How do thiazide diuretics help treat hypertension, and what is a common electrolyte disturbance?

• A. They inhibit NaCl reabsorption in the distal tubule, reducing plasma volume and arterial resistance; can cause hypokalemia and hyperglycemia.
• B. They block aldosterone receptors; hyperkalemia.
• C. They increase water reabsorption; hyponatremia.
• D. They inhibit carbonic anhydrase; metabolic acidosis.

Answer: (A)

Thiazide diuretics work by blocking the Na-Cl cotransporter in the distal convoluted tubule. This prevents reabsorption of sodium and chloride, which reduces overall fluid volume and, over time, lowers arterial resistance, helping to treat hypertension. A common electrolyte effect is potassium loss: more sodium reaches the collecting duct, where it is exchanged for potassium, leading to hypokalemia. They can also cause modest hyperglycemia, especially at higher doses or in susceptible individuals. The other mechanisms listed belong to different drug classes or renal actions (for example, aldosterone blockers raise potassium and work differently, while carbonic anhydrase inhibitors cause metabolic acidosis), so the described action and typical electrolyte disturbance best match thiazides.