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  • 1
    Electronic Resource
    Electronic Resource
    The insulinotropic action of D-erythrose (1977)
    Springer
    Diabetologia 13 (1977), S. 125-130 
    Details
    ISSN: 1432-0428
    Keywords: Insulin secretion ; glucose ; erythrose ; calcium ; isolated islets
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary D-erythrose (5.0 to 20.0 mM) stimulates insulin release. This insulinotropic action of erythrose displays several features in common with that of glucose. First, erythrose (20 mM) causes a shift to the left of the sigmoidal curve relating the secretory rate to the glucose concentration, but fails to enhance the maximal response to glucose. Second, the secretory response to erythrose occurs as an early peak followed by a phase of sustained release. Third, erythrose increases the output of lactate from the islets. Last, erythrose inhibits the efflux of45calcium and favours its accumulation in isolated islets. It is suggested that, whether in response to glucose or erythrose, an increase in glycolytic flux may represent the key process involved in the identification of the secretagogue, a subsequent remodelling of calcium fluxes being apparently responsible for the activation of the insulin-releasing system.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00745139
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  • 2
    Electronic Resource
    Electronic Resource
    The stimulus-secretion coupling of amino acid-induced insulin release (1981)
    Springer
    Diabetologia 21 (1981), S. 135-142 
    Details
    ISSN: 1432-0428
    Keywords: Insulin release ; proinsulin biosynthesis ; pancreatic islets ; amino acids ; L-leucine ; L-isoleucine ; L-norvaline ; L-valine ; L-norleucine ; glycine ; L-serine ; L-lysine ; L-phenylalanine ; L-arginine ; L-glutamine ; L-asparagine ; L-glutamate
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary L-glutamine dramatically augments insulin release evoked by L-leucine. The dynamics, specificity and environmental modifications of the insulin secretory response to the combination of L-glutamine and L-leucine were investigated. L-glutamine alone failed to stimulate proinsulin biosynthesis or insulin release in rat pancreatic islets, but augmented synthesis and secretion evoked by L-leucine. In relation to the secretory response, L-glutamine could be replaced by L-asparagine but not L-glutamate; L-leucine could be replaced by L-norvaline or L-isoleucine but not by L-valine, L-norleucine, glycine, L-serine, L-lysine, L-phenylalanine or L-arginine. The secretory response to L-leucine was rapid and biphasic, whereas the enhancing action of L-glutamine upon insulin release was progressive. The release of insulin evoked by the combination of L-leucine and L-glutamine was inhibited by antimycin A, menadione, ammonium ions, verapamil, adrenaline, and by the absence of extracellular Ca2+. It was increased at high carbon dioxide tension, and by glucose, theophylline and cytochalasin B. It is concluded that the enhancing action of L-glutamine upon insulin release evoked by certain amino acids represents a phenomenon dependent on the integrity of oxidative metabolism and involving essentially the same sequence of metabolic, ionic and motile events as that characterizing the process of glucose-induced insulin release.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00251281
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  • 3
    Electronic Resource
    Electronic Resource
    The glycolytic cascade in pancreatic islets (1982)
    Springer
    Diabetologia 23 (1982), S. 1-5 
    Details
    ISSN: 1432-0428
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Conclusion The present report emphasizes the view that the acceleration of glycolysis occurring in islets stimulated by a rise in the extracellular concentration of glucose involves increases in both the availability of glycolytic intermediates, such as glucose-6-P and fructose-6-P, and the activity of the key glycolytic enzyme phosphofructokinase. We initially thought that such a dual mechanism could help to reconcile the substrate-site and regulatory-site hypotheses for the process of glucose-induced insulin release [33]. However, our more recent study on the properties of fructose-6-P,2-kinase now suggests that the increase in the rate of fructose-2,6-P2 synthesis may be mainly due to an elevation in the fructose-6-P content of the islet cells, an elevation itself attributable to a mass action phenomenon. We were also unable to detect any direct effect of glucose on the activity of phosphoglucomutase, the enzyme catalyzing the synthesis of glucose-1,6P2, another activator of phosphofructokinase. Therefore, there is as yet no convincing evidence that the molecule of glucose, whether located in the extracellular or intracellular fluid, interacts with a specific receptor to induce activation of a hypothetical glucosensor system. Obviously, the latter statement is not meant to deny that glucose binds to the stereospecific carrier mediating glucose transport across the B cell plasma membrane and to those enzymes (hexokinase, glucokinase, aldose reductase) catalyzing the first steps of its intracellular metabolism. Such binding phenomena, however, cannot be equated with the situation in which the insulin secretory response depends solely on the allosteric activation of an enzyme by a given secretagogue, as appears to be the case in islets stimulated by the nonmetabolized analogue of L-leucine, 2-aminobicyclo [2,2,12] heptane-2-carboxylic acid [34,35].
