Abstract
The role of the reticuloendothelial system in the control of hormonal enzyme induction in liver was studied in relationship to endotoxicosis in rats. The effect of endotoxin and thorotrast, singly and in combination with hydrocortisone, on tryptophan oxygenase and tyrosine transaminase was determined in intact rats and in the isolated, perfused rat liver. Endotoxin and thorotrast both lowered tryptophanoxygenase activity, and prevented hydrocortisone induction of this enzyme, in the isolated, perfused rat liver. In contrast to their inhibitory effect on tryptophan oxygenase, endotoxin and thorotrast neither lowered tyrosine-transaminase activity in the perfused rat liver, nor altered the hydrocortisone induction of this enzyme. These effects are compatible with resume obtained after administration in vivo of these agents to intact rats. Partial purification of tryptophan oxygenase from livers of rats injected with either endotoxin or thorotrast indicated the presence of some inhibitory substance. Since histological studies revealed that thorotrast is localized in Kupffer cells, it is suggested that the reticuloendothelial system contributes to the control of enzyme induction in rat liver. In view of these and other findings it is now necessary to consider the role of the reticuloendothelial system, in addition to its phagocytic activity, at the metabolic level in an animal's response to stress.
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