Insulin replacement is the only effective therapy to manage hyperglycemia in type 1 diabetes mellitus (T1DM). Nevertheless, intensive insulin therapy has inadvertently led to insulin resistance. This study investigates mechanisms involved in the insulin resistance induced by hyperinsulinization. Wistar rats were rendered diabetic by alloxan injection, and 2 weeks later received saline or different doses of neutral protamine Hagedorn insulin (1 . 5, 3, 6, and 9 U/day) over 7 days.Insulinopenic-untreated rats and 6U-and 9U-treated rats developed insulin resistance, whereas 3U-treated rats revealed the highest grade of insulin sensitivity, but did not achieve good glycemic control as 6U-and 9U-treated rats did. This insulin sensitivity profile was in agreement with glucose transporter 4 expression and translocation in skeletal muscle, and insulin signaling, phosphoenolpyruvate carboxykinase/ glucose-6-phosphatase expression and glycogen storage in the liver. Under the expectation that insulin resistance develops in hyperinsulinized diabetic patients, we believe insulin sensitizer approaches should be considered in treating T1DM.

The increased GLUT4 protein expression and glucose utilization in oxidative muscle and the increased insulin sensitivity and glycogen storage in liver evidence the insulin-sensitizer effect of glimepiride, which must be important to enable the glimepiride drug to promote an efficient glycaemic control.

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We hypothesize that, in kidney of diabetic rats, hepatocyte nuclear factors (HNF-1alpha and HNF-3beta) play a critical role in the overexpression of solute carrier 2A2 (SLC2A2) gene. Diabetic rats submitted or not to rapid (up to 12h) and short-term (1, 4 and 6 days) insulin treatment were investigated. Twofold increase in GLUT2 mRNA was observed in diabetic, accompanied by significant increases in HNF-1alpha and HNF-3beta expression and binding activity. Additional 2-fold increase in GLUT2 mRNA and HNF-3beta expression/activity was observed in 12-h insulin-treated rats. Six-day insulin treatment decreased GLUT2 mRNA and HNF-1alpha expression and activity to levels of non-diabetic rats, whereas HNF-3beta decreased to levels of non-insulin-treated diabetic rats. Our results provide evidence for a link between the overexpression of SLC2A2 gene and the transcriptional activity of HNF-1alpha and HNF-3beta in kidney of diabetic rats. Furthermore, recovery of SLC2A2 gene after 6-day insulin treatment also involves HNF-1alpha and HNF-3beta activity.

The hypothalamic serotonergic system is involved in the regulation of food ingestion and energy metabolism. Since disturbances of both energy intake and expenditure can contribute to obesity, the objective of the present study was to evaluate the serotonergic response stimulated by food ingestion in two different models of obesity: the hyperphagic Zucker and the hypophagic and hypometabolic, monosodium glutamate (MSG) obese Wistar rat. For this we used microdialysis to examine the release of 5-hydroxytryptamine (serotonin, 5HT) and 5-hydroxyindoleacetic acid (5HIAA) in the lateral hypothalamus. Daily intake of MSG-obese rats was 40% lower while that of Zucker obese rats was 60% higher than that of the respective lean controls. In overnight-fasted animals, 20-min microdialysate samples were collected before (basal release) and during a 2-h period of access to a balanced palatable food mash. The animals began to eat during the first 20 min of food access, and food consumption was similar among the four groups in all six individual 20-min periods recorded. Ingestion of food increased 5HT release in all groups. In MSG-obese and lean Wistar rats, 5HT levels were similarly elevated during the whole experimental period. In the Zucker strain, 5HT increments of basal release tended to be higher in obese than in lean rats at 20 and 40 min, and a significantly higher increment was observed at 60 min after food access (40 and 135% for lean and obese, respectively). The area under the curve relating serotonin levels to the 120 min of food availability was significantly higher in Zucker obese (246.7 +/- 23.3) than MSG-obese (152.7 +/- 13.4), lean Wistar (151.9 +/- 11.1), and lean Zucker (173.5 +/- 24.0) rats. The present observation, of a food-induced serotonin release in the lateral hypothalamus of lean Wistar and Zucker rats, evidences that 5HT in the lateral hypothalamus is important in the normal response to feeding. In obese animals, the serotonin response was similar to (in the hypophagic-hypometabolic MSG model) or even higher than (in the hyperphagic Zucker model) that seen in the respective lean controls. This result indicates that the energy homeostasis disturbances of both these obesity models may not be ascribed to an impairment of the acute lateral hypothalamic serotonin response to a dietary stimulus.

