Predominant role of GIP in the development of a metabolic syndrome-like phenotype in female Wistar rats submitted to forced catch-up growth.

Catch-up growth has been associated with the appearance of metabolic dysfunctions such as obesity and type 2 diabetes in adulthood. Because the entero-insular axis is critical to glucose homeostasis control, we explored the relevance of the incretins glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide-1 (GLP-1) in the development of these pathologies. Offspring of rat dams fed ad libitum (control [C]) or 65% food-restricted during pregnancy and suckling time (undernourished [U]) were weaned onto a high-fat (HF) diet (CHF and UHF, respectively) to drive catch-up growth. Both male and female UHF rats showed an obese phenotype characterized by hyperphagy, visceral fat accumulation, and adipocyte hypertrophy. High-fat diet induced deterioration of glucose tolerance in a sex-dependent manner. Female UHF rats experienced much more severe glucose intolerance than males, which was not compensated by insulin hypersecretion, suggesting insulin resistance, as shown by homeostatic model assessment of insulin resistance values. Moreover, female, but not male, UHF rats displayed enhanced GIP but not GLP-1 secretion during oral glucose tolerance test. Administration of the GIP receptor antagonist (Pro3)GIP to UHF female rats over 21 days markedly reduced visceral fat mass and adipocyte hypertrophy without variations in food intake or body weight. These changes were accompanied by improvement of glucose tolerance and insulin sensitivity. In conclusion, the exacerbated production and secretion of GIP after the catch-up growth seems to represent the stimulus for insulin hypersecretion and insulin resistance, ultimately resulting in derangement of glucose homeostasis. Overall, these data evidence the role of GIP as a critical link between catch-up growth and the development of metabolic disturbances.

Type 2 diabetes - a matter of failing beta-cell neogenesis? Clues from the GK rat model.

Now that reduction in beta-cell mass has been clearly established in humans with type 2 diabetes mellitus (T2D), the debate focuses on the possible mechanisms responsible for decreased beta-cell number. Appropriate inbred rodent models are essential tools for this purpose. The information available from the Goto-Kakizaki (GK) rat, one of the best characterized animal models of spontaneous T2D, is reviewed in such a perspective. We propose that the defective beta-cell mass in the GK model reflects mostly a persistently decreased beta-cell neogenesis. The data discussed in this review are consistent with the notion that poor proliferation and/or survival of the endocrine precursor cells during GK foetal life will result in a decreased pool of endocrine precursors in the pancreas, and hence an impaired capacity of beta-cell neogenesis (either primary in the foetus or compensatory in the newborn and the adult). As we also demonstrated that beta-cell neogenesis can be pharmacologically reactivated in the GK model, our work supports, on a more prospective basis, the concept that facilitation of T2D treatment may be obtained through beta-cell mass expansion after stimulation of beta-cell regeneration/neogenesis in diabetic patients.

Defective IGF2 and IGF1R protein production in embryonic pancreas precedes beta cell mass anomaly in the Goto-Kakizaki rat model of type 2 diabetes.

AIMS/HYPOTHESIS: The Goto-Kakizaki (GK) rat is a spontaneous model of type 2 diabetes. Defective beta cell mass detectable in late fetal age precedes the onset of hyperglycaemia. Our hypothesis was that an embryonic IGF production deficiency might be involved in beta cell mass anomaly in the diabetic GK rat. To test this, we evaluated during pancreatic organogenesis: (1) the beta cell development in GK rats on embryonic day (E) 13.5 and E18.5; (2) IGF2 and IGF1 receptor (IGF1R) pancreatic protein production on E13.5 and E18.5; (3) the in vitro development of GK pancreatic rudiment on E13.5; and (4) the in vitro effect of IGF2 addition on beta cell mass. MATERIALS AND METHODS: Beta cell quantitative analyses were determined by immunohistochemistry and morphometry. IGF2 and IGF1R pancreatic protein production was evaluated using western blot analyses. Dorsal pancreatic rudiments were dissected on E13.5, separated from surrounding mesenchyme and cultured for 7 days without or with recombinant IGF2. RESULTS: While beta cell mass was already decreased on E18.5, the differentiation of the first beta cells was in fact normal in E13.5 GK pancreas. Moreover, defective IGF2 and IGF1R protein production was detected in GK pancreatic rudiment as early as E13.5. The isolated GK pancreatic rudiment as maintained in vitro mimics the GK beta cell deficiency observed in vivo. This last approach enabled us to show that GK beta cells were fully responsive to IGF2 as far as their net growth is concerned. CONCLUSIONS/INTERPRETATION: In diabetic GK rat, defective IGF2 and IGF1R protein production in embryonic pancreas precedes beta cell mass anomaly. IGF2 supplementation expands the pool of beta cells.

