Lithium treatment mitigates the diabetogenic effects of chronic cortico-therapy

BACKGROUND AND PURPOSE

Glucocorticoids (GCs) are the main treatment for autoimmune and inflammatory disorders and are also used as immunosuppressive therapy for patients with organ transplantation. However, these treatments have several side effects, including metabolic disorders. Indeed, cortico-therapy may induce insulin resistance, glucose intolerance, disrupted insulin and glucagon secretion, excessive gluconeogenesis, leading to diabetes in susceptible individuals. Recently, lithium has been shown to alleviate deleterious effects of GCs in various diseased conditions.

EXPERIMENTAL APPROACH

In this study, using two rat models of GC-induced metabolic disorders, we investigated the effects of Lithium Chloride (LiCl) in the mitigation of deleterious effects of GCs. Rats were treated either with corticosterone or dexamethasone, and with or without LiCl. Animals were then assessed for glucose tolerance, insulin sensitivity, in vivo and ex vivo glucose-induced insulin secretion and hepatic gluconeogenesis.

KEY RESULTS

We showed that in rats chronically treated with corticosterone, lithium treatment markedly reduced insulin resistance. In addition, in rats treated with dexamethasone, lithium administration improved glucose tolerance, associated with enhanced insulin secretion in vivo. Moreover, liver gluconeogenesis was reduced upon LiCl treatment. The improvement of insulin secretion in vivo appeared to be due to an indirect regulation of β cell function, since the ex vivo assessment of insulin secretion and β cell mass in islets from animals treated with LiCl revealed no difference compared to untreated animals.

CONCLUSION AND IMPLICATIONS

Collectively, our data provide evidences for the beneficial effects of lithium to mitigate the adverse metabolic effects of chronic cortico-therapy.

Preconceptional exposure of adult male rats to bisphenol S impairs insulin sensitivity and glucose tolerance in their male offspring

Since the use of bisphenol A (BPA) has been restricted because of its endocrine disruptor properties, bisphenol S (BPS) has been widely used as a substitute of BPA. However, BPS exerts similar effects on metabolic health as BPA. The effects of maternal exposure to BPA and BPS on the metabolic health of offspring have been largely documented during the past decade. However, the impact of preconceptional paternal exposure to BPS on progenies remains unexplored. In this study we investigated the impact of paternal exposure to BPS before conception, on the metabolic phenotype of offspring. Male Wistar rats were administered BPS through drinking water at the dose of 4 μg/kg/day (BPS-4 sires) or 40 μg/kg/day (BPS-40 sires) for 2 months before mating with females. The progenies (F1) were studied at fetal stage and in adulthood. We showed that preconceptional paternal exposure to BPS for 2 months did not alter the metabolic status of sires. The female offspring of sires exposed to lower or higher doses of BPS showed no alteration of their metabolic phenotype compared to females from control sires. In contrast, male offspring of BPS-4 sires exhibited increased body weight and body fat/lean ratio, decreased insulin sensitivity and increased glucose-induced insulin secretion at adult age, compared to the male offspring of control sires. Moreover, male offspring of BPS-4 sires developed glucose intolerance later in life. None of these effects were apparent in male offspring of BPS-40 sires. In conclusion, our study provides the first evidence of the non-monotonic and sex-specific effects of preconceptional paternal exposure to BPS on the metabolic health of offspring, suggesting that BPS is not a safe BPA substitute regarding the inter-generational transmission of metabolic disorders through the paternal lineage.

Type 2 Diabetes Mellitus and Alzheimer's Disease: Shared Molecular Mechanisms and Potential Common Therapeutic Targets

The global prevalence of diabetes mellitus and Alzheimer's disease is increasing alarmingly with the aging of the population. Numerous epidemiological data suggest that there is a strong association between type 2 diabetes and an increased risk of dementia. These diseases are both degenerative and progressive and share common risk factors. The amyloid cascade plays a key role in the pathophysiology of Alzheimer's disease. The accumulation of amyloid beta peptides gradually leads to the hyperphosphorylation of tau proteins, which then form neurofibrillary tangles, resulting in neurodegeneration and cerebral atrophy. In Alzheimer's disease, apart from these processes, the alteration of glucose metabolism and insulin signaling in the brain seems to induce early neuronal loss and the impairment of synaptic plasticity, years before the clinical manifestation of the disease. The large amount of evidence on the existence of insulin resistance in the brain during Alzheimer's disease has led to the description of this disease as "type 3 diabetes". Available animal models have been valuable in the understanding of the relationships between type 2 diabetes and Alzheimer's disease, but to date, the mechanistical links are poorly understood. In this non-exhaustive review, we describe the main molecular mechanisms that may link these two diseases, with an emphasis on impaired insulin and IGF-1 signaling. We also focus on GSK3β and DYRK1A, markers of Alzheimer's disease, which are also closely associated with pancreatic β-cell dysfunction and type 2 diabetes, and thus may represent common therapeutic targets for both diseases.

Kynurenine-3-monooxygenase expression is activated in the pancreatic endocrine cells by diabetes and its blockade improves glucose-stimulated insulin secretion

Type 2 diabetes is associated with an inflammatory phenotype in the pancreatic islets. We previously demonstrated that proinflammatory cytokines potently activate the tryptophan/kynurenine pathway (TKP) in INS-1 cells and in normal rat islets. Here we examined: (1) the TKP enzymes expression in the diabetic GK islets; (2) the TKP enzymes expression profiles in the GK islets before and after the onset of diabetes; (3) The glucose-stimulated insulin secretion (GSIS) in vitro in GK islets after KMO knockdown using specific morpholino-oligonucleotides against KMO or KMO blockade using the specific inhibitor Ro618048; (4) The glucose tolerance and GSIS after acute in vivo exposure to Ro618048 in GK rats. We report a remarkable induction of the kmo gene in GK islets and in human islets exposed to proinflammatory conditions. It occurred prominently in beta cells. The increased expression and activity of KMO reflected an acquired adaptation. Both KMO knockdown and specific inhibitor Ro618048 enhanced GSIS in vitro in GK islets. Moreover, acute administration of Ro618048 in vivo improved glucose tolerance, GSIS and basal blood glucose levels in GK rats. These results demonstrate that targeting islet TKP is able to correct defective GSIS. KMO inhibition could represent a potential therapeutic strategy for type 2 diabetes.

