Hormonal control of specific gene expression in the rat liver during the suckling-weaning transition

In the rat, the suckling-weaning transition is accompanied by marked changes in nutrition. During the suckling period, the pups are fed with milk which is a high-fat low-carbohydrate diet. At weaning, milk is progressively replaced by the rat chow which is a high-carbohydrate low-fat diet. This is accompanied by considerable hormonal modifications: an increase in plasma insulin and a decrease in plasma glucagon concentrations, as well as by marked changes in metabolic pathways in liver: decrease in hepatic gluconeogenesis, increase in lipogenesis, and appearance of liver glucokinase. Most of the data concerning these changes are related to maximal activity of enzymes. The recent availability of specific cDNA probes for phosphoenolpyruvate carboxykinase, acetyl-CoA carboxylase, fatty acid synthase and glucokinase has allowed study of the role of pancreatic hormones and of nutrition in the changes of the expression of these genes at weaning in the rat.