Atrial natriuretic peptide (ANP), atrial natriuretic factor (ANF), or atriopeptin, is a polypeptide hormone involved in the homeostatic control of body water, sodium, and adiposity. It is released by atrial myocytes, muscle cells in the atria of the heart, in response to high blood pressure. ANP acts to reduce the water, sodium and adipose loads on the circulatory system, thereby reducing blood pressure. ANP is a 28 amino acid peptide with a 17 amino acid ring in the middle of the molecule. The ring is formed by a disulfide bond between two cysteine residues at positions 7 and 23. ANP is closely related to BNP (brain natriuretic peptide) and CNP (C-type natriuretic peptide) which all share the same amino acid ring.

ANP is produced, stored and released by atrial myocytes, muscle cells in the atria of the heart. It is released in response to a variety of signals induced by hypervolaemia, exercise or caloric restriction. ANP is secreted in response to:
[1]. Atrial distention, stretching of the vessel walls.
[2]. Sympathetic stimulation of β-adrenoceptors.
[3].Raised sodium concentration (hypernatremia)
[4] Angiotensin-II
[5]. Endothelin, a potent vasoconstrictor

ANP binds to a specific set of receptors. Receptor-agonist binding causes a reduction in blood volume and therefore a reduction in cardiac output and systemic blood pressure. Lipolysis and renal sodium secretion and excretion are also increased. The overall effect of ANP on the body is to counter increases in blood pressure and volume caused by the renin-angiotensin system.

Mediation of the effects of ANP is achieved through gradual degradation of the peptide by the enzyme neutral endopeptidase (NEP). Recently NEP inhibitors have been developed, although they have not yet been licensed. They may be clinically useful in treating congestive heart disease.