A Holistic View of the Goto-Kakizaki Rat Immune System: Decreased Circulating Immune Markers in Non- Obese Type 2 Diabetes

Type-2 diabetes is a complex disorder that is now considered to have an immune component, with functional impairments in many immune cell types. Type-2 diabetes is often accompanied by comorbid obesity, which is associated with low grade inflammation. However,the immune status in Type-2 diabetes independent of obesity remains unclear. Goto-Kakizaki rats are a non-obese Type-2 diabetes model. The limited evidence available suggests that Goto-Kakizaki rats have a pro-inflammatory immune profile in pancreatic islets. Here we present a detailed overview of the adult Goto-Kakizaki rat immune system. Three converging lines of evidence: fewer pro-inflammatory cells, lower levels of circulating pro-inflammatory cytokines, and a clear downregulation of pro-inflammatory signalling in liver, muscle and adipose tissues indicate a limited pro-inflammatory baseline immune profile outside the pancreas. As Type-2 diabetes is frequently associated with obesity and adipocyte-released inflammatory mediators, the pro-inflammatory milieu seems not due to Type-2 diabetes per se; although this overall reduction of immune markers suggests marked immune dysfunction in Goto-Kakizaki rats.

Underlying mechanisms of glucocorticoid-induced β-cell death and dysfunction: a new role for glycogen synthase kinase 3

Glucocorticoids (GCs) are widely prescribed for their anti-inflammatory and immunosuppressive properties as a treatment for a variety of diseases. The use of GCs is associated with important side effects, including diabetogenic effects. However, the underlying mechanisms of GC-mediated diabetogenic effects in β-cells are not well understood. In this study we investigated the role of glycogen synthase kinase 3 (GSK3) in the mediation of β-cell death and dysfunction induced by GCs. Using genetic and pharmacological approaches we showed that GSK3 is involved in GC-induced β-cell death and impaired insulin secretion. Further, we unraveled the underlying mechanisms of GC-GSK3 crosstalk. We showed that GSK3 is marginally implicated in the nuclear localization of GC receptor (GR) upon ligand binding. Furthermore, we showed that GSK3 regulates the expression of GR at mRNA and protein levels. Finally, we dissected the proper contribution of each GSK3 isoform and showed that GSK3β isoform is sufficient to mediate the pro-apoptotic effects of GCs in β-cells. Collectively, in this work we identified GSK3 as a viable target to mitigate GC deleterious effects in pancreatic β-cells.

Paternal High-Protein Diet Programs Offspring Insulin Sensitivity in a Sex-Specific Manner

The impact of maternal nutrition on offspring is well documented. However, the implication of pre-conceptional paternal nutrition on the metabolic health of the progeny remains underexplored. Here, we investigated the impact of paternal high-protein diet (HPD, 43.2% protein) consumption on the endocrine pancreas and the metabolic phenotype of offspring. Male Wistar rats were given HPD or standard diet (SD, 18.9% protein) for two months. The progenies (F1) were studied at fetal stage and in adulthood. Body weight, glycemia, glucose tolerance (GT), glucose-induced insulin secretion in vivo (GIIS) and whole-body insulin sensitivity were assessed in male and female F1 offspring. Insulin sensitivity, GT and GIIS were similar between F1 females from HPD (HPD/F1) and SD fathers (SD/F1). Conversely, male HPD/F1 exhibited increased insulin sensitivity (p < 0.05) and decreased GIIS (p < 0.05) compared to male SD/F1. The improvement of insulin sensitivity in HPD/F1 was sustained even after 2 months of high-fat feeding. In male HPD/F1, the β cell mass was preserved and the β cell plasticity, following metabolic challenge, was enhanced compared to SD/F1. In conclusion, we provide the first evidence of a sex-specific impact of paternal HPD on the insulin sensitivity and GIIS of their descendants, demonstrating that changes in paternal nutrition alter the metabolic status of their progeny in adulthood.

The Goto-Kakizaki rat is a spontaneous prototypical rodent model of polycystic ovary syndrome

Polycystic ovary syndrome (PCOS) is characterized by an oligo-anovulation, hyperandrogenism and polycystic ovarian morphology combined with major metabolic disturbances. However, despite the high prevalence and the human and economic consequences of this syndrome, its etiology remains unknown. In this study, we show that female Goto-Kakizaki (GK) rats, a type 2 diabetes mellitus model, encapsulate naturally all the reproductive and metabolic hallmarks of lean women with PCOS at puberty and in adulthood. The analysis of their gestation and of their fetuses demonstrates that this PCOS-like phenotype is developmentally programmed. GK rats also develop features of ovarian hyperstimulation syndrome. Lastly, a comparison between GK rats and a cohort of women with PCOS reveals a similar reproductive signature. Thus, this spontaneous rodent model of PCOS represents an original tool for the identification of the mechanisms involved in its pathogenesis and for the development of novel strategies for its treatment.

Implication of glycogen synthase kinase 3 in diabetes-associated islet inflammation

Islet inflammation is associated with defective β cell function and mass in type 2 diabetes (T2D). Glycogen synthase kinase 3 (GSK3) has been identified as an important regulator of inflammation in different diseased conditions. However, the role of GSK3 in islet inflammation in the context of diabetes remains unexplored. In this study, we investigated the direct implication of GSK3 in islet inflammation in vitro and tested the impact of GSK3 inhibition in vivo, on the reduction of islet inflammation, and the improvement of glucose metabolism in the Goto-Kakizaki (GK) rat, a spontaneous model of T2D. GK rats were chronically treated with infra-therapeutic doses of lithium, a widely used inhibitor of GSK3. We analyzed parameters of glucose homeostasis as well as islet inflammation and fibrosis in the endocrine pancreas. Ex vivo, we tested the impact of GSK3 inhibition on the autonomous inflammatory response of non-diabetic rat and human islets, exposed to a mix of pro-inflammatory cytokines to mimic an inflammatory environment. Treatment of young GK rats with lithium prevented the development of overt diabetes. Lithium treatment resulted in reduced expression of pro-inflammatory cytokines in the islets. It decreased islet fibrosis and partially restored the glucose-induced insulin secretion in GK rats. Studies in non-diabetic human and rat islets exposed to inflammatory environment revealed the direct implication of GSK3 in the islet autonomous inflammatory response. We show for the first time, the implication of GSK3 in islet inflammation and suggest this enzyme as a viable target to treat diabetes-associated inflammation.

