noun, plural: angiotensins
A family of oligopeptides associated with increased blood pressure, mainly by causing vasoconstriction
Angiotensin is a family of oligopeptides known for their regulation of blood pressure. They range in the length of the amino acids in a peptide chain. The amino acid content also varies and changes in that content produce antagonistic or inactive compounds. Members of this family include angiotensin I, angiotensin II, angiotensin III, and angiotensin IV.
The angiotensin I, a ten-amino acid peptide (decapeptide), is the initial inactive form. It is derived from angiotensinogen (precursor). The precursor is a 60 kd polypeptide released mainly from the liver into the plasma where it is converted to angiotensin I through the action of renin. The renin cleaves the peptide bond between leucine and valine residues of angiotensinogen.
The angiotensin I is cleaved again via the action of the angiotensin-converting enzyme (ACE), converting it into angiotensin II (and thereby resulting in the latter being comprised of eight amino acids). The angiotensin II is an active form of angiotensin that is directly involved in the contraction of vascular smooth muscle. It does so by activating the Gq protein in vascular smooth muscle cell, which leads to the activation of the IP3-dependent mechanism. This leads to an increase in intracellular calcium levels, resulting in the vascular smooth muscle contraction. This role of angiotensin II brings about the increased blood pressure. Angiotensin II also stimulates the release of aldosterone from the adrenal glands.
Angiotensin III is involved mainly in activities causing the production of aldosterone whereas angiotensin IV is involved in activities in the central nervous system.