A man presents with hypertension and hypokalemia. Measurement of his arterial blood gases reveals a $\mathrm{pH}$ of 7.5 and a calculated $\mathrm{HCO}_{3}$ - of $32 \mathrm{mEq} / \mathrm{L}$. His serum cortisol and urinary vanillylmandelic acid (VMA) are normal, his serum aldosterone is increased, and his plasma renin activity is decreased. Which of the following is the most likely cause of his hypertension?

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[IV C 3 b; V B 4 b]. Hypertension, hypokalemia, metabolic alkalosis, elevated serum aldosterone, and decreased plasma renin activity are all consistent with a primary hyperaldosteronism (e.g., Conn syndrome). High levels of aldosterone cause increased $\mathrm{Na}^{+}$reabsorption (leading to increased blood pressure), increased $\mathrm{K}^{+}$secretion (leading to hypokalemia), and increased $\mathrm{H}^{+}$secretion (leading to metabolic alkalosis). In Conn syndrome, the increased blood pressure causes an increase in renal perfusion pressure, which inhibits renin secretion. Neither Cushing syndrome nor Cushing disease is a possible cause of this patient's hypertension because serum cortisol and adrenocorticotropic hormone (ACTH) levels are normal. Renal artery stenosis causes hypertension that is characterized by increased plasma renin activity. Pheochromocytoma is ruled out by the normal urinary excretion of vanillylmandelic acid (VMA).

A Man Presents with Hypertension and Hypokalemia pH\mathrm{pH}pH Of 75 and a Calculated

A Man Presents with Hypertension and Hypokalemia $\mathrm{pH}$ Of 75 and a Calculated