What is angiotensin
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These studies suggest angiotensin is a group of peptide hormones derived from angiotensinogen, playing crucial roles in cardiovascular homeostasis, blood pressure regulation, heart failure progression, and reproductive functions.
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Understanding Angiotensin: A Multifunctional Hormone
Introduction to Angiotensin
Angiotensin is a peptide hormone that plays a crucial role in regulating blood pressure, fluid balance, and cardiovascular homeostasis. It is part of the renin-angiotensin system (RAS), which is essential for maintaining vascular tone and electrolyte balance .
Angiotensin II: The Principal Effector
Synthesis and Pathways
Angiotensin II (Ang II) is the primary active form of angiotensin. It is derived from angiotensinogen, a precursor protein produced in the liver. The conversion process involves several steps, starting with the cleavage of angiotensinogen by renin to form angiotensin I (Ang I). Ang I is then converted to Ang II by the angiotensin-converting enzyme (ACE) . This conversion can occur in various tissues, including the kidneys, brain, and adrenal glands.
Biological Roles
Ang II is a potent vasoconstrictor, meaning it can narrow blood vessels, thereby increasing blood pressure. It also stimulates the release of aldosterone from the adrenal glands, which promotes sodium retention and potassium excretion, further influencing blood pressure and fluid balance . Additionally, Ang II has been implicated in the progression of myocardial hypertrophy to heart failure, making it a significant target for therapeutic interventions .
Angiotensin Receptors: AT1 and AT2
AT1 Receptor
The AT1 receptor mediates most of the well-known actions of Ang II, including vasoconstriction, aldosterone release, and cellular growth. It is widely distributed in various tissues, such as vascular smooth muscle, adrenal glands, and kidneys. The activation of AT1 receptors leads to several intracellular signaling events, including the mobilization of intracellular calcium and activation of protein kinase C (PKC), which are crucial for its vasoconstrictive and hypertrophic effects .
AT2 Receptor
The AT2 receptor, although less understood, appears to counteract many of the effects mediated by the AT1 receptor. It is involved in processes such as anti-proliferation, cellular differentiation, apoptosis, and vasodilation. The balance between AT1 and AT2 receptor activities is essential for maintaining cardiovascular homeostasis.
Angiotensin-(1-7) and the ACE2/Ang-(1-7)/Mas Axis
Formation and Function
Angiotensin-(1-7) [Ang-(1-7)] is another bioactive peptide within the RAS, formed either directly from Ang II or through the intermediate Ang-(1-9) by the action of ACE2 . Unlike Ang II, Ang-(1-7) exerts vasodilatory, anti-proliferative, and anti-hypertensive effects, often opposing the actions of Ang II .
Receptor and Actions
The effects of Ang-(1-7) are mediated by the Mas receptor, a G protein-coupled receptor. Activation of the Mas receptor leads to various beneficial cardiovascular effects, including vasodilation and improved endothelial function . This counterregulatory pathway is significant in conditions like hypertension and heart failure, where the balance between Ang II and Ang-(1-7) can influence disease progression .
Angiotensin in the Brain and Behavior
Angiotensin also plays a role in the central nervous system, influencing behaviors such as thirst and sodium appetite. When Ang II is injected into specific brain regions, it can significantly increase water and sodium intake, highlighting its role in fluid and electrolyte homeostasis. The brain's response to Ang II involves complex interactions with various neuroanatomic structures, including the hypothalamus and brain stem.
Conclusion
Angiotensin, particularly Ang II, is a multifaceted hormone with critical roles in cardiovascular regulation, fluid balance, and cellular growth. The interplay between different angiotensin peptides and their receptors, such as the AT1, AT2, and Mas receptors, underscores the complexity of the renin-angiotensin system. Understanding these interactions is vital for developing targeted therapies for hypertension, heart failure, and other cardiovascular diseases.
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