The increase in hepatic tyrosine aminotransferase activity following injection of insulin to male Sprague-Dawley rats occurs in greater magnitude and longer duration during aging. Current efforts include examination of the following potential mechanisms: 1. The rate of disappearance of insulin from the blood; 2. Binding of insulin to purified hepatic plasma membranes; and 3. The rates of synthesis and post-translational metabolism. BIBILIOGRAPHIC REFERENCES: Britton, G.W., Rotenberg, S. and Adelman, R.C., Impaired Regulation of Corticosterone Levels during Fasting in Aging Rats, Biochem. Biophys. Res. Commun., 64, 184 (1975). Adelman, R.C., Disruption of Hepatic Enzyme Regulation during Aging. in Enzyme Induction (D.V. Parke, ed.), Plenum Press, 303 (1975).