Characterization of insulin receptors in liver membranes and isolated hepatocytes during rat ontogenic development

The studies described in this paper were undertaken to characterize the hepatic insulin receptors in liver membranes and isolated hepatocytes, during rat ontogenic development. In liver membranes insulin binding was found to be the same in fetal and greater in suckling rats as compared with adult animals. Modifications of insulin binding reflect changes in the number of receptors, but not in the affinity constants. Time courses of insulin association and dissociation from liver membranes were unaffected by development. Degradation of insulin by liver membranes was significantly lower in fetal than in adult rats, but this does not seem to be responsible for the differences observed in binding. No significant differences in the degradation of insulin receptors between different groups of liver membranes were found. Similar results were obtained with isolated hepatocytes except for a reduced number of insulin receptors in fetal cells. This could be explained by the smaller cell surface of younger cells, since when the results were expressed by micron 2, insulin binding was almost the same in fetal and adult rats. These findings suggest that the early hepatic development of insulin receptors may play a significant role in the metabolic growth processes of the fetus and in the availability of nutrients after birth.