Undernutrition does not alter the activation of beta-cell neogenesis and replication in adult rats after partial pancreatectomy.

In previous work, we demonstrated that a 65% protein calorie food restriction started during the third trimester of gestation in rats caused a reduced beta-cell mass at 4 days of life that persisted until adult age. In this study with adult undernourished (U) rats, we investigated 1) whether undernutrition affects the beta-cell growth potential and both beta-cell proliferation and differentiation and 2) the implication of the IGFs, highly responsive to nutritional status, in these processes. To this end, we used the 90% pancreatectomy (Px) procedure in U and control (C) adult rats. The results show that, on day 2 after Px, beta-cell replication was significantly higher in C rats, whereas the beta-cell neogenesis was markedly increased in U/Px rats. Both the serum levels of IGF-I and the liver IGF-I mRNA expression were reduced in adult U rats before and after Px compared with C rats. Pancreatic IGF-I mRNA expression was reduced in U animals on day 0. However, on day 2 after Px, the increase of pancreatic IGF-I mRNA expression was significantly higher in U rats than in C rats. These data suggest that beta-cells still have the capacity to regenerate in the adult U rats, with a higher efficiency than C rats on day 2, and that both beta-cell neogenesis and beta-cell replication are stimulated. The increased pancreatic IGF-I mRNA may be instrumental in these processes.

Protein-caloric food restriction affects insulin-like growth factor system in fetal Wistar rat.

We have previously shown that fetuses from protein-caloric undernourished pregnant rats (35% of control diet during the last week of pregnancy) at 21.5 d post coitum exhibit increased beta-cell mass. This alteration is correlated with increased insulinemia and total pancreatic insulin content, a pattern similar to that reported in infants of mild diabetic mothers. In this work, we investigated in undernourished fetuses: 1) whether availability of growth factors such as insulin, GH, and IGFs and their binding proteins (IGFBPs) could be implicated in this alteration, and 2) the beta-cell mitogenic response to IGFs in vitro. The results show that maternal undernutrition increases pancreatic IGF-I expression and islet IGF-I receptor content in undernourished fetuses, whereas hepatic IGF-I expression and serum IGF-I levels were decreased. No changes were observed in serum IGF-II, and its expression was diminished in undernourished pancreases and unchanged in the liver, compared with control fetuses. Serum levels and liver and pancreatic mRNA expression of IGFBP-1 were found to be normal in undernourished fetuses, whereas the serum concentration and abundance of IGFBP-2 mRNA in pancreas were increased. Finally, the beta-cell mitogenic response to IGFs in vitro was significantly increased in undernourished fetal islets, compared with controls. In conclusion, in undernourished fetuses the increased beta-cell mass can be related to the stimulation of replicative beta-cell response due to locally increased pancreatic IGF-I mRNA; this effect is perhaps potentiated or favored by the enhanced islet IGF-I receptor content and pancreatic IGFBP-2 gene expression.

beta-cell function and viability in the spontaneously diabetic GK rat: information from the GK/Par colony.