Expression of the kynurenine pathway enzymes in the pancreatic islet cells. Activation by cytokines and glucolipotoxicity

The tryptophan/kynurenine pathway (TKP) is the main route of tryptophan degradation and generates several neuroactive and immunomodulatory metabolites. Experimental and clinical data have clearly established that besides fat, muscle and liver, pancreatic islet tissue itself is a site of inflammation during obesity and type 2 diabetes. Therefore it is conceivable that pancreatic islet exposure to increased levels of cytokines may induce upregulation of islet kynurenine metabolism in a way resembling that seen in the brain in many neurodegenerative disorders. Using normal rat islets and the INS-1 β-cell line, we have demonstrated for the first time that: 1/only some TKP genes are constitutively expressed, both in β-cells as well as non β-cells; 2/ the regulatory enzyme indoleamine 2,3-dioxygenase (IDO1) is not constitutively expressed; 3/ IDO1 and kynurenine 3-monoxygenase (KMO) expression are potently activated by proinflammatory cytokines (IFN-γ, IL-1β) and glucolipotoxicity respectively, rather in β-cells than in non β-cells; 4/ Islet kynurenine/kynurenic acid production ratio is enhanced following IFN-γ and glucolipotoxicity; 5/ acute exposure to KYN potentiates glucose-induced insulin secretion by normal islets; and 6/ oxidative stress or glucocorticoid modulates TKP genes only marginally. Pancreatic islets may represent a new target tissue for inflammation and glucolipotoxicity to activate the TKP. Since inflammation is now recognized as a crucial mechanism in the development of the metabolic syndrome and more specifically at the islet level, it is needed to evaluate the potential induction of the TKP in the endocrine pancreas during obesity and/or diabetes and its relationship to the islet cell functional alterations.

A euglycaemic/non-diabetic perinatal environment does not alleviate early beta cell maldevelopment and type 2 diabetes risk in the GK/Par rat model

AIMS/HYPOTHESIS

We used the GK/Par rat, a spontaneous model of type 2 diabetes with early defective beta cell neogenesis, to determine whether the development of GK/Par offspring in a non-diabetic intrauterine/postnatal environment would prevent the alteration of fetal beta cell mass (BCM) and ultimately decrease the risk of diabetes later in adult life.

METHODS

We used an embryo-transfer approach, with fertilised GK/Par ovocytes (oGK) being transferred into pregnant Wistar (W) or GK/Par females (pW and pGK). Offspring were phenotyped at fetal age E18.5 and at 10 weeks of age, for BCM, expression of genes of pancreatic progenitor cell regulators (Igf2, Igf1r, Sox9, Pdx1 and Ngn3), glucose tolerance and insulin secretion.

RESULTS

(1) Alterations in neogenesis markers/regulators and BCM were as severe in the oGK/pW E18.5 fetuses as in the oGK/pGK group. (2) Adult offspring from oGK transfers into GK (oGK/pGK/sGK) had the expected diabetic phenotype compared with unmanipulated GK rats. (3) Adult offspring from oGK reared in pW mothers and milked by GK foster mothers had reduced BCM, basal hyperglycaemia, glucose intolerance and low insulin, to an extent similar to that of oGK/pGK/sGK offspring. (4) In adult offspring from oGK transferred into pW mothers and milked by their W mothers (oGK/pW/sW), the phenotype was similar to that in oGK/pGK/sGK or oGK/pW/sGK offspring.

CONCLUSIONS/INTERPRETATION

These data support the conclusion that early BCM alteration and subsequent diabetes risk in the GK/Par model are not removed despite normalisation of the prenatal and postnatal environments, either isolated or combined.

The novel oral drug Subetta exerts an antidiabetic effect in the diabetic Goto-Kakizaki rat: comparison with rosiglitazone

The aim of the present study was to evaluate the potential antidiabetic effects of two-component drug Subetta and its components (release-active dilutions of antibodies to β -subunit insulin receptor (RAD of Abs to β -InsR) and to endothelial nitric oxide synthase (RAD of Abs to eNOS)) in Goto-Kakizaki (Paris colony) (GK/Par) diabetic rats. Subetta was administered orally for 28 days once daily (5 mL/kg) and compared to its two components (2.5 mL/kg), Rosiglitazone (5 mg/kg), and vehicle (5 mL water/kg). At day 28, fasting plasma glucose levels were significantly decreased only in Subetta and Rosiglitazone groups as compared to vehicle (P < 0.01): 147 ± 4 mg/dL and 145 ± 4 mg/dL and 165 ± 4 mg/dL, respectively. The data of glucose tolerance test showed that Subetta and RAD of Abs to β -InsR (similar to Rosiglitazone) prevented significantly (P < 0.01) the age-related spontaneous deterioration of glucose tolerance as seen in the control group. Subetta and RAD of Abs to β -InsR did not significantly modify the glucose-induced insulin secretion. Chronic administration of Subetta and RAD of Abs to β -InsR improves glucose control, to an extent similar to that of Rosiglitazone. We hypothesize that Subetta and RAD of Abs to β -InsR mostly act via an insulin-sensitizing effect upon target tissues.

Importance of mitochondrial dynamin-related protein 1 in hypothalamic glucose sensitivity in rats

AIMS

Hypothalamic mitochondrial reactive oxygen species (mROS)-mediated signaling has been recently shown to be involved in the regulation of energy homeostasis. However, the upstream signals that control this mechanism have not yet been determined. Here, we hypothesize that glucose-induced mitochondrial fission plays a significant role in mROS-dependent hypothalamic glucose sensing.

