Intracellular redox state and control of gluconeogenesis in perfused chicken liver.

Abstract

The role of the cellular redox state in the control of gluconeogenesis was studied in hemoglobin-free perfused chicken liver, by fluorimetric measurement of the redox states of intracellular pyridine nucleotides. The aminotransferase inhibitor, aminooxyacetate, completely inhibited gluconeogenesis from lactate in the perfused rat liver and to a small extent in the perfused chicken liver. In chicken liver, the highest rate of glucose production was seen with lactate, followed by fructose, pyruvate, and glycerol. When compared at 5 mM, the rate of glucose production from pyruvate was only 10% of that from lactate. Glucose production from a pyruvate/lactate mixture decreased with increasing proportions of pyruvate, together with redox changes of pyridine nucleotides to a more oxidized state. Increased reduction of pyridine nucleotides upon infusion of ethanol was associated with an increased glucose production from pyruvate, and the increase was abolished during octanoate infusion. This abolishment was accompanied by an increase in the acetoacetate to beta-hydroxybutyrate ratio with an oxidation of pyridine nucleotides. The octanoate-inhibited gluconeogenesis occurred at the higher lactate concentration (10 mM) with a transient oxidation of pyridine nucleotides. No significant inhibition was observed at 1 mM lactate, although an instant reduction of pyridine nucleotides was taking place. The rate of beta-hydroxybutyrate generation during octanoate infusion was 2.2 times higher at 1 mM than at 10 mM lactate. The inhibitory effect of octanoate on glyconeogenesis was completely relieved by the addition of NH4Cl. The results demonstrate that the regeneration of NADH in the cytosol is limited in chicken liver, and that gluconeogenesis is regulated, in part, by alteration in the redox states of mitochondria and cytosol.