**Core Concept**
Primary aldosteronism is a condition characterized by excess production of aldosterone, a mineralocorticoid hormone produced by the adrenal glands. This leads to hypertension, hypokalemia, and metabolic alkalosis due to the retention of sodium and water, and the excretion of potassium.

**Why the Correct Answer is Right**
The characteristic feature of primary aldosteronism is the suppression of renin-angiotensin-aldosterone system (RAAS) due to feedback inhibition. Aldosterone stimulates the sodium-potassium pump in the collecting ducts of the kidneys, leading to sodium retention and potassium excretion. This results in hypertension, hypokalemia, and metabolic alkalosis. The diagnosis of primary aldosteronism is often made by demonstrating suppressed plasma renin activity and aldosterone levels in the presence of high blood pressure.

**Why Each Wrong Option is Incorrect**
**Option A:** This option may be referring to the effect of aldosterone on blood pressure, but it does not capture the characteristic feature of primary aldosteronism, which is the suppression of RAAS.

**Option B:** This option is incorrect because it refers to the effect of aldosterone on potassium levels, but it does not address the characteristic feature of primary aldosteronism.

**Option C:** This option is incorrect because it refers to the effect of aldosterone on sodium levels, but it does not capture the characteristic feature of primary aldosteronism, which is the suppression of RAAS.

**Clinical Pearl / High-Yield Fact**
In primary aldosteronism, the plasma aldosterone-to-renin ratio (ARR) is typically elevated, and the plasma renin activity is suppressed. This is a useful diagnostic clue to distinguish primary aldosteronism from other causes of hypertension.

**Correct Answer: D. Suppressed plasma renin activity.**