A PARADOXICAL EFFECT OF ACTINOMYCIN D: THE MECHANISM OF REGULATION OF ENZYME SYNTHESIS BY HYDROCORTISONE

Abstract
The mechanism of hydrocortisone-induced tryptophan pyrrolase and tryosine transaminase synthesis in the liver of adrenalectomized rats was studied. Actinomycin D did not inhibit synthesis of the basal enzymes, but inhibited the induction of these enzymes when injected at early times after hormone administration. Actinomycin D and 5-fluorouracil stimulated tryptophan pyrrolase and tyrosine transaminase synthesis when injected 5 hr. or later after the hormone. It is proposed that repression of the synthesis of these enzymes occurs at the level of messenger ribonucleic acid (RNA) translation.