Angiotensine

Angiotensin, sometimes written angiotensine in some languages, is a peptide hormone central to the renin-angiotensin system (RAS) that regulates blood pressure, vascular tone, and fluid balance. The system starts with the liver-produced precursor angiotensinogen. When renal and systemic signals indicate low blood pressure or low sodium delivery, the kidney’s juxtaglomerular cells release renin, which cleaves angiotensinogen to angiotensin I (Ang I). Angiotensin-converting enzyme (ACE), mainly present in lung endothelium, then converts Ang I to angiotensin II (Ang II), the primary active peptide. Other enzymes can generate Ang II and related fragments, such as chymases.

Ang II exerts diverse physiological effects. It causes vasoconstriction, increasing vascular resistance and blood pressure. It stimulates aldosterone secretion from the adrenal cortex, promoting sodium and water reabsorption in the kidney, and it can enhance antidiuretic hormone release and sympathetic activity. Receptor subtypes mediate these actions: AT1 receptors carry the majority of Ang II’s cardiovascular effects, while AT2 receptors may oppose some AT1 actions and contribute to development and repair processes.

Beyond Ang II, other angiotensin peptides participate in the system. Angiotensin III and Angiotensin IV arise from Ang II and have distinct roles; Ang III has vasopressor activity, whereas Ang IV binds to the AT4 receptor (also known as IRAP) and has been implicated in cognitive processes in some studies.

Clinically, the renin-angiotensin system is a key therapeutic target. Drugs that block Ang II formation or action, such as ACE inhibitors and angiotensin receptor blockers (ARBs), are widely used to treat hypertension, heart failure, and chronic kidney disease. Direct renin inhibitors are another approach. ACE inhibitors can increase bradykinin levels, contributing to cough or angioedema in some patients.