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Currently it is unclear whether lipid accumulation occurs in a particular sequence and its relationship with whole body insulin resistance (IR). This study aimed to answer this question.Male Sprague-Dawley (SD) rats were fed on a normal or a high-fat diet for 20 weeks. Serum triglycerides (TG), serum free fatty acids (FFA), fasting plasma glucose (FPG), and liver and skeletal muscle TG were measured. The glucose infusion rate (GIR) and mRNA levels of acetyl-CoA carboxylase (ACC) and carnitine palmitoyltransferase-1 (CPT-1) in the liver and skeletal muscle were determined at different stages.Compared with rats fed on the normal diet, serum FFA was not significantly increased in rats fed on the high-fat diet until 20 weeks. In contrast, liver TG was significantly increased by the high-fat diet by four weeks (20-fold; P0.01), and remained elevated until the end of the study. However, skeletal muscle TG was not significantly increased by the high-fat diet until 20 weeks (10.6-fold; P0.01), and neither was the FPG. The GIR was significantly reduced (1.6-fold; P0.01) by the high-fat diet after 8 weeks. The mRNA levels of ACC gradually increased over time and CPT-1 decreased over time, in both the liver and skeletal muscle in rats fed the high-fat diet.Lipid accumulation in the liver occurs earlier than lipid accumulation in the skeletal muscle. Fatty liver may be one of the early markers of whole body IR. Changes in the gene expression levels of ACC and CPT-1 may have important roles in the process of IR development.

To investigate the effect of beta cell lipoapoptosis after long term high-fat feeding in rats, and to investigate the relationship between oxidative stress, gene expression and beta cell lipoapoptosis.Forty-one SD male rats were randomly divided into 2 groups: high-fat diet group (HF group) and control group (NC group). At the end of 28 weeks, the levels of malondialdehyde (MDA) and glutamylcysteinylglycine (GSH) in plasma and pancreatic tissue,the early-phase insulin secretion in beta cells, the beta cell apoptosis (TUNEL technology) and the uncoupling protein 2 (UCP2) gene expression in islets were measured.The concentrations of MDA both in plasma and pancreatic tissue were higher in HF group than those in NC group.In contrast, The contents of GSH both in plasma and pancreatic tissue were lower in HF group. Insulin secretion response to glucose load was significantly decreased in HF group (3.0 fold Compared with 5.7 fold, P0.01). Blood glucose levels at 3 min, 5 min and 10 min during IVGTT were significantly higher in HF group than those in NC group (P0.05). The frequency of beta cell apoptosis was increased by 40.0% in HF group (P0.01). The gene expression of UCP2 in islets was increased by 22.4% in HF group (P0.01).The frequency of beta cell apoptosis in high-fat feeding rats is affected by oxidative stress, which results in increasing UCP2 gene expression.

To study the effects of high fat diet on the functions of islet beta cells and the role of uncoupling protein-2 (UCP2) therein and possible mechanism.Forty SD rats were randomly divided into two equal groups: high-fat-(HF) diet group, fed with HF diet for 20 weeks, and normal diet control (NC) group, fed with normal diet. At the end of the twentieth week blood samples were collected from the heart to determine the serum fasting blood glucose (FBG) and fasting insulin (FINS), and plasma nitrotyrosine, malondialdehyde (MDA), and glutamylcysteinylglycine (GSH), indicators of oxidative stress. Glucose infusion rate (GIR) was measured using euglycemic hyperinsulinemic clamp test to evaluate the peripheral insulin resistance. Pancreatic islets were isolated and collected. Islet perfusion was conducted to evaluate the insulin secretion in the islet beta cells. Real-time PCR was used to detect the expression of insulin receptor substrate-1 (IRS-1), IRS-2, and uncoupling protein 2 (UCP2) genes in the islet. Immunohistochemistry was used to detect the protein expression of IRS-1 and IRS-2.(1) The concentrations of plasma nitrotyrosine and MDA of the HF group were both significantly higher than those of the NC group (both P0.05). However, the plasma GSH of the HF group was significantly lower than that of the NC group (P0.01). (2) The blood glucose of both groups became stable since 60 min after the experiment and the GIR of the HF group was (5.25 +/- 1.2) mg x min(-1) x kg(-1), significantly lower r than that of the NC group [(13.6 +/- 1l.7) mg x min(-1) x kg(-1), P0.01). (3) The peak of glucose-stimulated insulin secretion (GSIS) of the HF group was significantly lower than that of the NC group; and the GSIS peak increase In comparison with the NC group. (4) In comparison with the NC group, the mRNA expression levels of IRS-1 and IRS-2 genes of the HF group were significantly lower, by 42.3% and 28.1% respectively (both P0.05), and the expression of UCP2 was significantly higher, by 32.5% (P0.05). (5) Compared with the NC group, the protein expression levels of IRS-1 and IRS-2 in the islets of the HF group were lower, by 26.3% and 11.2% respectively, however not significantly (both P0.05). (6) There was a significantly negative correlation between the UCP2 and IRS-1/IRS-2 gene expression in islet beta cells in the HF group (r = -0.621 and r = -0.436, both P0.05).High-fat-diet impairs the expression of insulin signal transduction molecules and the function of islet beta cells that may be correlated with overexpression of UCP2. The basic insulin secretion of HF group was significantly higher than that of the NC group; but the glucose-stimulated insulin secretion (GSIS) peak decreased in comparison with the NC group. Compared with the NC group, the protein expression levels of IRS-1 and IRS-2 in the islets of the HF group were lower, by 26.3% (P0.05) and 11.2% (P0.05) respectively.

