Insulin resistance in uremia: in vitro model in the rat liver using human serum to study mechanisms

We have previously demonstrated in a rat model of chronic uremia that the liver is resistant to insulin. To further investigate the mechanism(s) of insulin resistance in uremia, primary cultures of normal rat hepatocytes were incubated with varying dilutions (1/10 to 1/10,000) of sera from undialyzed end stage uremic and normal humans for 20 hours. We then studied insulin action, binding, and postbinding events. Dilutions of uremic sera as low as 1/1,000 rendered the hepatocytes resistant to maximal concentrations of insulin with regard to [14C]acetate incorporation into lipids. The dose response curve for insulin-stimulated [14C]aminoisobutyric acid uptake demonstrated a shift to the right in hepatocytes incubated with uremic sera when compared with those incubated with normal sera. The 125I-insulin binding sites and affinity, 125I-insulin internalization and degradation, insulin receptor structure, autophosphorylation of the insulin receptor, and its tyrosine-specific kinase activity were normal in the hepatocytes rendered resistant to insulin by uremic sera. However, these cells failed to generate the chemical mediator or second messenger of insulin action, as assessed by its ability to stimulate pyruvate dehydrogenase (PDH) in liver mitochondria from normal rats. We concluded that uremic sera renders normal rat hepatocytes resistant to insulin. Insulin resistance is a postinsulin receptor kinase defect possibly due to lack of the generation of the chemical mediator of insulin action. This in vitro cell model may be useful to further define the mechanism(s) and the serum factor(s) responsible for insulin resistance in uremia in the absence of complicating hormonal and substrate changes that occur in vivo.