Effect of ethanol, noradrenaline and 3′,5′-cyclic AMP on oxidation of fatty acids and lipolysis in isolated rat hepatocytes

Abstract

Improved methods for the determination of the rate of fatty acid oxidation and lipolysis are presented and evaluated. Hepatocytes from fed rats were incubated with 1.3 mM palmitate. The rate of oxidation of exogenous fatty acids was determined with [1- 14C]palmitate. The rate of oxidation of endogenous fatty acids was determined either as the difference between total fatty acid oxidation and oxidation of exogenous fatty acids, or as the oxidatin of intrecellular lipids, prelabelled with 14C. The two methods agreed completely, indicating that the only endogenous source of acetylCoA was fatty acids. The rate of oxidation of exogenous and endogenous fatty acids was estimated to be 858 and 284 nmol C2-units/min 10 8 cells, respectively, and the rate of lipolysis to be 1640 nmol C2-units/min 10 8 cells. Ethanol caused a 17% and 70% inhibition of the oxidation of exogenous and endogenous fatty acids, respectively. Lipolysis was inhibited ≈ 10% by ethanol. Noradrenaline was without effect on the oxidation of exogenous and endogenous fatty acids and on lipolysis. 3′,5′-Cyclic AMP enhanced the oxidation of exogenous and endogenous fatty acids by 25% and 31%, respectively, and the rate of lipolysis by 38%, suggesting the presence in hepatocytes of a cAMP sensitive lipase.