Corticosteroid Inhibition of ACTH Secretion*

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Abstract
THE LEVEL of activity within the adrenocortical system is determined by endogenous (circadian) and exogenous (stress) excitatory inputs, by inhibitory neural modulation and also by corticosteroid negative feedback control. Although corticosteroid feedback on (CRF and) ACTH secretion is easily demonstrated by treatment of mammals with exogenous glucocorticoids and subsequent measurement of either basal or stimulated activity in the system, the physiological role of this negative feedback is not so easily discerned. It is likely that most disagreement about feedback regulation of ACTH secretion has arisen because of three characteristics of the system. First, it now appears that there are at least three distinct time domains in which negative feedback by glucocorticoids on ACTH secretion are exerted. These can be distinguished at the level of the corticotrope in vitro by the different cellular effects of glucocorticoid action. Thus, interpretation of results of in vivo experiments is critically dependent on the timing of the experiment relative to the glucocorticoid signal.

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