Effects of glimepiride on insulin and glucagon release from isolated rat pancreas at different glucose concentrations

The effects of glimepiride, the newest sulphonylureic compound, on pancreatic insulin and glucagon secretion were studied using the classical, isolated, perfused rat pancreas model. The influence of four different environmental glucose conditions (during a glycaemic stimulus with glucose increasing from 5 to 8.33 mM and at stable 0, 5 and 2.22 mM glucose levels) on the effects of glimepiride was also assessed. At a pharmacological concentration glimepiride strongly stimulated beta-cell activity, producing a characteristic biphasic insulin release with a sharp first-phase secretory peak, followed by a prolonged and sustained second phase. Environmental glucose concentrations markedly influenced the extent, but not the pattern of glimepiride-induced insulin secretion, as hormone release dropped significantly when the glucose level was reduced. Glimepiride failed to influence alpha-cell activity at any of the environmental glycaemic levels.     

Glucagon-like peptide-1 but not glucagon-like peptide-2 stimulates insulin release from isolated rat pancreatic islets

Summary Glucagon-like peptide-1 and glucagon-like peptide-2 are encoded by the m-RNA of pancreatic preproglucagon. They show high conservation in different species and substantial sequence homology to glucagon. Because no definite biological activity of these peptides has been reported, we investigated the effect of synthetic C-terminally amidated glucagon-like peptide-1 [1–36] and synthetic human glucagon-like peptide-2 [1–34] with a free C-terminus on insulin release from isolated precultured rat pancreatic islets in the presence of glucose. Glucagon-like peptide-1 stimulates insulin release at 10 and 16.7 mmol/l glucose in a dose-dependent manner. Significant stimulation starts at 2.5 nmol/l in the presence of 10 mmol/l glucose and near maximal release is observed at 250 nmol/l, with approximately 100% increase over basal at both glucose concentrations. The peptide reaches 63% of the maximal stimulatory effect of glucagon. No stimulation occurs in the presence of 2.8 mmol/l glucose. Glucagon-like peptide-2 has no effect on insulin secretion at any glucose concentration tested. It is concluded that glucagon-like peptide-1, in contrast to glucagon-like peptide-2, exhibits a glucose-dependent insulinotropic action on isolated rat pancreatic islets similar to that of glucagon and gastric inhibitory polypeptide.     

Effect of glucagon antibodies on plasma glucose,insulin and somatostatin in the fasting and fed rat

Summary A potent high-titre glucagon antibody pool was used to induce a state of acute glucagon deficiency in order to investigate the importance of glucagon in maintaining euglycaemia in the fed and fasted anaesthetised rat. Binding characteristics of the antiserum and evidence of its neutralisation of the biological effects of exogenous glucagon are described. The amount of antibody administered was capable of neutralising up to 12 times the total content of glucagon (approximately 1nmol) in the rat pancreas. The hyperglycaemic response to 1.43 nmol exogenous glucagon was significantly inhibited in the rat by glucagon antibodies given intravenously or intraperitoneally (p < 0.001). However, no changes in plasma glucose occurred in rats fasted 16 h (4.35±0.1 mmol/l or 24 h (4.0±0.05 mmol/l) after antibody administration. The same dose of glucagon antibodies produced no change in plasma glucose (6.1±0.2 mmol/l), immunoreactive insulin (1.85±0.05 g/l) or immunoreactive somatostatin (110±30 ng/l) in rats after antibody administration. Antibody excess, equivalent to a binding capacity for glucagon of 40 nmol/l in the plasma of recipient animals, was demonstrable at all times after passive immunisation. The absence of any affect on glucose concentrations following immunoneutralisation of glucagon suggests that glucagon secretion may not be a major factor in the maintenance of euglycaemia in the rat.     

