Control of fatty acid oxidation by intramitochondrial [NADH]/[NAD+] in developing rat small intestine

The oxidation of palmityl-coenzyme A and acetate to CO2 by mitochondria isolated from rat small intestine increases 10-fold at the time of weaning (18-21 days of age). Carnitine palmitoyltransferase (EC 2.3.1.21) activity is 2-fold greater in mitochondria of suckling rat intestine compared to postweaned intestine. These data indicate that carnitine palmitoyltransferase does not control the increase in intestinal fatty acid oxidation during weaning. We have previously reported that the estimated intramitochondrial [NADH]/[NAD+] as determined by the ratio of tissue levels of 3-hydroxybutyrate and acetoacetate is fivefold greater in suckling rat intestine compared to postwean animals. High intramitochondrial [NADH]/[NAD+] which is present in suckling rat small intestine is associated with a decrease in citric acid cycle activity and beta oxidation. The addition of acetoacetate causes a decrease in intramitochondrial [NADH]/[NAD+]. The oxidation of acetate and glucose to CO2 by suckling rat intestine mitochondria was stimulated by the addition of 1 mM acetoacetate. These data suggest that the lower rate of fatty acid oxidation by suckling rat small intestine is controlled by elevated intramitochondrial [NADH]/[NAD+].