A new diuretic is being studied in human volunteers. Compared with placebo, the new drug increases urine volume, increases urinary Ca2+, increases plasma pH, and decreases serum K+. If this new drug has a similar mechanism of action to an established diuretic, it probably
A. blocks the NaCl cotransporter in the DCT
B. blocks aldosterone receptors in the CT
C. inhibits carbonic anhydrase in the PCT
D. inhibits the Na+/K+/2Cl– cotransporter in the TAL
E. acts as an osmotic diuretic
Answer: D. The effects described are typical of loop diuretics, which inhibit
the Na
+
K
+2Cl
– cotransporter in the thick ascending limb. This action pre
vents the reabsorption of Ca2+ from the paracellular pathway and provides
for the use of these drugs in hypercalcemia. The increased load of Na
- in the
collecting tubules leads to increased excretion of both K - and H
+, so hypo
kalemia and alkalosis may occur.