Learning Objectives

• Identify the physiological triggers for ANP release from the heart.
• Explain the second messenger system (cGMP) utilized by natriuretic peptides.
• Analyze the renal hemodynamic changes (afferent vs. efferent arterioles) that promote diuresis.
• Understand the role of ANP in the “aldosterone escape” mechanism.

Mechanism of Atrial Natriuretic Peptide (ANP)

ANP is a powerful hormone involved in the long-term regulation of blood pressure and extracellular fluid volume.

• Release Trigger: Secreted by atrial myocytes specifically in response to increased blood volume and atrial pressure (stretch).
• Signal Transduction: Acts through a membrane-bound guanylyl cyclase receptor to increase levels of cGMP.
• Systemic Effect: Promotes vasodilation, which helps to lower systemic blood pressure.

Renal and Diuretic Effects

ANP functions as a “natural diuretic” by altering renal handling of sodium and water:

• Renal Arterioles: It dilates afferent arterioles and constricts efferent arterioles. This combination increases the glomerular filtration rate (GFR).
• Sodium Handling: It decreases Na+ reabsorption at the renal collecting tubule, leading to natriuresis (sodium excretion).
• Aldosterone Escape: By promoting sodium and water loss, ANP is a key contributor to the “aldosterone escape” mechanism, preventing indefinite fluid retention.

Activity