Insulin Sensitivity In Rats Research Articles

Metformin Improves Survival and Insulin Sensitivity in Rats Exposed to High Fat Diet and Pressure Overload

Background: Metformin is the most frequently prescribed antidiabetic drug and may be useful in cardiac surgery despite current contraindications. We tested whether metformin would be protective in rats under pressure overload displaying a diabetic phenotype.

Effect of Intermittent Hypoxia and Rimonabant on Glucose Metabolism in Rats: Involvement of Expression of GLUT4 in Skeletal Muscle.

BackgroundObstructive sleep apnea (OSA) and its main feature, chronic intermittent hypoxia (IH) during sleep, is closely associated with insulin resistance (IR) and diabetes. Rimonabant can regulate glucose metabolism and improve IR. The present study aimed to assess the effect of IH and rimonabant on glucose metabolism and insulin sensitivity, and to explore the possible mechanisms.Material/MethodsThirty-two rats were randomly assigned into 4 groups: Control group, subjected to intermittent air only; IH group, subjected to IH only; IH+NS group, subjected to IH and treated with normal saline; and IH+Rim group, subjected to IH and treated with 10 mg/kg/day of rimonabant. All rats were killed after 28 days of exposure. Then, the blood and skeletal muscle were collected. We measured fasting blood glucose levels, fasting blood insulin levels, and the expression of glucose transporter 4 (GLUT4) in both mRNA and protein levels in skeletal muscle.ResultsIH can slow weight gain, increase serum insulin level, and reduce insulin sensitivity in rats. The expressions of GLUT4 mRNA, total GLUT4, and plasma membrane protein of GLUT4 (PM GLUT4) in skeletal muscle were decreased. Rimonabant treatment was demonstrated to improve weight gain and insulin sensitivity of the rats induced by IH. Rimonabant significantly upregulated the expression of GLUT4 mRNA, PM GLUT4, and total GLUT4 in skeletal muscle.ConclusionsThe present study demonstrates that IH can cause IR and reduced expression of GLUT4 in both mRNA and protein levels in skeletal muscle of rats. Rimonabant treatment can improve IH – induced IR, and the upregulation of GLUT4 expression may be involved in this process.

The short-term effects of soft pellets on lipogenesis and insulin sensitivity in rats.

The purpose of the present study was to investigate the short-term effects of a 12-day, soft pellet (SP) diet with a 3-h restricted feeding schedule on caloric intake, body weight, lipid metabolism, and insulin sensitivity. Glucose and insulin levels were measured pre-, mid-, and post-feeding. The SP rats exhibited postprandial hyperglycemia compared to rats fed control pellets (CP). The insulin response of SP rats during a meal was significantly higher than that of CP rats. There were no significant differences in the hepatic triacylglycerol contents and lipogenesis gene mRNA levels of SP and CP rats. However, the hepatocytes of SP rats were slightly hypertrophic. In addition, histological analysis revealed that the pancreases of SP rats had more islet areas than those of CP rats. This study demonstrated that feeding an SP-only diet for 12 days induces glucose intolerance, suggesting that the consumption of absorbable food, like a soft diet, may trigger glucose metabolism insufficiency and lead to life-threatening diseases.

Conjugated linoleic acid improves glucose utilization in the soleus muscle of rats fed linoleic acid–enriched and linoleic acid–deprived diets

The effect that conjugated linoleic acid (CLA) has on glucose metabolism in experimental animals depends on nutritional conditions. Therefore, we hypothesized that CLA improves glucose utilization and insulin sensitivity in rats fed different levels of dietary linoleic acid (LA). We investigated the effect of CLA on the uptake, incorporation, and oxidation of glucose and glycogen synthesis in the soleus muscle of rats who were fed either LA-enriched (+LA) or LA-deprived (−LA) diets, under basal conditions and in the absence or presence of insulin and/or palmitate. For 60 days, male Wistar rats were fed 1 of 4 diets consisting of +LA, −LA, or +LA and −LA supplemented with CLA. Nutritional parameters and soleus glucose metabolism were evaluated. Under basal conditions, CLA enhanced soleus glucose oxidation, whereas increased glucose uptake and incorporation were observed in the −LA + CLA group. Conjugated linoleic acid–supplemented rats presented a lower response to insulin on glucose metabolism compared with non–CLA-supplemented rats. Palmitate partially inhibited the effect of insulin on the uptake and incorporation of glucose in the +LA and –LA groups but not in the +LA + CLA or −LA + CLA groups. Dietary CLA increased glucose utilization under basal conditions and prevented the palmitate-induced inhibition of glucose uptake and incorporation that is stimulated by insulin. The beneficial effects of CLA were better in LA-deprived rats. Conjugated linoleic acid may also have negative effects, such as lowering the insulin response capacity. These results demonstrate the complexities of the interactions between CLA, palmitate, and/or insulin to differentially modify muscle glucose utilization and show that the magnitude of the response is related to the dietary LA levels.