RESULTS

Glucose-triggered translocation of the fission protein dynamin-related protein 1 (DRP1) to mitochondria was first investigated in vivo in hypothalamus. Thus, we show that intracarotid glucose injection induces the recruitment of DRP1 to VMH mitochondria in vivo. Then, expression was transiently knocked down by intra-ventromedial hypothalamus (VMH) DRP1 siRNA (siDRP1) injection. 72 h post siRNA injection, brain intracarotid glucose induced insulin secretion, and VMH glucose infusion-induced refeeding decrease were measured, as well as mROS production. The SiDRP1 rats decreased mROS and impaired intracarotid glucose injection-induced insulin secretion. In addition, the VMH glucose infusion-induced refeeding decrease was lost in siDRP1 rats. Finally, mitochondrial function was evaluated by oxygen consumption measurements after DRP1 knock down. Although hypothalamic mitochondrial respiration was not modified in the resting state, substrate-driven respiration was impaired in siDRP1 rats and associated with an alteration of the coupling mechanism.

INNOVATION AND CONCLUSION

Collectively, our results suggest that glucose-induced DRP1-dependent mitochondrial fission is an upstream regulator for mROS signaling, and consequently, a key mechanism in hypothalamic glucose sensing. Thus, for the first time, we demonstrate the involvement of DRP1 in physiological regulation of brain glucose-induced insulin secretion and food intake inhibition. Such involvement implies DRP1-dependent mROS production.

cAMP-secretion coupling is impaired in diabetic GK/Par rat β-cells: a defect counteracted by GLP-1

cAMP-raising agents with glucagon-like peptide-1 (GLP-1) as the first in class, exhibit multiple actions that are beneficial for the treatment of type 2 diabetic (T2D) patients, including improvement of glucose-induced insulin secretion (GIIS). To gain additional insight into the role of cAMP in the disturbed stimulus-secretion coupling within the diabetic β-cell, we examined more thoroughly the relationship between changes in islet cAMP concentration and insulin release in the GK/Par rat model of T2D. Basal cAMP content in GK/Par islets was significantly higher, whereas their basal insulin release was not significantly different from that of Wistar (W) islets. Even in the presence of IBMX or GLP-1, their insulin release did not significantly change despite further enhanced cAMP accumulation in both cases. The high basal cAMP level most likely reflects an increased cAMP generation in GK/Par compared with W islets since 1) forskolin dose-dependently induced an exaggerated cAMP accumulation; 2) adenylyl cyclase (AC)2, AC3, and G(s)α proteins were overexpressed; 3) IBMX-activated cAMP accumulation was less efficient and PDE-3B and PDE-1C mRNA were decreased. Moreover, the GK/Par insulin release apparatus appears less sensitive to cAMP, since GK/Par islets released less insulin at submaximal cAMP levels and required five times more cAMP to reach a maximal secretion rate no longer different from W. GLP-1 was able to reactivate GK/Par insulin secretion so that GIIS became indistinguishable from that of W. The exaggerated cAMP production is instrumental, since GLP-1-induced GIIS reactivation was lost in the presence the AC blocker 2',5'-dideoxyadenosine. This GLP-1 effect takes place in the absence of any improvement of the [Ca(2+)](i) response and correlates with activation of the cAMP-dependent PKA-dependent pathway.

Diabetic beta-cells can achieve self-protection against oxidative stress through an adaptive up-regulation of their antioxidant defenses

Background

Oxidative stress (OS), through excessive and/or chronic reactive oxygen species (ROS), is a mediator of diabetes-related damages in various tissues including pancreatic β-cells. Here, we have evaluated islet OS status and β-cell response to ROS using the GK/Par rat as a model of type 2 diabetes.

Methodology/Principal Findings

Localization of OS markers was performed on whole pancreases. Using islets isolated from 7-day-old or 2.5-month-old male GK/Par and Wistar control rats, 1) gene expression was analyzed by qRT-PCR; 2) insulin secretion rate was measured; 3) ROS accumulation and mitochondrial polarization were assessed by fluorescence methods; 4) antioxidant contents were quantified by HPLC. After diabetes onset, OS markers targeted mostly peri-islet vascular and inflammatory areas, and not islet cells. GK/Par islets revealed in fact protected against OS, because they maintained basal ROS accumulation similar or even lower than Wistar islets. Remarkably, GK/Par insulin secretion also exhibited strong resistance to the toxic effect of exogenous H₂O₂ or endogenous ROS exposure. Such adaptation was associated to both high glutathione content and overexpression (mRNA and/or protein levels) of a large set of genes encoding antioxidant proteins as well as UCP2. Finally, we showed that such a phenotype was not innate but spontaneously acquired after diabetes onset, as the result of an adaptive response to the diabetic environment.

Conclusions

The GK/Par model illustrates the effectiveness of adaptive response to OS by β-cells to achieve self-tolerance. It remains to be determined to what extend such islet antioxidant defenses upregulation might contribute to GK/Par β-cell secretory dysfunction.

The GK rat beta-cell: a prototype for the diseased human beta-cell in type 2 diabetes?

Increasing evidence indicates that decreased functional beta-cell mass is the hallmark of type 2 diabetes (T2D) mellitus. Nowadays, the debate focuses on the possible mechanisms responsible for abnormal islet microenvironment, decreased beta-cell number, impaired beta-cell function, and their multifactorial aetiologies. This review is aimed to illustrate to what extend the Goto-Kakizaki rat, one of the best characterized animal models of spontaneous T2D, has proved be a valuable tool offering sufficient commonalities to study these aspects. We propose that the defective beta-cell mass and function in the GK model reflect the complex interactions of multiple pathogenic players: (i) several independent loci containing genes responsible for some diabetic traits (but not decreased beta-cell mass); (ii) gestational metabolic impairment inducing an epigenetic programming of the pancreas (decreased beta-cell neogenesis and/or proliferation) which is transmitted to the next generation; and (iii) loss of beta-cell differentiation due to chronic exposure to hyperglycemia/hyperlipidemia, inflammatory mediators, oxidative stress and to perturbed islet microarchitecture.

