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Angiotensin Receptor Blockers (ARBs)

Angiotensin II Receptor Blockers (ARBs): Understanding Their Role in Hypertension and Cardiovascular Protection

Definition:
Angiotensin II receptor blockers (ARBs) are a class of pharmaceuticals that selectively block the activation of angiotensin II type 1 receptors (AT1)[1]. These receptors mediate the effects of the renin-angiotensin system, which include arteriolar contraction and sodium retention[1]. By blocking AT1 receptors, ARBs lead to vasodilation, reduced vasopressin secretion, and decreased aldosterone production, ultimately lowering blood pressure[1]. ARBs are commonly known as angiotensin II receptor antagonists or AT~1~ receptor antagonists[1].

Therapeutic Uses
ARBs are primarily used in the treatment of several conditions[1]:

• Hypertension: ARBs effectively lower blood pressure by relaxing blood vessels, making it easier for the heart to pump blood[4].
• Diabetic Nephropathy: They protect the kidneys from damage caused by diabetes[1].
• Congestive Heart Failure: ARBs help manage heart failure by reducing the workload on the heart[1].
• Post-Myocardial Infarction: Valsartan is specifically approved to treat patients after a heart attack[3].

Mechanism of Action
ARBs function as AT~1~-receptor antagonists, preventing angiotensin II from binding to AT~1~ receptors located in smooth muscle cells of blood vessels, the adrenal gland, and adrenergic nerve synapses[1]. This blockage results in several beneficial effects[1][3]:

• Vasodilation: ARBs dilate arteries and veins, reducing arterial pressure and decreasing the heart’s preload and afterload[3].
• Downregulation of Sympathetic Activity: By interfering with angiotensin II’s effects on sympathetic nerve release and norepinephrine reuptake, ARBs can reduce sympathetic adrenergic activity[3].
• Blood Volume Reduction: ARBs promote the excretion of sodium and water by blocking angiotensin II’s effects in the kidneys, inhibiting aldosterone secretion, and reducing vasopressin release, which decreases thirst[3].
• Inhibition of Remodeling: ARBs help prevent cardiac and vascular remodeling associated with chronic hypertension, heart failure, and myocardial infarction[3].

Clinical Implications
ARBs have shown promise in several clinical areas[1]:

• Longevity: Studies in mice indicate that blocking the AT~1~ receptor may extend lifespan by reducing oxidative damage and enhancing renal protective genes[1].
• Fibrosis Regression: ARBs like losartan can reduce fibrosis in muscles, liver, heart, and kidneys[1].
• Aortic Root Dilation: Candesartan and valsartan have demonstrated the ability to regress dilated aortic root size[1].
• Increase of regenerative EPCs: ARBs increase the number of regenerative endothelial progenitor stem cells in patients with type 2 diabetes mellitus[2].

Diagnosis and Management
ARBs are prescribed based on a thorough evaluation of a patient’s condition. Management includes[1]:

• Regular Monitoring: Blood pressure and kidney function should be monitored regularly to ensure the medication is effective and to detect any potential side effects[4].
• Lifestyle Modifications: Lifestyle adjustments, such as dietary changes and regular exercise, can complement the effects of ARBs[4].

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References

Angiotensin II receptor blocker – Wikipedia[1]

Angiotensin Receptor Blockers: New Considerations in Their …[2]

Angiotensin Receptor Blockers (ARBs) – CV Pharmacology[3]

Angiotensin II Receptor Blockers (ARBs): Uses and Side Effects[4]