USA Biology Olympiad (USABO) Practice Exam

Cortisol medication has a feedback effect on the hypothalamic-pituitary-adrenal (HPA) axis, which regulates the production of various hormones including adrenocorticotropic hormone (ACTH) and corticotropin-releasing factor (CRF). When cortisol is administered, it increases the level of cortisol in the bloodstream. This elevation in cortisol signals the hypothalamus and pituitary gland to reduce the secretion of CRF and ACTH, respectively.

CRF is produced by the hypothalamus and stimulates the pituitary gland to secrete ACTH, which in turn stimulates the adrenal glands to produce cortisol. When cortisol levels are artificially increased through medication, the body interprets this as a signal that there is sufficient cortisol present, leading to decreased production of both CRF from the hypothalamus and ACTH from the pituitary gland.

Thus, the correct understanding is that the administration of cortisol results in a decrease of both ACTH and CRF due to this negative feedback mechanism.