EFFECTS OF ALIPHATIC ALCOHOLS AND FATTY ACIDS ON THE METABOLISM OF ACETATE BY RAT LIVER SLICES

[Hepatic lipids of intact or thyroidectomized rats after administration of tetracycline or ethanol]

The purpose of this work was to study the quantitative modifications of the hepatic lipids in adult thyroidectomized rats after administration of tetracycline or ethanol (acute dose or prolonged ingestion). 1. - Thyroidectomy did not inhibit the accumulation of fat in the liver of fed euthyroid or hypothyroid rats after intraperitoneal infusion of tetracycline (320 mg/body weight in 2 injections at an interval of 16 h, the diet containing 6% of lipids). 2. - Sixteen hours after the oral administration of a single large dose of ethanol (5 g/kg body weight), there were only found some small modifications of the lipid composition of the liver in fasting euthyroid or thyroidectomized rats, receiving a diet with 6% of lipids before the experiment; on the contrary, when the diet contained 19% of lipids, a fatty liver occurred in the intact rat, but not in the thyroidectomized rat. 3. - The prolonged ethanol intake (in a 20% solution in water) for 5 months with a diet containing 19% of lipids did not induce a fatty liver in intact rats but produced a decrease of hepatic non-phosphorus lipid and an increase of the cholesterol amounts. After the administration of L-thyroxin (10 mug/100 g body weight per day) to these alcoholic thyroidectomized rats during 2 weeks, it was found an increase of the hepatic non phosphorus lipids till an higher amount than in the euthyroid rats. 4. - The hepatic phospholipid amounts were relatively constant in the different experiments. These results accounting for this differential effects were discussed.

Metabolic correlates of ethanol, acetaldehyde, acetate and methanol in humans and animals

Following the administration of alcoholic beverages, ethanol exerts a number of direct and indirect effects on the body and in turn, ethanol is itself metabolized. Liver and brain are twomajor organs which are immediately concerned with the effects of ethanol. Ethanol acts as CNS depressant and as a source of energy. Since the metabolism of ethain the liver proceeds at a constant rate until completion,acetate is produced regardless of energy requirements of the body. Thus, ethanol plays the role of an aberrant nutrient. Although ethanol has no effect on oxygen consumption in the liver, it severely suppresses the productionof carbon dioxide in the Krebs cycle resulting in the corresponding suppressionof respiratory quotient. This indicates that ethanol diverts the utilizationof oxygen for the oxidationof reducing, equivalents which accumulate as a consequence of increased formation of NADH. This is reflected in the shift from the oxidative to reductive components of a number of oxido-reductive couples, e.g.: pyruvate-lactate, oxaloacetate-malate and acetoacetate-beta-hydroxybutyrate. These actions of ethanol are exarcerbated by the fact that the metabolism of ethanol is also associated with the diversion of the availability of a number of enzymes and coenzymes from the metabolism of endogenous substrates towards the metabolism of metabolites of ethanol, thus resulting in the competitive inhibitionof a number of enzyme catalyzed reactions, e.g., inhibition of methanol metabolism during long-term consumption resulting in the acumulation of methanol in body fluids; shift in the peripheral metabolism of biogenic amines from oxidative to reductive pathways; and formation of aberrant neurotransmitters (in vitro); inhibition of the oxidation of fatty acids in the liver...

Rate-limiting steps in ethanol metabolism and approaches to changing these rates biochemically

Ethanol is oxidized to acetate primarily by a system involving liver alcohol and aldehyde dehydrogenases coupled with reoxidation of NADH by the mitochondria. All of these steps are at least partially rate-limiting in ethanol metabolism, with alcohol dehydrogenase and oxidative phosphorylation probably slower than the others. More research is required to assess the quantitative roles of various steps. Many agents are ineffective in changing the rate of metabolism of ethanol, but fructose and dinitrophenol may increase the rate by up to 1.5-fold in vivo. The failure of single agents to increase the rate substantially may indicate that when one step is accelerated, another step becomes rate-limited. Therefore, combinations of agents that affect several steps simultaneously may be required for acceleration. Effective experimental methods for inhibiting alcohol dehydrogenase in vivo are available.

EFFECTS OF ALIPHATIC ALCOHOLS ON THE METABOLISM OF GLUCOSE AND FRUCTOSE IN RAT LIVER SLICES

Ethanol, at concentrations up to 3 mM, whilst having little inhibitory effect on the production of respiratory CO2of rat liver slices, has a marked suppressing action on the formation of labelled CO2from labelled glucose. The suppression of C14O2formation by ethanol from radioactive glucose is independent of the concentration of the latter and amounts to 57% with 3 mM ethanol after 1 hour's incubation. The results are consistent with the conclusion that ethanol gives rise more rapidly than glucose to acetyl CoA and that the large suppressing action of ethanol in rat liver slices is due to isotopic dilution of labelled acetyl CoA derived from the labelled sugars with the unlabelled acetyl CoA derived from ethanol. Ethanol exercises a larger inhibition of the rate of C14O2formation from glucose-6-C14than from glucose-1-C14. The difference between the effects of ethanol on C14O2formation from glucose-1-C14and glucose-6-C14is presumably due to operation of the hexosemonophosphate shunt.The higher aliphatic alcohols have about the same diminishing effect on C14O2formation from glucose-U-C14and fructose-U-C14as does ethanol. This observation may also be a consequence of dilution of labelled acetyl CoA derived from the sugars by unlabelled acetyl CoA coming from the added alcohol. Incorporation of radioactive carbon from the labelled sugars into liver proteins and lipids is inhibited by ethanol and higher aliphatic alcohols, and the inhibitions are similar in magnitude to those of C14O2formation. These may be accounted for by isotopic dilution. The amounts of C14incorporated into lipids and proteins from radioactive glucose and fructose are small, being about 1/10th of that appearing in the CO2.The higher aliphatic alcohols suppress total CO2formation during rat liver slice respiration much more than does ethanol at equivalent concentrations.