Changes in Adrenal Polysomes Following ACTH Administration1

The changes in rat adrenal ribosomes induced by ACTH have been further characterized in the present investigation by centrifugal analyses of ribosomal particles. Following ACTH administration the increase in adrenal ribosomes has been found to be due to increases in the number of both single ribosomes and polysomes (or ribosome clusters), and the percentage increase in polysomes is apparently greater than that of the total ribosomes. The increase in polysomes would by definition indicate that there is an increased availability of messenger RNA and/or an increased ability of ribosomes to combine with messenger RNA following ACTH administration. Since control ribosomes can combine with and utilize exogenous messenger RNA (polyU) as well as ribosomes from ACTH-stimulated adrenals, it would appear that the changes in adrenal polysomes following ACTH are directly correlated with changes in availability of messenger RNA. The present findings also suggest that the increase in amino acid-incorporating activity of adrenal microsomes and ribosomes following ACTH administration is due primarily to the increase in adrenal polysomes since: 1) only the polysomes have demonstrable activity in the cell-free, amino acid-incorporating system; and 2) the increase in polysomes can reasonably account for the increase in the amino acid-incorporating activity of the microsomal and ribosomal fractions. (Endocrinology77: 128, 1965)