Natriuretic Peptide B Type Test

Natriuretic peptides are key proteins that improve and regulate circulation. These proteins are essential for acting on blood vessels, causing them to widen or dilate. Natriuretic peptides are expressed predominantly by cardiomyocytes of the mixed secretory-contractile phenotype in atrial and ventricular walls. In addition to regulating blood pressure, natriuretic peptides inhibit cardiac hypertrophy and remodeling. In patients with decompensated heart failure due to volume overload, a treatment-induced drop in wedge pressure is often accompanied by a rapid drop in natriuretic peptide levels. Measurement of natriuretic peptide levels may thus assist with hemodynamic assessment and subsequent treatment titration. Natriuretic peptides can also be found in the kidneys and can cause the kidneys to excrete more water and salt.  B-type natriuretic peptide (BNP) was initially identified in porcine brain tissue in 1988 and was previously referred to as the brain natriuretic peptide. However, researchers later discovered that the primary site of BNP release is cardiac ventricular cells, particularly in response to ventricular distention. Following this discovery, a substantial body of literature emerged regarding the use of BNP as a potential biomarker to measure the presence and severity of heart failure. BNP is a member of the natriuretic peptide family that includes atrial natriuretic peptide (ANP), C-type natriuretic peptide, D-type natriuretic peptide, and urodilatin. ProBNP is a 108-amino acid precursor protein of BNP found in the ventricles and atria of the heart. Human ANP and BNP are encoded by genes located on chromosome 1. In situations of volume overload and myocardial muscle stretching, proBNP is upregulated at the genomic level. A small amount of BNP is found in the cytoplasmic granules of myocytes. Upon stimulation for production and release, proBNP is cleaved by corin to equimolar amounts of the biologically active BNP hormone and the biologically inactive amino-terminal proBNP (NT-proBNP), which is also released into circulation as the unprocessed precursor protein. When evaluating its effects on vascular smooth muscle cells, cardiac fibroblasts, and myocytes, this peptide does not appear to have any biological activity. C-type natriuretic peptide is primarily synthesized in the central nervous system. This peptide is also found in vascular endothelial cells and may play a role in the local regulation of vascular tone. Unlike ANP and BNP, the human gene encoding CNP, , is not located on chromosome 1 but on chromosome 2. In normal human subjects, the mean concentration of CNP is very low (1 fmol/mL). CNP levels are elevated in patients with heart failure, albeit to a much lower extent than ANP and BNP. The clearance of CNP-22 in human plasma is very rapid, with a calculated half-life of 2.6 minutes. The natriuretic peptide system comprises 3 receptors—natriuretic peptide receptor-A (NPR-A), natriuretic peptide receptor-B (NPR-B), and natriuretic peptide receptor-C (NPR-C). The human NPR-A gene is located on chromosome 1q21-22 and comprises 22 exons and 21 introns spanning approximately 16 kilobases. The human NPR-B gene is located on chromosome 9p12-21, and the murine version, , is located on chromosome 4. The human NPR-C gene is located on chromosome 5p13-14 and contains 8 exons and 7 introns spanning more than 65 kilobases. The natriuretic peptide receptors NPR-A and NPR-B catalyze the synthesis of a classic intracellular second messenger, cyclic guanosine monophosphate (cGMP). cGMP binds to proteins such as cGMP-dependent protein kinases, cGMP-binding phosphodiesterases, and cyclic nucleotide-gated ion channels. NPR-C controls the concentrations of natriuretic peptides through receptor-mediated internalization and degradation. An NPR-A to NPR-C ratio plays a role in regulating the biological activity of natriuretic peptides.