Angiotensin ii

Angiotensin II is a peptide hormone that plays a crucial role in the RAS (Renin-Angiotensin System). It is a potent vasoconstrictor, which means it can narrow (constrict) the blood vessels, thereby increasing blood pressure. Angiotensin II also stimulates the release of aldosterone, a hormone that promotes sodium retention in the kidneys, which also drives blood pressure up.

Biochemistry

Angiotensin II is derived from angiotensin I through the action of angiotensin-converting enzyme (ACE). Angiotensin I is itself produced by the action of renin, an enzyme produced in the kidneys, on a protein called angiotensinogen, which is produced and released into the bloodstream by the liver.

Physiological Effects

Angiotensin II has several effects on the body, all of which contribute to its role in maintaining blood pressure and fluid balance. These include:

• Vasoconstriction: Angiotensin II causes the muscles surrounding blood vessels to contract, narrowing the vessels and increasing blood pressure.
• Aldosterone secretion: Angiotensin II stimulates the adrenal glands to release aldosterone, a hormone that causes the kidneys to retain sodium and water, increasing blood volume and pressure.
• Thirst stimulation: Angiotensin II can stimulate the sensation of thirst, encouraging fluid intake and further contributing to blood volume and pressure.
• Release of vasopressin: Angiotensin II can stimulate the release of vasopressin (also known as antidiuretic hormone or ADH), another hormone that promotes water retention in the kidneys.

Clinical Significance

Due to its role in blood pressure regulation, angiotensin II is a target for several types of cardiovascular drugs, including ACE inhibitors and angiotensin II receptor blockers (ARBs). These drugs are used to treat conditions such as hypertension (high blood pressure), heart failure, and kidney disease in diabetes.

See Also

• Renin–angiotensin system
• Angiotensin-converting enzyme
• ACE inhibitors
• Angiotensin II receptor blockers