Pituitary ACTH and Plasma Free Corticosteroids Following Bilateral Adrenalectomy in the Rat.

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Abstract
Pituitary ACTH and plasma free corticosteroids were concurrently determined following bilateral adrenalectomy in the rat. Free corticosteroids disappeared from the plasma within 4 hours. Pituitary ACTH rose to 150% of the control level within the first 30 minutes, fell to 40% after 4 hours, to 30% after 12, stabilized at this level for the next 12 hours, rose from then on to supernormal levels, up to a crest of 575% on the 32nd day, and regressed, thereafter, to lower though still markedly elevated values. From a correlation of these findings with available data on blood ACTH levels under comparable conditions, it is inferred that, following a transient burst of synthesis reflected by the initial peak, a predominant, though gradually receding acceleration of the rate of release accounts for the pituitary ACTH depletion, a greater and sustained acceleration of synthesis, for its subsequent rise. It is further suggested that the ACTH-releasing effect of stress is markedly influenced by the level of circulating adrenal cortical hormones, and that withdrawal of these hormones enhances both release and synthesis of ACTH, but has a predominant effect on the latter.