EGF mediates calcium-activated chloride channel activation in the human bronchial epithelial cell line 16HBE14o-: involvement of tyrosine kinase p60c-src

Particulate atmospheric pollutants interact with the human airway epithelium, which releases cytokines, chemokines, and EGF receptor (EGFR) ligands leading to proinflammatory responses. There is little information concerning the short-term effects of EGFR activation by extracellular ligands on ionic regulation of airway surface lining fluids. We identified in the membrane of human epithelial bronchial cells (16HBE14o(-) line) an endogenous calcium- and voltage-dependent, outwardly rectifying small-conductance chloride channel (CACC), and we examined the effects of EGF on CACC activity. Ion channel currents were recorded with the patch-clamp technique. In cell-attached membrane patches, CACC were activated by exposure of the external surface of the cells to physiological concentrations of EGF without any change in cytosolic Ca(2+) concentration ([Ca(2+)](i)) and inhibited by tyrphostin AG-1478 (an inhibitor of EGFR that also blocks EGF-dependent Src family kinase activation). EGF activation of c-Src protein in 16HBE14o(-) cells was observed, and the signaling pathway elicited by EGFR was blocked by tyrphostin AG-1478. In excised inside-out membrane patches CACC were activated by exposure of the cytoplasmic face of the channels to the human recombinant Src(p60(c-src)) kinase with endogenous or exogenous ATP and inhibited by lambda-protein phosphatase. Secretion of EGFR ligands by epithelial airway cells exposed to pollutants would then elicit a rapid and direct ionic response of CACC mediated by EGFR activation via a Src kinase family-dependent signaling pathway.

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.

Restitution of defective glucose-stimulated insulin secretion in diabetic GK rat by acetylcholine uncovers paradoxical stimulatory effect of beta-cell muscarinic receptor activation on cAMP production

Because acetylcholine (ACh) is a recognized potentiator of glucose-stimulated insulin release in the normal beta-cell, we have studied ACh's effect on islets of the Goto-Kakizaki (GK) rat, a spontaneous model of type 2 diabetes. We first verified that ACh was able to restore the insulin secretory glucose competence of the GK beta-cell. Then, we demonstrated that in GK islets 1) ACh elicited a first-phase insulin release at low glucose, whereas it had no effect in Wistar; 2) total phospholipase C activity, ACh-induced inositol phosphate production, and intracellular free calcium concentration ([Ca2+]i) elevation were normal; 3) ACh triggered insulin release, even in the presence of thapsigargin, which induced a reduction of the ACh-induced [Ca2+]i response (suggesting that ACh produces amplification signals that augment the efficacy of elevated [Ca2+]i on GK exocytosis); 4) inhibition of protein kinase C did not affect [Ca2+]i nor the insulin release responses to ACh; and 5) inhibition of cAMP-dependent protein kinases (PKAs), adenylyl cyclases, or cAMP generation, while not affecting the [Ca2+]i response, significantly lowered the insulinotropic response to ACh (at low and high glucose). In conclusion, ACh acts mainly through activation of the cAMP/PKA pathway to potently enhance Ca2+-stimulated insulin release in the GK beta-cell and, in doing so, normalizes its defective glucose responsiveness.

The toxicity of H2O2 on the ionic homeostasis of airway epithelial cells in vitro

Oxygen species may be formed in the air spaces of the respiratory tract in response to environmental pollution such as particulate matter. The mechanisms and target molecules of these oxidants are still mainly unknown but may involve modifications of the ionic homeostasis in epithelial cells. Cytosolic concentrations of Ca2+ (Fura2) and Na+ (SBFI) and short-circuit current (Isc) were followed in primary cultures of human nasal epithelial cells and in the cell line 16HBE14o- after exposure to H2O2 or *OH (H2O2 + Fe2+). Cells were grown on glass coverslips for ionic imaging or on permeable snapwell inserts for Isc studies. Exposure of the apical as well as the basal side of the cultures to H2O2 or *OH induced a concentration-dependent transient increase in Isc which is due to a transient secretion of Cl-. Cai also increased transiently with approximately the same kinetics. The response was dependent on the release of calcium from intracellular stores. Nai on the contrary increased steadily over more than an hour. When the apical membrane was permeabilized with gramicidin, *OH inhibited the Na+ current (a measure of Na(+)-K(+)-ATPase activity in the baso-lateral membrane). The arrest of the pump was significant after 30 min exposure to oxidant. On the other hand no increase in the apical or baso-lateral sodium conductances could be detected. The progressive arrest of the Na+/K(+)-pump may contribute to the sustained elevation of Nai. This strong modification in the cellular ionic homeostasis may participate in the stress response of the respiratory epithelium through alterations in signal transduction pathways.

Glucagon-like peptide-1 and exendin-4 stimulate beta-cell neogenesis in streptozotocin-treated newborn rats resulting in persistently improved glucose homeostasis at adult age

In neonatal Wistar rats injected with streptozotocin (STZ) at birth (n0-STZ model), a recognized model of beta-cell regeneration, we investigated the capacity of early treatment with glucagon-like peptide 1 (GLP-1) or exendin-4 to promote beta-cell regeneration and thereby improve islet function in the long term, when animals become adults. To this end, n0-STZ rats were submitted to GLP-1 or exendin-4 from postnatal day 2 to day 6 only, and their beta-cell mass and pancreatic functions were tested on day 7 and at 2 months. On day 7, both treatments increased body weight, decreased basal plasma glucose, decreased insulinemia, and increased pancreatic insulin content in n0-STZ rats. At the same age, the beta-cell mass, measured by immunocytochemistry and morphometry methods, was strongly increased in n0-STZ/GLP-1 and n0-STZ/Ex rats compared with n0-STZ rats, representing 51 and 71%, respectively, of the beta-cell mass in Wistar rats, whereas n0-STZ beta-cell mass represented only 21% of the Wistar control value. Despite such early improved beta-cell mass, which is maintained at adult age, the basal and glucose-stimulated insulin secretion (in vivo after intravenous glucose load or in vitro using perfused pancreas) were not improved in the 2-month-old n0-STZ rats previously treated with GLP-1 or exendin-4 compared with untreated n0-STZ rats. However, both treated groups significantly exhibited a decreased basal plasma glucose level and an increased plasma glucose clearance rate compared with the 2-month-old untreated n0-STZ group at adult age. These findings in the n0-STZ model indicate for the first time that GLP-1 or exendin-4 applied during the neonatal diabetic period exert both short- and long-term beneficial effects on beta-cell mass recovery and glucose homeostasis. However, the increase in beta-cell mass, which is still present in the adult n0-STZ rats previously treated, contrasts with the poor beta-cell responsiveness to glucose. Further studies are needed to understand the dissociation between beta-cell regeneration and the lack of improvement in beta-cell function.