Intralipid decreases apolipoprotein M levels and insulin sensitivity in rats.

BackgroundApolipoprotein M (ApoM) is a constituent of high-density lipoproteins (HDL). It plays a crucial role in HDL-mediated reverse cholesterol transport. Insulin resistance is associated with decreased ApoM levels.AimsTo assess the effects of increased free fatty acids (FFAs) levels after short-term Intralipid infusion on insulin sensitivity and hepatic ApoM gene expression.MethodsAdult male Sprague-Dawley (SD) rats infused with 20% Intralipid solution for 6 h. Glucose infusion rates (GIR) were determined by hyperinsulinemic-euglycemic clamp during Intralipid infusion and plasma FFA levels were measured by colorimetry. Rats were sacrificed after Intralipid treatment and livers were sampled. Human embryonic kidney 293T cells were transfected with a lentivirus mediated human apoM overexpression system. Goto-Kakizaki (GK) rats were injected with the lentiviral vector and insulin tolerance was assessed. Gene expression was assessed by real-time RT-PCR and PCR array.ResultsIntralipid increased FFAs by 17.6 folds and GIR was decreased by 27.1% compared to the control group. ApoM gene expression was decreased by 40.4% after Intralipid infusion. PPARβ/δ expression was not changed by Intralipid. Whereas the mRNA levels of Acaca, Acox1, Akt1, V-raf murine sarcoma 3611 viral oncogene homolog, G6pc, Irs2, Ldlr, Map2k1, pyruvate kinase and RBC were significantly increased in rat liver after Intralipid infusion. The Mitogen-activated protein kinase 8 (MAPK8) was significantly down-regulated in 293T cells overexpressing ApoM. Overexpression of human ApoM in GK rats could enhance the glucose-lowering effect of exogenous insulin.ConclusionThese results suggest that Intralipid could decrease hepatic ApoM levels. ApoM overexpression may have a potential role in improving insulin resistance in vivo and modulating apoM expression might be a future therapeutic strategy against insulin resistance in type 2 diabetes.

Acupoint-specific, frequency-dependent, and improved insulin sensitivity hypoglycemic effect of electroacupuncture applied to drug-combined therapy studied by a randomized control clinical trial.

The application of electroacupuncture (EA) to specific acupoints can induce a hypoglycemic effect in streptozotocin-induced rats, normal rats, and rats with steroid-induced insulin resistance. EA combined with the oral insulin sensitizer rosiglitazone improved insulin sensitivity in rats and humans with type II diabetes mellitus (DM). There are different hypoglycemic mechanisms between Zhongwan and Zusanli acupoints by EA stimulation. On low-frequency (2 Hz) stimulation at bilateral Zusanli acupoints, serotonin was involved in the hypoglycemic effect in normal rats. Moreover, after 15 Hz EA stimulation at the bilateral Zusanli acupoints, although enhanced insulin activity mainly acts on the insulin-sensitive target organs, the muscles must be considered. In addition, 15 Hz EA stimulation at the bilateral Zusanli acupoints has the combined effect of enhancing cholinergic nerve activity and increasing nitric oxide synthase (NOS) activity to enhance insulin activity. Despite the well-documented effect of pain control by EA in many systemic diseases, there are few high-quality long-term clinical trials on the hypoglycemic effect of EA in DM. Combination treatment with EA and other medications seems to be an alternative treatment to achieve better therapeutic goals that merit future investigation.

