**Core Concept**
The patient in this scenario has a condition characterized by hypertension, hypokalemia, metabolic alkalosis, and decreased plasma renin activity, with a mass on the left suprarenal gland. This presentation is suggestive of primary aldosteronism, a condition where excess aldosterone production leads to sodium retention, potassium excretion, and hypertension. The treatment of this condition involves blocking the effects of aldosterone or reducing its production.

**Why the Correct Answer is Right**
Spironolactone is a potassium-sparing diuretic that acts as a competitive antagonist of aldosterone at the mineralocorticoid receptor. By blocking the effects of aldosterone, spironolactone reduces sodium reabsorption and potassium excretion in the collecting ducts of the kidneys, thereby lowering blood pressure and correcting hypokalemia. Additionally, spironolactone can help reduce the production of aldosterone by feedback inhibition, which is beneficial in cases of primary aldosteronism. The use of spironolactone in this patient would have helped alleviate symptoms and normalize laboratory values.

**Why Each Wrong Option is Incorrect**
**Option A:** Clonidine is an alpha-2 adrenergic agonist that decreases sympathetic tone and is used to treat hypertension. However, it does not directly address the underlying cause of primary aldosteronism and would not be effective in correcting hypokalemia and metabolic alkalosis.

**Option B:** Propranolol is a beta-blocker that reduces heart rate and cardiac output, but it does not affect the renin-angiotensin-aldosterone system and would not be effective in treating primary aldosteronism.

**Option C:** Hydrochlorothiazide is a thiazide diuretic that promotes sodium excretion and potassium loss, which would worsen hypokalemia and metabolic alkalosis in this patient.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that the diagnosis of primary aldosteronism requires a combination of clinical findings, laboratory tests (such as plasma aldosterone concentration and renin activity), and imaging studies (such as CT or MRI). Treatment with spironolactone or other potassium-sparing diuretics can help manage symptoms and normalize laboratory values, but surgical resection of the aldosterone-producing adenoma is often necessary for long-term cure.

**✓ Correct Answer: D. Spironolactone. It is a potassium-sparing diuretic that can help manage primary aldosteronism by blocking the effects of aldosterone and reducing its production.**