Lisinopril is an ACE inhibitor, meaning it blocks the actions of angiotensin-converting enzyme (ACE) in the renin–angiotensin–aldosterone system (RAAS), preventing angiotensin I from being converted to angiotensin II. Angiotensin II is a potent direct vasoconstrictor and a stimulator of aldosterone release. Reduction in the amount of angiotensin II results in relaxation of the arterioles. Reduction in the amount of angiotensin II also reduces the release of aldosterone from the adrenal cortex, which allows the kidney to excrete sodium along with water into the urine, and increases retention of potassium ions. Specifically, this process occurs in the peritubular capillaries of the kidneys in response to a change in Starling forces. The inhibition of the RAAS system causes an overall decrease in blood pressure.