Oxidation of glucose and fatty acids in normal and in A2-cell rich pancreatic islets isolated from guinea-pigs

Summary Glucose and fatty acid oxidation has been measured in normal guinea-pig islets of Langerhans, and in A₂-cell rich islets from streptozotocin-treated guinea-pigs. The rate of oxidation of these compounds in guinea-pig A₂-cells and B-cells has been estimated. In the B-cells, the oxidation of glucose and octanoic acid responded markedly to changes in the extracellular levels of these substrates. Palmitic acid did not appear to be oxidized by the B-cells. In contrast, the oxidation of octanoic acid and palmitic acid in the A₂-cells was very sensitive to changes in the extracellular fatty acid concentration. The sensitivity of glucose oxidation to changes in the glucose concentration was small by comparison. The high rate of oxidation of fatty acids in the A₂-cells supports the view that the rate of fatty acid metabolism in these cells plays an important role in the regulation of glucagon release.

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Die Oxidation von Glucose und Fettsäuren in normalen und isolierten, mit A₂-Zellen angereicherten Pankreasinseln vom Meerschweinchen

Zusammenfassung An normalen Langerhansschen Inseln vom Meerschweinchen und an mit A₂-Zellen angereicherten Inseln von streptozotozin-behandelten Meerschweinchen wurde die Oxidation von Glucose und Fettsäuren gemessen und die Oxidationsrate in A₂-Zellen und B-Zellen des Meerschweinchens bestimmt. In den B-Zellen hing die Oxidation von Glucose und Octansäure stark von den Änderungen der extracellulären Konzentrationen dieser Substanzen ab. Palmitinsäure schien in den B-Zellen nicht oxidiert zu werden. Dagegen war die Oxidation von Oktansäure und Palmitinsäure in den A₂-Zellen sehr von den Schwankungen der extracellulären Fettsäurekonzentration abhängig. Die Änderung der Glucoseoxidation bei Schwankungen der Glucosekonzentration war im Verhältnis dazu gering. Die hohe Oxidationsrate der Fettsäuren in den A₂-Zellen unterstützt die Theorie, daß der Fettsäuremetabolismus dieser Zellen eine wesentliche Rolle in der Regulierung der Glucose-sekretion spielt.

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Oxydation du glucose et des acides gras dans les îlots pancréatiques normaux et dans les îlots riches en cellules A₂ prélevés sur le cobaye

Résumé L'oxydation du glucose et des acides gras a été mesurée dans les îlots normaux de Langerhans chez le cobaye, ainsi que dans les îlots riches en cellules A₂ du cobaye traité à la streptozotocine. Le taux d'oxydation de ces composés dans les cellules A₂ et les cellules B du cobaye a été estimé. Dans les cellules B, l'oxydation du glucose et de l'acide octanoique a fortement répondu à des changements dans les taux extra-cellulaires de ces substrats. L'acide palmitique ne semble pas avoir été oxydé par les cellules B. Au contraire, l'oxydation de l'acide octanoique et de l'acide palmitique dans les cellules A₂ était très sensible aux changements dans la concentration des acides gras extra-cellulaires. La sensibilité de l'oxydation du glucose envers les changements dans la concentration du glucose était comparativement faible. Le taux élevé de l'oxydation des acides gras dans les cellules A₂ corrobore l'hypothèse que le degré du métabolisme des acides gras dans ces cellules joue un rôle important dans la régulation de la sécrétion du glucagon.

     

Effects of various modifiers of insulin release on the lanthanum-nondisplaceable45ca2+ uptake by isolated pancreatic islets

Summary The uptake of⁴⁵Ca²⁺ by a lanthanum-nondisplaceable pool in pancreatic islets was studied. Raising the extracellular D-glucose concentration from 3 to 20 mM stimulated the⁴⁵Ca²⁺ uptake in hand-dissected islets of ob/ob-mice as well as in collagenase-isolated islets of ob/ob or normal mice. The effect was dose-dependent in the range of 0–20 mM D-glucose and was seen throughout a wide range of extracellular calcium concentrations (16 mol — 2.56 mmol of Ca²⁺ added per litre of medium). The⁴⁵Ca²⁺ uptake was also enhanced by other known insulin secretagogues (D-mannose, L-leucine, tolbutamide) and was uninfluenced by compounds lacking insulinreleasing capacity (3-O-methyl-D-glucose, L-glucose, D-galactose, D-leucine). The stimulatory effect of D-glucose was blocked by inhibitors of glucoseinduced insulin release (D-mannoheptulose, diazoxide, L-adrenaline). The results support the view that the lanthanum-nondisplaceable calcium pool is related to the insulin-releasing mechanism, although the exact nature of this relationship is still unclear.On leave from the Institute of Pharmacology and Toxicology, University of Göttingen, D-34 Göttingen, Germany Recipient of a research grant from the Deutsche Forschungsgemeinschaft (Le 348/1)     

