MEDizzy - Furosemide’s main mechanism of action involves the

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The Renal System and Diuretics Pharmacology

Furosemide’s main mechanism of action involves the inhibition of a Na +, K +, 2Cl− cotransporter. In which part of the nephron is this cotransporter located?

ExplanationAs soon as you realize (it should be instantaneous) that furosemide (and bumetanide, torsemide, and ethacrynic acid) is a loop diuretic, you’re halfway toward picking the right answer. These agents inhibit a Na +, K +, 2Cl− cotransporter in the ascending limb. Recall that unimpaired Na + and Cl− reabsorption in the ascending limb is what is responsible and necessary for making the medullary milieu hypertonic, thereby providing the osmotic force necessary for withdrawing water (i.e., concentrating the urine) as the urine passes through the collecting ducts—the “countercurrent multiplier.” You may also recall that the ability of loop agents to increase Ca + and Mg2 + excretion also involves actions in the ascending limb.