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  • 1
    ISSN: 1432-0428
    Keywords: Isolated islets ; insulin release ; glucagon ; glucose ; cyclic adenosine monophosphate
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Glucose stimulation increased the cAMP content of collagenase-isolated rat pancreatic islets fourfold above baseline values. The elevation was transient, lasting about 5 min, and was dose-dependent. Insulin release continued at a constant rate throughout the incubation. — Glucagon, in the absence of glucose, increased cAMP for about 1 min, but only slightly, and had no effect on insulin release. In the presence of glucose, however, glucagon enhanced islet cAMP content 15-fold and increased the release of insulin. Glucagon was most effective at high glucose concentrations (16.6 and 25 mM). — This indicates that glucagon is critically dependent on the presence of glucose in order to increase the islet cAMP content and to stimulate insulin release. The inability of glucagon to generate sufficient cAMP in the absence of glucose might be one of the reasons why the hormone is a potentiator rather than an initiator of insulin release.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1432-0428
    Keywords: Islet hyperplasia ; islet DNA ; islet protein ; insulin release ; tolbutamide treatment ; theophylline
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Following prolonged administration of tolbutamide the DNA- and protein content per islet was enhanced but the IRI content per islet was diminished. Glucose-induced (2.0,8.0 or 16.6 mM) and leucine-induced (12.5 or 25.0 mM) IRI release from isolated islets, as well as 14CO2-production from U-14C glucose, were decreased. Theophylline (5.0 mM) restored the glucose sensitivity of the islets towards normal. The results indicate that tolbutamide-induced islet cell hyperplasia does not entail islet hyperfunction, as previously thought. Decreased IRI release may partially be explained by a tolbutamide-induced alteration of the adenylate cyclase/phosphodiesterase system of the B-cell.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Diabetologia 10 (1974), S. 85-87 
    ISSN: 1432-0428
    Keywords: Cytochalasin B ; microfilamentous system ; isolated pancreatic islets ; insulin release
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Cytochalasin B (200 μg/ml) completely inhibited the glucose-induced insulin release from isolated rat islets. Basal release was unaffected. The cytochalasin-induced inhibition was rapidly reversible. Pretreatment with cytochalasin B seemed to increase the sensitivity of islets to a subsequent glucose stimulation.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 1432-0428
    Keywords: Gastric inhibitory polypeptide ; insulin release ; isolated rat islets ; enteroinsular axis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Gastric Inhibitory Polypeptide (GIF; 1 or 10 μg/ml) potentiated glucose-induced (8 or 16.6 mM) insulin (IRI) release from isolated rat pancreatic islets. Basal release was unaffected. The threshold concentration of glucose necessary for GIF to modulate IRI release was between 6 and 8 mM. GIP had no effect on IRI release from islets submitted to a maximal glucose stimulus (25 mM).
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Springer
    Journal of molecular medicine 57 (1979), S. 825-830 
    ISSN: 1432-1440
    Keywords: Urämie ; α-Ketosäuren ; Stickstoff ; Proteinrestriktion ; Metabolismus ; Uremia ; α-Ketoacids ; Nitrogen ; Protein restriction ; Metabolism
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Description / Table of Contents: Summary Serum levels of branched-chain keto acids (BCKA's), i.e., α-keto-isocaproic acid (KICA), α-keto-isovaleric acid (KIVA) and α-keto-β-methyl-n-valeric acid (KMVA) as well as their corresponding amino acids were determined in uremic patients with compensated chronic renal failure, patients on hemodialysis, and in subjects without renal insufficiency. Uremic patients had significantly lower BCKA levels than controls without renal insufficiency. There was a negative correlation between serum BCKA's and the levels of blood urea and creatinine. BCKA's were detectable in the hemofiltrate. The concentrations of KICA and KMVA were significantly higher, that of KIVA identical compared to the respective concentrations in the hemofiltrate. This suggests a different protein binding of BCKA's. Oral administration of 5 g Ca-KICA to a healthy subject resulted in a transient increase in serum KICA and leucine. The maximum increase in KICA preceded the leucine peak. Serum BCKA levels did not change significantly in patients with compensated renal failure, who were — for 28 days each — first on an unrestricted diet plus supplementation, then solely on an unrestricted diet, followed by a protein-restricted diet (0.5 g/kg/day) plus supplementation and finally on a protein-restricted diet alone. Supplementation was with 5 essential amino acids, 4 keto acids and 1 hydroxyacid (6–9 g/day). The determination of BCKA's in serum offers a promising investigatory tool to study nitrogen metabolism in healthy and uremic subjects and might help to further evaluate the role of keto acids in the treatment of chronic renal failure.
