Abstract. The time course for changes in food intake, body weight, plasma glucose and insulin concentrations and HOMA index was monitored over a period of 8 weeks in rats exposed from the 8th week after birth to diets containing either starch or fructose and sunflower oil. In two further groups of rats exposed to the fructose-rich diet part of the sunflower oil was substituted by either salmon oil rich in long-chain polyunsaturated ω3 fatty acids or safflower oil rich in long-chain polyunsaturated ω6 fatty acids. Despite lower food intake, the gain in body weight was higher in fructose-fed rats than in starch-fed rats. The supplementation of the fructose-rich diet by either ω3 or ω6 fatty acids lowered both food intake and body weight gain. The measurements of plasma glucose and insulin concentrations, HOMA index and insulinogenic index performed after overnight starvation were in fair agreement with those recorded at the occasion of an intraperitoneal glucose tolerance test, with higher values for plasma glucose concentration and HOMA index in the fructose-fed rats exposed to the sunflower oil (with or without enrichment with ω6 fatty acids) than in the starch-fed rats exposed to the sunflower oil or fructose-fed rats exposed to a diet enriched with ω3 fatty acids. Such was also the case for the measurements of glycated albumin at sacrifice. Moreover, the insulinogenic index was lower in the fructose-fed rats with or without dietary enrichment in ω6 fatty acids than in the fructose-fed rats with dietary enrichment in ω3 fatty acids. The elucidation of the biochemical determinants of the later difference requires further investigations in isolated pancreatic islets. IntroductionIn the first report in this series, attention was drawn to the plasma D-glucose and insulin concentration, insulinogenic index and HOMA index for insulin resistance found during an intraperitoneal glucose tolerance test conducted in rats first exposed for 50 days to either a control diet containing 64% (w/w) starch and 5% (w/w) sunflower diet, or a diet in which starch was substituted by an equal amount of D-glucose (1). Two further groups of rats were exposed to the latter fructosecontaining diet, but with 1.6% (w/w) of sunflower diet being substituted by an equal amount of either salmon oil rich in polyunsaturated ω3 fatty acids or C18:2ω6-rich safflower oil. The present report deals mainly with the time course of changes in food intake, body weight, plasma D-glucose and insulin concentrations, as well as insulinogenic and HOMA indices recorded over an 8-week period of exposure to these four diets. Further variables, including the weight of parametrial and visceral adipose tissue, liver, kidney, heart and soleus muscle, glycated hemoglobin and plasma albumin and D-glucose concentrations were also measured at sacrifice after overnight starvation. Materials and methodsThe experimental design, the food composition, the methods for measuring plasma D-glucose and insulin concentrations and the procedure for statistical analysis were already ...
Abstract. The present series of experiments aim mainly at investigating the possible influence of changes in the com position of dietary lipids (sunflower oil, salmon oil, safflower oil) upon the metabolic syndrome found in rats exposed to a fructose-rich diet. For purpose of comparison, a control group of rats received the sunflower oil diet with substitution of fructose by starch. An intraperitoneal glucose tolerance test, performed after overnight starvation fifty days after the start of the experiments at the 6th week after birth, indicated, as expected, impaired tolerance to glucose and deterioration of insulin sensitivity (HOMA index), without changes in the insulinogenic index, when comparing the fructose-fed rats to the starch-fed rats both exposed to the sunflower oil diet. In the fructose-fed rats, enrichment of the diet by long-chain polyunsaturated ω3 fatty acids supplied by salmon oil, a modest improvement of insulin sensitivity was opposed, in term of glucose homeostasis, by a decreased secretory response to glucose of insulin-producing cells. Last, in the fructose-fed rats, the partial substitution of sunflower oil by safflower oil rich in long-chain polyunsaturated ω6 fatty acids further deteriorated glucose homeostasis, with a higher mean HOMA index and a severe decrease of the insulinogenic index. These findings justify further investigations on such items as the time course for changes in metabolic and hormonal variables and both the metabolic and secretory responses of isolated pancreatic islets to selected nutrient secretagogues. IntroductionA metabolic syndrome with insulin resistance, hyperinsulinemia and hypertension is known to prevail in rats exposed to a high dietary supply of D-fructose (1). Attention was recently drawn to both the comparison between rats exposed to either a fructose-enriched diet or fructose-enriched drinking water, as well as the reversibility of the fructose-induced metabolic perturbations (2).Rats deprived of a dietary supply of long-chain polyunsaturated ω3 fatty acids also develop a metabolic syndrome with liver steatosis, visceral obesity, insulin resistance, hypertension and resulting cardiac hypertrophy (3-8).The present experiments aim mainly at exploring the effects of long-chain polyunsaturated ω3 and ω6 fatty acids in rats exposed from the 8th week after birth and for the ensuing 8 weeks to a fructose-enriched diet. More precisely, a first comparison deals with rats fed a sunflower oil diet and given access to either a control diet or a fructose-enriched diet obtained by substitution of starch by D-fructose. In this first comparison, the two diets contained 5.0% (w/w) sunflower oil, containing <0.1% of its total fatty acid content as long-chain polyunsaturated ω3 fatty acids. In the second set of com parisons, the just-mentioned rats exposed to the fructose-rich and sunflower oil-containing diet served as the control fructose-fed rats. In another group of rats, part of the sunflower oil (1.6%, w/w) in the fructose-rich diet was replaced by an equal amount...
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