An octapeptide (eight-amino acid peptide) angiotensin derived from the inactive form, angiotensin I, and is involved in producing vasoconstriction and increased blood pressure
Angiotensin is an oligopeptide hormone that plays a part in the regulation of blood pressure. It particularly causes vasoconstriction, which in turn results in an increase in blood pressure. There are different forms of angiotensin. The initial inactive form is angiotensin I. It is a decapeptide derived from angiotensinogen. The angiotensinogen released into the plasma is converted into angiotensin I through the action of renin. The angiotensin I is cleaved again and converted into the octapeptide angiotensin II through the action of the angiotensin-converting enzyme (ACE). 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 contraction. This role of angiotensin II brings about the increased blood pressure. Angiotensin II is also involved in the release of aldosterone from the adrenal glands.
Angiotensin II is converted to angiotensin III through angiotensinases.
The clinically and experimentally used bovine form has valine in position 5 where the human form has isoleucine. As a medication, it acts as a vasoconstrictor agent.