Up-regulation of 'clearance' receptors in patients with chronic heart failure: a possible explanation for the resistance to biological effects of cardiac natriuretic hormones

Background: Three specific receptors for the cardiac natriuretic peptide system have been identified to date. Down-regulation of the biologically active binding sites (i.e. NPR-A and NPR-B) could explain the blunted response to cardiac natriuretic hormones observed in heart failure (HF), but not the increased metabolic clearance rate. Variations in the ratio between biological and clearance (NPR-C) receptors in target tissue may explain this increase. Aim: The aim of this study was to investigate the regulation of NPR-C receptors on platelets, in patients with HF. Methods: Eighteen patients with HF (NYHA class: I-II, n = 8; III-IV, n = 10) and 18 age-matched healthy subjects were studied. The affinity constant (K-d) and density (B-max) of binding sites were derived by saturation assays on platelet suspensions using I-125-ANP as radioligand. Results: B-max increased as a function of the severity of disease: 21.3 +/- 3.3 fmol/10(9) cells in class III-IV, 11.7 +/- 2.2 in class I-II, and 11.6 +/- 1.1 in controls, respectively (P = 0.0179 for class III-IV vs. controls and P = 0.0451 vs. NYHA I-II). Conclusions: The increase in density of 'clearance' receptors in severe HF is theoretically consistent with the reduction in cardiac natriuretic peptide biological activity, as well as the increase in metabolic clearance rate. This suggests that clearance receptor blockade may be of potential therapeutic value in HIT. (C) 2001 European Society of Cardiology. All rights reserved.