Loop diuretics are
diuretics that act on the ascending
loop of Henle in the
kidney. They are primarily used in
medicine to treat
hypertension and
edema often due to
congestive heart failure or
renal insufficiency. While
thiazide diuretics are more effective in patients with normal kidney function, loop diuretics are more effective in patients with impaired kidney function.
Mechanism of action
Loop diuretics act on the
Na<sup>+</sup>-K<sup>+</sup>-2Cl<sup>-</sup> symporter (
cotransporter) in the thick ascending limb of the
loop of Henle to inhibit sodium and chloride reabsorption. This is achieved by competing for the Cl<sup>-</sup> binding site. Because
magnesium and
calcium reabsorption in the thick ascending limb is dependent on sodium and chloride concentrations (primarily on the recycling of the potassium due to the lack of the electropositive gradient generation), loop diuretics also inhibit their reabsorption. By disrupting the reabsorption of these ions, loop diuretics prevent the urine from becoming concentrated and disrupt the generation of a
hypertonic renal medulla. Without such a concentrated medulla, water has less of an
osmotic driving force to leave the
collecting duct system, ultimately resulting in increased
urine production. Loop diuretics cause an increase in the renal blood flow by this mechanism. This diuresis leaves less water to be reabsorbed into the blood, resulting in a decrease in blood volume.
The...
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