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

The total quantity of beta-adrenoceptors and the relative amount of beta 1 and beta 2 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 beta 2-selective antagonist ICI 118 551 for the determination of beta-adrenoceptor subtypes. No differences were found in total beta-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 beta 1 and beta 2 receptor subtypes were similar, patients with HOCM had 82.1 +/- 4.9% of beta 1 and 14.4 +/- 3.9% of the beta 2 receptor subtype, compared with 76.3 +/- 11.5% of beta 1 and 20.7 +/- 11.0% of the beta 2 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 beta-adrenoceptor number or adenylate cyclase response to adrenergic agonists. Furthermore, HOCM is not associated with altered response of the AC system to histamine or NaF.