Angiotensin II is the active form of angiotensin, which is a peptide instrumental in the constriction of blood vessels and the resulting hypertension, or high blood pressure. The renin-angiotensin system is partially named after this agent, as it is one of this system’s major components. Sometimes abbreviated as RAS, the renin-angiotensin system regulates not only the body’s blood pressure, but its extracellular volume, or substances outside the cells, as well.
Specifically, angiotensin belongs to a peptide subdivision called oligopeptide, which means that it is formed by a limited number of amino acids, usually between two and 20. It traces its origin to a globular protein called angiotensinogen, which is produced by the liver. Upon release into the blood from the liver, angiotensinogen interacts with renin, which is a protein-digesting enzyme released by the kidneys. Renin is responsible for turning angiotensinogen into angiotensin I, thus completing the first part of the transformation process to angiotensin II.
Angiotensin I is not active until it is turned into angiotensin II. This occurs when the angiotensin-converting enzyme (ACE), found in the lungs’ capillaries, removes two of the angiotensin’s C-terminal residues. This peptide is the most active form, as the other forms, angiotensin III and IV, have lessened activity.
Increased blood pressure is the medical condition most commonly associated with angiotensin II. It accomplishes this by narrowing the blood vessels, primarily the arteries. This process and condition is known as vasoconstriction, or arterial vasoconstriction. The constricted passageways limit blood flow and cause blood pressure to jump up.
Additionally, the peptide releases aldosterone. Since this particular hormone carries out the reabsorption of sodium and water from the kidneys, such a task leads to an increase to the body’s extracellular volume. It also contributes to hypertension and the heightened risk of kidney problems or failure.
In direct response to the actions of the peptide, scientists have developed a group of pharmaceuticals called angiotensin II receptor antagonists, or angiotensin receptor blockers (ARBs). These include candesartan, losartan, irbesartan and valsartann. They are designed to suppress angiotensin II. Besides hypertension, ARBs are used for prevention of other diseases such as diabetic nephropathy, a type of progressive kidney disease caused by diabetes; and congestive heart failure, which is when the heart does not provide sufficient blood flow to the parts of the body for normal function.