Hormonal and metabolic regulation of hepatic ketogenesis will be studied utilizing isolated rat hepatocytes. The primary objective is to define more precisely the quantitative antiketogenic action of insulin and the ketogenic action of glucagon in the liver. Experiments will be performed in an attempt to define conditions in which the influences of these hormones on hepatic ketogenesis can be optimally manifested. A fundamental postulate in this work is that the relative caloric balance in the rat influences the ketogenic resonse of the liver to hormones. To investigate this possibility, we propose to study the influence of controlled caloric infusion on metabolic homeostasis in the rat, a concept we have termed "caloric clamping." Variable levels of calories in the form of glucose, amino acids, or fat, will be administered by constant intragastric infusion into conscious, freely moving rats. In initial studies concentrations of various key metabolites in blood (ketone, glucose, free fatty acids, and triglycerides) and liver (glycogen and triglycerides), as well as the plasma levels of the hormones, insulin and glucagon, will be measured. From these initial studies, it is envisioned that we will be able to define more precisely the conditions of caloric infusion which should result in optimal responsiveness of ketogenesis in isolated hepatocytes to insulin and glucagon.