The GK rat model of type 2 diabetes is especially convenient to dissect the pathogenic mechanism necessary for the emergence of overt diabetes because all adult rats obtained in our department (GK/Par colony) to date have stable basal mild hyperglycemia and because overt diabetes is preceded by a period of normoglycemia, ranging from birth to weaning. The purpose of this article is to sum up the information so far available related to the biology of the beta-cell in the GK/Par rat. In terms of beta-cell function, there is no major intrinsic secretory defect in the prediabetic GK/Par beta-cell, and the lack of beta-cell reactivity to glucose (which reflects multiple intracellular abnormalities), as seen during the adult period when the GK/Par rats are overtly diabetic, represents an acquired defect (perhaps glucotoxicity). In terms of beta-cell population, the earliest alteration so far detected in the GK/Par rat targets the size of the beta-cell population. Several convergent data suggest that the permanently reduced beta-cell mass in the GK/Par rat reflects a limitation of beta-cell neogenesis during early fetal life, and it is conceivable that some genes among the set involved in GK diabetes belong to the subset of genes controlling early beta-cell development.

Effect of gliclazide treatment on insulin secretion and beta-cell mass in non-insulin dependent diabetic Goto-Kakisaki rats.

The Goto-Kakisaki rat is a genetic non-overweight model of non-insulin-dependent diabetes mellitus. Adult Goto-Kakisaki rats exhibit a mild basal hyperglycaemia (11 mmol/l) with impaired glucose tolerance, elevated basal plasma insulin level, a failure of insulin release in response to glucose together with a 50% depletion of the total pancreatic beta-cell mass and insulin stores. We have examined the effects of long-term (4 weeks) gliclazide treatment on the severity of diabetes in adult male Goto-Kakisaki rats (10-12 weeks of age). Gliclazide was administered orally (10 mg/kg per day). Gliclazide-treated Goto-Kakisaki rats were evaluated against Wistar and untreated Goto-Kakisaki rats. In the gliclazide-treated Goto-Kakisaki rats, basal plasma glucose levels declined progressively reaching 8 mmol/l as a mean at the end of treatment, and their basal insulin levels decreased to values similar to those in non-diabetic Wistar rats. Despite their total pancreatic beta-cell remaining unaffected, their pancreatic insulin stores were twice increased, with a similar improvement of the insulin content per individual beta-cell. Furthermore, the glucose-stimulated insulin release as evaluated in vivo during an intravenous glucose tolerance-test was significantly improved (twice increased) in the gliclazide-treated Goto-Kakisaki rats. This was correlated with a modest but significant enhancement of the early phase of insulin release in vitro (isolated perfused pancreas), in response to glucose. However, the overall insulin response in vitro remained clearly defective with no reappearance of the late phase of insulin release. The in vitro response to arginine (which was basically amplified in the Goto-Kakisaki model) or to gliclazide were kept unchanged after the gliclazide treatment. In conclusion, chronic gliclazide does not exert any beta-cytotrophic effect, but improves beta-cell function in the adult Goto-Kakisaki rat as far as it lowers basal insulin release, increases beta-cell insulin stores, and increases the glucose-induced insulin release.

Specific inhibition of GLUT2 in arcuate nucleus by antisense oligonucleotides suppresses nervous control of insulin secretion.

We previously demonstrated the presence of the glucose transporter GLUT2 in specific brain areas which are mainly involved in the control of fuel metabolism and feeding behavior, i.e., nuclei of the hypothalamus and of the anterior brainstem. We hypothesized that GLUT2 acts as a 'glucose sensor' in these areas, as already described in pancreatic beta cells. In order to test this hypothesis, we injected antisense unmodified oligodeoxynucleotide (ODN) to GLUT2 into the arcuate nucleus. Antisense ODN efficiency on GLUT2 protein level was assessed on pancreatic islets in culture and they were shown to induce a 66% decrease in GLUT2 protein. Bilateral injections of GLUT2 antisense ODNs were performed twice daily over a two-day period in rats. Antisense ODNs induced a significant decline in body weight gain although total daily food intake was unchanged when compared both to control groups and to the period before treatment. Twenty hours after the last injection, anaesthetized rats received, via a catheter inserted into the carotid artery and directed towards the brain, a minute glucose load that by itself does not modify systemic blood glucose level but which induces increased insulinemia. This insulin response was completely abolished only in antisense-treated rats. These findings provide the first evidence for a physiological role of GLUT2 in the brain and support the hypothesis that this transporter is involved in a 'glucose sensing'

Impaired pancreatic beta cell function in the fetal GK rat. Impact of diabetic inheritance.

