Angiotensin II receptor antagonists are agents used to modify the renin-angiotensin-aldosterone system (RAAS) through blocking angiotensin receptors. This has the effect of lowering blood pressure.
Angiotensin II exerts its effects through binding to angiotensin II receptors and blocking these receptors therefore inhibits the actions of this hormone. Angiotensin II is mainly used in the treatment of high blood pressure (hypertension), diabetic kidney disease and congestive heart failure.
The RAAS is a complex physiological system that controls fluctuations in blood pressure. A protein called renin is released by the juxtaglomerular apparatus in the kidneys. Renin produces angiotensin, the active form of which stimulates the adrenal gland to produce a hormone called aldosterone. Aldosterone stimulates the reabsorption of water and conservation of sodium, therefore increasing water retention and blood pressure.
The RAAS is activated when blood pressure falls or when a disruption of the salt-water balance is indicated by a low blood volume or a low concentration of sodium in the kidney, for example. The kidneys then release renin, which goes on to cleave the first 10 amino acids present on the angiotensin protein. These cleaved residues are referred to as angiotensin I, which is converted by ACE into angiotensin II through the removal of a further two amino acids. Angiotensin II is the potent, active form of angiotensin that can stimulate aldosterone release.
Angiotensin-converting-enzyme (ACE inhibitors) are another form of medication used to modify the RAAS system but the effects of blocking angiotensin II receptors is more potent. In some cases, a combination of angiotensin II receptor antagonists and ACE inhibitors is used to treat patients.
Angiotensin II receptor antagonists are well absorbed after oral administration and can be taken in the form of tablets. Common side effects include dizziness, hyperkalemia and headache, while less common side effects are diarrhea, liver dysfunction, back pain, muscle cramp, renal impairment and nasal congestion.