A peptide formed from the action of the ENZYME, RENIN on alpha globulin (a protein) produced by the liver and passed into the blood. During passage of the blood through the lungs, the peptide (called angiotensin I) is converted into an active form, angiotensin II. This active form constricts blood vessels and stimulates the release of two hormones – VASOPRESSIN and ALDOSTERONE – which raise blood pressure. (See also ANGIOTENSIN-CONVERTING ENZYME (ACE) INHIBITORS.)