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00257721
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  • 4
    Electronic Resource
    Electronic Resource
    Effect of a phospho-oligosaccharidic putative insulin messenger on insulin release in rats (1989)
    Springer
    Diabetologia 32 (1989), S. 295-299 
    Details
    ISSN: 1432-0428
    Keywords: Insulin release ; pancreatic islets ; phospho-oligosaccharide ; insulin messenger
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary The phospho-oligosaccharide extracted from rat liver and supposed to act as the insulin second messenger inhibits glucose-stimulated insulin release. In the present study, this phospho-oligosaccharide was found not to affect D-[U-14C]glucose oxidation and 45Ca net uptake, but to inhibit insulin release evoked by either D-glucose or 2-ketoisocaproate in isolated rat islets. The relative extent of the latter inhibition was unaffected by either the concentration of D-glucose or the presence of dibutyryl-cyclic AMP, forskolin or glucagon in the incubation medium. At variance with the inhibitory effect of clonidine, that of the phospho-oligosaccharide was resistant to both blockade of α2-adrenergic receptors or pre-treatment with the toxin of Bordetella pertussis. It is speculated, therefore, that such a phospho-oligosaccharide might interfere with a distal event in the insulin secretory sequence.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00265545
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  • 5
    Electronic Resource
    Electronic Resource
    Preferential alteration of oxidative relative to total glycolysis in pancreatic islets of two rat models of inherited or acquired Type 2 (non-insulin-dependent) diabetes mellitus (1993)
    Springer
    Diabetologia 36 (1993), S. 305-309 
    Details
    ISSN: 1432-0428
    Keywords: Pancreatic islets ; GK rats ; streptozotocin ; glucose metabolism
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary In islets from both adult rats injected with streptozotocin during the neonatal period and spontaneously diabetic rats obtained by repeated selective breedings (GK rats), the ratio between d-[3, 4-14C]glucose oxidation and d-[5-3H]glucose conversion to 3HOH was 25% lower than in islets from control rats, indicating an impaired contribution of oxidative to total glycolysis. No primary defect in the Krebs cycle was found in the islets of diabetic rats, as judged from the ratio between either d-[2-14C]glucose or d-[6-14C]glucose and d-[3, 4-14C]glucose oxidation. Therefore, we propose that a preferential alteration of oxidative glycolysis in the pancreatic beta cell may contribute to the impairment of glucose-induced insulin release not only in a cytotoxic but also in a spontaneous model of non-insulin-dependent diabetes mellitus.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00400232
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  • 6
    Electronic Resource
    Electronic Resource
    Enzymatic, metabolic and secretory patterns in human islets of Type 2 (non-insulin-dependent) diabetic patients (1994)
    Springer
    Diabetologia 37 (1994), S. 177-181 
    Details
    ISSN: 1432-0428
    Keywords: Key words Pancreatic islets, Type 2 (non-insulin-dependent) diabetic patients, FAD-glycerophosphate dehydrogenase, glucose metabolism, insulin secretion.
