INHIBITION OF PITUITARY ACTH RELEASE: AN EXTRA-ADRENAL ACTION OF EXOGENOUS ACTH11

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Abstract
Pituitary ACTH concentration is approximately doubled after administration of ACTH for one week to adrenalectomized rats, in confirmation of previous studies in intact animals. Attempts to determine the mechanism responsible for this extra-adrenal effect of exogenous ACTH yielded the following results: Pre-treatment with ACTH inhibits the pituitary ACTH depletion observed in adrenalectomized rats after application of a scalding stress. Similarly, ACTH pre-treatment blocks the fall in adrenal ascorbic acid obtained in intact control rats after the stress of ether anesthesia. The data are compatible with the hypothesis that the increase in pituitary ACTH concentration produced by exogenous ACTH is due to inhibition of endogenous ACTH release by the pituitary gland. The possibility that stimulation of ACTH synthesis or pituitary adsorption of exogenous ACTH may also occur after administration of ACTH cannot be excluded.