Effects of Actinomycin D on ACTH-Induced Corticosteroidogenesis1

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Abstract
Actinomycin D was found to abolish completely fee in vitro steroidogenic effect of ACTH during incubations of cow adrenal slices. The antibiotic had no effect on base line (control) corticosteroid production or on fee enhanced production of corticosteroids due to addition of glucose-6-PO4 plus TPN. The inhibitory effects of actinomycin D were reversible and were evident only if fee antibiotic was present during fee prein-cubation and incubation wife ACTH. In contrast to fee results obtained wife bovine adrenal tissue slices, actinomycin D had little or no effect on ACTH-induced corticosteroid production during incubations of rat adrenal quarters, despite inhibition of precursor incorporation into RNA. The latter, however, was not complete, and, while a role for RNA synthesis was not apparent in fee rat adrenal, it could not be fully excluded. The incorporation of orotic acid-6-C14 into cow adrenal (but not rat adrenal) RNA was enhanced by ACTH, and a linear relationship between orotic acid incorporation and fee log of fee ACTH concentration was observed. Actinomycin D inhibited orotic acid incorporation and obliterated fee differences between control and ACTH-stimulated tissues.