Effect of 2-deoxyglucose on [32P] phosphate and insulin release from perifused rat pancreatic islets

Summary The effect of 2-deoxyglucose on glucose mediated insulin and [³²P]phosphate release was studied by perifusion of isolated rat pancreatic islets. When islets were perifused with media containing 2.8 mmol/l glucose and 20 mmol/l 2-deoxyglucose for 60 minutes and then exposed to media containing 8.3 or 16.7 mmol/l glucose and 20 mmol/l 2-deoxyglucose for the next 15 minutes, insulin release at either glucose concentration was prompt but blunted. Similarly, islets preincubated (90 min) with [³²P] orthophosphate, then perifused with 20 mmol/l 2 deoxyglucose for 75 min and stimulated by either 8.3 or 16.7 mmol/l glucose for the final 15 minutes of 2 deoxyglucose exposure demonstrated obtundation of [³²P]phosphate release. Perifusion of islets with 20 mmol/l 2-deoxyglucose alone induced no heightened³²P efflux. These studies suggest that 2-deoxyglucose affects initial events in stimulus-secretion coupling of glucose mediated insulin release.     

Evidence for an inhibitor of insulin release in the pancreatic islets

Summary The release of insulinin vitro from isolated mouse islets was significantly inhibited in the presence of an islet protein extract equivalent to more than 100 times the normal serum level of insulin. The nature of the inhibitory islet substance remains unclear. The possibility that the blood circulation through the islets may be important for the local regulation of insulin release by reducing high levels of this hormone in the immediate surroundings of the cells should be considered.Part of a project supported by the United States Public Health Service (AM-12535), Swedish Medical Research Council (12×-562) and the Medical Faculty of Umeå.     

Effects of streptozotocin in vitro on proinsulin biosynthesis,insulin release and ATP content of isolated rat islets of Langerhans

Summary Proinsulin synthesis, insulin release and intracellular ATP concentrations were measured in isolated rat islets of Langerhans under control conditions of in vitro incubation and after treatment with several concentrations of streptozotocin for different periods of time. It was found that streptozotocin inhibited proinsulin synthesis, as well as insulin release, in a time and concentration dependent manner. The characteristics of the inhibition of these two processes were similar in general terms, but one dissimilarity was noted, i.e. after 60 min exposure to a high concentration of streptozotocin, proinsulin synthesis was inhibited more than insulin release. ATP content was reduced by high concentrations of streptozotocin, but it was found that proinsulin synthesis and insulin release could be inhibited without any effect on ATP content by a low (0.22 mM) concentration of streptozotocin. The effect of streptozotocin on proinsulin synthesis was judged to be the result of a target specificity for the B-cell rather than a specific effect on proinsulin relative to total protein synthesis.This work was supported by the Swiss National Scientific Foundation (Grant No. 3106073), Berne, Switzerland, and by a grant-in-aid from Hoechst Pharmaceuticals, Frankfurt-Hoechst, GermanyPreliminary data from this work were presented at the European Symposium on Hypoglycemia, Rome, April 5–6, 1974     

Studies on insulin degradation inside the pancreatic B-cell: evidence for a regulating role of glucose

The present study aimed at testing whether insulin degradation inside the pancreatic B-cell is regulated by insulin release or by glucose per se. Radioactively prelabelled isolated rat islets were cultured in unlabelled medium for 24 h. During that chase period the media contained (a) 50 or 300 mg glucose/dl alone or (b) together with 100 micrograms diazoxide/ml and (c) 50 mg glucose/dl without or with 10 mM L-leucine or 300 mg glucose/dl. The content of labelled (pro-)insulin in islets and media was measured and related to degradation. No degradation was found at the high glucose concentration, not even when insulin release was blocked by diazoxide. Degradation was also inhibited in the presence of leucine. The results suggest that glucose per se or its metabolism prevents insulin from being degraded inside the B-cell.     

