This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Pharmacology
A 65-year-old man with mild hea failure is treated with a loop diuretic. A few days later the man complains of muscle weakness. Laboratory results are shown below. Aerial PCO2: 48 mm Hg Aerial pH: 7.49 Plasma HCO3-: 35 mEq/L Which of the following is most likely decreased in this man? 
Select and explain. 
A. Plasma angiotensin, B. Plasma potassium, C. Potassium excretion, D. Renin secretion
B: Plasma potassium
Answer: B: Plasma potassium 
Explanation: The lab repos indicate that the man has developed metabolic alkalosis (increased PCO2, pH, and HCO3-), which occurs commonly with overuse of diuretics (thiazides and loop diuretics). The overuse of a loop diuretic increases the excretion of sodium and potassium by the kidneys. The increase in potassium excretion leads to a decrease in plasma potassium levels. The sodium depletion stimulates renin secretion, which in turn raises angiotensin II levels in the plasma (which also stimulates aldosterone secretion).