Effects of leucine and creatine supplementation on insulin sensitivity of rats treated with dexamethasone

We aimed to evaluate the effects of leucine (Leu) and creatine (Cr) supplementation on dexamethasone (DEXA) treated animals on insulin sensitivity (IS). Adult male Wistar rats were randomly divided into DEXA, DEXA + Leu (DEXA-Leu), DEXA + Cr (DEXA-CR) and Control par-fed group. DEXA-treated groups received 5 mg/kg/d for 7 days; DEXA-LEU group received 0.135 g/kg/d of Leu; DEXA-CR group received 5 mg/kg/d of Cr. Blood samples were collected for measuring plasma glucose and insulin levels. Plantaris muscle was removed for protein expression.

Roux-en-Y gastric bypass increases hepatic and peripheral insulin sensitivity in rats with type 2 diabetes mellitus

BackgroundRoux-en-Y gastric bypass (RYGB) surgery for the treatment of obesity leads to long-term diabetes remission in approximately 80% of cases. The aim of this study was to investigate the effects of RYGB on hepatic and peripheral insulin sensitivity in type 2 diabetic rats and their possible mechanisms. We also tested the hypothesis that RYGB reduces lipid content and improves insulin sensitivity in hepatocytes and skeletal muscle cells. MethodsSprague–Dawley rats were divided into 4 groups: diabetic RYGB group (n = 18), diabetic RYGB sham group (n = 6), diabetic group (n = 6), and nondiabetic control group (n = 6). The hyperinsulinemic-euglycemic clamp with tracer infusion was completed at 2, 4, and 8 weeks postoperatively to assess insulin sensitivity. The lipid content in liver and muscle tissue was examined. ResultsPostoperatively, the diabetic RYGB group had significant decreases in weight, fat mass, and food intake. Two weeks after surgery, RYGB had significantly improved the hepatic insulin sensitivity index and decreased the hepatic triglyceride, total cholesterol, and fatty acyl-CoA content. The significantly increased insulin sensitivity and decreased lipid content in muscle were not detected until 4 weeks after RYGB surgery. The basal insulin and C-peptide concentrations were significantly lower than those in diabetic group by 2 weeks after RYGB. ConclusionThe increased insulin sensitivity after RYGB occurs earlier in the liver than in the muscle and both may contribute to long-term remission of type 2 diabetes. Reduced lipid content of hepatocytes and skeletal muscle cells after RYGB may contribute to the improved insulin sensitivity in these cells.

Overexpression of mitofusin 2 improves translocation of glucose transporter 4 in skeletal muscle of high-fat diet-fed rats through AMP-activated protein kinase signaling

Mitofusin 2 (Mfn2) is a mitochondrial membrane protein that plays a role in mitochondrial fusion and metabolism in mammalian cells. Previous studies have reported a positive correlation between Mfn2 expression and insulin sensitivity in non‑diabetic and type 2 diabetic subjects. Thus, the aim of the present study was to investigate whether Mfn2 overexpression improves insulin sensitivity of high‑fat diet (HFD) rats and the possible underlying mechanisms. Male SD rats were randomly divided into four groups: negative control; HFD; HFD plus adenoviral vectors; and HFD plus adenoviral vectors encoding Mfn2. Following an 11‑week treatment protocol, the euglycemic‑hyperinsulinemic clamp technique was applied to evaluate insulin sensitivity in rats. The skeletal muscles from rats in each group were analyzed by real‑time PCR and western blot analysis to determine glucose transporter 4 (GLUT4) expression, translocation and relative translocation signaling. Consistent with Mfn2 repression and glucose intolerance, HFD downregulates GLUT4 expression at the mRNA and protein levels, while Mfn2 overexpression activates AMP‑activated protein kinase (AMPK), increases GLUT4 expression and translocation and improves insulin resistance in the skeletal muscles of HFD rats. Results of the present study indicate that Mfn2 overexpression improves insulin sensitivity and may regulate GLUT4 translocation in an AMPK‑dependent manner in the skeletal muscles of HFD rats. This study is likely to provide insight into the unique role of Mfn2 in promoting glucose uptake, leading to modulation of GLUT4 translocation signaling and maintenance of glucose homeostasis in vivo.