Impaired insulin-stimulated glucose uptake involves reduced expression of the GLUT4 (solute carrier family 2 facilitated glucose transporter member 4, gene). 17β-estradiol (E) modulates /GLUT4 expression, but the involved mechanisms are unclear. Although E exerts biological effects by binding to estrogen receptors 1/2 (ESR1/2), which are nuclear transcriptional factors; extranuclear effects have also been proposed. We hypothesize that E regulates GLUT4 through an extranuclear ESR1 mechanism. Thus, we investigated the effects of E upon (1) subcellular distribution of ESRs and the proto-oncogene tyrosine-protein kinases (SRC) involvement; (2) serine/threonine-protein kinase (AKT) activation; (3) /GLUT4 expression and (4) GLUT4 subcellular distribution and glucose uptake in 3T3-L1 adipocytes. Differentiated 3T3-L1 adipocytes were cultivated or not with E for 24 h, and additionally treated or not with ESR1-selective agonist (PPT), ESR1-selective antagonist (MPP) or selective SRC inhibitor (PP2). Subcellular distribution of ESR1, ESR2 and GLUT4 was analyzed by immunocytochemistry; mRNA and GLUT4 were quantified by qPCR and Western blotting, respectively; plasma membrane GLUT4 translocation and glucose uptake were analyzed under insulin stimulus for 20 min or not. E induced (1) translocation of ESR1, but not of ESR2, from nucleus to plasma membrane and AKT phosphorylation, effects mimicked by PPT and blocked by MPP and PP2; (2) increased /GLUT4 expression and (3) increased insulin-stimulated GLUT4 translocation and glucose uptake. In conclusion, E treatment promoted a SRC-mediated nucleus-plasma membrane shuttle of ESR1, and increased AKT phosphorylation, /GLUT4 expression and plasma membrane GLUT4 translocation; consequently, improving insulin-stimulated glucose uptake. These results unravel mechanisms through which estrogen improves insulin sensitivity.

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Type 2 diabetes mellitus is characterized by disruption in glycemic homeostasis, involving impaired insulin-induced glucose disposal. For that, reduced glucose transporter GLUT4, encoded by Slc2a4 gene, plays a fundamental role. Conversely, increase in Slc2a4/GLUT4 expression improves glycemic homeostasis. Recent studies have proposed that estradiol is able to modulate Slc2a4 expression, according to distinct effects upon estrogen receptors ESR1/ESR2. We hypothesize that ESR1-agonist effect could stimulate Slc2a4 expression; thus, increasing cellular glucose disposal, which could be beneficial to glycemic control. Differentiated 3T3-L1 adipocytes were treated (24 hours) with selective ESR1- agonist PPT 1,3,5-tris(4-hydroxyphenyl)-4-propyl-1H-pyrazole, selective ESR1-antagonist MPP 1,3-Bis(4- hydroxyphenyl)-4-methyl-5-[4-(2-piperidinylethoxy)phenol]-1H-pyrazole dihydrochloride, and selective ESR2 agonist DPN 2,3-bis(4-Hydroxyphenyl)-propionitrile, with/without 17β-estradiol (E2). We analyzed Slc2a4 mRNA (real time PCR) and GLUT4 protein (Western blotting) expression, transcriptional activity of the Slc2a4 repressor Nuclear Factor- κB (NF-κB) (electrophoretic mobility shift assay), and cellular glucose disposal (2-deoxi-D-[(3)H]glucose uptake, 2-DG). ESR1-agonist PPT enhanced Slc2a4/GLUT4 expression (~30%) in the absence or presence of 0.1 and 10 nmol/L E2, and decreased the NF-κB binding activity (~50%). Conversely, ESR1-antagonist MPP, together with E2, decreased Slc2a4/GLUT4 expression (20-40%) and increased NF-κB binding activity (~30%). Furthermore, treatment with ESR2- agonist DPN decreased Slc2a4/GLUT4 expression (20-50%). 2-DG uptake was modulated in parallel to that observed in GLUT4 protein. The present results reveal that ESR1 activity enhances, whereas ESR2 activity represses, Slc2a4/GLUT4 expression. These effects are partially mediated by NF-κB, and allow parallel changes in adipocyte glucose disposal. Furthermore, the data provide evidences that ESR1-agonist PPT, as a Slc2a4/GLUT4 enhancer, can be a promising coadjuvant drug for diabetes mellitus therapy.