Role of the mitochondrial metabolism of pyruvate on the regulation of ketogenesis in rat hepatocytes.

In hepatocytes isolated from fed rats the inhibition of lipogenesis (-80%) by 5-tetradecyloxy-2-furoate (an inhibitor of acetylCoA carboxylase) and alpha-cyano-3-hydroxycinnamate (an inhibitor of pyruvate entry into mitochondria) increases the oxidation of 0.35 mM oleate respectively by 70% and 90%. 5-tetradecyloxy-2-furoate increases ketone body production from oleate only by 30% and has no effect on ketogenesis from octanoate, whereas alpha-cyano-3-hydroxycinnamate mimics the effects of fasting on ketone body production: It increases ketogenesis from 0.35 mM oleate by 90%, from 0.78 mM oleate by 25% and from 1.57 mM butyrate by 37%. alpha-cyano-3-hydroxycinnamate also decreases the activity of tricarboxylic acid cycle and the production of malate and citrate. In hepatocytes from fasted rats, alpha-cyano-3-hydroxycinnamate does not modify ketogenesis from oleate, unless cells are incubated with a mixture of lactate and pyruvate. A lactate and pyruvate mixture decreases ketogenesis from oleate and octanoate and increases citrate and malate production without modifying the uptake of fatty acids. This effect is potentiated by 3-mercaptopicolinate, an inhibitor of phosphoenolpyruvate carboxykinase. The results cannot be interpreted only by the effects of malonylCoA on carnitine acyltransferase. They are discussed with respect to the possible involvement of mitochondrial oxaloacetate concentration in the regulation of ketogenesis.