atrial natriuretic peptide

atrial natriuretic peptide - A substance produced in special cells in the muscular wall of the atria (see atrium) of the heart. Atrial natriuretic peptide is released into the bloodstream in response to swelling of the atrial muscle due, for example, to heart failure or hypertension. It lowers blood pressure by increasing the amount of sodium excreted in the urine, which reduces blood volume.