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ML Massa, MI Borelli, H Del Zotto and JJ Gagliardino

We correlated the changes in glucose-induced insulin secretion with those observed in glucose metabolism and hexokinase/glucokinase activity in islets from normal sucrose-fed hamsters. Blood glucose and insulin levels were measured in normal male hamsters fed with (S5) or without (C5) 10% sucrose in the drinking water for 5 weeks. Isolated islets (collagenase digestion) from both groups of animals were used to study insulin secretion, (14)CO(2) and (3)H(2)O production from D-[U-(14)C]-glucose and D-[5-(3)H]-glucose respectively, with 3.3 or 16.7 mM glucose in the medium, and hexokinase/glucokinase activity (fluorometric assay) in islet homogenates. Whereas S5 and C5 animals had comparable normal blood glucose levels, S5 showed higher insulin levels than C5 hamsters (2.3+/-0.1 vs 0.6+/-0.03 ng/ml, P<0.001). Islets from S5 hamsters released significantly more insulin than C5 islets in the presence of low and high glucose (3.3 mM glucose: 0.77+/-0.04 vs 0.20+/-0.06 pg/ng DNA/min, P<0.001; 16.7 mM glucose: 2.77+/-0.12 vs 0.85+/-0.06 pg/ng DNA/min, P<0.001) and produced significantly higher amounts of (14)CO(2) and (3)H(2)O at both glucose concentrations ((14)CO(2): 3.3 mM glucose: 0.27+/-0.01 vs 0.18+/-0.01, P<0.001; 16.7 mM glucose: 1.44+/-0.15 vs 0.96+/-0.08, P<0.02; (3)H(2)O: 3.3 mM glucose: 0.31+/-0.02 vs 0.15+/-0.01, P<0.001; 16.7 mM glucose: 1.46+/-0.20 vs 0.76+/-0.05 pmol glucose/ng DNA/min, P<0.005). The hexokinase K(m) and V(max) values from S5 animals were significantly higher than those from C5 ones (K(m): 100.14+/-7.01 vs 59.90+/- 3.95 microM, P<0.001; V(max): 0.010+/-0.0005 vs 0.008+/- 0.0006 pmol glucose/ng DNA/min, P<0.02). Conversely, the glucokinase K(m) value from S5 animals was significantly lower than in C5 animals (K(m): 15.31+/-2.64 vs 35.01+/-1.65 mM, P<0.001), whereas V(max) figures were within a comparable range in both groups (V(max): 0.048+/-0.009 vs 0.094+/-0.035 pmol glucose/ng DNA/min, not significant). The glucose phosphorylation ratio measured at 1 and 100 mM (hexokinase/glucokinase ratio) was significantly higher in S5 (0.26+/-0.02) than in C5 animals (0.11+/-0.01, P<0.005), and it was attributable to an increase in the hexokinase activity in S5 animals. In conclusion, sucrose administration increased the hexokinase/glucokinase activity ratio in the islets, which would condition the increase in glucose metabolism by beta-cells, and in beta-cell sensitivity and responsiveness to glucose. These results support the concept that increased hexokinase rather than glucokinase activity causes the beta-cell hypersensitivity to glucose, hexokinase being metabolically more active than glucokinase to up-regulate beta-cell function.

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MA Luque, N Gonzalez, L Marquez, A Acitores, A Redondo, M Morales, I Valverde and ML Villanueva-Penacarrillo

