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Diuretics are medications that increase the amount of urine flow by inhibiting transport proteins or enzymes in the nephron. Different classes of diuretics affect different parts of the nephron. Which of the following diuretics will also decrease the amount of calcium excreted from the kidney?

(A) Acetazolamide
(B) Amiloride
(C) Furosemide
(D) Hydrochlorothiazide
(E) Spironolactone 


in Pharmacology by

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The correct answer is D. Hydrochlorothiazide is a diuretic that inhibits NaCl reabsorption at the distal tubule and also reduces the excretion of calcium. The inhibition of the NaCl symporter on the luminal side of the cell results in decreased Na+ transport into the cells of the distal convoluted tubule. This results in an increased Na+ electrochemical gradient. On the interstitial side of the distal convoluted tubule cells, there is a Na+/Ca2+ antiporter, which responds to this change in the Na+ gradient by transporting more Na+ into the cell, while transporting more Ca2+ into the interstitium. Ca2+ is transported on the luminal side of the cell by a parathyroid hormone-controlled channel, which is not inhibited by the thiazide diuretics. Thus thiazide diuretics are often used to treat chronic renal stone formation (due to hypercalciuria).

Answer A is incorrect. Acetazolamide inhibits carbonic anhydrase at the proximal convoluted tubule to cause increased excretion of HCO3–. It has no effect on calcium excretion.

Answer B is incorrect. Amiloride is also a potassium-sparing diuretic that directly inhibits the Na+ reabsorption transport ion at the corti- cal collecting duct and thus reduces the K+ secretion at the same site. Amiloride has no effect on calcium excretion.

Answer C is incorrect. Furosemide is a loop diuretic that reduces the medullary concentration gradient by inhibiting the co-transport of ions (Na+, K+, and 2Cl–) in the thick ascending loop of Henle. Because of the blockade of this cotransporter and its creation of the lumen-positive potential, there is decreased reabsorption of divalent cations, including calcium. Therefore, furosemide actually increases calcium excretion from the kidney.

Answer E is incorrect. Spironolactone is a potassium-sparing diuretic that functions as an aldosterone antagonist so that Na+ reabsorption and K+ secretion are inhibited at the cortical collecting duct. It does not affect calcium excretion.