Renin

Renin, also known as an angiotensinogenase, is an enzyme that participates in the body's renin-angiotensin aldosterone system (RAAS)—also known as the renin-angiotensin-aldosterone axis—that mediates extracellular volume (i.e., that of the blood plasma, lymph and interstitial fluid), and arterial vasoconstriction. Thus, it regulates the body's mean arterial blood pressure. Renin is often improperly referred to as a hormone even though it has no peripheral receptors and rather has an enzymatic activity with which it hydrolyses angiotensinogen to angiotensin I.