Angiotensin is an oligopeptide in the blood that causes 
vasoconstriction, increased blood pressure, and release of 
aldosterone from the adrenal cortex. It is a powerful 
dipsogen. It is derived from the precursor molecule 
angiotensinogen, a serum globulin produced in the liver. It 
plays an important role in the renin-angiotensin system.

Angiotensinogen is an α-2-globulin that is produced 
constitutively and released into the circulation mainly by 
the liver, although other sites are thought to be involved 
also. It is a member of the serpin family, although it is 
not known to inhibit other enzymes, unlike most serpins. 
Plasma angiotensinogen levels are increased by plasma 
corticosteroid, estrogen, thyroid hormone, and angiotensin 
II levels.

Angiotensinogen consist of 453 amino acid residues.