One of the following diuretics does not require its presence in the tubular lumen for its pharmacological effects:: (A) Thiazide diuretics, (B) Loop diuretics, (C) Carbonic anhydrase inhibitors, (D) Aldosterone antagonists
Answer is D. Ans. (D) Aldosterone antagonists(Ref: KDT 8/e p634)*Most of the diuretics act from the luminal side of membrane in the nephron.*Thiazides, loop diuretics, carbonic anhydrase inhibitors and epithelial Na+ channel blockers (e.g. amiloride and triamterene) are secreted in the proximal tubules through organic anion/cation transport process.*Osmotic diuretics reach the lumen of proximal tubules via glomerular filtration.*Aldosterone antagonists like spironolactone do not act through luminal side rather they act from basolateral side of the membrane. Therefore, these agents do not require access to the tubular lumen.