Potassium secretion is decreased by action on late distal tubule by?
Correct Answer: Spironolactone
Description: Ans. is 'a' i.e., Spironolactone Potassium sparing diuretics* These drugs act in late DCT and CD. Examples:1) Aldosterone antagonists* Examples in this group are spironolactone, canrenone, prorenone, mexrenone and eplerenone.* Aldosterone acts on the late DT and CD cells by combining with an intracellular mineralocorticoid receptor -induces the formation of aldosterone induced proteins (AIPs) which promote Na+ reabsoiption and K+ secretion.* Spironolactone acts from the interstitial side of the tubular cells, combines with the mineralocorticoid receptor and inhibits the formation of AIPs in a competitive manner.* Spironolactone increases Ca+2 excretion by a direct action on renal tubules (amiloride decreases it).* Spironolactone is converted to active metabolites, the most important of which is canrenone.* All diuretics act from luminal (tubular) surface of tubular cells, except for aldosterone antogonists which act on interstitial surface. Therefore, aldosterone antagonists do not require access to tubular lumen, while other diuretics need access to tubular lumen.2) Renal epithelial Na+ channel inhibitors* The luminal membrane of late DT and CD cells expresses a distinct amiloride sensitive or renal epithelial Na+ channel through which Na+ enters the cell down its electrochemical gradient which is generated by Na+ K+ ATPase operating at the basolateral membrane.* These channels are inhibited by amiloride and triamterene.* Their most important action is to decrease K+ excretion, this is accompanied by a small increase in Na+ excretion.* Amiloride is more potent and longer acting than triamterene.* Amiloride blocks entry of Li+ through Na+ channels in the CD cells and mitigates DT induced by lithium - DOC for LT induced DI.* Given as an aerosol amiloride affords symptomatic improvement in cystic fibrosis by increasing fluidity of respiratory secretions.* Amiloride decreases Mg++ and Ca++ excretion and increases urate excretion.* Triametere is less often used because it is incompletely obsorbed, and causes photosensitivity, glucose intolerance, interstitial nephritis and renal stones. It is a weak folic acid antagonist and can cause megaloblastic anemia.
Category:
Pharmacology
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