Loop diuretics inhibit the tubular reabsorption of which substance?

Loop diuretics primarily work by inhibiting the reabsorption of sodium in the loop of Henle, which is a part of the nephron in the kidney. The mechanism involves blocking the sodium-potassium-chloride (NKCC2) transporter, which is responsible for transporting these ions from the tubular fluid back into the blood. By inhibiting this transporter, loop diuretics effectively increase the excretion of sodium, leading to diuresis, or increased urine production.

While potassium and calcium levels can also be affected by loop diuretics—often resulting in hypokalemia and hypercalcemia, respectively—the primary action of these drugs is on sodium reabsorption. This understanding is crucial as it highlights the direct relationship between loop diuretics and sodium handling in the kidneys, leading to their therapeutic effects in conditions such as heart failure and edema.