Effects of PGE2, misoprostol,and enprostil on guinea pig enterocyte adenylate cyclase

Prostaglandins of the E series (PGE) are known to stimulate intestinal water and electrolyte secretions via the activation of the enterocyte adenylate cyclase. Their methylated synthetic analogs misoprostol and enprostil induced diarrhea in 5–13% of the patients in most clinical studies. In order to elucidate the role of PGE-adenylate cyclase interaction in these phenomena, we studied the stimulation of adenylate cyclase by native prostaglandin E₂ (PGE₂) and synthetic PGE analogs on isolated guinea pig intestinal epithelial cells. PGE₂ stimulation of adenylate cyclase was dose-dependent, reaching a maximum for 3×10^–4 M, with an EC₅₀ of 3.7×10^–6 M. The Hill analysis of the concentration-response curve gave a straight line, with a slope close to 1. The effect of PGE₂ was strictly additive to that of 10^–5 M forskolin, whereas it was decreased in terms of potency by 10^–9 M cholera toxin. Somatostatin-14 markedly inhibited PGE₂ stimulation by 37% and 45% with 10^–9 M and 10^–6 M, respectively. The two PGE methylated analogs misoprostol and enprostil were less potent than PGE₂ in stimulating adenylate cyclase in our model. We conclude that (1) the mechanism of PGE₂-mediated intestinal water and electrolyte secretions involves the activation of one single class of specific receptors coupled to enterocyte adenylate cyclase via a cholera toxin-sensitive regulatory subunit (Gs); (2) somatostatin is a potent inhibitor of PGE-stimulated adenylate cyclase and thus could be a interest in the treatment of certain PGE-induced secretory diarrheas; and (3) the diarrheogenic effects of misoprostol and enprostil are unlikely to be mediated primarily by adenylate cyclase activation.     

Dynamics of calcium-induced insulin release

Summary Extracellular Ca²⁺, at concentrations exceeding 10 mmol/l, causes a dose-related stimulation of insulin release. The dynamics of Ca²⁺-induced insulin release are characterized by a quick onset, a progressive build-up and a later return towards basal secretory rate. The release of insulin evoked by Ca²⁺ is inhibited in the presence of either Mg²⁺ (10 mmol/l) or the organic Ca²⁺-antagonist verapamil (81 mol/l), both of which are known to inhibit Ca²⁺ entry in the B-cell. Glucose and theophylline, which are thought to affect the net uptake or intracellular distribution of Ca²⁺ in the B-cell, both enhance Ca²⁺-induced insulin release. As little as 2.7 mmol/l glucose is sufficient to augment Ca²⁺-induced insulin secretion. Exposure of the pancreas to somatostatin significantly retards the secretory response to Ca²⁺. Cytochalasin B potentiates the insulin release evoked by Ca²⁺ (12 mmol/l) and lowers the threshold concentration of Ca²⁺ required to stimulate secretion. These data suggest that high extracellular Ca²⁺ concentrations may sufficiently increase the amount of Ca²⁺ accumulated in the B-cell to eventually trigger insulin release. Agents known to cause a remodelling of Ca²⁺ fluxes across membrane systems in the B-cell interfere with Ca²⁺-induced insulin release, a process also dependent on the integrity of the cytochalasin B-sensitive microfilamentous effector system.     

Effects of growth hormone on insulin release in the rat

Summary Growth hormone injected intravenously in the rat elicited a 6-fold spike change in immunoreactive insulin with little variation in glucose. Subcutaneous administration of growth hormone for 4 days augmented by 56% the insulin-secretory response to glucose of isolated islets from hypophysectomised rats but not the response of control rat islets. When islets were cultured in the presence of growth hormone, the glucose-induced insulin release was increased by 35% in batch incubations of islets from both normal and hypophysectomised rats and by 70–110% in perifused islets. Thus the capacity for stimulated release of insulin is limited by hypophysectomy, and growth hormone is capable of directly influencing the secretory function of the - cell.     

