Hypertrophic cardiomyopathy characterised by -adrenoceptor density, relative amount of -adrenoceptor subtypes and adenylate cyclase activity

Abstract

The total quantity of β-adrenoceptors and the relative amount of β₁ and β₂ receptor subtypes were determined in heart biopsies of 10 patients with various heart diseases and 5 patients suffering from hypertrophic cardiomyopathy (HOCM). In membrane particle preparations from the same patients we also examined the activity of the adenylate cyclase (AC), and its response to isoprenaline, terbutaline, histamine and sodium fluoride (NaF). The high affinity ligand [¹²⁵I] (1)-cyanopindolol (CYP) was used in the binding assays, and the highly β₂-selective antagonist ICI 118 551 for the determination of β-adrenoceptor subtypes. No differences were found in total β-adrenoceptor density between patients with HOCM and “controls” (27.6 ± 14.2 vs 26.5 ± 10.7 fmol·mg⁻¹ protein). The relative amounts of β₁ and β₂ receptor subtypes were similar, patients with HOCM had 82.1 ± 4.9% of β₁ and 14.4 ± 3.9% of the β₂ receptor subtype, compared with 76.3 ± 11.5% of β₁ and 20.7 ± 11.0% of the β₂ subtype in the “control” patients. Both absolute activity of AC (pmol·mg⁻¹ protein·min) as well as the relative responses to the various stimulators were not significantly different between the two groups. Thus, this study does not support the hypothesis that HOCM is a disorder with altered β-adrenoceptor number or adenylate cyclase respose to adrenergic agonists. Furthermore, HOCM is not associated with altered response of the AC system to histamine or NaF.