To study the effects of fenofibrate (FF), a peroxisome proliferator activated receptor (PPAR) alpha activator, on the expression of carnitine palmitoyltransferase 1 (CPT-1) mRNA in liver and muscle and its influence on insulin sensitivity.Thirty-two normal 8 week-old male SD rats were randomly divided into 3 groups: normal control group, fed with normal food for 3 weeks (NC group, n = 10), high fat diet group, fed with high fat food (HF group, n = 10), and high fat diet supplemented with FF group, fed with high fat food and given with gastric perfusion of FF (50 mg x kg(-1) x d(-1)) (FF group, n = 12). Fast serum triglyceride (TG) level was tested by automatic biochemical analyzer after 8-10 h fasting. Euglycemic-hyperinsulinemic clamp method was used to calculate the glucose infusion rate (GIR) so as to evaluate the insulin sensitivity. By the end of experiment the rats were killed with their internal organs taken out. The triglyceride (TG) contents of liver and skeletal muscle were measured using Folch method. Real-time PCR was used to detect the mRNA expression. of CPT-1 in the liver and skeletal muscles.As compared with the NC group, the TG levels of serum, liver, and skeletal muscle of the HF group were higher than those of the NC group by 0.45-fold, 2.14-fold, and 10.64-fold respectively. The GIR of the HF group was (6.2 +/- 0.8) mg x kg(-1) x min(-1), significantly lower than that of the NC group (15.8 +/- 2.1) mg x kg(-1) x min(-1), (P0.01), and that of the P0.01. The CPT-1 mRNA expression in liver of the HF group was not significantly different from that of the NC group (P0.05); the expression of CPT-1 mRNA in skeletal muscle of the HF group was lower than that of the NC group by 71% (P0.01). The CPT-1 mRNA expression in liver and skeletal muscle of the FF group were significantly higher than those of the HF group by 1.00 and 1.05 times respectively (both P05). The GIR was negatively correlated with the levels in the liver (r = -0.87, P0.01) and in the skeletal muscle (r = -0.78, P0.01).Fenofibrate promotes the oxygenation of fatty acids by up-regulating the CPT-1 mRNA expression in the liver and skeletal muscles, thus improving the insulin sensitivity.

To observe the relationship between changes of genes expression related to lipid metabolism and insulin resistance induced by high fat diet in SD rats.Normal 8-week old male SD rats were randomly divided into 3 groups. They were fed with normal chow (NC, n = 10), high fat diet (HF, n = 10) and high fat diet supplemented with pioglitazone 15 mg x kg(-1) x d(-1) (HP, n = 12). The TG content of liver and skeletal muscle of the rats was measured. Glucose infusion rate (GIR) was used to evaluate the insulin sensitivity by using euglycemic-hyperinsulinemic clamp method. Genes expression was investigated using real-time PCR method.After high fat feeding for 20 weeks, the serum TG, the content of TG in the liver and skeletal muscle of the rats in the HF group increased 0.45, 2.28 and 9.31 fold respectively as compared with those in the NC group. The change of TG content in the liver and skeletal muscle was associated with the reduction of GIR [(6.16 +/- 0.75) mg x kg(-1) x min(-1) vs (15.82 +/- 2.10) mg x kg(-1).min(-1) (P0.01)]. As compared with the NC group, the expression of hormone-sensitive lipase (HSL) and fatty-acid synthase (FAS) gene in the HF group was enhanced by 28.2% and 21.3%, respectively (P0.05). In addition, the expression of acetyl-CoA carboxylase1 (ACC1) mRNA in the liver increased 48.3% (P0.05), increased 101.1% (P0.01) and carnitine palmitoyltransferase 1 (CPT-1) decreased 71.0% (P0.01) in the skeletal muscle in the rats of HF group. As compared with those in the HF group, GIR increased 1.54 fold in the HP group and on the contrary, serum TG, liver TG and muscle TG decreased about 66%, 64.5% and 59.6% respectively in the HP group (P0.05). Accordingly, the expression of FAS and HSL in the adipose tissue and the expression of ACC1 in the liver were reduced (P0.05) and the expression of CPT-1 was enhanced and ACC2 was reduced in the muscle (P0.01) in the HP group.The changing expression of genes related to lipid metabolism may play a role in the accumulation of lipids in non-adipose tissue and the induction of insulin resistance in rats fed with high fat diet.

