Pathways of reducing equivalents in hepatocytes from starved, ethanol-induced, and hyperthyroid rats during ethanol and xylitol metabolism (original) (raw)
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The redox-state in relation to ethanol metabolism by rat and guinea pig liver in vitro
Archives of Biochemistry and Biophysics, 1972
Effect of hepatic redox-state on the rate of ethanol metabolism and citric acid cycle activity has been studied in rat and guinea pig liver. Cytoplasmic (NADH)/ (NAD>l ratio in guinea pig liver is about &fold higher than in rat liver. Although, hepatic alcohol dehydrogenase (EC 1.1.1.1) activity is similar in the two species, ethanol metabolism by rat liver in vitro, is about 3 times greater than by guinea pig liver. Addition of ethanol results in a a-fold increase in the hepatic redox-state in the rat but, causes a small increase in the guinea pig. Ethanol-induced increase in hepatic (NADH)/(NAD) ratio, results in a 49-60y0 inhibition of 14COz formation from various radioactive substrates in the rat. However, in guinea pig liver where this ratio is high, W02 formation is already lower by 39-50% than in rat liver and et,hanol addition does not result in a further decrease. The inhibitory effect of ethanol on 'CO2 formation is also observed in rat kidney cortex slices. However, this effect can be abolished by the addition of methylene blue or pyrasole. This study shows that in normal liver cytoplasmic redox-state regulates the rate of ethanol metabolism and that the activity of hepatic alcohol dehydrogenase is not a rate-limiting factor. Furthermore, the inhibitory effect of ethanol on COZ production and therefore on citric acid cycle activity is a consequence of increased (NADH)/(NAD) ratio in liver.
Ethanol metabolism and lipid synthesis by isolated liver cells from fed rats
Biochimica et Biophysica Acta (BBA) - General Subjects, 1976
1. The fatty acid synthesis in isolated liver cells from fed rats was studied with tritiated water as the radioactive precursor. The cells incorporated 3H20 at a rate of 1.26 pmol per min per g packed cells. 2. Addition of ethanol caused a 20% decrease in the incorporation of tritium into fatty acids. The decrease was correlated to the increase in the NAD-redox level. Probably, the decreased tritium incorporation into fatty acids during ethanol metabolism is due to a decrease in the specific activity of the NADPH used for the synthesis of fatty acids, rather than to a real inhibition of the fatty acid synthesis. 3. Ethanol oxidation via NADPH-consuming pathways and ethanol per se at a concentration of 80 mM had no effect upon the incorporation of tritium into fatty acids. 4. Fructose in a concentration of 15 mM inhibited the fatty acid synthesis by 75%, and this inhibition was further augmented by ethanol. 5. The isolated rat liver cells oxidized ethanol at a rate of 2.72, 2.93 and 3.48 pmol per min per g packed cells at 5, 20 and 80 mM ethanol, respectively. Fructose had no effect upon ethanol oxidation neither at low nor at high concentrations of ethanol. 6. Ethanol oxidation via the non alcohol dehydrogenase pathway(s) may involve a transfer of reducing equivalents from mitochondrial NADH to cytosolic NADP รท as judged from measurements of metabolite levels. This conclusion is supported by determinations of '4C yield in glucose from [1-'4C] ethanol, and the results are taken as evidence for the presence of hydrogen shuttle activity during metabolism of ethanol, catalyzed by the NAD-dependent alcohol dehydrogenase. A metabolic scheme is proposed to account for the observed changes at low and high concentrations of ethanol.
The time-course of the effects of ethanol on the redox and phosphorylation states of rat liver
The Biochemical journal, 1972
1. The time-course of the effects of ethanol administration on the metabolite concentrations, redox states and phosphorylation state was studied in the freeze-clamped liver of starved rats. The response was found to vary with the time after ethanol administration. 2. Administration of ethanol caused an immediate decrease in the [NAD(+)]/[NADH] ratio of both cytoplasm and mitochondria, which persisted over the 30min studied. 3. The free cytoplasmic [NADP(+)]/[NADPH] ratio in liver decreases immediately after ethanol administration but returns nearly to control values after 15min. 4. The cytoplasmic [ATP]/[ADP][HPO(4) (2-)] ratio is elevated 15min after ethanol administration in the starved rat. 5. The rapid and large changes in most metabolite concentrations measured appeared to result from the maintenance of near-equilibrium in a wide interlinked network. 6. Differences between fed and starved rats 15min after ethanol administration were slight.
