Adrenal Disorders USMLE Step 1 Practice Question

A 50-year-old woman with hypertension (BP 168/104 mmHg, HR 88/min) is found to have a 2-cm adrenal adenoma on CT imaging producing elevated aldosterone (28 ng/dL; normal <16). Laboratory studies show hypokalemia (K+ 3.2 mEq/L) and metabolic alkalosis (HCO3− 32 mEq/L), with normal ACTH levels. She denies headaches or palpitations. Which of the following factors is the primary physiologic regulator of aldosterone secretion under normal conditions?