What is angiotensin?
Angiotensin is a naturally produced hormone that forms part of a complex interaction of hormones, known as the renin-angiotensin hormone system that regulates blood volume, body fluid levels and blood pressure. Angiotensin is produced by the liver as angiotensinogen, which is converted to angiotensin I by the action of renin, released by the kidney when blood pressure and volume is low. Angiotensin I is the inactive precursor for Angiotensin II, which is produced by the action of Angiotensin Converting Enzyme (ACE) mainly in the lungs, but also in the kidney and endothelial cells lining the blood vessels.
Angiotensin II is a highly vasoactive hormone that has potent effects on blood pressure and fluid balance. It stimulates vascular smooth muscle to contract, which causes blood vessels to constrict (narrow). This increases blood volume while at the same time reducing blood vessel volume, which increases blood pressure. Angiotensin II also stimulates the production of the hormone aldosterone from the adrenal gland. Aldosterone stimulates the tubule cells of the kidney to reabsorb salt (sodium and potassium) and water from the blood, which also increase blood volume and pressure.
ACE also degrades the enzyme bradykinin, which is a potent vasoldilator, and this action of ACE further increases blood pressure.
ACE inhibitors for hypertension and heart failure
If the renin-angiotensin is out of balance, then blood pressure will remain too high and can result in hypertension, heart failure and kidney failure. This is why angiotensin is the target of several drugs for cardiovascular disease, including ACE inhibitors that prevent the formation of angiotensin II from Angiotensin I.
ACE inhibitors are used to treat hypertension and congestive heart failure and work by inhibiting the action of Angiotensin Converting Enzyme and this action reduces blood volume, widens blood vessels and lowers blood pressure. They also reduce the production of aldosterone, which reduces uptake of salt and water by the kidneys and reduces blood volume and fluid retention in the tissues. ACE inhibitors also prevent the degradation of bradykinin, which further lowers blood pressure.
The combined actions of ACE inhibitors reduces the force needed for the heart to pump blood around the body and helps weakened heart muscle to work more efficiently, also reducing excess water that is retained in body tissues causing swelling (oedema), as a result of congestive heart failure.