Renin-Angiotensin-Aldosterone System (RAAS)
A hormonal cascade that regulates blood pressure, fluid balance, and electrolyte homeostasis through the peptide hormones angiotensin I and II and the steroid hormone aldosterone. RAAS biology intersects with several peptide therapeutic areas, including cardiovascular and renal disease management.
Technical Context
The RAAS cascade: renin (an aspartyl protease from renal juxtaglomerular cells) cleaves angiotensinogen (452 aa liver-derived protein) to angiotensin I (10 aa). ACE (angiotensin-converting enzyme, a metalloprotease on pulmonary endothelium) cleaves angiotensin I to angiotensin II (8 aa). Angiotensin II acts on AT1 receptors (vasoconstriction, aldosterone release, sodium retention, sympathetic activation) and AT2 receptors (vasodilation, anti-proliferative). ACE also degrades bradykinin, connecting the RAAS and kinin systems. ACE inhibitors and ARBs (angiotensin receptor blockers) are major cardiovascular drug classes. The RAAS demonstrates how a peptide signalling cascade can be therapeutically targeted at multiple points.