Nitric oxide mediates the insulin sensitizing effects of β-sitosterol in high fat diet-fed rats

β-Sitosterol has been shown to have antidiabetic and antioxidant effects in animal models. The objective of the study is to investigate the effects of β-sitosterol on insulin sensitivity, oxidative and nitrosative stress and lipid abnormalities in liver of high fat-fed rat model of insulin resistance (IR) and to assess whether nitric oxide (NO) is involved in its action. Adult male albino Wistar rats of body weight 150–180g were fed either control diet (CON) or high fat diet (HFD). Each dietary group was divided into two and treated or untreated with β-sitosterol (10mg/kgb.w.−1day−1) for 4weeks. Inhibition of total nitric oxide synthase (NOS) by administration of nitro-l-arginine methyl ester (L-NAME) and inducible NOS (iNOS) by aminoguanidine (AG) in HFD and HFD+ β-sitosterol groups were accomplished to identify the role of NO. After 28days, assays were performed in plasma and liver. HFD-fed rats showed hyperglycemia, hyperinsulinemia, IR, oxidative damage, nitrosative stress, lipid accumulation and elevated serum aminotransferases. Increased expression of iNOS and decreased expression of endothelial NOS (eNOS) were observed in them. Hepatic fat accumulation was further confirmed by histology. The biochemical and histological abnormalities associated with HFD feeding were significantly reduced by β-sitosterol administration. Administration of L-NAME to HFD-fed rats caused decrease in insulin sensitivity and increase in oxidative stress. Co-administration of L-NAME for the last seven days to β-sitosterol-treated HFD rats abolished the glucose lowering effect of β-sitosterol, but the ability to decrease oxidative stress remained unaltered. On the other hand, administration of AG resulted in improved glucose homeostasis and antioxidant levels but decreased oxidative stress and enhanced antioxidant potential in both HFD and HFD+ β-sitosterol treated groups. Thus, β-sitosterol promotes insulin sensitivity in rats fed HFD possibly by improving NO levels. With additional studies, β-sitosterol might be used as a functional drug or as an adjuvant in the management of IR and associated fatty liver disease.

Yuzu (Citrus junos Tanaka) improves cognitive function and glucose homeostasis in β‐amyloid infused rats

Our preliminary study revealed that dementia induced by β‐amyloid accumulation itself exacerbates peripheral glucose homeostasis in rats. We were interested to study that long‐term oral consumption of Yuzu extract improves cognitive dysfunction and glucose homeostasis in the β‐‐amyloid‐induced rats. Male rats received intracerebralventricular infusions of β‐amyloid (25–35) (AMY) or β‐amyloid (35–25) (RAMY), at a rate of 3.6 nmol/day for 14 days. AMY‐infused rats were divided into two groups: one group received 3% lyophilized 70% ethanol extracts of Yuzu in a high fat diet and the other group received 3% dextrin. After 6 weeks of treatment, AMY increased β‐amyloid deposition in the hippocampus and the accumulation was not detected in RAMY. AMY attenuated hippocampal insulin signaling to induce hyperphosphorylation of tau. Yuzu treatment prevented the attenuation of the hippocampal insulin signaling in AMY‐infused rats and reduced tau phosphorylation. As a result, AMY induced cognitive dysfunction in comparison to RAMY while yuzu reversed cognitive impairment. AMY decreased body weight without lowering visceral fat accumulation by decreasing food intake and yuzu treatment blocked the decrease. However, yuzu treated rats had less visceral fat. AMY did not disrupt glucose tolerance due to increased insulin secretion although AMY exacerbated insulin resistance as indicated by HOMA‐IR and insulin tolerance tests. Yuzu treatment tended to improve the first phase of glucose tolerance and it was related to improved insulin sensitivity since it decreased insulin secretion. In conclusion, yuzu treatment alleviated cognitive dysfunction and impaired energy and glucose homeostasis by improving insulin sensitivity in rats with AMY‐induced cognitive dysfunction.

