Relationship between ACTH Secretion and Corticoid Binding to Specific Receptors in Perifused Adenohypophyses

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Abstract
This study reports on the kinetics of glucocorticoid-induced inhibition of ACTH release, together with steroid binding to specific pituitary receptors. It was shown that corticosterone (CORT) inhibited ACTH output provoked by either corticotropin-releasing factor (CRF) extracts or dbcAMP, in a manner which was both dose- and time-dependent. A close correlation appeared to exist between the degree of ACTH blockade and the percentage of filled steroid-binding sites. However, exposure of hypophyses to CORT for a critical period of time was a prerequisite for such a relationship to develop. Furthermore, it was found that dexamethasone (DEX) was more potent than CORT in inhibiting ACTH secretion and, in addition, bound to a greater extent to nuclei of pituitary cells. These data suggest the existence of a close correlation between occupancy of pituitary glucocorticoid receptors and modulation of ACTH secretion.