Augmentation of β adrenergic receptors in cardiomyopathic hamsters (BIO 14.6) with heart failure

Abstract

Objective: The aim was to characterise the transmural distribution of β adrenergic receptors in failing myocardium in cardiomyopathy. Methods: Using a quantitative autoradiographic technique with l25I-cyanopindolol (ICYP), the density and transmural distribution of β adrenergic receptors were compared between eight cardiomyopathic BIO 14.6 Syrian hamsters with heart failure and six normal age matched controls (BIO 14.6HAM). Results: Binding of ICYP to transmural slices of hamster myocardium was rapid, saturable, stereoselective, and displaceable by antagonists. The binding isotherm showed a significant increase in the total tissue content of β adrenergic receptors in the failing myocardium of cardiomyopathic hamsters: 15.3(SEM 1.6) fmol·mg-1 protein v 9.4(1.2) fmol·mg-1 protein in normal myocardium of control hamsters (p<0.05). There was no difference in receptor affinity. Quantitative autoradiography showed regional heterogeneity of β adrenergic receptors in cardiomyopathic hamsters, with an increase of β adrenergic receptor density in the septal and subendocardial regions. In addition, the regions with increased interstitial fibrosis corresponded to the sites of increased β adrenergic receptor density. Conclusions: The transmural distribution of β adrenergic receptor is heterogeneous in the failing myocardium of cardiomyopathic hamsters and an increased β adrenergic receptor density may be associated with the development of cardiomyopathy.