In a subject with intact pituitary-adrenal function, following administration of metyrapone, a fall in cortisol production is seen, with a subsequent fall in plasma cortisol levels (Fig. 7.16). This causes a compensatory release of ACTH for as long as the drug is administered. ACTH, acting on the adrenal cortex, accelerates the early stages of steroid biosynthesis and therefore increases the production of all of the steroids up to the step that is blocked by metyrapone. The increased production of 11-deoxycortisol can be measured directly in the blood, where it appears as a 17-hydroxy-corticosteroid. A patient with hypothalamic, pituitary, or adrenal insufficiency will show a diminished or absent response.
