Brain natriuretic peptide 32
Brain natriuretic peptide 32
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Brain natriuretic peptide 32

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Brain natriuretic peptide 32

Brain natriuretic peptide (BNP), also known as B-type natriuretic peptide, is a peptide hormone secreted by cardiomyocytes in the heart ventricles in response to stretching caused by increased ventricular blood volume. BNP is one of the three natriuretic peptides, in addition to atrial natriuretic peptide (ANP) and C-type natriuretic peptide (CNP). BNP was first discovered in porcine brain tissue in 1988, which led to its initial naming as "brain natriuretic peptide", although subsequent research revealed that BNP is primarily produced and secreted by the ventricular myocardium (heart muscle) in response to increased ventricular blood volume and stretching. To reflect its true source, BNP is now often referred to as "B-type natriuretic peptide" while retaining the same acronym.

The 32-amino acid polypeptide BNP-32 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 receptor 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.

The physiologic actions of BNP are similar to those of ANP and include decrease in systemic vascular resistance and central venous pressure as well as an increase in natriuresis. The net effect of these peptides is a decrease in blood pressure due to the decrease in systemic vascular resistance and, thus, afterload. Additionally, the actions of both BNP and ANP result in a decrease in cardiac output due to an overall decrease in central venous pressure and preload as a result of the reduction in blood volume that follows natriuresis and diuresis.

BNP is synthesized as a 134-amino acid preprohormone (preproBNP), encoded by the human gene NPPB. Removal of the 26-residue N-terminal signal peptide generates the prohormone, proBNP, which is stored intracellularly as an O-linked glycoprotein; proBNP is subsequently cleaved between arginine-102 and serine-103 by a specific convertase (probably furin or corin) into NT-proBNP and the biologically active 32-amino acid polypeptide BNP-32, which are secreted into the blood in equimolar amounts. Cleavage at other sites produces shorter BNP peptides with unknown biological activity. Processing of proBNP may be regulated by O-glycosylation of residues near the cleavage sites. The synthesis of BNP in cardiomyocytes is stimulated by pro-inflammatory cell factors, such as interleukin-1β, interleukin-6 and tumor necrosis factor-α.

BNP decreases sodium reabsorption in the distal convoluted tubule (interaction with NCC) and cortical collecting duct of the nephron via guanosine 3',5'-cyclic monophosphate (cGMP) dependent phosphorylation of ENaC.

BNP and NT-proBNP are measured by immunoassay.

A preoperative BNP can be predictive of a risk of an acute cardiac event during vascular surgery. A cutoff of 100 pg/ml has a sensitivity of approximately 100%, a negative predictive value of approximately 100%, a specificity of 90%, and a positive predictive value of 78% according to data from the United Kingdom.

BNP is cleared by binding to natriuretic peptide receptors (NPRs) and neutral endopeptidase (NEP). Less than 5% of BNP is cleared renally. NT-proBNP is the inactive molecule resulting from cleavage of the prohormone Pro-BNP and is reliant solely on the kidney for excretion. The achilles heel of the NT-proBNP molecule is the overlap in kidney disease in the heart failure patient population.

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