Characterization of immunoreactive brain natriuretic peptide in human cardiac atrium

Based on cDNA sequence data for human brain natriuretic peptide (BNP) precursor (1), a radioimmunoassay (RIA) system highly specific to human BNP (hBNP) was developed and used to characterize immunoreactive (ir-) hBNP in cardiac atrium. Gel filtration of ir-hBNP in atrium indicated that ir-hBNP was mainly comprised of two molecular forms of 13-15K and 4K. In reverse phase high performance liquid chromatography (HPLC), the low molecular weight (MW) ir-hBNP emerged as a single peak at an elution time identical to that of synthetic hBNP-32. The high MW ir-hBNP was also eluted as a single peak. On the other hand, tissue concentrations of ir-hBNP in cardiac atria were found to be 9.98-593.22 pmol/g in 13 specimens, being about 1/150 the concentration of ir-human atrial natriuretic peptide (hANP). These results demonstrate that hBNP is present as a peptide in human heart, suggesting that hBNP is secreted from heart and functions together with hANP as a hormone.