Atrial natriuretic peptide (ANP), atrial natriuretic factor (ANF), atrial natriuretic hormone (ANH), or atriopeptin, is a powerful vasodilator, and a polypeptide hormone secreted by heart muscle cells. It is involved in the homeostatic control of body water, sodium, potassium and fat (adipose tissue). It is released by muscle cells in the upper chambers (atria) of the heart (atrial myocytes) 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 was discovered in 1981 by a team in Kingston, Ontario, Canada after they made the seminal observation that injection of atrial (but not ventricular) tissue extracts into rats caused copious natriuresis.
ANP is produced, stored and released by cardiac myocytes of the atria of the heart. It is released in response to atrial stretch and a variety of other signals induced by hypervolemia, exercise or caloric restriction. The hormone is constitutively expressed in the ventricle in response to stress induced by increased afterload (e.g. increased ventricular pressure from aortic stenosis) or injury (e.g. myocardial infarction).
ANP is secreted in response to:
- Atrial distention, stretching of the vessel walls
- Sympathetic stimulation of β-adrenoceptors
- Raised sodium concentration (hypernatremia), though sodium concentration is not the direct stimulus for increased ANP secretion
- Endothelin, a potent vasoconstrictor
The atria become distended by high extracellular fluid and blood volume, and atrial fibrillation. Notably, ANP secretion increases in response to immersion of the body in water, which causes atrial stretch due to an altered distribution of intravascular fluid. ANP secretion in response to exercise has also been demonstrated in horses.
Four peptide hormones [e.g., atrial natriuretic peptide (ANP), long-acting natriuretic peptide (LANP), vessel dilator, and kaliuretic peptide] are synthesized by this gene. Each of these peptide hormones has biological effects, e.g., natriuresis and diuresis, mediated via the kidney. LANH, long-acting natriuretic hormone (a different nomenclature for LANP); a.a., amino acids.
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