Periapical Lesions Decrease Insulin Signal and Cause Insulin Resistance

IntroductionInflammatory cytokines are associated with decreased insulin signal transduction. Moreover, local oral inflammation, such as that accompanying periodontal disease, is associated with insulin resistance and type 2 diabetes mellitus. The aim of this study was to evaluate the effect of periapical lesions (PLs) on insulin signaling and insulin sensitivity in rats. We hypothesized that PLs alter systemic insulin signaling and insulin sensitivity via elevated plasmatic tumor necrosis factor α (TNF-α). MethodsWistar rats were divided into control (CN) and PL groups. PLs were induced by exposing pulpal tissue to the oral environment. After 30 days, insulin sensitivity was measured using the insulin tolerance test. After euthanization, maxillae were processed for histopathology. Plasmatic concentrations of tumor necrosis factor α (TNF-α) were determined via the enzyme-linked immunosorbent assay. Insulin signal transduction was evaluated using insulin receptor substrate tyrosine phosphorylation status and serine phosphorylation status in periepididymal white adipose tissue via Western blotting. For insulin signaling and insulin tolerance tests, the analyses performed were analysis of variance followed by the Tukey post hoc test. For TNF-α analysis, the Student's t test was used. In all tests, P < .05 was considered significant. ResultsThe rats with PLs showed higher plasmatic TNF-α, lower constant rate for glucose disappearance values, and reduced pp185 tyrosine phosphorylation status but no change in serine phosphorylation status in white adipose tissue after insulin stimulation. ConclusionsPLs can cause alterations to both insulin signaling and insulin sensitivity, probably because of elevation of plasmatic TNF-α. The results from this study emphasize the importance of the prevention of local inflammatory diseases, such as PLs, with regard to the prevention of insulin resistance.

Factors involved in rosuvastatin induction of insulin sensitization in rats fed a high fat diet

Background and AimTo investigate whether rosuvastatin can improve insulin sensitivity in overweight rats having a high fat diet (HFD). The potential mechanisms involved in this action were evaluated, including SIRT-1, other factors involved in glucose metabolism and stress signaling pathways. Methods and ResultsMale Wistar rats (n = 30) were divided into three groups: (i) rats fed a standard diet (3.5% fat); (ii) rats fed a HFD (33.5% fat); and (iii) rats fed a HFD and treated with rosuvastatin (15 mg/kg/day). Evolution: 7 weeks. HFD rats showed increased body, epididymal and lumbar adipose tissue weights. Plasma levels of cholesterol, triglycerides, VLDL, glucose and insulin and leptin/adiponectin ratio were higher in HFD rats, and rosuvastatin treatment reduced them. SIRT-1, p53, PGC-1α, PPAR-γ and GLUT-4 protein levels in white adipose tissue (WAT) were lower, and JNK was higher in HFD rats compared to controls. Rosuvastatin treatment normalized expression of these mediators. Endothelium-dependent relaxation was reduced in mesenteric rings from HFD rats compared to controls and rosuvastatin enhanced it in HFD rats. ConclusionRosuvastatin treatment reduced insulin resistance without affecting body weight or WAT loss in HFD rats. Reduction of leptin and JNK, and enhancement of SIRT-1, p53, PGC-1α, PPAR-γ and GLUT-4 expression in WAT could contribute to insulin sensitization. Normalization of SIRT-1 expression in WAT could be considered a key novel mechanism that aids in explaining the beneficial effects of rosuvastatin on the amelioration of glucose metabolism and the arrangement of multiple signaling pathways participating in insulin resistance in overweight HFD rats.

Chronic leucine supplementation increases body weight and insulin sensitivity in rats on high‐fat diet likely by promoting insulin signaling in insulin‐target tissues

This study investigated the effect of chronic leucine supplementation on insulin sensitivity and the associated mechanisms in rats on high-fat diet (HFD). Male Sprague-Dawley rats were fed either normal chow diet or HFD supplemented with 0, 1.5, 3.0, and 4.5% leucine for 24weeks. We found that chronic leucine supplementation increased insulin sensitivity together with increased body weight in rats on HFD, but had no effect on insulin sensitivity in rats on normal chow diet. The increased insulin sensitivity by leucine supplementation was not associated with altered ectopic fat accumulation in liver and muscle, plasma levels of lipids and cytokines, but is associated with reduced oxidative stress and improved insulin signaling. Chronic leucine supplementation did not enhance insulin receptor substract-1 (IRS-1) phosphorylation on serine 302, but elevated basal IRS-1 phosphorylation on tyrosine 632 and improved insulin-stimulated protein kinase B (Akt) and mammalian target of rapamycin (mTOR) phosphorylation in liver, skeletal muscle, and adipose tissue of rats on HFD rats, indicating leucine supplementation prevented HFD-induced insulin resistance in insulin-target tissues. Chronic leucine supplementation can increase insulin sensitivity and body weight likely by reducing oxidative stress and improving insulin signaling pathway in rats on HFD.

