What is the mechanism of action of ANP/BNP on blood pressure?

• A. They promote natriuresis and vasodilation, lowering blood volume and systemic vascular resistance
• B. They increase heart rate
• C. They cause vasoconstriction and water retention
• D. They inhibit aldosterone secretion

Answer: (C)

Natriuretic peptides lower blood pressure by opposing fluid retention and vasoconstriction. They are released when the heart chambers are stretched from increased volume. In the kidneys, they promote natriuresis and diuresis by increasing glomerular filtration and reducing Na+ reabsorption in the collecting ducts, which lowers extracellular fluid volume. In the vasculature, they cause vasodilation through cGMP signaling, decreasing systemic vascular resistance. They also suppress renin and aldosterone, further reducing sodium and water reabsorption. The combined effect is reduced blood volume and decreased afterload, producing a drop in blood pressure. Choices that imply increased heart rate, vasoconstriction, or water retention don’t reflect the actual action of ANP/BNP.