The Goto-Kakisaki (GK) rat is a genetic model of non-insulin-dependent diabetes. At 21.5 d of age we found that GK fetuses had an increased plasma glucose concentration, a decreased plasma insulin level, and a reduced pancreatic beta cell mass. To investigate the beta cell function during fetal life we used a hyperglycemic clamp protocol applied to the mothers, which allowed us to obtain a steady-state hyperglycemia in the corresponding fetuses. At variance, with Wistar (W) fetuses, plasma insulin concentration in GK fetuses did not rise in response to hyperglycemia. In contrast, GK fetal pancreas released insulin in response to glucose in vitro to the same extent as W fetal pancreas. Such a discrepancy between the in vivo and in vitro results suggests that the lack of pancreatic reactivity to glucose as seen in vivo is extrinsic to the fetal GK beta cell. Finally, the importance of gestational hyperglycemia was investigated by performing crosses between GK and W rats. Fetuses issued from crosses between W mother and GK father or GK mother and W father had a beta cell mass close to normal values and were still able to increase their plasma insulin levels in response to hyperglycemia in vivo. Our data suggest that hyperglycemia in utero does not influence the severity of the decrease of the beta cell mass or the lack of the insulin secretory response to glucose in the fetal GK rat. Moreover they indicate that conjunction of GK genes originating from both parents is necessary in order for these defects to be fully expressed.

Impaired development of pancreatic beta-cell mass is a primary event during the progression to diabetes in the GK rat.

In the endocrine pancreas of the GK rat, a genetic model of non-insulin-dependent diabetes mellitus (NIDDM), it is not clear whether the histopathological changes reported up to now are related to the pathogenesis of hyperglycaemia or whether they occur secondarily to metabolic alterations. Using GK rats from the Paris colony, our study chronicles for the first time the pathophysiologic changes that occur in the GK pancreas from the late fetal period (day 21.5) until adult age (18 weeks). As compared to Wistar controls, GK fetuses exhibited higher plasma glucose level, lower plasma insulin level and normal plasma glucagon level. Their pancreatic insulin content and the relative volume and the total mass of their beta cells were sharply decreased, representing only 23, 38 and 23% of control values, respectively. During the period from 4 days to 14 days after birth, GK neonates exhibited normal basal plasma glucose and glucagon levels despite decreased plasma insulin level. Their pancreatic insulin content represented only 31-40% of values found in the age-related control pancreases and their total beta-cell mass was only 35% on day 4, 30% on day 7 and 37% on day 14. The adult diabetic GK rats exhibited higher basal plasma glucose and insulin levels while their basal plasma glucagon level remained normal. Their pancreatic insulin content and the total beta-cell mass remained decreased, representing only 32% and 47% of control values, respectively. Moreover, the adult GK pancreases exhibited noticeable alteration in the architecture of the large islet subpopulation which displayed considerable fibrosis with clusters of beta cells widely separated from each other by strands of connective tissue. Concerning the development of alpha cells in the GK rats, their relative volume was found to be normal during fetal and early neonatal periods. It was found to be moderately decreased (representing 64-67% of corresponding control values) in 14-day-old neonates and adult GK rats. Our findings demonstrate that in the GK rat, the deficit of total beta-cell mass as observed in the adult animal is related to impaired beta-cell development. The restriction of the beta-cell mass must be considered as a primary and crucial event in the sequence leading to overt diabetes in this NIDDM model.

