Nakai T, Kutsumi Y, Sakamoto Y, Oida K, Miyabo S, Takeda R
Tohoku J Exp Med. 1984 Nov;144(3):245-56. doi: 10.1620/tjem.144.245.
The purpose of the present study was to investigate the mechanisms of the long-term effects of insulin on protein synthesis in rat liver parenchymal cells. Three kinds of soluble and stable insulin-dextran complexes (I: Mr 150,000; II: Mr 450,000; III: Mr 2,000,000) were prepared. The effects of insulin or insulin-dextran complexes on protein synthesis were evaluated in the primary monolayer culture of adult rat liver. To avoid the effects of serum factors, the primary monolayer culture of adult rat liver in serum free medium was established. The cultured hepatocytes well maintained the metabolic and morphological characteristics of the adult rat liver. The incorporation of [14C]-leucine into trichloroacetic acid insoluble proteins and immunoprecipitates by anti-rat albumin serum were measured in cultured hepatocytes prepared either from the control or streptozotocin-induced rats. An addition of insulin-dextran complexes to the culture medium of the hepatocytes from diabetic rats stimulated the protein synthesis as well as the native insulin. The maximal effect of insulin-dextran complex (I) on protein synthesis was comparable to native insulin. However, insulin-dextran complex (II) caused a 67% stimulation of native insulin. Insulin-dextran complexes (III) induced only a slight increase of protein synthesis. Furthermore, an addition of insulin-dextran complexes into the medium caused a more tight cellular attachment to the dish and more extensive spreading. These results favor the view that the stimulation by insulin of protein synthesis in rat hepatocytes does not require the entry of insulin into cells.
