angiotensin

either of two peptides: angiotensin I or angiotensin II. Angiotensin I is derived, by the action of the enzyme RENIN , from a protein (alpha globulin) secreted by the liver into the bloodstream. As blood passes through the lungs, another enzyme acts on angiotensin I to form angiotensin II. This peptide causes constriction of blood vessels and stimulates the release of the hormones VASOPRESSIN and ALDOSTERONE , which increase blood pressure. See also ACE INHIBITOR , ANGIOTENSIN II ANTAGONIST .