Danielle Bailbe

Hypothalamic serotonin-insulin signaling cross-talk and alterations in a type 2 diabetic model

Serotonin and insulin are key regulators of homeostatic mechanisms in the hypothalamus. However, in type 2 diabetes, the hypothalamic responsiveness to serotonin is not clearly established. We used a diabetic model, the Goto Kakizaki (GK) rats, to explore insulin receptor expression, insulin and serotonin efficiency in the hypothalamus and liver by means of Akt phosphorylation. Insulin or dexfenfluramine (stimulator of serotonin) treatment induced Akt phosphorylation in Wistar rats but not in GK rats that exhibit down-regulated insulin receptor. Studies in a neuroblastoma cell line showed that serotonin-induced Akt phosphorylation is PI3-kinase dependent. Finally, in response to food intake, hypothalamic serotonin release was reduced in GK rats, indicating impaired responsiveness of this neurotransmitter. In conclusion, hypothalamic serotonin as insulin efficiency is impaired in diabetic GK rats. The insulin-serotonin cross-talk and impairment observed is one potential key modification in the brain during the onset of diabetes.

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 μU/ml) was obtained in the paratopic group, while the heterotopic group showed hyperinsulinism (132.0 ± 15.2 μU/ml). Perfect metabolic control justifies the additional technical difficulties of total paratopic pancreatic transplantation with portal venous drainage.

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.

Prolonged Improvement of Total Pancreatic Allograft Function by Previous Intrathymic Bone Marrow Cell Injection in Rats

Donor-specific induction of tolerance was previously achieved in the diabetic rat by intrathymic injection of pancreatic islets. It allowed a secondary islet graft in any site without immunosuppression. Since total pancreatic graft in man is metabolically more proficient than islet graft, we attempted tolerance induction for total vascularized pancreas transplantation in diabetic BN recipient rats by an intrathymic bone marrow cell (BMC) injection from Lewis donor rats, associated to an antilymphocyte antibody (ALS) administration. Control groups consisted of isogenic grafts, allogenic grafts without tolerance induction and allogenic grafts with ALS alone. In all grafted groups, mean blood glucose and plasma insulin were normalised within 24 h. Graft rejection (clinically suggested by diabetes recurrence and later confirmed by histology) appeared at 18 ± 2 postoperative days in the absence of intrathymic BMC injection and at 36 ± 8 days in the group with BMC injection (p < 0.05). Intrathymic bone marrow graft was successful in delaying rejection in our study.

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)

0061 : Exercice training impaired energy metabolism and function of the type 2 diabetic Goto-Kakizaki (GK) rat heart during ischaemiareperfusion injury

Background Informations about the effects of exercice training on diabetesinduced myocardial dysfunctions are lacking. Consequently, we investigated the effect of exercice training on the sensitivity of the type 2 diabetic Goto-Kakizaki (GK) rat heart to ischaemia-reperfusion injury by using a multiparametric approach combining 31P magnetic resonance spectroscopy (MRS) with simultaneous measurement of contractile function and biochemical assays. Materials and Methods 8-month-old male GK rat (n=11, trained GK) rats ran 60 min on a treadmill 5 days/week at a speed of 20 m/min for 7 weeks and compared with age-matched male Control (n=6) and untrained GK (n=11) rats. Then, isolated rat hearts were perfused with a physiological buffer containing 0.4 mM palmitate, for 24 min before switching to 1.2mM palmitate during 32min low-flow (0.5 ml/min-1.g wet wt-1) ischaemia. Next, flow was restored with 0.4 mM palmitate buffer for 32 minutes. High energy compounds and intracellular pH were followed using 31P MRS with simultaneous measurement of contractile function. Total adenine nucleotides (TAN) and energy charge (EC) were determined in freeze-clamped tissues by H.P.L.C. Results Heart to body weight ratios were significantly higher in both untrained and trained diabetic groups (p Conclusion The intensity of exercice training exacerbed the sensitivity of the type 2 diabetic 8-month-old Goto-Kakizaki rat to myocardial ischaemiareperfusion by impairing energy metabolism and myocardial performance. Other exercice protocols and/or therapeutic approaches need to be explored to limit myocardial ischaemia-reperfusion injury in type 2 diabetes.

Transplantation of Syngenic Pancreatic Islets into Rats with Streptozotocin Induced Non Insulin Dependent Diabetes Mellitus

An important concept in understanding the pathogenesis of Non Insulin Dependent Diabetes Mellitus (NIDDM) has recently emerged: the concept that hyperglycemia is not only the principal metabolic derangement of diabetes but also a pathogenetic factor in its own right. Once it develops, either from insulin deficiency or from insulin resistance, hyperglycemia will exacerbate both defects, thereby closing a pathologic feedback loop1. Recognition of the important pathogenetic role of hyperglycemia per se in the evolution of NIDDM has important therapeutic implication. First normalization of the plasma glucose profile, should lead to an impairment in insulin secretion in NIDDM subjects. In fact significant improvements in insulin secretion and insulin action have been demonstrated after weight loss, sulfonylurea administration or insulin therapy, each of these therapeutic interventions leading to an improvement of glycemic control2.