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Islets were isolated by automatic digestion from non-diabetic cadaveric organ donors and from Type 2 (non-insulin-dependent) diabetic subjects. The activity of FAD-glycerophosphate dehydrogenase, but not that of either glutamate dehydrogenase, glutamate-oxalacetate transaminase or glutamate-pyruvate transaminase, was lower in Type 2 diabetic patients than control subjects. Hexokinase, glucokinase and glutamate decarboxylase activities were also measured in islets from control subjects. The utilization of D-[5-3H]glucose, oxidation of D-[6-14C]glucose and release of insulin evoked by D-glucose were all lower in Type 2 diabetic patients than control subjects. The secretory response to the combination of L-leucine and L-glutamine appeared less severely affected. Islets from Type 2 diabetic patients may thus display enzymatic, metabolic and secretory anomalies similar to those often observed in animal models of Type 2 diabetes, including a deficiency of beta-cell FAD-linked glycerophosphate dehydrogenase, the key enzyme of the glycerol phosphate shuttle. [Diabetologia (1994) 37: 177–181]
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s001250050090
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  • 7
    Electronic Resource
    Electronic Resource
    Comparison of the effects of D-mannoheptulose and its hexaacetate ester on D-glucose metabolism and insulinotropic action in rat pancreatic islets (1998)
    Springer
    Diabetologia 41 (1998), S. 1109-1113 
    Details
    ISSN: 1432-0428
    Keywords: Keywords D-mannoheptulose (hexaacetate) ; pancreatic islets ; insulin release ; D-glucose metabolism
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary It was recently, and surprisingly, found that D-mannoheptulose did not affect D-glucose metabolism and insulinotropic action in pancreatic islets incubated at a low concentration of D-glucose. To explain this finding, the metabolism and secretory response to the hexose were investigated in rat islets exposed to D-mannoheptulose hexaacetate, which was recently found to inhibit D-glucose catabolism in cells that are otherwise fully resistant to the heptose. At a high concentration of D-glucose (16.7 mmol/l), the utilisation of D-[5-3H]glucose and oxidation of D-[U-14C]glucose, as well as the insulinotropic action of the hexose, were affected less by D-mannoheptulose tetraacetate than by unesterified D-mannoheptulose. This coincided with a reduced uptake of the ester by intact islets and a lower rate of hydrolysis of the ester in islet homogenates compared with findings in other monosaccharide esters such as D-glucose pentaacetate. At a low concentration of D-glucose (2.8 mmol/l), D-mannoheptulose hexaacetate was slightly more efficient than the unesterified heptose in reducing D-glucose catabolism, but still failed to suppress the secretory response to the hexose. These findings do not necessarily mean that unesterified D-mannoheptulose enters beta-cells more efficiently at high than at low extracellular D-glucose concentrations, especially if possible differences in the respective contributions of distinct islet cell types to the overall catabolism of D-glucose by whole islets is allowed for. These data do not rule out the possibility that D-glucose phosphorylation is more resistant to D-mannoheptulose in beta cells incubated at a low than a high concentration, independently of any difference in the intracellular concentration of the heptose. However, the mechanism of this resistance is still not explained. [Diabetologia (1998) 41: 1109–1113]
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s001250051037
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  • 8
    Electronic Resource
    Electronic Resource
    Impairment of the mitochondrial oxidative response to D-glucose in pancreatic islets from adult rats injected with streptozotocin during the neonatal period (1990)
    Springer
    Diabetologia 33 (1990), S. 654-660 
    Details
    ISSN: 1432-0428
    Keywords: Pancreatic islets ; insulin release ; streptozotocin ; glucose metabolism ; leucine metabolism
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Pancreatic islets removed from adult rats injected with streptozotocin during the neonatal period display an impaired secretory response to D-glucose and, to a lesser extent, to L-leucine. Despite normal to elevated hexokinase and glucokinase activities in the islets of these glucose-intolerant animals and despite normal mitochondrial binding of the hexokinase isoenzymes, the metabolic response to a high concentration of D-glucose is severely affected, especially in terms of D-[6-14C]glucose oxidation. Thus, the ratio in D-[6-14C]glucose oxidation/D-[5-3H]glucose utilization is much less markedly increased in response to a rise in hexose concentration and, at a high concentration of D-glucose (16.7 mmol/l), less markedly decreased by the absence of Ca2+ and presence of cycloheximide in diabetic than control rats. This metabolic defect contrasts with (1) a close-to-normal or even increased capacity of the islets of diabetic rats to oxidize