In the RAS cascade, the hormone angiotensinogen is converted to angiotensin I by the enzyme renin, and angiotensin I is then converted to the powerful vasoconstrictor angiotensin II by angiotensin-converting enzyme (ACE). This enzyme is found on the surface of endothelial cells in blood vessels.
Angiotensin II, a key component of the RAS system, binds to two receptors: the angiotensin-1 receptor (AT-1) and the angiotensin-2 (AT-2) receptor.
The AT-1 receptor mediates the classical actions of angiotensin II, including constriction of blood vessels, sodium retention, and cell growth. However, one consequence of AT-1 receptor activation is an increase in fibroblasts, resulting in fibrosis. Conversely, AT-2 receptor activation promotes dilatation of blood vessels, inhibition of cell growth and cell death, and is considered to play a beneficial regulatory role to the effects of AT-1 receptor activation.