The effect of w-6 polyunsaturated fat and vitamin E intakes on insulin resistance in 90% pancreatectomized rats / 대한내과학회지

ABSTRACT

High intake of omega-6 polyunsaturated fat (PUFA) can increase oxidative stress, which may in turn increase insulin resistance and be the cause of metabolic syndrome X (diabetes mellitus). One of the ways to reduce oxidative stress is through the consumption of antioxidants, such as vitamin E. However, it is controversial whether the consumption of vitamin E alleviates insulin resistance. The purpose of this study was to determine whether the excessive intake of omega-6 polyunsaturated fat and vitamin E influences the whole body glucose disposal rate (GDR), glycogen deposits in the liver and muscles, and the triglyceride content of muscles in 90% pancreatectomized rats. METHODS: Mildly diabetic rats were produced by removing 90% of the pancreas from Sprague Dawley rats aged 8 weeks. One week after surgery, the blood glucose levels of rats were more than 9.4 mmol/L, according to which the rats are considered to be diabetic. Two factors were examined in the 90% pancreatectomized rats polyunsaturated fat levels with 40% and 10% of total energy intakes, and vitamin E contents with 300 IU and 30 IU per kg of diet mixture. Four different diets were given for 8 weeks. After 7 weeks of diet consumption indwelling catheters were inserted in the carotid artery and jugular vein of all rats so that the GDR could be measured while the rats were awake and in a relaxed state. RESULTS: Daily calorie and PUFA fat intake levels were higher in the high PUFA groups of diabetic rats. Daily vitamin E intake of the high vitamin E groups was ten times higher than that of the low vitamin E groups (p<0.0001). The GDR was lower in high PUFA groups, and the high intake of vitamin E tended to decrease the GDR in diabetic rats. The GDR of DHPHE was significantly lower than that of DLPLE (p<0.05). Sham operated rats (the control group) had a higher GDR by 44% than diabetic rats. Vitamin E deposits in the liver in DHPHE were higher in DLPLE (p<0.05). Glycogen deposits in the liver of diabetic rats were significantly higher in DLPLE than DHPLE. Muscle glycogen content showed a similar tendency to liver glycogen content in different diet groups of diabetic rats. Triglyceride deposits in muscles did not differ according to dietary fat and vitamin E contents in diabetic rats. CONCLUSIONS: High intake of omega-6 PUFA increased insulin resistance, and high vitamin E intake did not alleviate insulin resistance. Thus, increased oxidative stress may be an independent factor for increased insulin resistance in high intake of omega-6 PUFA. It is necessary to consume a minimum amount of omega-6 PUFA as well as the Recommended Daily Allowance of vitamin E.