Drugs to modify renal function

Question 1

What is a natriuretic drug?

Answer 1

A diuretic that works by increasing renal sodium loss

Inhibit sodium reabsorption at luminal surface of tubular cells

Question 2

What is an example of a PCT-acting diuretic? How does it work and what is an associated risk?

Answer 2

Carbonic anhydrase inhibitors e.g diamox
Inhibit C.A and therefore splitting of H2CO3 in the tubule to CO2 and H2O, preventing H+ return to the tubule cell and depriving the apical Na+/H+ exchanger of one necessary ligand. The result is natriuresis leading to osmotic diuresis. Also get loss of HCO3-; potential for electrolyte imbalance.

Question 3

What is an example of a LOH-acting diuretic? How does it work and what is an associated risk?

Answer 3

Frusemide acts at the ascending LOH to block the sodium/chloride/potassium cotransporter. Acts to reduce the medullary interstitial osmotic gradient as well as keep solutes in the urine. Strongest available diuretic. Risk of hypokalaemia due to inhibited K+ uptake and increased flow rate.

Question 4

What is an example of a DCT acting diuretic? How does it work and what is an associated risk?

Answer 4

Thiazides - Act to inhibit the Na-Cl cotransporter on the apical membrane. This causes Na+ to remain in urine and osmotic diuresis. Increases flow rate more substantially than CA inhibitors, so also confers some risk of potassium loss & hypokalaemia, or hyponatremia

Question 5

What are some examples of CD acting diuretics? How do they work? How is this safer than CA inhibitors, frusemide, thiazides?

Answer 5

Spironolactone - inhibits Na channels in principal cells to prevent Na absorption from filtrate, creating osmotic diuresis. Also inhibits Na/K ATPase, which prevents K+ uptake from the blood by principal cell and therefore reduced K+ loss into the urine
Amiloride triamterene inhibits apical Na+ channels to the same effect. Depriving the basolateral ATPase of substrate conserves K+