Function of microdissected pancreatic islets cultured in a chemically defined medium. I. Insulin content and release

Summary Microdissected pancreatic islets from non-inbredob/ob-mice, were cultured for 6 or 7 days in serum-free tissue culture medium 199. The insulin content of the islets decreased 60% during culture in 17 mM or 28 mM glucose and about 70% in the presence of 3.3 mM or 5.6 mM glucose. At the end of a culture period in high glucose, the sum of the insulin in the islet plus that in the culture medium was almost twice as high as the insulin content of fresh islets, indicating an active insulin biosynthesis. The maximal insulin response to glucose after culture in 17 mM or 28 mM glucose was about 40% of that in fresh islets; after culture in 3.3 mM glucose it was 10%. Half-maximal stimulation was observed at a glucose concentration of 5 mM for islets cultured with high glucose as compared to 9 mM for fresh islets. Like glucose, glibenclamide was a more effective insulin stimulator after culture with a high glucose concentration than with a low one. However, leucine-induced insulin release was not affected by the glucose concentration in the preceding culture medium. Whereas potentiation of glucose-stimulated release by arginine or dibutyryl-cAMP was independent of glucose concentration during the culture, theophylline released three times more insulin when the islets had been cultured with high glucose.     

Dynamics of O2 consumption in rat pancreatic islets

Summary The O₂ consumption of rat pancreatic islets was determined by monitoring pO₂ in the perifusate from groups of 200–300 islets. Basal respiration was maintained for up to 2 h. The insulin secretagogues, glucose and 4-methyl-2-oxopentanoate, provoked an immediate (<5 s) increase in islet respiration which attained a new steady-state within 10–40 min. The respiratory changes were immediately reversible upon removal of the substrate and were parallelled by changes in insulin release and substrate oxidation. The concentration dependence of glucose-induced respiratory changes was sigmoidal with a threshold at 3 mmol/l. The concentration dependence with 4-methyl-2-oxopentanoate was characterised by a hyperbolic relationship. The weak insulin secretagogues 3-methyl-2-oxobutyrate and d,1-3-methyl-2-oxopentanoate, although stimulating islet respiration were not more effective than 4-methyl-2-oxopentanoate at non-insulinotropic concentrations. Rotenone, antimycin and oligomycin inhibited both basal O₂ consumption and the ability of glucose and 4-methyl-2-oxopentanoate to increase islet respiration. 2,4-Dinitrophenol increased islet O₂ consumption. The omission of Ca²⁺ and Mg²⁺ from the perifusing media, or the addition of the ionophore A23187, had little effect on respiration. The omission of K⁺ inhibited glucose-induced changes but had a lesser effect in the absence of substrate or in the presence of 4-methyl-2-oxopentanoate. The omission of HCO₃ ^- reduced both basal and secretagogue-induced changes in islet respiration. It is concluded that mitochondrial O₂ consumption linked to oxidative phosphorylation is a major component in the respiratory response, and that some energy consuming process in the islets depends on the availability of HCO₃ ^-. Mitochondrial reactions may generate a signal initiating the secretory process.     

Effect of a selective thromboxane A2 synthetase inhibitor on the systemic changes induced by circulating pancreatic phospholipase A2

