## Angiotensin II Receptor Subtypes and Their Roles **Key Point:** Angiotensin II acts via TWO main receptor subtypes (AT₁ and AT₂), but the **AT₁ receptor** mediates virtually all the classical physiological and pathophysiological effects in the kidney and vasculature. ### AT₁ Receptor: The Dominant Effector **High-Yield:** AT₁ receptors are responsible for: - **Vasoconstriction** of afferent and efferent arterioles (efferent > afferent) - **Aldosterone secretion** from adrenal zona glomerulosa - **Sodium reabsorption** in proximal tubule and collecting duct - **Increased sympathetic tone** (CNS and peripheral) - **Vasopressin (ADH) release** from posterior pituitary - **Renal fibrosis and inflammation** (pathological) - **Cardiac hypertrophy and remodeling** (pathological) ### Comparison of Angiotensin II Receptors | Receptor | Location | Primary Effects | Clinical Relevance | |----------|----------|-----------------|--------------------| | **AT₁** | Kidney, vasculature, heart, adrenal, brain | Vasoconstriction, aldosterone, Na⁺ reabsorption, sympathetic activation | TARGET of ARBs and ACE inhibitors | | **AT₂** | Fetal tissues, adrenal medulla, brain | Vasodilation, anti-inflammatory, anti-fibrotic | Antagonizes AT₁ effects; minimal in adults | | **AT₃ & AT₄** | Not physiologically relevant in humans | — | Not clinically important | **Clinical Pearl:** ARBs (losartan, valsartan, olmesartan) selectively block AT₁ receptors. This is why they are so effective in hypertension, heart failure, and diabetic nephropathy—they prevent the harmful effects of angiotensin II while allowing AT₂-mediated vasodilation. **Warning:** ~~AT₂ receptors mediate the main effects of angiotensin II~~ — this is incorrect. AT₂ receptors are present in small amounts in adults and generally counteract AT₁ effects. **Mnemonic:** **AT₁ = All The (main) effects** [cite:Harrison 21e Ch 297]
Sign up free to access AI-powered MCQ practice with detailed explanations and adaptive learning.