Angiotensinogen is a protein in the blood that is produced by the liver. It is the precursor to angiotensin, a peptide hormone that plays an important role in regulating blood pressure and fluid balance in the body. Synonyms for angiotensinogen include pre-angiotensinogen, renin substrate, serpin A8, and AGT. Pre-angiotensinogen and renin substrate both refer to the fact that angiotensinogen is converted into angiotensin through the action of renin, an enzyme produced by the kidneys. Serpin A8 is a reference to the fact that angiotensinogen is a member of the serine protease inhibitor family of proteins, while AGT is simply an abbreviation of angiotensinogen.