Glucagon-like peptide-1 (GLP-1) has been shown to have insulin-like effects upon the metabolism of glucose in rat liver, muscle and fat, and on that of lipids in rat and human adipocytes. These actions seem to be exerted through specific receptors which, unlike that of the pancreas, are not - at least in liver and muscle - cAMP-associated. Here we have investigated the effect, its characteristics, and possible second messengers of GLP-1 on the glucose metabolism of human skeletal muscle, in tissue strips and primary cultured myocytes. In muscle strips, GLP-1, like insulin, stimulated glycogen synthesis, glycogen synthase a activity, and glucose oxidation and utilization, and inhibited glycogen phosphorylase a activity, all of this at physiological concentrations of the peptide. In cultured myotubes, GLP-1 exerted, from 10(-13) mol/l, a dose-related increase of the D-[U-(14)C]glucose incorporation into glycogen, with the same potency as insulin, together with an activation of glycogen synthase a; the effect of 10(-11) mol/l GLP-1 on both parameters was additive to that induced by the equimolar amount of insulin. Synthase a was still activated in cells after 2 days of exposure to GLP-1, as compared with myotubes maintained in the absence of peptide. In human muscle cells, exendin-4 and its truncated form 9-39 amide (Ex-9) are both agonists of the GLP-1 effect on glycogen synthesis and synthase a activity; but while neither GLP-1 nor exendin-4 affected the cellular cAMP content after 5-min incubation in the absence of 3-isobutyl-1-methylxantine (IBMX), an increase was detected with Ex-9. GLP-1, exendin-4, Ex-9 and insulin all induced the prompt hydrolysis of glycosylphosphatidylinositols (GPIs). This work shows a potent stimulatory effect of GLP-1 on the glucose metabolism of human skeletal muscle, and supports the long-term therapeutic value of the peptide. Further evidence for a GLP-1 receptor in this tissue, different from that of the pancreas, is also illustrated, suggesting a role for an inositolphosphoglycan (IPG) as at least one of the possible second messengers of the GLP-1 action in human muscle.

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ER Busby, GA Cooper and TP Mommsen

Prostaglandin E(2) (PGE(2)) potently activated glycogenolysis and gluconeogenesis in isolated rockfish (Sebastes caurinus) hepatocytes. The average degree of activation for glycogenolysis was 6.4+/-0.67-fold (mean+/-S.E.M.; n=37), and could be as much as 19-fold. Analysis of dose-concentration relationships between glycogenolytic actions and PGE(2) concentrations yielded an EC(50) around 120 nM in hepatocyte suspensions and 2 nM for hepatocytes immobilized on perifusion columns. For the activation of gluconeogenesis (1.74+/-0.14-fold; n=10), the EC(50) for suspensions was 60 nM. Intracellular targets for PGE(2) actions are adenylyl cyclase, protein kinase A and glycogen phosphorylase. Concentrations of cAMP increased with increasing concentrations of PGE(2), and peaked within 2 min of hormone application. In the presence of the phosphodiesterase inhibitor, isobutyl-3-methylxanthine, peak height was increased and peak duration extended. The protein kinase A inhibitor, Rp-cAMPS, counteracted the activation of glycogenolysis by PGE(2), implying that the adenylyl cyclase/protein kinase A pathway is the most important, if not exclusive, route of message transduction. PGE(2) activated plasma membrane adenylyl cyclase and hepatocyte glycogen phosphorylase in a dose-dependent manner. The effects were specific for PGE(2); smaller degrees of activation of glycogenolysis were noted for PGE(1), 11-deoxy PGE(1), 19-R-hydroxy-PGE(2), and prostaglandins of the A, B and Falpha-series. The selective EP(2)-receptor agonist, butaprost, was as effective as PGE(2), suggesting that rockfish liver contains prostaglandin receptors pharmacologically related to the EP(2) receptors of non-hepatic tissues of mammals. Rockfish hepatocytes quickly degraded added PGE(2) (t((1/2))=17-26 min). A similar ability to degrade PGE(2) has been noted in catfish (Ameiurus nebulosus) hepatocytes, but no glycogenolytic or gluconeogenic actions of the hormone are noted for this species. We conclude that PGE(2) is an important metabolic hormone in fish liver, with cAMP-mediated actions on glycogen and glucose metabolism, and probably other pathways regulated by cAMP and protein kinase A. The constant presence of EP(2)-like receptors is a unique feature of the fish liver, with interesting implications for function and evolution of prostaglandin receptors in vertebrates.

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FP O'Harte, AM Gray and PR Flatt

