Angiotensin II is a small protein (peptide) that has a wide range of biological effects. In general, however, the effects of angiotensin II all work to increase blood pressure. For this reason, angiotensin II has become an attractive target for researchers looking for ways to lower blood pressure. Simply put, if you can give a drug that interferes with angiotensin II, you can lower someone’s blood pressure.
Side Effects of Angiotensin II Medications
ACE inhibitors may cause several side effects, some of which may keep patients from taking them. ACE
inhibitors may cause hypotension (abnormally low blood pressure), increased potassium levels in the blood, and kidney problems. One of the more troubling and persistent side effects of ACE inhibitors is a dry cough. In rare cases, ACE inhibitors may cause a severe swelling of the mouth and throat called angioedema.
ARBs may cause the same side effects as ACE inhibitors. ARBs are less likely to cause cough than ACE inhibitors, but ARBs are more likely to cause hypotension. The risk of angioedema is lower with ARBs than with ACE inhibitors.
The Many Actions of Angiotensin II
Angiotensin II is the active molecule in the renin-angiotensin-aldosterone system. It binds to angiotensin II receptors throughout the body. When these receptors are activated, they create specific biological effects.
Angiotensin II has four major actions:
Blood vessel constriction – Angiotensin II constricts small blood vessels called arterioles
Sympathetic nervous system stimulation – The sympathetic nervous system controls the “fight or flight” response (e.g. increases heart rate)
Aldosterone secretion – Angiotensin II binds to receptors in the adrenal gland and increases secretion of the hormone aldosterone. Aldosterone keeps water and sodium in the bloodstream, among other effects.
Antidiuretic hormone secretion – Angiotensin II stimulates the pituitary gland to release antidiuretic hormone (ADH). ADH acts in the kidneys to retain water.
Taken together, angiotensin II can potently increase blood pressure by increasing water and sodium (blood volume), increasing heart rate, and constricting blood vessels.
How Does the Body Make Angiotensin II?
Since it is so potent, angiotensin II is only produced after a series of enzymatic changes in various organs. First, the liver produces angiotensinogen and releases it into the blood. Angiotensinogen travels to the liver, where another enzyme called renin converts angiotensinogen into angiotensin I. Angiotensin I then moves to the lung, where it encounters angiotensin-converting enzyme (ACE). ACE then converts angiotensin I into angiotensin II, then active molecule.
Angiotensin II as a Target for Blood Pressure Control
While the regulation of angiotensin II is complex, understanding this complex system has allowed researchers to discover two major classes of blood pressure lowering drugs: ACE inhibitors and angiotensin II receptor blockers (ARBs).
As the name suggests, ACE inhibitors block the action of angiotensin-converting enzyme. This prevents angiotensin I from becoming angiotensin II. An ARB directly blocks angiotensin II receptors. This prevents any angiotensin II in the body from binding to receptors and increasing blood pressure.
Am I Taking an Angiotensin II Medication?
Fortunately, all ACE inhibitors and all ARBs have the same suffix, making it easy to identify them. ACE inhibitors end in the suffix –pril and ARBs end in the suffix –sartan.
Angiotensin II receptor blockers (ARBs)