Ethanol Oxidation in Isolated Hepatocytes
In isolated hepatocytes from fed and starved rats, rates of ethanol oxidation were 1.15 and 0.71 μmol x min−1 x (g wet wt)−1 respectively and were unchanged over the ethanol concentration range 8-96mM. The addition of the competitive inhibitors of alcohol dehydrogenase (ADH), pyrazole and particularly 4-methyl pyrazole (4-MP) abolished the oxidation of 8 mM ethanol and subsequently inhibited oxidation of 96 mM ethanol.
In hepatocytes isolated from rats treated with ethanol, phenobarbitone or 3-amino-triazole, rates of ethanol oxidation were the same at ethanol concentrations of 8 and 96mM and the rates were similar to, and never exceeded the rate found in hepatocytes from normal fed rats. Pyrazole inhibited ethanol oxidation to the same extent in all preparations; 4-methyl pyrazole did likewise, but was more inhibitory than pyrazole.
Pyruvate greatly stimulated cellular ethanol oxidation irrespective of the prior treatment of the donor animal. This stimulation together with the excess accumulation of lactate was totally abolished by 4-methyl pyrazole.
Methylene blue, phenazine methosulphate and menadione stimulated both ethanol oxidation and respiration irrespective of prior treatment of the donor animal, but again the enhancement of ethanol oxidation and respiration was totally abolished by 4-methyl pyrazole. It is probable that these agents, like pyruvate, act by stimulating the oxidation of NADH generated in the cytoplasm by the alcohol dehydrogenase catalysed conversion of ethanol to acetaldehyde.
These results indicate that under a wide variety of experimental conditions the contribution of the postulated microsomal ethanol oxidising system (MEOS) in isolated intact liver cells appears minimal. Thus they cast considerable doubt on its physiological role in vivo.
KeywordsMethylene Blue Ethanol Oxidation Donor Animal Isolate Liver Cell Artificial Electron Acceptor
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