Duration of rise in free fatty acids determines salicylate's effect on hepatic insulin sensitivity

We have shown in rats that sodium salicylate (SS), which inhibits IkBa kinase B (IKKB), prevents hepatic and peripheral insulin resistance caused by short-term (7 h) i.v. administration of Intralipid and heparin (IH). We wished to further determine whether this beneficial effect of SS persisted after prolonged (48 h) IH infusion, which better mimics the chronic free fatty acid (FFA) elevation of obesity. Hence, we performed hyperinsulinemic euglycemic clamps with tritiated glucose methodology to determine hepatic and peripheral insulin sensitivity in rats infused with saline, IH, IH and SS, or SS alone. SS prevented peripheral insulin resistance (P<0.05) caused by prolonged plasma FFA elevation; however, it did not prevent hepatic insulin resistance. In skeletal muscle, protein levels of phospho-IkBa were augmented by prolonged IH administration and this was prevented by SS, suggesting that IH activates while SS prevents the activation of IKKB. Markers of IKKB activation, namely protein levels of phospho-IkBa and IkBa, indicated that IKKB is not activated in the liver after prolonged FFA elevation. Phosphorylation of serine 307 at insulin receptor substrate (IRS)-1, which is a marker of proximal insulin resistance, was not altered by IH administration in the liver, suggesting that this is not a site of hepatic insulin resistance in the prolonged lipid infusion model. Our results suggest that the role of IKKB in fat-induced insulin resistance is time and tissue dependent and that hepatic insulin resistance induced by prolonged lipid elevation is not due to an IRS-1 serine 307 kinase.

Mitofusin-2 ameliorates high-fat diet-induced insulin resistance in liver of rats

To investigate the effects of mitofusin-2 (MFN2) on insulin sensitivity and its potential targets in the liver of rats fed with a high-fat diet (HFD). Rats were fed with a control or HFD for 4 or 8 wk, and were then infected with a control or an MFN2 expressing adenovirus once a week for 3 wk starting from the 9(th) wk. Blood glucose (BG), plasma insulin and insulin sensitivity of rats were determined at end of the 4(th) and 8(th) wk, and after treatment with different amounts of MFN2 expressing adenovirus (10(8), 10(9) or 10(10) vp/kg body weight). BG levels were measured by Accu-chek Active Meter. Plasma insulin levels were analyzed by using a Rat insulin enzyme-linked immunosorbent assay kit. Insulin resistance was evaluated by measuring the glucose infusion rate (GIR) using a hyperinsulinemic euglycemic clamp technique. The expression or phosphorylation levels of MFN2 and essential molecules in the insulin signaling pathway, such as insulin receptor (INSR), insulin receptor substrate 2 (IRS2), phosphoinositide-3-kinase (PI3K), protein kinase beta (AKT2) and glucose transporter type 2 (GLUT2) was assayed by quantitative real-time polymerase chain reaction and Western-blotting. After the end of 8 wk, the body weight of rats receiving the normal control diet (ND) and the HFD was not significantly different (P > 0.05). Compared with the ND group, GIR in the HFD group was significantly decreased (P < 0.01), while the levels of BG, triglycerides (TG), total cholesterol (TC) and insulin in the HFD group were significantly higher than those in the ND group (P < 0.05). Expression of MFN2 mRNA and protein in liver of rats was significantly down-regulated in the HFD group (P < 0.01) after 8 wk of HFD feeding. The expression of INSR, IRS2 and GLUT2 were down-regulated markedly (P < 0.01). Although there were no changes in PI3K-P85 and AKT2 expression, their phosphorylation levels were decreased significantly (P < 0.01). After intervention with MFN2 expressing adenovirus for 3 wk, the expression of MFN2 mRNA and protein levels were up-regulated (P < 0.01). There was no difference in body weight of rats between the groups. The levels of BG, TG, TC and insulin in rats were lower than those in the Ad group (P < 0.05), but GIR in rats infected with Ad-MFN2 was significantly increased (P < 0.01), compared with the Ad group. The expression of INSR, IRS2 and GLUT2 was increased, while phosphorylation levels of PI3K-P85 and AKT2 were increased (P < 0.01), compared with the Ad group. HFDs induce insulin resistance, and this can be reversed by MFN2 over-expression targeting the insulin signaling pathway.

