LOCALIZATION AND MECHANISM OF SECRETION OF B-TYPE NATRIURETIC PEPTIDEIN COMPARISON WITH THOSE OF A-TYPE NATRIURETIC PEPTIDE IN NORMAL SUBJECTS AND PATIENTS WITH HEART-FAILURE

Background B-type or brain natriuretic peptide (BNP) is a novel natriu retic peptide secreted from the heart that forms a peptide family with A-type or atrial natriuretic peptide (ANP), and its plasma level has been shown to be increased in patients with congestive heart failure. This study was designed to examine the sources and mechanisms of the s ecretion of BNP in comparison with those of ANP in control subjects an d in patients with heart failure. Methods and Results We measured the plasma levels of BNP as well as ANP in 16 patients with dilated cardio myopathy (11 men and 5 women; mean age, 59 years) and 18 control subje cts (9 men and 9 women; mean age, 54 years) by sampling blood from the femoral vein, the aortic root, the anterior interventricular vein (AI V), and the coronary sinus using the newly developed immunoradiometric assay systems. In the control subjects, there was no significant diff erence in the plasma ANP level between the aortic root and the AIV (24 .0+/-5.2 pg/mL versus 32.2+/-17.0 pg/mL), but there was a highly signi ficant step-up of the level between the AN and the coronary sinus (32. 2+/-17.0 pg/mL versus 371.4+/-111.1 pg/mL, P<.001). In contrast, there was a significant step-up of the plasma BNP level between the aortic root and the AIV (8.6+/-6.4 pg/mL versus 19.0+/-11.5 pg/mL, P<.01) but not between the AIV and the coronary sinus (19.0+/-11.5 pg/mL versus 28.8+/-14.0 pg/mL). On the other hand, in patients with dilated cardio myopathy, there was a significant step-up in the plasma ANP level betw een the aortic root and the AIV (280.6+/-183.7 pg/mL versus 612.3+/-43 1.6 pg/mL, P<.01) and between the AIV and the coronary sinus (612.3+/- 431.6 pg/mL versus 1229.0+/-772.7 pg/mL, P<.01). There was a significa nt step-up in the plasma BNP level between the aortic root and the AIV (268.4+/-293.2 pg/mL versus 511.6+/-458.1 pg/mL, P<.01) but not betwe en the AIV and the coronary sinus (511.6+/-458.1 pg/mL versus 529.7+/- 455.3 pg/mL) in patients with dilated cardiomyopathy. The arteriovenou s difference at the AIV of the plasma level of BNP had a significant p ositive correlation with left ventricular end-systolic volume index (r =0.859, P<.001) and a significant negative correlation with left ventr icular ejection fraction (r=-.735, P<.001). Conclusions We conclude th at (1) BNP is secreted mainly from the left ventricle in normal adult humans as well as in patients with left ventricular dysfunction, where as ANP is secreted from atria in normal adult humans and also from the left ventricle in patients with left ventricular dysfunction; (2) sec retion of BNP as well as ANP from the left ventricle increases in prop ortion to the severity of the left ventricular dysfunction, suggesting that the secretions of ANP and BNP from the left ventricle are regula ted mainly by wall tension of the left ventricle; and (3) the peripher al plasma levels of ANP and BNP reflect the secretion rate of these ho rmones from the left ventricle and may be used as a marker of the degr ee of left ventricular dysfunction in patients with left ventricular d ysfunction.