| Insulin resistance (IR) is the common pathophysiological foundation for many diseases associated with dysfunction of endocrinology and metabolism. Furthermore, IR is an independent risk factor of type 2 diabetes mellitus. Insulin resistance is a pathophysiological state in which the tissues and organs are insensitive to insulin actions. Genetic and environmental factors play major roles in the development of insulin resistance. Obesity is characterized by increases in both the size and number of adipocytes leading to excessive storage of adipose tissue. In recent years, more and more studies indicate that adipose tissue was an endocrine organ. Many adipokines secreted by adipocyte such as leptin, resistin and adiponectin are all related with insulin resistance. Apelin, as a novel adipokine, is produced and secreted by adipose tissue of human and rodent, which has numerous biological functions via binding its receptor APJ ( receptor protein related to the angiotensin receptor AT1,APJ). Moreover, Apelin plays a critical role in insulin resistance and obesity-related metabolic disorders.In the present study, we observe serum apelin level and its mRNA expression in the adipose tissue of the insulin-resistant rats induced by high fat diets, and investigate the relationship between serum apelin and hyperinsulinemia, obesity, glucose and lipid metabolism. We explore the relation between apelin and insulin resistance, providing a new study direction to improve insulin resistance. The paper contains two parts below.Part one: Serum Apelin level and its influence factors in insulin-resistant rats induced by high-fat feedingObjective: To establish and evaluate the insulin resistance rat model induced by high-fat feeding; To observe serum apelin level in insulin resistance rats which were induced by high fat diet and the relationship between serum apelin level and blood glucose, insulin, lipid, body weight and visceral fat; To investigate the correlation between serum apelin level and hyperinsulinemia, obesity, glucose and lipid metabolism.Methods: Total 30 clean male Wistar rats weighed 280～320 grams were randomly divided into two groups: normal control group (NC) and high-fat-fed group (HF). The rats in NC group were fed with standard rat chow containing 10.3% fat, 24.2% protein, and 65.5% carbohydrate as percentage of total calories,and the total calories was 348 kcal per 100g rat chow. The rats in HF group were fed with high fat diet containing 59.8% fat, 20.1% protein and 20.1% carbohydrate as a percentage of total calories, and the total calories was 501 kcal of per 100g rat chow. The rats in each group were fed equal calories every day. Body weight was observed every week. Five weeks later, 8 rats were chosen randomly from each group. After fasted for 10 hours, the rats were taken blood sample from angular vein; the serum was separated for the detection of lipids, insulin and apelin-36. The concentration of apelin-36 was determined by ELISA. The hyperinsulinaemic- euglycaemic clamp was performed to detect the change of GIR in two groups and to confirm whether the insulin resistant rat model was duplicated successfully. After the clamp, the rats were sacrificed by depletion, the adipose pad around kidneys and epididymides was weighed exactly as the content of visceral fat. The renal or epididymal adipose pad were removed respectively and flash-frozen in liquid nitrogen, then stored at -70°C for further detections.Results: 1. The insulin resistance was evaluated by glucose infusion rate (GIR) of hyperinsulinemic -euglycemic clamp technique. Compared with NC group, GIR were lower in the HF group at the end of 5 week(P<0.01); 2. The body weight of HF group rats was higher than that of NC group, but there was no statistical difference between the two groups (P>0.05). The serum apelin -36, fasting blood glucose, fasting serum insulin, total cholesterol, triglyceride and visceral fat in HF group rats increased remarkably; and there were significant differences when compared with the NC group (P<0.01). 3. The serum apelin was positively correlated with fasting serum insulin, visceral fat,fasting blood glucose , total cholesterol, triglyceride, and weight (r=0.612, r=0.564, r=0.487, P<0.01; r=0.444, r=0.375, r=0.367, P<0.05; respectively). 4. In a multiple linear regression analysis, serum insulin level enters regression equation: Y=0.227×Fins-6.795.Conclusions: 1 The GIR was decreased significantly in high-fat-fed group at the end of 5 week, which suggested the existence of insulin resistance of high-fat-fed rats. 2 The visceral adipose tissue of high-diets feeding rats was increased, demonstrating that rats in HF group existed the abdominal obesity. 3 The serum apelin level was higher in the insulin resistance rats, which has a positive correlation with hyperinsulinemia, abdominal fat, body weight, blood glucose and lipid. The serum FINS level was the independant risk factor to apelin. We proposed apelin may contribute to the development of insulin resistance syndrome.Part two: Expression of Apelin mRNA in adipose tissue of insulin resistance rats induced by high-fat feeding Objective: To observe apelin mRNA expression in visceral fat (white adipose tissue) of insulin-resistant rats induced by high-fat diets, and explore the role of the apelin in obesity and insulin resistance.Methods: Animal grouping and the samples acquirement were the same as mentioned in part one. The mRNA expression of apelin in visceral fat was measured by semiquantitative RT-PCR. RNAiso plus was used to extract RNA from the adipose tissue. The integrity of RNA was evaluated by agarose gel caraphoresis and purity was evaluated by OD260/OD280 through ultraviolet spectrophotometer. RT-PCR was carried out in mRNAs with better integrity and ratio of OD 260nm to 280nm in 1.8-2.0.Results: Compared with NC group, the mass of visceral fat was higher, and apelin mRNA expression was significantly increased in HC group. There were significant differences when compared with NC group (P<0.05).Conclusions: Apelin was produced by fat cells. Also, a higher expression of apelin mRNA in the visceral adipose tissue was detected. This suggested that apelin is over-produced in adipocytes in hyperinsulinemia associated with abdominal obesity. Furthermore, the result demonstrated that apelin was closely associated with abdomen obesity and insulin resistance. |
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