Liver phosphatidylinosital 3-kinase/protein kinase B pathway is involved in the decrease of insulin sensitivity in rats with fetal growth restriction

Objective To investigate the effect of liver phosphatidylinosital 3-kinase/protein kinase B (PI3-K/AKT) pathway on the decrease of insulin sensitivity in fetal growth restriction (FGR) rats.Methods Twenty pregnant female rats were randomly divided into two groups one day after conception:normal-protein group and low protein group (n=10,respectively).Rats in low-protein group was given low protein diet (8.00％ protein) during pregnancy to build FGR model,while normal-protein group was given normal protein diet (20.00％ protein).On day 3,7,14,30,60 and 90 after birth,fasting blood samples of 8 male FGR offsprings from low-protein group and 8 normal offsprings from normal-protein group were collected to measure fasting plasma glucose and insulin level.Then insulin resistance index and insulin sensitivity index were calculated to determine insulin sensitivity.On day 7,14,30,60 and 90 after birth,liver tissue of 8 male FGR and normal offsprings were collected,insulin receptor substrate 1,2 (IRS1/IRS2)and glucose transporter 4 (GLUT4) mRNA expression were measured by real-time fluorescence polymerase chain reaction and the protein expressions of IRS1,PI3-K (subunit p110β),and AKT and phosphorylated AKT (pAKT) were measured by Western blot.The relationships between the expression changes of key molecules of PI3-K/AKT pathway and insulin sensitivity were analyzed by correlation and multiple linear regression method.Results (1) Mean birth weight of baby rats in low-protein group was significantly lower than that of normal-protein group [(4.92±0.36) g vs (6.43±0.59) g,t=14.73,P＜0.05].The incidence of FGR in low-protein group was 88.2％ (97/110); and for male offsprings,it was 94.1 ％ (48/51).(2) Compared to normal offsprings,fasting plasma glucose levels of male FGR offsprings were significantly higher from the age of 60 days to 90 days.Insulin levels and insulin resistance index were significantly higher and insulin sensitivity index was lower from the age of 30 days to 90 days,P＜0.05 respectively.(3) Compared to normal offsprings,IRS1 (0.45 ± 0.02 vs 0.68± 0.03,t=16.633,P＜0.05) and IRS2 mRNA (0.34±0.10 vs 0.70±0.19,t=4.864,P＜0.05) expressions in FGR offsprings were lower from day 7 after birth to day 90 (0.48±0.03 vs 0.59±0.05,t=5.237,P＜0.05; 0.49±0.20 vs 0.70±0.11,t=2.253,P＜0.05).There were no differences in expressions of GIUT4 mRNA and AKT protein between two groups (P＞ 0.05).IRS1,PI3-K and pAKT protein expressions of FGR offsprings decreased significantly from day 14 (0.22±0.05 vs 0.52±0.11,t=7.024,P＜0.05; 0.46±0.03 vs 0.97±0.08,t=17.508,P＜0.05; 0.62±0.10 vs 0.89±0.08,t=6.100,P＜0.05) to day 90 (1.11±0.08 vs 1.32±0.14,t=3.714,P＜0.05; 0.63±0.07 vs 1.00±0.19,t=5.206,P＜0.05;0.28±0.03 vs 0.45±0.10,t=4.880,P＜0.05).(4) The pAKT protein expression level of FGR rats was positively correlated with insulin sensitivity index (r=0.704,P＜0.05) ; while negatively correlated to the level of fasting plasma glucose (r=-0.609,P＜0.05),fasting insulin (r=-0.561,P＜0.05) and insulin resistance index (r =0.577,P＜ 0.05).Conclusions The changes of some key molecules' expressions of PI3-K/AKT pathway in liver might be involved in the insulin resistance in FGR rats. Key words: Fetal growth retardation; Insulin resistance; 1-Phosphatidylinositol 3-kinase; Protooncogene proteins c-akt; Liver; Disease models,animal

Fish oil supplementation for two generations increases insulin sensitivity in rats

