Any of several peptide hormones that promote the excretion of sodium ions in the urine (i.e. natriuresis). The first to be discovered was atrial natriuretic peptide (ANP), which is produced by an upper chamber (atrium) of the heart. ANP is released from atrial muscle cells in response to various factors, including stretching of the atrial walls, raised concentration of sodium in the blood, angiotenism II, and stimulation of β‎-adrenoceptors. The overall effects are a decrease in blood volume and lowering of cardiac output and blood pressure. Brain natriuretic peptide (BNP, or B-type natriuretic peptide) is released in the brain and also the heart ventricles in response to stretching of the chambers; it has vasodilator and natriuretic properties, and levels increase markedly in cases of heart failure. C-type natriuretic peptide (CNP) is produced more generally in the cardiovascular system and serves as a regulator of vascular tone and growth.