Which renal tubular process is inhibited by hydrochlorothiazide?

• A. Inhibition of NaCl reabsorption in the distal convoluted tubule, increasing calcium reabsorption
• B. Inhibition of Na-K-2Cl cotransport in the thick ascending limb
• C. Blocking aldosterone receptors in the collecting duct
• D. Inhibition of carbonic anhydrase in the proximal tubule

Answer: (A)

Hydrochlorothiazide blocks the Na-Cl cotransporter in the distal convoluted tubule, reducing NaCl reabsorption and driving diuresis. This site of action also promotes increased calcium reabsorption in the distal nephron, lowering urinary calcium. The other options point to different diuretic targets—loop diuretics inhibit the Na-K-2Cl cotransporter in the thick ascending limb, aldosterone receptor antagonists act in the collecting duct, and carbonic anhydrase inhibitors act in the proximal tubule. So the key action is inhibition of NaCl reabsorption in the distal convoluted tubule, with a concurrent rise in calcium reabsorption.