The acute effects of ethanol on liver and brain tryptophan metabolism

1. The effects of acute ethanol administration of liver and brain tryptophan metabolism are reviewed. 2. Ethanol enhances the activity of rat liver tryptophan pyrrolase by increasing the availability of circulating free tryptophan to the liver by catecholamine-mediated lipolysis followed by displacement of protein-bound serum tryptophan. 3. The response of the mouse liver enzyme to ethanol is strain-dependent. Ethanol activates the enzyme in CBA/CA but not in C57/BL mice. 4. Ethanol exerts a biphasic effect on the concentrations of rat brain tryptophan, 5-hydroxytryptamine and 5-hydroxyindol-3-ylacetic acid. 5. Both aspects of this biphasic effect are associated with an altered availability of circulating free tryptophan. 6. The initial enhancement by ethanol of brain tryptophan metabolism may be due to the above-mentioned lipolytic mechanism, whereas the subsequent decrease in brain indoles may be caused by the enhanced tryptophan pyrrolase activity. 7. Brain tryptophan metabolism is decreased by ethanol in CBA/CA whereas no change is observed in that in C57/BL mice. 8. These results are discussed in relation to previous work on the acute effects of ethanol on rat and mouse brain 5-hydroxytryptamine metabolism.