Background In acute pancreatitis, pancreatic phospholipase A₂ (PLA2) in the circulating blood hydrolyzes phospholipids contained in plasma lipoproteins, liberating eicosanoid precursors that are subsequently converted to various eicosanoids. The pathophysiological significance of eicosanoid synthesis via this pathway is unknown. The aim of this study was to clarify the role of thromboxane A₂ (TXA₂) synthesis by circulating pancreatic PLA₂ in the pathogenesis of the systemic complications of acute pancreatitis. Methods Guinea pigs were divided into two groups: a control group and an ozagrel group, which received intravenous administration of ozagrel, a selective TXA₂ synthetase inhibitor. Pancreatic PLA₂ was infused intravenously in both groups for 30 min, and systemic changes during the infusion were examined. Results In the control group, there was an increase in plasma thromboxane B₂ (TXB₂) concentration, a decrease in mean arterial pressure and heart rate, a decrease in arterial base excess (BE), bicarbonate concentration (HCO₃ ⁻), and pH, a decrease in platelet count and plasma fibrinogen concentration, and a shortened prothrombin time during the infusion of pancreatic PLA₂. In the ozagrel-treated group, changes in plasma TXB₂ concentration, BE, HCO₃ ⁻, and platelet count were significantly inhibited. Conclusions TXA₂ synthesis by circulating pancreatic PLA₂ contributes to metabolic acidosis and thrombocytopenia during acute pancreatitis.     

Acute effects of alloxan- and streptozotocin-induced insulin deficiency on somatostatin and glucagon secretion by the perfused isolated rat pancreatico-duodenal preparation

Summary The secretion of somatostatin and glucagon by the perfused rat pancreatico-duodenal preparation was examined in situ under control conditions and after the induction of acute insulin deficiency by alloxan or streptozotocin. A 10 min 0.625 mmol/l alloxan perfusion resulted in an immediate and transient increase in basal insulin and glucagon release and a slightly delayed and persistent increase in basal somatostatin secretion. The insulin responses to 16.7 mmol/l glucose, 1 mmol/l theophylline, and 19 mmol/l arginine alone or in combination were virtually eliminated by alloxan treatment, Somatostatin secretion in response to the stimuli was completely inhibited or markedly attenuated. The glucagon-suppressive effect of glucose was unaltered by alloxan and the stimulatory effect of arginine was enhanced. Addition of 1 g/ml porcine insulin to the perfusion medium did not modify the alterations in somatostatin and glucagon responses to arginine. Streptozotocin treatment 90 min prior to the onset of perfusion resulted in changes in somatostatin, glucagon, and insulin responses to glucose and arginine similar to those of alloxan. The present results are consistent with an effect of alloxan and streptozotocin on the D cell similar to that on the B cell, namely, interference with a glucose-mediated effect on hormone secretion.     

Isolated mouse pancreatic islets in culture: Effects of serum and different culture media on the insulin production of the islets

Summary Various conditions for tissue culture of collagenase-isolated mouse pancreatic islets were studied in an attempt to optimize the maintenance of glucose stimulated insulin biosynthesis and release in the cultured specimens. Islets which had been cultured at a physiological glucose concentration (5.5 mmol/l) in the absence of serum had an impaired glucose-stimulated insulin biosynthesis and release as well as a reduced insulin content. Thus, insulin biosynthesis was three times higher after culture in a serum supplemented medium. Further, the insulin secretion of islets cultured in the presence of serum was markedly enhanced in acute incubations with high concentrations of glucose. This response was most pronounced in islets which had been cultured free-floating. A comparison between different culture media showed that islets cultured in RPMI 1640 had the highest insulin production. The present data suggest that the most favourable conditions for long-term storage of isolated islets in culture may be obtained when the islets are maintained as free-floating explants in a culture medium consisting of RPMI 1640 supplemented with serum.     

Pancreatic islets from hypothalamic obese rats maintain K+ATP channel-dependent but not -independent pathways on glucose-induced insulin release process

