Regulation of Insulin-like Growth Factor-I and -II by Glucose in Primary Cultures of Fetal Rat Hepatocytes

Abstract

A selective primary culture of fetal rat hepatocytes was established in our laboratory in order to elucidate the molecular mechanisms of action of different factors and conditions on insulin-like growth factor (IGF)-I and -II gene expression during the perinatal period of the rat. In this model we report that, in a serum-free condition and the presence of non-stimulatory doses of insulin, 5-20 mM glucose evoked an increase of IGF-I and -II mRNA abundance. Glucose regulated in a parallel manner IGF peptide secretion, and an excellent correlation was observed between IGF-I and -II mRNA and IGF-I and -II peptide levels in the conditioned media in response to the carbohydrate. The experiment with 2-deoxyglucose suggests that glucose 6-phosphate, but not its further metabolism, is necessary for the induction of IGF transcript abundance in cultured fetal hepatocytes. Finally, the glucose-induced rise in IGF-II mRNA, the main IGF in fetal stages, was mediated by stimulation of gene transcription and increased transcript stability. The results support the idea that IGFs belong to a family of genes that are positively regulated by glucose.