Angiotensin

• Angiotensin refers to a family of peptides that play a critical role in regulating blood pressure, fluid balance, and electrolyte homeostasis.
• The most important member is Angiotensin II (Ang II).

Synthesis and Activation:

1. Renin Release: Produced by the kidneys in response to low blood pressure or low sodium levels.
2. Angiotensinogen Conversion: Renin converts angiotensinogen (produced by the liver) to angiotensins I (Ang I).
3. Angiotensin-Converting Enzyme (ACE): Converts Ang I to Ang II, primarily in the lungs.

Functions of Angiotensin II:

• Vasoconstriction: Increases systemic vascular resistance, raising blood pressure.
• Aldosterone Secretion: Stimulates the adrenal cortex to release aldosterone, promoting sodium and water retention by the kidneys.
• Antidiuretic Hormone (ADH) Release: Enhances water reabsorption in the kidneys.
• Sympathetic Nervous System Activation: Increases heart rate and vasoconstriction.
• Cardiac and Vascular Remodeling: Contributes to hypertrophy and fibrosis in chronic hypertension.

Receptors:

1. AT1 Receptors: Mediate most of the known effects of Ang II, including vasoconstriction and aldosterone secretion.
2. AT2 Receptors: Generally counter-regulate AT1 effects, involved in vasodilation and anti-proliferative actions.

Clinical Relevance of Angiotensin:

1. Hypertension Management: ACE inhibitors and angiotensins II receptor blockers (ARBs) are key antihypertensive agents.
2. Heart Failure and Chronic Kidney Disease: Modulating the renin-angiotensins-aldosterone system (RAAS) improves outcomes.

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