Evidence that the flux control coefficient of the respiratory chain is high during gluconeogenesis from lactate in hepatocytes from starved rats. Implications for the hormonal control of gluconeogenesis and action of hypoglycaemic agents

Abstract

1. Increasing concentrations of 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU), a mild respiratory-chain inhibitor [Halestrap (1987) Biochim. Biophys. Acta 927, 280-290], caused progressive inhibition of glucose production from lactate + pyruvate by hepatocytes from starved rats incubated in the presence or absence of oleate and gluconeogenic hormones. 2. No significant changes in tissue ATP content were observed, but there were concomitant decreases in ketone-body output and cytochrome c reduction and increases in NADH fluorescence and the ratios of [lactate]/[pyruvate] and [beta-hydroxybutyrate]/[acetoacetate]. 3. The inhibition by DCMU of palmitoylcarnitine oxidation by isolated liver mitochondria was used to calculate a flux control coefficient of the respiratory chain towards gluconeogenesis. In the presence of 1 mM-oleate, the calculated values were 0.61, 0.39 and 0.25 in the absence of hormone and in the presence of glucagon or phenylephrine respectively, consistent with activation of the respiratory chain in situ as previously suggested [Quinlan & Halestrap (1986) Biochem. J. 236, 789-800]. 4. Cytoplasmic oxaloacetate concentrations were shown to decrease under these conditions, implying inhibition of pyruvate carboxylase. 5. Inhibition of gluconeogenesis from fructose and dihydroxyacetone was also observed with DCMU and was accompanied by an increased output of lactate + pyruvate, suggesting that activation of pyruvate kinase was occurring. With the latter substrate, measurements of tissue ADP and ATP contents showed that DCMU caused a small fall in [ATP]/[ADP] ratio. 6. Two inhibitors of fatty acid oxidation, pent-4-enoate and 2-tetradecylglycidate, were shown to abolish and to decrease respectively the effects of hormones, but not valinomycin, on gluconeogenesis from lactate + pyruvate, without changing tissue ATP content. 7. It is concluded that the hormonal increase in mitochondrial matrix volume stimulates fatty acid oxidation and respiratory-chain activity, allowing stimulation of pyruvate carboxylation and thus gluconeogenesis to occur without major changes in [ATP]/[ADP] or [NADH]/[NAD+] ratios. 8. The high flux control coefficient of the respiratory chain towards gluconeogenesis may account for the hypoglycaemic effect of mild respiratory-chain inhibitors.

Fructose Induces Gluconeogenesis and Lipogenesis Through a Sirt1-Dependent Mechanism

“…This is in agreement with previous studies reporting inhibition of fructose-mediated induction of electron transport chain activity and gluconeogenesis (Pryor et al 1987). However, the mechanisms responsible for fructose-mediated activation of the electron transport chain are unclear.…”

“…Fructose-induced gluconeogenesis can be suppressed by inhibition of the electron transport chain. This may be due to a decrease in NAD C / NADH ratio that occurs in parallel (Pryor et al 1987), but the role of SIRT1 in the hepatic response to fructose has yet to be examined.…”

Glucagon: acute actions on hepatic metabolism

“…Gluconeogenic flux is tightly coupled with the rate of respiration and ATP production [35]; glucagon increases mitochondrial oxygen consumption, consistent with the notion that an increase in energy production is required for glucagon's stimulation of gluconeogenesis [36][37][38]. One of the ways in which glucagon stimulates mitochondrial respiration is through increased intracellular and mitochondrial calcium levels [39][40][41].…”

The malonyl-CoA–long-chain acyl-CoA axis in the maintenance of mammalian cell function

“…Fatty acid oxidation provides ATP and reducing equivalents required for gluconeogenesis. β-Oxidation also produces intramitochondrial acetyl-CoA, which is essential for activation of pyruvate carboxylase [143], a key regulatory enzyme of gluconeogenesis [144]. There are many studies which confirm the important role that increased fatty acid mobilization from adipose tissue is linked to increased gluconeogenesis [145], e.g.…”