Differential Regulation of Cardiac Angiotensin Converting Enzyme Binding Sites and AT1Receptor Density in the Failing Human Heart

BACKGROUND: The regulation and interaction of ACE and the angiotensin II (Ang II) type I (AT1) receptor in the failing human heart are not understood. METHODS AND RESULTS: Radioligand binding with 3H-ramiprilat was used to measure ACE protein in membrane preparations of hearts obtained from 36 subjects with idiopathic dilated cardiomyopathy (IDC), 8 subjects with primary pulmonary hypertension (PPH), and 32 organ donors with normal cardiac function (NF hearts). 125I-Ang II formation was measured in a subset of hearts. Saralasin (125I-(Sar1,Ile8)-Ang II) was used to measure total Ang II receptor density. AT1 and AT2 receptor binding were determined with the AT1 receptor antagonist losartan. Maximal ACE binding (Bmax) was 578+/-47 fmol/mg in IDC left ventricle (LV), 713+/-97 fmol/mg in PPH LV, and 325+/-27 fmol/mg in NF LV (P<0.001, IDC or PPH versus NF). In IDC, PPH, and NF right ventricles (RV), ACE Bmax was 737+/-78, 638+/-137, and 422+/-49 fmol/mg, respectively (P=0.02, IDC versus NF; P=0.08, PPH versus NF). 125I-Ang II formation correlated with ACE binding sites (r=0.60, P=0.00005). There was selective downregulation of the AT1 receptor subtype in failing PPH ventricles: 6.41+/-1.23 fmol/mg in PPH LV, 2.37+/-0.50 fmol/mg in PPH RV, 5.38+/-0.53 fmol/mg in NF LV, and 7.30+/-1.10 fmol/mg in NF RV (P=0.01, PPH RV versus PPH LV; P=0.0006, PPH RV versus NF RV). CONCLUSIONS: ACE binding sites are increased in both failing IDC and nonfailing PPH ventricles. In PPH hearts, the AT1 receptor is downregulated only in the failing RV.