angiotensin II

Angiotensin II is the body’s emergency “pressure booster.” When blood pressure or blood volume drops, this hormone springs into action to bring pressure back up by several routes at once, making it one of the most powerful blood-pressure-raising molecules in the body.

It is a short peptide produced by a two-step cleavage: the liver protein angiotensinogen is cut by renin to make angiotensin I, which is then cut by angiotensin-converting enzyme to make active angiotensin II. Acting through AT1 receptors, it tightens blood vessels to raise resistance, stimulates the adrenal gland to release aldosterone (which retains sodium and water), triggers thirst in the brain, and prompts vasopressin release. It also acts directly on the kidney to reabsorb sodium.

Because angiotensin II sits at the heart of blood-pressure control, it is a major drug target. ACE inhibitors block its production, and angiotensin-receptor blockers prevent it from binding its receptor; both lower blood pressure and protect the heart and kidneys. Its everyday job, though, is the constant fine-tuning of pressure and salt balance, not just crisis response.