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 ß-cell line, we have demonstrated for the first time that: 1/only some TKP genes are constitutively expressed, both in ß-cells as well as non ß-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-1ß) and glucolipotoxicity respectively, rather in ß-cells than in non ß-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.

Maternal diabetes, programming of beta-cell disorders and intergenerational risk of type 2 diabetes.

A substantial body of evidence suggests that an abnormal intra-uterine milieu elicited by maternal metabolic disturbances as diverse as malnutrition, placental insufficiency, diabetes and obesity may be able to programme susceptibility of the foetus to later develop chronic degenerative diseases such as obesity, hypertension, cardiovascular diseases and type 2 diabetes (T2D). As insulin-producing cells have been placed centre stage in the development of T2D, this review examines developmental programming of the beta-cell mass (BCM) in various rodent models of maternal protein restriction, calorie restriction, overnutrition and diabetes. The main message is that whatever the initial maternal insult (F0 generation) and whether alone or in combination, it gives rise to the same programmed BCM outcome in the daughter generation (F1). The altered BCM phenotype in F1 females prohibits normal BCM adaptation during pregnancy and, thus, diabetes (gestational diabetes) ensues. This gestational diabetes is then passed from one generation (F1) to the next (F2, F3 and so on). This review highlights a number of studies that have identified epigenetic mechanisms that may contribute to altered BCM development and beta-cell failure, as observed in diabetes. In addition to their role in instilling the programmed defect, these non-genomic mechanisms may also be involved in its intergenerational transmission.

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 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.

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.

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.

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 early dietary restriction on insulin action and secretion in the GK rat, a spontaneous model of NIDDM.

The availability of the Goto-Kakisaki (GK) rat model of non-insulin-dependent diabetes mellitus prompted us to test the effect of a limited period of undernutrition in previously diabetic young rats on their insulin secretion and insulin action during adult age. Four-week-old female GK rats were either food restricted (35% restriction, 15% protein diet) or protein and energy restricted (35% restriction, 5% protein diet) for 4 wk. Food restriction in the young GK rat lowered weight gain but did not aggravate basal hyperglycemia or glucose intolerance, despite a decrease in basal plasma insulin level. Furthermore, the insulin-mediated glucose uptake by peripheral tissues in the GK rat was clearly improved. We also found that food restriction, when it is coupled to overt protein deficiency in the young GK rat, altered weight gain more severely and slightly decreased basal hyperglycemia but conversely aggravated glucose tolerance. Improvement of basal hyperglycemia was related to repression of basal hepatic glucose hyperproduction, despite profound attenuation of basal plasma insulin level. Deterioration of tolerance to glucose was related to severe blunting of the residual glucose-induced insulin secretion. It is, however, likely that the important enhancement of the insulin-mediated glucose uptake helped to limit the deterioration of glucose tolerance.

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.

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.

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.

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.