engleski

Metabolic changes in rats fed with raw sunflower.

Aims: A high level of dietary fat intake is believed to be a major factor in the development of obesity and insulin resistance. The type of dietary fat is thought to be important in this regard. The aim of this study was to determine metabolic changes and insulin effects in vivo and in vitro in rats fed for three weeks with raw sunflower containing high levels of polyunsaturated fatty acids (PUFA). Methods: Experiments were carried out on male rats of Wistar strain. Control animals were on standard diet and experimental animals were fed ad libitum with raw sunflower for free weeks. Oral and intravenous glucose tolerance test was performed after 12 hours of fasting and than administrated directly into stomach or intravenously 1 ml/100 g body weight 10% glucose. Liver glucose production was measured during in situ liver perfusion in a 37oC cabinet. Hepatocytes were isolated by a collagenase perfusion technique and cultured for 24 h in M199 serum-free medium. For glucose incorporation in glycogen, the medium was removed and the cells were incubated in the same medium containing 14C-U-glucose to final concentration of 5, 5 mmol/l. To assess amino acid transport hepatocytes were incubated in Hanks-Hepes medium containing ?-amino14C-isobutyric acid (AIB) to the final concentration of 1 mmol/l. Results: Body weight was approximately 13% lower in rats fed the raw sunflower. Oral and intravenous glucose tolerance tests were normal. Glucose production during glucose free perfusion of liver in situ was more than 50 % lower in rats fed with row sunflower. During perfusion of liver with medium containing 5, 5 mmol/l glucose production was still high and 25 minutes after insulin infusion was completely inhibited in rats on standard diet. In rats fed on high fat diet glucose production was very low and there was not any insulin effect on this production. In hepatocytes obtained from rats on standard diet insulin produced more than 100% increase of glucose incorporation in glycogen. In rats on high fat diet basic glucose incorporation was very low and insulin did not change rate of glucose incorporation. In hepatocytes obtained from rats on standard diet insulin produced 80% increase of AIB transport. In hepatocytes obtained from rats on high fat diet basic AIB transport was 20% higher, but insulin effect was strongly reduced. Conclusions: These results clearly demonstrate that altering the macronutrient proportion of the standard diet from high carbohydrate/low fat to low carbohydrate/high PUFA fat causes the development of insulin resistance, without development of obesity. Glucose and glycogen metabolism in liver was inhibited probably by substrate competition.

AIB- transport; dietary fat; glycogen; glucose production; hepatocytes; insulin; liver perfusion;

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