Diuretics: Mechanism of action, uses | Renal Physiology | Pharmacology

Diuretics are substances which increase the flow rate of urine. Most of the classes of diuretics work by increasing both the solute as well as water loss.

 1. Carbonic anhydrase inhibitors: They inhibit the carbonic anhydrase enzyme present in epithelial cells lining the proximal convultae tubule. Thus, they decrease the reabsorptionof sodium as well as that of bicarbonate. Due to this, there is decrease in pH causing metabolic acidosis. They ae used mianly to block carbonic anhydrase enzyme in eyes especially in open angle glaucoma and in high altitude sickness where they prevent the development of metabolic alkalosis.

 2. Loop diuretics: Loop diuretics inhibit sodium potassium 2cl- transporter. This interefers with both the concentration as well as dilution of urine. They are very effective diuretics since they interfere with absorptiono f approximatelu 25% of sodium reabsorptionin nephron.

 3. Thiazide diuretics: These diuretics act on distal convulated tubule where they block sodium chloride symporter. They mainly interfere with dilutionof urine and not with concentrationo f urine. They are moderately effective diuretics which interfere with 5-10% of reabsorption of filtered sodium.

 4. Potassium sparing diuretics: They act on late distal tubule and collecting ducts. They act by inhibiting either epithelial sodium channels or mineralocorticoid receptors. They are not very effective diuretics as such but when combined with other diuretics, they help in preventing the development of hypokalmeic alkalosis.

 5. Osmotic diuretics. Osmotic diuretics interfere mainly with reabsorption of water and not of solutes.Osmotic diuretics, are filtered from the glomerulus but are not absorbed and tend to remain in the tubular fluid. Hence,in descending limb of loop of henle which is permeable to water, they prevent the movement of water out from tubular lumen since they exert on osmotic pull on water.