Serpin A8 also known as angiotensinogen (AGT) , is a member of the serpin family. It is an ¦Á-2-globulin that is expressed by the liver and secreted in plasma. As essential component of the renin-angiotensin system (RAS), Angiotensinogen is cleaved into three chains: Angiotensin-1 (Ang I), Angiotensin-2 (Ang II), and Angiotensin-3 (Ang III) in lowered blood pressure by the enzyme renin. Angiotensin-1 is a substrate of ACE (angiotensin converting enzyme) that removes a dipeptide to yield the physiologically active peptide angiotensin-2. Angiotensin-2 acts directly on vascular smooth muscle as a potent vasoconstrictor, affects cardiac contractility and heart rate through its action on the sympathetic nervous system, and alters renal sodium and water absorption through its ability to stimulate the zona glomerulosa cells of the adrenal cortex to synthesize and secrete aldosterone. Angiotensin-3 stimulates aldosterone release. Defects in AGT are a cause of renal tubular dysgenesis (RTD).