**Core Concept**
Metyrapone is a medication that affects the adrenal gland's production of cortisol, a glucocorticoid hormone. It works by inhibiting the enzyme 11β-hydroxylase, which is crucial for cortisol synthesis in the adrenal cortex.

**Why the Correct Answer is Right**
Metyrapone specifically targets the 11β-hydroxylase enzyme, preventing the conversion of 11-deoxycortisol to cortisol. This leads to a decrease in cortisol production, which can be used to diagnose or treat conditions like Cushing's syndrome or adrenal insufficiency. The inhibition of 11β-hydroxylase results in an accumulation of 11-deoxycortisol, which can be measured to assess the effectiveness of metyrapone therapy. This mechanism of action is specific to the adrenal cortex, where cortisol is produced.

**Why Each Wrong Option is Incorrect**
**Option A:** Metyrapone does not inhibit aldosterone synthase, which is involved in the production of aldosterone, a mineralocorticoid hormone. Aldosterone is produced in a different part of the adrenal gland and is not directly affected by metyrapone.
**Option B:** Metyrapone does not affect the production of sex hormones like testosterone or estrogen, which are produced in the gonads (ovaries or testes) and not in the adrenal gland.
**Option C:** Metyrapone is not a stimulator of the adrenal gland; it actually inhibits cortisol production. This option is the opposite of the correct answer.

**Clinical Pearl / High-Yield Fact**
Metyrapone can be used to diagnose or treat Cushing's syndrome, a condition characterized by excess cortisol production. The drug works by inhibiting cortisol production, allowing for the measurement of 11-deoxycortisol levels to assess adrenal function.

**Correct Answer:** D.