Renin, or angiotensinogenase, is an enzyme released by the juxtaglomerular cells of the kidney. It takes part in the body's renin-angiotensin system (RAS) that mediates extracellular volume and arterial vasoconstriction. Thus renin regulates the body's mean arterial blood pressure. A test can be done to measure the amount of renin in the blood.
Renin is released when the sodium levels in the body, or blood volume, has decreased. Renin also plays an important role in the release of aldosterone, a hormone that helps control the body's salt and water balance.
The primary structure of renin precursor consists of 406 amino acids with a pre- and a pro- segment carrying 20 and 46 amino acids respectively. Mature renin contains 340 amino acids and has a mass of 37 kDa. Renin circulates in the blood stream and breaks down (hydrolyzes) angiotensinogen secreted from the liver into the peptide angiotensin I.