One of the main features of obesity is hyperinsulinemia, which is related to insulin oversecretion. Glucose is by far the major physiological stimulator of insulin secretion. Glucose promotes an increase in the ATP/ADP ratio, which inactivates ATP-sensitive K⁺ channels (K⁺ _ATP) and induces beta cell depolarization with consequent calcium influx. Increased intracellular calcium concentration triggers insulin exocytosis. K⁺ _ATP channel function is important for K⁺ _ATP channel-dependent pathways involved in glucose-stimulated insulin secretion (GSIS). However, K⁺ _ATP channel-independent pathway has been identified and it has been found that this pathway sustains GSIS. Both pathways are critical to better GSIS control. GSIS was studied in pancreatic islets from hyperinsulinemic adult obese rats obtained by monosodium l-glutamate (MSG) neonatal treatment. Islets from MSG-obese rats were more glucose responsive than control ones. Diazoxide, a drug which maintains the K⁺ _ATP channels open without interfering with cell metabolism, blocked GSIS in islets from both groups. High extracellular potassium concentration plus diaz-oxide was used to study an alternative to the K⁺ _ATP channel pathway; in these conditions islets from MSG-obese rats did not respond, while islets from control animals showed enhanced GSIS. Results indicate that MSG-obese rats oversecreted insulin, even though the K⁺ _ATP channel-independent pathway is impaired in their beta cells.     

Effect of Methylene Blue on pyridine nucleotides and insulin secretion of rat pancreatic islets

Summary Methylene Blue, which is known to oxidise NADPH in red blood cells, was used to assess a possible role of NADPH in the glucose-stimulated secretion of insulin. When islets from rats were incubated with 3 mg/ml of glucose, Methylene Blue (0.5, 1.0, 2.0 or 5.0 g/ml) significantly decreased the concentration of NADPH, increased that of NADP⁺ and decreased the NADPH/NADP⁺ ratio in a dose-dependent manner. This effect was associated with inhibition of the glucose-induced insulin release. No significant change of NADH, NAD⁺ and ATP could be observed. It is suggested that the secretory response of the pancreatic islet to glucose stimulation depends on the NADPH/NADP⁺ ratio.     

Long-term gliclazide treatment improves the in vitro glucose-induced insulin release in rats with Type 2 (non-insulin-dependent) diabetes induced by neonatal streptozotocin

Summary Neonatal rats treated with streptozotocin on the day of birth (n0-STZ) or on day 5 (n5-STZ) exhibited when fully grown a very mild or frank basal hyperglycaemia respectively and a specific failure of insulin release in response to glucose. To determine whether short (1 day) or long-term (30 days) gliclazide treatment modifies the pancreatic insulin content and the B-cell response to secretagogues, diabetic rats were given oral gliclazide (10 mg/kg per day) and compared to control diabetic and non-diabetic rats. Insulin secretion in the isolated perfused pancreas was studied the day after the last gliclazide administration. In severely hyperglycaemic n5-STZ rats (plasma glucose levels >16 mmol/l) long-term gliclazide treatment did not lower the plasma glucose values, did not affect the pancreatic insulin stores, nor did it significantly modify the insulin release in vitro in response to glucose or arginine. In moderately hyperglycaemic n5-STZ rats (plasma glucose levels <16 mmol/l) the plasma glucose levels declined progressively reaching 8 mmol/l as a mean at the end of the gliclazide therapy. In the n5-STZ rats responsive to gliclazide the pancreatic insulin stores were increased twofold as compared to values in untreated n5-STZ rats, however, this difference did not reached significance and the pancreatic in sulin stores in the responsive gliclazide treated rats remained depleted by 76% compared to normal insulin stores. In the n0-STZ rats (very mild hyperglycaemia) the long-term gliclazide treatment did not significantly modify the plasma glucose levels or the pancreatic insulin stores. After the 30-day gliclazide therapy in both the n5-STZ gliclazide responder group and the n0-STZ group: (1) the in vitro glucose-induced insulin secretion was increased three to fivefold, (2) the response to arginine which was basically increased in the untreated diabetic rats was again amplified two to threefold, (3) the insulin release in response to gliclazide was unchanged. In conclusion, long-term gliclazide therapy augments stimulated insulin secretion in these two rat models of Type 2 (non-insulin-dependent) diabetes and does not induce any refractoriness to acute sulfonylurea stimulation. The improvement of B-cell function observed here was not related to the concomitant variations of hyperglycaemia and/or pancreatic insulin contentThis work was presented in part at the 24th Annual Meeting of the European Association of the Study of Diabetes, Paris, France, 5–8 September 1988