Angiotensin

Angiotensinogen

Renin-angiotensin-aldosterone system

Angiotensin is a peptide hormone that plays a crucial role in the regulation of blood pressure, fluid balance, and sodium homeostasis in the body. It is part of the renin-angiotensin system (RAS), a hormone system that regulates blood pressure and fluid balance. When blood pressure is low, the liver releases a protein called angiotensinogen. This protein is then converted by renin, an enzyme produced by the kidneys, into angiotensin I, an inactive decapeptide. Angiotensin I is subsequently converted into angiotensin II by angiotensin-converting enzyme (ACE), which is found in the lungs and other tissues.

Angiotensin II is a potent vasoconstrictor, meaning it narrows the blood vessels, which increases blood pressure. It also stimulates the release of aldosterone from the adrenal glands and antidiuretic hormone (ADH) from the pituitary gland, leading to increased absorption of sodium and water by the kidneys, further increasing blood pressure and blood volume. Additionally, angiotensin II affects the sympathetic nervous system, enhancing the release of norepinephrine, which also contributes to vasoconstriction.

The regulation of angiotensin is critical for maintaining blood pressure within a normal range. Dysregulation of the renin-angiotensin system can lead to hypertension (high blood pressure), which is a risk factor for heart disease, stroke, and kidney failure. Drugs that inhibit the production or actions of angiotensin II, such as ACE inhibitors and angiotensin II receptor blockers (ARBs), are commonly used to treat hypertension and heart failure.

Classification

Angiotensin peptides are classified based on their amino acid length and function:

• Angiotensin I: A decapeptide that is the precursor to angiotensin II.
• Angiotensin II: An octapeptide that is the most active form, involved in vasoconstriction and increasing blood pressure.
• Angiotensin III: A heptapeptide that also has some activity in stimulating aldosterone release but is less potent than angiotensin II.
• Angiotensin IV: A hexapeptide with roles in blood flow and neurological function.

Function

The primary functions of angiotensin include:

• Regulation of blood pressure and volume
• Regulation of sodium and water reabsorption by the kidneys
• Stimulation of aldosterone secretion
• Modulation of sympathetic nervous system activity

Clinical Significance

Angiotensin plays a significant role in the pathophysiology of several cardiovascular and renal diseases. Its overactivity can lead to hypertension, heart failure, and chronic kidney disease. Therefore, the renin-angiotensin system is a common target for cardiovascular and renal therapeutics.

Therapeutic Use

Medications that target the renin-angiotensin system include:

• ACE inhibitors: Block the conversion of angiotensin I to angiotensin II, lowering blood pressure.
• Angiotensin II receptor blockers (ARBs): Prevent angiotensin II from binding to its receptor, also lowering blood pressure.
• Renin inhibitors: Block the activity of renin, reducing the production of angiotensin I and II.

See Also

• Hypertension
• Heart failure
• Renin-angiotensin system
• Aldosterone
• Vasoconstriction