What is the primary action of atrial natriuretic peptide on sodium?

• A. Sodium reabsorption
• B. Sodium excretion
• C. No effect on sodium
• D. Increases sodium production

Answer: (B)

The main effect of atrial natriuretic peptide on sodium is excretion. ANP is released when the atria are stretched due to increased blood volume and acts on the kidney to promote natriuresis—increasing sodium excretion in the urine. It does this by raising glomerular filtration and inhibiting sodium reabsorption in the renal tubules, especially the collecting ducts, while also dampening the renin-angiotensin-aldosterone system. So the primary action is to promote sodium loss, not reabsorption or production.