Loop diuretics act by: (PGI Dec 2008)
**Core Concept**
Loop diuretics are a class of medications used to treat fluid overload conditions such as edema and hypertension. They work by inhibiting the sodium-potassium-chloride cotransporter (NKCC2) in the thick ascending limb of the loop of Henle, leading to increased excretion of sodium, chloride, and water.
**Why the Correct Answer is Right**
Loop diuretics, such as furosemide and bumetanide, bind to the NKCC2 transporter in the proximal part of the thick ascending limb of the loop of Henle. This binding inhibits the reabsorption of sodium, potassium, and chloride ions, resulting in increased excretion of these ions in the urine. As a consequence, water follows osmotically, leading to increased urine production. The inhibition of NKCC2 also leads to a decrease in the reabsorption of calcium ions, which can contribute to hypocalcemia.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because loop diuretics do not act by inhibiting the sodium-chloride cotransporter (NCC) in the distal convoluted tubule, which is the site of action of thiazide diuretics.
**Option B:** This option is incorrect because loop diuretics do not primarily act by inhibiting the angiotensin-converting enzyme (ACE), which is the site of action of ACE inhibitors.
**Option C:** This option is incorrect because loop diuretics do not primarily act by blocking the alpha-adrenergic receptors, which is the site of action of alpha-blockers.
**Clinical Pearl / High-Yield Fact**
It is essential to remember that loop diuretics can lead to hypokalemia, hypomagnesemia, and hypocalcemia due to the increased excretion of these ions in the urine. This can be particularly problematic in patients with pre-existing electrolyte imbalances or those taking other medications that affect electrolyte balance.
**Correct Answer: C. Inhibition of NKCC2 in the loop of Henle**