Defective glucose-dependent cytosolic Ca2+ handling in islets of GK and nSTZ rat models of type 2 diabetes

We examined to what extent the abnormal glucose-dependent insulin secretion observed in NIDDM (non-insulin-dependent diabetes mellitus) is related to alterations in the handling of cytosolic Ca2+ of islets of Langerhans. Using two recognized rat models of NIDDM, the GK (Goto-Kakizaki) spontaneous model and the nSTZ (neonatal streptozotocin) induced model, we could detect several common alterations in the glucose-induced [Ca2+]i cytosolic responses. First, the initial reduction of [Ca2+]i following high glucose (16.7 mM) observed routinely in islets obtained from non-diabetic Wistar rats could not be detected in GK and nSTZ islets. Second, a delayed response for glucose to induce a subsequent 3% increase of [Ca2+]i over basal level was observed in both GK (321+/-40 s, n=11) and nSTZ (326+/-38 s, n=13) islets as compared with Wistar islets (198+/-20 s, n=11), values representing means+/-s.e.m. Third, the rate of increase in [Ca2+]i in response to a high glucose challenge was 25% and 40% lower in GK and nSTZ respectively, as compared with Wistar islets. Fourth, the maximal [Ca2+](i) level reached after 10 min of perifusion with 16.7 mM glucose was lower with GK and nSTZ islets and represented respectively 60% and 90% of that of Wistar islets. Further, thapsigargin, a blocker of Ca2+/ATPases (SERCA), abolished the initial reduction in [Ca2+]i observed in response to high glucose and induced fast [Ca2+]i oscillations with high amplitude in Wistar islets. The latter effect was not seen in GK and nSTZ islets. In these two NIDDM models, several common alterations in glucose-induced Ca2+ handling were revealed which may contribute to their poor glucose-induced insulin secretion.

Total pancreatico-duodenal transplantation with portal venous drainage: metabolic assessments in diabetic rats

A perfect metabolic correction of diabetes is essential to completely eradicate long-term chronic complications. Only a total pancreatic graft with portal venous drainage enables such an achievement. Isogenic Lewis rats were used for donors, recipients and controls. Pancreatico-duodenal transplantation was either heterotopic with systemic venous drainage (n = 12) or paratopic with portal drainage (n = 11). All animals were regularly monitored for non-fasting plasma glucose and insulin. Both techniques promptly restored the non-fasting plasma glucose to normal values (p<0.003). Normo-insulinemia (47.4+/-6.4 microU/ml) was obtained in the paratopic group, while the heterotopic group showed hyperinsulinism (132.0+/-15.2 microU/ml). Perfect metabolic control justifies the additional technical difficulties of total paratopic pancreatic transplantation with portal venous drainage.

Glucose-induced insulin mRNA accumulation is impaired in islets from neonatal streptozotocin-treated rats

According to the glucose toxicity hypothesis, hyperglycemia contributes to defective beta-cell function in type 2, non-insulin-dependent diabetes mellitus. This concept is supported by substantial data in rodent models of diabetes. However, the ability of glucose to stimulate the accumulation of insulin mRNA, a critical feature of normal beta-cell physiology, has not been investigated in in vivo models of chronic hyperglycemia. The aim of this study was to determine whether glucose-induced insulin mRNA accumulation is impaired in the neonatal streptozotocin-treated rat (n0-STZ rat), a model of non-obese, non-insulin-dependent diabetes mellitus. Islets of Langerhans isolated from n0-STZ and control rats were cultured for 24 h in the presence of 2.8 or 16.7 mmol/L glucose, and insulin mRNA levels were measured by Northern analysis. Insulin mRNA levels were increased more than twofold by glucose in control islets. In contrast, no significant effect of glucose was found on insulin mRNA levels in n0-STZ islets. We conclude that insulin gene regulation by glucose is impaired in n0-STZ rat islets.

Glucose-induced insulin mRNA accumulation is impaired in islets from neonatal streptozotocin-treated rats

According to the "glucose toxicity" hypothesis, hyperglycemia contributes to defective beta-cell function in type 2, non-insulin-dependent diabetes mellitus. This concept is supported by substantial data in rodent models of diabetes. However, the ability of glucose to stimulate the accumulation of insulin mRNA, a critical feature of normal beta-cell physiology, has not been investigated in in vivo models with chronic hyperglycemia. The aim of this study was to determine whether glucose-induced insulin mRNA accumulation is impaired in the neonatal streptozotocin-treated rat (n0-STZ rat), a model of non-obese, non-insulin-dependent diabetes mellitus. Islets of Langerhans isolated from n0-STZ and control rats were cultured for 24 h in the presence of 2.8 or 16.7 mmol/l glucose, and insulin mRNA levels were measured by Northern analysis. Insulin mRNA levels were increased more than twofold by glucose in control islets. In contrast, no significant effect of glucose was found on insulin mRNA levels in n0-STZ islets. We conclude that insulin gene regulation by glucose is impaired in n0-STZ rat islets.

Glucose metabolism and beta-cell mass in adult offspring of rats protein and/or energy restricted during the last week of pregnancy

An association between low birth weight and later impaired glucose tolerance was recently demonstrated in several human populations. Although fetal malnutrition is probably involved, the biological bases of such a relationship are not yet clear, and animal studies on the matter are scarce. The present study was aimed to identify, in adult (8-wk) female offspring, the effects of reduced protein and/or energy intake strictly limited to the last week of pregnancy. Thus we have tested three protocols of gestational malnutrition: a low-protein isocaloric diet (5 instead of 15%), with pair feeding to the mothers receiving the control diet; a restricted diet (50% of the control diet); and a low-protein restricted diet (50% of low-protein diet). Only the low-protein diet protocols, independent of total energy intake, led to a lower birth weight. The adult offspring female rats in the three deprived groups exhibited no decrease in body weight and no major impairment in glucose tolerance, glucose utilization, or glucose production (basal state and hyperinsulinemic clamp studies). However, pancreatic insulin content and beta-cell mass were significantly decreased in the low-protein isocaloric diet group compared with the two energy-restricted groups. Such impairment of beta-cell mass development induced by protein deficiency limited to the last part of intrauterine life could represent a situation predisposing to impaired glucose tolerance.