Interaction of cytoplasmic dehydrogenases: Quantitation of pathways of ethanol metabolism
Pharmacology Biochemistry and Behavior, 1983
VIND, C. AND N. GRUNNET. Interaction of cytoplasmic dehydrogenases: Quantitation of pathways of ethanol metabolism. PHARMACOL BIOCHEM BEHAV 18: Suppl. 1, 209-213, 1983.--The interaction between xylitol, alcohol and lactate dehydrogenase has been studied in hepatocytes from rats by applying specifically tritiated substrates. A simple model, describing the metabolic fate of tritium from [2-:~H] xylitol and (IR) [1-'~H]ethanol is presented. The model allows calculation of the specific radioactivity of free, cytosolic NADH, based on transfer of tritium to lactate, glucose and water. From the initial labelling rate of lactate and the specific radioactivity of cytosolic NADH, we have determined the reversible flow through the lactate dehydrogenase catalyzed reaction to 1-5/~mol/min.g wet wt. The results suggest that xylitol, alcohol and lactate dehydrogenase share the same pool of NAD(H) in the cytoplasma. This finding allows estimation of the ethanol oxidation rate by the non-alcohol dehydrogenase pathways from the relative yield of tritium in water and glucose. The calculations are based on a comparison of the fate of the l-pro-R hydrogen of ethanol and the hydrogen bound to carbon 2 of xylitol or carbon 2 of lactate under identical conditions.
Biochemical Pharmacology, 1985
Treatment of rats with 20/zg of 3,3' ,5-triiodo-L-thyronine (T3) per 100 g body wt for a period of 6 days led to a 45% decrease in total liver alcohol dehydrogenase and a 36% decrease in total liver aldehyde dehydrogenase. Most of the latter decrease was directly attributable to a 57% fall in the level of the physiologically-important low Km mitochondrial isoenzyme. The high Km isoenzyme of the postmitochondrial and soluble fractions was much less affected by T3-treatment. T3, at concentrations up to 0.1 mM, did not inhibit the activity of aldehyde dehydrogenase in vitro. Despite these large losses of the two enzymes most intimately involved in ethanol metabolism, the rate of ethanol elimination in vivo was the same in T3-treated and control animals. Moreover, there was no difference between the two groups in the susceptibility of ethanol elimination to inhibition by 4-methylpyrazole, making it unlikely that an alternative route of ethanol metabolism had been significantly induced by treatment with T3. As it had been suggested that T3 might create a "hypermetabolic state" in which constraints normally imposed on alcohol dehydrogenase and aldehyde dehydrogenase are removed, thereby compensating for any loss in total enzymic activity, 2,4-dinitrophenol (0.1 mmoles/kg body wt) was administered to rats in order to raise the general metabolic rate. However, the uncoupler proved to be lethal to T3-treated animals and did not stimulate ethanol elimination in controls. The results do not support the notion that ethanol elimination in vivo is normally governed either by the level of alcohol dehydrogenase or by that of hepatic aldehyde dehydrogenase. However, the mode of control remains unclear.
The Influence of 2,4-Dinitrophenol on Metabolic Changes Caused by Ethanol in the Perfused Rat Liver
Acta Pharmacologica et Toxicologica, 2009
The experiments were undertaken in order to investigate the mechanism by which ethanol inhibits the tricarboxylic acid cycle. Isolated livers were perfused with human erythrocytes suspended in an artificial "plasma". Ethanol was added 45 min. after the start of the perfusions. In some experiments dinitrophenol was added after ethanol. The 0 2 consumption in the perfused rat liver was unaltered by the addition of ethanol to the medium, whereas the COe production fell considerably, resulting in a decrease in the RQ from 0.8 to 0.4. The addition of ethanol caused an increase in both lactatelpyruvate and hydroxybutyrate/ acetoacetate ratios in the perfusion medium. When DNP was added to the perfusion medium, half an hour after the addition of ethanol, both the 0 2 uptake and COe production increased. The RQ increased from 0.4 to 0.6. The lactate/pyruvate ratio was increased by the addition of DNP because the amount of lactate liberated from the liver was increased, while the pyruvate concentration was almost unchanged. The addition of DNP caused a fall in the hydroxybutyratel acetoacetate ratio from 2.2 to 0.6, and a net disappearance of ketone bodies was observed. An opposite change in the extra-and intramitochondrial NADH/NAD ratio was observed, favouring the hypothesis that they are really independent of each other. A correlation between the intramitochondrial NADH/NAD ratio and the tricarboxylic acid cycle inhibition was demonstrated.
Dependence on dose of the acute effects of ethanol on liver metabolism in vivo
Journal of Clinical Investigation, 1975
A B S T R A C T The dose dependence of the acute effects of ethanol upon liver intermediary metabolism in vivo has been demonstrated in rats. Ethanol was given i.p. in doses of 0.69, 1.7, and 3.0 g/kg in equal volumes (20 ml/kg). The liver was freeze-clamped 120 min after injection, and multiple metabolites were measured in the perchloric acid extract of the tissue. Each group showed a significantly different pattern of metabolites, redox states, and phosphorylation potentials although the rate of ethanol disappearance, at least between the two highest dose groups, was not significantly different. The mitochondrial free [NAD+]/[NADH] ratios and the cytoplasmic free [NADP+]/ [NADPH] ratio were paradoxically most reduced with the lowest dose of ethanol and became progressively more oxidized with increasing dose. Once established, the differences in these ratios between the groups tended to persist with time, relatively independent of the concentration of ethanol. In a somewhat different pattern, the phosphorylation potential ([ATP]/[ADP][P.]) remained at the control level in the low-dose group but was significantly elevated in the two higher-dose groups.