What is the function of atrial natriuretic peptide (ANP) and B-type natriuretic peptide (BNP) in cardiovascular regulation?

• A. Promote vasoconstriction and water retention.
• B. Increase ADH secretion.
• C. Promote vasodilation and natriuresis, inhibit renin, aldosterone, and ADH, lowering blood volume and pressure.
• D. Increase renin release.

Answer: (C)

Natriuretic peptides act to lower blood volume and pressure by counteracting fluid-retaining systems. They are released when the heart chambers are stretched from increased blood volume (ANP from the atria, BNP from the ventricles). They promote vasodilation, which lowers systemic vascular resistance, and increase sodium and water excretion by the kidneys (natriuresis and diuresis). They also suppress the renin-angiotensin-aldosterone system and ADH release, reducing sodium reabsorption and water retention. The net result is a decrease in preload and afterload, helping to lower blood volume and blood pressure.