Changes in [14C]glycine-incorporating activities of rat-adrenal microsomes and soluble cell fraction during prolonged adrenocorticotropin administration

• 1.

  1. During the first several days of ACTH administration the activities of the 105 000 × g supernatant and microsomes for supporting incorporation of [¹⁴C]glycine in vitro into rat adrenal protein are increased. Concomitantly, there are progressive increases in adrenal weight, protein content and RNA content, with little or no change in DNA content.

• 2.

  2. Over the next several days of ACTH administration a period of DNA replication occurs accompanied by the following changes: (a) a decrease in total adrenal-RNA content; (b) a decrease in microsomal-RNA concentration; (c) an interruption of the effect of ACTH on adrenal weight and net protein synthesis; and (d) a decrease in activities of the 105 × 000 g supernatant and microsomes for supporting [¹⁴C]glycine incorporation. These inhibitory changes are subsequently reversed with further ACTH administration and completion of the DNA-replication period.

• 3.

  3. It is suggested that the soluble (? transfer enzyme) and microsomal (increased ribosomal and messenger RNA) factors responsible for the effects of ACTH on adrenal protein synthesis are metabolically unstable, and that the induction of these factors by ACTH is mediated through (or requires) DNA-directed RNA synthesis.