    Notes: Zusammenfassung Die Serumkonzentrationen verzweigtkettiger Ketosäuren (BCKA's), d.h. α-Ketoisocapronsäure (KICA), α-Keto-isovaleriansäure (KIVA) und α-Keto-β-methyl-n-valeriansäure (KMVA) sowie ihrer korrespondierenden Aminosäuren wurden bei Urämikern mit kompensierter chronischer Niereninsuffizienz sowie bei hämodialysierten Urämikern und bei nierengesunden Kontrollen bestimmt. Urämiker hatten signifikant niedriger BCKA-Konzentrationen im Serum als nierengesunde Kontrollen. Es bestand eine negative Korrelation zwischen der BCKA-Konzentration und derjenigen von Kreatinin bzw. von Harnstoff. BCKA's ließen sich im Hämofiltrat nachweisen. Die Konzentrationen von KICA und KMVA waren signifikant höher, diejenige von KIVA identisch verglichen mit den entsprechenden Konzentrationen im Hämofiltrat. Daraus läßt sich eine unterschiedliche Eiweißbindung der BCKA's vermuten. Orale Einnahme von 5 g Ca-KICA führte bei einer gesunden Versuchsperson zu einem vorübergehenden, deutlichen Anstieg von Serum-KICA und Leuzin. Der maximale Anstieg der KICA trat früher ein als das Leuzinmaximum. Die jeweils 28tägige Gabe eines Gemisches verzweigtkettiger Keto- und Aminosäuren (6–9 g/Tag) mit oder ohne Eiweißbeschränkung der Kost auf 0,5 g/kg/Tag führte bei Patienten mit kompensierter chronischer Niereninsuffizienz zu keiner Änderung der BCKA-Konzentrationen im Serum. Die Bestimmung verzweigtkettiger Ketosäuren im Blut bietet neue Möglichkeiten zur Erforschung des Stickstoffmetabolismus sowie zur Überprüfung des Stellenwerts von Ketosäuren bei der Behandlung von Patienten mit chronischer Niereninsuffizienz.
    Type of Medium: Electronic Resource
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  • 6
    ISSN: 1432-1440
    Keywords: Uremia ; Oral glucose tolerance test ; α-Keto acids ; Insulin ; C-Peptide ; Urämie ; oraler Glukosetoleranztest ; α-Ketosäuren ; Insulin ; C-Peptid
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Description / Table of Contents: Zusammenfassung Der Einfluß eines oralen Glukosetoleranztests (oGTT) auf die Serumkonzentrationen verzweigtkettiger Ketosäuren (BCKA), d.h. α-Ketoisocapronsäure (KICA), α-Keto-isovaleriansäure (KIVA) und α-Keto-β-methyl-n-valeriansäure (KMVA) sowie auf die Konzentrationen von Seruminsulin, C-Peptid und Blutglukose wurde bei Urämikern mit kompensierter chronischer Niereninsuffizienz und bei gesunden Kontrollen untersucht. Bei den Kontrollen fielen nach oraler Gabe von 100 g Glukose die Blutkonzentrationen von KICA, KMVA und KIVA signifikant ab. Bei Urämikern ließ sich kein Abfall von KICA nachweisen, während der Abfall von KMVA deutlich vermindert war. Nur die Blutkonzentrationen von KIVA wurden im Verlaufe des oGTT im gleichen Ausmaß gesenkt wie bei den Kontrollen. Sechs von acht Urämikern zeigten eine gestörte Glukosetoleranz, obwohl sich bei ihnen die Konzentrationen von Seruminsulin und C-Peptid vor und während des oGTT nicht signifikant von denen der Kontrollen unterschieden. Die Untersuchungen zeigen, daß der bei Gesunden zu beobachtende Abfall der BCKA-Blutspiegel nach oraler Glukosebelastung bei Urämikern gestört ist. Diese Störung betrifft vorwiegend KICA und ist wahrscheinlich durch Insulinresistenz und/oder durch ungenügende Insulinsekretion bedingt.
    Notes: Summary The effect of an oral glucose tolerance test (oGTT) on serum levels of branched-chain keto acids (BCKA), i.e. α-keto-isocaproic acid (KICA), α-ketoisovaleric acid (KIVA) and α-keto-β-methyl-n-valeric acid (KMVA) as well as on serum insulin, C-peptide and blood glucose levels was determined in uremic patients and in healthy control subjects. In controls, blood levels of KICA, KMVA and KIVA declined significantly following oral administration of 100 g glucose. In uremic patients no declinc of KICA was observed. The fall of KMVA was diminished, while suppression of KIVA blood levels in response to the oGTT remained unimpaired. Although serum insulin and C-peptide levels in uremic patients were not significantly different from the controls before and throughout the oGTT, six out of eight displayed abnormal glucose tolerance. It is suggested that the response of blood BCKA levels to an oGTT is altered in uremia, an abnormality restricted primarily to KICA and possibly explained by insulin antagonism and/or by insufficient insulin secretion.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    Amsterdam : Elsevier
    Biochemical and Biophysical Research Communications 67 (1975), S. 701-705 
    ISSN: 0006-291X
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Biology , Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
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  • 8
    ISSN: 0006-291X
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Biology , Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    Amsterdam : Elsevier
    Analytical Biochemistry 82 (1977), S. 317-326 
    ISSN: 0003-2697
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Biology , Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    Amsterdam : Elsevier
    BBA Section Nucleic Acids And Protein Synthesis 224 (1970), S. 644-646 
    ISSN: 0005-2787
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Biology
    Type of Medium: Electronic Resource
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