D-[6-14C]glucose, [2-14C]pyruvate, L-[U-14C]glutamine and L-[U-14C]leucine at low, non-insulinotropic, concentrations of these substrates; (2) a lesser impairment of the oxidation of L-[U-14 C]leucine tested in high concentration (20 mmol/l), the effect of Ca2+ deprivation upon the latter variable being comparable in diabetic and control rats; (3) an unaltered transamination of either [2-14 C]pyruvate or L-[U-14C]leucine; and (4) a modest perturbation of glycolysis. The most obvious alteration in glycolysis consists in a lesser increase of the glycolytic flux in response to a rise of D-glucose concentration in diabetic than control rats, this coinciding with an apparent decrease in affinity of glucokinase for the hexose. It is speculated that the preferential impairment of the metabolic and secretory response to D-glucose may be mainly attributable to an altered coupling between calcium accumulation and the stimulation of oxidative events in Beta-cell mitochondria of diabetic rats.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00400566
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  • 9
    Electronic Resource
    Electronic Resource
    Deficient activity of FAD-linked glycerophosphate dehydrogenase in islets of GK rats (1993)
    Springer
    Diabetologia 36 (1993), S. 722-726 
    Details
    ISSN: 1432-0428
    Keywords: GK rats ; pancreatic islets ; liver ; FAD-linked glycerophosphate dehydrogenase
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary In pancreatic islet extracts of rats with hereditary non-insulin-dependent diabetes mellitus (GK rats), the activity of the mitochondrial FAD-linked glycerophosphate dehydrogenase, as measured by either a radioisotopic or colorimetric procedure, only represented 30 to 40% of that found in control rats. This decrease in enzymic activity was not attributable to any sizeable change in either islet DNA content or the relative contribution of insulin-producing beta cells to total islet mass. It contrasted with a normal activity of other mitochondrial dehydrogenases and hexokinase isoenzymes. It coincided, however, with an increased activity of glutamate-pyruvate transaminase, as already observed in adult rats injected with streptozotocin during the neonatal period. The decreased activity of islet FAD-linked glycerophosphate dehydrogenase also contrasted with an increased activity of the same enzyme in the liver of GK, as compared to control rats. In the light of these findings and recent metabolic data collected in intact islets of GK rats, it is proposed that a deficiency of beta-cell FAD-linked glycerophosphate dehydrogenase, the key enzyme of the glycerol phosphate shuttle, may represent a cause of inherited non-insulin-dependent diabetes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00401142
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  • 10
    Electronic Resource
    Electronic Resource
    Glucokinase is not the pancreatic B-cell glucoreceptor (1985)
    Springer
    Diabetologia 28 (1985), S. 520-527 
    Details
    ISSN: 1432-0428
    Keywords: Pancreatic islets ; insulin-producing tumoral cells ; glucose anomers ; glucokinase ; hexokinase
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary A series of recent experimental findings are reviewed to indicate that glucokinase does not represent the pancreatic B-cell glucoreceptor. (1) Whether in liver, pancreatic islet or insulin-producing tumoral cell homogenates, glucokinase fails to yield a higher reaction velocity with α-than β-D-glucose. (2) At a high glucose concentration (40 mmol/l), when the phosphorylation of glucose by glucokinase is indeed higher with β- than α-D-glucose, no preference for β-D-glucose is observed in intact islets, as judged from the utilization of D-[5-3H]glucose, production of lactic acid, oxidation of D-[U-14C] glucose, net uptake of 45Ca or release of insulin. (3) The glucose 6-phosphate content of intact islets is higher in the presence of β- than α-D-glucose. (4) At a low glucose concentration (3.3 mmol/l), when the participation of glucokinase to hexose phosphorylation is minimal, α-D-glucose is still better metabolized and stimulates both 45Ca net uptake and insulin release more efficiently than β-D-glucose, despite the fact that hexokinase yields a higher reaction velocity with β- than α-D-glucose. (5) In intact islets, β-D-glucose is used preferentially to α-D-glucose in the pentose cycle pathway as judged from the oxidation of α- or β-D-[1-14C]glucose relative to that of α- or β-D-[6-14C]glucose. (6) In islets removed from fasted rats, the rate of glycolysis is more severely decreased than expected from the repression of glucokinase. (7) The metabolism of glucose in tumoral insulin-producing cells differs, in several respects, from that in normal pancreatic islets, although the pattern of hexokinase and glucokinase activities is similar in these two types of cells. All these observations point to the participation of regulatory sites distal to glucose phosphorylation in the control of glucose metabolism in islet cells.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00281986
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