Angiotensin I (human, mouse, rat) is the precursor to the vasoconstrictor peptide angiotensin II, cleaved by the angiotensin-converting enzyme (ACE).Angiotensin is a peptide hormone that causes vasoconstriction and an increase in blood pressure. It is part of the renin–angiotensin system, which regulates blood pressure. Angiotensin also stimulates the release of aldosterone from the adrenal cortex to promote sodium retention by the kidneys.