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Brain natriuretic peptide or B-type natriuretic peptide (BNP) (also ventricular natriuretic peptide or natriuretic peptide B) is a 32-amino acid polypeptide secreted by the ventricles of the heart in response to excessive stretching of heart muscle cells (cardiomyocytes). The release of BNP is modulated by calcium ions. BNP is named as such because it was originally identified in extracts of porcine brain, although in humans it is produced mainly in the cardiac ventricles.
BNP is secreted attached to a 76–amino acid N-terminal fragment in the prohormone called NT-proBNP (BNPT), which is biologically inactive. Once released, BNP binds to and activates the atrial natriuretic factor receptors NPRA, and to a lesser extent NPRB, in a fashion similar to atrial natriuretic peptide (ANP) but with 10-fold lower affinity. The biological half-life of BNP, however, is twice as long as that of ANP, and that of NT-proBNP is even longer, making these peptides better targets than ANP for diagnostic blood testing.