Genetic analyses of glucose transporter genes in French non-insulin-dependent diabetic families.

Impaired glucose-stimulated insulin secretion and impaired insulin-mediated glucose uptake are both prominent phenotypic features of non-insulin-dependent diabetes mellitus (NIDDM). Membrane proteins GLUT1 (HepG2), GLUT2 (liver/islet), and GLUT4 (muscle/adipose tissue) facilitate glucose uptake into cells, and their genes are candidates for NIDDM. To assess their role in primary defects of diabetes, we performed linkage analyses between NIDDM and 10 polymorphic markers near GLUT1, GLUT2 and GLUT4 genes in 79 multiplex French NIDDM families. Linkage analyses were performed using both parametric (lodscore) and non-parametric (allele sharing among affected sib pairs) methods. No evidence was found for linkage between NIDDM and GLUT1, GLUT2 and GLUT4 regions, regardless of the methods or models used for analyses. Thus, these familial linkage studies demonstrate that GLUT1, GLUT2 and GLUT4 loci did not contribute significantly to NIDDM in this cohort. The decreased expression of glucose transporters observed in some NIDDM patients may be secondary to other genetic or environmental defects.

Insulin secretion and glucose tolerance after islet transplantation in rats with noninsulin-dependent diabetes induced by neonatal streptozotocin.

The present study was designed to identify in a model of noninsulin-dependent diabetes induced by neonatal streptozotocin (n0-STZ), the long-term consequences of an islet graft upon 1) glucose handling of the recipient and, 2) glucose response of the residual beta cells in the recipient pancreas. We have examined, 4 and 8 wk after islet implantation under the kidney capsule of syngeneic diabetic n0-STZ rats, their tolerance to glucose administered in vivo, together with their insulin release in response to glucose in vivo (oral glucose tolerance test) as well as in vitro (perfused pancreas). The results in the islet-grafted n0-STZ rats, were compared to those obtained in nongrafted nondiabetic rats and nongrafted n0-STZ rats. Our study shows that transplanting a limited number (900) of adult islets under the kidney capsule reverses to normal, many parameters of the noninsulin-dependent diabetic state in the n0-STZ rat model: these include body weight, basal plasma glucose in both the nonfasted and postabsorptive states, and basal plasma insulin in the postabsorptive state. Furthermore, tolerance to oral glucose administration was greatly improved in the transplanted rats and it was correlated with restoration of a manifest glucose-induced insulin secretion in vivo as evaluated (delta 1) during an oral glucose tolerance test. Our data clearly show that the insulin response to glucose from the endogenous pancreas of n0-STZ diabetic rat was not really improved by long-term (8 wk) basal normoglycemia. More precisely, we were able to detect a slight but significant improvement of the early phase of insulin release in vitro in response to glucose; however, the overall insulin response remained 15 times lower than the normal one with no reappearance of the late phase of insulin release. After cessation of glucose stimulation in vivo, off-response of insulin, which is also a landmark of the impaired insulin release by the beta cells of n0-STZ rats, was still detectable in the perfused pancreas of the transplanted n0-STZ rats. Finally, because the reactivity to glucose of the endogenous residual beta cells was not regained, the insulin released in vivo during the oral glucose test in the graft-bearing n0-STZ rats can be attributed mainly to functioning of the grafted islets population.

Glucagon-like peptide-1(7-36)-amide confers glucose sensitivity to previously glucose-incompetent beta-cells in diabetic rats: in vivo and in vitro studies.

