angiotensiin

Angiotensin is a peptide hormone that forms part of the renin–angiotensin system, a hormonal cascade that regulates blood pressure and fluid and electrolyte balance. The liver continuously secretes angiotensinogen, a large precursor protein. When the kidneys detect reduced renal perfusion, juxtaglomerular cells release renin, which cleaves angiotensinogen to form angiotensin I. Angiotensin-converting enzyme (ACE), mainly in pulmonary endothelium, then converts angiotensin I to the active peptide angiotensin II. Additional enzymes also generate angiotensin II in some tissues.

Angiotensin II is the main effector peptide. It constricts arterioles, increasing systemic vascular resistance, and stimulates aldosterone release from the adrenal cortex, promoting sodium and water reabsorption in the distal nephron. It also stimulates antidiuretic hormone release and can enhance sympathetic activity. Angiotensin II signals primarily via the AT1 receptor to produce these effects; AT2 receptor activation may oppose some actions or contribute to development and repair.

Other angiotensin peptides include angiotensin I and II, angiotensin III and IV, and angiotensin-(1-7). Angiotensin-(1-7), generated in part by ACE2, often counteracts angiotensin II by promoting vasodilation through the Mas receptor, contributing to protective cardiovascular and renal effects.

Clinical relevance: Excess renin–angiotensin system activity is linked to hypertension, heart failure, and chronic kidney disease. Therapies include ACE inhibitors (for example, enalapril), angiotensin II receptor blockers (ARBs, for example, losartan), and direct renin inhibitors (aliskiren). Aldosterone antagonists (spironolactone, eplerenone) may be used in certain conditions. The system is tightly regulated, and disturbances can be harmful; pregnancy is particularly sensitive to RAS-modulating drugs.