Hepatic Tryptophan Oxygenase Activity as a Marker of Changes in Protein Metabolism during Chronic Ethanol Treatment

Abstract

Rats were given ethanol daily to provide 22, 30 or 38 per cent of the total calories consumed. Sucrose substituted ethanol isocalorically in the respective control groups. The two diets providing the largest amount of ethanol caused a significant reduction of hepatic tryptophan oxygenase, TO, activity, which occurred after 7 days (38 per cent of the calories as ethanol), or after 21 days (30 per cent of the calories as ethanol). The reduction of enzyme activity persisted throughout the remainder of the experimental period. Hepatic triglycerides, plasma lipids, plasma enzymes (alkaline phosphatase, GOT and GPT) and hepatic histology was only slightly or transiently affected during the period of ethanol treatment. The reduction of TO‐activity was accompanied by reduced dexamethasone induction of TO and tyrosine aminotransferase, TAT, during liver perfusion. The incorporation of labelled amino acids into hepatic protein was reduced in perfused livers and also in vivo when TO‐activity was decreased. It was concluded that the activity of tryptophan oxygenase was most probably an indicator of the synthesis of this enzyme and other proteins sensitive to the chronic administration of ethanol.