PNMT catalyzes the conversion of norepinephrine to epinephrine in the adrenal medulla. This enzyme's activity is dependent on high levels of which hormone?

• A. Aldosterone
• B. Cortisol
• C. Insulin
• D. Thyroid hormone

Answer: (B)

High cortisol drives the conversion of norepinephrine to epinephrine by upregulating PNMT in the adrenal medulla. PNMT (phenylethanolamine N-methyltransferase) is the enzyme that methylates norepinephrine to form epinephrine, and its expression and activity increase when glucocorticoids like cortisol rise. This makes sense in the stress response: cortisol from the adrenal cortex signals chromaffin cells to boost PNMT, producing more epinephrine to prepare the body for action.

Aldosterone, insulin, and thyroid hormone don't have this specific upregulating effect on PNMT. Aldosterone mainly regulates sodium and water balance, insulin governs glucose metabolism, and thyroid hormone controls overall metabolic rate without directly enhancing PNMT activity.