[A specific and highly sensitive radioimmunoassay of human brain natriuretic peptide]

We established specific and highly sensitive radioimmunoassay (RIA) for the detection of human brain natriuretic peptide (BNP), and confirmed the presence of BNP-like immunoreactivity (BNP-LI) in human circulating blood and the heart. The antibody used in this RIA did not react any known human atrial natriuretic peptide (ANP). Gel permeation chromatography coupled with the RIA revealed that BNP-LI in atrium is composed with high molecular BNP and low molecular BNP. Furthermore, dominant form of BNP-LI in human plasma was thought to be low molecular BNP. Mean concentration of BNP-LI in plasma from normal subjects was 5.9 pg/ml, which was about 5 times lower than that of ANP-LI. Mean concentration of BNP-LI in human cardiac atrium was 45.6 ng/mg protein, which was about 40-fold lower than that of ANP-LI. Furthermore, concentration of BNP-LI in human cardiac ventricle was in a range of 0.1-4.8 ng/mg protein, being about 1/20 that of cardiac atrium. These data suggest that BNP synthesized in human heart and secreted into circulation.