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:
Renin Release: Produced by the kidneys in response to low blood pressure or low sodium levels.
Angiotensinogen Conversion: Renin converts angiotensinogen (produced by the liver) to angiotensin I (Ang I).
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:
AT1 Receptors: Mediate most of the known effects of Ang II, including vasoconstriction and aldosterone secretion.
AT2 Receptors: Generally counter-regulate AT1 effects, involved in vasodilation and anti-proliferative actions.
Clinical Relevance:
Hypertension Management: ACE inhibitors and angiotensin II receptor blockers (ARBs) are key antihypertensive agents.
Heart Failure and Chronic Kidney Disease: Modulating the renin-angiotensin-aldosterone system (RAAS) improves outcomes.