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.

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.

Impaired phosphoinositide metabolism in glucose-incompetent islets of neonatally streptozotocin-diabetic rats

The effects of nutrient and neurotransmitter stimuli on insulin release, loss of phosphoinositides (PI), and production of inositol phosphates (InsP) were investigated in islets from neonatally streptozotocin-injected (nSTZ) rats. In islets from nSTZ rats, insulin secretory responses to 16.7 mM D-glucose and 10.0 mM D-glyceraldehyde were reduced compared with controls. Contents in phosphatidylinositol 4-monophosphate [PtdIns(4)P] and phosphatidylinositol 4,5-bisphosphate [PtdIns(4,5)P2], but not in phosphatidylinositol, were diminished. Glucose effects on breakdown of PtdIns(4)P and PtdIns(4,5)P2 and on total InsP accumulation were both reduced. D-Glucose was unable to increase the levels of both inositol trisphosphate isomers, Ins(1,3,4)P3 and Ins(1,4,5)P3. Glyceraldehyde also failed to promote InsP formation. By contrast, the ability of 1.0 mM carbachol or 300 nM cholecystokinin to stimulate insulin secretion and InsP generation was still observed. Thus a disturbed coupling between nutrient recognition and activation of phospholipase C, possibly together with a shortage of available polyphosphoinositides, could be responsible for the altered islet PI turnover in the nSTZ rats. It is proposed that such defects may contribute to the impairment of glucose-stimulated insulin secretion in this model of non-insulin-dependent diabetes mellitus.

Impaired insulin secretion and excessive hepatic glucose production are both early events in the diabetic GK rat

Adult Goto-Kakisaki Wistar (GK) rats exhibit a spontaneous non-insulin-dependent diabetes characterized by impaired glucose-induced insulin secretion, decreased beta-cell mass, hepatic glucose overproduction, and moderate insulin resistance in muscles and adipose tissues. To elucidate the pathogenesis of hyperglycemia in this animal model, we have studied insulin secretion and insulin action in 4-wk-old GK pups, just before weaning. In the postabsorptive state, their basal plasma glucose level was elevated (P < 0.001), and their tolerance to intravenous glucose was impaired. Their kinetics of insulin release in response to glucose was impaired, with a low acute phase of insulin release in vivo and in vitro (perfused pancreas). Basal glucose production was increased in the GK pups by 40% (P < 0.05). During euglycemic clamp performed at submaximal hyperinsulinemia, suppression of liver glucose production was less effective (P < 0.01) in the GK rats, whereas their overall glucose utilization was similar to that of the control group. This was correlated with a normal insulin-stimulated glucose utilization by epitrochlearis, soleus, and extensor digitorum longus muscles, diaphragm, and white adipose tissues. These data give body to the primacy of the beta-cell defects in the etiology of non-insulin-dependent diabetes mellitus in the GK rat. They also highlight a possible primary role of the liver defect. Peripheral insulin resistance does not contribute to the development of postnatal glucose intolerance in this diabetes model.

d-Fenfluramine improves hepatic insulin action in streptozotocin-diabetic rats

We have examined the effect of chronic (21 days) oral administration of the serotoninergic anorectic drug d-fenfluramine (5 mg/kg) in a rat model of non-insulin-dependent diabetes (without obesity), as induced by injection of a low dose (45 mg/kg) of streptozotocin at 6 weeks, and characterized by marked hyperglycaemia and hepatic and peripheral insulin resistance. The following parameters were assessed: (1) basal blood glucose and insulin levels, and (2) basal and insulin-stimulated in vivo glucose production and glucose utilization, using the insulin-clamp technique in conjunction with isotopic measurement of glucose turnover. In the d-fenfluramine-treated diabetic rats, postabsorptive basal plasma glucose levels were decreased (7.8 +/- 0.3 mM as compared to 14.9 +/- 0.1 mM in the untreated diabetic rats) while the basal plasma insulin levels were unchanged. A similar reduction of the basal plasma glucose levels was observed in the pair-fed untreated diabetic group (8.3 +/- 0.2 mM). Basal glucose turnover was reduced by 45% (P < 0.01) in the d-fenfluramine-treated diabetic rats as well as in the pair-fed untreated diabetic rats. The impaired suppression of hepatic glucose output by insulin, caused by diabetes, was totally reversed by d-fenfluramine, while pair-feeding did not modify hepatic insulin resistance. The whole body insulin-mediated glucose uptake in the diabetic rats was also significantly improved by d-fenfluramine treatment. Such an effect was also found in the pair-fed untreated group.(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.

In vivo and in vitro increased pancreatic beta-cell sensitivity to glucose in normal rats submitted to a 48-h hyperglycaemic period

We investigated the importance of the level and the duration of glucose stimulation on the in vivo and in vitro insulin response to glucose in normal rats previously submitted to hyperglycaemia. Rats were made hyperglycaemic by a 48-h glucose infusion. Glucose-induced insulin secretion was investigated in vivo by a 20-min hyperglycaemic clamp and in vitro by the isolated perfused pancreas technique, 3 h after the end of the in vivo glucose infusion. In glucose-infused rats, as compared to controls, in vivo incremental plasma insulin values above baseline integrated over the 20-min hyperglycaemic clamp (delta I) were five times higher during 8 mmol/l glucose clamp, only two times higher in 11 mmol/l glucose clamp and no different in 16.5 mmol/l. Compared to the controls, in vitro incremental plasma insulin concentration above baseline integrated over a 20-min period (delta I) in glucose-infused rats was 16 times higher in response to 2.8 mmol/l glucose, two times higher in response to 5.5 mmol/l, similar in response to 8.3 mmol/l and significantly lower in response to 16.5 mmol/l. In conclusion, our data suggest that a 48-h hyperglycaemic period results in an increased response of the pancreatic beta cell to low glucose. The response is immediately maximal and can not be increased with higher glucose concentrations. This situation could explain the apparent minimal effect of high concentrations on in vitro insulin secretion in previously hyperglycaemic rats and may provide insights into the sequence of events leading to the impairment of beta-cell function in Type 2 (non-insulin-dependent) diabetes mellitus.