The effects of glucagon-like peptide-1(7-36)-amide (GLP-1) on cAMP content and insulin release were studied in islets isolated from diabetic rats (n0-STZ model) which exhibited impaired glucose-induced insulin release. We first examined the possibility of re-activating the insulin response to glucose in the beta-cells of the diabetic rats using GLP-1 in vitro. In static incubation experiments, GLP-1 amplified cAMP accumulation (by 170%) and glucose-induced insulin release (by 140%) in the diabetic islets to the same extent as in control islets. Using a perifusion procedure, GLP-1 amplified the insulin response to 16.7 mM glucose by diabetic islets and generated a clear biphasic pattern of insulin release. The incremental insulin response to glucose in the presence of GLP-1, although lower than corresponding control values (1.56 +/- 0.37 and 4.53 +/- 0.60 pg/min per ng islet DNA in diabetic and control islets respectively), became similar to that of control islets exposed to 16.7 mM glucose alone (1.09 +/- 0.15 pg/min per ng islet DNA). Since in vitro GLP-1 was found to exert positive effects on the glucose competence of the residual beta-cells in the n0-STZ model. we investigated the therapeutic effect of in vivo GLP-1 administration on glucose tolerance and glucose-induced insulin release by n0-STZ rats. An infusion of GLP-1 (10 ng/min per kg; i.v.) in n0-STZ rats enhanced significantly (P < 0.01) basal plasma insulin levels, and, when combined with an i.v. glucose tolerance and insulin secretion test, it was found to improve (P < 0.05) glucose tolerance and the insulinogenic index, as compared with the respective values of these parameters before GLP-1 treatment.

Decreased glucose-induced cAMP and insulin release in islets of diabetic rats: reversal by IBMX, glucagon, GIP.

The first aim of the study was to investigate the possibility that a defect on the islet adenosine 3',5'-cyclic monophosphate (cAMP) production could be involved in the failure of the glucose-induced insulin secretion in the neonatal streptozotocin diabetic rats. Exposure to glucose concentration that induced a rise of the cAMP content in the control islets did not elicit any significant increase in cAMP in diabetic islets. Forskolin, isobutyl methylxanthine (IBMX), glucagon, or pertussis toxin amplified the cAMP accumulation and the insulin release to the same extent in both types of islets. Somatostatin, prostaglandin E2, UK-14304, or galanin inhibited cAMP accumulation and insulin release to the same extent in both types of islets. Our second purpose was to investigate whether the use of activators of adenylate cyclase could restore the beta-cell competence to glucose in diabetic rats. The addition of IBMX, glucagon, or gastric inhibitory polypeptide (GIP) to perifused islets of diabetic rats amplified their insulin response to glucose, and a clear biphasic pattern of the release was regained. In conclusion, although there is no major alteration of the functionality of the adenylate cyclase in the beta-cells of the diabetic rats, we have identified a defective glucose-induced cAMP generation that could be explained by a block in the step(s) linking glucose metabolism and activation of adenylate cyclase.

Mitochondrial deoxyribonucleic acid content is specifically decreased in adult, but not fetal, pancreatic islets of the Goto-Kakizaki rat, a genetic model of noninsulin-dependent diabetes.

Considerable interest has recently been focused on the putative role of mutations in the mitochondrial genome for the development of noninsulin-dependent diabetes. The Goto-Kakizaki (GK) rat, a genetic model of defective insulin secretion and hyperglycemia, is characterized by partial maternal inheritance. Because the mitochondrial genome is known to be maternally transmitted, the aim of this study was to investigate whether the GK syndrome can be explained in terms of alterations of the mitochondrial DNA (mtDNA). For this purpose, pancreatic islets were isolated from adult and fetal control Wistar and diabetic GK rats. Using electron microscopy, the ultrastructural morphology of beta-cell mitochondria was analyzed in control and GK islets. It was found that the beta-cells of adult GK rats had a significantly smaller mitochondrial volume and an increased number of mitochondria per unit tissue volume as compared with the beta-cells of corresponding control islets. Moreover, mtDNA and mtRNA were isolated from the islets and, as a control tissue, from liver, and subsequently analyzed using Southern and Northern blot techniques. No major deletions or restriction fragment polymorphism could be detected in mtDNA from both GK liver and GK islets. The mtDNA sequence of the transfer RNAleu(UUS) gene was identical in both strains of rats. mtDNA contents of fetal GK islets and fetal GK liver were not different from those of fetal Wistar rats. However, adult GK islets contained markedly less mtDNA than the corresponding control islets, contrary to the mtDNA contents of adult liver, which were similar in the two strains. The lower islet mtDNA contents were paralleled by a decreased content of islet mtRNA (12S ribosomal RNA and cytochrome b messenger RNA). Islet insulin messenger RNA contents were similar in GK and Wistar rats. In conclusion, our results do not support a role of a genetic defect in mtDNA as a cause of the GK syndrome. Instead, mtDNA damage may occur specifically in islet cells as a consequence of the disturbed metabolic environment of the adult GK rat. It is speculated that a long-lasting metabolic dysfunction may induce mtDNA damage and/or inhibition of mtDNA replication leading to a gradual and late decrease in the mitochondrial volume fraction and subsequently an impaired capacity for oxidative metabolism.

