By Dr Ananya Mandal, MD
Angiotensin converting enzyme (ACE) inhibitors are used to decrease the activity of the renin-angiotensin-aldosterone system (RAAS) and lower blood pressure.
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 then 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. Renin released by the kidneys cleaves 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.
ACE inhibitors such as enalapril and captopril block the conversion of angiotensin I to angiotensin II and the effects of angiotensin II are therefore prevented. This leads to an increase in the amount of sodium and urine excreted, reduced resistance in kidney blood vessels, an increase in venous capacity and decreases in cardiac output, stroke work and volume.
Reviewed by Sally Robertson, BSc
Last Updated: Sep 11, 2014