Increased insulin action in the rat after protein malnutrition early in life

The effect of a limited period of low protein feeding in young rats on insulin secretion and insulin action during adult-age has been studied. Four-week-old rats were maintained for 4 weeks on isocaloric diets containing 5% protein (low protein) or 15% protein (control). The low protein rats gained weight at a considerably lower rate than the control rats. This was obtained in the absence of any decrease of spontaneous food intake. Basal plasma insulin levels were decreased (p less than 0.01) by 40% in low protein rats. However, the glucose-stimulated insulin secretion obtained in vivo after an i.v. glucose load remained normal. The basal plasma glucose level in the low protein rats was only marginally decreased (by 20%). The tolerance to i.v. glucose was found to be slightly enhanced in the low protein rats as compared to the control rats as shown by a significantly increased K value (p less than 0.01). In vivo insulin action in the low protein rats was investigated using the euglycaemic-hyperinsulinaemic clamp technique in conjunction with isotopic measurements of glucose turnover. The overall glucose utilization rate was normal in the basal state but significantly increased (p less than 0.05) when measured at a submaximal plasma insulin level. The basal hepatic glucose production in the low protein rats was similar to that in the control rats. During the clamp studies, the suppression of endogenous glucose production was found to be similar in the low protein rats and the control rats but this was obtained at significantly lower (p less than 0.01) steady-state insulin levels in the low protein group than in the control group. In conclusion, the current results indicate that the modest improvement of glucose tolerance which is revealed in the low protein rats results from changes in the insulin action upon the target tissues: both the insulin-mediated glucose uptake by peripheral tissues and the ability of insulin to suppress hepatic glucose output are enhanced.

Beta-cell insensitivity to glucose in the GK rat, a spontaneous nonobese model for type II diabetes

In early 1988, a colony of GK rats was started in Paris with progenitors issued from F35 of the original colony reported by Goto and Kakisaki. When studied longitudinally up to 8 mo, GK rats showed as early as 1 mo (weaning) significantly higher basal plasma glucose (9 mM) and insulin levels (doubled), altered glucose tolerance (intravenous glucose), and a very poor insulin secretory response to glucose in vivo compared with Wistar controls. Males and females were similarly affected. Studies of in vitro pancreatic function were carried out with the isolated perfused pancreas preparation. Compared with nondiabetic Wistar rats, GK rats at 2 mo showed a significantly increased basal insulin release, no insulin response to 16 mM glucose, and hyperresponse to 19 mM arginine. Pancreatic insulin stores were only 50% of that in Wistar rats. Perfusion of GK pancreases for 50 or 90 min with buffer containing no glucose partially improved the insulin response to 16 mM glucose and markedly diminished the response to 19 mM arginine, whereas the responses by Wistar pancreases were unchanged. These findings are similar to those reported in rats with non-insulin-dependent diabetes induced by neonatal streptozocin administration and support the concept that chronic elevation in plasma glucose may be responsible, at least in part, for the beta-cell desensitization to glucose in this model. The GK rat seems to be a valuable model for identifying the etiology of beta-cell desensitization to glucose.

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

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 greater than 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 less than 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 insulin 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.(ABSTRACT TRUNCATED AT 250 WORDS)

Relation of insulin deficiency to impaired insulin action in NIDDM adult rats given streptozocin as neonates

We assessed the impact of chronic insulin deficiency on basal and insulin-stimulated glucose utilization by the whole-body mass in vivo in female albino Wistar rats. This assessment was based on a comparison of results in rats given streptozocin (STZ) on day of birth (n0-STZ), when 2 days old (n2-STZ), or when 5 days old (n5-STZ). At 10 wk of age, the n2-STZ rats exhibited characteristics similar to those obtained in the n0-STZ rats: normal growth, modest elevation of basal plasma glucose (8.23 +/- 0.24 mM), glucose intolerance, depleted pancreatic insulin stores (approximately 50% of normal value), and lack of insulin release in response to glucose in vivo. In contrast, the n5-STZ rats exhibited frank basal hyperglycemia (glucose 11.9 +/- 1.1 mM) and glucose intolerance, increased glycosylated hemoglobins, strong reduction of the pancreatic insulin stores (10% of normal value), decreased basal plasma insulin levels (50% of normal value), and lack of insulin release in response to glucose in vivo. Changes in the sensitivity of the neonatal beta-cell to STZ and the regeneration capacity of the beta-cells during the 1st postnatal wk were liable factors for the contrast. In vivo insulin action was assessed with the euglycemic-hyperinsulinemic clamp technique in 10-wk-old anesthetized animals. In the n2-STZ rats compared with controls 1) endogenous glucose production was significantly higher despite a normal plasma insulin level in the basal state, 2) endogenous glucose production rate was similarly suppressed by hyperinsulinemia, and 3) glucose utilization by the whole-body mass was similarly increased by hyperglycemia.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of high sucrose diet on insulin secretion and insulin action: a study in the normal rat

The effects of chronic high sucrose feeding for 1 month on in vivo and in vitro insulin secretion and on in vivo insulin action were studied in normal male rats. As compared to the standard chow diet, the high sucrose diet induced excess in vivo insulin response to an intravenous glucose load; the high sucrose diet also slightly improved glucose tolerance, as demonstrated by significantly higher rate of glucose disappearance (p less than 0.02). The increased insulin secretion in response to glucose in vivo seems to be related to an hyper-reactivity of the pancreatic B cell to glucose, since it was still observed in vitro with the isolated perfused pancrease preparation. By contrast, B cells of sucrose-fed rats exhibited in vitro a normal response to arginine and a significantly lowered (p less than 0.05) response to acetylcholine. The insulin action in the sucrose-fed rats was quantified in vivo with the insulin-glucose clamp technique. The effects of different concentrations of insulin on glucose production and glucose utilization were studied in anaesthetized rats while in the postabsorptive state. The basal glucose utilization was found significantly higher (p less than 0.001) in sucrose-fed rats. During the clamp studies the glucose utilization induced by submaximal (400 microU/ml) or maximal (7500 microU/ml) insulin levels was significantly more important (p less than 0.02) in the sucrose-fed rats than in the chow-fed rats. This suggests that insulin-mediated glucose uptake is enhanced over a large range of plasma insulin levels in the sucrose-fed rats.(ABSTRACT TRUNCATED AT 250 WORDS)