The metabolic syndrome of fructose-fed rats: effects of long-chain polyunsaturated ω3 and ω6 fatty acids. II. Time course of changes in food intake, body weight, plasma glucose and insulin concentrations and insulin resistance.

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.

The metabolic syndrome of fructose-fed rats: effects of long-chain polyunsaturated ω3 and ω6 fatty acids. I. Intraperitoneal glucose tolerance test.

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.