This study investigates the effects of gastric inhibitory polypeptide (GIP) and glycated GIP (glucitol adduct of GIP) on glucose uptake and metabolism in muscle. Glycated GIP (molecular mass 5147.2 Da) was purified by HPLC following in vitro incubation under hyperglycaemic reducing conditions (24 h at pH 7.4). GIP (10(-10)-10(-8) mol/l) significantly stimulated (1.4- to 1.5-fold, P < 0.001) 2-deoxy-D-[1-3H]glucose uptake in abdominal muscle pieces from 3- to 5-week-old lean mice compared with control incubations (without GIP). This stimulatory effect on glucose uptake at 10(-10)-10(-9) mol/l was decreased by 13-20% following glycation of the peptide (P < 0.05). GIP (10(-9) and 10(-8) mol/l) induced a stepwise 1.4- to 1.7-fold increase (P < 0.01, P < 0.001 respectively) in [14C]glucose oxidation compared with controls. This effect on glucose oxidation was diminished by 32% with 10(-8) mol/l glycated GIP (P < 0.05). GIP (10(-9) and 10(-8) mol/l) induced a 1.4- to 1.8-fold increase in [14C]glucose incorporation into muscle glycogen (glycogenesis) compared with controls. Glycated GIP (10(-8) mol/l) exhibited a 41% decrease in glycogenic activity (P < 0.01). GIP (10(-10)-10(-8) mol/l) stimulated lactate production in isolated abdominal muscle (1.2- to 1.3-fold, P < 0.05); however glycated GIP did not exert a significant effect. This study demonstrates for the first time that GIP promotes glucose uptake, glucose oxidation and glycogenesis in muscle tissue. Furthermore, modification of GIP through glycation diminishes its biological effectiveness.

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Neele S Dellschaft, Marie-Cecile Alexandre-Gouabau, David S Gardner, Jean-Philippe Antignac, Duane H Keisler, Helen Budge, Michael E Symonds and Sylvain P Sebert

Dandrea J Keisler DH Stephenson T Symonds ME 2005 Programming of glucose-insulin metabolism in adult sheep after maternal undernutrition . American Journal of Physiology. Regulatory, Integrative and Comparative Physiology 289 R947 – R954

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D Patiag, X Qu, S Gray, I Idris, M Wilkes, JP Seale and R Donnelly

Angiotensin II (ANGII) increases insulin sensitivity in diabetic and non-diabetic subjects, even at subpressor doses, and because there is 'crosstalk' between ANGII and insulin-signaling pathways the underlying mechanism may not be due solely to changes in regional blood flow. A series of experimental studies was undertaken to evaluate the effects of ANGII on glucose and lipid metabolism in vivo and in vitro. Groups of fructose-fed, insulin-resistant Sprague-Dawley (SD) rats were pre-treated with 0.3 mg/kg per day of the AT(1)-receptor antagonist L-158 809 (n=16), or vehicle (n=16), by oral gavage. This was prior to an oral glucose tolerance test (day 5) and measurement of the effects of ANGII infusion (20 ng/kg per min i.v. for 3 h) on whole-body insulin sensitivity using the insulin suppression test (day 7). The effect of ANGII infusion on total triglyceride secretion rate (TGSR) was evaluated in normal SD rats pretreated for 7 days with L-158 809 (n=12) or vehicle (n=12). AT(1)- and AT(2)- receptor mRNA expression and [(3)H]2-deoxyglucose uptake were assessed in cultured L6 myoblasts. Short-term treatment with L-158 809 had no effect on glucose tolerance or fasting triglyceride levels in fructose-fed rats. ANGII infusion had no effect on insulin sensitivity in fructose-fed rats pretreated with vehicle (steady-state plasma glucose (SSPG) values 8.1+/-1.6 vs 8. 4+/-0.4 mmol/l), but pretreatment with L-158 809 resulted in ANGII having a modest insulin antagonist effect in this insulin-resistant model (SSPG values 9.6+/-0.3 vs 7.1+/-0.6, P<0.03). ANGII infusion had no significant effect on TGSR (e.g. 24.6+/-1.4 vs 28.4+/-0.9 mg/100 g per h in vehicle-treated animals). RT-PCR analysis showed that L6 cells express both AT(1)- and AT(2)-receptor mRNA. Incubation with ANGII (10(-9) and 10(-8) M) had no significant effect on the dose-response curve for insulin-stimulated [(3)H]2-deoxyglucose uptake. For example, C(I200) values (dose of insulin required to increase glucose uptake by 200%) were 4.5 x 10(-9) M (control) vs 3.9 x 10(-9) M and 6.2 x 10(-9) M, whereas the positive control (glucagon-like peptide-1) increased insulin sensitivity. Thus, ANGII infusion may have a modest insulin antagonist effect on glucose disposal in insulin-resistant fructose-fed rats pretreated with an AT(1)-blocker, but ANGII has no effect on TGSR or in vitro glucose uptake in L6 myoblasts. These findings are relevant to recent clinical discussions about the metabolic effects of ANGII and renin-angiotensin system blockade.