Glucose refractoriness of pancreatic beta-cells in rat models of non-insulin dependent diabetes.

A decreased insulin response, preferentially to glucose, has been considered a hallmark of non-insulin dependent diabetes mellitus (Type 2) in humans. Syndromes resembling human diabetes occur spontaneously in many animal species and can also be induced by treating animals with drugs or viruses, excising their pancreases or manipulating their diet. Among these models, rat diabetes induced by neonatal streptozotocin administration (n-STZ models) has been first recognized as an adequate tool to study the long-term consequences of a gradually reduced beta-cell mass. More recently, the GK (Goto Kakisaki) Wistar rat has become available and is now considered as a promising spontaneous rat model of non-insulin dependent diabetes. We and others have found that defects in insulin secretion and action develop in the n-STZ and the GK models, which in many ways resemble those described in human non-insulin dependent diabetes. This review is aimed to sum up with a comparative approach, the informations so far collected in the n-STZ and GK models concerning the cellular mechanisms leading to the desensitization of their beta-cells to glucose. Taken together, the data reinforce the view that the impairment of glucose-induced insulin release in n-STZ and GK rats is clearly related to a defect in oxidative glycolysis. This leads to a severe decrease in the mitochondrial oxidative catabolism of glucose-derived pyruvate. Its coincides with a lower ATP/ADP ratio in glucose-stimulated islets and a subsequent alteration of ionic events tightly coupled to the fuel function of the hexose in islet cells, i.e. the decrease in K+ conductance.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of benfluorex on insulin secretion and insulin action in streptozotocin-diabetic rats.

We have examined the effect of chronic (20 days) oral administration of benfluorex (35 mg/kg) in a rat model of non-insulin-dependent diabetes mellitus (NIDDM), as induced by injection of streptozotocin 5 days after birth and characterized by frank hyperglycaemia, hypoinsulinaemia, and hepatic and peripheral insulin resistance. In the benfluorex-treated diabetic rats, basal plasma glucose levels were decreased (7.9 +/- 0.2 mM as compared with 17.2 +/- 1.1 mM in the pair-fed untreated diabetic and 6.7 +/- 0.2 mM in the benfluorex-treated non-diabetic rats) while the basal and the glucose-stimulated (IVGTT) plasma insulin levels were not improved. The lack of improvement of glucose-induced insulin release after benfluorex treatment was confirmed under in vitro conditions (perfused pancreas). In the benfluorex-treated diabetic rats, basal glucose production and overall glucose utilization were normalized. Following hyperinsulinaemia (euglycaemic clamp), glucose production was normally suppressed while overall glucose utilization was not significantly improved. Since benfluorex exerts a predominant action on the liver in the present rat model of diabetes, and since increased basal hepatic glucose output is a major metabolic abnormality and is responsible for much of the elevated fasting blood glucose levels in NIDDM, the use of such a compound in NIDDM may be potentially relevant.

Benfluorex normalizes hyperglycemia and reverses hepatic insulin resistance in STZ-induced diabetic rats.

