stimulatory effects of 4β-PMA were observed at a substimulatory concentration of glucose (2 mM) but were not additive to the stimulatory effects of 20 mM glucose on insulin biosynthesis. Prolonged exposure to 4β-PMA caused a marked down-regulation of PKC activity in islets. PKC-depleted islets showed a much reduced biosynthetic response to 20 mM glucose, but this was caused, at least in part, by an enhanced basal rate of (pro)insulin synthesis. These elevations in the basal rate of insulin synthesis were not secondary to an inerease in the amount of preproinsulin mRNA in PKC-depleted islets since Northern blot analysis showed that prolonged exposure to 4β-PMA, and the subsequent loss of PKC activity, did not detectably alter basal levels of preproinsulin mRNA. These results suggest that the activation of PKC stimulates (pro)insulin synthesis in rat islets by enhancing translation of existing preproinsulin mRNA, and that this may play some part in the biosynthetic responses of β-cells to glucose.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00578222
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    Protein phosphorylation in the regulation of insulin secretion: the use of site-directed inhibitory peptides in electrically permeabilised islets of Langerhans (1995)
    Springer
    Acta diabetologica 32 (1995), S. 32-37 
    Details
    ISSN: 1432-5233
    Keywords: Islet of Langerhans ; Insulin secretion ; Protein phosphorylation ; Protein kinase C ; Protein kinase A ; Inhibitory peptides
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract We have used electrically permeabilised rat islets of Langerhans to investigate the role of protein phosphorylation in the regulation of insulin secretion using pseudosubstrate inhibitory peptides for cyclic AMP-dependent protein kinase (PKA) and for protein kinase C (PKC). The protein kinase inhibitor (PKI) peptide, PKI(6–22), completely inhibited the effects of cyclic AMP on islet PKA activity in vitro, on endogenous protein phosphorylation and on insulin secretion. This peptide had no significant effect on islet PKC activity in vitro, on CA2+-induced protein phosphorylation and on secretory responses to Ca2+ or to the PKC activator, 4β-phorbol myristate acetate (PMA). The PKC pseudosubstrate inhibitory peptide, PKC(19–36), caused a marked inhibition of islet PKC activity in vitro and inhibite PMA-induced insulin secretion without affecting secretory responses to cyclic AMP and Ca2+. These results demonstrate that PKA-and PKC-induced protein phosphorylation is obligatory for cyclic AMP-and PMA-stimulated insulin secretion, respectively, and suggest that there is little “crosstalk” between the response elements of the secretory pathways to the different, second messengers, at least after the generation of the messengers within the β-cells.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00581042
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    Paper (German National Licenses)
    Fulltext
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