Myocardial beta adrenoceptor density in primary and secondary left ventricular hypertrophy

Objectives. Myocardial β-adrenoceptor density has been found to be reduced in hypertrophic cardiomyopathy, even when systolic function is preserved. Our purpose in the current study was to investigate whether β-adrenoceptor down-regulation was unique to hypertrophic cardiomyopathy, or is also present in secondary myocardial hypertrophy. Methods. Myocardial β-adrenoceptor density was measured in 11 patients with hypertrophic cardiomyopathy, eight patients with left ventricular hypertrophy secondary to arterial hypertension or aortic valve disease and 18 normal control subjects, using positron emission tomography with ¹¹C-CGP-12177 as the myocardial β-adrenoceptor ligand. Results. Reflecting the natural incidence of the conditions, the age of the hypertrophic cardiomyopathy patients was 37 (10) [mean (SD), range 20-51] years and that of the secondary hypertrophy patients 64 (18), [range 26-80] years; P < 0.01. The controls' ages were 50 (13), [range 21-65] years; however, since β-adrenoceptor density is known to he influenced by age, the controls' data was split into groups matched to the hypertrophic cardiomyopathy and secondary hypertrophy patient sets. For the hypertrophic cardiomyopathy patients, mean left ventricular β-adrenoceptor was 7.70 (1.86) pmol.g^-1 compared to 10.17 (2.44) pmol.g^-1 for a matched set of 15 controls; P < 0.01. In secondary left ventricular hypertrophy, β-adrenoceptor was 6.35 (1.70) pmol.g^-1 compared to 9.16 (2.00) pmol.g^-1 for a matched set of 10 controls; P < 0.01. Plasma noradrenaline was 5.5 (2.2) nmol.l^-1 in hypertrophic cardiomyopathy and 2.5 (1.0) nmol.l^-1 for the matched controls; P < 0.01. The results for adrenaline were 2.2 (1.1) vs 0.4 (0.3) nmol.l^-1 respectively P < 0.001. For the secondary hypertrophy patients, the corresponding figures were 2.5 (1.2) vs 2.5 (1.0) nmol.l^-1 for nonadrenaline for patients and controls respectively (P = ns); and for adrenaline 0.2 (0.1) and 0.3 (0.2) nmol.l^-1 respectively, P = ns. On multiple regression analysis, no relationships could be demonstrated amongst plasma catecholamine β-adrenoceptor, myocardial blood flow and echocardiographic E/A ratio and fractional shortening. Conclusion Myocardial β-adrenoceptor density appears to be comparably decreased in both primary and secondary left ventricular hypertrophy in the presence of preserved left ventricular systolic function.