We have examined the effect of chronic (20 days) oral administration of benfluorex (35 mg/kg) in a rat model of NIDDM, induced by injection of STZ 5 days after birth and characterized by frank hyperglycemia, hypoinsulinemia, and hepatic and peripheral insulin resistance. We assessed the following: 1) basal blood glucose and insulin levels, 2) glucose tolerance and glucose-induced insulin release in vivo and in vitro, and 3) basal and insulin-stimulated in vivo glucose production and glucose utilization, using the insulin-clamp technique in conjunction with isotopic measurement of glucose turnover. The in vivo insulin response of several individual tissues also was evaluated under the steady-state conditions of the clamp, using the uptake of the glucose analogue 2-deoxy-D-glucose as a relative index of glucose metabolism. In the benfluorex-treated diabetic rats, postabsorptive basal plasma glucose levels were decreased (8.1 +/- 0.2 mM compared with 10.5 +/- 0.5 mM in the pair-fed untreated diabetic rats and 6.1 +/- 0.2 mM in the benfluorex-treated nondiabetic rats), whereas the basal and glucose-stimulated intravenous glucose tolerance test plasma insulin levels were not improved. Such a lack of improvement in the glucose-induced insulin release after benfluorex treatment was confirmed under in vitro conditions (perfused pancreas). In the pair-fed untreated diabetic rats, the basal glucose production and overall glucose utilization were significantly increased, and during hyperinsulinemia both liver and peripheral tissues revealed insulin resistance. In the benfluorex-treated diabetic rats, the basal glucose production and basal overall glucose utilization were normalized. After hyperinsulinemia, glucose production was normally suppressed, whereas overall glucose utilization was not significantly improved.(ABSTRACT TRUNCATED AT 250 WORDS)

Improvement in glucose-induced insulin secretion in diabetic rats after long-term gliclazide treatment: a comparative study using different models of non-insulin-dependent diabetes mellitus induced by neonatal streptozotocin.

Understanding of the long-term action of sulfonylureas in humans with non-insulin-dependent diabetes mellitus (NIDDM) may be facilitated by studying the effect of long-term sulfonylurea administration to animal models of the disease. In this study two different versions of the neonatal streptozotocin-induced diabetes (STZ) rat model of NIDDM were used. The n5-STZ model (STZ on day 5 after birth), which is characterized by basal hyperglycemia, a marked reduction of pancreatic insulin stores, and insulin resistance, and the n0-STZ model (STZ on day of birth), which develops mild hyperglycemia, have an approximately 50% reduction in pancreatic insulin content, and no insulin resistance. The diabetic rats were given oral gliclazide (10 mg/kg/day) and compared with untreated diabetic rats and nondiabetic rats. Insulin secretion was studied the day after the last gliclazide dose using the isolated perfused pancreas preparation. In severely hyperglycemic n5-STZ rats (plasma glucose levels greater than 16 mmol/L) the long-term gliclazide treatment did not lower the plasma glucose values, did not affect pancreatic insulin stores, and did not significantly modify in vitro insulin release in response to glucose or arginine. In moderately hyperglycemic n5-STZ rats (plasma glucose levels less than 16 mmol/L) the plasma glucose levels declined progressively and reached a mean of 8 mmol/L at the end of gliclazide therapy. The increase in pancreatic insulin stores in n5-STZ rats remained marginal. In the n0-STZ rats gliclazide treatment did not significantly modify the plasma glucose levels or the pancreatic insulin stores. After gliclazide therapy in both the n5-STZ gliclazide responder group and the n0-STZ group: (a) in vitro glucose-induced insulin secretion was increased three- to fivefold; (b) the response to arginine, which is increased in diabetic rats, was amplified by two- to threefold; (c) insulin release in response to gliclazide was unchanged. In conclusion, long-term gliclazide therapy augments stimulated insulin secretion in these two rat models of NIDDM and does not induce any refractoriness to short-term sulfonylurea administration. The improvement of beta-cell function observed here was not related to the concomitant variations of hyperglycemia and/or pancreatic insulin content.