Brain natriuretic peptide (BNP) is a 32 amino acid polypeptide that is secreted by the ventricles of the heart in response to stretching of heart muscles1.
BNP was first discovered in porcine brain extracts based on its resemblance to atrial natriuretic peptide (a hormone secreted by mammalian atria) 1.
BNP belongs to the natriuretic family of peptides that contain three structurally related paracrine factors: Atrial, Brain and C-type natruirectic peptides2. Both atrial and brain natriuretic peptides are secreted in the atria and ventricles of the heart while C-type peptide is secreted in the bone2. BNP is co-secreted along with a 76 amino acid N-terminal fragment (NT-proBNP) which is biologically inactive3. 
clipped from: bio-synthesis.blogspot.com