In metyrapone testing, what indicates an intact hypothalamic-pituitary-adrenal axis?

In metyrapone testing, what indicates an intact hypothalamic-pituitary-adrenal axis?

• A. A rise in ACTH and 11-deoxycortisol indicates an intact HPA axis
• B. No changes in ACTH or 11-deoxycortisol after metyrapone
• C. A fall in 11-deoxycortisol without ACTH change
• D. An abnormal response with low ACTH

Answer: (A)

The key idea is how metyrapone reveals the feedback control of the HPA axis. Metyrapone blocks 11-beta-hydroxylase, so cortisol synthesis drops. In a person with an intact HPA axis, this drop reduces negative feedback, triggering the pituitary to release more ACTH. The increased ACTH then pushes the adrenal cortex to produce more upstream steroids, notably 11-deoxycortisol. Because the block prevents conversion to cortisol, 11-deoxycortisol accumulates and can be measured. Therefore, a rise in both ACTH and 11-deoxycortisol after metyrapone indicates an intact, responsive HPA axis. If either hormone fails to rise, it suggests some degree of axis impairment at the hypothalamic-pituitary or adrenal level.

The key idea is how metyrapone reveals the feedback control of the HPA axis. Metyrapone blocks 11-beta-hydroxylase, so cortisol synthesis drops. In a person with an intact HPA axis, this drop reduces negative feedback, triggering the pituitary to release more ACTH. The increased ACTH then pushes the adrenal cortex to produce more upstream steroids, notably 11-deoxycortisol. Because the block prevents conversion to cortisol, 11-deoxycortisol accumulates and can be measured. Therefore, a rise in both ACTH and 11-deoxycortisol after metyrapone indicates an intact, responsive HPA axis. If either hormone fails to rise, it suggests some degree of axis impairment at the hypothalamic-pituitary or adrenal level.