To study the changes of inflammatory path molecules in the islet alpha cells in high-fat-diet fed plus beta cell-deleted rat models and the effects of pioglitazone intervention.Forty five normal male SD rats, 8 week old, were randomly divided into 3 groups, i.e., a normal diet group (NC), a high fat diet fed group (HF), and a high fat diet fed and pioglitazone treated group (HP, pioglitazone 15 mg kg(-1) d(-1)). At the end of twenty weeks of feeding, fasting serum insulin (FIns), glucagon, free fatty acid (FFA) and high sensitive C reactive protein (hsCRP) were determined. Glucose infusion rate (GIR) was measured by using euglycemic hyperinsulinemia clamp to evaluate the peripheral insulin resistance. The contents of glucagon in perfusion medium during islet cell perfusion was measured with RIA. At the same time, beta cell-deleted rat models were established by injecting large dose streptozocin (100 mg/kg) in 8 rats in each of the three groups, i.e., HF-B group, P-B group and NC-B group. Five days later, the rats were sacrificed and the pancreatic islets were isolated and collected. The expression of NF-kappaB and inhibitor kappaBalpha (IkappaBalpha) gene in the islets was detected with real-time PCR.(1) GIR was decreased significantly in HF group as compared with NC group (P0.01). The concentrations of serum FIns, glucagon, FFA and hsCRP in HF group were higher than those in NC group. Pioglitazone intervention could reverse these effects. (2) 16.7 mmol/L glucose could inhibit the glucagon secretion by the islet alpha cells of the NC group rats, but not of the HF group rats. Pioglitazone intervention could reverse these effects. (3) The gene expression of NF-kappaB was significantly increased by 20.5% in the HF-B group than in the NC-B group (P0.01). In contrast, the expression of IkappaBalpha was significantly decreased by 24.3% (P0.01). The expression of NF-kappaB and IkappaBalpha mRNAs in HP-B group, when compared with that of HF-B group, was improved 78.3% and 58.8%, respectively.High-fat-diet feeding induces islet alpha cell insulin resistance and activates the mRNA expression of inflammatory path molecules in beta cell-deleted rat models and it may relate with the increased plasma FFA concentration. Pioglitazone intervention can reverse these effects.

To study the changes of insulin signal transduction molecules in islet alpha cells in high-fat-diet plus beta cell-deleting rat models and its underlying mechanism.Thirty SD rats were randomly divided into 2 equal groups and fed with high-fat-diet (HF group) or normal diet (normal control group, NC group) respectively. At the end of twenty-week feeding, the fasting serum insulin (Ins), glucagon (Glc), free fatty acid (FFA), and triglyceride (TG were measured. The glucose infusion rate (GIR) was measured by using euglycemic hyperinsulinemia clamp to evaluate the peripheral insulin resistance. At the same time, large dose streptozocin (100 mg/kg) was injected so as to establish beta cell-deleting rat models, i.e., HF-B group (n = 8) and NC-B group (n = 8). Five days later, the rats of the HF-B and NC-B subgroups were sacrificed, and the pancreatic islets were isolated and collected. The expression of Glc, insulin receptor substrate-1 (IRS-1), IRS-2, and phosphatidylinositol-3-kinase (PI3K) gene in the islets were detected by RT-PCR.(1) The serum FFA, insulin and Glc concentrations of the HF group were 508 (394 - 622) micromol/L, 23.7 (14.0 - 33.4) mIU/L, and 345 (298.6 - 391.4) pg/ml respectively, all significantly higher than those of the NC group [325 (240 - 410) micromol/L, 11.5 (3.6 - 19.4) mIU/L, 256 (226.4 - 285.6) pg/ml; respectively, all P0.05]. The GIR of the HF group was 5.25 mgxmin(-1)xkg(-1) +/- 1.2 mgxmin(-1)xkg(-1), significantly lower than that of the NC group (13.6 mgxmin(-1)xkg(-1) +/- 1.7 mgxmin(-1)xkg(-1), P0.01)). (2) The gene expression of Glc of the HF-B subgroup was significantly higher than that of the NC-B subgroup by 34.2% +/- 2.1%. In contrast, the expression of IRS-2, and PI3K of the HF-B subgroup was significantly lower than that of the NC-B subgroup by 28.5% +/- 1.8% and 21.3% +/- 1.6% respectively (both P0.01). (3) The plasma FFA concentration was asignificantly negatively correlated with GIR (r = -0.675, P0.05) and IRS-2 gene expression in islet alpha cells (r = -0.458, P0.05) in the HF-B group.High-fat-diet feeding plus beta cell-deleting rat model shows an impaired expression of insulin signal transduction molecules in islet alpha cells which may relate with the increased plasma FFA concentration.