Plasma concentrations of insulin and free fatty acids in dietary-induced obesity of Wistar-rats before and after glucose stimulation.

Colony-bred Wistar-rats develop obesity after long term feeding with a high-fat diet (50% fat, w/w). According to previous investigations a disturbed glucose tolerance after i.v. glucose load could be described for obese rats. Therefore, we measured peripheral IRI-concentrations before and after glucose stimulation in controls and fat-fed rats. In obese animals we observed a basal hyperinsulinemia in the dynamic phase of development of obesity. In controls and fatty rats, no differences in the peripheral insulin response to an i.v. glucose stimulation could be demonstrated, nor did we find indications of an impaired early insulin response in fatty rats. In accordance with the glucose tolerance study, obese rats in the dynamic phase showed lower FFA-levels (fasting state) and a slower decrease of FFA-concentrations after the glucose-induced insulin enhancement. Changing the feeding schedule at 20 weeks of age, e.g. feeding control diets to fatty rats for 4 weeks, reduced basal IRI-concentrations in these animals to control values. Assuming the secondary nature of the basal hyperinsulinemia in obese rats, our present results demonstrate that the observed impairment of glucose tolerance may be related to the peripheral insulin resistance of skeletal muscle and/or hypertrophied adipose tissue.