Über die Substrat‐ und Hormoninduktion der Tryptophan‐Oxygenase in der isoliert perfundierten Rattenleber

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Abstract
This paper deals with investigations in isolated perfused rat livers on tryptophan‐oxygenase activity under various experimental conditions. Enzyme‐activity showed a linear rise with rising amounts of tryptophan (0; 125 and 250 mg of tryptophan/kg) in the perfusate. Adrenalectomized and sham‐operated animals have been compared and activity in the adrenalectomized rats were significantly lower in all cases.A significant decrease in the substrate induced increase of tryptophan‐oxygenase‐activity occured 12 h after adrenalectomy. Substrate‐concentration was 250 mg/kg in these experiments.The influence of substrate and cortisol on tryptophan‐oxygenase‐activity has been investigated 7 days after operation. Combined application of both substrate and steroid resulted in no difference to sham‐operated animals when compared to substrate only in the same concentration. On the other hand, in livers from adrenalectomized rats values were significantly higher with combined application than in livers of adrenalectomized animals which received substrate only.The substrate‐dependent rise in tryptophan‐oxygenase‐activity could not be influenced by actinomycin D in contrast to the cortisol effect which was significantly inhibited under these conditions. Both “inducers” were inhibited by cycloheximid.These inhibition‐experiments suggest and confirm two different mechanisms of the substrate‐activation and steroid‐induction of tryptophan‐oxygenase.