Alterations in the regional adrenergic system in experimental left ventricular hypertrophy

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Abstract
Study objective – The aim of the study was to determine the changes in the β adrenergic system induced by cardiac hypertrophy due to valvular aortic stenosis. Design – Density of β adrenoceptors, cardiac tissue noradrenalime concentrations, coronary blood flow (using radioactive microspheres), and haemodynamic variables were compared in a model of experimental aortic valve stenosis of 6 month's duration and in sham operated controls. Subjects – 14 mongrel dogs with aortic stenosis and eight sham operated litter mates were used in the studies. Measurements and results – Heart weight to body weight ratio was 33% greater in dogs with aortic valve stenosis than in controls. There were no haemodynamic differences except for a left ventricular to aortic systolic pressure gradient of 38 (SD 22) mm Hg in the aortic stenosis group. Response of left ventricular dP/dtmax to dopamine was similar in the two groups, as was coronary flow. Density of β adrenoceptors (Bmax) as measured by (125I)-iodopindolol binding was reduced in ventricles from the aortic stenosis group compared to control: 41.2(13.3) v 59.1(8.1) fmol·mg−1 protein, pv 438(13) ng·g−1 initial wet weight (aortic stenosis), pv subendocardial differences in any variable. Conclusions – Cardiac hypertrophy induced by aortic valve stenosis over a 6 month period is accompanied by a decrease in the density of ventricular β adrenoceptors per gram and a decrease in ventricular noradrenaline concentration, though responsiveness of the whole heart is maintained.