INACTIVATION OF ACTH BY ISOLATED RAT ADRENALS AND INHIBITION OF CORTICOID FORMATION BY ADRENOCORTICAL HORMONES1

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Abstract
The response by isolated rat adrenals to ACTH is dependent upon the amount of ACTH added per unit weight of tissue and is independent of the concentration of ACTH in the medium. Incubated rat adrenals respond to moderate doses of ACTH with an increased rate of corticoid formation for a limited time only. Contact with adrenal tissue causes a decrease in amount and eventual disappearance of ACTH activity in the medium. Exposure for five minutes to ACTH stimulates the corticoid formation by adrenals subsequently placed in ACTH-free medium. These and other observations suggest that ACTH is bound and inactivated by adrenal tissue. The formation of corticoids by rat adrenals is inhibited by the addition of medium in which other adrenals have been incubated, by the residue from a lipid soluble extract of such medium, and by crystalline compounds F and B. Concentrations of corticoid as low as 10-5M are inhibitory, indicating the possibility that the inhibition of the pituitary-adrenal system by adrenal cortical steroids may occur, to some extent at least, at the level of the adrenal cortex.