A high fructose diet affects the early steps of insulin action in muscle and liver of rats

A high fructose diet induces insulin resistance in rats, although the exact molecular mechanism involved is unknown. In this study, we used immunoprec ipitation and immunoblotting to examine the levels and phosphorylation stat us of the insulin receptor (IR) and insulin receptor substrate-1 (IRS-1), a s well as the association of the IRS-I with phosphatidylinositol 3-kinase ( PI 3-kinase), and phosphotyrosine phosphatase (SHP2) in the liver and muscl e of rats fed a control or high fructose diet for 28 d. There were no diffe rences in IR and the IRS-I protein levels in the liver and muscle of rats f ed the control and high fructose diets. However, tyrosine-phosphorylation o f the insulin receptor after insulin stimulation was reduced to 71 +/- 2% ( P < 0.05) of control in the liver of the fructose-fed rats. In samples prev iously immunoprecipitated with anti-IRS-l antibody and blotted with antipho sphotyrosine antibody, the insulin-stimulated IRS-1 phosphorylation levels in the liver and muscle of the fructose-fed group were only 70 +/- 6% (P < 0.05) and 76 +/- 5% (P < 0.05) of those of control rats, respectively. The insulin-stimulated IRS-1 association with PI 3-kinase was reduced to 84 +/- 3% (P < 0.05) in the liver and to 84 +/- 4% (P < 0.05) in the muscle of th e fructose-fed group compared with control rats. Insulin-stimulated IRS-1 a ssociation with SHP2 was reduced to 79 +/- 5% (P < 0.05) in liver of the fr uctose-fed rats. These data suggest that changes in the early steps of insu lin signal transduction may have an important role in the insulin resistanc e observed in these rats.