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A. Ü. PARMAN

SUMMARY

The effects of hypophysectomy and short-term GH replacement on insulin release and on some aspects of glucose metabolism in isolated rat islets of Langerhans were investigated. The effects on body, pancreas and adrenal gland weights, and on the levels of blood plasma constituents were also measured. Three to four weeks after hypophysectomy the early and late phases of insulin release from islets incubated with high concentrations of glucose, but not with low concentrations of glucose or with xylitol, leucine, arginine, tolbutamide, citrate or butyrate, were significantly lowered. Short-term GH replacement partially reversed the depression in glucose-stimulated insulin release. This reversal effect was not dependent on the increase in body weight of rats after GH replacement when the fall in adrenal gland but not in pancreas weight was also reversed. Nine out of the 12 plasma constituents measured, including glucose, were maintained in the control range of levels, but albumin, inorganic phosphate and urea nitrogen levels were altered after hypophysectomy or GH replacement.

Three to four weeks after hypophysectomy, total glucose oxidation and glucose utilization by the islets were slightly depressed. Hypophysectomy appeared to slow down glucose 6-phosphate utilization in the islets. However, the functional capacity of the glucose phosphorylating, glucose-6-phosphate and 6-phosphogluconate dehydrogenase activities were not changed. Short-term GH replacement caused improvements in these islet functions.

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Maristela Mitiko Okamoto, Gabriel Forato Anhê, Robinson Sabino-Silva, Milano Felipe dos Santos Ferreira Marques, Helayne Soares Freitas, Rosana Cristina Tieko Mori, Karla Fabiana S Melo and Ubiratan Fabres Machado

lipid metabolism ( Taniguchi et al . 2005 ), recent studies using Irs2 knockout mice have shown hepatic insulin resistance and increased gluconeogenesis, showing the importance of IRS2 in hepatic glucose metabolism. In addition, an important

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N Welsh, B Margulis, K Bendtzen and S Sandler

Abstract

The aim of the present investigation was to evaluate the putative involvement of oxygen free radicals in interleukin-1β (IL-1β)-induced suppression of islet glucose oxidation. Isolated adult rat pancreatic islets were exposed for 1 h to liposomally encapsulated superoxide dismutase (SOD; 10 mg/ml), catalase (CAT; 10 mg/ml) and glutathione peroxidase (GPX; 5 mg/ml), after which IL-1β (25 U/ml) or hydrogen peroxide (H2O2; 0·1 mm) was added, and the incubation was continued overnight. The following day, samples were taken from the incubation media for nitrite determinations, and islet glucose oxidation rates were measured. The CAT activity increased fourfold after addition of CAT-containing liposomes. It was found that IL-1β induced a marked increase in islet nitrite production, as an index of nitric oxide formation, and that this was paralleled by a decrease in islet glucose oxidation rates. H2O2-treated islets exhibited a modest decrease in glucose oxidation rates and a minor increase in the release of nitrite to the media. Treatment of islets with liposomes containing the antioxidant enzymes SOD, CAT and GPX, either alone or in combination, did not decrease the effect of IL-1β. However, the H2O2-induced decrease in glucose oxidation rates was counteracted by the combination of the antioxidants. It was concluded that, provided the intracellular delivery of the antioxidant enzymes to the islet cells was effective, oxygen free radicals probably do not play a decisive role in IL-1β suppression of islet glucose metabolism.

Journal of Endocrinology (1994) 143, 151–156

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A. Faure, M.-Th. Vergnaud, M.-Th. Sutter-Dub and B. Ch. J. Sutter

ABSTRACT

The changes in the effects of oestradiol-17β on body weight, food intake and [1-14C]glucose oxidation in adipocytes were followed in sham-operated, ovariectomized and adrenalectomized–ovariectomized rats to eliminate effects of endogenous progesterone and corticosterone. During the first 5 days oestradiol induced a dramatic fall in food intake and body weight concomitant with a decrease in glucose oxidation by adipocytes, when tested 12 h and 3 days after the beginning of treatment. In-vitro incubations with oestradiol showed that this was a direct effect of this hormone. On the other hand, from days 5 to 14 of treatment, body weight and food intake increased, though they were still lower than in sham-operated controls. On day 14, as values of treated rats tended to reach those of controls, glucose oxidation in adipocytes was stimulated by oestradiol treatment. An insulin effect was still observable and none of these effects was dependent on the adrenal gland.

These biphasic changes in the parameters studied could be closely related; moreover, a relationship with other oestradiol actions on metabolism that are known to be corticosterone-dependent could be eliminated.

J. Endocr. (1984) 101, 13–19