Angiotensin I/II (1-9) is a peptide (ASP-ARG-VAL-TYR-ILE-HIS-PRO-PHE-HIS) containing the amino acids 1-9 that are converted from Angiotensin I/II peptide.
Angiotensin I is formed by the action of renin on angiotensinogen, which has 12 amino acids and is an ǁ-2-globulin produced constitutively and released into the circulation mainly by the liver. Renin cleaves the peptide bond between the leucine (Leu) and valine (Val) residues on angiotensinogen, creating the ten-amino acid peptide angiotensin I. Angiotensin I is converted to angiotensin II (AII) through removal of two C-terminal residues by the enzymeangiotensin-converting enzyme (ACE), primarily through ACE within the lung.
Angiotensin is a peptide hormone that causes vasoconstriction and a subsequent increase in blood pressure. Angiotensin also stimulates the release of aldosterone, which promotes sodium retention in the distal nephron so that drives blood pressure up.
References:
1. Basso N, Terragno NA (December 2001). "History about the discovery of the renin-angiotensin system". Hypertension 38 (6): 1246-9.
2. Richard A. Preston. et. (1998). pAge-Race Subgroup Compared With Renin Profile as Predictors of Blood Pressure Response to Antihypertensive Therapyq. JAMA. 1998;280(13):1168-1172.
3. Williams GH, Dluhy RG (2008). "Chapter 336: Disorders of the Adrenal Cortex". In Loscalzo J, Fauci AS, Braunwald E, Kasper DL, Hauser SL, Longo DL. Harrison's principles of internal medicine. McGraw-Hill Medical.