We investigated the effect of fish oil supplementation for two consecutive generations on insulin sensitivity in rats. After the nursing period (21 days), female rats from the same prole were divided into two groups: (a) control group and (b) fish oil group. Female rats were supplemented with water (control) or fish oil at 1 g/kg body weight as a single bolus for 3 months. After this period, female rats were mated with male Wistar rats fed on a balanced chow diet (not supplemented). Female rats continued to receive supplementation throughout gestation and lactation periods. The same treatment was performed for the next two generations (G1 and G2). At 75 days of age, male offspring from G1 and G2 generations from both groups were used in the experiments. G1 rats did not present any difference with control rats. However, G2 rats presented reduction in glycemia and lipidemia and improvement in in vivo insulin sensitivity (model assessment of insulin resistance, insulin tolerance test) as well as in vitro insulin sensitivity in soleus muscle (glucose uptake and metabolism). This effect was associated with increased insulin-stimulated p38 MAP kinase phosphorylation and lower n-6/n-3 fatty acid ratio, but not with activation of proteins from insulin signaling (IR, IRS-1 and Akt). Global DNA methylation was decreased in liver but not in soleus muscle. These results suggest that long-term fish oil supplementation improves insulin sensitivity in association with increased insulin-stimulated p38 activation and decreased n-6:n-3 ratio in skeletal muscle and decreased global DNA methylation in liver.

In vitro antioxidant and in vivo antidiabetic, antihyperlipidemic activity of linseed oil against streptozotocin‐induced toxicity in albino rats

AbstractThe intake of omega‐3 unsaturated fatty acids has a beneficial effect on insulin sensitivity in rats and in subjects with type 2 diabetes. It has been reported that these omega‐3 fatty acids are useful in the treatment of hypertriglyceridemia and in the enhancement of high‐density lipoprotein (HDL)‐cholesterol levels in diabetic patients. The present study was therefore aimed to evaluate the antioxidant, antihyperglycemic and antihyperlipidemic effect of L. usitatissimum fixed oil. The antioxidant activity was evaluated in vitro using 1,1‐diphenyl‐2‐picryl hydrazyl (DPPH) and hydrogen peroxide (H2O2) assay. The oil exhibited significant in vitro antioxidant activity in the DPPH and H2O2 assay. The oil (1, 2, 3 mL/kg) was further investigated against streptozotocin (STZ)‐induced hyperglycemia and hyperlipidemia in albino rats, subjected to 3 weeks of treatment. The oil manifested decrease in blood glucose and glycated hemoglobin levels at higher dose and significant dose dependent negating action on antioxidant enzymes in the heart, liver and kidney tissues. The oil also normalized the various hematological parameters and electrolyte levels in the STZ treated rats. Treatment with oil significantly increased the level of serum HDL and decreased the levels of total cholesterol, triglycerides, and low‐density lipoprotein‐cholesterol in STZ‐diabetic rats in comparison to normal control. The antioxidant, antihyperglycemic and antihyperlipidemic activity of the oil could be attributed to the presence of linolenic acid (ALA, 18:3 n‐3) and its metabolic products, eicosapentanoic acid (EPA, 20:5 n‐3) and docosahexanoic acid (DHA, 22:6 n‐3).

Regulation of the Intracerebroventricular Administration of Brain-Derived Neurotrophic Factor on Baroreflex Function and Insulin Sensitivity in Rats

"In addition to its well-established neurotrophic effects, brain-derived neurotrophic factor (BDNF) has also been shown to regulate glucose metabolism. The present study was conducted to determine whether BDNF has effects on baroreflex sensitivity (BRS) and whole-body insulin sensitivity through modulation of autonomic nervous function in normal rats. Male Sprague-Dawley rats were treated with intracerebroventricular BDNF (20 μg per rat, 10μl; BDNF) or artificial cerebrospinal fluid (10 μl; control) at an infusion rate of 1 μl/min in conscious state. The whole-body insulin sensitivity was determined by the euglycemic hyperinsulinemic clamp technique. BRS in response to phenylephrine (PE-BRS) or sodium nitroprusside (NP-BRS) was assessed using linear regression analysis. The sympathetic and parasympathetic influences on BRS were investigated by pharmacological autonomic blockade. When compared to the control rats, blood glucose levels were slightly but significantly decreased in BDNF-treated rats. However, plasma insulin levels were reduced by about 30%. The whole-body insulin sensitivity was increased in BDNF-treated rats. In addition, blood pressure was increased but heart rate remained unchanged after BDNF treatment. Enhanced PE-BRS was also observed in the BDNF-treated rats, which was attributed to the abnormal parasympathetic activation as revealed by the results of the pharmacological blockade study with methylatropine. Results of the present demonstrate that central BDNF plays an important role in the regulation of whole-body insulin sensitivity and baroreflex function. The data indicate that the alteration of autonomic nervous function may play a role in the effects of BDNF."