| Background:Diabetes is a metabolic disease which with the character of increasing glucose levels in blood chronically, and it is caused by the interaction of genetic and environmental factors. Type 2 diabetes mellitus causes serious harm to human, often leading to the disorder metabolic of carbohydrates, protein and fat. It can result in serious complications of blood vessels, nerves, heart, kidneys and other organs.Insulin resistance plays an important role and has been proved to be an original factor in pathogenesis of the type 2 diabetes mellitus. The functions of insulin depend on whether insulin signal can be successfully transducted. So the number and functions of insulin transduction molecules have been the point of this research.In recent years, more and more epidemiology studies have shown that different doses of chronic alcohol intake have different effects on insulin sensitivity. Moderate alcohol intake can promote the insulin sensitivity and decrease the risk of type 2 diabetes mellitus, while chronic heavy alcohol intake has the opposite effects. China is a big country about the production and consumption of alcohol. The average alcohol intake in long-term alcohol drinkers is 10% of the total daily energy intake. Along with the economic development in China, the dietary pattern is shifting to the high-fat Western diet. The traditional alchol intake style in Chian is with the meals, therefore the high-fat diet and alcohol intake is getting more and more popular. But the effect of high-fat diet and chronic alcohol intake on the insulin sensitivity and type 2 diabetes mellitus is little known.Liver is one of the most important target organs of insulin, and it is the major organ of ethanol and lipid metabolism. Insulin resistance of hepatic tissue partly attributes to the cause of type 2 diabetes mellitus. At present, there is still little report on how insulin signal transduction and function effected by different doses of alcohol and high-fat diet.Object:This study was performed to investigate the effect of a high-fat diet and alcohol (high-fat, alcohol) intake on insulin sensitivity in rats. To explore the molecule mechanisms of insulin sensitivity of long-term alcohol intake and high fat diet, the mRNA and protein expression of the key molecules of insulin signal transduction in liver were examined.Method:Wistar rats were housed at 17–27℃, 40–60% relative humidity with at 12:12 h dark–light schedule. To initiate the study, the animals were weighed and randomly assigned to two control group-normal diet and high fat diet and five test groups .The test groups were maintained on high fat diet and subjected to daily intragastric injections (10ml/kg body weight per day) containing different levels (5, 10, 20, 30, 40%v/v) of alcohol. Weight was measured once a week. 13 weeks later, the rats were sacrificed by decapitation to test the serum total cholesterol (TC), triglyceride (TG), high density lipoprotein (HDL), fasting blood glucose concentration (FPG), blood insulin concentration (FINS), then insulin resistance index (Homeostasis Model Assessment HOMA-IR) and HOMA-βfunction index (HOMAβ-cell index) were calculated. Total RNA from liver was isolated to test the mRNA expression of insulin receptor substrate-1 (IRS-1), phosphatidylinositol 3 kinase (PI-3K) and glucose transporter-2 (GLUT-2) by RT-PCR. Liver protein was isolated to test the protein expression of PI-3K (p85α) and GLUT-2 by western blotting.Results:1. Weight change(1) The body weight of each group increased during the experiment.(2) Body weight of high-fat diet control group significantly increased compared with normal control group (P< 0.05).(3) Body weight of high-fat diet with the does of 5%, 10%, 20%, 30% alcohol groups significantly increased compared with normal control group(P< 0.05).(4) Body weight of high-fat diet with the does of 40% alcohol group significantly decreased compared with high-fat diet control group (P< 0.05).2. Parameters of TC, TG and HDL-C(1) TC, TG, HDL-C of normal control group have no significance compared with high-fat diet control group.(2) TC of high-fat diet with the does of 5%, 10% groups significantly increased (P< 0.05) compared with normal control group, but there is no significance about TC, TG and HDL-C.(3) TC of high-fat diet with the does of 20% alcohol significantly increased (P< 0.05) compared with each control group, but there is no significance about TG and HDL-C.(4) TC and TG of high-fat diet with the does of 30%, 40% significantly increased, at the same time HDL-C significantly decreased (P< 0.05) compared with each control group.3. FPG, FINS, HOMA-IR and HOMA-βfunction index (HBCI)(1) FPG: High-fat diet control group have no significance compared with normal control group. High-fat diet with each dose of alcohol groups significantly increased compared with normal control group (P< 0.05). High-fat diet with dose of 20%, 30%, 40% alcohol groups significantly increased compared with high fat control group (P< 0.05). (2) FINS: High-fat diet control group significantly increased compared with normal control group (P< 0.05). High-fat diet with the does of 5%, 10%, 20% alcohol groups significantly increased compared with normal control group (P< 0.05). But high-fat diet with the does of 30%, 40% alcohol groups significantly decreased compared with high-fat diet control group (P< 0.05).(3) HOMA-IR: High-fat diet control group significantly increased compared with normal control group (P< 0.05). High-fat diet with each dose of alcohol groups significantly increased compared with normal control group (P< 0.05).(4) HBCI: High-fat diet control group significantly increased compared with normal control group (P< 0.05). High-fat diet with alcohol groups decreased with the increasing of alcohol compared with high-fat diet control group (P< 0.05). It is obviously at the dose of 30% and 40%.4. The expression of mRNA and protein(1) The expression of IRS-1 mRNA: High-fat diet with each dose of alcohol groups significantly decreased compared with each control group (P< 0.05). It is obviously at the dose of 30% and 40%.(2) The expression of PI-3K(p85α)mRNA: High-fat diet with each dose of alcohol groups significantly decreased compared with each control group (P< 0.05). It is obviously at the dose of 30% and 40%.(3) The expression of GLUT-2 mRNA: High-fat diet control group significantly decreased compared with normal control group (P< 0.05). High-fat diet with each dose of alcohol groups significantly decreased compared with normal control group (P< 0.05). It is obviously at the dose of 30% and 40%.(4) The expression of PI-3K(p85α)protein: High-fat diet with each dose of alcohol groups significantly decreased compared with each control group (P< 0.05). It is obviously at the dose of 30% and 40%.(5) The expression of GLUT-2 protein: High-fat diet control group significantly decreased compared with normal control group (P< 0.05). High-fat diet with each dose of alcohol groups significantly decreased compared with high-fat control group (P< 0.05). It is obviously at the dose of 30% and 40%.Conclusion:This study showed that chronic high fat diet and alcohol intake Increased in body weight. It is obviously in the high fat diet with dose of 40% alcohol group. HCBI in high fat diet with alcohol group increased first and then decreased with alcohol dose increasing compared with normal control group. FPG, FINS and HOMA-IR significantly increased compared with high fat control group (P< 0.05). It decreased the insulin sensitivity and impaired the function ofβcells especially in the the high fat diet with dose of 30%, and 40% alcohol group. At the same time, chronic high fat diet and alcohol intake inhibited the mRNA and protein expression of IRS-1, PI-3K, GLUT-2 in the liver, especially in the the high fat diet with dose of 30%, and 40% alcohol group. It is probably the mechanism of high fat diet with dose of alcohol descreasing insulin sensitivity. Chronic high fat diet and high dose of alcohol intake decreased the insulin sensitivity more seriously.
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