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Loop diuretic
Loop diuretics are diuretics that act at 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+-K+-2Cl− symporter (cotransporter) in the thick ascending limb of the loop of Henle to inhibit sodium, chloride and potassium reabsorption. This is achieved by competing for the Cl− binding site. Because magnesium and calcium reabsorption in the thick ascending limb is dependent on the positive lumen voltage gradient set up by potassium recycling through renal outer medullary potassium channel, loop diuretics also inhibit their reabsorption. By disrupting the reabsorption of these ions, loop diuretics prevent 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 a decrease 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.
A secondary effect of loop diuretics is to increase the production of prostaglandins, which results in vasodilation and increased blood supply to the kidney. NSAIDs block the COX pathway that synthesizes prostaglandins, so NSAIDs can reduce the efficacy of loop diuretics.
The collective effects of decreased blood volume and vasodilation decrease blood pressure and ameliorate edema.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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