EVIDENCE THAT AN EXTRAHYPOTHALAMIC PITUITARY CORTICOTROPIN-RELEASING HORMONE (CRH) ADRENOCORTICOTROPIN (ACTH) SYSTEM CONTROLS ADRENAL GROWTH AND SECRETION IN RATS

Within two weeks, hypophysectomy induced in rats a striking decrease i n the level of circulating ACTH (the concentration of which was at the limit of sensitivity of our assay system), coupled with a net reducti on in the plasma corticosterone concentration and an evident adrenal a trophy. Zona fasciculata, the main producer of glucocorticoids, was de creased in volume, due to a lowering in both the number and average vo lume of its parenchymal cells. Subcutaneous ACTH infusion (0.1 pmol . min-1), administered during the last week following hypophysectomy, re stored the normal blood level of ACTH and completely reversed all effe cts of hypophysectomy on the adrenals. Subcutaneous infusion for one w eek with alpha-helical-CRH or corticotropin-inhibiting peptide (1 nmol . min-1), which are competitive inhibitors of CRH and ACTH, evoked a further significant lowering of plasma corticosterone concentration an d markedly enhanced adrenal atrophy in hypophysectomized rats. These f indings strongly suggest that an extrahypothalamic pituitary CRH/ACTH system may be involved in the maintenance of the growth and steroidoge nic secretory activity of the rat adrenal cortex.