Angiotensin II
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Angiotensin II in the Renin-Angiotensin System and Blood Pressure Regulation
Angiotensin II (Ang II) is a key hormone in the renin-angiotensin system (RAS), which is essential for regulating blood pressure, water and salt balance, and electrolyte homeostasis. Ang II acts mainly through its receptors, which are found in the blood vessels, heart, kidneys, and lungs, to control vascular tone and fluid balance 126.
Angiotensin II Receptors: AT1R and AT2R Functions
The effects of Ang II are primarily mediated by two receptors: the angiotensin II type 1 receptor (AT1R) and type 2 receptor (AT2R). AT1R is responsible for most of the classic actions of Ang II, such as vasoconstriction, sodium retention, cell proliferation, inflammation, and oxidative stress, all of which contribute to hypertension and organ damage 2610. In contrast, AT2R is thought to counteract many of the harmful effects of AT1R and may have protective roles in blood pressure regulation, metabolism, and organ protection, especially under pathological conditions .
Angiotensin II and Vascular Diseases
Ang II is closely linked to the development of several vascular diseases, including atherosclerosis, aortic aneurysm, ischemic stroke, hypertension, pulmonary hypertension, and type 2 diabetes. It promotes vascular lesions by increasing inflammation, oxidative stress, and the recruitment of immune cells to the vessel wall 1578. In animal studies, high levels of Ang II have been shown to rapidly worsen atherosclerotic lesions and induce abdominal aortic aneurysms, especially in the presence of high cholesterol .
Angiotensin II in Cardiac and Renal Pathology
Ang II plays a major role in the progression of myocardial hypertrophy to heart failure by directly affecting heart muscle cells and interacting with other hormones and cytokines. It also contributes to cardiac remodeling, vascular thickening, and glomerulosclerosis in the kidneys by activating multiple signaling pathways and promoting cell growth and inflammation 310. These effects are mediated through complex intracellular signaling cascades, including mitogen-activated protein kinases and transcription factors 210.
Angiotensin II, Oxidative Stress, and Endothelial Dysfunction
Excessive Ang II production leads to oxidative stress in endothelial cells, which impairs their function and drives vascular anomalies. This oxidative stress is a key mechanism by which Ang II induces endothelial dysfunction, contributing to the development of cardiovascular diseases 78. Nitric oxide plays a protective role against Ang II-induced oxidative stress in the endothelium 37.
Angiotensin II as a Biomarker and Therapeutic Target
Given its central role in vascular and organ pathology, Ang II is being explored as a biomarker for vascular diseases and as a therapeutic target. Drugs that block Ang II receptors (especially AT1R) or inhibit its production are widely used to treat hypertension, heart failure, and kidney diseases, and ongoing research aims to refine these therapies for better outcomes 1210.
Angiotensin II in Clinical Practice and Emergency Medicine
Synthetic Ang II has been approved for use as a vasopressor in cases of refractory hypotension and shock, providing a new tool for emergency physicians to manage critically low blood pressure when other treatments fail .
Angiotensin II Metabolism and Conversion to Angiotensin-(1-7)
Ang II is converted to Angiotensin-(1-7), a peptide with opposing effects, through enzymes such as prolyloligopeptidase (POP) in the circulation and ACE2 in the kidneys. This conversion pathway is important for balancing the harmful and protective effects within the RAS .
Conclusion
Angiotensin II is a central hormone in cardiovascular and renal physiology and pathology. It regulates blood pressure and fluid balance but also drives inflammation, oxidative stress, and tissue remodeling in various diseases. Understanding its mechanisms and targeting its actions remain crucial for diagnosing and treating a wide range of vascular, cardiac, and renal conditions 1235+5 MORE.
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